Values Of Τ2 Research Articles

Context-Aware Embedding Techniques for Addressing Meaning Conflation Deficiency in Morphologically Rich Languages Word Embedding: A Systematic Review and Meta Analysis

This systematic literature review aims to evaluate and synthesize the effectiveness of various embedding techniques—word embeddings, contextual word embeddings, and context-aware embeddings—in addressing Meaning Conflation Deficiency (MCD). Using the PRISMA framework, this study assesses the current state of research and provides insights into the impact of these techniques on resolving meaning conflation issues. After a thorough literature search, 403 articles on the subject were found. A thorough screening and selection process resulted in the inclusion of 25 studies in the meta-analysis. The evaluation adhered to the PRISMA principles, guaranteeing a methodical and lucid process. To estimate effect sizes and evaluate heterogeneity and publication bias among the chosen papers, meta-analytic approaches were utilized such as the tau-squared (τ2) which represents a statistical parameter used in random-effects, H-squared (H2) is a statistic used to measure heterogeneity, and I-squared (I2) quantify the degree of heterogeneity. The meta-analysis demonstrated a high degree of variation in effect sizes among the studies, with a τ2 value of 8.8724. The significant degree of heterogeneity was further emphasized by the H2 score of 8.10 and the I2 value of 87.65%. A trim and fill analysis with a beta value of 5.95, a standard error of 4.767, a Z-value (or Z-score) of 1.25 which is a statistical term used to express the number of standard deviations a data point deviates from the established mean, and a p-value (probability value) of 0.2 was performed to account for publication bias which is one statistical tool that can be used to assess the importance of hypothesis test results. The results point to a sizable impact size, but the estimates are highly unclear, as evidenced by the huge standard error and non-significant p-value. The review concludes that although contextually aware embeddings have promise in treating Meaning Conflation Deficiency, there is a great deal of variability and uncertainty in the available data. The varied findings among studies are highlighted by the large τ2, I2, and H2 values, and the trim and fill analysis show that changes in publication bias do not alter the impact size’s non-significance. To generate more trustworthy insights, future research should concentrate on enhancing methodological consistency, investigating other embedding strategies, and extending analysis across various languages and contexts. Even though the results demonstrate a significant impact size in addressing MCD through sophisticated word embedding techniques, like context-aware embeddings, there is still a great deal of variability and uncertainty because of various factors, including the different languages studied, the sizes of the corpuses, and the embedding techniques used. These differences show how future research methods must be standardized to guarantee that study results can be compared to one another. The results emphasize how crucial it is to extend the linguistic scope to more morphologically rich and low-resource languages, where MCD is especially difficult. The creation of language-specific models for low-resource languages is one way to increase performance and consistency across Natural Language Processing (NLP) applications in a practical sense. By taking these actions, we can advance our understanding of MCD more thoroughly, which will ultimately improve the performance of NLP systems in a variety of language circumstances.

Excited state lifetime of electron trapping centres in alkali feldspars

The development of the infrared photoluminescence (IRPL) signal enables the direct non-destructive probing of the trapped electron population in feldspars. Whilst IRPL offers new perspectives for luminescence dating, it also enables detailed, site-selective measurements of the dosimetric defects emitting IRPL at 880 nm (IRPL880) and 955 nm (IRPL955), allowing improved understanding of luminescence phenomena in feldspars.We perform time-resolved IRPL measurements to investigate the excited state lifetimes of IRPL880 and IRPL955 electron trapping centres in chemically and structurally different feldspars. We analyse the time-resolved off-time data with three exponentially decaying components. The contribution of the fast component (τ1) fitted to the IRPL880 data is minor and its lifetime is consistent with the switch off time of the 830 nm excitation laser. The two longer lifetimes (τ2 and τ3) dominate the IRPL880 and IRPL955 signals. The τ2 values range from 2 μs to 6 μs for IRPL880 and from 2 μs to 7 μs for IRPL955, whereas τ3 ranges from 7 μs to 25 μs for IRPL880 and from 8 μs to 22 μs for IRPL955, with an average cluster value of ∼20 μs. We observe a weak decreasing trend in τ3 lifetime with decreasing K-feldspar content. Systematic thermal depletion of the trapped electron population results in decreasing τ2 lifetimes with increasing preheat temperature, but a negligible change in τ3. We suggest that time-resolved-IRPL lifetimes not only reflect the exited state lifetime of the electron trapping centre, affected by excited-to-ground state transition as well as tunnelling, but also a direct recombination from the band-tail states. The long excited-state lifetime of the order of 20 ∼ μs (the average cluster value) allows for tunnelling induced recombination from the excited state, which is supported by the fact that reported lifetimes for time-resolved-IRSL (infra-red stimulated luminescence) are shorter than those of time-resolved-IRPL.

Rehabilitation Interventions for Physical Capacity and Quality of Life in Adults With Post–COVID-19 Condition

Current rehabilitation guidelines for patients with post-COVID-19 condition (PCC) are primarily based on expert opinions and observational data, and there is an urgent need for evidence-based rehabilitation interventions to support patients with PCC. To synthesize the findings of existing studies that report on physical capacity (including functional exercise capacity, muscle function, dyspnea, and respiratory function) and quality of life outcomes following rehabilitation interventions in patients with PCC. A systematic electronic search was performed from January 2020 until February 2023, in MEDLINE, Scopus, CINAHL, and the Clinical Trials Registry. Key terms that were used to identify potentially relevant studies included long-covid, post-covid, sequelae, exercise therapy, rehabilitation, physical activity, physical therapy, and randomized controlled trial. This study included randomized clinical trials that compared respiratory training and exercise-based rehabilitation interventions with either placebo, usual care, waiting list, or control in patients with PCC. This study followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses. A pairwise bayesian random-effects meta-analysis was performed using vague prior distributions. Risk of bias was assessed using the Cochrane risk of bias tool version 2, and the certainty of evidence was evaluated using the GRADE system by 2 independent researchers. The primary outcome was functional exercise capacity, measured at the closest postintervention time point by the 6-minute walking test. Secondary outcomes were fatigue, lower limb muscle function, dyspnea, respiratory function, and quality of life. All outcomes were defined a priori. Continuous outcomes were reported as standardized mean differences (SMDs) with 95% credible intervals (CrIs) and binary outcomes were summarized as odds ratios with 95% CrIs. The between-trial heterogeneity was quantified using the between-study variance, τ2, and 95% CrIs. Of 1834 identified records, 1193 were screened, and 14 trials (1244 patients; 45% female participants; median [IQR] age, 50 [47 to 56] years) were included in the analyses. Rehabilitation interventions were associated with improvements in functional exercise capacity (SMD, -0.56; 95% CrI, -0.87 to -0.22) with moderate certainty in 7 trials (389 participants). These improvements had a 99% posterior probability of superiority when compared with current standard care. The value of τ2 (0.04; 95% CrI, 0.00 to 0.60) indicated low statistical heterogeneity. However, there was significant uncertainty and imprecision regarding the probability of experiencing exercise-induced adverse events (odds ratio, 1.68; 95% CrI, 0.32 to 9.94). The findings of this systematic review and meta-analysis suggest that rehabilitation interventions are associated with improvements in functional exercise capacity, dyspnea, and quality of life, with a high probability of improvement compared with the current standard care; the certainty of evidence was moderate for functional exercise capacity and quality of life and low for other outcomes. Given the uncertainty surrounding the safety outcomes, additional trials with enhanced monitoring of adverse events are necessary.

Formation of a hard-soft core-shell structure by controlled annealing

A soft τ1 (Al2.68Ag0.32Zr) shell and hard τ2 (Al1.84Ag0.16Zr) core, were formed in the Al0.46Ag0.32Zr0.22 alloy by annealing. The microstructure, crystal structure, and hardness of the core–shell structure were characterised in detail. Compared with the as-cast sample, the sample annealed at 500 °C for 120 days formed τ1 at the interface of the τ2 phase. The coexistence of some τ1 grains and the (Ag) matrix was observed. Additionally, nano-indentation demonstrated that the hardness values of τ1 and τ2 were 3.82 and 10.20 Gpa, respectively. The formation of a hard-soft core–shell structure may enhance comprehensive performance of the material.

Photoluminescence Modulation of Ruddlesden-Popper Perovskite via Phase Distribution Regulation.

The intrinsic chaotic phase distribution in Ruddlesden-Popper Perovskite (RPP) hinders its further improvement of photoluminescence (PL) emission and limits its application in optical devices. In this work, we achieve the phase distribution regulation of RPP by varying the composition ratio of organic bulky spacer cations 1-naphthylmethylamine (NMA) and phenylethyl-ammonium (PEA), which is controllable and nondestructive for structures of RPP. By suppressing the small n-phase, the PL intensity emission of RPP is further improved. Through the time-resolved PL (TRPL) measurements, we find the PL lifetime of the sample with 66% PEA concentration increases with the temperature initially and possesses the highest values of τ1 and τ2 at ~255 K, indicating the immediate state assisting exciton radiative recombination, and it can be modulated by phase manipulation in RPP. The immediate state may outcompete other non-radiative decay channels for excited carriers, leading to the PL enhancement in RPP, and broadening its further application.

Competition Pathways of Energy Relaxation of Hot Electrons through Coupling with Optical, Surface, and Acoustic Phonons

The hot electrons in carbon-based materials exhibit interesting ballistic transport behaviors for designing high-performance single-electron transistors. However, the cooling of such hot electrons back to the equilibrium state may be slowed down by the excessively populated optical phonons, thus limiting their ballistic transport. Therefore, a thorough understanding of the coupling between hot electrons and optical phonons is of critical importance. Here, by varying the thickness of a multilayer graphene film on a supporting substrate, we investigated the competition pathways of the energy relaxation of the photoinduced hot electrons through coupling with the optical, surface, and acoustic phonons. The difference in the τ2 values indicates that thickness plays an important role in the optical phonon population. For the multilayer graphene film thickness less than 3 nm, the super-collision model describes the hot electron cooling dynamics that is strongly affected by the surface phonons from the supporting substrate. As the multilayer graphene film thickness increases from 3 to 20 nm, the accumulation of the optical phonons induces a hot optical phonon effect, resulting in a bottleneck of cooling of the hot electrons. As the multilayer graphene film thickness further increases from 20 to 40 nm, a direct coupling between the hot electrons and acoustic phonons starts to dominate. The surface states of the interfaces at the inner layers of the multilayer graphene film contribute to this direct coupling as an additional cooling channel. The quantitative understanding of the energy relaxation pathways of the hot electrons offers insights into designing high-performance single-electron transistors.

A novel method for determining murine skeletal muscle fiber type using autofluorescence lifetimes.

This work describes a simple way to identify fiber types in living muscles by fluorescence lifetime imaging microscopy (FLIM). We quantified the mean values of lifetimes τ1 and τ2 derived from a two-exponential fit in freshly dissected mouse flexor digitorum brevis (FDB) and soleus muscles. While τ1 values changed following a bimodal behavior between muscles, the distribution of τ2 is shifted to higher values in FDB. To understand the origin of this difference, we obtained maps of autofluorescence lifetimes of flavin mononucleotide and dinucleotide (FMN/FAD) in cryosections, where excitation was set at 440 nm and emission at a bandwidth of between 500 and 570 nm, and paired them with immunofluorescence images of myosin heavy chain isoforms, which allowed identification of fiber types. In soleus,τ2was 3.16 ns for type I (SD 0.11, 97 fibers), 3.45 ns for IIA (0.10, 69), and 3.46 ns for IIX (0.12, 65). In FDB muscle,τ2was 3.17 ns for type I (0.08, 22), 3.46 ns for IIA (0.16, 48), and 3.66 ns for IIX (0.15, 43). Fromτ2distributions, it follows that an FDB fiber withτ2> 3.3 ns is expected to be of type II, and of type I otherwise. This simple classification method has first and second kind errors estimated at 0.02 and 0.10, which can be lowered by reducing the threshold for identification of type I and increasing it for type II. Lifetime maps of autofluorescence, therefore, constitute a tool to identify fiber types that, for being practical, fast, and noninvasive, can be applied in living tissue without compromising other experimental interventions.

Lifetime of autofluorescence: A novel method to determine murine skeletal muscle fiber types

This work describes a simple way to identify fiber types in living muscles by fluorescence lifetime imaging microscopy (FLIM). We quantified the mean values of lifetimes derived from a two-exponential fit (τ1 and τ2) in freshly dissected mouse FDB and soleus muscles. While τ1 values did not change between muscles, the distribution of τ2 shifted to higher values in FDB. To understand the origin of this difference, we obtained maps of autofluorescence lifetimes in cryosections of both muscles and paired them with immunofluorescence images of myosin heavy chain isoforms (MHC), which allow identification of fiber types. In soleus, τ2 was 3.1 ns for type I (SEM = 0.009, n = 49), 3.4 ns for type IIA (SEM = 0.01, n = 30), and 3.3 ns for type IIX (SEM = 0.01, n = 21). In FDB muscle, τ2 was 3.17 ns for type I (SEM = 0.04, n = 18), 3.5 ns for type IIA (SEM = 0.03, n = 27), and 3.62 ns for type IIX (SEM = 0.03, n = 22). From the distribution of measures, it follows that an FDB fiber with τ2 >3.3 ns is expected to be of type II, and of type I otherwise. This simple classification method has first- and second-class errors estimated at 0.06 and 0.27, respectively. Studies in progress aim at further elucidating the reasons for the different lifetimes, not just among fiber types but between fibers of the same type in the two muscles. Preliminary results point at differences in both the oxidation-reduction and protein-bound versus free states of flavins as causes for the observed divergence of fluorescence lifetimes. Lifetime maps of autofluorescence therefore constitute a tool to identify fiber type that, being practical, fast, and noninvasive, can be applied in living tissue without compromising other experimental interventions.

Diverse simulations of time-resolved photoluminescence in thin-film solar cells: A SnO2/CdSeyTe1−y case study

Time-resolved photoluminescence (TRPL) is widely used to measure carrier lifetime in thin-film solar cell absorbers. However, the injection dependence of data and frequent non-exponential decay shapes complicate the interpretation. Here, we develop a numerical model to simulate injection-dependent TRPL measurements in a SnO2/CdSeyTe1−y solar cell structure, considering parameters of interest to researchers in industry and academia. Previous simulations have shown that in low injection, excess electrons and holes injected by the laser pulse are rapidly separated in the electric field formed by the pn junction. As a result, at early times, the PL signal can decay faster than the Shockley–Read–Hall lifetime in the absorber bulk (τbulk). Prior simulations have shown that the charge stored in the junction can slowly leak out to affect decays at late times. However, it has not been clear if and to what degree charge storage can affect the slopes extracted from TRPL decays—τ2—commonly cited as the TRPL-measured lifetime. Here, we show that charge storage can, in some cases, result in τ2 values that substantially overestimate τbulk. Previous simulations indicate that high-injection conditions can screen the junction field and minimize charge separation. Here, we show that continued injection increases can drive down τ2 below τbulk as radiative recombination becomes dominant. We catalog charge storage and radiative recombination impacts for a diverse set of material parameters and compare results to double-heterostructure models.

The decay of the refocused Hahn echo in DEER experiments

Abstract. Double electron–electron resonance (DEER) is a pulse electron paramagnetic resonance (EPR) technique that measures distances between paramagnetic centres. It utilizes a four-pulse sequence based on the refocused Hahn spin echo. The echo decays with increasing pulse sequence length 2(τ1 + τ2), where τ1 and τ2 are the two time delays. In DEER, the value of τ2 is determined by the longest inter-spin distance that needs to be resolved, and τ1 is adjusted to maximize the echo amplitude and thus sensitivity. We show experimentally that for typical spin centres (nitroxyl, trityl, Gd(III)) diluted in frozen protonated solvents, the largest refocused echo amplitude for a given τ2 is obtained neither at very short τ1 (which minimizes the pulse sequence length) nor at τ1 = τ2 (which maximizes dynamic decoupling for a given total sequence length), but rather at τ1 values smaller than τ2. Large-scale spin dynamics simulations including the electron spin and several hundred neighbouring protons reproduce the experimentally observed behaviour almost quantitatively. They show that electron spin dephasing is driven by solvent protons via the flip-flop coupling among themselves and their hyperfine couplings to the electron spin.

Delay Cournot Duopoly Game with Gradient Adjustment: Berezowski Transition from a Discrete Model to a Continuous Model

This paper investigates the asymptotical behavior of the equilibrium of linear classical duopolies by reconsidering the two-delay model with two different positive delays. In a two-dimensional analysis, the stability switching curves were first analytically determined. Numerical studies verified and illustrated the theoretical results. In the sensitivity analysis it was demonstrated that the inertia coefficient has a twofold effect: enlarges the stability region as well as simplifies the complicated dynamics with period-halving cascade. In contrary, the adjustment speed contracts the stability region and complicates simple dynamics with period-doubling bifurcation. In addition, for various values of τ1 and τ2, a wide variety of dynamics appears ranging from simple cycle via a Hopf bifurcation to chaotic oscillations.

Structural Defects in TiNi-Based Alloys after Warm ECAP

The microstructure, martensitic transformations and crystal structure defects in the Ti50Ni47.3Fe2.7 (at%) alloy after equal-channel angular pressing (ECAP, angle 90°, route BC, 1–3 passes at T = 723 K) have been investigated. A homogeneous submicrocrystalline (SMC) structure (grains/subgrains about 300 nm) is observed after 3 ECAP passes. Crystal structure defects in the Ti49.4Ni50.6 (at%) alloy (8 ECAP passes, angle 120°, BC route, T = 723 K, grains/subgrains about 300 nm) and Ti50Ni47.3Fe2.7 (at%) alloy with SMC B2 structures after ECAP were studied by positron lifetime spectroscopy at the room temperature. The single component with the positron lifetime τ1 = 132 ps and τ1 = 140 ps were observed for positron lifetime spectra (PLS) obtained from ternary and binary, correspondingly, annealed alloys with coarse-grained structures. This τ1 values correspond to the lifetime of delocalized positrons in defect-free B2 phase. The two component PLS were found for all samples exposed by ECAP. The component with τ2 = 160 ps (annihilation of positrons trapped by dislocations) is observed for all samples after 1–8 ECAP passes. The component with τ3 = 305 ps (annihilation of positrons trapped by vacancy nanoclusters) was detected only after the first ECAP pass. The component with τ3 = 200 ps (annihilation of positrons trapped by vacancies in the Ti sublattice of B2 structure) is observed for all samples after 3–8 ECAP passes.

The Effect of Strain Rate on the Stress Relaxation of the Pig Dermis: A Hyper-Viscoelastic Approach.

The understanding of strain rate-dependent mechanical properties of the skin is important for accurate prediction of its biomechanics under different loading conditions. This study investigated the effect of strain rate, i.e., 0.025/s (low), 0.5/s (medium), and 1.25/s (high), ranging in the physiological loading rate of connective tissue, on the stress-relaxation response of the porcine dermis. Results show that in the initial phase of the relaxation, the value of stress relaxation (extent of relaxation) was found higher for high strain rate. However, the equilibrium stress was found strain rate independent. A Mooney-Rivlin-based five-term quasi-linear viscoelastic (QLV) model was proposed to determine the effect of strain rate on the stress-relaxation behavior of the porcine dermis. The value of relaxation modulus G1 and G2 were found higher for the high strain rate, whereas the reverse trend was observed for G3, G4, and G5. Moreover, the value of time constants τ1,τ2,τ3τ4, and τ5 were found higher for low strain rate. Statistical analysis shows no significant difference in the values of G5, τ4, and τ5 among the three strain rates. The proposed model was found capable to fit the stress-relaxation response of skin with great accuracy, e.g., root-mean-squared-error (RMSE) value equal to 0.015 ± 0.00012 MPa. Moreover, this hyper-viscoelastic model can be utilized: to quantify the effects of age and diseases on the skin; to simulate the stresses on sutures during large wound closure and impact loading.

Effect of Co Content on Structural Stability and Soft Magnetic Properties for (Fe1 – xCox)86Hf7B6Cu1 Amorphous Alloy

Amorphous (Fe1–xCox)86Hf7B6Cu1 ribbons were prepared by using the single-roller melt-spinning technique. The microstructure, crystallization activation energy, soft magnetic properties and structural defects of the samples have been investigated by XRD, TEM, DTA, VSM and positron annihilation lifetime spectra. The results show that the as-quenched alloy ribbons are structurally amorphous. The positron annihilation technique results show that for the (Fe1–xCox)86Hf7B6Cu1 (x = 0.4) amorphous alloy, the annihilation lifetime τ1 is 149.0 ps in the monovacancy-like free volume. The annihilation lifetime τ2 is 344.5 ps in the microvoid. The values of τ1 and τ2 of (Fe1–xCox)86Hf7B6Cu1 (x = 0.4) amorphous alloy are the Minimum in all of the samples, which indicates that the volumes of the monovacancy-like free volume and the microvoid in this alloy is the smallest. Combined with DTA results, the structural stability of (Fe1–xCox)86Hf7B6Cu1 (x = 0.4) is the best. The VSM results show that (Fe1–xCox)86Hf7B6Cu1 (x = 0.4) amorphous alloys display more excellent soft magnetic property.

Investigation of dielectric relaxation in dipolar liquids

A graphical method has been used to evaluate the double relaxation time τ1 and τ2 for rotation of the flexible part and whole molecule of four butyl alcohols in p-xylene under 2.50 GHz (S-Band), 9.313 GHz (X-Band), 16.20 GHz (Ku-Band) and 23.98 GHz (K-Band) electric field at 25 °C using Frohlich and Debye model. The fixed τ1 and τ2 obtained from graphical method at those frequencies agree well with the reported average τ’s. This reveals τ’s are independent of the electric field frequencies signifying the material properties of chemical systems in identical environment. This method is making no approximation, and the infinite number of solutions clearly shows that observation at one single frequency is not sufficient to determine the correct values of τ1 and τ2. The dipole moments µ1 and µ2 are measured at all the frequencies in terms of graphically obtained τ1 and τ2 and reported τ. Estimated penetration depth indicates development of a new simple and rapid sensor for determination of alcohol concentration.

Sorption of Atmospheric Gases (N2, O2, Ar, CO2, and H2O) by Silica Aerogel

Adsorption and desorption of atmospheric gases (N2, O2, Ar, CO2, and H2O) in silica aerogel is studied. Static parameters of adsorption and kinetic parameters of adsorption and desorption are determined based on the pressure vs time dependence P(t) in the buffer vacuum chamber of an experimental setup during adsorption and desorption of gases in a SiO2 aerogel sample V = 42.8 cm3 in volume and ρ = 0.34 g/cm3 in density. The ratios of adsorbate molecular density to aerogel molecular density at room temperature T = 293 K and equilibrium pressure Pe ≈ 1 bar are found: γ(N2) = (9 ± 3)% (nine N2 molecules adsorbed by pore surface to 100 N2 molecules in the gas at equilibrium), γ(O2) = (7 ± 3)%, and γ(CO2) = (222 ± 8)%; for water vapor, γ(H2O) = (5.9 ± 0.3) × 104% at Pe = 5.7 mbar. It is ascertained that Ar atoms are not adsorbed by the aerogel. It is suggested to use argon as a “zero” gas in spectroscopy of molecules adsorbed by SiO2 aerogel to determine the amount of adsorbate in a sample. A sum of two exponential functions of kinetic parameters τ1 and τ2 is used to fit the P(t) dependence, where τ1 and τ2 values are estimated during the adsorption and desorption of each gas under study.

On the variation in maternal birth canal in vivo viscoelastic properties and their effect on the predicted length of active second stage and levator ani tears

The pubovisceral muscles (PVM) help form the distal maternal birth canal. It is not known why 13% of vaginal deliveries end in PVM tears, so insights are needed to better prevent them because their sequelae can lead to pelvic organ prolapse later in life. In this paper we provide the first quantification of the variation in in vivo viscoelastic properties of the intact distal birth canal in healthy nulliparous women using Fung’s Quasilinear Viscoelastic Theory and a secondary analysis of data from a clinical trial of constant force birth canal dilation to 8 cm diameter in the first stage of labor in 26 nullipara. We hypothesized that no significant inter-individual variation would be found in the long time constant, τ2, which characterizes how long it takes the birth canal to be dilated by the fetal head. That hypothesis was rejected because τ2 values ranged 20-fold above and below the median value. These data were input to a biomechanical model to calculate how such variations affect the predicted length of the active second stage of labor as well as PVM tear risk. The results show there was a 100-fold change in the predicted length of active second stage for the shortest and longest τ2 values, with a noticeable increase for τ2 values over 1000 s. The correlation coefficent between predicted and observed second stage durations was 0.51. We conclude that τ2 is a strong theoretical contributor to the time a mother has to push in order to deliver a fetal head larger than her birth canal, and a weak predictor of PVM tear risk.

239Pu alpha spectrum analysis based on PIPS detector response function and variations with vacuum and distance

Effect factors of the absorption of the source, air, entrance window, and dead layer of a detector must be considered in the measurement of monoenergetic alpha particles, along with statistical noise and other factors that collectively cause the alpha spectrum to exhibit a well-known low-energy tail. Therefore, the establishment of an alpha spectrum detector response function from the perspective of a signaling system must consider the various factors mentioned above. The detector response function is the convolution of an alpha-particle pulse function, two exponential functions, and a Gaussian function, followed by calculation of the parameters of the detector response function using the weighted least-squares fitting method as proposed in this paper. In our experiment, 239Pu alpha spectra were measured by a high-resolution, passivated implanted planar silicon (PIPS) detector at 10 levels of vacuum and 10 source-detector distances. The spectrum-fitting results were excellent as evaluated by reduced Chi-square (χ 2) and correlation coefficients. Finally, the variation of parameters with vacuum level and source-detector distance was studied. Results demonstrate that σ, τ1, and τ2 exhibit no obvious trend of variation with vacuum in the range 2000–20,000 mTorr, and at a confidence level of 95%, the values of τ1 and τ2 decline in a similar fashion with source-detector distance by the power exponential function, while the value of σ declines linearly.

Non-photochemical fluorescence quenching in photosystem II antenna complexes by the reaction center cation radical

In direct experiments, rate constants of photochemical (kP) and non-photochemical (kP(+)) fluorescence quenching were determined in membrane fragments of photosystem II (PSII), in oxygen-evolving PSII core particles, as well as in core particles deprived of the oxygen-evolving complex. For this purpose, a new approach to the pulse fluorometry method was implemented. In the "dark" reaction center (RC) state, antenna fluorescence decay kinetics were measured under low-intensity excitation (532nm, pulse repetition rate1Hz), and the emission was registered by a streak camera. To create a "closed" [P680(+)QA(-)] RC state, a high-intensity pre-excitation pulse (pump pulse, 532nm) of the sample was used. The time advance of the pump pulse against the measuring pulse was 8ns. In this experimental configuration, under the pump pulse, the [P680(+)QA(-)] state was formed in RC, whereupon antenna fluorescence kinetics was measured using a weak testing picosecond pulsed excitation light applied to the sample 8ns after the pump pulse. The data were fitted by a two-exponential approximation. Efficiency of antenna fluorescence quenching by the photoactive RC pigment in its oxidized (P680(+)) state was found to be ~1.5 times higher than that of the neutral (P680) RC state. To verify the data obtained with a streak camera, control measurements of PSII complex fluorescence decay kinetics by the single-photon counting technique were carried out. The results support the conclusions drawn from the measurements registered with the streak camera. In this case, the fitting of fluorescence kinetics was performed in three-exponential approximation, using the value of τ1 obtained by analyzing data registered by the streak camera. An additional third component obtained by modeling the data of single photon counting describes the P680(+)Pheo(-) charge recombination. Thus, for the first time the ratio of kP(+)/kP= 1.5 was determined in a direct experiment. The mechanisms of higher efficiency for non-photochemical antenna fluorescence quenching by RC cation radical in comparison to that of photochemical quenching are discussed.

Lattice distortion mechanism study of TiO2 nanoparticles during photocatalysis degradation and reactivation

In this paper, the photocatalytic process of TiO2 (P25) is directly characterized by using a positron annihilation lifetime spectroscopy (PALS), high-resolution transmission electron microscopy (HRTEM), Photoluminescence spectroscopy (PL) and UV Raman spectroscopy (Raman). The experimental results reveal that: 1) From PALS measurements, because τ1 and τ2 values and their intensity (I1 and I2) assigned to the different size and amounts of defects, respectively, their variations indicate the formation of different types and amounts of defects during the absorption and degradation. 2) HRTEM observations show that the lattice images become partly blurring when the methylene blue is fully degradated, and clear again after exposed in the air for 30 days. According to the results, we propose a mechanism that the lattice distortion induces the defects as electron capture sites and provides energy for improving photocatalytic process. Meanwhile, the lattice distortion relaxation after exposing in the air for 30 days perfectly explains the gradual deactivation of TiO2, because the smaller vacancy defects grow and agglomerate through the several photocatalytic processes. The instrumental PL and Raman are also used to analyze the samples and approved the results of PALS and HRTEM.