Kinetics of the persistent photocurrent in semiconductors: a case example for amorphous chalcogenides

Although the persistent photocurrent or the residual photocurrent decay (RPD) in photoconductive semiconductors is known to be dominated by dispersive recombination kinetics which produce the stretched exponential functional decay, exp(-Ct^β), where β (<1.0) is the dispersion parameter, the reason for the occurrence of the RPD is still not clear. We discuss the origin of the dispersive nature of long-term photocurrent decay in amorphous chalcogenides (a-Chs) as a case example. The slow recombination path of excess photocarriers in a-Chs can be attributed to their characteristic feature of negative-U defects at which lattice relaxation with multiphonon process may play a role.     

Interpretation of the low-temperature photoconductivity in a-Si

Abstract

The paper is concerned with the interpretation of steady-state photoconductivity results on undoped a-Si at temperatures of 50K and below which lead to an essentially constant value of the (photogeneration efficiency x mobility x lifetime) product νμτ?10^?11 cm² V^?1. Measurements on p⁺-i-n⁺ junctions and Cr-i-n⁺ barriers were carried out to determine the above parameters separately: (i) steadystate reverse saturation currents gave a generation efficiency of ν? 5×10-² below 50K, suggesting that geminate recombination limits the generation process. (ii) the electron drift mobility μ_e through the tail states and the charge extracted from the absorption region of the incident light were investigated by transient experiments, these showed that μ_eτ_a is limited to about 3×10^?10cm²V^?1 at low T. The independent results account for the observed νμτ values and suggest that, contrary to the interpretation of Hoheisel, Carius and Fuhs (1984), the main contribution to the low-temperature photoconductivity arises from transport in tail states.     

Kinetics of persistent photoconductivity in crystalline III–V semiconductors

Although persistent photocurrent (PPC) in photoconductive III–V semiconductors is known to be dominated by dispersive reaction kinetics, which produce a stretched exponential function decay, exp[?(t/τ)^β], where τ is the effective reaction time and β (<1.0) is the dispersion parameter, the reason for the occurrence of the PPC is still not clear. Here, we discuss the origin of dispersive kinetic relaxation associated with a DX-like centre, i.e. deep levels associated with donors in III–V semiconductors. It is suggested that lattice relaxation of DX-like centres, accompanied by multi-phonon processes, may play a role in the dispersive nature of the PPC.     

Hopping in a Gaussian distribution of energy states: Transition from dispersive to non-dispersive transport

Abstract

By means of Monte Carlo simulation techniques the relaxation of a packet of charge carriers migrating in a Gaussian density of states of width σ has been studied. The relaxation time determines the transition from dispersive to non-dispersive transport seen in a time-of-flight signal. For a 10 μm thick sample under a bias field of 10⁵ V cm^?1 the critical disorder parameter σ/kT turns out to be 4·4. Consistency with experimental results from polymers is found.     

Bias in Estimation of Misclassification Rates

When a simple random sample of size n is employed to establish a classification rule for prediction of a polytomous variable by an independent variable, the best achievable rate of misclassification is higher than the corresponding best achievable rate if the conditional probability distribution is known for the predicted variable given the independent variable. In typical cases, this increased misclassification rate due to sampling is remarkably small relative to other increases in expected measures of prediction accuracy due to samplings that are typically encountered in statistical analysis. This issue is particularly striking if a polytomous variable predicts a polytomous variable, for the excess misclassification rate due to estimation approaches 0 at an exponential rate as n increases. Even with a continuous real predictor and with simple nonparametric methods, it is typically not difficult to achieve an excess misclassification rate on the order of n ⁻¹. Although reduced excess error is normally desirable, it may reasonably be argued that, in the case of classification, the reduction in bias is related to a more fundamental lack of sensitivity of misclassification error to the quality of the prediction. This lack of sensitivity is not an issue if criteria based on probability prediction such as logarithmic penalty or least squares are employed, but the latter measures typically involve more substantial issues of bias. With polytomous predictors, excess expected errors due to sampling are typically of order n ⁻¹. For a continuous real predictor, the increase in expected error is typically of order n ^−2/3     

Effectiveness of an MP3 Christian mindfulness intervention on mindfulness and perceived stress

ABSTRACT

Mindfulness is enfolded in therapies addressing mental health conditions and is informed by secular and Buddhist models. However, mindfulness interventions can be rooted in other theoretical and spiritual frameworks including Christianity, which parallels Buddhist-based mindfulness practices. This study evaluates a mindfulness–based intervention drawing from Christian spiritual practices and discusses its practical implications. The researcher explored whether a Moving Picture Experts Group-3 (MP3)-based Christian mindfulness intervention would improve mindfulness states and decrease stress, measured by the Mindful Attention and Awareness Scale (MAAS) and Perceived Stress Scale (PSS), respectively. An analysis of covariance (ANCOVA) resulted in significant differences between pre- and post-test scores in experimental versus control groups on the MAAS and PSS after a 6–8-week intervention of a student sample (n?=?80) from two private, religiously-affiliated universities. Higher MAAS scores reflected improved mindfulness states, F(1,80)?=?11.947, p?=?.01 with a partial η^2?=?.134. Lower PSS scores reflect lowered perceived stress, F(1,80)?=?3.849, p?=?.053 with a partial η^2?=?.047.     

Axiomatizing logics closely related to varieties

Let V be a s.f.b. (strongly finitely based, see below) variety of algebras. The central result is Theorem 2 saying that the logic defined by all matrices (A, d) with d A V is finitely based iff the A V have 1^st order definable cosets for their congruences. Theorem 3 states a similar axiomatization criterion for the logic determined by all matrices (A, ^A), A V, a term which is constant in V. Applications are given in a series of examples.     

Conduction-electron mediated 1H nuclear spin-lattice relaxation in Ti45Zr38Ni17H x icosahedral quasicrystals

Nuclear magnetic resonance spin-lattice relaxation rates for ¹H in quasicrystalline Ti₄₅Zr₃₈Ni₁₇H _x are presented as a function of temperature and hydrogen concentration x. The temperature dependence demonstrates that the relaxation is via interaction with conduction electrons. The relaxation rate is extremely sensitive to hydrogen content, with the rate changing by a factor of as much as two for samples that differ in x     

Characterization of platelet-related infrared luminescence in diamond

Characterization of the platelet-related infrared emission in diamond using photoluminescence (PL) and PL excitation techniques is reported. It is suggested that the emission originates from the radiative recombination of electrons and holes at platelet-induced bands of electron states separated by a gap of about 1.7eV.     

Habituation to a stressor predicts adolescents' adiposity

Background and Objectives: Stress is associated with gains in adiposity. One factor that determines how much stress is experienced is how quickly an adolescent reduces responding (habituates) across repeated stressors. The purpose of this study was to determine the association of body mass index (BMI) percentile and the rate of habituation to a stressor. Design: Thirty-four adolescents completed anthropometric measures and a habituation protocol using a within study design. Methods: The habituation protocol measured the rate of decline in perceived stress and heart rate (HR) across four, two-minute serial subtraction trials. Results: Multivariate linear regression revealed the habituation rate of the HR predicted BMI percentile after adjusting for gender, socioeconomic status, and initial HR (β?=?17.2, p?Conclusions: Slower habituation to a laboratory stressor was associated with greater BMI percentiles in adolescents.     

Coping as a building mechanism to explain the unique association of affect and goal motivation with changes in affective states

Background and objectives: In this study, we examined the mediating role of university students’ coping strategies in the unique/additive influence of affective states and goal motivation on upward changes in affect during a midterm exam period. Design: Using a short-term prospective design, key assumptions from the self-concordance model and the broaden-and-build theory were drawn upon to determine whether coping strategies are influenced by goal motivation and affective states, while also subsequently influencing short-term changes in affective states during a semester. Method: A sample of 272 students (79% females and 21% males) participated in a study in which they completed questionnaires twice during the semester. Results: Results of structural equation modeling, using a true latent change approach, have generally supported our hypotheses. Positive affective states and autonomous goal motivation prospectively predicted task-oriented coping which, in turn, was associated with increases in positive affect. Negative affective states and controlled goal motivation prospectively predicted disengagement-oriented coping which, in turn, was associated with increases in negative affect. Conclusion: Coping partially mediates the unique association of affect and goal motivation with changes in affective states of university students.     

The flow stress contribution of the dislocation 'forest' in bcc lattices

The athermal flow stress contribution by junction reactions of a glide dislocation with a 'forest' of density rho is usually written as tau = alpha mu b rho ^1/2. The strength coefficient alpha has been computed for the bcc lattice by virtual displacement of triple nodes following the method of Puschl et al. (1982, Physica status solidi (a), 74, 211). In the isotropic approximation, the values for glide dislocations with 0, 30, 60 and 90^o character are as alpha = 0.18, 0.21, 0.19 and 0.22 respectively. A comparison with values calculated previously by Frydman is made, and good agreement is found when differences in the cut-off radii of the linear elastic solution are accounted for.     

Planar dissociations and recombination energy of [110] superdislocations in Ni3Al: Generalized Peierls model in combination with ab initioelectron theory

Planar dissociation configurations of the [110] superdislocation in stoichiometric Ni₃Al are investigated by the generalized Peierls model using the {111} γ-surface energies calculated by the ab initio electron theory. The dissociation into four Shockley partials with the formation of an antiphase boundary and two complex stacking fault (CSF) ribbons turned out to be the energetically most favourable configuration. For the edge superdislocation the obtained dissociation widths should be large enough to be resolved in a weakbeam image, whereas for the corresponding configuration of the screw superdislocation the CSF ribbon has a rather small width which may be beyond the limit of the resolution. A twofold dissociation involving a superlattice intrinsic stacking fault is energetically less favourable. The recombination energy of the two Shockley partials in one superpartial is found to be 0.24eV/b.     

Toward an understanding of aging in plutonium from direct measurements of stored energy

ABSTRACT

We present here the first direct measurement of the radiation-damage-induced energy stored in δ-phase plutonium. The primary mode of radioactive decay of ²³⁹Pu occurs with a time constant of τ=1.1?×?10¹²?s. Each decay imparts about 85?keV of recoil energy to the uranium byproduct, 5.2?Mev to the alpha particle, and a spectrum of mostly low energy gamma rays with the most probable at 51?keV [1]. Most of the decay energy is converted immediately to heat, releasing about 1.9?mW/g. However, some thermally-recoverable energy remains trapped. Reported here are measurements of that stored energy using differential scanning calorimetry (DSC) applied to ²³⁹Pu-2.0 at.%Ga δ-phase alloy. Retained energy of ～2 J/g saturates at about 5 months and is unchanged after 30 years. The magnitude of the stored energy agrees with a short-bond defect model that that we present here. This model treats radiation damage as a Pu impurity with shortened bond lengths. It explains the change in known properties with age and predicts that density increases with age, contrary to current thinking. The short-bond impurities proposed are expected to act like other impurities, affecting strength, phase transitions, grain boundaries and other metallurgical properties.     

Walking versus biofeedback: a comparison of acute interventions for stressed students

Background: High rates of stress-related problems in college students and low utilization of treatment options demonstrate the need for effective stress-reducing interventions that can be self-regulated. This study compared the effect of brief paced-breathing with biofeedback and exercise interventions on heart rate variability, state anxiety and affect. Methods: Students (n?=?32) with high levels of perceived stress completed three 10-min interventions on separate days: paced-breathing with biofeedback (Biofeedback), a self-paced walk (Exercise), and an attention control condition of quiet studying (Quiet Study). Anxiety and affect were measured before (Pre), immediately after (Post0) and 15 mins after (Post15) the intervention. Heart rate variability was measured pre- and post-intervention using electrocardiogram. Results: Biofeedback reduced anxiety more than the exercise condition (Pre to Post0: Biofeedback d?=??0.48, Exercise d?=??0.13). Secondly, Exercise temporarily increased energy (Pre to Post0: d?=?0.67), whereas Biofeedback temporarily increased calmness (Pre to Post0: d?=?0.51). All conditions significantly increased total heart rate variability (p?Conclusions: Biofeedback and Exercise interventions improved emotional states in high-stress college students, but the type of change observed (i.e. energizing, calming or anxiety reducing) depended upon the condition.     

Gleason's Theorem Has a Constructive Proof

Gleason's theorem for R ³ says that if f is a nonnegative function on the unit sphere with the property that f(x) + f(y) + f(z) is a fixed constant for each triple x,y,z of mutually orthogonal unit vectors, then f is a quadratic form. We examine the issues raised by discussions in this journal regarding the possibility of a constructive proof of Gleason"s theorem in light of the recent publication of such a proof.     

The kinetics of anodic oxide growth

Abstract

The process of anodic oxide growth has been investigated. It is shown that the obtained experimental results confirm the Fehlner-Mott oxidation model in the case of InSb, a typical compound of the 111-V group. We also present a kinetic theory of the anion migration in the formed oxide. The theory is based on the following assumptions. (a) The only species which moves through the formed oxide is the OH^? anion. (b) The chemical reactions of OH^? with In³⁺ and Sb³⁺ cations take place simultaneously and independently, in a thin layer of the oxide/InSb interface. The resulting solution of the kinetic equations describes the anion distribution in the formed oxide. A simple expression for the rate of oxidation is obtained. Another possible application of the presented theory is suggested.     

Organizing the voice questionnaire for transgender persons

Abstract

Background: The validated Transsexual Voice Questionnaire Male to Female (TVQ^MtF) and the adapted TVQ Female to Male (FtM) (TVQ^FtM) are both 30-item-long questionnaires used to evaluate self-perception of voice in transgender persons. They are part of a series of questionnaires completed by transgender persons during follow-up of cross-sex hormone therapy (CSHT).

Aim: The aim of this study was to examine if these questionnaires can be organized.

Methods: The TVQ^MtF or the TVQ^FtM was filled out at the start of CSHT, by 145 trans women and 83 trans men. Data were analyzed by factor analyses on both the questionnaires.

Results: The factor analyses resulted in a three-factor solution for both the TVQ^MtF and the TVQ^FtM. The three factors were labeled as anxiety and avoidance, vocal identity, and vocal function.

Conclusion: Both the questionnaires can be organized into three factors. This could contribute to making shorter versions of the questionnaires. Shorter versions would be useful to hormone prescribing physicians to track down more quickly voice problems in trans people undergoing virilizing or feminizing hormone treatment.     

Insomnia symptoms are associated with elevated C-reactive protein in young adults

Abstract

Objective: Insomnia is associated with elevated inflammation; however, studies have not investigated if this relationship is confounded with depression and neuroticism, which are associated with insomnia and inflammation. The current study examined the association of insomnia symptoms with C-reactive protein (CRP) and with interleukin-6 (IL-6), independently and after controlling for depressive symptoms and neuroticism. Design: Fifty-two young adults (mean age?=?25.2?±?3.9 years, 52% female) completed a baseline survey to assess psychological characteristics, followed by a plasma blood draw. Main outcome measures: Plasma CRP and IL-6. Results: When examined alone, insomnia symptoms were significantly associated with elevated CRP (β?=?0.52; R²?=?0.27), as was neuroticism (β?=?0.41, R²?=?0.17), but not depressive symptoms (β?=?0.21, R²?=?0.05). The association between insomnia symptoms and CRP remained significant when depressive symptoms and neuroticism were entered into the model simultaneously; this model did not explain more variance than the model with insomnia symptoms alone. No variables were associated with IL-6. Conclusions: Results suggest that insomnia symptoms are independently associated with elevated CRP in young adults, even after controlling for presumed overlapping psychological constructs. Findings highlight the potential importance of treating insomnia to reduce systemic inflammation.     

Majority merging by adaptive counting

The present paper introduces a belief merging procedure by majority using the standard format of Adaptive Logics. The core structure of the logic ADM ^c (Adaptive Doxastic Merging by Counting) consists in the formulation of the conflicts arising from the belief bases of the agents involved in the procedure. A strategy is then defined both semantically and proof-theoretically which selects the consistent contents answering to a majority principle. The results obtained are proven to be equivalent to a standard majority operator for bases with partial support.