Impact-ionization and noise characteristics of thin III-V avalanche photodiodes

It is, by now, well known that McIntyre\u27s localized carrier-multiplication theory cannot explain the suppression of excess noise factor observed in avalanche photodiodes (APDs) that make use of thin multiplication regions. We demonstrate that a carrier multiplication model that incorporates the effects of dead space, as developed earlier by Hayat et al. provides excellent agreement with the impact-ionization and noise characteristics of thin InP, In/sub 0.52/Al/sub 0.48/As, GaAs, and Al/sub 0.2/Ga/sub 0.8/As APDs, with multiplication regions of different widths. We outline a general technique that facilitates the calculation of ionization coefficients for carriers that have traveled a distance exceeding the dead space (enabled carriers), directly from experimental excess-noise-factor data. These coefficients depend on the electric field in exponential fashion and are independent of multiplication width, as expected on physical grounds. The procedure for obtaining the ionization coefficients is used in conjunction with the dead-space-multiplication theory (DSMT) to predict excess noise factor versus mean-gain curves that are in excellent accord with experimental data for thin III-V APDs, for all multiplication-region widths

Reducing childbirth-related intrusive memories and PTSD symptoms via a single-session behavioural intervention including a visuospatial task: A proof-of-principle study.

Intrusive memories (IMs) of traumatic events are a key symptom of posttraumatic stress disorder (PTSD), and contribute to its maintenance. This translational proof-of-principle study tested whether a single-session behavioural intervention reduced the number of childbirth-related IMs (CB-IMs) and childbirth-related PTSD (CB-PTSD) symptoms, in women traumatised by childbirth. The intervention was assumed to disrupt trauma memory reconsolidation. In this pre-post study, 18 participants, whose traumatic childbirth had occurred between seven months and 6.9 years before, received an intervention combining childbirth-related reminder cues (including the return to maternity unit) with a visuospatial task. They recorded their daily CB-IMs in the two weeks pre-intervention (diary 1), the two weeks post-intervention (diary 2; primary outcome), and in week 5 and 6 post-intervention (diary 3). CB-PTSD symptom severity was assessed five days pre-intervention and one month post-intervention. Compared to diary 1, 15/18 participants had ≥ 50% fewer CB-IMs in diary 2. The median (IQR) reduction of the number of CB-IMs was 81.89% (39.58%) in diary 2, and persisted in diary 3 (n = 17). At one month post-intervention, CB-PTSD symptom severity was reduced by ≥ 50% in 10/18 participants. Of the 8 participants with a CB-PTSD diagnosis pre-intervention, none met diagnostic criteria post-intervention. The intervention was rated as highly acceptable. The design limits the causal interpretation of observed improvements. This is the first time such a single-session behavioural intervention was tested for old and real-life single-event trauma. The promising results justify a randomized controlled trial, and may be a first step toward an innovative CB-PTSD treatment

Spontaneous childbirth-related mental images among pregnant women: a mixed-method study.

Mental imagery may reflect the present, past or future. Childbirth is often anticipated with joy but also in some cases with fear, which may negatively impact on the childbirth experience. So far, research on birth-related mental imagery in pregnancy is lacking. This study aimed to investigate in detail the phenomenology of spontaneous childbirth-related mental images and the association between main imagery characteristics (valence, positive/negative percentage ratio and impact on behaviour and decision-making) and fear of childbirth. A concurrent triangulation mixed methods design was employed. Thirty-seven nulliparous, French-speaking women, aged ≥ 18 years in their third trimester of pregnancy completed self-report questionnaires assessing fear of childbirth, spontaneous use of mental imagery, prenatal depression and trait anxiety, and participated in a mental imagery interview to assess spontaneous childbirth-related mental images. Women with a prenatal diagnosis of malformation were excluded. All participants reported having spontaneous mental images of their impending childbirth. The images captured were rich in detail and included a variety of sensory modalities. More positive mental images were associated with less fear of childbirth (r = -0.533, p = .008) and women who had a higher proportion of negative mental images had a higher fear of childbirth (r = 0.428, p = .005). The impact of the most negative mental images on behaviour and decision-making was positively correlated with fear of childbirth (r = 0.342, p = .038). Our results indicate that negative spontaneous childbirth-related imagery is associated with fear of childbirth. Intervention techniques could be developed that focus on enhancing positive childbirth-related mental images during pregnancy and thus fostering a more positive childbirth experience

Playing the computer game Tetris prior to viewing traumatic film material and subsequent intrusive memories: Examining proactive interference.

Visuospatial working memory (WM) tasks performed concurrently or after an experimental trauma (traumatic film viewing) have been shown to reduce subsequent intrusive memories (concurrent or retroactive interference, respectively). This effect is thought to arise because, during the time window of memory consolidation, the film memory is labile and vulnerable to interference by the WM task. However, it is not known whether tasks before an experimental trauma (i.e. proactive interference) would also be effective. Therefore, we tested if a visuospatial WM task given before a traumatic film reduced intrusions. Findings are relevant to the development of preventative strategies to reduce intrusive memories of trauma for groups who are routinely exposed to trauma (e.g. emergency services personnel) and for whom tasks prior to trauma exposure might be beneficial. Participants were randomly assigned to 1 of 2 conditions. In the Tetris condition (n = 28), participants engaged in the computer game for 11 min immediately before viewing a 12-min traumatic film, whereas those in the Control condition (n = 28) had no task during this period. Intrusive memory frequency was assessed using an intrusion diary over 1-week and an Intrusion Provocation Task at 1-week follow-up. Recognition memory for the film was also assessed at 1-week. Compared to the Control condition, participants in the Tetris condition did not report statistically significant difference in intrusive memories of the trauma film on either measure. There was also no statistically significant difference in recognition memory scores between conditions. The study used an experimental trauma paradigm and findings may not be generalizable to a clinical population. Compared to control, playing Tetris before viewing a trauma film did not lead to a statistically significant reduction in the frequency of later intrusive memories of the film. It is unlikely that proactive interference, at least with this task, effectively influences intrusive memory development. WM tasks administered during or after trauma stimuli, rather than proactively, may be a better focus for intrusive memory amelioration

Stress-dependent relocalization of translationally primed mRNPs to cytoplasmic granules that are kinetically and spatially distinct from P-bodies

Cytoplasmic RNA granules serve key functions in the control of messenger RNA (mRNA) fate in eukaryotic cells. For instance, in yeast, severe stress induces mRNA relocalization to sites of degradation or storage called processing bodies (P-bodies). In this study, we show that the translation repression associated with glucose starvation causes the key translational mediators of mRNA recognition, eIF4E, eIF4G, and Pab1p, to resediment away from ribosomal fractions. These mediators then accumulate in P-bodies and in previously unrecognized cytoplasmic bodies, which we define as EGP-bodies. Our kinetic studies highlight the fundamental difference between EGP- and P-bodies and reflect the complex dynamics surrounding reconfiguration of the mRNA pool under stress conditions. An absence of key mRNA decay factors from EGP-bodies points toward an mRNA storage function for these bodies. Overall, this study highlights new potential control points in both the regulation of mRNA fate and the global control of translation initiation