Radiation from a Uniformly Accelerated Charge

The emission of radiation by a uniformly accelerated charge is analyzed. According to the standard approach, a radiation is observed whenever there is a relative acceleraion between the charge and the observer. Analyzing difficulties that arose in the standard approach, we propose that a radaition is created whenever a relative acceleration between the charge and its own electric field exists. The electric field induced by a charge accelerated by an external (nongravitational) force, is not accelerated with the charge. Hence the electric field is curved in the instantanous rest frame of the accelerated charge. This curvature gives rise to a stress force, and the work done to overcome the stress force is the source of the energy carried by the radiation. In this way, the "energy balance paradox" finds its solution.Comment: Latex, uses aasms4.sty, 14 pages, Accepted for publication in General Relativity and Gravitation. For a postscript file please contact Noam Soker: [email protected]

Prediction-learning in Infants as a Mechanism for Gaze Control during Object Exploration

We are pursuing the hypothesis that visual exploration and learning in young infants is achieved by producing gaze-sample sequences that are sequentially predictable. Our recent analysis of infants\u27 gaze patterns during image free-viewing (Schlesinger & Amso, 2013) provides support for this idea. In particular, this work demonstrates that infants\u27 gaze samples are more easily learnable than those produced by adults, as well as those produced by three artificial-observer models. In the current study, we extend these findings to a well-studied object-perception task, by investigating 3-month-olds\u27 gaze patterns as they view a moving, partially-occluded object. We first use infants\u27 gaze data from this task to produce a set of corresponding center-of-gaze (COG) sequences. Next, we generate two simulated sets of COG samples, from image-saliency and random-gaze models, respectively. Finally, we generate learnability estimates for the three sets of COG samples by presenting each as a training set to an SRN. There are two key findings. First, as predicted, infants COG samples from the occluded-object task are learned by a pool of simple recurrent networks faster than the samples produced by the yoked, artificial-observer models. Second, we also find that resetting activity in the recurrent layer increases the network’s prediction errors, which further implicates the presence of temporal structure in infants’ COG sequences. We conclude by relating our findings to the role of image-saliency and prediction-learning during the development of object perception

Image Free-Viewing as Intrinsically-Motivated Exploration: Estimating the Learnability of Center-of-Gaze Image Samples in Infants and Adults

We propose that free viewing of natural images in human infants can be understood and analyzed as the product of intrinsically-motivated visual exploration. We examined this idea by first generating five sets of center-of-gaze (COG) image samples, which were derived by presenting a series of natural images to groups of both real observers (i.e., 9-month-olds and adults) and artificial observers (i.e., an image-saliency model, an image-entropy model, and a random-gaze model). In order to assess the sequential learnability of the COG samples, we paired each group of samples with a simple recurrent network, which was trained to reproduce the corresponding sequence of COG samples. We then asked whether an intrinsically-motivated artificial agent would learn to identify the most successful network. In Simulation 1, the agent was rewarded for selecting the observer group and network with the lowest prediction errors, while in Simulation 2 the agent was rewarded for selecting the observer group and network with the largest rate of improvement. Our prediction was that if visual exploration in infants is intrinsically-motivated—and more specifically, the goal of exploration is to learn to produce sequentially-predictable gaze patterns—then the agent would show a preference for the COG samples produced by the infants over the other four observer groups. The results from both simulations supported our prediction. We conclude by highlighting the implications of our approach for understanding visual development in infants, and discussing how the model can be elaborated and improved

Children retain implicitly learned phonological sequences better than adults: A longitudinal study

This is the peer reviewed version of the following article: Eleonore H. M. Smalle, Mike P. A. Page, Wouter Duyck, Martin Edwards, and Arnaud Szmalec, 'Children retain implicitly learned phonological sequences better than adults: a longitudinal study', Developmental Science, December 2017, which has been published in final form at DOI: 10.1111/desc.12634. Under embargo until 17 December 2018. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.Whereas adults often rely on explicit memory, children appear to excel in implicit memory, which plays an important role in the acquisition of various cognitive skills, such as those involved in language. The current study aimed to test the assertion of an age-dependent shift in implicit versus explicit learning within a theoretical framework that explains the link between implicit sequence memory and word-form acquisition, using the Hebb repetition paradigm. We conducted a one-year, multiple-session longitudinal study in which we presented auditory sequences of syllables, co-presented with pictures of aliens, for immediate serial recall by a group of children (8–9 years) and by an adult group. The repetition of one Hebb sequence was explicitly announced, while the repetition of another Hebb sequence was unannounced and, therefore, implicit. Despite their overall inferior recall performance, the children showed better offline retention of the implicit Hebb sequence, compared with adults who showed a significant decrement across the delays. Adults had gained more explicit knowledge of the implicit sequence than children, but this could not explain the age-dependent decline in the delayed memory for it. There was no significant age-effect for delayed memory of the explicit Hebb sequence, with both age groups showing retention. Overall performance by adults was positively correlated with measures of post-learning awareness. Performance by children was positively correlated with vocabulary knowledge. We conclude that children outperform adults in the retention over time of implicitly learned phonological sequences that will gradually consolidate into novel word-forms. The findings are discussed in the light of maturational differences for implicit versus explicit memory systems that also play a role in language acquisition. A video abstract of this article can be viewed at: https://youtu.be/G5nOfJB72t4.Peer reviewedFinal Accepted Versio

Feasibility and acceptability of text messaging to support antenatal healthcare in Iraqi pregnant women: a pilot study

Objective: To determine the feasibility and acceptability of mobile health technology and its potential to improve antenatal care (ANC) services in Iraq. Methods: This was a controlled experimental study conducted at primary health care centers. One hundred pregnant women who attended those centres for ANC were exposed to weekly text messages varying in content, depending on the week of gestation, while 150 women were recruited for the unexposed group. The number of ANC visits in the intervention and control groups, was the main outcome measure. The Mann-Whitney test and the Poisson regression model were the two main statistical tests used. Results: More than 85% of recipients were in agreement with the following statements: “the client recommends this program for other pregnant women”, “personal rating for the message as a whole” and “obtained benefit from the messages”. There was a statistically significant increase in the median number of antenatal clinic visits from two to four per pregnancy, in addition to being relatively of low cost, and could be provided for a larger population with not much difference in the efforts. Conclusions: Text messaging is feasible, low cost and reasonably acceptable to Iraqi pregnant women, and encourages their ANC visits

Studies of the Fallopian tube environment and an assessment of its role in assisted reproduction

The role of the Fallopian tube in assisted reproduction remains unclear. The work described in this thesis was undertaken; (1) to study cyclical oestrogen and progesterone receptor changes in the endometrium and Fallopian tube, (2) to determine ultrastructural similarities and differences between endometrial and endosalpingeal epithelia at the different stages of the cycle, (3) to collect tubal fluid and attempt to isolate tubal specific proteins, and (4) to determine the clinical impact of tubal environment in assisted reproduction by conducting a randomised trial comparing tubal and uterine embryo replacements after in vitro fertilization of oocytes. Oestrogen (ER) and progesterone receptors were studied with specific monoclonal antibodies and employing an immunohistochemical technique. The results showed that, in the tube, both the isthmic and ampullary epithelial and stromal ER increased in the follicular phase to a peak at mid cycle, then declined in the late luteal phase whilst the fimbrial end depicted an opposite pattern of staining. Progesterone receptors persisted in all tubal wall layers and endometrial stroma throughout the cycle, but disappeared completely from endometrial gland epithelium in the late luteal phase. The ultrastructural study showed; (1) an increase in ciliated cells along the tube being highest at the fimbria, (2) late follicular phase increase in cytoplasmic fragments and cellular material within the isthmic lumen, but not in the outer tubal segments and (3) similar secretory pattern and surface epithelial changes in the endometrial gland, isthmic and ampullary tubal epithelia. Gel electrophoresis of tubal flushing demonstrated two non-serum bands appearing in the late follicular and luteal phases of the cycle. One hundred and two women were included in the randomised controlled study. Analysis of all treatment cycles (n=227) showed that; (1) the first attempt resulted in a pregnancy rate per embryo transfer (PR/ET) of 29% for tubal and 20% for uterine replacements, and an implantation rate (IR) of 15% and 12% respectively, and (2) women with unexplained infertility benefit most following tubal transfer (PR/ET; tubal 32%, uterine 15% - IR; 14% and 7% respectively). Factors associated with increased PR in the first attempt include previous pregnancies, absent female or male factors, unexplained infertility, and human chorionic gonadotrophin luteal support. Despite an apparently higher PR and IR following tubal transfer, no significant differences were observed in the multiple pregnancy and live birth rates, nor in the implantation rate in cycles resulting in pregnancy. These findings suggest that the embryos' quality is not enhanced following tubal transfer

The opposites task: Using general rules to test cognitive flexibility in preschoolers

A brief narrative description of the journal article, document, or resource. Executive functions play an important role in cognitive development, and during the preschool years especially, children's performance is limited in tasks that demand flexibility in their behavior. We asked whether preschoolers would exhibit limitations when they are required to apply a general rule in the context of novel stimuli on every trial (the "opposites" task). Two types of inhibitory processing were measured: response interference (resistance to interference from a competing response) and proactive interference (resistance to interference from a previously relevant rule). Group data show 3-year-olds have difficulty inhibiting prepotent tendencies under these conditions, whereas 5-year-olds' accuracy is near ceiling in the task. (Contains 4 footnotes and 1 table.

Across space and time: infants learn from backward and forward visual statistics

within temporal and spatial visual streams. Two groups of 8-month-old infants were familiarized with an artificial grammar of shapes, comprised of backward and forward base pairs (i.e., two shapes linked by strong backward or forward transitional probability) and part-pairs (i.e., two shapes with weak transitional probabilities in both directions). One group viewed the continuous visual stream as a temporal sequence, while the other group viewed the same stream as a spatial array. Following familiarization, infants looked longer at test trials containing part- pairs than base pairs, though they had appeared with equal frequency during familiarization. This pattern of looking time was evident for both forward and backward pairs, in both the temporal and spatial conditions. Further, differences in looking time to part-pairs that were consistent or inconsistent with the predictive direction of the base pairs (forward or backward) indicated that infants were indeed sensitive to direction when presented with temporal sequences, but not when presented with spatial arrays. These results suggest that visual statistical learning is flexible in infancy and depends on the nature of visual input

Quality Assurance and its impact on ovarian visualisation rates in the multicentre United Kingdom Collaborative Trial of Ovarian Cancer Screening (UKCTOCS)

OBJECTIVE: To describe the quality assurance (QA) processes and their impact on visualisation of postmenopausal ovaries in the ultrasound arm of a multicentre ovarian cancer screening trial. METHODS: In UKCTOCS, 50,640 women aged 50-74 at recruitment were randomised to the ultrasound arm and underwent annual transvaginal scans. QA processes were developed during the course of the trial and included regular monitoring of Visualisation Rate (VR) of right ovary. Non-subjective factors previously identified as impacting on VR of right ovary were included in a generalised estimating equation(GEE) model for binary outcomes to enable comparison of observed versus adjusted VR between individual sonographers who had undertaken >1000scans on trial /centres. Analysis of annual VR of sonographers / centres was undertaken. RESULTS: Between June 2001 and December 2010, across 13 centres, 48230 (of 50639) women attended for 270035 annual transvaginal scans. One or both ovaries were seen in 84.5% (228145/270035) of scans. The observed VR of the right ovary was 72.7% (196426/270035). For the 78 sonographers included in the model, the median difference between observed and adjusted VR was 2% (range 0-8%) and median change in rank was 3 (range 0-18). For the 13 centres, the median difference between observed versus adjusted VR was 0% (range 0-2%) with no change in ranking. The median adjusted VR for sonographers was 73% (IQR 65-82%) and for centres was 74.7% (IQR 67.1-79.0%). Despite increasing age of the cohort, there was a steady decrease in the number of sonographers with VR80% (14.3% in 2002 to 40.8 % in 2010). Median centre VR increased from 65.5% (range 55.7-81.0%) in 2001 to 80.3% (range74.5%-90.9%) in 2010. CONCLUSIONS: A robust QA programme can improve visualisation of postmenopausal ovaries and is an essential component of ultrasound-based ovarian cancer screening trials. While VR should be adjusted for non-subjective factors that impact on ovarian visualisation, subjective factors are likely to be the largest contributors to VR differences

Self-reported transvaginal ultrasound visualization of normal ovaries in postmenopausal women is not reliable: results of expert review of archived images in UKCTOCS.

OBJECTIVE: In UKCTOCS self-reported visualization rates(srVR) at annual TVS scan was a key quality control(QC) metric. Our objective was to independently assess srVR using expert review and develop software capable of monitoring it. METHODS: Images from 1,000 examinations randomly selected from 68,951 archived annual TVS exams undertaken between 2008-2011 where the ovaries were reported as 'seen and normal' were reviewed by a single expert. Software was developed to identify exact images used to measure ovaries by measuring caliper dimensions and matching them to that recorded by the sonographer. A logistic regression classifier to determine visualization was trained and validated using ovarian dimension and visualization data reported by the expert . RESULTS: The expert confirmed both ovaries were visualized (cVR-Both) in 50.2%(502/1000) of the exams. The software identified the measurement image in 534 exams which were split 2:1:1 providing training, validating and testing data. Classifier accuracy on validation data was 70.9%(CI-95% 70.0,71.8). Analysis of test data (133 exams) resulted in sensitivity of 90.5%(CI-95% 80.9,95.8) and specificity of 47.5%(CI-95% 34.5,60.8) in detecting expert confirmed cVR-Both. CONCLUSIONS: Our results suggest that in a significant proportion of TVS annual screens the sonographers may have mistaken other structures for normal ovaries. It is uncertain whether or not this affected the sensitivity and stage at detection of ovarian cancer in the ultrasound arm of UKCTOCS, but we conclude QC metrics based on self-reported visualization of normal ovaries are unreliable. The classifier shows some potential for addressing this problem, though further research is needed