Identification and Suppression of Point Defects in Bromide Perovskite Single Crystals Enabling Gamma-Ray Spectroscopy.

Methylammonium lead tribromide (MAPbBr3) stands out as the most easily grown wide-band-gap metal halide perovskite. It is a promising semiconductor for room-temperature gamma-ray (γ-ray) spectroscopic detectors, but no operational devices are realized. This can be largely attributed to a lack of understanding of point defects and their influence on detector performance. Here, through a combination of crystal growth design and defect characterization, including positron annihilation and impedance spectroscopy, the presence of specific point defects are identified and correlated to detector performance. Methylammonium (MA) vacancies, MA interstitials, and Pb vacancies are identified as the dominant charge-trapping defects in MAPbBr3 crystals, while Br vacancies caused doping. The addition of excess MABr reduces the MA and Br defects and so enables the detection of energy-resolved γ-ray spectra using a MAPbBr3 single-crystal device. Interestingly, the addition of formamidinium (FA) cations, which converted to methylformamidinium (MFA) cations by reaction with MA+ during crystal growth further reduced MA defects. This enabled an energy resolution of 3.9% for the 662 keV 137Cs line using a low bias of 100 V. The work provides direction toward enabling further improvements in wide-bandgap perovskite-based device performance by reducing detrimental defects.

A new Asian version of the CFMT: The Cambridge Face Memory Test - Chinese Malaysian (CFMT-MY).

The Cambridge Face Memory Test (CFMT) is one of the most important measures of individual differences in face recognition and for the diagnosis of prosopagnosia. Having two different CFMT versions using a different set of faces seems to improve the reliability of the evaluation. However, at the present time, there is only one Asian version of the test. In this study, we present the Cambridge Face Memory Test - Chinese Malaysian (CFMT-MY), a novel Asian CFMT using Chinese Malaysian faces. In Experiment 1, Chinese Malaysian participants (N = 134) completed two versions of the Asian CFMT and one object recognition test. The CFMT-MY showed a normal distribution, high internal reliability, high consistency and presented convergent and divergent validity. Additionally, in contrast to the original Asian CFMT, the CFMT-MY showed an increasing level of difficulties across stages. In Experiment 2, Caucasian participants (N = 135) completed the two versions of the Asian CFMT and the original Caucasian CFMT. Results showed that the CFMT-MY exhibited the other-race effect. Overall, the CFMT-MY seems to be suitable for the diagnosis of face recognition difficulties and could be used as a measure of face recognition ability by researchers who wish to examine face-related research questions such as individual differences or the other-race effect.

Null effect of anodal and cathodal transcranial direct current stimulation (tDCS) on own- and other-race face recognition.

Successful face recognition is important for social interactions and public security. Although some preliminary evidence suggests that anodal and cathodal transcranial direct current stimulation (tDCS) might modulate own- and other-race face identification, respectively, the findings are largely inconsistent. Hence, we examined the effect of both anodal and cathodal tDCS on the recognition of own- and other-race faces. Ninety participants first completed own- and other-race Cambridge Face Memory Test (CFMT) as baseline measurements. Next, they received either anodal tDCS, cathodal tDCS or sham stimulation and finally they completed alternative versions of the own- and other-race CFMT. No difference in performance, in terms of accuracy and reaction time, for own- and other-race face recognition between anodal tDCS, cathodal tDCS and sham stimulation was found. Our findings cast doubt upon the efficacy of tDCS to modulate performance in face identification tasks.

Investigating the role of the fusiform face area and occipital face area using multifocal transcranial direct current stimulation.

The functional role of the occipital face area (OFA) and the fusiform face area (FFA) in face recognition is inconclusive to date. While some research has shown that the OFA and FFA are involved in early (i.e., featural processing) and late (i.e., holistic processing) stages of face recognition respectively, other research suggests that both regions are involved in both early and late stages of face recognition. Thus, the current study aims to further examine the role of the OFA and the FFA using multifocal transcranial direct current stimulation (tDCS). In Experiment 1, we used computer-generated faces. Thirty-five participants completed whole face and facial features (i.e., eyes, nose, mouth) recognition tasks after OFA and FFA stimulation in a within-subject design. No difference was found in recognition performance after either OFA or FFA stimulation. In Experiment 2 with 60 participants, we used real faces, provided stimulation following a between-subjects design and included a sham control group. Results showed that FFA stimulation led to enhanced efficiency of facial features recognition. Additionally, no effect of OFA stimulation was found for either facial feature or whole face recognition. These results suggest the involvement of FFA in the recognition of facial features.

Eye movements are made to the centre of gravity of texture-defined targets.

Saccadic localisation of targets of various properties has been extensively studied, but rarely for texture-defined figures. In this paper, three experiments that investigate the way information from a texture target is processed in order to provide a signal for eye movement control are presented. Participants made saccades to target regions embedded in a background structure, and the saccade landing position and latency were measured. The textures comprised line elements, with orientations of the lines configured to form the figure and ground. Various orientation profile configurations (Block, Blur, and Cornsweet), were used in order to measure the role of edge profiles in driving eye movements and producing salience. We found that in all cases the visual system is in fact able to effectively segregate a texture figure from the ground in order to accurately plan a saccade to the target-figure. While saccadic latency was the highest for the Blur profile, the mean saccadic landing position was mostly unaffected by the various profiles (Experiment 1). More specifically, we showed that saccades were directed to the centre-of-gravity of the target (Experiment 2). We also found that figures with information of orientation contrast at both the edge and centre of figure (i.e. Block) produced the highest level of saliency in attracting eye movements (Experiment 3). Overall, the results show that saccades are planned on the representation of the whole target shape rather than a local salient region based on orientation contrast cues, and that the various texture profiles were important only to the extent that they affected the time to programme a saccade.

Do they 'look' different(ly)? Dynamic face recognition in Malaysians: Chinese, Malays and Indians compared.

Previous cross-cultural eye-tracking studies examining face recognition discovered differences in the eye movement strategies that observers employ when perceiving faces. However, it is unclear (1) the degree to which this effect is fundamentally related to culture and (2) to what extent facial physiognomy can account for the differences in looking strategies when scanning own- and other-race faces. In the current study, Malay, Chinese and Indian young adults who live in the same multiracial country performed a modified yes/no recognition task. Participants' recognition accuracy and eye movements were recorded while viewing muted face videos of own- and other-race individuals. Behavioural results revealed a clear own-race advantage in recognition memory, and eye-tracking results showed that the three ethnic race groups adopted dissimilar fixation patterns when perceiving faces. Chinese participants preferentially attended more to the eyes than Indian participants did, while Indian participants made more and longer fixations on the nose than Malay participants did. In addition, we detected statistically significant, though subtle, differences in fixation patterns between the faces of the three races. These findings suggest that the racial differences in face-scanning patterns may be attributed both to culture and to variations in facial physiognomy between races.

Evaluation of Steam-Ultrasound Decontamination on Naturally Contaminated Broilers through the Analysis of Campylobacter, Total Viable Count, and Enterobacteriaceae.

ABSTRACT: This study aimed to evaluate the decontamination effects of steam-ultrasound application, through specially designed nozzles installed inside a constructed machine, with a capacity of 10,500 birds per h on naturally contaminated broilers. Using three different skin-sampling areas-back, breast, and neck skin-microbial analysis of Campylobacter, Enterobacteriaceae, and total viable count (TVC) was performed before and after steam-ultrasound treatment. In total, 648 skin samples were analyzed for Campylobacter, and 216 samples were analyzed for Enterobacteriaceae and TVC. Results showed Campylobacter reductions (P < 0.001) of 0.8, 1.1, and 0.7 log, analyzed from back, breast, and the neck skin samples, respectively. Furthermore, reductions of Enterobacteriaceae (P < 0.001) by 1.6, 1.9, and 1.1 log and reductions of TVC (P < 0.001) by 2.0, 2.4, and 1.3 log were found on back, breasts, and neck, respectively. Campylobacter levels were evaluated after 8 days of refrigeration at 4°C in control and steam-ultrasound-treated broilers to determine contamination stability in a small 12-sample trial. The results showed no changes in reductions during refrigeration, indicating that reduced Campylobacter numbers remained stable in treated broilers. This study showed significant bacterial reduction was achieved in three different broiler surface areas at a slaughter speed of 10,500 birds per h at temperatures more than 80°C. The rapid treatment of less than 1.5-s exposure time inside the chamber makes this technology potentially suitable for modern and fast poultry processing lines.

Identification of lead vacancy defects in lead halide perovskites.

Perovskite photovoltaics advance rapidly, but questions remain regarding point defects: while experiments have detected the presence of electrically active defects no experimentally confirmed microscopic identifications have been reported. Here we identify lead monovacancy (VPb) defects in MAPbI3 (MA = CH3NH3+) using positron annihilation lifetime spectroscopy with the aid of density functional theory. Experiments on thin film and single crystal samples all exhibited dominant positron trapping to lead vacancy defects, and a minimum defect density of ~3 × 1015 cm-3 was determined. There was also evidence of trapping at the vacancy complex [Formula: see text] in a minority of samples, but no trapping to MA-ion vacancies was observed. Our experimental results support the predictions of other first-principles studies that deep level, hole trapping, [Formula: see text], point defects are one of the most stable defects in MAPbI3. This direct detection and identification of a deep level native defect in a halide perovskite, at technologically relevant concentrations, will enable further investigation of defect driven mechanisms.

The other-race effect and holistic processing across racial groups.

It is widely accepted that holistic processing is important for face perception. However, it remains unclear whether the other-race effect (ORE) (i.e. superior recognition for own-race faces) arises from reduced holistic processing of other-race faces. To address this issue, we adopted a cross-cultural design where Malaysian Chinese, African, European Caucasian and Australian Caucasian participants performed four different tasks: (1) yes-no face recognition, (2) composite, (3) whole-part and (4) global-local tasks. Each face task was completed with unfamiliar own- and other-race faces. Results showed a pronounced ORE in the face recognition task. Both composite-face and whole-part effects were found; however, these holistic effects did not appear to be stronger for other-race faces than for own-race faces. In the global-local task, Malaysian Chinese and African participants demonstrated a stronger global processing bias compared to both European- and Australian-Caucasian participants. Importantly, we found little or no cross-task correlation between any of the holistic processing measures and face recognition ability. Overall, our findings cast doubt on the prevailing account that the ORE in face recognition is due to reduced holistic processing in other-race faces. Further studies should adopt an interactionist approach taking into account cultural, motivational, and socio-cognitive factors.

The Own-Race Bias for Face Recognition in a Multiracial Society.

The own-race bias (ORB) is a reliable phenomenon across cultural and racial groups where unfamiliar faces from other races are usually remembered more poorly than own-race faces (Meissner and Brigham, 2001). By adopting a yes-no recognition paradigm, we found that ORB was pronounced across race groups (Malaysian-Malay, Malaysian-Chinese, Malaysian-Indian, and Western-Caucasian) when faces were presented with only internal features (Experiment 1), implying that growing up in a profoundly multiracial society does not necessarily eliminate ORB. Using a procedure identical to Experiment 1, we observed a significantly greater increment in recognition performance for other-race faces than for own-race faces when the external features (e.g. facial contour and hairline) were presented along with the internal features (Experiment 2)-this abolished ORB. Contrary to assumptions based on the contact hypothesis, participants' self-reported amount of interracial contact on a social contact questionnaire did not significantly predict the magnitude of ORB. Overall, our findings suggest that the level of exposure to other-race faces accounts for only a small part of ORB. In addition, the present results also support the notion that different neural mechanisms may be involved in processing own- and other-race faces, with internal features of own-race faces being processed more effectively, whereas external features dominate representations of other-race faces.

The Muslim headscarf and face perception: "they all look the same, don't they?".

The headscarf conceals hair and other external features of a head (such as the ears). It therefore may have implications for the way in which such faces are perceived. Images of faces with hair (H) or alternatively, covered by a headscarf (HS) were used in three experiments. In Experiment 1 participants saw both H and HS faces in a yes/no recognition task in which the external features either remained the same between learning and test (Same) or switched (Switch). Performance was similar for H and HS faces in both the Same and Switch condition, but in the Switch condition it dropped substantially compared to the Same condition. This implies that the mere presence of the headscarf does not reduce performance, rather, the change between the type of external feature (hair or headscarf) causes the drop in performance. In Experiment 2, which used eye-tracking methodology, it was found that almost all fixations were to internal regions, and that there was no difference in the proportion of fixations to external features between the Same and Switch conditions, implying that the headscarf influenced processing by virtue of extrafoveal viewing. In Experiment 3, similarity ratings of the internal features of pairs of HS faces were higher than pairs of H faces, confirming that the internal and external features of a face are perceived as a whole rather than as separate components.

The significance of hair for face recognition.

Hair is a feature of the head that frequently changes in different situations. For this reason much research in the area of face perception has employed stimuli without hair. To investigate the effect of the presence of hair we used faces with and without hair in a recognition task. Participants took part in trials in which the state of the hair either remained consistent (Same) or switched between learning and test (Switch). It was found that in the Same trials performance did not differ for stimuli presented with and without hair. This implies that there is sufficient information in the internal features of the face for optimal performance in this task. It was also found that performance in the Switch trials was substantially lower than in the Same trials. This drop in accuracy when the stimuli were switched suggests that faces are represented in a holistic manner and that manipulation of the hair causes disruption to this, with implications for the interpretation of some previous studies.

Distance determination in heterogeneous DNA model systems by pulsed EPR.

Many biological systems, especially those based on nucleic acids, are structurally heterogeneous in solution. We demonstrate here the ability to measure multiple distances, of between 2 and 7 nm, from a heterogeneous mixture of double-spin-labeled DNA duplexes. We have constructed a DNA distance ruler based on the attachment of nitroxide spin labels to 2'-amino-modified nucleosides. The distribution of distances between the spin labels was obtained by Tikhonov regularization analysis of the dipolar coupling evolution data measured by using the electron paramagnetic resonance method, pulsed-electron double resonance (PELDOR). Optimization of the conditions and techniques used in the preparation of the samples has allowed us to increase the sensitivity and reduce aggregation artifacts. As a result, we have been able to demonstrate deconvolution of distances from structurally heterogeneous samples and show the limits of the technique by examining data derived from up to five DNA duplexes, in a single mixture, in which the concentration of each species was as low as 5 microM.

Tilt aftereffect for texture edges is larger than in matched subjective edges, but both are strong adaptors of luminance edges.

The tilt aftereffect (TAE) has been used previously to probe whether contours defined by different attributes are subserved by the same or by different underlying mechanisms. Here, we compare two types of contours between texture surfaces, one with texture orientation contrast across the edge (orientation contrast contour; OC) and one without, commonly referred to as a subjective contour (SC). Both contour types produced curves of TAE versus adapting angle displaying typical positive and negative peaks at approximately 15 and 70 deg, respectively. The curves are well fit by difference of Gaussian (DoG) functions, with one Gaussian accounting for the contour adaptation effect and the other accounting for the texture orientation adaptation effect. Adaptation to OC elicited larger TAEs than did adaptation to SC, suggesting that they more effectively activate orientation-selective neurons in V1/V2 during prolonged viewing. Surprisingly, both contour types adapted a luminance contour (LC) as strongly as did an LC itself, suggesting that the second-order orientation cue contained in the texture edge activates the same set of orientation-selective neurons as does an LC. These findings have implications for the mechanisms by which the orientations of texture edges and SCs are encoded.

Pulling the other one: 1st- and 2nd-order visual information interact to determine perceived location.

We demonstrate that the 1st- and 2nd-order characteristics of a visual stimulus can have a profound influence on each other in terms of perceived position. We use the parameter of spatial separation to selectively manipulate the effect of one characteristic upon the other. 1st-order features have their largest effect upon the perceived position of 2nd-order structure when separation is small, whilst the reciprocal effect is maximal at large separations. Implications for models of 1st- and 2nd-order interaction are discussed.

Nulling the motion aftereffect with dynamic random-dot stimuli: limitations and implications.

We used biased random-dot dynamic test stimuli to measure the strength of the motion aftereffect (MAE) to evaluate the usefulness of this technique as a measure of motion adaptation strength. The stimuli consisted of noise dots whose individual directions were random and of signal dots moving in a unique direction. All dots moved at the same speed. For each condition, the nulling percentage (percentage of signal dots needed to perceptually null the MAE) was scaled with respect to the coherence threshold (percentage needed to perceive the coherent motion of signal dots without prior adaptation). The increase of these scaled values with the density of dots in the test stimulus suggests that MAE strength is underestimated when measured with low densities. We show that previous reports of high nulling percentages at slow speeds do not reflect strong MAEs, but are actually due to spatio-temporal aliasing, which dramatically increases coherence thresholds. We further show that MAE strength at slow speed increases with eccentricity. These findings are consistent with the idea that using this dynamic test stimulus preferentially reveals the adaptation of a population of high-speed motion units whose activity is independent of adapted low-speed motion units.