Systematic observation of biexciton AXX and A2s excited state of A exciton along with ground state (A1s) in monolayer MoS2 at 4 K, by temperature dependent and power dependent non-resonant ...photoluminescence spectroscopy.
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•Systematic observation of biexciton from 4 K to room temperature by photoluminescence study of monolayer MoS2.•Distinction of biexciton from A- trion and ground state of A exciton in MoS2.•Exciton bound to sulfur vacancies have been distinguished from biexciton having binding energy ∼ 60 meV.
Being direct band gap semiconductor, two-dimensional monolayer (ML) MoS2 has remarkable optical transitions arising from excitons, trions, biexciton and defects mediated bound states. However, experimental realization of biexciton in ML MoS2 has been challenging due to broad spectral feature of exciton. Here, we report on systematic observation of biexciton (AXX ∼ 1.90 eV) along with A- trion ∼ 1.92 eV and ground state exciton A1s ∼ 1.96 eV in ML MoS2 at 4 K, by laser-power and temperature-dependent non-resonant photoluminescence (PL) spectroscopy. At low temperatures the excited state of A exciton has also been observed, A2s ∼ 2.13 eV, which consequently merges in thermal broadening of B excitons, with rise in temperature. With excitation energy and power dependent PL, emission arising from exciton bound to sulfur vacancy (∼1.82 eV) have been distinguished from biexciton. Thus understanding of such excitonic states and biexcitons is useful for future quantum information processing, optoelectronic, photonics and THz applications.
Universal screening is recommended to reduce the age of diagnosis for autism spectrum disorder (ASD). However, there are insufficient data on children who screen negative and no study of outcomes ...from truly universal screening. With this study, we filled these gaps by examining the accuracy of universal screening with systematic follow-up through 4 to 8 years.
Universal, primary care-based screening was conducted using the Modified Checklist for Autism in Toddlers with Follow-Up (M-CHAT/F) and supported by electronic administration and integration into electronic health records. All children with a well-child visit (1) between 16 and 26 months, (2) at a Children's Hospital of Philadelphia site after universal electronic screening was initiated, and (3) between January 2011 and July 2015 were included (
= 25 999).
Nearly universal screening was achieved (91%), and ASD prevalence was 2.2%. Overall, the M-CHAT/F's sensitivity was 38.8%, and its positive predictive value (PPV) was 14.6%. Sensitivity was higher in older toddlers and with repeated screenings, whereas PPV was lower in girls. Finally, the M-CHAT/F's specificity and PPV were lower in children of color and those from lower-income households.
Universal screening in primary care is possible when supported by electronic administration. In this "real-world" cohort that was systematically followed, the M-CHAT/F was less accurate in detecting ASD than in previous studies. Disparities in screening rates and accuracy were evident in traditionally underrepresented groups. Future research should focus on the development of new methods that detect a greater proportion of children with ASD and reduce disparities in the screening process.
Fundamental understanding of the correlation between chemical bonding and lattice dynamics in intrinsically low thermal conductive crystalline solids is important to thermoelectrics, thermal barrier ...coating, and more recently to photovoltaics. Two-dimensional (2D) layered halide perovskites have recently attracted widespread attention in optoelectronics and solar cells. Here, we discover intrinsically ultralow lattice thermal conductivity (κL) in the single crystal of all-inorganic layered Ruddlesden–Popper (RP) perovskite, Cs2PbI2Cl2, synthesized by the Bridgman method. We have measured the anisotropic κL value of the Cs2PbI2Cl2 single crystal and observed an ultralow κL value of ∼0.37–0.28 W/mK in the temperature range of 295–523 K when measured along the crystallographic c-axis. First-principles density functional theory (DFT) analysis of the phonon spectrum uncovers the presence of soft (frequency ∼18–55 cm–1) optical phonon modes that constitute relatively flat bands due to localized vibrations of Cs and I atoms. A further low energy optical mode exists at ∼12 cm–1 that originates from dynamic octahedral rotation around Pb caused by anharmonic vibration of Cl atoms induced by a 3s2 lone pair. We provide experimental evidence for such low energy optical phonon modes with low-temperature heat capacity and temperature-dependent Raman spectroscopic measurements. The strong anharmonic coupling of the low energy optical modes with acoustic modes causes damping of heat carrying acoustic phonons to ultrasoft frequency (maximum ∼37 cm–1). The combined effect of soft elastic layered structure, abundance of low energy optical phonons, and strong acoustic–optical phonon coupling results in an intrinsically ultralow κL value in the all-inorganic layered RP perovskite Cs2PbI2Cl2.
Brain enlargement has been observed in children with autism spectrum disorder (ASD), but the timing of this phenomenon, and the relationship between ASD and the appearance of behavioural symptoms, ...are unknown. Retrospective head circumference and longitudinal brain volume studies of two-year olds followed up at four years of age have provided evidence that increased brain volume may emerge early in development. Studies of infants at high familial risk of autism can provide insight into the early development of autism and have shown that characteristic social deficits in ASD emerge during the latter part of the first and in the second year of life. These observations suggest that prospective brain-imaging studies of infants at high familial risk of ASD might identify early postnatal changes in brain volume that occur before an ASD diagnosis. In this prospective neuroimaging study of 106 infants at high familial risk of ASD and 42 low-risk infants, we show that hyperexpansion of the cortical surface area between 6 and 12 months of age precedes brain volume overgrowth observed between 12 and 24 months in 15 high-risk infants who were diagnosed with autism at 24 months. Brain volume overgrowth was linked to the emergence and severity of autistic social deficits. A deep-learning algorithm that primarily uses surface area information from magnetic resonance imaging of the brain of 6-12-month-old individuals predicted the diagnosis of autism in individual high-risk children at 24 months (with a positive predictive value of 81% and a sensitivity of 88%). These findings demonstrate that early brain changes occur during the period in which autistic behaviours are first emerging.
Understanding the mechanism that correlates phonon transport with chemical bonding and solid-state structure is the key to envisage and develop materials with ultralow thermal conductivity, which are ...essential for efficient thermoelectrics and thermal barrier coatings. We synthesized thallium selenide (TlSe), which is comprised of intertwined stiff and weakly bonded substructures and exhibits intrinsically ultralow lattice thermal conductivity (κL) of 0.62–0.4 W/mK in the range 295–525 K. Ultralow κL of TlSe is a result of its low energy optical phonon modes which strongly interact with the heat carrying acoustic phonons. Low energy optical phonons of TlSe are associated with the intrinsic rattler-like vibration of Tl+ cations in the cage constructed by the chains of (TlSe2) n n–, as evident in low temperature heat capacity, terahertz time-domain spectroscopy, and temperature dependent Raman spectroscopy. Density functional theoretical analysis reveals the bonding hierarchy in TlSe which involves ionic interaction in Tl+–Se while Tl3+–Se bonds are covalent, which causes significant lattice anharmonicity and intrinsic rattler-like low energy vibrations of Tl+, resulting in ultralow κL.
Objective:Previous research has demonstrated that the amygdala is enlarged in children with autism spectrum disorder (ASD). However, the precise onset of this enlargement during infancy, how it ...relates to later diagnostic behaviors, whether the timing of enlargement in infancy is specific to the amygdala, and whether it is specific to ASD (or present in other neurodevelopmental disorders, such as fragile X syndrome) are all unknown.Methods:Longitudinal MRIs were acquired at 6–24 months of age in 29 infants with fragile X syndrome, 58 infants at high likelihood for ASD who were later diagnosed with ASD, 212 high-likelihood infants not diagnosed with ASD, and 109 control infants (1,099 total scans).Results:Infants who developed ASD had typically sized amygdala volumes at 6 months, but exhibited significantly faster amygdala growth between 6 and 24 months, such that by 12 months the ASD group had significantly larger amygdala volume (Cohen’s d=0.56) compared with all other groups. Amygdala growth rate between 6 and 12 months was significantly associated with greater social deficits at 24 months when the infants were diagnosed with ASD. Infants with fragile X syndrome had a persistent and significantly enlarged caudate volume at all ages between 6 and 24 months (d=2.12), compared with all other groups, which was significantly associated with greater repetitive behaviors.Conclusions:This is the first MRI study comparing fragile X syndrome and ASD in infancy, demonstrating strikingly different patterns of brain and behavior development. Fragile X syndrome–related changes were present from 6 months of age, whereas ASD-related changes unfolded over the first 2 years of life, starting with no detectable group differences at 6 months. Increased amygdala growth rate between 6 and 12 months occurs prior to social deficits and well before diagnosis. This gradual onset of brain and behavior changes in ASD, but not fragile X syndrome, suggests an age- and disorder-specific pattern of cascading brain changes preceding autism diagnosis.
Autism spectrum disorder (ASD) is diagnosed more frequently in boys than girls, even when girls are equally symptomatic. Cutting-edge behavioral imaging has detected "camouflaging" in girls with ASD, ...wherein social behaviors appear superficially typical, complicating diagnosis. The present study explores a new kind of camouflage based on language differences. Pauses during conversation can be filled with words like UM or UH, but research suggests that these two words are pragmatically distinct (e.g., UM is used to signal longer pauses, and may correlate with greater social communicative sophistication than UH). Large-scale research suggests that women and younger people produce higher rates of UM during conversational pauses than do men and older people, who produce relatively more UH. Although it has been argued that children and adolescents with ASD use UM less often than typical peers, prior research has not included sufficient numbers of girls to examine whether sex explains this effect. Here, we explore UM vs. UH in school-aged boys and girls with ASD, and ask whether filled pauses relate to dimensional measures of autism symptom severity.
Sixty-five verbal school-aged participants with ASD (49 boys, 16 girls, IQ estimates in the average range) participated, along with a small comparison group of typically developing children (8 boys, 9 girls). Speech samples from the Autism Diagnostic Observation Schedule were orthographically transcribed and time-aligned, with filled pauses marked. Parents completed the Social Communication Questionnaire and the Vineland Adaptive Behavior Scales.
Girls used UH less often than boys across both diagnostic groups. UH suppression resulted in higher UM ratios for girls than boys, and overall filled pause rates were higher for typical children than for children with ASD. Higher UM ratios correlated with better socialization in boys with ASD, but this effect was driven by increased use of UH by boys with greater symptoms.
Pragmatic language markers distinguish girls and boys with ASD, mirroring sex differences in the general population. One implication of this finding is that typical-sounding disfluency patterns (i.e., reduced relative UH production leading to higher UM ratios) may normalize the way girls with ASD sound relative to other children, serving as "linguistic camouflage" for a naïve listener and distinguishing them from boys with ASD. This first-of-its-kind study highlights the importance of continued commitment to understanding how sex and gender change the way that ASD manifests, and illustrates the potential of natural language to contribute to objective "behavioral imaging" diagnostics for ASD.
The screening power of the CBCL/1½–5’s Withdrawn and Diagnostic and Statistical Manual of Mental Disorders-Pervasive Developmental Problems (DSM-PDP) scales to identify children diagnosed with autism ...spectrum disorder at 24 months was tested in a longitudinal, familial high-risk study. Participants were 56 children at high risk for autism spectrum disorder due to an affected older sibling (high-risk group) and 26 low-risk children with a typically developing older sibling (low-risk group). At 24 months, 13 of the 56 high-risk children were diagnosed with autism spectrum disorder, whereas the other 43 were not. The high-risk children diagnosed with autism spectrum disorder group had significantly higher scores on the CBCL/1½–5’s Diagnostic and Statistical Manual of Mental Disorders-Pervasive Developmental Problems and Withdrawn scales than children in the low-risk and high-risk children not diagnosed with autism spectrum disorder groups
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. Receiver operating characteristic analyses yielded very high area under the curve values (0.91 and 0.89), and a cut point of T ⩾ 60 yielded sensitivity of 77% and specificity of 97% to 99% between the high-risk children diagnosed with autism spectrum disorder and the combination of low-risk and high-risk children not diagnosed with autism spectrum disorder. Consistent with several previous studies, the CBCL/1½–5’s Diagnostic and Statistical Manual of Mental Disorders-Pervasive Developmental Problems scale and the Withdrawn syndrome differentiated well between children diagnosed with autism spectrum disorder and those not diagnosed.
Narrative abilities are linked to social impairment in autism spectrum disorder (ASD), such that reductions in words about cognitive processes (e.g.,
,
) are thought to reflect underlying deficits in ...social cognition, including Theory of Mind. However, research suggests that typically developing (TD) boys and girls tell narratives in sex-specific ways, including differential reliance on cognitive process words. Given that most studies of narration in ASD have been conducted in predominantly male samples, it is possible that prior results showing reduced cognitive processing language in ASD may not generalize to autistic girls. To answer this question, we measured the relative frequency of two kinds of words in stories told by autistic girls and boys: nouns (words that indicate object-oriented storytelling) and cognitive process words (words like
and
that indicate mentalizing or attention to other peoples' internal states).
One hundred two verbally fluent school-aged children girls with ASD (
= 21) and TD (
= 19), and boys with ASD (
= 41) and TD (
= 21) were matched on age, IQ, and maternal education. Children told a story from a sequence of pictures, and word frequencies (nouns, cognitive process words) were compared.
Autistic children of both sexes consistently produced a greater number of nouns than TD controls, indicating object-focused storytelling. There were no sex differences in cognitive process word use in the TD group, but autistic girls produced significantly more cognitive process words than autistic boys, despite comparable autism symptom severity. Thus, autistic girls showed a unique narrative profile that overlapped with autistic boys
typical girls/boys. Noun use correlated significantly with parent reports of social symptom severity in all groups, but cognitive process word use correlated with social ability in boys only.
This study extends prior research on autistic children's storytelling by measuring sex differences in the narratives of a relatively large, well-matched sample of children with and without ASD. Importantly, prior research showing that autistic children use fewer cognitive process words is true for boys only, while object-focused language is a sex-neutral linguistic marker of ASD. These findings suggest that sex-sensitive screening and diagnostic methods-preferably using objective metrics like natural language processing-may be helpful for identifying autistic girls, and could guide the development of future personalized treatment strategies.
Autism spectrum disorders (ASD) often go undetected in toddlers. The Modified Checklist for Autism in Toddlers (M-CHAT) was used to screen 3,793 children aged 16–30 months from low- and high-risk ...sources; screen positive cases were diagnostically evaluated. Re-screening was performed on 1,416 children aged 42–54 months. Time1 Positive Predictive Value (PPV) was .36 for the initial screening and .74 for the screening plus follow-up telephone interview; values were similar for Time2 PPV. When separating referral sources, PPV was low for the low-risk sample but acceptable with the follow-up telephone interview. Children with ASD from the low-risk and high-risk samples were highly similar. Results indicate that the M-CHAT continues to be a promising instrument for the early detection of ASD.
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