Ultranarrow bandwidth single-photon sources operating at room-temperature are of vital importance for viable optical quantum technologies at scale, including quantum key distribution, cloud-based ...quantum information processing networks, and quantum metrology. Here we show a room-temperature ultranarrow bandwidth single-photon source generating single-mode photons at a rate of 5 MHz based on an inorganic CsPbI3 perovskite quantum dot embedded in a tunable open-access optical microcavity. When coupled to an optical cavity mode, the quantum dot room-temperature emission becomes single-mode, and the spectrum narrows down to just ∼1 nm. The low numerical aperture of the optical cavities enables efficient collection of high-purity single-mode single-photon emission at room-temperature, offering promising performance for photonic and quantum technology applications. We measure 94% pure single-photon emission in a single-mode under pulsed and continuous-wave (CW) excitation.
We explored the uptake of metal chloride salts with +1 to +3 metals of Na+, K+, Zn2+, Cd2+, Sn2+, Cu2+, and In3+ by PbSe QD solar cells. We also compared CdCl2 to Cd acetate and Cd nitrate ...treatments. PbSe QD solar cells fabricated with a CdCl2 treatment are stable for more than 270 days stored in air. We studied how temperature and immersion times affect optoelectronic properties and photovoltaic cell performance. Uptake of Cd2+ and Zn2+ increase open circuit voltage, whereas In3+ and K+ increase the photocurrent without influencing the spectral response or first exciton peak position. Using the most beneficial treatments we varied the bandgap of PbSe QD solar cells from 0.78 to 1.3 eV and find the improved V OC is more prevalent for lower bandgap QD solar cells.
Some ligand–nanocrystal combinations exhibit rapid cooling of highly excited electronic states while other nanocrystal/shell combinations do not appear to have this effect. There remains a need to ...identify the distinguishing properties of ligand–nanocrystal interactions that avoid such rapid relaxation processes to guide the design of colloidal quantum dots (QDs) that take advantage of multiple exciton generation or hot-carrier extraction processes. Here, we use mid-infrared transient absorption spectroscopy to investigate the influence that carboxylate ligands with distinct excited state surface chemistries has on exciton–phonon coupling and hot exciton relaxation in PbS quantum dot (QD) films. Our findings reveal that despite significant differences in the excited state surface chemistry of oleate (OA) and iodide/mercaptopropionic acid (I–/MPA) ligands, PbS QD films passivated with both ligand types exhibit identical electronic relaxation rates and exciton–phonon coupling strengths within experimental precision. The data suggest that the inorganic lattice is the principal source of exciton–phonon coupling that influences hot exciton relaxation, rather than the vibronic modes of carboxylate ligands. The size-dependent nature of the exciton–phonon coupling strength is consistent with the localization of charge on the QD surfaces, which enhances the mixing of electronic and nuclear coordinates particularly when the electronic states are more quantum confined in smaller nanocrystals.
Within cognitive neuroscience, there is burgeoning interest in how the body is represented in the adult brain. However, there are large gaps in the understanding of neural body representations from a ...developmental perspective. Of particular interest are the interconnections between somatosensation and vision, specifically infants' abilities to register correspondences between their own bodies and the bodies of others. Such registration may play an important role in social learning and in engendering feelings of connectedness with others. In the current study, we further explored the interpersonal aspects of neural body representations by examining whether responses to tactile stimulation in 7-month-old infants are influenced by viewing another's body. During EEG recording, infants (
= 60) observed a live presentation of an experimenter's hand or foot being touched. During the presentation of touch to the adult's hand or foot, the infant received a brief tactile touch to their right hand or right foot. This resulted in four conditions: (i) receive hand stimulation/observe hand stimulation, (ii) receive hand stimulation/observe foot stimulation, (iii) receive foot stimulation/observe hand stimulation, and (iv) receive foot stimulation/observe foot stimulation. Analyses compared responses overlying hand and foot regions when the observed limb matched the stimulated limb (congruent) and did not match (incongruent). In line with prior work, tactile stimulation elicited a somatotopic pattern of results in the somatosensory evoked potential (SEP) and the sensorimotor mu rhythm (6-9 Hz). Cross-modal influences were observed in the beta rhythm (11-13 Hz) response and in the late potential of the SEP response (400-600 ms). Beta desynchronization was greater for congruent compared to incongruent conditions. Additionally, tactile stimulation to the foot elicited larger mean amplitudes for congruent compared to incongruent conditions. The opposite was true for stimulation to the hand. This set of novel findings suggests the importance of considering cross-modal effects in the study of neural body representations in the infant brain. Continued work in this new area of infant neuroscience research can inform how interpersonal aspects of body representations may serve to undergird early social learning.
Observations of the hot-phonon bottleneck, which is predicted to slow the rate of hot carrier cooling in quantum confined nanocrystals, have been limited to date for reasons that are not fully ...understood. We used time-resolved infrared spectroscopy to directly measure higher energy intraband transitions in PbS colloidal quantum dots. Direct measurements of these intraband transitions permitted detailed analysis of the electronic overlap of the quantum confined states that may influence their relaxation processes. In smaller PbS nanocrystals, where the hot-phonon bottleneck is expected to be most pronounced, we found that relaxation of parity selection rules combined with stronger electron–phonon coupling led to greater spectral overlap of transitions among the quantum confined states. This created pathways for fast energy transfer and relaxation that may bypass the predicted hot-phonon bottleneck. In contrast, larger, but still quantum confined nanocrystals did not exhibit such relaxation of the parity selection rules and possessed narrower intraband states. These observations were consistent with slower relaxation dynamics that have been measured in larger quantum confined systems. These findings indicated that, at small radii, electron–phonon interactions overcome the advantageous increase in energetic separation of the electronic states for PbS quantum dots. Selection of appropriately sized quantum dots, which minimize spectral broadening due to electron–phonon interactions while maximizing electronic state separation, is necessary to observe the hot-phonon bottleneck. Such optimization may provide a framework for achieving efficient hot carrier collection and multiple exciton generation.
Substantial policy changes to control obesity, limit chronic disease, and reduce air pollution emissions, including greenhouse gasses, have been recommended. Transportation and planning policies that ...promote active travel by walking and cycling can contribute to these goals, potentially yielding further co-benefits. Little is known, however, about the interconnections among effects of policies considered, including potential unintended consequences.
We review available literature regarding health impacts from policies that encourage active travel in the context of developing health impact assessment (HIA) models to help decision-makers propose better solutions for healthy environments. We identify important components of HIA models of modal shifts in active travel in response to transport policies and interventions.
Policies that increase active travel are likely to generate large individual health benefits through increases in physical activity for active travelers. Smaller, but population-wide benefits could accrue through reductions in air and noise pollution. Depending on conditions of policy implementations, risk tradeoffs are possible for some individuals who shift to active travel and consequently increase inhalation of air pollutants and exposure to traffic injuries. Well-designed policies may enhance health benefits through indirect outcomes such as improved social capital and diet, but these synergies are not sufficiently well understood to allow quantification at this time.
Evaluating impacts of active travel policies is highly complex; however, many associations can be quantified. Identifying health-maximizing policies and conditions requires integrated HIAs.
► Active travel policies are growing in popularity worldwide. ► We review multiple benefits and potential risks associated with policies. ► Quantitative relationships for health impact assessments are discussed. ► Major health benefits are especially expected from physical activity outcomes. ► Well designed policies may enhance co-benefits and mitigate risks.
Highlights • ERP and mu rhythm were measured following cues signaling impending tactile stimuli. • Anticipatory mu ERD and CNV were elicited before stimulation of participants’ hands. • Both ...components were stronger in the contralateral sites prior to right hand stimuli. • Mu ERD and CNV were not present when stimuli to a task partner were expected.
Abstract There is growing interest within the field of social-cognitive neuroscience in the dynamics of sensorimotor EEG rhythms during the observation of actions performed by others. However, there ...remain important gaps in the literature regarding the effects of perceptual aspects of the observed hand movements. This study investigated two visual influences on the EEG response to hand actions. Specifically, the perspective of the action in relation to the participant (egocentric/allocentric) was varied and the effect of the hand used to carry out the action (left/right) was also assessed. While EEG was recorded, 28 undergraduate participants observed video clips showing an actor’s hand reaching for, grasping, and lifting a cylindrical object across four conditions (right-hand egocentric, left-hand egocentric, right-hand allocentric, and left-hand allocentric). For actions viewed from an egocentric perspective, significantly greater event-related desynchronization (ERD) was present in the 7–9 Hz range over right mid-frontal, right central, and bilateral mid-parietal sites for right-handed actions compared to left-handed actions. In addition, greater ERD was observed within the 7–9 Hz band during the observation of right-handed egocentric actions compared to actions viewed from the allocentric perspective. This finding was present at bilateral central and mid-parietal sites, and emerged as an anticipatory effect prior to the onset of the observed hand movements.
•The classic game of Simon Says is known to be very difficult for young children.•Seeing the actions in Simon Says does not make the game more difficult.•Simon Says becomes easier for children if the ...instructions are given by two people.•An adult’s inconsistency in rule use may present challenges for young children.
Compared with conceptually similar response inhibition tasks, the game of Simon Says is particularly challenging for young children. However, possible reasons for this difference have not been systematically investigated. Here we tested the relative influence of two dissociable characteristics of the standard Simon Says task: receiving both inhibition and activation commands from the same experimenter and seeing the experimenter perform the movement along with the commands. A sample of 74 children (mean age=55months) were randomly assigned to complete one of five possible tasks. Four of the five tasks were variations of Simon Says involving combinations of one or two experimenters and the presence versus absence of the experimenter’s movements. The fifth task was Bear–Dragon, a commonly used executive function task in which one experimenter employed two puppets to give action commands to children. Analyses revealed that children’s performance was significantly worse on the one-person Simon Says tasks compared with the two-person tasks and the Bear–Dragon task. The presence of the experimenters’ movements alongside their commands did not have a significant effect on children’s performance. The requirement to respond to one person who is changing how different rules apply to similar actions appears to be an important determinant of the difficulty of Simon Says for young children. In terms of implications, inconsistency in how an adult applies rules to children’s actions may be a detrimental social influence on the development of cognitive control during early childhood.
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