Mindful Awareness Practices (MAPs) in Adolescents With ADHD and Cognitive Disengagement Syndrome (CDS): A Pilot Open Trial.

Objective: Very few studies have investigated intervention approaches that may be efficacious for youth with ADHD and co-occurring cognitive disengagement syndrome (CDS) symptoms. This study examined the feasibility, acceptability, and preliminary efficacy of a mindfulness-based intervention for adolescents with ADHD and co-occurring CDS symptoms. Methods: Fourteen adolescents ages 13 to 17 years (35.71% female; 64.29% White, 7.14% Black, 28.57% Multiracial) with ADHD and elevated CDS symptoms completed the 8-week group-based Mindful Awareness Practices (MAPs) program developed for individuals with ADHD. We collected measures of CDS, ADHD, mind-wandering, mindfulness, and other difficulties and functioning at baseline, 1-month post-intervention, and 3-month post-intervention to examine preliminary efficacy. We measured participant session attendance, session engagement, at-home practice adherence, and satisfaction of adolescents and caregivers at 1-month post-intervention to examine feasibility and acceptability. We also collected qualitative feedback from adolescents and caregivers at 1-month post-intervention. Results: The intervention was overall feasible to administer, and caregivers and adolescents reported satisfaction with the intervention despite some difficulties with attendance and engagement. We observed improvements to both caregiver- and adolescent-reported CDS symptoms and ADHD-inattentive symptoms from pre-intervention to post-intervention time points, though findings across 1- and 3-month follow-up differed based on informant. We also observed improvements to some indices of adolescent-reported mind-wandering, mindfulness, brooding rumination, and academic functioning. For caregiver report, the only other noted improvement was for executive functioning. No improvements were reported by teachers. Conclusions: Findings support the initial feasibility, acceptability, and preliminary efficacy of MAPs for adolescents with ADHD and co-occurring CDS symptoms on a range of outcomes. Larger trials with a randomized design are warranted to further examine mindfulness-based interventions for adolescents with ADHD and co-occurring CDS symptoms.

Cognitive Disengagement Syndrome-Clinical Interview (CDS-CI): Psychometric support for caregiver and youth versions.

Cognitive disengagement syndrome (CDS), formerly termed sluggish cognitive tempo, is a set of symptoms characterized by excessive daydreaming, mental confusion, and slowed behavior/thinking. CDS is distinct from symptoms of attention-deficit/hyperactivity disorder (ADHD) and other psychopathologies and uniquely associated with functional impairment. However, despite significant progress in developing and evaluating rating scale measures of CDS, no clinical interview of CDS exists with established psychometric properties that can facilitate a multimethod approach assessing CDS. Accordingly, the present study evaluated the psychometric properties of the semistructured Cognitive Disengagement Syndrome-Clinical Interview (CDS-CI). The CDS-CI and the ADHD inattention (ADHD-IN) and hyperactive-impulsivity (ADHD-HI) modules from the Kiddie Schedule of Affective Disorders and Schizophrenia for School-Age Children (K-SADS) were administered to a sample of early adolescents (N = 341, ages 10-12 years) and their caregivers. Adolescents and caregivers also completed rating scale measures of CDS and ADHD symptoms. The CDS-CI demonstrated high internal consistency and interrater reliability. CDS-CI scores showed excellent same-source discriminant validity from K-SADS, ADHD-IN, and ADHD-HI scores and encouraging convergent and discriminant validity with rating scale measures, especially for caregivers. Above and beyond K-SADS, ADHD-IN, and ADHD-HI scores, higher parent and adolescent CDS-CI scores were both significantly associated with greater functional impairment. A threshold of ≥ 6 out of 15 symptoms was selected as an initial threshold for determining clinically elevated CDS using the CDS-CI. Findings provide psychometric support for the CDS-CI as a tool in the multimethod assessment of CDS. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

From Slow Shifts to Fast Flips: Unraveling problem-based learning group function dynamics.

PURPOSE: Problem-Based Learning (PBL) relies on self-directed learning in small groups in the presence of a tutor. While the effectiveness of PBL is often attributed to the dynamics of group function, change in group function over time and factors influencing group function development are less understood. This study aims to explore the development of PBL group function over time to better understand the factors that give rise to high-functioning groups. METHOD: We examined time-function graphs of group function and conducted semi-structured focus group discussions in 2023 with medical students enrolled in a PBL curriculum. Students reflected on their experiences in four different PBL groups, creating time-function graphs to characterize development of group function over 8-12-week periods. We analyzed graphs and transcripts in a staged approach using qualitative description and direct content analysis, sensitized by two frameworks: Tuckman's Stages of Group Development and the Dimensions of PBL Group Function. RESULTS: Three archetypes of PBL group function development were identified: Slow Shifters, Fast Flippers, and Coasters. (1) Slow Shifters were characterized by a complex and extended pattern of growth consistent with Tuckman's model, typically occurring amongst inexperienced groups, or groups faced with a novel task. (2) Fast Flippers were characterized by abrupt state changes in group function arising from internal or external disruptions. (3) Coasters were characterized by plateaus, where maintenance of group function was a frequently cited challenge. Abrupt changes and plateaus occurred more among mature groups and groups with significant PBL experience. CONCLUSIONS: PBL group function varies over time in 3 different patterns. Classic Tuckman's stages are apparent among inexperienced groups, or groups facing novel tasks, whereas experienced groups often face abrupt change or plateaus. PBL educators and students should consider the need for novelty and disruption in more experienced groups to incite growth.

An artificial intelligence-generated model predicts 90-day survival in alcohol-associated hepatitis: A global cohort study.

BACKGROUND AND AIMS: Alcohol-associated hepatitis (AH) poses significant short-term mortality. Existing prognostic models lack precision for 90-day mortality. Utilizing artificial intelligence in a global cohort, we sought to derive and validate an enhanced prognostic model. APPROACH AND RESULTS: The Global AlcHep initiative, a retrospective study across 23 centers in 12 countries, enrolled patients with AH per National Institute for Alcohol Abuse and Alcoholism criteria. Centers were partitioned into derivation (11 centers, 860 patients) and validation cohorts (12 centers, 859 patients). Focusing on 30 and 90-day postadmission mortality, 3 artificial intelligence algorithms (Random Forest, Gradient Boosting Machines, and eXtreme Gradient Boosting) informed an ensemble model, subsequently refined through Bayesian updating, integrating the derivation cohort's average 90-day mortality with each center's approximate mortality rate to produce posttest probabilities. The ALCoholic Hepatitis Artificial INtelligence Ensemble score integrated age, gender, cirrhosis, and 9 laboratory values, with center-specific mortality rates. Mortality was 18.7% (30 d) and 27.9% (90 d) in the derivation cohort versus 21.7% and 32.5% in the validation cohort. Validation cohort 30 and 90-day AUCs were 0.811 (0.779-0.844) and 0.799 (0.769-0.830), significantly surpassing legacy models like Maddrey's Discriminant Function, Model for End-Stage Liver Disease variations, age-serum bilirubin-international normalized ratio-serum Creatinine score, Glasgow, and modified Glasgow Scores ( p < 0.001). ALCoholic Hepatitis Artificial INtelligence Ensemble score also showcased superior calibration against MELD and its variants. Steroid use improved 30-day survival for those with an ALCoholic Hepatitis Artificial INtelligence Ensemble score > 0.20 in both derivation and validation cohorts. CONCLUSIONS: Harnessing artificial intelligence within a global consortium, we pioneered a scoring system excelling over traditional models for 30 and 90-day AH mortality predictions. Beneficial for clinical trials, steroid therapy, and transplant indications, it's accessible at: https://aihepatology.shinyapps.io/ALCHAIN/ .

Regional impacts of warming on biodiversity and biomass in high latitude stream ecosystems across the Northern Hemisphere.

Warming can have profound impacts on ecological communities. However, explorations of how differences in biogeography and productivity might reshape the effect of warming have been limited to theoretical or proxy-based approaches: for instance, studies of latitudinal temperature gradients are often conflated with other drivers (e.g., species richness). Here, we overcome these limitations by using local geothermal temperature gradients across multiple high-latitude stream ecosystems. Each suite of streams (6-11 warmed by 1-15°C above ambient) is set within one of five regions (37 streams total); because the heating comes from the bedrock and is not confounded by changes in chemistry, we can isolate the effect of temperature. We found a negative overall relationship between diatom and invertebrate species richness and temperature, but the strength of the relationship varied regionally, declining more strongly in regions with low terrestrial productivity. Total invertebrate biomass increased with temperature in all regions. The latter pattern combined with the former suggests that the increased biomass of tolerant species might compensate for the loss of sensitive species. Our results show that the impact of warming can be dependent on regional conditions, demonstrating that local variation should be included in future climate projections rather than simply assuming universal relationships.

Predictors of executive function trajectories in adolescents with and without ADHD: Links with academic outcomes.

Changes in executive function (EF) occur during adolescence with several factors (e.g., parenting styles, socioeconomic status) influencing the development of EF abilities. These changes are important as EF has been strongly linked with a range of outcomes including academic achievement, job performance, and social-emotional well-being. However, few studies have examined variability in EF trajectories during this critical developmental period, or trajectories in samples known to have specific impairments with EF, such as adolescents diagnosed with attention-deficit/hyperactivity disorder (ADHD). The present study examined differential trajectories of three domains of parent-rated EF in 302 adolescents (167 males; Mage = 13.17 years) with and without ADHD (53.6% with ADHD) from grade 8 to 10. The study also explored whether adolescent ADHD, parent ADHD, and parents' own EF predicted EF trajectories in addition to the longitudinal relation between trajectories and academic outcomes. Findings suggest that adolescence is marked by significant variability in EF development due to factors such as ADHD status, parent ADHD, and parent EF ability. Additionally, adolescents who displayed poor EF abilities throughout middle and high school had significantly lower grade point averages and poorer parent-, teacher-, and self-reported academic outcomes. Implications for interventions targeting EF deficits among adolescents with and without ADHD are discussed.

Corrigendum: A Mini-Review of Pharmacological and Psychosocial Interventions for Reducing Irritability Among Youth With ADHD.

[This corrects the article DOI: 10.3389/fpsyt.2022.794044.].

A Mini-Review of Pharmacological and Psychosocial Interventions for Reducing Irritability Among Youth With ADHD.

Approximately a third of children and adolescents with attention-deficit/hyperactivity disorder (ADHD) experience significant irritability; despite this, no study has reviewed whether interventions for youth with ADHD can improve irritability. This mini review sought to address this gap in the literature by discussing existing pharmacological and psychosocial interventions for irritability among children and adolescents with ADHD. A literature search was conducted in April 2021, with a total of 12 intervention articles identified (six pharmacological, one psychosocial, five combined). Studies were excluded if they did not involve an intervention, a measure of irritability, or the population was not youth with ADHD. Of these articles, two were with an ADHD only sample; seven included ADHD with comorbid disruptive behavior, disruptive mood dysregulation disorder (DMDD), or severe mood dysregulation (SMD); and three included ADHD with comorbid autism spectrum disorder (ASD). Findings suggest that central nervous system stimulants used alone or in combination with behavior therapy are effective at reducing irritability in youth with ADHD only or comorbid ADHD and DMDD/SMD. Less evidence was found for the efficacy of guanfacine and atomoxetine for youth with ADHD only or comorbid ADHD and ASD. Parent training alone or in combination with atomoxetine was found to be effective at reducing irritability in youth with comorbid ADHD and ASD. Future research assessing the efficacy of other psychosocial interventions, particularly cognitive behavioral therapy is necessary, as are randomized trials assessing intervention sequencing and intensity among youth with ADHD. Researchers are advised to utilize well-validated measures of irritability in future research.

COVID-19 Resulted in Lower Grades for Male High School Students and Students With ADHD.

OBJECTIVE: Researchers have speculated that the COVID-19 pandemic may expand the academic performance gap experienced by at-risk students. We examined learning experiences during the 2020 to 2021 school year and the impact the pandemic has had on high school student grade point average (GPA), including predictors of change in GPA from 2019-2020 to 2020-2021. METHOD: Participants were 238 adolescents (55.5% male), 49.6% with attention-deficit/hyperactivity disorder (ADHD), in the United States. Adolescents reported on their GPAs via online surveys. RESULTS: GPA significantly decreased on average from 2019-2020 to 2020-2021 school year. ADHD status and biological sex significantly moderated change-students with ADHD and male students reported decreased GPA, whereas students without ADHD and female students' GPA did not change. Low income and Black/Latinx students had lower GPAs in both school years. CONCLUSION: It is imperative that additional supports be provided for at-risk students to help them catch up on missed learning during the pandemic.

Practical considerations for quantitative clinical SPECT/CT imaging of alpha particle emitting radioisotopes.

Rationale: Alpha particle emitting radiopharmaceuticals are generating considerable interest for the treatment of disseminated metastatic disease. Molecular imaging of the distribution of these agents is critical to safely and effectively maximize the clinical potential of this emerging drug class. The present studies aim to investigate the feasibility and limitations of quantitative SPECT for 223Ra, 225Ac and 227Th. Methods: Three state-of-the-art SPECT/CT systems were investigated: the GE Discovery NM/CT 670, the GE Optima NM/CT 640, and the Siemens Symbia T6. A series of phantoms, including the NEMA IEC Body phantom, were used to compare and calibrate each camera. Additionally, anthropomorphic physical tumor and vertebrae phantoms were developed and imaged to evaluate the quantitative imaging protocol. Results: This work describes and validates a methodology to calibrate each clinical system. The efficiency of each gamma camera was analyzed and compared. Using the calibration factors obtained with the NEMA phantom, we were able to quantify the activity in 3D-printed tissue phantoms with an error of 2.1%, 3.5% and 11.8% for 223Ra, 225Ac, and 227Th, respectively. Conclusion: The present study validates that quantitative SPECT/CT imaging of 223Ra, 225Ac, and 227Th is achievable but that careful considerations for camera configuration are required. These results will aid in future implementation of SPECT-based patient studies and will help to identify the limiting factors for accurate image-based quantification with alpha particle emitting radionuclides.

Complete mitochondrial genome of the gray reef shark, Carcharhinus amblyrhynchos (Carcharhiniformes: Carcharhinidae).

We report the first mitochondrial genome sequences for the gray reef shark, Carcharhinus amblyrhynchos. Two specimens from the British Indian Ocean Territory were sequenced independently using two different next generation sequencing methods, namely short read sequencing on the Illumina HiSeq and long read sequencing on the Oxford Nanopore Technologies' MinION sequencer. The two sequences are 99.9% identical and are 16,705 base pairs (bp) and 16,706 bp in length. The mitogenome contains 22 tRNA genes, two rRNA genes, 13 protein-coding genes and two non-coding regions; the control region and the origin of light-strand replication (OL).

Mitochondrial genome of the Silvertip shark, Carcharhinus albimarginatus, from the British Indian Ocean Territory.

The Chagos archipelago in the British Indian Ocean Territory (BIOT) has been lacking in detailed genetic studies of its chondrichthyan populations. Chondrichthyes in Chagos continue to be endangered through illegal fishing operations, necessitating species distribution and abundance studies to facilitate urgent monitoring and conservation of the species. Here, we present a complete mitochondrial genome of the Silvertip Shark, Carcharhinus albimarginatus sampled in the Chagos archipelago. The mitochondrial genome of C. albimarginatus was 16,706 bp in length and consisted of 13 protein-coding genes, 22 tRNA genes, two rRNA genes, a replication origin and a D-loop region. GC content was at 38.7% and the control region was 1,065 bp in length. We expect that mitogenomes presented here will aid development of molecular assays for species distribution studies. Overall these studies will promote effective conservation of marine ecosystemes in the BIOT.

Simple Simulation Model for Exploring the Effects of Solvent and Structure on Asphaltene Aggregation.

Asphaltenes are operationally defined as the fraction of crude oil that is soluble in toluene but insoluble in n-heptane. According to the Yen-Mullins model, typical asphaltenes are relatively small molecules consisting of a single aromatic core flanked by aliphatic chains. The Yen-Mullins model posits that asphaltene aggregation proceeds via a hierarchical mechanism involving small nanoaggregates with stacked aromatic cores surrounded by a corona of aliphatic tails. In this work, we introduce a coarse-grained (CG) model for investigating the physical picture underlying the Yen-Mullins model and, more generally, the effects of the solvent character and molecular structure upon asphaltene self-assembly. By representing proposed asphaltenes in united atom detail, this CG model accurately describes their shape and conformational properties. Conversely, the CG model mimics varying solvent conditions by modulating the effective attraction between aliphatic and aromatic groups. Given the simplicity of this model, we performed long, replicate simulations of 147 different asphaltene solutions. As proposed by the Yen-Mullins model, island-type molecules readily form stacked aggregates under conditions that promote aromatic interactions. Interestingly, the onset of nanoaggregation appears to be insensitive to the aliphatic tails, although these tails may sterically stunt further growth of nanoaggregates. Consequently, nanoaggregates form more readily and grow larger under conditions that promote both aliphatic and aromatic interactions. In contrast, archipelago-type molecules also form large aggregates, but they do not demonstrate significant stacking interactions. Thus, the CG model reasonably describes the physical intuition of the Yen-Mullins picture and may prove to be useful for exploring later stages of asphaltene aggregation.

BOCS: Bottom-up Open-source Coarse-graining Software.

We present the BOCS toolkit as a suite of open source software tools for parametrizing bottom-up coarse-grained (CG) models to accurately reproduce structural and thermodynamic properties of high-resolution models. The BOCS toolkit complements available software packages by providing robust implementations of both the multiscale coarse-graining (MS-CG) force-matching method and also the generalized-Yvon-Born-Green (g-YBG) method. The g-YBG method allows one to analyze and to calculate MS-CG potentials in terms of structural correlations. Additionally, the BOCS toolkit implements an extended ensemble framework for optimizing the transferability of bottom-up potentials, as well as a self-consistent pressure-matching method for accurately modeling the pressure equation of state for homogeneous systems. We illustrate these capabilities by parametrizing transferable potentials for CG models that accurately model the structure, pressure, and compressibility of liquid alkane systems and by quantifying the role of many-body correlations in determining the calculated pair potential for a one-site CG model of liquid methanol.

Behavior and season affect crayfish detection and density inference using environmental DNA.

Although the presence/absence of aquatic invertebrates using environmental DNA (eDNA) has been established for several species, inferring population densities has remained problematic. The invasive American signal crayfish, Pacifastacus leniusculus (Dana), is the leading cause of decline in the UK's only native crayfish species, Austropotamobius pallipes (Lereboullet). Methods to detect species at low abundances offer the opportunity for the early detection, and potential eradication, of P. leniusculus before population densities reach threatening levels in areas occupied by A. pallipes. Using a factorial experimental design with aquaria, we investigated the impacts of biomass, sex ratio, and fighting behavior on the amount of eDNA released by P. leniusculus, with the aim to infer density per aquarium depending on treatments. The amount of target eDNA in water samples from each aquarium was measured using the quantitative Polymerase Chain Reaction. We show that the presence of eggs significantly increases the concentration of crayfish eDNA per unit of mass, and that there is a significant relationship between eDNA concentration and biomass when females are egg-bearing. However, the relationship between crayfish biomass and eDNA concentration is lost in aquaria without ovigerous females. Female-specific tanks had significantly higher eDNA concentrations than male-specific tanks, and the prevention of fighting did not impact the amount of eDNA in the water. These results indicate that detection and estimate of crayfish abundance using eDNA may be more effective while females are ovigerous. This information should guide further research for an accurate estimation of crayfish biomass in the field depending on the season. Our results indicate that detection and quantification of egg-laying aquatic invertebrate species using eDNA could be most successful during periods when eggs are developing in the water. We recommend that practitioners consider the reproductive cycle of target species when attempting to study or detect aquatic species using eDNA in the field.

Van der Waals Perspective on Coarse-Graining: Progress toward Solving Representability and Transferability Problems.

Low-resolution coarse-grained (CG) models provide the necessary efficiency for simulating phenomena that are inaccessible to more detailed models. However, in order to realize their considerable promise, CG models must accurately describe the relevant physical forces and provide useful predictions. By formally integrating out the unnecessary details from an all-atom (AA) model, "bottom-up" approaches can, at least in principle, quantitatively reproduce the structural and thermodynamic properties of the AA model that are observable at the CG resolution. In practice, though, bottom-up approaches only approximate this "exact coarse-graining" procedure. The resulting models typically reproduce the intermolecular structure of AA models at a single thermodynamic state point but often describe other state points less accurately and, moreover, tend to provide a poor description of thermodynamic properties. These two limitations have been coined the "transferability" and "representability" problems, respectively. Perhaps, the simplest and most commonly discussed manifestation of the representability problem regards the tendency of structure-based CG models to dramatically overestimate the pressure. Furthermore, when these models are adjusted to reproduce the pressure, they provide a poor description of the compressibility. More generally, it is sometimes suggested that CG models are fundamentally incapable of reproducing both structural and thermodynamic properties. After all, there is no such thing as a "free lunch"; any significant gain in computational efficiency should come at the cost of significant model limitations. At least in the case of structural and thermodynamic properties, though, we optimistically propose that this may be a false dichotomy. Accordingly, we have recently re-examined the "exact coarse-graining" procedure and investigated the intrinsic consequences of representing an AA model in reduced resolution. These studies clarify the origin and inter-relationship of representability and transferability problems. Both arise as consequences of transferring thermodynamic information from the high resolution configuration space and encoding this information into the many-body potential of mean force (PMF), that is, the potential that emerges from an exact coarse-graining procedure. At least in principle, both representability and transferability problems can be resolved by properly addressing this thermodynamic information. In particular, we have demonstrated that "pressure-matching" provides a practical and rigorous means for addressing the density dependence of the PMF. The resulting bottom-up models accurately reproduce the structure, equilibrium density, compressibility, and pressure equation of state for AA models of molecular liquids. Additionally, we have extended this approach to develop transferable potentials that provide similar accuracy for heptane-toluene mixtures. Moreover, these potentials provide predictive accuracy for modeling concentrations that were not considered in their parametrization. More generally, this work suggests a "van der Waals" perspective on coarse-graining, in which conventional structure-based methods accurately describe the configuration dependence of the PMF, while independent variational principles infer the thermodynamic information that is necessary to resolve representability and transferability problems.

The origin of efficient triplet state population in sulfur-substituted nucleobases.

Elucidating the photophysical mechanisms in sulfur-substituted nucleobases (thiobases) is essential for designing prospective drugs for photo- and chemotherapeutic applications. Although it has long been established that the phototherapeutic activity of thiobases is intimately linked to efficient intersystem crossing into reactive triplet states, the molecular factors underlying this efficiency are poorly understood. Herein we combine femtosecond transient absorption experiments with quantum chemistry and nonadiabatic dynamics simulations to investigate 2-thiocytosine as a necessary step to unravel the electronic and structural elements that lead to ultrafast and near-unity triplet-state population in thiobases in general. We show that different parts of the potential energy surfaces are stabilized to different extents via thionation, quenching the intrinsic photostability of canonical DNA and RNA nucleobases. These findings satisfactorily explain why thiobases exhibit the fastest intersystem crossing lifetimes measured to date among bio-organic molecules and have near-unity triplet yields, whereas the triplet yields of canonical nucleobases are nearly zero.

Bottom-up coarse-grained models with predictive accuracy and transferability for both structural and thermodynamic properties of heptane-toluene mixtures.

This work investigates the promise of a "bottom-up" extended ensemble framework for developing coarse-grained (CG) models that provide predictive accuracy and transferability for describing both structural and thermodynamic properties. We employ a force-matching variational principle to determine system-independent, i.e., transferable, interaction potentials that optimally model the interactions in five distinct heptane-toluene mixtures. Similarly, we employ a self-consistent pressure-matching approach to determine a system-specific pressure correction for each mixture. The resulting CG potentials accurately reproduce the site-site rdfs, the volume fluctuations, and the pressure equations of state that are determined by all-atom (AA) models for the five mixtures. Furthermore, we demonstrate that these CG potentials provide similar accuracy for additional heptane-toluene mixtures that were not included their parameterization. Surprisingly, the extended ensemble approach improves not only the transferability but also the accuracy of the calculated potentials. Additionally, we observe that the required pressure corrections strongly correlate with the intermolecular cohesion of the system-specific CG potentials. Moreover, this cohesion correlates with the relative "structure" within the corresponding mapped AA ensemble. Finally, the appendix demonstrates that the self-consistent pressure-matching approach corresponds to minimizing an appropriate relative entropy.

Bottom-up coarse-grained models that accurately describe the structure, pressure, and compressibility of molecular liquids.

The present work investigates the capability of bottom-up coarse-graining (CG) methods for accurately modeling both structural and thermodynamic properties of all-atom (AA) models for molecular liquids. In particular, we consider 1, 2, and 3-site CG models for heptane, as well as 1 and 3-site CG models for toluene. For each model, we employ the multiscale coarse-graining method to determine interaction potentials that optimally approximate the configuration dependence of the many-body potential of mean force (PMF). We employ a previously developed "pressure-matching" variational principle to determine a volume-dependent contribution to the potential, UV(V), that approximates the volume-dependence of the PMF. We demonstrate that the resulting CG models describe AA density fluctuations with qualitative, but not quantitative, accuracy. Accordingly, we develop a self-consistent approach for further optimizing UV, such that the CG models accurately reproduce the equilibrium density, compressibility, and average pressure of the AA models, although the CG models still significantly underestimate the atomic pressure fluctuations. Additionally, by comparing this array of models that accurately describe the structure and thermodynamic pressure of heptane and toluene at a range of different resolutions, we investigate the impact of bottom-up coarse-graining upon thermodynamic properties. In particular, we demonstrate that UV accounts for the reduced cohesion in the CG models. Finally, we observe that bottom-up coarse-graining introduces subtle correlations between the resolution, the cohesive energy density, and the "simplicity" of the model.

Observation of size-dependent thermalization in CdSe nanocrystals using time-resolved photoluminescence spectroscopy.

We report heat dissipation times in semiconductor nanocrystals of CdSe. Specifically, a previously unresolved, subnanosecond decay component in the low-temperature photoluminescence decay dynamics exhibits longer decay lifetimes (tens to hundreds of picoseconds) for larger nanocrystals as well as a size-independent, ~25-meV spectral shift. We attribute the fast relaxation to transient phonon-mediated relaxation arising from nonequilibrium acoustic phonons. Following acoustic phonon dissipation, the dark exciton state recombines more slowly via LO-phonon assistance resulting in the observed spectral shift. The measured relaxation time scales agree with classical calculations of thermal diffusion, indicating that interfacial thermal conductivity does not limit thermal transport in these semiconductor nanocrystal dispersions.