A theoretical investigation of the hydrolysis of uranium hexafluoride: the initiation mechanism and vibrational spectroscopy.

Depleted uranium hexafluoride (UF6), a stockpiled byproduct of the nuclear fuel cycle, reacts readily with atmospheric humidity, but the mechanism is poorly understood. We compare several potential initiation steps at a consistent level of theory, generating underlying structures and vibrational modes using hybrid density functional theory (DFT) and computing relative energies of stationary points with double-hybrid (DH) DFT. A benchmark comparison is performed to assess the quality of DH-DFT data using reference energy differences obtained using a complete-basis-limit coupled-cluster (CC) composite method. The associated large-basis CC computations were enabled by a new general-purpose pseudopotential capability implemented as part of this work. Dispersion-corrected parameter-free DH-DFT methods, namely PBE0-DH-D3(BJ) and PBE-QIDH-D3(BJ), provided mean unsigned errors within chemical accuracy (1 kcal mol-1) for a set of barrier heights corresponding to the most energetically favorable initiation steps. The hydrolysis mechanism is found to proceed via intermolecular hydrogen transfer within van der Waals complexes involving UF6, UF5OH, and UOF4, in agreement with previous studies, followed by the formation of a previously unappreciated dihydroxide intermediate, UF4(OH)2. The dihydroxide is predicted to form under both kinetic and thermodynamic control, and, unlike the alternate pathway leading to the UO2F2 monomer, its reaction energy is exothermic, in agreement with observation. Finally, harmonic and anharmonic vibrational simulations are performed to reinterpret literature infrared spectroscopy in light of this newly identified species.

Advanced concepts in electronic structure (ACES) software programs.

The advanced concepts in electronic structure (ACES) programs are products of the Bartlett research group at the University of Florida. They consist of ACES II, which is serial, and ACES III and Aces4, which are massively parallel. All three programs are publically available free of charge. The focus of the ACES implementations is coupled cluster theory and many-body-perturbation theory. We give an overview of the ACES programs, discuss the many features of the program systems, and document the number of benchmarks.

Predictive coupled-cluster isomer orderings for some SinCm (m, n ≤ 12) clusters: A pragmatic comparison between DFT and complete basis limit coupled-cluster benchmarks.

The accurate determination of the preferred Si12C12 isomer is important to guide experimental efforts directed towards synthesizing SiC nano-wires and related polymer structures which are anticipated to be highly efficient exciton materials for the opto-electronic devices. In order to definitively identify preferred isomeric structures for silicon carbon nano-clusters, highly accurate geometries, energies, and harmonic zero point energies have been computed using coupled-cluster theory with systematic extrapolation to the complete basis limit for set of silicon carbon clusters ranging in size from SiC3 to Si12C12. It is found that post-MBPT(2) correlation energy plays a significant role in obtaining converged relative isomer energies, suggesting that predictions using low rung density functional methods will not have adequate accuracy. Utilizing the best composite coupled-cluster energy that is still computationally feasible, entailing a 3-4 SCF and coupled-cluster theory with singles and doubles extrapolation with triple-ζ (T) correlation, the closo Si12C12 isomer is identified to be the preferred isomer in the support of previous calculations [X. F. Duan and L. W. Burggraf, J. Chem. Phys. 142, 034303 (2015)]. Additionally we have investigated more pragmatic approaches to obtaining accurate silicon carbide isomer energies, including the use of frozen natural orbital coupled-cluster theory and several rungs of standard and double-hybrid density functional theory. Frozen natural orbitals as a way to compute post-MBPT(2) correlation energy are found to be an excellent balance between efficiency and accuracy.

Approximating electronically excited states with equation-of-motion linear coupled-cluster theory.

A new perturbative approach to canonical equation-of-motion coupled-cluster theory is presented using coupled-cluster perturbation theory. A second-order Møller-Plesset partitioning of the Hamiltonian is used to obtain the well known equation-of-motion many-body perturbation theory equations and two new equation-of-motion methods based on the linear coupled-cluster doubles and linear coupled-cluster singles and doubles wavefunctions. These new methods are benchmarked against very accurate theoretical and experimental spectra from 25 small organic molecules. It is found that the proposed methods have excellent agreement with canonical equation-of-motion coupled-cluster singles and doubles state for state orderings and relative excited state energies as well as acceptable quantitative agreement for absolute excitation energies compared with the best estimate theory and experimental spectra.

Tuning ultracold chemical reactions via Rydberg-dressed interactions.

We show that ultracold chemical reactions with an activation barrier can be tuned using Rydberg-dressed interactions. Scattering in the ultracold regime is sensitive to long-range interactions, especially when weakly bound (or quasibound) states exist near the collision threshold. We investigate how, by Rydberg dressing a reactant, one enhances its polarizability and modifies the long-range van der Waals collision complex, which can alter chemical reaction rates by shifting the position of near-threshold bound states. We carry out a full quantum mechanical scattering calculation for the benchmark system H(2)+D, and show that resonances can be moved substantially and that rate coefficients at cold and ultracold temperatures can be increased by several orders of magnitude.

At what chain length do unbranched alkanes prefer folded conformations?

Short unbranched alkanes are known to prefer linear conformations, whereas long unbranched alkanes are folded. It is not known with certainty at what chain length the linear conformation is no longer the global minimum. To clarify this point, we use ab initio and density functional methods to compute the relative energies of the linear and hairpin alkane conformers for increasing chain lengths. Extensive electronic structure calculations are performed to obtain optimized geometries, harmonic frequencies, and accurate single point energies for the selected alkane conformers from octane through octadecane. Benchmark CCSD(T)/cc-pVTZ single point calculations are performed for chains through tetradecane, whereas approximate methods are required for the longer chains up to octadecane. Using frozen natural orbitals to unambiguously truncate the virtual orbital space, we are able to compute composite CCSD FNO(T) single point energies for all the chain lengths. This approximate composite method has significant computational savings compared to full CCSD(T) while retaining ∼0.15 kcal/mol accuracy compared to the benchmark results. More approximate dual-basis resolution-of-the-identity double-hybrid DFT calculations are also performed and shown to have reasonable 0.2-0.4 kcal/mol errors compared with our benchmark values. After including contributions from temperature dependent internal energy shifts, we find the preference for folded conformations to lie between hexadecane and octadecane, in excellent agreement with recent experiments [ Lüttschwager , N. O. ; Wassermann , T. N. ; Mata , R. A. ; Suhm , M. A. Angew. Chem. Int. Ed. 2013 , 52 , 463 ].

Correlation correction to configuration interaction singles from coupled cluster perturbation theory.

A new state specific correlation correction to configuration interaction singles (CIS) excitation energies is presented using coupled cluster perturbation theory (CCPT). General expressions for CIS-CCPT are derived and expanded explicitly to first-order in the wavefunction and second-order in the energy. By virtue of the nature of CCPT this method is a priori size extensive and incorporates infinite-order effects into the wavefunction. This results in a balanced singles space excited state theory that at second-order is an improvement over the ubiquitous CIS(D) method and comparable in quality to equation of motion coupled cluster (EOM-CC). A modest test set composed of the first four excited states from nine small organic molecules was used to quantify the accuracy and consistency of the CIS-CCPT2 excitation energies and density of states. We find that CIS-CCPT2 has a standard deviation error of 0.18 eV for excitation energies and 0.14 eV for density of states compared to EOM-CC, a factor of two better than CIS(D) with a significant reduction in the maximum deviation as well.

Initial blow fly (Diptera: Calliphoridae) colonization of cats (Felis catus) in Indiana.

Many disciplines are utilized within the field of veterinary forensic sciences, including forensic entomology. Understanding the initial colonization period by flies of forensic importance can contribute to estimating the minimum postmortem interval. There is limited data regarding the time of colonization of animals with fur, and the interpretation of this data is difficult due to the variation in animal models used. The purpose of this study was to examine the initial insect colonization of cats (Felis catus), with light and dark fur. Twelve domestic short-haired cats were placed in cages 15.2 m apart in a grassy field in West Lafayette, IN, United States. Weather data (temperature, precipitation, sun/cloud exposure, humidity), insect activity, time to oviposition, and decomposition changes were documented. Eggs from initial oviposition events were collected and reared to identify the primary colonizing species. Although the time of first oviposition event was not different between the treatments, fur color did affect fly colonization, and cats with dark fur had more oviposition events than cats with light fur (t = 2.639, df = 4, P = 0.029). Three species of Lucilia (Diptera: Calliphoridae) colonized the cats on the initial day of placement. Further studies in cats should include the decompositional studies to understand the unique characteristics that occur during each stage of decomposition, which could aid in developing a scoring system for animals with fur. Additional studies could include analyzing how fur length would affect colonization.

Review of the current and potential use of biological and molecular methods for the estimation of the postmortem interval in animals and humans.

We provide here an overview of the state of applied techniques in the estimation of the early period of the postmortem interval (PMI). The biological methods included consist of body cooling, CSF potassium, body cooling combined with CSF potassium, and tissue autolysis. For each method, we present its application in human and veterinary medicine and provide current methodology, strengths, and weaknesses, as well as target areas for improvement. We examine current and future molecular methods as they pertain to DNA and primarily to messenger RNA degradation for the estimation of the PMI, as well as the use of RNA in aging wounds, aging blood stains, and the identification of body fluids. Various types of RNA have different lengths, structures, and functions in cells. These differences in RNAs determine various intrinsic properties, such as their half-lives in cells, and, hence, their decay rate as well as their unique use for specific forensic tests. Future applications and refinements of RNA-based techniques provide opportunities for the use of molecular methods in the estimation of PMI and other general forensic applications.

A case of facultative ophthalmomyiasis externa due to Calliphoridae and review of the literature.

Purpose: To describe a case of bilateral facultative ophthalmomyiasis externa due to Calliphoridae in a 30-year-old male assault victim at a suburban hospital in New York and review the relevant literature. Observations: An adult male was found to have maggot infestation of both eyes and severe secondary injury to the left cornea and ocular surface. He was treated with manual larvae removal, oral ivermectin, broad spectrum IV antibiotics, and topical antibiotics. Anterior segment reconstruction was required. Conclusions and importance: We report the first case of ophthalmomyiasis due to Calliphoridae in the United States and document the vision threatening potential of this rare condition. Timely examination by an ophthalmologist with early debridement may help prevent vision-threatening sequelae.

Corrigendum: Evolution, ecology, and zoonotic transmission of betacoronaviruses: A review.

[This corrects the article DOI: 10.3389/fvets.2021.644414.].

Corrigendum: Evolution, ecology, and zoonotic transmission of betacoronaviruses: a review.

[This corrects the article DOI: 10.3389/fvets.2021.644414.].

Controllable binding of polar molecules and metastability of one-dimensional gases with attractive dipole forces.

We explore one-dimensional samples of ultracold polar molecules with attractive dipole-dipole interactions and show the existence of a repulsive barrier caused by a strong quadrupole interaction between molecules. This barrier can stabilize a gas of ultracold KRb molecules and even lead to long-range wells supporting bound states between the molecules. The properties of these wells can be controlled by external electric fields, allowing the formation of long polymerlike chains of KRb and studies of quantum phase transitions by varying the effective interaction between molecules. We discuss the generalization of those results to other systems.

Structure, energetics, and reactions of alkali tetramers.

Electronic structure calculations have been carried out for all possible alkali tetramers that can be formed from X(2) + X(2) → X(2)X(2), X(2) + Y(2) → X(2)Y(2), and XY + XY → X(2)Y(2) alkali dimer association reactions. Vibrationally stable rhombic (D(2h)) and planar (C(s)) structures are found for all possible tetramers formed from the alkali metals, Li to Cs. All tetramer formation reactions (from ground state singlet homonuclear or heteronuclear dimers) are found to be exothermic with binding energies ranging from 6282 cm(-1) for Li(2)Li(2) to 1985 cm(-1) for Cs(2)Cs(2). Extensive calculations, carried out at long-range for several reactant pairs, indicate that there are barrier-less pathways for the formation of tetramers from dimer association reactions. At low temperatures, direct formation of tetramers is unlikely, owing to the large exothermicity associated with these association reactions, but atom exchange reactions (X(2) + Y(2) ↔ XY + XY) are possible for some species.

Long-range interactions between like homonuclear alkali metal diatoms.

Long-range electrostatic and van der Waals coefficients up to terms of order R(-8) have been evaluated by the sum over states method using ab initio and time-dependent density functional theory. We employ several widely used density functionals and systematically investigate the convergence of the calculated results with basis set size. Static electric moments and polarizabilities up to octopole order are also calculated. We present values for Li(2) through K(2) which are in good agreement with existing values, in addition to new results for Rb(2) and Cs(2). Interaction potential curves calculated from these results are shown to agree well with high level ab initio theory. Preliminary results are reported that demonstrate the applicability of the method to larger alkali clusters.

Evolution, Ecology, and Zoonotic Transmission of Betacoronaviruses: A Review.

Coronavirus infections have been a part of the animal kingdom for millennia. The difference emerging in the twenty-first century is that a greater number of novel coronaviruses are being discovered primarily due to more advanced technology and that a greater number can be transmitted to humans, either directly or via an intermediate host. This has a range of effects from annual infections that are mild to full-blown pandemics. This review compares the zoonotic potential and relationship between MERS, SARS-CoV, and SARS-CoV-2. The role of bats as possible host species and possible intermediate hosts including pangolins, civets, mink, birds, and other mammals are discussed with reference to mutations of the viral genome affecting zoonosis. Ecological, social, cultural, and environmental factors that may play a role in zoonotic transmission are considered with reference to SARS-CoV, MERS, and SARS-CoV-2 and possible future zoonotic events.

Long range intermolecular interactions between the alkali diatomics Na(2), K(2), and NaK.

Long range interactions between the ground state alkali diatomics Na(2)-Na(2), K(2)-K(2), Na(2)-K(2), and NaK-NaK are examined. Interaction energies are first determined from ab initio calculations at the coupled-cluster with singles, doubles, and perturbative triples [CCSD(T)] level of theory, including counterpoise corrections. Long range energies calculated from diatomic molecular properties (polarizabilities and dipole and quadrupole moments) are then compared with the ab initio energies. A simple asymptotic model potential E(LR)=E(elec)+E(disp)+E(ind) is shown to accurately represent the intermolecular interactions for these systems at long range.

The door-to-balloon alliance for quality: who joins national collaborative efforts and why?

BACKGROUND: The Door-to-Balloon (D2B) Alliance is a collaborative effort of more than 900 hospitals aimed at improving D2B times for ST-segment elevation myocardial infarction. Although such collaborative efforts are increasingly used to promote improvement, little is known about the types of health care organizations that enroll and their motivations to participate. METHODS: To examine the types of hospitals enrolled and reasons for enrollment, a cross-sectional study was conducted of 915 D2B Alliance hospitals and 654 hospitals that did not join the D2B Alliance. Data were obtained from the American Hospital Association's Annual Survey of Hospitals and a Web-based survey completed by 797 enrolled hospitals (response rate, 87%). Chi-square statistics were used to examine statistical associations, and qualitative data analysis was used to characterize reported reasons for enrolling. RESULTS: Hospitals that enrolled in the D2B Alliance were significantly (p values < .05) more likely to be larger, nonprofit (versus for-profit), and teaching (versus nonteaching) hospitals. Earlier- versus later-enrolling hospitals were more likely to have key recommended strategies already in place at the time of enrollment. Improving quality and "doing the right thing" were commonly reported reasons for enrolling; however, hospitals also reported improving market share, meeting regulatory and accreditation requirements, and enhancing reputation as primary reasons for joining. CONCLUSIONS: The findings highlight the underlying goals of organizations to improve their position in the external environment--including economic, regulatory, accreditation, and professional environments. Designing quality improvement collaborative efforts to appeal to these goals may be an important strategy for enhancing participation and, in turn, increasing the uptake of evidence-based innovations.

Interdisciplinary workshop yields new entomological data for forensic sciences: Chrysomya rufifacies (Diptera: Calliphoridae) established in North Carolina.

ABSTRACT Workshops are used for educating law enforcement personnel on the application of entomological, anthropological, and botanical techniques to gather forensically important information from a body recovery site. From 8 to 11 June 2004, such a workshop was conducted in the metropolitan area of Charlotte, NC, by the American Academy of Applied Forensics at Central Piedmont Community College. For this workshop, three pig carcasses weighing individually between 40 and 60 kg were placed in the field 4 June, whereas three pigs similar in size were placed in the field 7 June. During the afternoon session on 11 June, workshop participants collected three Chrysomya rufifacies (Macquart) (Diptera: Calliphoridae) third instar larvae from a pig carcass placed in the field on 7 June. These data represent the first records of this forensically important insect in North Carolina; furthermore, these data provide evidence of this species expansion into new geographic regions of the United States. This finding is an example of the benefits derived from an experiential and interdisciplinary approach to educating death scene investigators. Learners acquired new knowledge, put it into practice through the "body" recovery exercise, and ultimately contributed to science by way of the discovery and first documentation of a forensically important insect previously not known to inhabit North Carolina.