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Abstract Structure and electronic properties of two unusual boron clusters obtained by fusion of borozene rings have been studied by means of first principles calculations based on the generalized-gradient approximation of the density functional theory. Moreover, a semiempirical tight-binding model has been appropriately calibrated for transport calculations on these clusters. Results show that the pure boron clusters are topologically planar and characterized by (3c–2e) bonds, which can explain, together with the aromaticity (estimated by means of NICS), the remarkable cohesive energy values obtained. Such feature makes these systems competitive with the most stable boron clusters to date. The energy gap values indicate that these clusters possess a semiconducting character, while when the larger system is considered, zero-values of the density of states are found exclusively within the HOMO–LUMO gap. Electron transport calculations within the Landauer formalism confirm these indications, showing semiconductor-like low bias differential conductance for these structures. Differences and similarities with carbon clusters are highlighted in the discussion.

Opioids are often the mainstay of postoperative pain management, despite strong evidence of their ill effects and potential for long-term addiction. The goal of this study was to quantify opioid use and contrast pain management strategies of multiple international institutions performing fibula free flap reconstruction. A retrospective multicenter cohort study was designed, including five international centers. For inclusion, the patients had to have undergone a primary fibula free flap reconstruction of the mandible. A total of 185 patients were included. The median opioid use across all centers at 72 hours was 133 oral morphine equivalents. The highest utilization was in the USA (P < 0.001), which was approximately six times that of Italy, four times that of Argentina, and twice that of India, despite all centers performing a similar procedure. Based on this study there are clear differences in prescribing practices and ideologies among surgeons from different countries. [ABSTRACT FROM AUTHOR]

The 30-day readmission rate is a highly scrutinized metric of quality surgical care, because readmission is costly and perceived to be avoidable with planning and patient education. Head and neck surgery patients generally have multiple risk factors for readmission, as readmitted patients are generally older, with more co-morbidities, lower socio-economic status, and a history of multiple emergency department visits and readmissions. A retrospective cohort study was implemented to determine the incidence and etiology of 30-day readmission after microvascular head and neck reconstructive surgery, focusing on social risk factors. Data were analyzed by χ2 test, analysis of variance, t -test, and logistic regression, with statistical significance set at P < 0.05. Of 209 patients included in this study, 35 (16.7%) had a 30-day readmission. Increased needs at discharge were associated with increased readmission, while other social risk factors were less significant for a readmission in this study. [ABSTRACT FROM AUTHOR]

Virtual surgical planning (VSP) promises higher accuracy, efficiency, and superior patient outcomes, helping normalize outcomes from surgeons of different experience levels. A systematic review was conducted in agreement with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. The objective was to evaluate the accuracy and secondarily efficiency of VSP compared with free-hand surgery, for mandibular reconstruction with free flaps. Six studies met inclusion criteria and had quantitative data suitable for meta-analysis. Intercondylar distance and gonion angle were used to assess accuracy, evaluated by mean change from preoperative VSP and postoperative imaging. The mean weighted difference in VSP intercondylar distance was 2.0 mm, compared with 3.9 mm for free hand (P = 0.101) and mean change in gonion angle for VSP was 3.6°, compared with 7.7° for free hand (P < 0.05). Efficiency assessed by mean ischemia time, was 73.8 min and 109.9 min, for VSP and free hand, respectively (P = 0.203), and by total operative time, which was 391.8 min and 457.6 min in the VSP and free hand, respectively (P = 0.340). VSP is consistently proven to be more accurate and efficient than traditional free-hand surgery; however, a standardized method for accuracy and efficiency measurements is still missing, causing heterogeneity among the scientific reports. [ABSTRACT FROM AUTHOR]

In a recent study by Kornath et al. [J. Chem. Phys. 118, 6957 (2003)], the Lin clusters with n=2, 4, and 8 have been isolated in argon matrices at 15 K and characterized by Raman spectroscopy. This has prompted us to carry out a theoretical study on such clusters up to n=10, using Hartree–Fock theory, plus low-order Møller–Plesset perturbation corrections. To check against the above study of Kornath et al., as a by-product we have made the same approximations for n=6 and 8 as we have for n=10. This has led us to emphasize trends with n through the Lin clusters for (i) ground-state energy, (ii) HOMO–LUMO energy gap, (iii) dissociation energy, and (iv) Hartree–Fock eigenvalue sum. The role of electron correlation in distinguishing between low-lying isomers is plainly crucial, and will need a combination of experiment and theory to obtain decisive results such as that of Kornath et al. for Li8. In particular, it is shown that Hartree–Fock theory plus bond order correlations does account for the experimentally observed symmetry Td symmetry for Li8. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We introduce an algorithm that couples the molecular dynamics (MD) method to the modified neglect of diatomic overlap (MNDO) approximation. This approach is applied to the study of the carbon clusters Cn with n ranging from 20 to 60. We calculate the relative stability of some well-known structures as polyacetylenic rings and fullerenes. The results obtained are in substantial agreement with calculations available in the literature. The main emphasis of the paper is on the possibility of finding, with our approach, new isomers starting from different initial configurations or after thermal excursions. For some values of n, new stable isomers are found. The results allow us also to give explanations of the observed low abundance in the mass spectra of the clusters with n ranging between 30 and 40 (the so-called ‘‘dead’’ region). [ABSTRACT FROM AUTHOR]

In the present work we have studied the thermal isomerization process of polyacetylene (PA) from the trans-cisoid (TC) and cis-transoid (CT) forms to the trans-transoid (TT) form. We have used the molecular dynamics-modified neglect of diatomic overlap (MD-MNDO) method, which combines a molecular dynamics algorithm with the MNDO approximation. The thermal isomerization mechanism from TC-to-TT form is fully described. In our simulation, starting from the CT form in its ground state and heating the system up to T=450 K, there is no evidence of an isomerization process. However, a model, which simulate the subtraction of some charge from the double bonds of the PA chains, is able to give important insights into the isomerization mechanism from the CT to the TT form. This charge subtraction is essential to induce a CT-to-TC local transformation followed by the TC-to-TT isomerization. [ABSTRACT FROM AUTHOR]