Photoisomerization of Trans Ortho‐, Meta‐, Para‐Nitro Diarylbutadienes: A Case of Regioselectivity

A series of ortho‐, meta‐ and para‐substituted trans‐nitro aryl (phenyl and pyridyl) butadienes have been synthesized and characterized. The effect of substitution and positional selectivity on their fluorescence and photoisomerization were systematically investigated. Among all dienes, meta‐ and para‐nitro phenyl‐substituted derivatives exhibit remarkable solvatochromic emission shifts due to intramolecular charge transfer. On the other hand, ortho derivatives undergo regioselective isomerization upon photoexcitation in contrast to inefficient isomerization of para and meta nitro‐substituted dienes. Single crystal X‐ray analysis revealed existence of intramolecular hydrogen bonding between the nitro group and the hydrogen of the proximal double bond. This restricts the rotation of the proximal double bond thereby allowing regioselective isomerization. The observations were also supported by NMR spectroscopic studies.     

Molecular-dynamics-based study of the collisions of hyperthermal atomic oxygen with graphene using the ReaxFF reactive force field

In this work, we have investigated the hyperthermal collisions of atomic oxygens with graphene through molecular dynamics simulations using the ReaxFF reactive force field. First, following Paci et al. (J. Phys. Chem. A 2009, 113, 4677 - 4685), 5-eV energetic collisions of atomic oxygen with a 24-atom pristine graphene sheet and a sheet with a single vacancy defect, both functionalized with oxygen atoms in the form of epoxides, were studied. We found that the removal of an O(2) molecule from the surface of the graphene sheet occurs predominantly through an Eley-Rideal-type reaction mechanism. Our results, in terms of the number of occurrences of various reactive events, compared well with those reported by Paci et al. Subsequently, energetic collisions of atomic oxygen with a 25-times-expanded pristine sheet were investigated. The steady-state oxygen coverage was found to be more than one atom per three surface carbon atoms. Under an oxygen impact, the graphene sheet was always found to buckle along its diagonal. In addition, the larger sheet exhibited trampoline-like behavior, as a result of which we observed a much larger number of inelastic scattering events than those reported by Paci et al. for the smaller system. Removal of O(2) from the larger sheet occurred strictly through an Eley-Rideal-type reaction. Investigation of the events leading to the breakup of a pristine unfunctionalized graphene sheet and the effects of the presence of a second layer beneath the graphene sheet in an AB arrangement was done through successive impacts with energetic oxygen atoms on the structures. Breakup of a graphene sheet was found to occur in two stages: epoxide formation, followed by the creation and growth of defects. Events leading to the breakup of a two-layer graphene stack included epoxide formation, transformation from an AB to an AA arrangement as a result of interlayer bonding, defect formation and expansion in the top layer, and finally erosion of the bottom layer. We observed that the breakup of the two-layer stack occurred through a sequential, layer-by-layer, erosion process.     

Conformally invariant field theories in two dimensions and corresponding statistical mechanical models

Belavin, Zamlodochikov and Polyakov have recently proposed a class of conformally invariant field theories in two dimension with exactly determined rational critical indices. We establish a tentative identification of a subset of these theories in terms of the O(n) model and theq-state Potts model in 2-dimensions for appropriaten andq. The results of this work were reported in the conference on “Structural Similarities in Exactly Solved Models” at I.T.P. Santa Barbara, August 1984.     

Quantum corrections to liquid correlations

Sudarshan's semi-classical treatment of correlation functions is applied to the study of quantum corrections to the Van Hove function. In its generalised form, it enables one to choose the best correlation function for a given potential. Higher-order correlations are also sketched briefly and the details are similar to those considered by Oppenheim and Bloom.     

Active nematics are intrinsically phase separated

Two-dimensional nonequilibrium nematic steady states, as found in agitated granular-rod monolayers or films of orientable amoeboid cells, were predicted [Europhys. Lett. 62, 196 (2003)10.1209/epl/i2003-00346-7] to have giant number fluctuations, with the standard deviation proportional to the mean. We show numerically that the steady state of such systems is macroscopically phase separated, yet dominated by fluctuations, as in the Das-Barma model [Phys. Rev. Lett. 85, 1602 (2000)10.1103/PhysRevLett.85.1602]. We suggest experimental tests of our findings in granular and living-cell systems.     

Size‐dependent Tumor Response to Photodynamic Therapy and Irinotecan Monotherapies Revealed by Longitudinal Ultrasound Monitoring in an Orthotopic Pancreatic Cancer Model

Longitudinal monitoring of tumor size in vivo can provide important biological information about disease progression and treatment efficacy that is not captured by other modes of quantification. Ultrasound enables high‐throughput evaluation of orthotopic mouse models via fast acquisition of three‐dimensional tumor images and calculation of volume with a reasonable degree of accuracy. Herein, we compare orthotopic pancreatic tumor volume measurements determined by ultrasound with volume measured by calipers and tumor weight, and found strong correlations between the three modalities over a large range of tumor sizes, suggesting ultrasound can accurately quantify tumor volumes in this model. Furthermore, we demonstrate the unique ability of longitudinal treatment monitoring to reveal a tumor size‐dependent response to Benzoporphyrin Derivative photodynamic therapy (BPD‐PDT) and irinotecan. Small tumors (5–35 mm³) were found to respond well to a single round of PDT, while large tumors (35–65 mm³) showed no response to the same treatment. These results highlight the role that tumor size can play in preclinical interpretation of treatment response and more generally suggest that careful evaluation of subtle biological features such as this must be carefully considered in order to grant a more comprehensive understanding of disease biology in vivo.     

Variable spaced particle in mesh-free method to handle wave-floating body interactions

In this work, the motion of a two-dimensional rectangular freely floating body under waves is simulated using Improved Meshless Local Petrov-Galerkin method with Rankine Source function (IMLPG_R) with variable spacing resolutions. The IMLPG_R method is a particle method that solves Navier–Stokes equations using the fractional step method to capture the wave properties. However, many existing particle methods are computationally intensive to model the wave-floating body due to the requirement of fine particles, needing uniform distribution throughout the domain. To improve the computational efficiency and capture the body response properly, variable spaced particle distribution with fine resolution near the floating body and coarse resolution far from the body is implemented. Numerical schemes to handle variable resolutions are reported. An iterative scheme to handle the wave-floating body is implemented in the particle method. Two test cases, one with small wave and another with steep waves, are simulated for uniform particle distribution and the result shows good agreement with literature. Based on this, the performance of the variable spaced particle distribution is tested in coupling with floating body solver. The application of the method for wave impact load from the green water loading of the floating structure is also simulated.