Computational Spectroscopy in Solution by Integration of Variational and Perturbative Approaches on Top of Clusterized Molecular Dynamics

Multiscale QM/MM approaches have become the most suitable and effective methods for the investigation of spectroscopic properties of medium-or large-size chromophores in condensed phases. On these grounds, we are developing a novel workflow aimed at improving the generality, reliability, and ease of use of the available tools. In the present paper, we report the latest developments of such an approach with specific reference to a general workplan starting with the addition of acetonitrile to the panel of solvents already available in the General Liquid Optimized Boundary (GLOB) model enforcing nonperiodic boundary conditions (NPBC). Next, the solvatochromic shifts induced by acetonitrile on both rigid (uracil and thymine) and flexible (thyrosine) chromophores have been studied introducing in our software a number of new features ranging from rigid-geometry NPBC molecular dynamics based on the quaternion formalism to a full integration of variational (ONIOM) and perturbative (perturbed matrix method (PMM)) approaches for describing different solute-solvent topologies and local fluctuations, respectively. Finally, thymine and uracil have been studied also in methanol to point out the generality of the computational strategy. While further developments are surely needed, the strengths of our integrated approach even in its present version are demonstrated by the accuracy of the results obtained by an unsupervised approach and coupled to a computational cost strongly reduced with respect to that of conventional QM/MM models without any appreciable accuracy deterioration

Enhancing the Accuracy of Ab Initio Molecular Dynamics by Fine Tuning of Effective Two-Body Interactions: Acetonitrile as a Test Case

Grimme’s dispersion-corrected density functional theory (DFT-D) methods have emerged among the most practical approaches to perform accurate quantum mechanical calculations on molecular systems ranging from small clusters to microscopic and mesoscopic samples, i.e., including hundreds or thousands of molecules. Moreover, DFT-D functionals can be easily integrated into popular ab initio molecular dynamics (MD) software packages to carry out first-principles condensed-phase simulations at an affordable computational cost. Here, starting from the well-established D3 version of the dispersion-correction term, we present a simple protocol to improve the accurate description of the intermolecular interactions of molecular clusters of growing size, considering acetonitrile as a test case. Optimization of the interaction energy was performed with reference to diffusion quantum Monte Carlo calculations, successfully reaching the same inherent accuracy of the latter (statistical error of ∼0.1 kcal/mol per molecule). The refined DFT-D3 model was then used to perform ab initio MD simulations of liquid acetonitrile, again showing significant improvements toward available experimental data with respect to the default correction

An IMU and USBL-aided buoy for underwater localization

Autonomous underwater navigation remains, as of today, a challenging task. The marine environment limits the number of sensors available for precise localization, hence Au- tonomous Underwater Vehicles (AUVs) usually rely on inertial and velocity sensors to obtain an estimate of their position either through dead reckoning or by means of more sophisticated navigation filters (such as Kalman filters and its extensions [1]). On the other hand, acoustic localization makes possible the determination of a reliable vehicles pose estimate exploiting suit- able acoustic modems [3]; such estimate can even be integrated within the navigation filter of the vehicle in order to increase its accuracy. In this paper, the authors discuss the development and the performance of an Ultra-Short BaseLine (USBL)-aided buoy to improve the localization of underwater vehicles. At first, the components and the physical realization of the buoy will be discussed; then, the procedure to compute the position of the target will be analyzed. The following part of the paper will be focused on the development of a recursive state estimation algorithm to process the measurements computed by the buoy; specifically, Extended Kalman Filter [4] has been adopted to deal with the nonlinearities of the sensors housed on the buoy. A validation of the measurement filtering through experimental tests is also proposed

An IMU and USBL-aided buoy for underwater localization

Autonomous underwater navigation remains, as of today, a challenging task. The marine environment limits the number of sensors available for precise localization, hence Au- tonomous Underwater Vehicles (AUVs) usually rely on inertial and velocity sensors to obtain an estimate of their position either through dead reckoning or by means of more sophisticated navigation filters (such as Kalman filters and its extensions [1]). On the other hand, acoustic localization makes possible the determination of a reliable vehicles pose estimate exploiting suit- able acoustic modems [3]; such estimate can even be integrated within the navigation filter of the vehicle in order to increase its accuracy. In this paper, the authors discuss the development and the performance of an Ultra-Short BaseLine (USBL)-aided buoy to improve the localization of underwater vehicles. At first, the components and the physical realization of the buoy will be discussed; then, the procedure to compute the position of the target will be analyzed. The following part of the paper will be focused on the development of a recursive state estimation algorithm to process the measurements computed by the buoy; specifically, Extended Kalman Filter [4] has been adopted to deal with the nonlinearities of the sensors housed on the buoy. A validation of the measurement filtering through experimental tests is also proposed

Rider Variables Affecting the Stirrup Directional Force Asymmetry during Simulated Riding Trot

Riders' asymmetry may cause back pain in both human and equine athletes. This pilot study aimed at documenting in a simple and quick way asymmetry in riders during a simulation of three different riding positions on wooden horseback using load cells applied on the stirrup leathers and identifying possible associations between riders' asymmetry and their gender, age, level of riding ability, years of riding experience, riding style, motivation of riding, primary discipline and handedness. After completing an interview to obtain the previously mentioned information, 147 riders performed a standardized test on a saddle fixed on a wooden horseback-shaped model. The riding simulation was split into three phases of 1 min each: (1) sit in the saddle, (2) standing in the stirrups and (3) rising trot. The directional force on the left and the right stirrup leathers was recorded every 0.2 s. A paired t-test was performed on the recorded data to test the difference (i.e., asymmetry) in each phase. In phases 1, 2 and 3, 99.3% (53.4% heavier on the right (R)), 98% (52.8% heavier on the left (L)) and 46.3% (51.5% heavier on the left (L)) of the riders were asymmetrical, respectively. Chi-square tests showed a significant association between riding ability and riding experience, but no significant association between reported handedness and calculated leg-sidedness (p > 0.05). Univariate logistic (1: asymmetry, 0: symmetry) regression analysis was performed only on the phase 3 data. One-hand riders were found twice more likely to be asymmetrical than two-hand riders (Odds Ratio (OR): 2.18, Confidence Interval (CI): 1.1-4.29; p = 0.024). This preliminary study confirmed that the majority of the riders are asymmetrical in load distribution on stirrups and suggested the riding style as a possible risk factor for asymmetry