Data and pilot combining for composite GNSS signal acquisition

With the advent of new global navigation satellite systems (GNSS), such as the European Galileo, the Chinese Compass and the modernized GPS, the presence of new modulations allows the use of special techniques specifically tailored to acquire and track the new signals. Of particular interest are the new composite GNSS signals that will consist of two different components, the data and pilot channels. Two strategies for the joint acquisition of the data and pilot components are compared. The first technique, noncoherent combining, is fromthe literature and it is used as a comparison term, whereas the analysis of the second one, coherent combining with sign recovery, represents the innovative contribution of this paper. Although the analysis is developed with respect to the Galileo E1 Open Service (OS) modulation, the obtained results are general and can be applied to other GNSS signals

Dynamic simulation of liquid molecular nanoclusters: structure, stability and quantification of internal (pseudo)symmetries

The atom\u2013atom intermolecular force field AA-CLP is applied to the molecular dynamics simulation of liquid nanoclusters of benzene, chloroform, methanol and pyridine. Bulk liquids are also simulated for validation and comparison with experimental data. The applied software has been produced de novo to deal with the unusual analytical form of the intermolecular potential, and it includes some novel features for the control of net rotational momenta in isolated systems. The nanoclusters have been studied as a function of size (150\u20131000 molecules) in relation to cohesion energies, rotational correlation, self-diffusion coefficients, and evaporation rates. Internal structure has been studied with traditional radial distribution functions, plus diagrams of the distribution of intermolecular vectors for flat compounds. In addition, a new algorithm for the quantification of pseudo- or near-symmetries between molecules in aggregates of any structure has been developed and tested, with reference to the inversion, mirror plane and rotation axis symmetries of organic crystals, with possible importance in the investigation of crystallization processes. The results confirm the reliability of the AA-CLP formulation for molecular dynamics simulation and throw some light on relationships between cluster and bulk properties. The computer codes are available for open-source download to ensure full reproducibility of all results

A crystallographic route to understand drug solubility: the case of 4- aminoquinoline antimalarials

Most Active Pharmaceutical Ingredients (API) can be prepared in various crystalline forms [1] displaying largely different physical/chemical properties and bioavailability. Salt formation represents the most common and simplest chemical way to modify the overall features but also the toxicity and biopharmaceutical availability of a drug substance. However, it is often unclear how and why the chemical and crystallographic characters can cooperate in determining these changes. We here face the problem from the perspective of the antiplasmodial drug piperaquine (PQ, C29H32Cl2N6) [2]. Being highly lipophilic, both neutral PQ and its commercial hydrogen phosphate tetrahydrate salt are poorly soluble in water, resulting in a reduced oral bioavailability. We synthesized five novel PQ salts and characterized them by both single crystal X\u2013ray diffraction methods and T-dependent (20 \u2013 50 \ubaC) UV\u2013Vis spectroscopy. Our aim was to explore possible relationships among non-covalent interaction networks in the crystals and measured solubilities. We also estimated changes in thermodynamic state functions related to the solvation process by DFT simulations, both in vacuo and in the solid state. We found that solubilities of PQ salts conform in most cases to the Hard and Soft Acid and Bases (HSAB) rules, i.e. less soluble compounds bear ions of comparable hardness. Crystal packing plays a far less important role, even though disorder-related entropic effects can influence the response of solubility to temperature. A possible take-home message is that intensive thermodynamic properties stem from a non-trivial cooperation several physicochemical effects. A first-principle understanding of the drug solubility cannot rely just on the description of the crystal packing, but must take into account the explicit evaluation of interaction energetics and pertinent electronic factors. [1] R. Hilfiker and M. von Raumer, Polymorphism in the Pharmaceutical Industry: Solid Form and Drug Development. 2019, Wiley-VCH, Weinheim (Germany). ISBN: 978-3-527-34040-8. [2] P. Sacchi, L. Loconte, G. Macetti, S. Rizzato and L. Lo Presti Crystal Growth Des. 2019. 19, 139

CLPdyn: a cheap and reliable tool for molecular dynamics studies of organic molecules in condensed phase

We present CLPdyn, a freely available code intended to perform Molecular Dynamics simulations of organic molecules in condensed phase.[1\u20133] CLPdyn can handle both continuous phases (liquids, crystals) and finite-size clusters (liquid droplets, nanoparticles), and exploits the thoroughly tested Coulomb-London-Pauli atom-atom intermolecular potential[4,5]. The implementation relies on standard MD algebra, but also includes new algorithms, specifically designed to deal with isolated clusters, to (i) suppress net overall translational and rotational momenta, (ii) handle the evaporation of molecules from the cluster surface, and (iii) measure the amount of residual symmetry from the number and kind of isometries present in the cluster. Application to organic solvents (benzene, chloroform, methanol and pyridine) [2] and crystals spanning very different intermolecular recognition patterns (maleic/succinic anhydrides, alanine/glutamic acid, methylurea, 1,4-cyclohexadiene and methyl-2-amino-5-hydroxybenzoate) [3], shows that CLPdyn reliably reproduces macroscopic thermodynamic quantities, and highlights the effect of the relative strengths of intermolecular forces on rotational correlation times, self-diffusion coefficients and pair distribution functions. Possible applications of CLPdyn to the molecular\u2013level study of non\u2013equilibrium solution chemistry, including the early stages of crystal nuclei formation, are also discussed. [1] A. Gavezzotti, CLPdyn, Monte Carlo and Molecular Dynamics modules, Description and user manual, www.angelogavezzotti.it (2018). [2] A. Gavezzotti, L. Lo Presti, New J. Chem., 2019,43, 2077-2084. [3] A. Gavezzotti, L. Lo Presti, in preparation [4] A. Gavezzotti, New J. Chem. 2011, 35, 1360\u20131368. [5] A. Gavezzotti and L. Lo Presti, Crystal Growth Des. 2016, 16, 2952\u20132962

Optical Module Front-End for a Neutrino Underwater Telescope: PMT interface

A proposal for a new system to capture signals in the Optical Module (OM) of an Underwater Neutrino Telescope is described. It concentrates on the problem of power consumption in relation to precision. In particular, a solution for the interface between the photomultiplier (PMT) and the front-end electronics is presented

Gaining insights on chemistry from the analysis of the charge density

The increasing attention to supramolecular chemistry mirrors a growing interest in chemical bonding. The understanding of factors that influence selforganization of matter lies at the core of the development of functional materials, bioactive compounds and drugs. In this context, the charge density scalar field, rho(r), plays a central role, as it conveys all the observable physics determined by the equilibrium distribution of electrons and nuclei. Relevant chemistry can be extracted from rho(r) by studying its topology. Modern experimental and theoretical tools for the topological analysis of the charge density will be here discussed, with focus on molecular recognition and polymorphism

Joint Alignment and Modeling of Correlated Behavior Streams

The Variable Time-Shift Hidden Markov Model (VTS- HMM) is proposed for learning and modeling pairs of cor- related streams. Unlike previous coupled models for time series, the VTS-HMM accounts for varying time shifts be- tween correlated events in pairs of streams having different properties. The VTS-HMM is learned on a set of pairs of unaligned streams and, thus, learning entails simultaneous estimation of the varying time shifts and of the parameters of the model. The formulation is demonstrated in the analysis of videos of dyadic social interactions between children and adults in the Multimodal Dyadic Behavior Dataset (MMDB). In dyadic social interactions, an agent starts an interaction with one or more \u201cinitiating behaviors\u201d that elicit one or more \u201cresponding behaviors\u201d from the partner within a temporal window. The proposed VTS-HMM explicitly accounts for varying time shifts between initiating and responding behaviors in these behavior streams. The experiments confirm that modeling of these varying time shifts in the VTS-HMM can yield improved estimation of the level of engagement of the child and adult and more accurate dis- crimination among complex activities

The TACO Puzzle: A Phase-Transition Mystery Revisited

The organic salt (5-methyl-1-thia-5-azacyclo-octane-1-oxide) perchlorate (TACO) is known to undergo a single-crystal-to-single-crystal phase transition in the 276-298 K T range without a change in the external shape of the sample. Despite extensive computational and experimental investigations, no safe conclusions about the transition mechanism could be drawn till now. The two packing patterns are very similar, and symmetry is conserved, apart from an interchange of cell axes from P21/c (\u3b1-TACO, low-T) to P21/a (\u3b2-TACO, high-T). Yet, the phase transition implies a significant conformational rearrangement, coupled with 3c180\ub0-wide rotations, of 1/2 of the cations, in conjunction with reorientation of the anions. Here, we analyze the crystal packing of the two phases in terms of pairwise molecule-molecule interaction energies, as derived from the PIXEL approach. Rigid-body molecular reorientations are simulated by solid-state Monte Carlo calculations, while the likelihood of conformational rearrangements is estimated through gas-phase density functional theory M06/6-311G(p,d) simulations. We demonstrate that rotational motion of the cations is not hampered by substantial energetic barriers, while the ring flip can be described as a two-step process with a main kinetic barrier of 3c45 kJ\ub7mol-1, which might explain the metastable behavior of the \u3b2 phase at low T. A possible mechanism of the phase transition is proposed, accounting for the present computational evidences in the context of the former experimental findings