ML-Based Analysis of Particle Distributions in High-Intensity Laser Experiments: Role of Binning Strategy

When entering the phase of big data processing and statistical inferences in experimental physics, the efficient use of machine learning methods may require optimal data preprocessing methods and, in particular, optimal balance between details and noise. In experimental studies of strong-field quantum electrodynamics with intense lasers, this balance concerns data binning for the observed distributions of particles and photons. Here we analyze the aspect of binning with respect to different machine learning methods (Support Vector Machine (SVM), Gradient Boosting Trees (GBT), Fully-Connected Neural Network (FCNN), Convolutional Neural Network (CNN)) using numerical simulations that mimic expected properties of upcoming experiments. We see that binning can crucially affect the performance of SVM and GBT, and, to a less extent, FCNN and CNN. This can be interpreted as the latter methods being able to effectively learn the optimal binning, discarding unnecessary information. Nevertheless, given limited training sets, the results indicate that the efficiency can be increased by optimizing the binning scale along with other hyperparameters. We present specific measurements of accuracy that can be useful for planning of experiments in the specified research area.     

Novel Osmium‐based Coordination Complexes as Photosensitizers for Panchromatic Photodynamic Therapy

Cancer remains a major global malaise requiring the advent of new, efficient and low‐cost treatments. Photodynamic therapy, which combines a photosensitizer and photons to produce cytotoxic reactive oxygen species, has been established as an effective cancer treatment but has yet to become mainstream. One of the main limitations has been the paucity of photosensitizers that are effective over a wide range of wavelengths, can exert their cytotoxic effects in hypoxia, are easily synthesized and produce few if any side effects. To address these shortfalls, three new osmium‐based photosensitizers (TLD1822, TLD1824 and TLD1829) were synthesized and their photophysical and photobiological attributes determined. These photosensitizers are panchromatic (i.e. black absorbers), activatable from 200 to 900 nm and have strong resistance to photobleaching. In vitro studies show photodynamic therapy efficacy with both red and near‐infrared light in normoxic and hypoxic conditions, which translated to good in vivo efficacy of TLD1829 in a subcutaneous murine colon cancer model.     

Concerted C-N and C-H bond formation in a magnesium-catalyzed hydroamination

Coordinatively saturated To(M)MgMe (1; To(M) = tris(4,4-dimethyl-2-oxazolinyl)phenylborate) is an active precatalyst for intramolecular hydroamination/cyclization at 50 °C. The empirical rate law of -d[substrate]/dt = k'(obs)[Mg](1)[substrate](1) and Michaelis-Menten-type kinetics are consistent with a mechanism involving reversible catalyst-substrate association prior to cyclization. The resting state of the catalyst, To(M)MgNHCH(2)CR(2)CH(2)CH═CH(2) [R = Ph, Me, -(CH(2))(5)-], is isolable, but isolated magnesium amidoalkene does not undergo unimolecular cyclization at 50 °C. However, addition of trace amounts of substrate allows cyclization to occur. Therefore, we propose a two-substrate, six-center transition state involving concerted C-N bond formation and N-H bond cleavage as the turnover-limiting step of the catalytic cycle.     

Heterometallic hexanuclear isobutyrate clusters based on di- and tripodal alcohols

Four hexanuclear coordination clusters containing $\{{\mathrm{M}}_4^{\mathrm{II}}{\mathrm{M}}_2^{\mathrm{III}}\}$ cores of edge-sharing coordination octahedra exemplify how mixed-spin derivatives of a homonuclear parent structure, [${\mathrm{Mn}}_4^{\mathrm{II}}{\mathrm{Mn}}_2^{\mathrm{III}}{\mathrm{L}}_8$(N–O)₄], can be realized by a ligand ‘shrink-wrapping’ approach, resulting in [${\mathrm{Mn}}_2^{\mathrm{II}}{\mathrm{Co}}_2^{\mathrm{II}}{\mathrm{Mn}}_2^{\mathrm{III}}{\mathrm{L}}_8$(N–O)₄]- and [${\mathrm{Co}}_4^{\mathrm{II}}{\mathrm{Fe}}_2^{\mathrm{III}}{\mathrm{L}}_8$(N-O)₄]-type clusters (L = isobutyrate, N–O = methyldiethanolamine, n-butyldiethanolamine, or triethanolamine). The resulting core structures are either virtually isostructural to the parent structure or differ in the placement of the peripheral metal ions, depending on the mix of structure-directing carboxylate and alkoxyamine ligands with large, flexible alkyl chains. Whereas the $\{{\mathrm{Mn}}_4^{\mathrm{II}}{\mathrm{Mn}}_2^{\mathrm{III}}\}$ and {${\mathrm{Co}}_4^{\mathrm{II}}{\mathrm{Fe}}_2^{\mathrm{III}}$} complexes show dominant antiferromagnetic exchange, ferrimagnetic coupling features are exhibited by two {${\mathrm{Mn}}_2^{\mathrm{II}}{\mathrm{Co}}_2^{\mathrm{II}}{\mathrm{Mn}}_2^{\mathrm{III}}$} clusters.     

[Cr8(PhCO2)16O4]·4CH3CN·2H2O: structural origin of magnetic anisotropy in a molecular spin cluster

The Cr₄O₄ hetero‐cubane‐centered octachromium(III) cluster [Cr₈(PhCO₂)₁₆O₄] crystallizes from fluorobenzene–acetonitrile as dodeca‐μ₂‐benzoato‐tetrabenzoatotetra‐μ₄‐oxido‐octachromium(III) acetonitrile tetrasolvate dihydrate, [Cr₈(C₇H₅O₂)₁₆O₄]·4C₂H₃N·2H₂O, (I). Crystals produced by this method are significantly more stable than the originally published dichloromethane pentasolvate, [Cr₈(PhCO₂)₁₆O₄]·5CH₂Cl₂ [Atkinson et al. (1999). Chem. Commun. pp. 285–286], leading to a significantly higher quality structure and allowing the production of large quantities of high‐quality nondeuterated and deuterated material suitable for inelastic neutron scattering (INS) measurements. Compound (I) reveals a higher symmetry structure in which the cluster sits on a twofold rotation axis, and is based on an asymmetric unit containing four crystallographically independent Cr positions, two oxide ligands, eight benzoate ligands, two acetonitrile solvent molecules and one disordered water molecule. All the Cr atoms are six‐coordinate, with an octahedral geometry for the inner cubane and a more highly distorted coordination environment in the outer positions. Despite the higher symmetry, the coordination geometries observed in (I) are largely similar to the dichloromethane pentasolvate structure, indicating that crystal‐packing effects have little influence on the molecular structure of [Cr₈(PhCO₂)₁₆O₄]. Close structural analysis reveals that the high magnetic anisotropy observed in the INS measurements is a consequence of the distorted coordination geometry of the four outer Cr atoms.     

Reconstructing phase dynamics of oscillator networks

We generalize our recent approach to the reconstruction of phase dynamics of coupled oscillators from data [B. Kralemann et al., Phys. Rev. E 77, 066205 (2008)] to cover the case of small networks of coupled periodic units. Starting from a multivariate time series, we first reconstruct genuine phases and then obtain the coupling functions in terms of these phases. Partial norms of these coupling functions quantify directed coupling between oscillators. We illustrate the method by different network motifs for three coupled oscillators and for random networks of five and nine units. We also discuss nonlinear effects in coupling.     

Attractor of Smale - Williams type in an autonomous distributed system

We consider an autonomous system of partial differential equations for a one-dimensional distributed medium with periodic boundary conditions. Dynamics in time consists of alternating birth and death of patterns with spatial phases transformed from one stage of activity to another by the doubly expanding circle map. So, the attractor in the Poincaré section is uniformly hyperbolic, a kind of Smale - Williams solenoid. Finite-dimensional models are derived as ordinary differential equations for amplitudes of spatial Fourier modes (the 5D and 7D models). Correspondence of the reduced models to the original system is demonstrated numerically. Computational verification of the hyperbolicity criterion is performed for the reduced models: the distribution of angles of intersection for stable and unstable manifolds on the attractor is separated from zero, i.e., the touches are excluded. The example considered gives a partial justification for the old hopes that the chaotic behavior of autonomous distributed systems may be associated with uniformly hyperbolic attractors.