Crossed Molecular Beams and Theoretical Studies of the O(3P)+1,2-Butadiene Reaction: Dominant Formation of Propene+CO and Ethylidene+Ketene Molecular Channels

Detailed understanding of the mechanism of the combustion relevant multichannel reactions of O(³P) with unsaturated hydrocarbons (UHs) requires the identification of all primary reaction products, the determination of their branching ratios and assessment of intersystem crossing (ISC) between triplet and singlet potential energy surfaces (PESs). This can be best achieved combining crossed-molecular-beam (CMB) experiments with universal, soft ionization, mass-spectrometric detection and time-of-flight analysis to high-level ab initio electronic structure calculations of triplet/singlet PESs and RRKM/Master Equation computations of branching ratios (BRs) including ISC. This approach has been recently demonstrated to be successful for O(³P) reactions with the simplest UHs (alkynes, alkenes, dienes) containing two or three carbon atoms. Here, we extend the combined CMB/theoretical approach to the next member in the diene series containing four C atoms, namely 1,2-butadiene (methylallene) to explore how product distributions, branching ratios and ISC vary with increasing molecular complexity going from O(³P))+propadiene to O(³P)+1,2-butadiene. In particular, we focus on the most important, dominant molecular channels, those forming propene+CO (with branching ratio ∽0.5) and ethylidene+ketene (with branching ratio ∽0.15), that lead to chain termination, to be contrasted to radical forming channels (branching ratio ∽0.35) which lead to chain propagation in combustion systems.     

Finite-Size Scaling in the Driven Lattice Gas

We present a Monte Carlo study of the high-temperature phase of the two-dimensional driven lattice gas at infinite driving field. We define a finite-volume correlation length, verify that this definition has a good infinite-volume limit independent of the lattice geometry, and study its finite-size-scaling behavior. The results for the correlation length are in good agreement with the predictions based on the field theory proposed by Janssen, Schmittmann, Leung, and Cardy. The theoretical predictions for the susceptibility and the magnetization are also well verified. We show that the transverse Binder parameter vanishes at the critical point in all dimensions $d \geqslant 2$ and discuss how such result should be expected in the theory of Janssen et al. in spite of the existence of a dangerously irrelevant operator. Our results confirm the Gaussian nature of the transverse excitations.     

Interaction of lipoplexes with anionic lipids resulting in DNA release is a two-stage process

We propose a mechanism for DNA release from lipoplexes in cells that accounts for various observations of lipoplex-anionic lipid interactions. We examined the structural evolution of lipoplexes upon interaction with cellular lipids by synchrotron small-angle X-ray diffraction (SAXD), and the extent of DNA release from lipoplexes was determined by gel electrophoresis. We find that the interaction of lipoplexes with anionic cellular lipids is a two-stage process. In the first step, anionic lipids laterally diffuse into the complex and neutralize the cationic lipids. As a result, the membrane charge density of lipoplexes decreases and interactions between cationic lipids and DNA become weaker, but DNA is extremely poorly released. Only after the cationic charge of lipoplex membranes is completely neutralized by anionic lipids does DNA starts to be released significantly.     

Structural stability against disintegration by anionic lipids rationalizes the efficiency of cationic liposome/DNA complexes

Reported here is the correlation between the transfection efficiency of cationic liposome/DNA complexes (lipoplexes) and the structural evolution that they undergo when interacting with anionic membrane lipids. Multicomponent lipoplexes, incorporating from three to six lipid species simultaneously, presented a much higher transfection efficiency than binary lipoplexes, which are more commonly used for gene-delivery purposes. The discovery that a high transfection efficiency can be achieved by employing multicomponent complexes at a lower-than-ever-before membrane charge density of lipoplexes was of primary significance. Synchrotron small-angle X-ray diffraction (SAXD) experiments showed that anionic liposomes made of dioleoylphosphatidylglycerol (DOPG) disintegrated the lamellar phase of lipoplexes. DNA unbinding was measured by electrophoresis on agarose gels. Most importantly, structural changes induced by anionic lipids strictly depended on the lipid composition of lipoplexes. We found evidence of the existence of three different regimes of stability related to the interaction between complexes and anionic membranes. Both unstable (with low membrane charge density, sigmaM) and highly stable lipoplexes (with high sigmaM) exhibited low transfection efficiency whereas highly efficient multicomponent lipoplexes exhibited an "optimal stability". This intermediate regime reflects a compromise between two opposing constraints: protection of DNA in the cytosol and endosomal escape. Here we advance the concept that structural stability, upon interaction with cellular anionic lipids, is a key factor governing the transfection efficiency of lipoplexes. Possible molecular mechanisms underlying experimental observations are also discussed.     

Bogoliubov transformations and fermion condensates in lattice field theories

We apply generalized Bogoliubov transformations to the transfer matrix of relativistic field theories regularized on a lattice. We derive the conditions these transformations must satisfy to factorize the transfer matrix into two terms which propagate fermions and antifermions separately, and we solve the relative equations under some conditions. We relate these equations to the saddle point approximation of a recent bosonization method and to the Foldy-Wouthuysen transformations which separate positive from negative energy states in the Dirac Hamiltonian.     

150-ps pulse Raman generator pumped by a 1-kHz sub-nanosecond passively Q-switched laser system

Raman conversion with a single Ba(NO₃)₂ crystal (barium nitrate) either in single- and double-pass travelling-wave setups has been investigated. A Master-Oscillator-Power-Amplifier (MOPA) system, based on a passively Q-switched (PQS) laser generating 500-ps pulses and delivering a total energy of 350 μJ at 1 kHz, was used as pump source for the Raman generator. The two-passes setup yielded 116-μJ, 150-ps Fourier- and diffraction-limited pulses at 1198 nm for ≈3× the Raman threshold with no additional Stokes lines, and conversion efficiency of 35%. Such results are interesting not only for direct applications of the wavelength-shifted laser source, but also for further pulse-compression and supercontinuum generation in fibers. Indeed, self-phase modulation up to 0.82 nm has been demonstrated (pulse compression down to 5 ps) as well as 120-nm supercontinuum.     

Multiple and inverse topplings in the Abelian Sandpile Model

The Abelian Sandpile Model is a cellular automaton whose discrete dynamics reaches an out-of-equilibrium steady state resembling avalanches in piles of sand. The fundamental moves defining the dynamics are encoded by the toppling rules. The transition monoid corresponding to this dynamics in the set of stable configurations is abelian, a property which seems at the basis of our understanding of the model. By including also antitoppling rules, we introduce and investigate a larger monoid, which is not abelian anymore. We prove a number of algebraic properties of this monoid, and describe their practical implications on the emerging structures of the model.     

Simple and direct communication of dynamical supersymmetry breaking

Journal of High Energy Physics - It was shown in a previous study that a lightest neutralino with mass below 30 GeV was severely constrained in the minimal supersymmetric standard model (MSSM),...     

Label-free quantitative analysis for studying the interactions between nanoparticles and plasma proteins

A shotgun proteomics approach was used to compare human plasma protein binding capability with cationic liposomes, DNA–cationic lipid complexes (lipoplexes), and lipid–polycation–DNA (LPD) complexes. Nano-high-performance liquid chromatography coupled with a high-resolution LTQ Orbitrap XL mass spectrometer was used to characterize and compare their protein corona. Spectral counting and area under curve methods were used to perform label-free quantification. Substantial qualitative and quantitative differences were found among proteins bound to the three different systems investigated. Protein variety found on lipoplexes and LPD complexes was richer than that found on cationic liposomes. There were also significant differences between the amounts of protein. Such results could help in the design of gene-delivery systems, because some proteins could be more selectively bound rather than others, and their bio-distribution could be driven in vivo for more efficient and effective gene therapy.     

Spanning Forests on Random Planar Lattices

The generating function for spanning forests on a lattice is related to the q-state Potts model in a certain q→0 limit, and extends the analogous notion for spanning trees, or dense self-avoiding branched polymers. Recent works have found a combinatorial perturbative equivalence also with the (quadratic action) O(n) model in the limit n→?1, the expansion parameter t counting the number of components of the forest. We give a random-matrix formulation of this model on the ensemble of degree-k random planar lattices. For k=3, a correspondence is found with the Kostov solution of the loop-gas problem, which arise as a reformulation of the (logarithmic action) O(n) model, at n=?2. Then, we show how to perform an expansion around the t=0 theory. In the thermodynamic limit, at any order in t we have a finite sum of finite-dimensional Cauchy integrals. The leading contribution comes from a peculiar class of terms, for which a resummation can be performed exactly.