Fluctuation-theory constraint for extensive entropy in Monte-Carlo simulations

The entropy per particle in most Monte-Carlo simulations is size dependent due to correlated energy fluctuations. Guided by nanothermodynamics, we find a constraint for the Ising model that enhances the fluctuations and lowers the free energy, while making the entropy homogeneous, additive, and extensive. Although the average interaction energy becomes size dependent, the resulting distribution of energies provides a mechanism for the heterogeneity found in the dynamics of many materials.     

Twistor Actions for Self-Dual Supergravities

We give holomorphic Chern-Simons-like action functionals on supertwistor space for self-dual supergravity theories in four dimensions, dealing with supersymmetries, the cases where different parts of the R-symmetry are gauged, and with or without a cosmological constant. The gauge group is formally the group of holomorphic Poisson transformations of supertwistor space where the form of the Poisson structure determines the amount of R-symmetry gauged and the value of the cosmological constant. We give a formulation in terms of a finite deformation of an integrable -operator on a supertwistor space, i.e., on regions in . For , we also give a formulation that does not require the choice of a background.     

Transport by Molecular Motors in the Presence of Static Defects

The transport by molecular motors along cytoskeletal filaments is studied theoretically in the presence of static defects. The movements of single motors are described as biased random walks along the filament as well as binding to and unbinding from the filament. Three basic types of defects are distinguished, which differ from normal filament sites only in one of the motors’ transition probabilities. Both stepping defects with a reduced probability for forward steps and unbinding defects with an increased probability for motor unbinding strongly reduce the velocities and the run lengths of the motors with increasing defect density. For transport by single motors, binding defects with a reduced probability for motor binding have a relatively small effect on the transport properties. For cargo transport by motors teams, binding defects also change the effective unbinding rate of the cargo particles and are expected to have a stronger effect.     

Validation of reduced mechanisms for nitrogen chemistry in numerical simulation of a turbulent non-premixed flame

In this paper, the formation of nitrogen pollutants in computational fluid dynamics simulation of turbulent non-premixed flame was modelled by coupling reduced nitrogen chemical reaction mechanisms with comprehensive combustion model.     

Mechanistic Insight into Formation of Oxo‐Iron(IV) Porphyrin π‐Cation Radicals from Enzyme Mimics of Cytochrome P450 in Organic Solvents

Two new models for cytochrome P450 in which the thiolate axial ligand is replaced by an RSO₃^? group, form oxo‐iron(IV) porphyrin π‐cation radicals as sole oxidation products in “peroxo shunt” reactions (see scheme) independent of the nature of the employed solvent (polar or non‐polar) and electronic nature of the porphyrin rings.

     

Current versus gate voltage hysteresis in organic field effect transistors

Abstract  

Research into organic field effect transistors (OFETs) has made significant advances—both scientifically and technologically—during the last decade, and the first products will soon enter the market. Printed electronic circuits using organic resistors, diodes and transistors may become cheap alternatives to silicon-based systems, especially in large-area applications. A key parameter for device operation, besides long term stability, is the reproducibility of the current–voltage behavior, which may be affected by hysteresis phenomena. Hysteresis effects are often observed in organic transistors during sweeps of the gate voltage (V _GS). This hysteresis can originate in various ways, but comparative scientific investigations are rare and a comprehensive picture of “hysteresis phenomena” in OFETs is still missing. This review provides an overview of the physical effects that cause hysteresis and discusses the importance of such effects in OFETs in a comparative manner.     

Aqueous normal-phase retention of nucleotides on silica hydride columns

The use of silica hydride-based stationary phases for the retention and analysis of nucleotides has been investigated. Both reversed-phase columns with a hydride surface underneath as well as those with an unmodified or a minimally modified hydride material were tested. With these systems, an aqueous normal-phase mode was used with high organic content mobile phases in combination with an additive to control pH for the retention of the hydrophilic nucleotides. Isocratic and gradient elution formats have been used to optimize separations for mixtures containing up to seven components. All conditions developed are suitable for methods that utilize mass spectrometry detection.     

Suppressed Particle Formation by Kinetically Controlled Ozone Removal: Revealing the Role of Transient‐Species Chemistry during Alkene Ozonolysis

The new approach of kinetically controlled ozone removal suppresses particle formation in laboratory ozonolysis experiments for methylcyclohexene and methylenecyclohexane (MCHa) at excess alkene concentrations (see graph). The results support the hypothesis that peroxy radicals are involved in organic nucleation and particle‐growth mechanisms.

     

Redox Economy in Organic Synthesis

Stimulus package for organic synthesis : The economy of step and atom usage has been widely reviewed and acknowledged as being useful frameworks to evaluate the efficiency of synthesis. This Review brings to attention another form of economy which should be considered in the planning and evaluation of a multistep synthesis: redox economy. Several guidelines and examples are included to illustrate the logic of this approach and to stimulate the design of syntheses.

     

Cover Picture: A Phosphorus Analogue of Bis(η4‐cyclobutadiene)iron(0) (Angew. Chem. Int. Ed. 17/2009)

A rare phosphorus analogue of the elusive complex bis(η⁴‐cyclobutadiene)iron(0) is reported by K. Lammertsma et al. in their Communication on page 3104 ff. The background of the cover picture shows John Montagu (1718–1792), 4th Earl of Sandwich and 1st Lord of the Admiralty, who certainly would not have dreamt that an important class of organometallic compounds, sandwich complexes, would bear his name one day. The synthesis of [Fe(P₂C₂tBu₂)₂] shows that sandwich complexes are still topical objects of research.