Stochastic single-molecule videomicroscopy methods to measure electrophoretic DNA migration modalities in polymer solutions above and below entanglement

We have studied the effects of polymer molar mass and concentration on the electrophoretic migration modalities of individual molecules of DNA in LPA, HEC, and PEO solutions via epifluorescent videomicroscopy. While both transient entanglement coupling (TEC) and reptation have been studied in the past, the transition between them has not. Understanding this transition will allow for polymer network properties to be optimized to enhance the speed and resolution of DNA separations in microfluidic devices. Near the overlap threshold concentration, C*, TEC is the dominant observed mode of DNA migration, and the observation frequency of TEC increases with increasing polymer molar mass. As polymer concentration is increased, observed TEC events reduce to zero while DNA reptation events become the only detected mechanism. Individual DNA molecules undergoing both migration mechanisms were counted in solutions of varying polymer molar masses and concentrations and were plotted against a dimensionless polymer concentration, C/C*. The data for LPA reduce to form universal curves with a sharp increase in DNA reptation at approximately 6.5C*. Analogous transition concentrations for PEO and HEC were observed at 5C* and 3.5C*, respectively, reflecting the different physical properties of these polymers. This transition correlates closely with the polymer network entanglement concentration, Ce, as measured by rheological techniques. The electrophoretic mobility of lambda-DNA in LPA polymer solutions was also measured and shows how a balance can be struck between DNA resolution and separation speed by choosing the desired prevalence of DNA reptation.     

Coefficient of restitution and linear–dashpot model revisited

With the assumption of a linear–dashpot interaction force, the coefficient of restitution, , can be computed as a function of the elastic and dissipative material constants, k and γ by integrating Newton’s equation of motion for an isolated pair of colliding particles. If we require further that the particles interact exclusively repulsive, which is a common assumption in granular systems, we obtain an expression which differs even qualitatively from the known result . The expression allows to relate Molecular Dynamics simulations to event-driven Molecular Dynamics for a widely used collision model. This research was supported by German Science Foundation and by the G.I.F., the German-Israeli Foundation for Scientific Research and Development.     

Anlagen‐ und Prozesstechnik für die Mikrobearbeitung mit Vakuum‐UV Excimer‐Laser

With the F₂‐Excimer laser a tool has now become available for the precise structuring of challenging materials like fused silica or PTFE (Teflon®). However, the short wavelength of 157 nm with a characteristic photon energy of 7.9 eV has special requirements regarding beam guiding and the optical components like mirrors lenses or objectives. The process and system technology introduced here is capable to produce micro‐structures with a lateral resolution in the μm‐range with a depth resolution in the sub‐μm range.     

Ruthenium‐Catalyzed Diastereoselective syn‐Cyclopropanation of Trisubstituted Alkenes with Diazoacetates

Supporting Information for this article is available on the WWW under http://www.wiley‐vch.de/home/asc Cyclopropanation of trisubstituted alkenes with diazoacetates can be achieved with remarkabe syn‐selectivity when the polymeric ruthenium(I) complex [Ru₂(CO)₄(μ‐OAc)₂]_n is used as catalyst.     

Covariance Structure Maximum-Likelihood Estimates in Compound Gaussian Noise: Existence and Algorithm Analysis

Recently, a new adaptive scheme [Conte (1995), Gini (1997)] has been introduced for covariance structure matrix estimation in the context of adaptive radar detection under non-Gaussian noise. This latter has been modeled by compound-Gaussian noise, which is the product c of the square root of a positive unknown variable tau (deterministic or random) and an independent Gaussian vector x, c=radictaux. Because of the implicit algebraic structure of the equation to solve, we called the corresponding solution, the fixed point (FP) estimate. When tau is assumed deterministic and unknown, the FP is the exact maximum-likelihood (ML) estimate of the noise covariance structure, while when tau is a positive random variable, the FP is an approximate maximum likelihood (AML). This estimate has been already used for its excellent statistical properties without proofs of its existence and uniqueness. The major contribution of this paper is to fill these gaps. Our derivation is based on some likelihood functions general properties like homogeneity and can be easily adapted to other recursive contexts. Moreover, the corresponding iterative algorithm used for the FP estimate practical determination is also analyzed and we show the convergence of this recursive scheme, ensured whatever the initialization.     

More Than Stories With Buttons: Narrative,Mechanics, and Context as Determinants of Player Experience in Digital Games

Recent research has attempted to describe meaningful experiences with entertainment media that go beyond hedonic enjoyment. Most of this research focuses on noninteractive media, such as film and television. When applied to digital games, however, such research needs to account for not only the content of the medium, but also the unique dimensions of digital games that distinguish them from noninteractive media. Experiences with digital games are shaped by the game mechanics that define the users' interaction with game content, as well as by the opportunities for social interaction that many games offer. We argue that the complex interplay of these dimensions (narrative, mechanics, and context) facilitates or inhibits meaningful user experiences in ways that are unique to digital games.