Time-dependent alignment of molecules trapped in octahedral crystal fields

The hindered rotational states of molecules confined in crystal fields of octahedral symmetry, and their time-dependent alignment obtained by pulsed nonresonant laser fields, are studied computationally. The control over the molecular axis direction is discussed based on the evolution of the rotational wave packet generated in the cubic crystal-field potential. The alignment degree obtained in a cooperative case, where the alignment field is applied in a favorable crystal-field direction, or in a competitive direction, where the crystal field has a saddle point, is presented. The investigation is divided into two time regimes where the pulse duration is either ultrashort, leading to nonadiabatic dynamics, or long with respect to period of molecular libration, which leads to synchronous alignment due to nearly adiabatic following. The results are contrasted to existing gas phase studies. In particular, the irregularity of the crystal-field energies leads to persistent interference patterns in the alignment signals. The use of nonadiabatic alignment for interrogation of crystal-field energetics and the use of adiabatic alignment for directional control of molecular dynamics in solids are proposed as practical applications.     

Predicting supercontinuum pulse collisions with simulations exhibiting temporal aliasing

Interactions between supercontinuum (SC) light pulses, produced by the propagation of rapidly sequenced picosecond pump laser pulses along a photonic crystal fiber, result in spectral broadening, which we attribute to interpulse soliton collisions. This phenomenon was measured experimentally, following our observation of spectral broadening in numerical simulations that exhibit so-called "pulse wraparound" or "temporal aliasing." This occurs in simulations with narrow time grids: as early parts of the SC pulse leave the computational time domain, they "reenter" at the beginning and so interact with later parts of the evolving SC pulse. We show that this provides an effective model to predict the experimentally observed spectral changes.     

A priori and a posteriori estimates for three‐dimensional Stokes equations with nonstandard boundary conditions

In this article, we study the Stokes problem with some nonstandard boundary conditions. The variational formulation decouples into a system for the velocity and a Poisson equation for the pressure. The corresponding discrete system do not need an inf‐sup condition. Hence, the velocity is approximated with “ curl ” conforming finite elements and the pressure with standard continuous elements. Next, we establish optimal a priori and a posteriori estimates and we finally concluded with numerical tests. © 2011 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2012     

Investigating the impact of an urban community school effort on middle school STEM-related student outcomes over time through propensity score matched methods

This study investigates the impact of an urban community school reform initiative that focuses on an immigrant and refugee population in middle school. A 6th–8th grade cohort of students in the community school are followed over time and compared to a propensity score matched group on overall GPA, mathematics, and science academic outcomes and traditional college preparedness indicators. Further, a deeper dive into the intersection of gender and race/ethnicity was examined on all outcomes. Findings revealed that students in the urban community school demonstrated significantly more preparedness to enroll in college and move into a STEM field if they desired compared to the matched students. All gender/racial groups in the community school performed significantly higher than those in the matched group. Further, all gender/racial groups of students in the urban community school defied standard academic achievement drops common over time in middle school, and instead increase overall, math, and science grades from 6th to 8th grade.     

Orlicz-Sobolev extensions and measure density condition

We study the extension properties of Orlicz-Sobolev functions both in Euclidean spaces and in metric measure spaces equipped with a doubling measure. We show that a set E⊂R satisfying a measure density condition admits a bounded linear extension operator from the trace space W1,Ψ(Rn)E_| to W1,Ψ(Rn). Then we show that a domain, in which the Sobolev embedding theorem or a Poincaré-type inequality holds, satisfies the measure density condition. It follows that the existence of a bounded, possibly non-linear extension operator or even the surjectivity of the trace operator implies the measure density condition and hence the existence of a bounded linear extension operator.     

Preparation of 2-iodotryptamine and 2-iodo-5-methoxytryptamine

The regiospecific iodination of indole and 5-methoxyindole, and the elaboration of these 2-iodoindoles to the corresponding tryptamines, are described.     

Kinetic studies of composite propellants by differential scanning calorimetry : Effect of heating rate and sample geometry

Differential scanning calorimetry has been used to calculate some kinetic parameters of a typical composite solid propellant (PBAA based). The heating-rate affects the development of thermograms and also the apparent activation energy. Sample geometry has a definitive influence on thermograms and on sample ignition but seems to have no effect on activation energy calculations.     

Experimental boundaries of the quantum rotor induced polarization (QRIP) in liquid state NMR

The Haupt‐effect is a rather seldom used hyperpolarization method. It is based on the interdependence between nuclear spin states and rotational states of nearly free rotating methyl groups having C₃ symmetry. A sudden change in temperature from 4.2 K to room temperature by fast dissolution yields considerably enhanced ¹³C and ¹H resonance signals. This phenomenon is now termed quantum rotor induced polarization. More than 40 substances have been studied by this approach in order to identify them as polarizable by the ‘Haupt‐effect in the liquid state’. Influencing factors have been analyzed systematically. It could be concluded that substances having a high tunneling frequency, which is due to a small and narrow potential barrier, are most likely to feature quantum rotor induced polarization‐enhanced signals. Copyright © 2013 John Wiley & Sons, Ltd.     

13CMR-Tieftemperatur-Untersuchungen an Cyclooctan-Konformeren

The conformational equilibria of a variety of monosubstituted cyclooctanes is determined by low temperature ¹³CMR spectroscopy. ¹³C shifts allow conclusions to be made regarding the geometry of the conformers. For some conformational processes ΔG^# is obtained by complete line shape analysis.