Synthesis of Highly Substituted Cyclobutane Fused‐Ring Systems from N‐Vinyl β‐Lactams through a One‐Pot Domino Process

In this contribution, aminocyclobutanes, as well as eight‐membered enamide rings, have been made from N‐vinyl β‐lactams. The eight‐membered products have been formed by a [3,3]‐sigmatropic rearrangement, whereas the aminocyclobutanes have been derived from a domino [3,3]‐rearrangement/6π‐electrocyclisation process. The aminocyclobutanes have been obtained in a highly diastereoselective fashion. The cyclobutane ring system tolerates fusion even if adjacent quaternary centres are present. Systems containing up to four fused rings are readily accessible. The reaction profile has been investigated by using Gaussian 03. This study suggests that two reaction pathways for aminocyclobutane formation are possible. In one pathway the [3,3]‐sigmatropic rearrangement is the rate‐limiting step and in the second pathway the electrocyclisation is rate limiting. Taken together, these reactions should facilitate the construction of fused heterocycles.     

On the hydration of the phosphocholine headgroup in aqueous solution

The hydration of the phosphocholine headgroup in 1,2-dipropionyl-sn-glycero-3-phosphocholine (C(3)-PC) in solution has been determined by using neutron diffraction enhanced with isotopic substitution in combination with computer simulation techniques. The atomic scale hydration structure around this head group shows that both the -N(CH(3))(3) and -CH(2) portions of the choline headgroup are strongly associated with water, through a unique hydrogen bonding regime, where specifically a hydrogen bond from the C-H group to water and a strong association between the water oxygen and N(+) atom in solution have both been observed. In addition, both PO(4) oxygens (P=O) and C=O oxygens are oversaturated when compared to bulk water in that the average number of hydrogen bonds from water to both X=O oxygens is about 2.5 for each group. That water binds strongly to the glycerol groups and is suggestive that water may bind to these groups when phosophotidylcholine is embedded in a membrane bilayer.     

Time Resolved Microwave Interferometry Measurement of the Electron Density in a Pulsed 1,3-Butadiene Discharge

Pulsed plasmas containing organic precursors are becoming increasingly common for multiple applications. To understand the nature of such discharges, in-situ time resolved microwave interferometry measurements of the electron density in a 60 W pulsed inductively coupled 1,3-butadiene discharge have been made. Measurements were also made for continuous wave plasmas at 40, 50, 60 and 70 W power for comparison. The data shows that the time averaged electron densities are independent of pulse width at a particular duty cycle. In addition, time averaged values increase approximately linearly with increasing duty cycle. Such linearity in average density is tied to the ambipolar loss rate. This knowledge is important for understanding the growth kinetics of plasma polymerized films.     

Highly charged supramolecular oligomers based on the dimerization of corannulene tetraanion

The supramolecular dimerization of tetraanionic corannulene is utilized as a self-assembly motif for the construction of highly charged, buckybowl-based supramolecular oligomers. Oligomers of up to 7 units (3900 g mol(-1)) of reduced dicorannulenic monomers are identified and characterized by various NMR techniques, and the reversibility of their assembly is established through the concentration dependence of their molecular weight and the effect of monofunctional chain-stoppers.     

Nonminimum phase adaptive inverse control for settle performance applications

Single-track hard disk drive (HDD) seek performance is measured by settle time, $t_s$, defined as the time from the arrival of a seek command until the measured position reaches and stays within an acceptable distance from the target track. Our previous work has shown feedforward dynamic inversion, coupled with an aggressive desired trajectory $y_d$, is capable of achieving high performance settle times when the closed-loop dynamics are time-invariant and accurately modeled. In contrast, we describe an adaptive inversion procedure in this paper which removes the requirement for accurate initial models and tracks the position-variant dynamics present in our Servo Track Writer (STW) experimental apparatus. The proposed indirect adaptive inversion algorithm relies on a recursive least squares (RLS) estimate of the closed-loop dynamics. Pre-filtering of the RLS input signals, covariance resetting, and relative NMP system partitioning are necessary additions to the baseline adaptive algorithm in order to achieve fast settle times. Compared to the nonadaptive solution with accurate system identification, we show the adaptive algorithm achieves a 22% reduction in average settle time and a 53% reduction in settle time standard deviation.     

A nonlinear PSE method for two-fluid shear flows with complex interfacial topology

A nonlinear stability method is developed for laminar two-fluid shear flows which undergo changes in the interface topology. The method is based on the nonlinear parabolized stability equations (PSE) and incorporates a scalar-based interface capturing (IC) scheme in order to track complex deformations of the fluid interface. In doing so, the formulation retains the flexibility and physical insight of instability-wave based methods, while providing hydrodynamic modeling capabilities similar to direct numerical calculations: the new formulation, referred to as the IC-PSE, can capture the nonlinear physical mechanisms responsible for generating large-scale, two-fluid structures, without incurring heavy computational costs. This approach is valid for spatially developing, laminar two-fluid shear flows which are convectively unstable, and can naturally account for the growth of finite amplitude interfacial waves, along with changes to the interfacial topology. We demonstrate the accuracy of the IC-PSE against direct Navier–Stokes calculations for two-fluid mixing layers with density and viscosity stratification. The comparisons show that the IC-PSE can predict the dynamics of the instability waves and capture the formation of Kelvin–Helmholtz vortex rolls and large scale liquid structures, at an order of magnitude less computational cost than direct calculations. The role of surface tension in the IC-PSE formulation is shown to be valid for flows in which Re/We ? 1, and the method accurately predicts the formation and non-linear evolution of flow structures in this limit. This is demonstrated for spatially developing mixing layers which lead to vortex roll-up and ligaments, prior to droplet formation. The pinch-off process itself is a high surface tension phenomenon and in not considered herein. The method also accurately captures the effect of interfacial waves on the mean flow, and the topology changes during the non-linear evolution of the two-fluid structures.     

Analysis of KrF excimer laser beam modification resulting from ablation under closed thick film flowing filtered water

The application of a closed thick film flowing filtered water to immerse the ablation etching mechanism of an excimer laser poses interesting possibilities concerning debris control, modification of machined feature topography and modification of the ablation rate. Furthermore, these parameters have been shown to be dependent on flow velocity; hence, offering further user control of machining characteristics. However, the impact of this technique requires investigation. This contribution offers comparison of the calculated ablation pressure and the effect on feature surface characteristics given for laser ablation of bisphenol A polycarbonate using KrF excimer laser radiation in ambient air against laser ablation of the same substrate under closed thick film flowing filtered water immersion. Also, an impact of such immersion equipment on the optical performance of the micromachining centre used is quantified and reviewed. The pressure is calculated to have risen by a magnitude of 48, when using the liquid immersed ablation technique. This increase in pressure is proposed to have an increased surface roughness, promoting the number of asperities with a surface area lower than 16 μm²; resulting in a diffuse reflection of light and an apparent darkening of features. The focal length of the optical system was accurately predicted to increase by 2.958 mm, when using the closed flowing liquid immersion equipment. This equipment is predicted to have increased the optical depth of focus via reduction in the angle of convergence of the two defining image rays; yet the perceived focus, measured discretely by mean feature wall angle, was found to be 25% smaller when using the closed thick film flowing filtered water immersion technique instead of similar laser ablation in ambient air. A compressed plume interaction is proposed as a contributing factor in this change.     

Fat-water selective excitation in balanced steady-state free precession using short spatial-spectral RF pulses

Fat suppression is important but challenging in balanced steady-state free precession (bSSFP) acquisitions, for a number of clinical applications. In the present work, the practicality of performing fat-water selective excitations using spatial-spectral (SPSP) RF pulses in bSSFP sequence is examined. With careful pulse design, the overall duration of these SPSP pulses was kept short to minimize detrimental effects on TR, scan time and banding artifact content. Fat-water selective excitation using SPSP pulses was demonstrated in both phantom and human bSSFP imaging at 3T, and compared to results obtained using a two-point Dixon method. The sequence with SPSP pulses performed better than the two-point Dixon method, in terms of scan time and suppression performance. Overall, it is concluded here that SPSP RF pulses do represent a viable option for fat-suppressed bSSFP imaging.     

Fast fat-suppressed reduced field-of-view temperature mapping using 2DRF excitation pulses

The purpose of this study is to develop a fast and accurate temperature mapping method capable of both fat suppression and reduced field-of-view (rFOV) imaging, using a two-dimensional spatially-selective RF (2DRF) pulse. Temperature measurement errors caused by fat signals were assessed, through simulations. An 11×1140μs echo-planar 2DRF pulse was developed and incorporated into a gradient-echo sequence. Temperature measurements were obtained during focused ultrasound (FUS) heating of a fat-water phantom. Experiments both with and without the use of a 2DRF pulse were performed at 3T, and the accuracy of the resulting temperature measurements were compared over a range of TE values. Significant inconsistencies in terms of measured temperature values were observed when using a regular slice-selective RF excitation pulse. In contrast, the proposed 2DRF excitation pulse suppressed fat signals by more than 90%, allowing good temperature consistency regardless of TE settings. Temporal resolution was also improved, from 12 frames per minute (fpm) with the regular pulse to 28 frames per minute with the rFOV excitation. This technique appears promising toward the MR monitoring of temperature in moving adipose organs, during thermal therapies.     

Noninvasive observation of cervical spinal cord activity in children by functional MRI during cold thermal stimulation

Functional magnetic resonance imaging (fMRI) is a non-invasive neuroimaging tool that indirectly identifies areas of neural activity in the brain and more recently has been applied to the adult spinal cord (spinal fMRI). Spinal fMRI could clearly benefit pediatric populations as well. The purpose of this work was to characterize the response observed with spinal fMRI in the brainstem and cervical (C) spinal cord of awake, healthy children during thermal stimulation (17°C and 27°C) applied to the right hand. Functional MRI detected neuronal activity in the expected region of the spinal cord (C6 and C7) as well as in the brainstem and thalamus. The observed magnitudes of signal change of the responses to 17°C and 27°C were similar; however, the spatial distribution of active pixels was greater during 17°C stimulation. The results of this study indicate that fMRI can be used to assess activity in the spinal cords of children, with good sensitivity and reliability.