Use of helical parameters to generate candidate conformations for crystal packing: illustrative application to a polyimide

This communication describes the application and extension of a method for calculating the helical parameters with which to describe molecular conformations. The method, which was originally developed by Shimanouchi and others, is applied to a polyimide of 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA) and 2,2-dimethyl-1,3-(4-aminophenoxy)propane (DMDA) which has eight torsional bonds in the chemical repeat unit. Discrete low energy states for these torsions were determined by Ramanchandran energy maps of sequential dihedral pairs or single bond torsional energy diagrams. The total number of possible low energy conformations for these states is 1152 including conformationally related isoenantiomorphs. The method conveniently generates the conformations for subsequent crystal structure packing and refinement. Consideration of these together with the X-ray data of Cheng and co-workers reduces the number to about 15 with about a 2/1 conformation and a c axis of approximately 49.2 Å. Of these, about half appear to be good candidates for crystal packing.     

Order—disorder transitions in polytetrafluoroethylene

The phase diagram of polytetrafluoroethylene is enlarged by differential scanning calorimetry to include the concentration of hexafluoropropylene comonomer units. The two transitions near 292 and 303 K in the homopolymer move to lower temperatures and apparently become one at small concentrations. Analysis of the data yields 295 K for the temperature and 13.2 J/g for the heat of transition of an infinitely large homopolymer crystal. The heat of transition associated with the formation of a crystal defect is 0.021 eV. The qualitative features of the transition can be accounted for by a mean-field model which involves two order parameters corresponding to planar units and helix reversals. This model yields two transitions which move closer together and to lower temperatures with increasing comonomer concentration. Decreasing lamella thickness will have a qualitatively similar effect.     

Driving behaviors in early stage dementia: A study using in-vehicle technology

According to the Alzheimer's Association (2011), (1) in 8 people age 65 and older, and about one-half of people age 85 and older, have Alzheimer's disease in the United States (US). There is evidence that drivers with Alzheimer's disease and related dementias are at an increased risk for unsafe driving. Recent advances in sensor, computer, and telecommunication technologies provide a method for automatically collecting detailed, objective information about the driving performance of drivers, including those with early stage dementia. The objective of this project was to use in-vehicle technology to describe a set of driving behaviors that may be common in individuals with early stage dementia (i.e., a diagnosis of memory loss) and compare these behaviors to a group of drivers without cognitive impairment. Seventeen drivers with a diagnosis of early stage dementia, who had completed a comprehensive driving assessment and were cleared to drive, participated in the study. Participants had their vehicles instrumented with a suite of sensors and a data acquisition system, and drove 1–2 months as they would under normal circumstances. Data from the in-vehicle instrumentation were reduced and analyzed, using a set of algorithms/heuristics developed by the research team. Data from the early stage dementia group were compared to similar data from an existing dataset of 26 older drivers without dementia. The early stage dementia group was found to have significantly restricted driving space relative to the comparison group. At the same time, the early stage dementia group (which had been previously cleared by an occupational therapist as safe to drive) drove as safely as the comparison group. Few safety-related behavioral errors were found for either group. Wayfinding problems were rare among both groups, but the early stage dementia group was significantly more likely to get lost.     

Disorder in the crystal structures of phases I and II of copolymers of tetrafluoroethylene and hexafluoropropylene

X-ray diffraction patterns for oriented and unoriented copolymers of tetrafluoroethylene and hexafluoropropylene are presented. They show a transition between 229 and 243K for a copolymer with about 3.4 CF₃ per hundred main chain carbon atoms. The lower temperature phase (II) appears to be similar to that of the homopolymer. A primary difference is the presence in the copolymer crystals of small longitudinal displacements of the molecules caused by the randomly located CF₃ groups. The displacements increase with increasing CF₃ concentration. The higher temperature phase (I) is similar to that of the homopolymer with a difference again being the longitudinal disorder of the copolymer. The difference disappears at higher temperatures as longitudinal disorder is introduced thermally in the homopolymer. At 296K (phase I) the molecular stems in a copolymer with about 3.4 CF₃ per hundred main chain carbon atoms are at an angle of 37.1 degrees with respect to the normal to the basal plane of the lamellas. In phase II, this number is the same within the limits of error.     

Differences in safety belt use by race

The purpose of the study was to identify daytime differences in safety belt use by race. Safety belt use was investigated in a direct observation survey of drivers and front-outboard passengers throughout Michigan. Data were weighted to calculate statewide safety belt use rates by race. Race was assessed visually by trained observers. The study showed that motor vehicle occupants identified as Black had significantly lower safety belt use than those occupants identified as White or Other.     

Driver hand-held mobile phone use and safety belt use

The purposes of the study were to identify hand-held mobile phone use trends for Michigan and to compare safety belt use between users and nonusers. Mobile phone and safety belt use was investigated by a direct observation survey of drivers at intersections in Michigan. Data were weighted to calculate mobile phone use and safety belt use rates statewide. The study showed 2.7% of Michigan drivers were using a mobile phone at any given daylight time. Safety belt use of current mobile phone users was significantly lower than those not using mobile phones.     

Placement of Substrate Contacts to Minimize Substrate Noise in Mixed-Signal Integrated Circuits

The placement of substrate contacts in epi and non-epi technologies is analyzed in order to control and reduce the substrate noise amplitude and spreading. The choice of small or large substrate contacts or rings for each of the two major technologies is highlighted. Design guidelines for placing substrate contacts so as to improve the noise immunity of digital circuits in mixed-signal smart-power systems are also presented.     

Characterization of the interfacial bond in paper-polypropylene laminates and the effects of aging under service conditions

This study focused on the behavior of the paper-polypropylene-paper (PPP) laminate while aging in hot oil in the absence of voltage stress. The results provide an understanding of both the quality of the interfacial bond and the performance of this bond during service. X-ray photoelectron spectroscopy performed on two different peeled laminates suggest that the bond failed primarily adhesively. Weibull statistical analysis of the peel strength data obtained on unaged laminates and those aged in polybutene oil at 90°C for 120 hours showed that the strength loss is consistent with one failure mechanism and the failure rate increases with applied stress. For the aged sample, Weibull analysis results are consistent with the prior loss of peel strength due to the aging. Experiments on the solubility of the oil show that lamination reduces the amount of absorption in comparison to the unlaminated composite. Swelling experiments on the individual components show differential swelling between the paper and polypropylene to be the source of the strength loss. The polypropylene swells, and the paper shrinks. Measurements on the laminate show that both paper and polypropylene shrink, indicating that the paper governs the laminate swelling process. During aging, the differential swelling generates internal stresses on the interface. In addition to yielding the magnitudes of these stresses, finite element analysis also predicts plastic deformation and creeping of the polypropylene as well as tensile stresses between the paper and polypropylene at a free edge. Very likely these processes damage the bond and contribute to the loss of bond strength.