Glasslike arrest in spinodal decomposition as a route to colloidal gelation.

Colloid-polymer mixtures can undergo spinodal decomposition into colloid-rich and colloid-poor regions. Gelation results when interconnected colloid-rich regions solidify. We show that this occurs when these regions undergo a glass transition, leading to dynamic arrest of the spinodal decomposition. The characteristic length scale of the gel decreases with increasing quench depth, and the nonergodicity parameter exhibits a pronounced dependence on scattering vector. Mode coupling theory gives a good description of the dynamics, provided we use the full static structure as input.

Weak correlations between local density and dynamics near the glass transition.

We perform experiments on two different dense colloidal suspensions with confocal microscopy to probe the relationship between local structure and dynamics near the glass transition. We calculate the Voronoi volume for our particles and show that this quantity is not a universal probe of glassy structure for all colloidal suspensions. We correlate the Voronoi volume to displacement and find that these quantities are only weakly correlated. We observe qualitatively similar results in a simulation of a polymer melt. These results suggest that the Voronoi volume does not predict dynamical behavior in experimental colloidal suspensions; a purely structural approach based on local single particle volume likely cannot describe the colloidal glass transition.

A short-term, three-year epidemiological study of median nerve sensitivity in practicing dental hygienists.

PURPOSE: Hand-intensive, repetitive motion procedures such as those performed by dental hygienists can lead to median nerve dysfunction which, left untreated, can degenerate into clinical carpal tunnel syndrome (CTS). Vibrometry has been used as a method for early detection of sensory nerve impairment. METHODS: A cohort of 16 university-educated dental hygienists was evaluated by means of programmed frequency stimuli for median nerve dysfunction at graduation and at one, two, and three years postgraduation. RESULTS: The results indicate that median nerve dysfunction was not detected in this cohort. However, further analysis suggests that a significant loss of median nerve sensitivity, or permanent "threshold shift," has occurred in the three years since graduation. CONCLUSION: Whether this is a harbinger of future events is unknown at this time.

A short-term epidemiological study of median nerve dysfunction in practicing dental hygienists.

The purpose of this study was to assess over time changes in median nerve function in a group of 20 students who entered the University of Minnesota dental hygiene program in 1986. This is a follow-up report on 16 of the 20 students who were evaluated two years postgraduation in 1990. Comparisons were made with prior evaluations of the subjects completed at graduation in 1988, and one year postgraduation in 1989. Digital vibrometry was used to evaluate median nerve sensibility threshold at each of the time periods studied. Analysis revealed that after one year of clinical practice, there was a mean sensibility threshold shift of 11.04% in the left median nerve and 8.42% in the right median nerve as measured by digital vibrometry. Results at two years postgraduation indicated that the threshold shift observed in an earlier study had been arrested. The reasons appeared to be twofold: (1) a period of work hardening with a concept of neuromuscular ligamentous tissue hypertrophy or adaptation to the rigors of dental hygiene practice, and/or (2) the practicing dental hygienist had learned to become more efficient in the provision of hygiene procedures. There were no reported symptoms of median nerve dysfunction and none of the subjects had been diagnosed as having CTS at any time during the two years since graduation. Continued evaluations will be necessary to determine whether the observations noted during the second year postgraduation evaluation indicated temporary or permanent slowing of the conditions necessary for the development of CTS.

Peripheral nerve dysfunction in practicing dental hygienists.

Hand-intensive repetitive procedures such as those performed by dental hygienists can lead to cumulative trauma disorders of the upper extremity. One such disorder is median nerve dysfunction leading to carpal tunnel syndrome (CTS). Vibrometry has been used in industrial settings as a method of early detection of sensory nerve impairment. This technique uses vibratory stimuli to assess the level of sensory perception in the fingertips. Using programmed frequency stimuli, 58 practicing dental hygienists were evaluated bilaterally for median nerve dysfunction. Results indicated that 15 (25.9%) of the dental hygienists reported the presence of CTS symptoms, while 7 (12.0%) tested positive for mild median nerve dysfunction. The findings suggest that vibrometry testing could aid in the early detection of CTS, thereby reducing its effects on clinical practice and facilitating early treatment.

Moments and distribution functions for polypeptide chains. Poly-L-alanine.

Statistical mechanical averages of vectors and tensors characterizing the configurations of polypeptides have been calculated for poly-L-alanines (PLA) of xu = 2-400 peptide units. These quantities are expressed in the reference frame of the first peptide unit, the X axis being situated along the virtual bond, the Y axis in the plane of the peptide unit. The persistence vector a identical to (r) converges rapidly with chain length to its limit a infinity which lies virtually in the XZ plane. Configurational averages of Cartesian tensors up to the sixth rank formed from the displacement vector p = r-a have been computed. For xu greater than 50 the even moments of fourth and sixth rank formed from the reduced vector p for the real chain are well repreented by the freely jointed chain with 21.7 virtual bonds equivalent to one of the model. The moments of p display assymmetry for xu less than 50. Density distribution functions Wa(p), evaluated from the three-dimensional Hermite series truncated at the term in the polynomial involving the tensors of p of sixth rank, display no obvious symmetry for xu less than 50. Approximate spherical symmetry of the distribution of p about a is observed only for xu greater than or equal to 100.