Diffuse-double layer at a membrane-aqueous interface measured with x-ray standing waves.

The ion distribution in an electrolyte solution in contact with a charged polymerized phospholipid membrane was directly measured with long-period x-ray standing waves. The 27-angstrom-thick lipid monolayer was supported on a tungsten/silicon mirror. X-ray standing waves were generated above the mirror surface by total external reflection of a 9.8-kiloelectron volt x-ray beam from a synchrotron undulator. The membrane surface, which contained negatively charged phosphate headgroups, was bathed in a dilute ZnCl2 solution. The concentration of Zn2+ in the condensed layer at the membrane surface and the Zn2+ distribution in the diffuse layer were measured as a function of headgroup charge. The Debye length of the diffuse layer varied between 3 and 58 angstroms. The results qualitatively agree with the Gouy-Chapman-Stern model.

[Sonographic screening of the newborn hip at the university hospital Marburg--a long-run analysis]. / Sonografisches Screening der Neugeborenenhüfte am Universitätsklinikum Marburg--eine Langzeitanalyse.

BACKGROUND: Since 1985 the hips of the newborns have been sonographically screened at the University Hospital Marburg by staff of the Orthopaedic Department. This study was conducted to collect data on the local incidence of DDH (developmental dysplasia of the hip). Moreover, the diagnostic findings were checked critically to detect weak points. Another aim was to analyse the influence of investigators' experience on the treatment recommendation. MATERIAL AND METHODS: In a retrospective study, 18 247 hip sonograms in a treatment period from 1985 to 2009 were analysed. The following parameters were evaluated: perinatal incidents (e.g., breech presentation, Caesarean section, premature delivery), orthopaedic findings (e.g., club foot, limitation of hip abduction). Bony roof, superior bony rim and cartilaginous roof were analysed; α- and ß-angles and hip type according to Graf were documented. Comparisons between variables were calculated by means of adequate statistic tests. χ(2)-values and coefficients of correlation were used to detect significance. RESULTS: All in all 55 physicians of our Orthopaedic Department conducted 350 measurements on average (min. 1; max. 1993). Accuracy of documentation improved over time. In particular in the beginning of the screening, the hip angles according to Graf were not completely determined and sonograms were classified by "visual diagnosis". The ß-angle was not measured at the outset. In the course of time we measured a decrease of the diagnosis hip type II a according to Graf. In the years 1985-1989 more than 40 % of the hips were described as physiologically immature. We evaluated a numerical regression of hip type II a to 16 % in time period 1990-1994 and 9 % in time period 2005-2009. There was a significant correlation between breech presentation and decentering and eccentric hips. Inexperienced physicians recommend more often therapeutic interventions (p ≤ 0.01). Treatment of hip type II a according to Graf was inconsistent over time. CONCLUSION: This study demonstrates the necessity of standardised hip sonography. Treatment according to measured hip type should be concise. Training programmes both for instructors and medical assistant staff is mandatory. "Bedside teaching" is not constructive.

Evaluation of neck muscle strength with a modified sphygmomanometer dynamometer: reliability and validity.

OBJECTIVE: Determine test-retest reliability, normative data and clinical validity of isometric muscle strength testing in the neck with a modified sphygmomanometer dynamometer (MSD). DESIGN: Analytic survey. Paired trials of various muscle strength tests were conducted on convenience samples of normal subjects and consecutive samples of symptomatic subjects. SETTING: Outpatient chiropractic research clinic. PATIENTS/SUBJECTS: For study 2, 40 normal male subjects, average age 25 +/- 2 yr, were studied for reliability and normative data. For study 3, 24 symptomatic patients, 12 males and 12 females, average age 39 +/- 7 yr, were studied, 8 with "whiplash"-type injuries (average duration 22.5 wk) and 16 with nontraumatic chronic neck pain (average duration 110 wk). INTERVENTION: No therapeutic intervention is reported. MAIN OUTCOME MEASURE: Pressure levels generated by subjects against a modified sphygmomanometer-type dynamometer as measured in kilopascals. RESULTS: Study 1. Repeated paired trials of a standardized weight column (20 lbs) produced a coefficient of variation of 0.84% and virtually no difference between the means of the first vs. second trials. Study 2. High test-retest correlation coefficients were found for all ranges of motion (.79-.97). Right-to-left asymmetry in rotation and lateral flexion was within 6-8%. The flexion/extension ratio was .57:1, indicating that in normal subjects, flexion was approximately 40% lower than extension. Lower cutoffs were established as the mean--1 SD as follows (in kPa): flexion--3300, extension--5800, rotation--5200 and lateral flexion--6200. Coefficients of variation ranged from 25 to 29%. Study 3. Differences between paired trials were analyzed by intraclass coefficients, which were very high (.95-.99), and by percentages, which ranged from 4 to 10.4%, with an average of 7%, indicating a high degree of test-retest consistency. The mean values for all symptomatic subjects for flexion, extension, right rotation and right lateral bending were all well below the normal cutoff values as found in study 2. The flexion/extension ratio for whiplash subjects was 0.25:1.00, which is half of that of normal subjects. CONCLUSIONS: The MSD has been found to be a reliable instrument for the evaluation of isometric muscle strength in the neck in normal and symptomatic subjects. Normative values for absolute test levels, bilateral symmetry and flexion/extension ratios have been determined. A symptomatic group demonstrated significant deviations from these norms in the form of reduced strength levels and reduced flexion/extension ratios, while still maintaining very high levels of test-retest consistency and bilateral symmetry. The MSD appears very promising in the evaluation of neck-injured patients.

Structural studies of membranes and surface layers up to 1,000 A thick using X-ray standing waves.

The X-ray standing wave (XSW) method, developed in the 1960s, was used originally to determine heavy atom positions in and on silicon and germanium single crystals. An X-ray standing wave generated by the interference of coherent incident and reflected beams excites X-ray fluorescence from the heavy atom, the intensity of which as a function of incident angle provides an indication of the atom's distance from the X-ray reflecting surface. The availability of X-ray mirrors and the ability to prepare layered synthetic microstructures has made possible the study of biologically relevant structures using the XSW technique on length scales of typically tens to hundreds of ångströms, allowing heavy atoms in such structures to be located with ångström or subångström resolution. Many model biological systems (such as Langmuir-Blodgett films, which mimic membranes) require access to still larger scales, but it is not obvious that an XSW will remain coherent over such length scales. Here we report studies of a lipid multilayer system using the XSW method, in which we have been able to locate the metal atoms in a zinc arachidate bilayer with ångström resolution at a distance of almost 1,000 A above the surface of a gold mirror. Our results indicate that the XSW technique should be useful for structural studies of supramolecular aggregates, receptor-ligand interactions and multi-membrane stacks, in which length scales of this order are encountered.