High-pressure cell for simultaneous dielectric and neutron spectroscopy.

In this article, we report on the design, manufacture, and testing of a high-pressure cell for simultaneous dielectric and neutron spectroscopy. This cell is a unique tool for studying dynamics on different time scales, from kilo- to picoseconds, covering universal features such as the α relaxation and fast vibrations at the same time. The cell, constructed in cylindrical geometry, is made of a high-strength aluminum alloy and operates up to 500 MPa in a temperature range between roughly 2 and 320 K. In order to measure the scattered neutron intensity and the sample capacitance simultaneously, a cylindrical capacitor is positioned within the bore of the high-pressure container. The capacitor consists of two concentric electrodes separated by insulating spacers. The performance of this setup has been successfully verified by collecting simultaneous dielectric and neutron spectroscopy data on dipropylene glycol, using both backscattering and time-of-flight instruments. We have carried out the experiments at different combinations of temperature and pressure in both the supercooled liquid and glassy state.

A cryostat and temperature control system optimized for measuring relaxations of glass-forming liquids.

An experimental setup, including a cryostat and a temperature control system, has been constructed to meet the demands of measuring linear and nonlinear macroscopic relaxation properties of glass-forming liquids in the extremely viscous state approaching the glass transition. In order to be able to measure such frequency-dependent response functions accurately (including dielectric permittivity, specific heat, thermal expansivity, and shear and bulk moduli), as well as nonlinear relaxations following a temperature jump, one must have the ability to hold temperatures of liquids steady over the span of several days or even several weeks. To maximize temperature stability, special care is taken to thermally isolate the sample chamber of the cryostat. The main temperature control system is capable of maintaining temperatures within a few millikelvins. If liquid is deposited into a special transducer assembly that includes a subcryostat unit, the temperature of liquids can be maintained even more precisely, within a few tenths of a millikelvin. This subcryostat unit is more responsive to temperature changes because (i) it is equipped with a Peltier element that provides secondary heating and cooling, (ii) the transducer contains a layer of liquid that is only 50 micfom thick, and (iii) feedback proportional-integral-derivative temperature control is implemented by a fully analog circuit. The subcryostat permits us to change and stabilize temperatures quickly; it takes only 10 s to stabilize the temperature within tenths of a millikelvin after a jump of 1 K, for example, a capability that is highly advantageous for accurately observing relaxation processes following a temperature step.

An impedance-measurement setup optimized for measuring relaxations of glass-forming liquids.

An electronics system has been assembled to measure frequency-dependent response functions of glass-forming liquids in the extremely viscous state approaching the glass transition. We determine response functions such as dielectric permittivity and shear and bulk moduli by measuring electrical impedances of liquid-filled transducers, and this technique requires frequency generators capable of producing signals that are reproducible over the span of several days or even several weeks. To this end, we have constructed a frequency generator that produces low-frequency (1 mHz-100 Hz) sinusoidal signals with voltages that are reproducible within 10 ppm. Two factors that partly account for this precision are that signals originate from voltages stored in a look-up table and that only coil-less filters are used in this unit, which significantly reduces fluctuations of output caused by changes of temperatures of circuits. This generator also includes a special triggering facility that makes it possible to measure up to 512 voltages per cycle that are spaced apart at uniform phase intervals. Fourier transformations of such data yield precise determinations of complex amplitudes of voltages and currents applied to a transducer, which ultimately allows us to determine electrical impedances of transducers with a reproducibility error that is only a few parts per hundred thousand. This equipment is used in tandem with a commercial LCR meter and/or impedance analyzer that give(s) impedance measurements at higher frequencies, up to 1 MHz. The experimental setup allows measurements of the transducer impedance over nine decades of frequency within a single run.

Primary and repeated stapled hemorrhoidopexy for prolapsing hemorrhoids: follow-up to five years.

PURPOSE: Treating hemorrhoids by stapled hemorrhoidopexy has become increasingly common, because the procedure results in less pain and allows the patient to return to work earlier than with open hemorrhoidectomy. However, the durability of stapled hemorrhoidopexy has not been evaluated. This study was designed to assess initial results, analyze complications and failures, and document both the need for repeated procedures and the outcomes of follow-up to five years. METHODS: From 1998 to 2004, 258 patients underwent modified stapled hemorrhoidopexy. The appearance of the anus was scored preoperatively, immediately after the procedure, at three months, and at one to five years postoperatively. The anatomy score ranged from 1 (normal anus) to 7 (worst prolapse). We also evaluated operation time, analgesia, staple line position, postoperative pain score, technical failures, postoperative complications, need for repeated procedures, and patient satisfaction. Statistical analyses were used to identify correlations and differences, and the variables were analyzed in relation to the final outcome. RESULTS: The patients were observed for a median of 34 (range, 18-78) months. The median postoperative pain score was 4 (Visual Analog Scale 1-10) on the day of stapled hemorrhoidopexy; additional external procedures resulted in significantly higher pain (P<0.05). Stapled hemorrhoidopexy was repeated in 31 patients (12 percent), and 38 patients (14.7 percent) had subsequent excisions. Technical failures occurred in 18 of 258 patients (7 percent). The median anatomy score decreased from 6 (range, 3-7) preoperatively to 1 (range, 1-6) at last follow-up, irrespective of one or a repeated stapled hemorrhoidopexy, surgical excision, or technical failure. The risk of reintervention was greatest during the first year after a stapled hemorrhoidopexy. Overall, patient satisfaction was high and correlated significantly with the anatomy score (r=0.46, P<0.05). CONCLUSIONS: The pain after stapled hemorrhoidopexy was low, recovery was rapid, complications were few, and patient satisfaction was high. A recurrent (or persistent) prolapse was alleviated by a repeated stapled hemorrhoidopexy for cure. However, there was a high risk of reintervention after a stapled hemorrhoidopexy, and this should be further evaluated.

Evaluating iodine deficiency in pregnant women and young infants-complex physiology with a risk of misinterpretation.

OBJECTIVE: To review methods for evaluating iodine deficiency in pregnant women and young infants and to discuss factors to be considered in the interpretation of their results. DESIGN: Review of the literature regarding the various methods available for assessing iodine status. SETTING: Population surveys and research studies. SUBJECTS: Pregnant women and young infants. RESULTS: Several factors to consider when assessing iodine status in pregnant women and young infants include: 1) the urinary iodine (UI) concentration (microg l-1) is not interchangeable with 24 h UI excretion (microg per 24 h); 2) the concentration of iodine in a spot or casual urine sample cannot be used to diagnose iodine deficiency in an individual; 3) a moderate fall in the concentration of serum free T4 during pregnancy is not a sign of maternal iodine deficiency; 4) an increase in the concentration of serum thyroglobulin (Tg) during pregnancy is not a sign of maternal iodine deficiency; 5) a higher concentration of TSH and Tg in cord blood than in maternal blood is not a sign of iodine deficiency in the mother or neonate; and 6) thyroid function in a full-term foetus, a neonate or a small child is not more sensitive to a mild iodine deficiency than in the mother. CONCLUSIONS: If the iodine status of pregnant women and small children is not to be misjudged, the above six factors need to be taken into account.