Sitting Position as an Alternative for Sagittal Balance Assessment: A Cross-Sectional Study

Background: The sagittal vertical axis (SVA) is used for spinal sagittal balance evaluation. Patients with sagittal imbalance are assessed by whole spine standing lateral radiography, with some patients demonstrating standing difficulty during the examination. We propose new positioning methods to facilitate SVA assessment in patients with sagittal imbalance who cannot tolerate the standing position.Methods: Thirty healthy subjects had their SVA evaluated by whole spine lateral radiography in four positions: standard position by standing with the hands on the clavicles with elbows touching the trunk (TC), standing with the hands holding on to a front stationary railing within arm’s reach (TS), sitting with the hands on the clavicles (IC), and sitting with the hands holding on to a stationary railing (IS). The SVA was evaluated for differences and correlations between the standard position (TC) and the new proposed positions.Results: The mean difference in the SVA between the TC and TS group was 1.55 mm, with a limit of agreement of -36.62 to 39.72 mm and Lin’s correlation of 0.63. The mean difference in the SVA between the TC and IC or IS positions indicated greater positive SVA difference with no correlation. The TS position had good regional spinal parameter correlation with the TC position, as well as pelvic parameter correlation. The IC and IS positions showed poor pelvic and other regional spinal parameter correlations. Conclusions: The TS position can be used as an alternative method in measuring the SVA in patients with standing difficulty during radiography. Though measurement using the sitting position can be conveniently performed, this position does not correlate well with the standard SVA measurement.

Technical support of plastic product machining quality

The investigation results of plastic cutting are shown. The results of single-factor and multi-factor experiments on plastic cutting by multi-toothed milling cutters are stated. There are shown empirical equations of the roughness parameter correlation of the surface Ra and the height of the barb h from cutting modes: feed, speed and tooth number in a milling cutter.

Three-parameter correlation for the surface tension of saturated liquids

In this paper, we study the multiple-parameter correlations for the surface tension of saturated liquids. The proposed three-parameter correlation requires only the critical temperature as inputs and is tested by using the NIST REFPROP data for 72 saturated liquids including refrigerants, alkanes and some other simple liquids such as argon, carbon dioxide, etc. It is found that this correlation well stands in the whole temperature range from the triple point to the critical point with high accuracy for 71 liquids with average absolute deviations (AADs) less than 5% and for 66 liquids with AADs less than 1%. These results are clearly better than the ones of other available correlations. This correlation can be directly used to estimate the value of the surface tension of the corresponding liquids at any temperature point from the triple point to the critical point. The accuracy of the predictions would clearly have economic benefits since it would allow improvement of process operating conditions, the development of new processes, the reduction of oversizing in the design of new equipment and even reduction of energy requirements.