Impacts of vehicle automation on traffic flow stability

This dissertation is motivated by the possibility of a small number of autonomous vehicles (AVs) or partially autonomous vehicles that may soon be present on our roadways. This automation may take the form of fully autonomous vehicles without human intervention (Society of Automotive Engineers, SAE Level 5) or, as is already the case in many modern vehicles, may take the form of driver assist features such as adaptive cruise control (ACC), or other SAE Level 1 features. Regardless of the extent of automation, changing the vehicle dynamics of a small number of vehicles in the bulk traffic flow may have substantial implications on the underlying traffic flow and may influence the development of emergent phenomena such as phantom traffic jams, or traffic stability. This dissertation has four main contributions: (i) experimental evidence to validate that human driving behavior alone is sufficient for the development of phantom jams, (ii) theoretical work as well as experimental work to demonstrate that current commercially-available ACC systems may be string unstable under certain circumstances, (iii) theoretical and experimental results that demonstrate the ability of autonomous vehicles to stabilize traffic flow and prevent phantom jams from arising even at low autonomous vehicle penetration rates (∼5%), and (iv) experimental evidence for the emissions impacts of phantom traffic jams, and the potential for AVs to substantially reduce these emissions

Risk factors for L5 pedicle fractures after single-level posterior spinal fusion

BACKGROUND CONTEXT Pedicle fractures are a rare but potentially devastating complication of posterior instrumented spinal fusion (PSF). Preoperative awareness of the possible risk factors may help prevent these fractures by modifying the surgical plan. However, the risk factors have not yet been identified. PURPOSE To determine the preoperative parameters associated with postoperative L5 pedicle fracture after L4/5 PSF. STUDY DESIGN Case control study. PATIENT SAMPLE Patients undergoing L4/5 PSF at a single academic institution between 2014 and 2020. OUTCOME MEASURES Occurrence of postoperative L5 pedicle fracture. METHODS Of 253 patients (female:male, 145:108) undergoing L4/5 PSF from 2014 to 2020, patients with postoperative L5 pedicle fractures were identified retrospectively as "cases" (n = 8, all female, age: 70 ± 10.7 years). As a control group all remaining patients with a follow-up of more than 12 months were allocated (n = 184, 104 females, age: 64.27 ± 13.00 years). In all but 16 cases, anterior support with transforaminal or posterior interbody fusion was performed. Demographic and clinical data (body mass index (BMI)), surgical factors, and comorbidities) were compared. Radiological assessment of spinopelvic parameters was performed using pre- and postoperative standing lateral radiographs. RESULTS The overall incidence of L5 pedicle fractures after L4/5 spinal fusion was 3.16%, with a median time from index surgery to diagnosis of 25 days (range, 6-199 days) (75% within the first 32 days postoperatively). Patients with L5 pedicle fractures had higher pelvic incidence (PI) (71° ± 9° vs. 56° ± 11°; p=.001), sacral slope (SS) (45° ± 7° vs. 35° ± 8°; p=.002), L5 slope (30° ± 11° vs. 15° ± 10°, p=.001), L5 incidence (42° ± 14° vs. 26° ± 11°; p= .003), L1-S1 lumbar lordosis (LL) postop (57° ± 10° vs. 45° ± 11°; p=.006), and L4 -S1 LL postop (33° ± 7° vs. 28° ± 7°; p=.049) compared with the control group. Pelvic tilt and PI- LL mismatch were not significantly different. Female gender was a significant risk factor for L5 pedicle fractures (p=.015). BMI (kg/m$^{2}$) was statistically equal in patients with or without pedicle fractures (28.37 ± 5.96 vs. 28.53 ± 16.32; p=.857). There was no significant difference between the groups for approximative bone mineral density assessment (Hounsfield units; 113 ± 60 vs. 120 ± 43; p=.396) using the L3 trabecular region of interest (ROI) measurement. The correlation analysis demonstrated that most of the identified risk factors except for the postoperative L4-S1 lordosis show significant positive associations among each other. All eight patients in the fracture group underwent revision surgery, and the instrumented fusion was extended to the sacrum, with the addition of sacral-alar-iliac or iliac screws, in six cases. CONCLUSIONS L5 pedicle fractures occurred in 3% of the patients after single level L4/5 PSF. Risk factors are female gender, higher PI, SS, L5 slope, L5 incidence, and LL postop but not high BMI. These findings can be used for surgical planning and decision of fusion levels

The effect of natural organic matter on the adsorption of mercury to bacterial cells

We investigated the ability of non-metabolizing Bacillus subtilis, Shewanella oneidensis MR-1, and Geobacter sulfurreducens bacterial species to adsorb mercury in the absence and presence of Suwanee River fulvic acid (FA). Bulk adsorption and X-ray absorption spectroscopy (XAS) experiments were conducted at three pH conditions, and the results indicate that the presence of FA decreases the extent of Hg adsorption to biomass under all of the pH conditions studied. Hg XAS results show that the presence of FA does not alter the binding environment of Hg adsorbed onto the biomass regardless of pH or FA concentration, indicating that ternary bacteria–Hg–FA complexes do not form to an appreciable extent under the experimental conditions, and that Hg binding on the bacteria is dominated by sulfhydryl binding. We used the experimental results to calculate apparent partition coefficients, Kd, for Hg under each experimental condition. The calculations yield similar coefficients for Hg onto each of the bacterial species studies, suggesting there is no significant difference in Hg partitioning between the three bacterial species. The calculations also indicate similar coefficients for Hg–bacteria and Hg–FA complexes. S XAS measurements confirm the presence of sulfhydryl sites on both the FA and bacterial cells, and demonstrate the presence of a wide range of S moieties on the FA in contrast to the bacterial biomass, whose S sites are dominated by thiols. Our results suggest that although FA can compete with bacterial binding sites for aqueous Hg, because of the relatively similar partition coefficients for the types of sorbents, the competition is not dominated by either bacteria or FA unless the concentration of one type of site greatly exceeds that of the other

Material culture of the land of the bible in the Persian per. 538-332

Englandxix, 287 p.; 28 c

ON A CLUSTERING PROBLEM IN THE INDUSTRY

In this paper we consider problems from the industry that have characteristic of clustering. We show how to model these problems as clustering trees problems and use our solutions in order to solve the problems. The problems we consider are problems of manufacturing, robotics and all of them can be applied also for communication networks. For the application from manufacturing we want to construct a minimum clustering tree where each cluster induces a complete star in the solution tree. For this case we have a structure theorem and based on it a polynomial algorithm. We prove that our algorithm provides the same construction for the setting up of a system and for the efficient running of a system. The application from robotics is where we want to find a minimum clustering TSP-path. We prove that the general case is NP-complete and we have polynomial algorithms for some restricted cases. 1