Angle-Only Cooperative Orbit Determination Considering Attitude Uncertainty.

In this paper, a novel concept for cooperative orbit determination (OD) using inter-spacecraft angle-only measurements is proposed. Different from the conventional cooperative OD that only estimates orbit states, the attitude of the observer spacecraft is considered by incorporating the attitude into the estimated vector. The observability of a two-spacecraft system is analyzed based on the observability matrix. Observability analysis reveals that inter-spacecraft angle-only measurements are inadequate to estimate both the attitude and the orbit states in two-body dynamics. The observability of the two-spacecraft system can be improved by considering high-order gravitational perturbation or executing an attitude maneuver on the observer spacecraft. This is the first time that we present the observability analysis and orbit estimation results for a two-spacecraft system considering attitude uncertainty for the observer. Finally, simulation results demonstrate the effectiveness of the proposed method. The results in this paper can be potentially useful for autonomous managements of a spacecraft constellation and formation.

Root morphology and development of labial inversely impacted maxillary central incisors in the mixed dentition: a retrospective cone-beam computed tomography study.

INTRODUCTION: The aim of this study was to analyze 3-dimensional data of root morphology and development in labial inversely impacted maxillary central incisors. METHODS: Cone-beam computed tomography images from 41 patients with impacted incisors were divided into early and late dental age groups according to their dental age. Sagittal slices in which the labiolingual width of the tooth was the widest in the axial view were evaluated. The inverse angle, the dilaceration angle, and the length of both impacted and homonym teeth were evaluated with SimPlant Pro software (version 13.0; Materialise Dental NV, Leuven, Belgium). RESULTS: The Student t test indicated that the lengths of the impacted teeth were significantly shorter than those of the homonym teeth (P <0.05), and the root lengths of the early dental age group were significantly shorter than those of the late dental age group. The results from chi-square tests indicated that the incidence of dilacerations was significantly higher in the late dental age group when compared with the early dental age group. Multiple regression analyses indicated that the independent variables for root length of the impacted teeth were dental age (ß = 0.958; P <0.001) and length of the nondilacerated part of the root (ß = 0.435; P <0.001). CONCLUSIONS: Dilaceration was more common in the late dental age group. The roots of labial inversely impacted maxillary central incisors continue developing, but their potential is limited.

[The effect of modified Nance arch on treating maxillary impacted canine transposed with first premolar].

PURPOSE: To explore the effect of modified Nance arch on treating maxillary canine-first premolar transposition cases, in which the anchorage and force direction were discussed. METHODS: Modified Nance arch was applied to 5 cases with maxillary impacted canine-first premolar transposition. First, a lingual knot button was bonded on the surface of the canine crown. Modified Nance arch was decorated with a hook that moved horizontally and buccally. Then the location of the hook was gradually adjusted in order to move the canine cross the root of the first premolar and move the canine to the right position. At last the canine was moved downward by straight wire appliance. RESULTS: Five maxillary transposed canines were fully erupted in their right position, with normal pulp activity and gingival morphology. No obvious root resorption was detected. The mean treatment time was 30 months. CONCLUSIONS: Modified Nance arch has advantages in treating canine-first premolar transposition.