8 research outputs found
Co-Operative RF Ranging and Time Transfer Definitions for Mega Constellations and Space Traffic Management
Satellite conjunctions in space are a major problem for operators and governments due to the lack of coherent space situational awareness solutions. The tracking accuracy for two-line elements (TLEs) averages in kilometres with similar error boundaries making it limited for critical satellite collision prediction. The common practice using GPS provides high accuracy from centimetres to metres. However, satellite state data (position and velocity) are often never shared and orbit determination methods provide limited solutions at quantifying near-miss events. In the advent of mega-constellations, there is an urgent need for in-situ measurements to develop real satellite traffic management solutions and associated satellite traffic data standardisation to complement and refine the existing techniques. This research presents ToF range estimation techniques adapted for the increasing low Earth orbit satellite traffic that requires co-operative monitoring. Two techniques are investigated namely, two-way time transfer (TWTT) and two-way ranging using direct sequence spread spectrum (TWR-DSSS). Although both techniques reached centimetre-level accuracies (7 to 15 cm) in perfect communications conditions, this accuracy drops quickly when considering the real-world limitations. TWTT technique is affected by processing delay and relative clock drifts. Consequently, the ranging errors standard deviation for TWTT is 210 and 2075 m respectively for the delays 1 and 10 ÎĽs. It is also found that the relative clock drifts used for both satellites cause bias ranging errors as the best achieved accuracy is 170 m even when the delays are nullified. On the other hand, TWR-DSSS shows a robust performance against low signal-to-noise (SNR) levels. For instance, relative range is resolved with sub-kilometre accuracy for -20 dB SNR. Ultimately, inter-satellite cooperative RF ranging based on time of flight can offer real opportunities of a new measurement instrument complementing the existing satellite conjunction assessment tools
Élastographie du col utérin: prédiction du délai dgaccouchement lors dgun déclenchement par prostaglandines
International audienceObjective. Induction of labor for medical indications has become a routine practice. To date, the Bishop score remains as the standard method to predict the duration of induced labor. Elastography is an objective method of assessing the relative consistency of tissues. Therefore, we sought to assess strain elastography of cervix to predict delay from induction to delivery in pregnant women with a low Bishop score.Patients and methods. Ultrasound elastography was immediately performed before induction of labor for medical indications among patients with a singleton pregnancy at > 36 weeks of gestation and a Bishop score < 6. Patients received 50 mg of misoprostol intravaginally, repeated 6 hours later if regular painful uterine contractions had not started. A second ultrasound elastography was also performed 6 hours after starting the induction before the second dose of misoprostol if regular painful uterine contractions had not started. At each examination, a color map from blue (hardest tissue) to red (softest tissue) was produced. The cervical elastography was considered as positive if at least one part of its anterior wall was red. We assessed the predictive value of elastography on vaginal delivery within 24 hours. Patients delivering by cesarean section were excluded from this study.Results. Elastography was initially performed in 48 patients. Twelve patients delivering by cesarean section after induction of labor were excluded, leading to 36 patients evaluated in this study. Among these 36 patients with elastography performed before induction of labor, 20 had a second elastography before the second dose of misoprostol. Sensibility, specificity, positive predictive value (PPV) and negative predictive value (NPV) of elastography performed before induction of labor on vaginal delivery within 24 hours were 40%, 27.3%, 55.6%, and 16.7%, respectively. Sensibility, specificity, PPV and NPV of elastography performed before the second dose of misoprostol were 64.3%, 16.7%, 64.3% and 16.7%, respectively. Among the 8 patients with red color occurring on the second cervical color map, sensibility, specificity, PPV and NPV were 83.3%, 0%, 62.5%, and 0%.Discussion and conclusion. Qualitative cervical elastography is a poor predictor for delay from induction to delivery in pregnant women with a low Bishop score
An international expert consensus statement focusing on pre and post hair transplantation care
Aim To achieve international expert consensus and give recommendations on best practices in hair transplantation surgery, focusing on pre- and post-transplantation care. Methods A modified Delphi method was used to reach consensus. An international scientific committee developed an 81-statement questionnaire. A panel of 38 experts in hair transplantation from 17 countries across 4 continents assessed the questionnaire. Results Two consensus rounds were carried out, with 59 out of 81 statements (73%) reaching consensus. Expert recommendations emphasize the correct selection of candidates for hair transplantation and the need for patients to have received adequate medical treatment for alopecia before transplant. Comorbidities should be assessed and considered while planning surgery, and an individualized plan for perioperative care should be drawn up before transplant. Certain medications associated with increased risk of bleeding should be withdrawn before surgery. Specific recommendations for post-transplantation care are given. After transplantation, patients should gradually resume their normal haircare regimen. Close follow-up should be carried out during the first year after transplant. Conclusions This study presents numerous consensus-based recommendations on general aspects of hair transplantation, including candidate selection, medical therapy prior to transplantation, anesthesia, and resuming haircare after transplantation
Prenatal BACs-on-Beads (TM): the prospective experience of five prenatal diagnosis laboratories
Objective We previously reported on the validation of Prenatal BACs-on-Beads (TM) on retrospectively selected and prospective prenatal samples. This bead-based multiplex assay detects chromosome 13, 18, 21 and X/Y aneuploidies and the nine most frequent microdeletion syndromes. We demonstrated that Prenatal BACs-on-Beads (TM) is a new-generation, prenatal screening tool. Here, we describe the experience of five European prenatal diagnosis laboratories concerning the ongoing use of Prenatal BACs-on-Beads (TM). Methods Some 1653 samples were analyzed. All results were confirmed by conventional karyotyping or another appropriate technique. All indications for invasive prenatal diagnosis were included. Amniotic fluid and chorionic villus samples were analyzed in equivalent proportions. Results The failure rate was 3.3% and the overall abnormality detection rate was similar to 1/10. Eighty-five percent of the detected abnormalities were common aneuploidies. Eleven microdeletions and duplications were identified, thus giving an overall yield for microdeletion and microduplication detection of 1/145. Compared with QF-PCR, Prenatal BACs-on-Beads (TM) provides an additional detection rate of similar to 1/250 for low-risk pregnancies. The false positive and negative rates were both <1%. Conclusion When associated with conventional karyotyping, the Prenatal BACs-on-Beads (TM) assay combines a short turnaround time (typical of rapid aneuploidy detection tests) with valuable detection of the most frequent microdeletion syndromes that cannot be detected in cytogenetic analyses. (C) 2012 John Wiley & Sons, Ltd