An hybrid system approach to nonlinear optimal control problems

We consider a nonlinear ordinary differential equation and want to control its behavior so that it reaches a target by minimizing a cost function. Our approach is to use hybrid systems to solve this problem: the complex dynamic is replaced by piecewise affine approximations which allow an analytical resolution. The sequence of affine models then forms a sequence of states of a hybrid automaton. Given a sequence of states, we introduce an hybrid approximation of the nonlinear controllable domain and propose a new algorithm computing a controllable, piecewise convex approximation. The same way the nonlinear optimal control problem is replaced by an hybrid piecewise affine one. Stating a hybrid maximum principle suitable to our hybrid model, we deduce the global structure of the hybrid optimal control steering the system to the target

Security Architecture for Point-to-Point Splitting Protocols

International audienceThe security of industrial supervisory control and data acquisition systems (SCADA) has become a major concern since the Stuxnet worm in 2010. As these systems are connected to the physical world, this makes them possibly hazardous if a malicious attacker is able to take over their control. SCADA can live up to 40 years, are particularly hard to patch, and quite often have no security feature at all. Thus, rather than securing them, network segregation is often used to prevent attackers from entering the industrial system. In this paper, we propose a generic solution: embed a point-to-point splitting protocol within a physical device, thus able to physically isolate networks, perform deep packet inspection and also provide encryption if necessary. We obtain a kind of next generation firewall, encompassing at least both diode and firewall features, for which conformity to security policies can be ensured. Then we define a set of associated security properties for such devices and the requirements for such a device's security architecture and filtering rules. Finally, we propose a secure hardware implementation

Foot mechanics during the first six years of independent walking

Recognition of the changes during gait that occur normally as a part of growth is essential to prevent mislabeling those changes from adult gait as evidence of gait pathology. Currently, in the literature, the definition of a mature age for ankle joint dynamics is controversial (i.e., between 5 and 10 years). Moreover, the mature age of the metatarsophalangeal (MP) joint, which is essential for the functioning of the foot, has not been defined in the literature. Thus, the objective of the present study explored foot mechanics (ankle and MP joints) in young children to define a mature age of foot function. Forty-two healthy children between 1 and 6 years of age and eight adults were measured during gait. The ground reaction force (GRF), the MP and ankle joint angles, moments, powers, and 3D angles between the joint moment and the joint angular velocity vectors (3D angle aM.o) were processed and compared between four age groups (2, 3.5, 5 and adults). Based on statistical analysis, the MP joint biomechanical parameters were similar between children (older than 2 years) and adults, hinting at a quick maturation of this joint mechanics. The ankle joint parameters and the GRFs (except for the frontal plane) showed an adult-like pattern in 5-year-old children. Some ankle joint parameters, such as the joint power and the 3D angle aM.o still evolved significantly until 3.5 years. Based on these results, it would appear that foot maturation during gait is fully achieved at 5 years

Early Metabolic Alteration Predicts Outcome With Middle Cerebral Artery Occlusion Treated by Mechanical Thrombectomy

Background Predicting clinical outcome based on either the postprocedural recanalization score (modified treatment in cerebral infarction) or the initial National Institute of Health Stroke Scale (NIHSS) clinical score performed immediately after the acute phase remains controversial. The gold standard to predict clinical outcome is the NIHSS score with diffusion weighted imaging. However, magnetic resonance spectroscopy could provide useful metabolic informations. Our study aimed to determine early metabolic factors predictive of long‐term clinical outcome after acute ischemic stroke in patients with middle cerebral artery occlusion successfully treated by mechanical thrombectomy. Methods Patients with proximal middle cerebral artery occlusion, an NIHSS score greater than 6 and successfully treated by mechanical thrombectomy with or without intravenous therapy were included. All patients underwent within 24 hours after mechanical thrombectomy, brain magnetic resonance imaging examination with multivoxel proton‐phosphorus‐magnetic resonance spectroscopy. Functional disability at 90 days with reference to pre‐stroke activities was categorized using the modified Rankin scale. Metabolite ratios were measured and confronted to modified Rankin scale. Results A total of 49 patients were included with initial mean NIHSS of 15.19±5.48. Time delay between: onset‐thrombectomy was 6.77 hours±3.22, thrombectomy‐magnetic resonance imaging was 29.83 hours±15.01. Results in the lesion compared with the contralateral area show an increase of Lac/Cr (0.88 versus 0.21; P<10−10) and a decrease of PhosphoMonoEster/PhosphoDiEster (0.80 versus 0.83; P=0.00165). Lac/Cr in the lesion was significantly higher in the poor outcome group than in the favorable outcome group (1.03±0.41 and 0.75±0.42; P=0.01). Our model built with NIHSS+proton‐magnetic resonance spectroscopy compared with the gold standard model (NIHSS+diffusion weighted imaging) is better (85.29% versus 77.55%) to predict clinical outcome. Conclusion Our study shows that early Lac/Cr alteration visible 24 hours after stroke is a strong predictor of 90 days clinical outcome for middle cerebral artery occlusion patients successfully treated by mechanical thrombectomy. Our NIHSS+proton‐magnetic resonance spectroscopy model is the first to predict patients’ long‐term functional outcome with an accuracy of 85.3%, superior to existing models including diffusion weighted imaging

Security Architecture for Point-to-Point Splitting Protocols

International audienceThe security of industrial supervisory control and data acquisition systems (SCADA) has become a major concern since the Stuxnet worm in 2010. As these systems are connected to the physical world, this makes them possibly hazardous if a malicious attacker is able to take over their control. SCADA can live up to 40 years, are particularly hard to patch, and quite often have no security feature at all. Thus, rather than securing them, network segregation is often used to prevent attackers from entering the industrial system. In this paper, we propose a generic solution: embed a point-to-point splitting protocol within a physical device, thus able to physically isolate networks, perform deep packet inspection and also provide encryption if necessary. We obtain a kind of next generation firewall, encompassing at least both diode and firewall features, for which conformity to security policies can be ensured. Then we define a set of associated security properties for such devices and the requirements for such a device's security architecture and filtering rules. Finally, we propose a secure hardware implementation

Mottling score is a strong predictor of 14-day mortality in septic patients whatever vasopressor doses and other tissue perfusion parameters

International audienceBACKGROUND: Mottling score, a tissue perfusion parameter, is correlated with outcome in septic shock patients. However, its predictive value on mortality according to prognostic covariates such as vasopressor dose and other tissue perfusion parameters remains unknown.METHODS: Mottling score and tissue perfusion parameters were recorded at ICU admission (H0), H-6, H 12, and H-24 and used to assess the predictive value of mottling score on 14-day mortality in a development cohort. Results were then validated in an independent cohort of septic shock patients in Brazil.RESULTS: Overall, 259 patients with sepsis or septic shock were included, 14-day mortality was 37%. Factors associated with death were mottling score (OR 2.26 [95% CI, 1.72-2.97]), arterial lactate level (OR 1.29 [1.11-1.5]), and urine output  0.8 μg/kg/min). There was no difference in the effect of mottling score on mortality according to mean arterial pressure, heart rate, cardiac index, and urine output, but we found a significant interaction between arterial lactate level and mottling score (p = 0.04). The predictive value of the mottling score remains significant when using the recent SEPSIS-3 definition of septic shock. Finally, a decrease of mottling score during resuscitation was significantly associated with better outcome after adjustment on SOFA score (p = 0.001).CONCLUSIONS: Our results support the high prognostic value of mottling score for 14-day mortality in septic patients, whatever vasopressor dosage and other perfusion parameters. Mottling score variations during resuscitation are also predictive of mortality

French ICU's health care workers have a poor knowledge of the cost of the devices they use for patient care: A prospective multicentric study

International audiencePurpose: ICU patient's care may require the use of onerous devices, which contributes to make this department one of the most expensive in the hospital. It seemed us relevant to assess healthcare workers' (HCWs) knowledge of the cost of the devices daily used in ICU.Materials and methods: An anonymous questionnaire was administered on a voluntary basis to HCWs of 3 ICUs.Measurements and main results: Cost estimations were expressed as percentage of the real cost; an estimation was considered correct if it was ±50% of the true price. 107 HCWs (66 physicians and 41 nurses and nurse aids) answered the survey. Only 29% of estimations were within 50% of the real cost. The prices of the cheapest devices were overestimated, while the costs of the most expensive ones were underestimated. In multivariate analysis, cost less than50 euros [OR = 3.2; CI 95%(1.6-6.3)], professional experience <10 years [OR = 1.5; CI 95%(1.1-2.1)], being a medical student [OR = 2.0; CI 95%(1.3-3.0)], and working in a university affiliated hospital [OR = 0.6; CI 95%(0.4-0.9)] were associated with an incorrect estimation.Conclusions: ICU's HCWs have a poor knowledge of the price of devices they regularly use for the care of their patients

Sonometric assessment of cough predicts extubation failure: SonoWean—a proof-of-concept study

Abstract Background Extubation failure is associated with increased mortality. Cough ineffectiveness may be associated with extubation failure, but its quantification for patients undergoing weaning from invasive mechanical ventilation (IMV) remains challenging. Methods Patients under IMV for more than 24 h completing a successful spontaneous T-tube breathing trial (SBT) were included. At the end of the SBT, we performed quantitative sonometric assessment of three successive coughing efforts using a sonometer. The mean of the 3-cough volume in decibels was named Sonoscore. Results During a 1-year period, 106 patients were included. Median age was 65 [51–75] years, mainly men (60%). Main reasons for IMV were acute respiratory failure (43%), coma (25%) and shock (17%). Median duration of IMV at enrollment was 4 [3–7] days. Extubation failure occurred in 15 (14%) patients. Baseline characteristics were similar between success and failure extubation groups, except percentage of simple weaning which was lower and MV duration which was longer in extubation failure patients. Sonoscore was significantly lower in patients who failed extubation (58 [52–64] vs. 75 [70–78] dB, P < 0.001). After adjustment on MV duration and comorbidities, Sonoscore remained associated with extubation failure. Sonoscore was predictive of extubation failure with an area under the ROC curve of 0.91 (IC95% [0.83–0.99], P < 0.001). A threshold of Sonoscore < 67.1 dB predicted extubation failure with a sensitivity of 0.93 IC95% [0.70–0.99] and a specificity of 0.82 IC95% [0.73–0.90]. Conclusion Sonometric assessment of cough strength might be helpful to identify patients at risk of extubation failure in patients undergoing IMV