Is there an optimal strategy for real-time continuous glucose monitoring in pediatrics? A 12-month French multi-center, prospective, controlled randomized trial (Start-In!)

AIM: To compare the efficacy of three strategies for real-time continuous glucose monitoring (RT-CGM) over 12 months in children and adolescents with type 1 diabetes. METHODS: A French multicenter trial (NCT00949221) with a randomized, controlled, prospective, open, and parallel-group design was conducted. After 3 months of RT-CGM, patients were allocated to one of three groups: return to self-monitoring of blood glucose, continuous CGM (80% of the time), or discontinuous CGM (40% of the time). The primary outcome was hemoglobin A1c (HbA1c) levels from 3 to 12 months. The secondary outcomes were acute metabolic events, hypoglycemia, satisfaction with CGM and cost. RESULTS: We included 151 subjects, aged 2 to 17 years, with a mean HbA1c level of 8.5% (SD0.7; 69 mmol/mol). The longitudinal change in HbA1c levels was similar in all three groups, at 3, 6, 9 and 12 months. The medical secondary endpoints did not differ between groups. The rate of severe hypoglycemia was significantly lower than that for the pretreatment year for the entire study population. Subjects reported consistent use and good tolerance of the device, regardless of age or insulin treatment. The use of full-time RT-CGM for 3 months costs the national medical insurance system €2629 per patient. CONCLUSION: None of the three long-term RT-CGM strategies evaluated in pediatric type 1 diabetes was superior to the others in terms of HbA1c levels. CGM-use for 3 months decreased rates of severe hypoglycemia. Our results confirm the feasibility of long-term RT-CGM-use and the need to improve educational support for patients and caregivers

The influence of the dynamic loading rate on tensile failure properties of metallic materials

The influence of the dynamic loading rate on the tensile failure properties of a series of tungsten alloys and an austenitic stainless steel were investigated by evaluating the flexural strength with unnotched and notched Charpy specimens. These data were generated with a newly developed Hopkinson pressure bar technique. The technique consists in impacting with a striker, at velocities ranging from 25 to 160 m/s, a round bar specimen placed against two incident Hopkinson pressure bars. Through the recording of the striker velocity before and after impact, failure energy is deduced. At impact velocities greater than 30 m/s, the results reveal a surprising increase of the Charpy energy with the increase of the impact velocity for both types of metallic materials. The results have been interpreted through numerical simulations of the Charpy test, the dependence of the material flow stress with the strain rate, and observations of the failure mechanisms. It was found that at impact velocities greater than 30 m/s, tangential strain rates exceed 3000s−1 at the failure initiation site of the Charpy specimen. These strain rates are within the strain rate regime where strengthening occurred due to the viscous behaviour of the dislocations. Data generated with moderate stress concentration using notched round bar Charpy specimens indicate that the strengthening occurring at high strain rates continues to pilot the tensile failure processes

Effect of loading rate on the plane stress fracture toughness properties of an aluminum alloy

L'effet de la vitesse de chargement sur les propriétés de ténacité en contrainte plane de plaques de 3.2 mm d'épaisseur en alliage d'aluminium 2219-T87 a été examiné à l'aide d'échantillons de traction à fissure centrale. Des courbes J de résistance à la rupture ont été obtenues à des vitesses de déplacements de 10-6 et 5.7 m s-1. L'essai dynamique de rupture fut conduit avec des plaques de pression couplées (coupled pressure plates). Les résultats montrent que les ténacités d'initiation et de propagation augmentent avec l'accroissement de la vitesse de chargement. Il est montré que l'augmentation de la ténacité est liée aux propriétés de la contrainte en fonction de la vitesse de déformation et au comportement ductile intrinsèque de l'alliage d'aluminium.The effect of loading rate on the plane stress fracture toughness properties of a 3.2-mm thick 2219-T87 aluminum alloy plate was investigated with center-cracked panels. Plane-stress J-resistance curves were generated at a constant displacement rate of 10-6 and 5.7 m s-1. Dynamic fracture testing was performed with a coupled pressure plates technique. Fracture initiation and propagation toughnesses were found to increase with an increased loading rate. The toughness increase was found to be related to the rate sensitivity characteristics and intrinsic ductile behavior of the aluminum alloy

A hydrodynamic hat specimen to investigate pressure and strain rate dependence on adiabatic shear band formation

An investigation was conducted to examine adiabatic shear band formation under a pressure of 1.5 GPa with a modified version of the hat specimen. Using tungsten alloy data generated with a symmetric Taylor test, the influence of pressure on the critical strain associated with adiabatic shear banding formation was found to increase with the increase of pressure. In another hand, steel results reveal an increase of the shear band temperature with the increase of the loading duration

The influence of the dynamic loading rate on tensile failure properties of metallic materials

The influence of the dynamic loading rate on the tensile failure properties of a series of tungsten alloys and an austenitic stainless steel were investigated by evaluating the flexural strength with unnotched and notched Charpy specimens. These data were generated with a newly developed Hopkinson pressure bar technique. The technique consists in impacting with a striker, at velocities ranging from 25 to 160 m/s, a round bar specimen placed against two incident Hopkinson pressure bars. Through the recording of the striker velocity before and after impact, failure energy is deduced. At impact velocities greater than 30 m/s, the results reveal a surprising increase of the Charpy energy with the increase of the impact velocity for both types of metallic materials. The results have been interpreted through numerical simulations of the Charpy test, the dependence of the material flow stress with the strain rate, and observations of the failure mechanisms. It was found that at impact velocities greater than 30 m/s, tangential strain rates exceed 3000s−1 at the failure initiation site of the Charpy specimen. These strain rates are within the strain rate regime where strengthening occurred due to the viscous behaviour of the dislocations. Data generated with moderate stress concentration using notched round bar Charpy specimens indicate that the strengthening occurring at high strain rates continues to pilot the tensile failure processes

Symmetric Taylor testing procedures for material strength ranging from 400 to 2000 MPa

Symmetric Taylor testing procedures to evaluate dynamic mechanical properties under uniaxial compression of a variety of materials including aluminum alloys, tungsten alloys and steels are described. For material strength greater than 800 MPa, symmetric Taylor testing involved Teflon sabots deforming along with the Taylor specimens. For low strength materials, 400-800 MPa, the test is conducted with Teflon ring supports that can be easily crushed. The testing procedures have been validated though numerical simulation of tests conducted with a tungsten alloy and an aluminium alloy

On the use of the compression split Hopkinson pressure bar to high strain rate

La réponse en compression d'un cuivre, d'un acier et d'alliages de tungstènes a été obtenue à l'aide de barres d'Hopkinson (split Hopkinson pressure bar) pour des vitesses de déformation variant de 3 x 103 à 7 x 103 s-1. L'hypothèse de déformation à vitesse constante a été examinée à l'aide de jauges de contrainte placées sur l'échantillon. Au début de la déformation plastique, des vitesses de déformation près de la face avant de l'échantillon supérieures à la vitesse de déformation conventionnelle ont été observées. Cette discontinuité fut confiée à l'aide de la simulation numérique utilisant un hydrocode d'un essai conduit à 7160 s-l. Les résultats numériques indiquent également une discontinuité de l'état de contrainte impliquant que la réponse du matériau pour des déformations allant jusqu'à 0.1 n'a pas lieu sous un état uniaxial de la contrainte.The compressive response of copper, steel, and tungsten alloys was generated with a split Hopkinson pressure bar technique at strain rates varying from 3 x 103 to 7 x 103 s-1. Constant strain rate assumptions were examined using specimen surface strain records. During the early stage of the plastic deformation specimen strain rates near the loading interface were found to exceed the conventionally measured strain rate. This discontinuity was confirmed from the simulation of a test conducted at a strain rate of 7160 s-1 using a hydrocode. Numerical results also indicate a stress state discontinuity implying that the material response is not a uniaxial state of stress for strain less than 0.1

Conditions for Shear Band Formation in Tungsten Alloys

Local loading conditions associated with shear banding formation in laboratory tungsten alloy specimens are examined. The specimens consist of compression specimens of large length to diameter ratio made of 91W-6Ni-3Co swaged tungsten alloys tested with the Hopkinson pressure bar and symmetric Taylor techniques. Experimental and numerical results provide insights on the effect of the hydrostatic pressure on shear band formation in tungsten alloys.Les conditions locales de chargement liées aux observations expérimentales de bandes de cisaillement des alliages de tungstène sont examinées. Ces bandes ont été observées avec des échantillons de compression dynamique à grand rapport de longueur sur diamètre composés d'alliages corroyés de tungstène 91W-6Ni-3Co. Les échantillons ont été testés à l'aide des techniques aux barres d'Hopkinson et de Taylor symétrique. Les résultats expérimentaux et numériques révèlent le rôle de la pression hydrostatique sur la formation de bandes de cisaillement dans les alliages de tungstène