Strain controlled biaxial stretch: An experimental characterization of natural rubber

In this paper we provide new experimental data showing the response of 40A natural rubber in uniaxial, pure shear and biaxial tension. Real-time biaxial strain control allows for independent and automatic variation of the velocity of extension and retraction of each actuator to maintain the pre-selected deformation rate within the gage area of the specimen. The remaining part of the paper focuses on the Valanis-Landel hypothesis that is used to verify and validate the consistency of the data. We use a three term Ogden model to derive stress-stretch relations to validate the experimental data. The material model parameters are determined using the primary loading path in uniaxial and equibiaxial tension. Excellent agreement is found when the model is used to predict the response in biaxial tension for different maximum in-plane stretches. The application of the Valanis-Landel hypothesis also results in excellent agreement with the theoretical prediction

First prototypes of two-tier avalanche pixel sensors for particle detection

In this paper, we present the implementation and preliminary evaluation of a new type of silicon sensor for charged particle detection operated in Geiger-mode. The proposed device, formed by two vertically-aligned pixel arrays, exploits the coincidence between two simultaneous avalanche events to discriminate between particle-triggered detections and dark counts. A proof-of-concept two-layer sensor with per-pixel coincidence circuits was designed and fabricated in a 150 nm CMOS process and vertically integrated through bump bonding. The sensor includes a 48×16 pixel array with 50 μm X 75 μm pixels. This work describes the sensor architecture and reports a selection of results from the characterization of the avalanche detectors in the two layers. Detectors with an active area of 43 X 45μm² have a median dark count rate of 3 kHz at 3.3 V excess bias and a breakdown voltage non-uniformity lower than 20 mV

Scanning of the e+e- to pi+pi- cross--section below 1 GeV by radiative events with untagged photon

We discuss an inclusive approach to the measurement of the e+e- --> pi+ pi- cross--section by the radiative return method without photon tagging. The essential part of this approach is the choice of rules for event selection which provide rejection of events with 3 (or more) pions and decrease the final--state radiation background. The radiative corrections to the initial--state radiation process are computed for DAPhNE conditions, using the quasi--real electron approximation for both, the cross--section and the underlying kinematics. The two cases of restricted and unrestricted pion phase space are considered. Some numerical calculations illustrate our analytical results.Comment: 25 pages, 4 figures, late