Sensitivity-Tunable Oscillator-Accelerometer Based on Optical Fiber Bragg Grating

We demonstrate a fiber Bragg grating (FBG)-based oscillator-accelerometer in which the acceleration sensitivity can be tuned by controlling the location of the mass oscillator. We theoretically and experimentally investigated the performance of the proposed accelerometer. Theoretical analysis showed that both the mass and location of the oscillator affect the sensitivity and resonant frequency of the accelerometer. To simplify the analysis, a nondimensional parameter, P, was introduced to tune the sensitivity of the FBG-based oscillator-accelerometer, which is related to the location of the mass oscillator. Numerical analysis showed that the accelerometer sensitivity is linearly proportional to the P parameter. In the experiment, six FBG-based oscillator-accelerometers with different P parameters (0.125, 0.25, 0.375, 0.5, 0.625, 0.75) were fabricated and tested. The experimental results agree very well with the numerical analysis, in which the sensitivity of the proposed accelerometer linearly increased with the increase in parameter P (7.6 pm/g, 15.8 pm/g, 19.3 pm/g, 25.4 pm/g, 30.6 pm/g, 35.7 pm/g). The resonance frequency is quadratically proportional to parameter P, and the resonance frequency reaches the minimum of 440 Hz when P is equal to 0.5. The proposed oscillator-accelerometer showed very good orthogonal vibration isolation.

The SUrvey for Pulsars and Extragalactic Radio Bursts – IV. Discovery and polarimetry of a 12.1-s radio pulsar

ABSTRACT We report the discovery of PSR J2251−3711, a radio pulsar with a spin period of 12.1 s, the second longest currently known. Its timing parameters imply a characteristic age of 15 Myr, a surface magnetic field of 1.3 × 1013 G, and a spin-down luminosity of 2.9 × 1029 erg s−1. Its dispersion measure of 12.12(1) pc cm−3 leads to distance estimates of 0.5 and 1.3 kpc according to the NE2001 and YMW16 Galactic free electron density models, respectively. Some of its single pulses show an uninterrupted 180-deg sweep of the phase-resolved polarization position angle, with an S-shape reminiscent of the rotating vector model prediction. However, the fact that this sweep occurs at different phases from one pulse to another is remarkable and without straightforward explanation. Although PSR J2251−3711 lies in the region of the $P-\dot{P}$ parameter space occupied by the X-ray isolated neutron stars (XINS), there is no evidence for an X-ray counterpart in our Swift XRT observation; this places a 99 per cent-confidence upper bound on its unabsorbed bolometric thermal luminosity of $1.1 \times 10^{31}~(d / 1~\mathrm{kpc})^2~\mathrm{erg\, s}^{-1}$ for an assumed temperature of 85 eV, where d is the distance to the pulsar. Further observations are needed to determine whether it is a rotation-powered pulsar with a true age of at least several Myr, or a much younger object such as an XINS or a recently cooled magnetar. Extreme specimens like PSR J2251−3711 help bridge populations in the so-called neutron star zoo in an attempt to understand their origins and evolution.

Parameter Optimization

Parameter optimization is treated as an introduction. Unconstrained and constrained cases are analysed. Necessary and sufficient conditions are derived and illustrated. Parameter optimization utilizes the theory of ordinary maxima and minima. The problem is to determine the value of the m-vector u of independent parameters (decision variables) to minimize the cost function.

Parameter-free predictions of the viscoelastic response of glassy polymers from non-affine lattice dynamics

Parameter-free predictions of viscoelastic moduli at finite temperature are obtained by accounting for internal stresses and instantaneous normal modes within athermal non-affine theory.

Zinc glutarate-mediated copolymerization of CO2 and PO – parameter studies using design of experiments

Parameter studies of the PO/CO2-copolymerization revealed the importance of the surface coverage of a nanoscopic ZnGA catalyst.

Measurement System of Pyroelectric Coefficient for Pyroelectric Material Using Dynamic Current Method

A dynamic current method used to measure pyroelectric coefficient (p) for pyroelectric material is described in detail in this paper. The hardware part of the system includes pre-converting circuit, post amplifier circuit, wave-filter circuit, analog-to-digital conversion circuit, temperature test circuit and LCD display panel circuit. The maximum magnification time of amplifier circuit of system is 11300 and the band-stop frequency center for wave-filter circuit is 50 Hz and it's second harmonics 100 Hz. Finally, the measurement system is used to test p parameter of LiTaO3crystal slice. The lowest p parameter of LiTaO3crystal with a value of 6.08×10-9C/cm2 oC is achieved at 32.5°C.

The Effect of Pressure on Martensitic Phase Transformations

Stability of the crystal structure is determined by the competition between attractive and repulsive interatomic forces. Using many-body exponential potentials it can be shown that the bcc structure corresponding to austenitic phases is more stable for low values of the q-parameter characterising the attractive forces for a fixed value of the p-parameter describing the repulsive forces. The structural stability can be changed with the acting pressure that may alter the martensitic transformations from the bcc-austenite to a close-packed structure. The effect of pressure is examined in a generic model employing many-body potentials and the results are compared with ab initio calculations for zirconium representing a monoatomic material with displacive phase transformation.