Comparison of the methods for discriminating temperature and strain in spontaneous Brillouin-based distributed sensors

A recently proposed method of measuring the two Brillouin frequencies in a multicompositional fiber core for unambiguously resolving temperature and strain in a distributed sensor is compared with the previously established technique of measuring the intensity and frequency of the single Brillouin peak in a standard single-mode fiber.     

A 5 cm spatial resolution temperature compensated distributed strain sensor evaluated using a temperature controlled strain rig

Sensing rigs used for Brillouin scattering based distributed strain and temperature measurements so far have comprised separate sections of sensing fiber subjected to either temperature or strain influences. We demonstrate a scheme that allows for temperature corrected distributed strain measurements under environments involving simultaneous application of strain and temperature, with enhanced spatial resolution of 5 cm. Strain and temperature resolution of 63 με and 2 °C are reported. To the best of our knowledge, this is the highest spatial resolution temperature compensated distributed strain sensor result so far.     

s- and p-wave neutron spectroscopy: Part VII. Widths of Neutron Resonances

Neutron reduced widths Γ_n⁰ and Γ_n¹ are reported for about 200 resonances observed in neutron total cross sections of Ca^{40, 44}, Ti⁴⁸, Cr^{50, 52, 54}, Fe^{54, 56}, Ni^{58, 60}, Sr⁸⁸, Y⁸⁹, Sn¹²⁴, Te¹³⁰, Ba^{136, 138}, and Pb^{206, 207, 208}, in the energy region 1 to 200 ^kev. Average parameters $\text{Γ}{}_{\mathrm{n}}{}^0$, $\text{Γ}{}_{\mathrm{n}}{}^0\text{D}$, and $\text{Γ}{}_{\mathrm{n}}{}^{\mathrm{(1)}}\text{D}$ have been derived and the Wigner distribution for local spacings and the Porter-Thomas distribution for reduced widths are verified for the resonances in the even-even nuclei Ca⁴⁰, Fe⁵⁶, Ni⁵⁸, and Ni⁶⁰. A simple method of area analysis which is less tedious and time consuming than the method reported before in Part III is also described.     

s- and p-wave neutron spectroscopy Xc. Intermediate structure: 88Sr

Neutron total cross section measurements of natural Sr were made from 50–875 keV using a high resolution proton beam and the ⁷Li(p, n) reaction as a neutron source. These data were analyzed with the help of an R-Matrix code to extract resonance (energies and other) parameters up to about 850 keV. 2p-1h and particle-vibration doorway interpretation of the s-, p- and d-wave resonances is attempted in terms of the sum rule Σγ_n² = γ_d². Predictions based on both of these models agree with the experimental results. As expected the p-wave resonances are stronger than either s- and d-wave structure. Theory accounts for the p-wave strength remarkably well. Possible location of the p-wave s.p. resonance is reproduced with a real potential and its damping due to the imaginary potential is calculated.More fragmentation of the strong p-wave doorways is observed than was expected for a compound nucleus so near ⁹⁰Zr, but a larger strength function is observed apparently due to the p-wave giant resonance.     

S- and P-wave neutron spectroscopy Part Xd: Intermediate structure, particle-vibration states

The weak coupling particle-vibration model is extended to lowlying neutron resonances in certain even-even or odd-odd nuclei by coupling the extra particle to core excited states of the odd mass target. The odd hole or particle in the target is treated as a passive spectator. ²⁰⁸Pb and ²¹⁰Bi are studied as test cases and the calculated resonance quantities are in good general agreement with the average features of high resolution experiments. The resonances in ²⁰⁸Pb and ²¹⁰Bi are related to the same intrinsic doorway in ²⁰⁹Pb. The ²¹⁰Bi data is presented here for the first time.     

Brillouin-based fiber-optic distributed temperature sensor with optical preamplification

Optical preamplification has been used in a fiber-optic distributed temperature sensor based on spontaneous Brillouin scattering and the use of direct detection, resulting in improved signal-to-noise ratios. The fiber-based optical preamplifier system comprises a three-port circulator, an erbium-doped fiber amplifier with a small-signal gain of 27 dB, and a fiber Bragg grating with 47-GHz bandwidth. An improvement of 17 dB in the optical signal-to-noise ratio for the Brillouin signal is demonstrated in a 23-km sensor. The limit to the signal-to-noise ratio is attributed to spontaneous-spontaneous beat noise generated at the photodetector by amplified spontaneous emission from the optical amplifier.     

Theoretical and experimental demonstrations of a microfiber-based flexural disc accelerometer

The proof-of-concept demonstration of a microfiber-based flexural disc accelerometer is presented. The reduced microfiber size and bending radii give rise to high device compactness and responsivity. A flexural disc accelerometer manufactured from a 10 mm long microfiber showed a performance of ~2.2 rad/g, with the responsivity expected to increase proportionally with the microfiber length.     

High-resolution proton scattering on 46Ti

Differential cross sections were measured for ⁴⁶Ti(p, p) and ⁴⁶Ti(p, p₁) at four angles between E_p = 1.5 and 3.1 MeV, with an overall energy resolution of about 300 eV. Spins, parities, total and partial widths were extracted for 144 resonances. Six analogue states were identified. The s-wave states have expected spacing and width distributions, while the $\text{p}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ states behave anomalously. The $\text{s}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$, $\text{p}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ and $\text{p}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ strength functions were determined.     

Optical fibre sensors for earth sciences: : from basic concepts to optimising glass composition for high temperature applications

This paper reviews the technical evolution of optical fibre sensors relevant to earth sciences with particular reference to high temperature measurements. Optimisation of fibre composition and system design to fully realise the potential of these sensors has led to the substantial advances in both distributed and point sensor systems. Applications of these sensors in the field of earth sciences are discussed to provide a deeper understanding of the potential for monitoring geodynamical and chemical processes in areas of high seismic and volcanic risk.