Effect of spatial heterogeneity on level of rejuvenation in Ni80P20 metallic glass

Understanding the relation between spatial heterogeneity and structural rejuvenation is one of the hottest topics in the field of metallic glasses (MGs). In this work, molecular dynamics (MD) simulation is implemented to discover the effects of initial spatial heterogeneity on the level of rejuvenation in the Ni$_{80}$P$_{20 }$MGs. For this purpose, the samples are prepared with cooling rates of $10^{10}$ K/s-$10^{12}$ K/s to make glassy alloys with different atomic configurations. Firstly, it is found that the increase in the cooling rate leads the Gaussian-type shear modulus distribution to widen, indicating the aggregations in both elastically soft and hard regions. After the primary evaluations, the elastostatic loading is also used to transform structural rejuvenation into the atomic configurations. The results indicate that the sample with intermediate structural heterogeneity prepared with 10$^{11}$ K/s exhibits the maximum structural rejuvenation which is due to the fact that the atomic configuration in an intermediate structure contains more potential sites for generating the maximum atomic rearrangement and loosely packed regions under an external excitation. The features of atomic rearrangement and structural changes under the rejuvenation process are discussed in detail.     

Monitoring the absorption of organic vapors to a solid phase extraction medium applications to detection of trace volatile organic compounds by integration of solid phase absorbents with fiber optic Raman spectroscopy

By combining fiber optic Raman spectroscopy with a C-18 solid phase extraction medium, real time in situ detection of organic vapors is demonstrated. The response of the probe is fully reversible for benzene, trichloroethylene and carbon tetrachloride vapors. Because of the high degree of selectivity afforded by Raman spectroscopy, the composition of mixtures of the vapors can also be determined using the C-18 probe. The detection of ppm levels of benzene in water via headspace analysis using the C-18 probe is demonstrated.     

A study of some parameters relevant to the response of harwell PMMA dosimeters to gamma and electron irradiation

The effects on the radiation response of Harwell polymethylmethacrylate (PMMA) dosimeters of dose-rate, radiation type, temperature during irradiation and post-irradiation storage, and post-irradiation stability, are of importance to the operators of commercial irradiation facilities.

This paper describes recent studies of the effects of some of these parameters on the radiation response of Harwell Red 4034, Amber 3042, and Gammachrome YR Perspex dosimeters, and provides data on batch to batch variation and shelf-life.     

Stochastic analysis of recurrence plots with applications to the detection of deterministic signals

Recurrence plots have been widely used for a variety of purposes such as analyzing dynamical systems, denoising, as well as detection of deterministic signals embedded in noise. Though it has been postulated previously that recurrence plots contain time correlation information here we make the relationship between unthresholded recurrence plots and the covariance of a random process more precise. Computations using examples from harmonic processes, autoregressive models, and outputs from nonlinear systems are shown to illustrate this relationship. Finally, the use of recurrence plots for detection of deterministic signals in the presence of noise is investigated and compared to traditional signal detection methods based on the likelihood ratio test. Results using simulated data show that detectors based on certain statistics derived from recurrence plots are sub-optimal when compared to well-known detectors based on the likelihood ratio.     

Preparation of radio-Sm by neutron activation for accelerator mass spectrometry

Field measurement of isotopic ratios may be used to fingerprint an element’s origin, be it from commercial power, industrial, medical or historical weapons fallout. Samples of samarium radionuclides were prepared by neutron activation for subsequent analysis using accelerator mass spectrometry (AMS). High purity samarium (III) oxide powder was irradiated in the University of Texas at Austin TRIGA reactor to a total neutron fluence of 5 × 10¹⁵ cm^?2. An initial determination of the isotopic ratios was made using activation calculations with a BURN card in an MCNPX-based model of the TRIGA core. Experimental validation of the MCNP results was achieved by analyzing gamma spectra of the irradiated oxide powers after irradiation. Subsequent measurement of ¹⁵¹Sm will be conducted at the CAMS facility at LLNL demonstrating the first measurement of this isotope at this facility.     

Preferred conformations of enol ethers in solution: Detection of an equilibrium by kinetic nuclear overhauser effects

n.O.e. difference spectra reveal that the preferred solution conformation of methyl enol ethers has the methyl group $\text{syn}$-periplanar to the double bond; n.O.e kinetics in a methoxy—heptatriene demonstrate the presence of both possible periplanar conformations, the energy difference being $\text{ca}$ 1 kcal/mole.