17,374 research outputs found
Intensities of backscatter Mössbauer spectra
The intensities of γ‐ray and x‐ray backscatter Mössbauer spectra of ^(57)Fe nuclei in different matrix materials were studied theoretically and experimentally. A previous analysis by J. J. Bara [Phys. Status Solidi A 58, 349 (1980] showed that negative peak intensities occur in backscatter γ‐ray spectra when the ^(57)Fe nuclei are in a matrix of light elements. We report a confirmation of this work and offer a simple explanation of the phenomenon. The present paper extends Bara’s analysis to the case of conversion x‐ray spectra; expressions for the intensity of conversion x‐ray spectra as a function of absorber thickness and absorber material parameters are presented. We show that negative peak intensities are expected in conversion x‐ray spectra when the ^(57)Fe nuclei are in a matrix of heavy elements
Thermal Decomposition of the Murchison CM2 Carbonaceous Chondrite: Implications of Space Weathering Processes for Sample Return Missions
Primitive carbonaceous asteroids are the target bodies for the JAXA Hayabusa2 mission to Ryugu and the NASA OSIRIS-REx mission to Bennu. Both asteroids share spectral characteristics of CI/CM type carbonaceous chondrites. Ryugu, in particular, appears to have undergone thermal processing that has modified its spectral properties. The nature and extent of space weathering processes on the surfaces of Bennu and Ryugu are under active investigation using remote sensing data from the missions [4] and through laboratory studies on analog materials. The analog studies are needed in order to understand the mineralogical and chemical changes that occur in space weathered samples that give rise to the observed optical effects measured by remote-sensing and to prepare for the analysis of returned samples. The space weathering effects of micrometeorite impact and solar wind irradiation on primitive carbonaceous chondrites have been simulated by analog studies on the Murchison CM2 chondrite. We performed a coordinated mineralogical, chemical and spectroscopic study to examine in detail the effects of thermal metamorphism on Murchison samples as an analog to processes that may have occurred on Ryugu. The bulk measurements including X-ray diffraction (XRD), Mssbauer spectroscopy, UV-VIS-NIR spectroscopy, thermogravimetric analysis, and evolved gas analysis are reported in a companion paper. Here we report on our preliminary nanoscale mineralogical and chemical analyses of pre- and post-heated Murchison samples using multiple electron beam techniques to understand how the mineralogical, chemical, and physical characteristics of carbonaceous chondrites change with increasing thermal effects
The Liquidus Temperature for Methanol-Water Mixtures at High Pressure and Low Temperature, with Application to Titan
Methanol is a potentially important impurity in subsurface oceans on Titan
and Enceladus. We report measurements of the freezing of methanol-water samples
at pressures up to 350~MPa using a volumetric cell with sapphire windows. For
low concentrations of methanol, the liquidus temperature is typically a few
degrees below the corresponding ice freezing point, while at high
concentrations it follows the pure methanol trend. In the Ice-III regime, we
observe several long-lived metastable states. The results suggest that methanol
is a more effective antifreeze than previously estimated, and might have played
an important role in the development of Titan's subsurface ocean
Coordination polymers of 5-substituted isophthalic acid
This work was funded by the British Heart Foundation (NH/11/8/29253) and the EPSRC (EP/K005499/1).The synthesis and characterisation of five coordination polymers - Ni2(mip)2(H2O)8·2H2O ( 1 ), Zn6(mip)5(OH)2(H2O)4·7.4H2O ( 2 ), Zn6(mip)5(OH)2(H2O)2·4H2O ( 3 ), Mn(HMeOip)2 ( 4 ), and Mn3(tbip)2(Htbip)2(EtOH)2 ( 5 ) - are reported. Preliminary nitric oxide release data on compounds 2 and 3 are also given.Publisher PDFPeer reviewe
Dynamical description of vesicle growth and shape change
We systematize and extend the description of vesicle growth and shape change
using linear nonequilibrium thermodynamics. By restricting the study to shape
changes from spheres to axisymmetric ellipsoids, we are able to give a
consistent formulation which includes the lateral tension of the vesicle
membrane. This allows us to generalize and correct a previous calculation. Our
present calculations suggest that, for small growing vesicles, a prolate
ellipsoidal shape should be favored over oblate ellipsoids, whereas for large
growing vesicles oblates should be favored over prolates. The validity of this
prediction is examined in the light of the various assumptions made in its
derivation.Comment: 6 page
Athlete and practitioner insights regarding a novel Coping Oriented Personal-Disclosure Mutual-Sharing (COPDMS) intervention in youth soccer
This paper provides athlete and practitioner insights regarding a novel coping-oriented personal-disclosure mutual-sharing (COPDMS) intervention developed and administered in a youth soccer context. Participants were 18 male soccer athletes (mean age 17.29 ± 0.73 years) who belonged to the same professional academy in England. The COPDMS intervention comprised an initial sport psychology education session (Week 1), a session introducing COPDMS (Week 2), a COPDMS session (Week 4), and a follow-up session (Week 9). During the COPDMS session, athletes mutually shared personal stories and/or information about transitions as they approached a time when they would gain a professional contract or would be released from their soccer academy. Athletes communicated a range of contextually relevant demand and resource appraisals during the COPDMS session. Several athlete and practitioner insights about the COPDMS process and outcomes were provided that can guide future researchers and practitioners seeking to develop and deliver bespoke PDMS interventions in sport
Molecular dynamic simulation of a homogeneous bcc -> hcp transition
We have performed molecular dynamic simulations of a Martensitic bcc->hcp
transformation in a homogeneous system. The system evolves into three
Martensitic variants, sharing a common nearest neighbor vector along a bcc
direction, plus an fcc region. Nucleation occurs locally, followed by
subsequent growth. We monitor the time-dependent scattering S(q,t) during the
transformation, and find anomalous, Brillouin zone-dependent scattering similar
to that observed experimentally in a number of systems above the transformation
temperature. This scattering is shown to be related to the elastic strain
associated with the transformation, and is not directly related to the phonon
response.Comment: 11 pages plus 8 figures (GIF format); to appear in Phys. Rev.
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