Micro- and nano-size hydrogrossular-like clusters in pyrope crystals from ultra-high-pressure rocks of the Dora-Maira Massif, western Alps

The supracrustal metamorphic rocks of the Dora-Maira Massif, western Alps, have been intensively studied. Certain ultra-high-pressure lithologies contain coesite and nearly end-member composition pyrope, Mg₃Al₂Si₃O₁₂, making this locality petrologically and mineralogically unique. Structural OH⁻, loosely termed “water”, in pyrope crystals of different composition has been investigated numerous times, using different experimental techniques, by various researchers. However, it is not clear where the minor OH⁻ is located in them. IR single-crystal spectra of two pyropes of composition {Mg_(2.79),Fe²⁺_(0.15),Ca_(0.04)}_(Σ2.98)[Al]_(2.02)(Si)_(2.99)O₁₂ and {Mg_(2.90),Fe²⁺_(0.04),Ca_(0.02)}_(Σ2.96)[Al]_(2.03)(Si)₃O₁₂ were recorded at room temperature (RT) and 80 K. The spectra show five distinct OH⁻ bands located above 3600 cm⁻¹ at RT and seven narrow bands at 80 K and additional fine structure. The spectra were curve fit and the OH⁻ stretching modes analyzed and assigned. It is argued that OH⁻ is located in microscopic- and nano-size Ca₃Al₂H₁₂O₁₂-like clusters. The basic substitution mechanism is the hydrogarnet one, where (H₄O₄)⁴⁻ ⇔ (SiO₄)⁴⁻, and various local configurations containing different numbers of (H₄O₄)⁴⁻ groups define the cluster type. The amounts of H₂O range between 5 and 100 ppm by weight, depending on the IR calibration adopted, and are variable among crystals. Hydrogrossular-like clusters are also present in a synthetic pyrope with a minor Ca content grown hydrothermally at 900 °C and 20 kbar, as based on its IR spectra at RT and 80 K. Experiment and nature are in agreement, and OH⁻ groups are partitioned into various barely nano-size hydrogrossular-like clusters. This proposal is new and significant mineralogical, petrological, and geochemical implications result. Ca and proton ordering occur. Hypothetical “defect” and/or coupled-substitution mechanisms to account for structural OH⁻ are not needed to interpret experimental results. OH⁻ incorporation in pyrope of different generations at Dora-Maira is discussed and OH- could potentially be used as an indicator of changing P_(H₂O)(a_(H₂O)) – T conditions in a metamorphic cycle. Published experimental hydration, dehydroxylation, and hydrogen diffusion results on Dora-Maira pyropes can now be interpreted atomistically

Heat capacity and entropy behavior of andradite: a multi-sample and −methodological investigation

Andradite, ideal end-member formula Ca_3 Fe^(3+)_2Si_3O_(12), is one of the common rock-forming garnets found in the Earth's crust. There are several outstanding questions regarding andradite's thermodynamic and physical property behavior. Three issues are: i) Could there be differences in the thermodynamic properties, namely heat capacity, C_p , between synthetic and natural andradite crystals, as observed in the Ca-garnet grossular, Ca_3Al_2Si_3O_(12)? ii) What is the thermal nature of the low-temperature magnetic-phasetransition behavior of andradite? and iii) How quantitative are older published calorimetric (i. e., adiabatic and DSC) heat-capacity results? In this work, four natural nearly end-member single crystals and two synthetic polycrystalline andradite samples were carefully characterized by optical microscope examination, X-ray powder diffraction, microprobe analysis, and IR and UV/VIS single-crystal spectroscopy. The IR spectra of the different samples commonly show a main intense OH stretching band located at 3563 cm^(-1), but other OH bands can sometimes be observed as well. Structural OH concentrations, calculated from the IR spectra, vary from about 0.006 to 0.240 wt% H_2O. The UV/VIS spectra indicate that there can be slight, but not fully understood, differences in the electronic state between synthetic and natural andradite crystals. The C_p behavior was determined by relaxation calorimetry between 2 and 300 K and by differential scanning calorimetry (DSC) methods between 150/300 and 700/950 K, employing the same andradite samples that were used for the other characterization measurements. The low-temperature C_p results show a magnetic phase transition with a Néel temperature of 11.3 ± 0.2 K, which could be slightly affected by the precise electronic state of Fe^(2+/3+) in the crystals. The published adiabatic calorimetry results on andradite do not provide a full and correct thermal description of this magnetic transition. The calorimetric Cp measurements give a best estimate for the standard third-law entropy at 298.15 K for andradite of S^o ≈ 324 ± 2 J/mol · K vs. the value of 316.4 ± 2.0 J/mol · K, as given in an early adiabatic investigation. Both natural and synthetic crystals give similar S o values within experimental uncertainty of about 1.0%, but one natural andradite, richer in OH, may have a very slightly higher value around S^o≈ 326 J/mol·K. Low-temperature DSC measurements made below 298 K agree excellently with those from relaxation calorimetry. The DSC measurements above 298 K show a similarity in C_p behavior among natural and synthetic andradites. A C_p polynomial for use above room temperature to approximately 1000 K was calculated from the data on synthetic andradite giving: C_p (J/mol·K) = 599.09 (±14) 2709.5 (±480)· T^(0.5) 1.3866 (±0.26)· 10^7 · T^2 + 1.6052 (±0.42) · 10^9 · T^3

IR spectroscopy and OH^– in silicate garnet: The long quest to document the hydrogarnet substitution

There has been much research undertaken on structural OH^– in various nominally anhydrous minerals including the common silicate garnets (i.e., X_3Y_2Si_3O_(12), where X = Mg, Fe^(2+), Mn^(2+), and Ca and Y = Al, Fe^(3+), and Cr^(3+)). However, it is still largely not understood where small concentrations of H atoms are incorporated in the garnet crystal structure. In this work, the IR single-crystal spectra of end-member or approaching end-member composition andradite, pyrope, and almandine are measured. Both a natural and synthetic andradite sample show a broad, asymmetric OH^–-stretching mode at 3563 cm^(–1) that splits into two narrower modes at lower temperatures. They are located at 3575 and 3557 cm^(–1) at 80 K with the higher wavenumber mode being considerably more intense compared to that at lower energy. These results are analyzed together with published IR spectra of synthetic end-member katoite, pyrope, and almandine also recorded at low temperature. These garnets show similar IR behavior with a broad OH^– band at room temperature that splits into two narrower bands at lower temperatures and with a similar intensity relationship as shown by andradite. This behavior is indicative of the hydrogarnet substitution. The measured IR spectra of natural almandine- and pyrope-rich (Dora Maira, Italy) crystals, on the other hand, show different spectroscopic features with several OH^– modes that are not consistent with the hydrogarnet mechanism. An analysis of the energy of the OH^–-stretching mode is made for various composition hydrogarnet clusters [i.e., X_3Y_2(O_4H_4)_3, where X = Mg, Fe^(2+), Mn^(2+) and Ca and Y = Al and Fe^(3+)] in terms of crystal-chemical properties and local atomic configurations. The OH^– mode energy, which lies roughly between 3660 and 3550 cm^(–1) at RT for various end-member garnets, is a function of the mass of the X- and Y-cations due to mode coupling and/or mixing. In addition, the strength of the chemical bonding between the X- and Y-cations and the O^2–anion of the OH^– dipole plays a role in affecting the wavenumber of the OH^–-stretching vibration. OH^– mode broadening, observed in the spectra of end-member garnets, is primarily a result of thermal anharmonic disorder, especially with regard to the light H cation. OH mode broadening in intermediate solid-solution composition garnets is a function of both thermal effects and variations in local cation configurations around the OH^– dipole(s). Published IR spectra of certain high-pressure pyrope-rich garnets, both synthetic and natural, are analyzed and arguments made that OH^– can often be incorporated as the hydrogarnet or hydropyrope substitution. IR spectra similar in appearance, having multiple relatively narrow OH^– modes that are distinct from those indicating the hydrogarnet substitution, can be observed for certain synthetic end-member and various composition natural pyropes from Dora Maira and some natural spessartines. This indicates that other common OH^– substitution mechanisms, which have yet to be determined, can also occur in different silicate garnets

Heat capacity and entropy behavior of andradite: a multi-sample and −methodological investigation

Andradite, ideal end-member formula Ca_3 Fe^(3+)_2Si_3O_(12), is one of the common rock-forming garnets found in the Earth's crust. There are several outstanding questions regarding andradite's thermodynamic and physical property behavior. Three issues are: i) Could there be differences in the thermodynamic properties, namely heat capacity, C_p , between synthetic and natural andradite crystals, as observed in the Ca-garnet grossular, Ca_3Al_2Si_3O_(12)? ii) What is the thermal nature of the low-temperature magnetic-phasetransition behavior of andradite? and iii) How quantitative are older published calorimetric (i. e., adiabatic and DSC) heat-capacity results? In this work, four natural nearly end-member single crystals and two synthetic polycrystalline andradite samples were carefully characterized by optical microscope examination, X-ray powder diffraction, microprobe analysis, and IR and UV/VIS single-crystal spectroscopy. The IR spectra of the different samples commonly show a main intense OH stretching band located at 3563 cm^(-1), but other OH bands can sometimes be observed as well. Structural OH concentrations, calculated from the IR spectra, vary from about 0.006 to 0.240 wt% H_2O. The UV/VIS spectra indicate that there can be slight, but not fully understood, differences in the electronic state between synthetic and natural andradite crystals. The C_p behavior was determined by relaxation calorimetry between 2 and 300 K and by differential scanning calorimetry (DSC) methods between 150/300 and 700/950 K, employing the same andradite samples that were used for the other characterization measurements. The low-temperature C_p results show a magnetic phase transition with a Néel temperature of 11.3 ± 0.2 K, which could be slightly affected by the precise electronic state of Fe^(2+/3+) in the crystals. The published adiabatic calorimetry results on andradite do not provide a full and correct thermal description of this magnetic transition. The calorimetric Cp measurements give a best estimate for the standard third-law entropy at 298.15 K for andradite of S^o ≈ 324 ± 2 J/mol · K vs. the value of 316.4 ± 2.0 J/mol · K, as given in an early adiabatic investigation. Both natural and synthetic crystals give similar S o values within experimental uncertainty of about 1.0%, but one natural andradite, richer in OH, may have a very slightly higher value around S^o≈ 326 J/mol·K. Low-temperature DSC measurements made below 298 K agree excellently with those from relaxation calorimetry. The DSC measurements above 298 K show a similarity in C_p behavior among natural and synthetic andradites. A C_p polynomial for use above room temperature to approximately 1000 K was calculated from the data on synthetic andradite giving: C_p (J/mol·K) = 599.09 (±14) 2709.5 (±480)· T^(0.5) 1.3866 (±0.26)· 10^7 · T^2 + 1.6052 (±0.42) · 10^9 · T^3

Interpreting the Neutron's Electric Form Factor: Rest Frame Charge Distribution or Foldy Term?

The neutron's electric form factor contains vital information on nucleon structure, but its interpretation within many models has been obscured by relativistic effects. I demonstrate that, to leading order in the relativistic expansion of a constituent quark model, the Foldy term cancels exactly against a contribution to the Dirac form factor F_1 to leave intact the naive interpretation of G^n_E as arising from the neutron's rest frame charge distribution.Comment: 13 page

Prophylactic Surgery for Multiple Endocrine Neoplasia Type IIa after Genetic Diagnosis: Is Parathyroid Transplantation Indicated?

RET proto-oncogene predisposing to multiple endocrine neoplasia type IIa (MEN-IIa) has allowed a DNA-based approach to diagnosis and treatment by prophylactic thyroidectomy in children testing genetically positive. Although total thyroidectomy is the accepted operation for C cell disease, the necessity of routine total parathyroidectomy and autotransplantation as previously described in these asymptomatic children is questionable, particularly given the low occurrence of hyperparathyroidism in MEN-IIa (10–20%). Thirty-six children (ages 1 month to 12 years) from four MEN-IIa kindreds at risk for disease underwent genetic testing. Mutational analysis was done using a highly sensitive PCR-based denaturing gradient gel electrophoresis technique. Parathyroid or serum calcium concentrations were determined preoperatively. Of the 36 children at risk, 18 were found to have a MEN-IIa mutation; 11 have undergone prophylactic thyroidectomy at ages ranging from 2 to 12 years (mean 7.5 years). In each case, there was no biochemical evidence of hypercalcemia preoperatively, and all parathyroid glands were identified and were found to be grossly normal at exploration. Glands were carefully dissected and left in situ. Postoperatively, 10 of the 11 children maintained normocalcemia, allowing discharge within 24 to 36 hours. Resected thyroid glands contained C cell hyperplasia in nine, medullary carcinoma in one, and normal histology in one. We conclude that an alternative to routine parathyroidectomy may be desirable for prophylactic treatment of MEN-IIa. In situ parathyroid preservation can be safely achieved without compromising the completeness of the thyroid resection. This conservative approach obviates the potential morbidity associated with total parathyroidectomy and autotransplantation.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/42406/1/268-20-7-814_20n7p814.pd

A meta-analysis of third wave mindfulness-based cognitive behavioral therapies for older people

Objectives: The aim of this study is to review the effectiveness of third wave mindfulness-based cognitive behavioral therapies (CBTs) for depressive or anxiety symptomatology in older adults across a wide range of physical and psychological conditions. Methods: Electronic literature databases were searched for articles, and random-effects meta-analysis was conducted. Results: Ten studies met the inclusion criteria, of which nine reported the efficacy of interventions on depressive symptoms and seven on anxiety symptoms. Effect-size estimates suggested that mindfulness-based CBT is moderately effective on depressive symptoms in older adults (g = 0.55). The results demonstrated a similar level of overall effect size for anxiety symptoms (g = 0.58). However, there was a large heterogeneity, and publication bias was evident in studies reporting outcomes on anxiety symptoms, and thus, this observed efficacy for late-life anxiety may not be robust. The quality of the included studies varied. Only one study used an active psychological control condition. There were a limited number of studies that used an intent-to-treat (last observation carried forward method) analysis and reported appropriate methods for clinical trials (e.g., treatment-integrity reporting). Conclusions: Third wave mindfulness-based CBT may be robust in particular for depressive symptoms in older adults. We recommend that future studies (i) conduct randomized controlled trials with intent-to-treat to compare mindfulness-based CBT with other types of psychotherapy in older people and (ii) improve study quality by using appropriate methods for checking treatment adherence, randomization, and blinding of assessors. Copyright © 2016 John Wiley & Sons, Ltd

MAPPIN'SDM – The Multifocal Approach to Sharing in Shared Decision Making

BACKGROUND: The wide scale permeation of health care by the shared decision making concept (SDM) reflects its relevance and advanced stage of development. An increasing number of studies evaluating the efficacy of SDM use instruments based on various sub-constructs administered from different viewpoints. However, as the concept has never been captured in operable core definition it is quite difficult to link these parts of evidence. This study aims at investigating interrelations of SDM indicators administered from different perspectives. METHOD: A comprehensive inventory was developed mapping judgements from different perspectives (observer, doctor, patient) and constructs (behavior, perception) referring to three units (doctor, patient, doctor-patient-dyad) and an identical set of SDM-indicators. The inventory adopted the existing approaches, but added additional observer foci (patient and doctor-patient-dyad) and relevant indicators hitherto neglected by existing instruments. The complete inventory comprising a doctor-patient-questionnaire and an observer-instrument was applied to 40 decision consultations from 10 physicians from different medical fields. Convergent validities were calculated on the basis of Pearson correlation coefficients. RESULTS: Reliabilities for all scales were high to excellent. No correlations were found between observer and patients or physicians neither for means nor for single items. Judgements of doctors and patients were moderately related. Correlations between the observer scales and within the subjective perspectives were high. Inter-perspective agreement was not related to SDM performance or patient activity. CONCLUSION: The study demonstrates the contribution to involvement made by each of the relevant perspectives and emphasizes the need for an inter-subjective approach regarding SDM measurement