Back Conversion Research Articles

Comparative genomics and evidence for an unusual polyamine oxidation pathway in aquatic duckweed (Spirodela polyrhiza L.)

Polyamines (PA) cellular levels are maintained through a balance between synthesis and catabolism, achieved by two classes of enzymes polyamine oxidases (PAOs) and copper amine oxidases (CuAO). Here we investigated the occurrence, molecular evolution and role(s) of PAOs and CuAO gene families in aquatic duckweed and their comparison with other aquatic plants -sea eelgrass, bladderwort, and Lotus. We identified eight bona fide PAO genes (SpPAO1–SpPAO8) and one SpCuAO1 in the greater duckweed genome from three genome assemblies. Interestingly, duckweed PAO genes increased their number through a tandem duplication event, while contrary to this CuAO genes were significantly lost to a single gene SpCuAO1. Phylogenetic analysis revealed that tandemly duplicated SpPAO2–7 share close similarity to well-known terminal catabolism (TC) pathway PAO genes while SpPAO1 and SpPAO8 seem to segregate along with back conversion (BC) participating known PAO genes, suggesting that all tandem duplicated PAOs are involved in TC pathway which is contrary to known trend in land plants where CuAOs are mainly involved in TC pathway. Comparative transcript abundance studies indicated that all eight PAOs and one CuAO gene respond to multiple stresses and principal component analysis identifies SpPAO4 as a highly active gene in response to multiple stresses. Results showed that oxidation of higher polyamines (SPD/SPM) through the TC pathway is diversified in duckweeds. Taken together this study reveals unique insights into the genomic losses and gains of polyamine metabolism possibly involved in achieving the structural and physiological adaptations required for aquatic lifestyle of duckweeds.

Development status of the in-situ measurement system for ortho-to-parahydrogen fractions for the ESS cryogenic moderator system

The Cryogenic Moderator System (CMS) is equipped with a catalyst to convert hydrogen from the ortho state to the para state in order to keep desirably high parahydrogen fractions of 99.5%. An in-situ measurement system for the ortho and para fractions of liquid hydrogen (OPMS) by means of a Raman spectroscopy with an accuracy of 0.1% is being developed to detect any undesirable shift towards a high orthohydrogen fraction caused by neutron scattering driven para-to-ortho back conversion. We have demonstrated that our developed sapphire window, through which the laser and backscattered photon travel, has endured the required pressure and thermal cycles in a liquid hydrogen environment. Meanwhile, a Raman optics system has been developed using normal hydrogen. Eventually, we have succeeded in detecting the parahydrogen peak at J = 4, which is our primary goal, because the peak ratio of parahydrogen at 1245 cm−1 to ortho hydrogen at 587 cm−1 corresponds to 0.5%. It can be expected that it would achieve our requirement for liquid hydrogen with higher density.

Physiologically Based Pharmacokinetic Modeling: The Reversible Metabolism and Tissue-Specific Partitioning of Methylprednisolone and Methylprednisone in Rats.

The pharmacokinetics (PK) of methylprednisolone (MPL) exhibited tissue-specific saturable binding and reversible conversion with its metabolite, methylprednisone (MPN). Blood and 11 tissues were collected in male rats after intravenous (i.v.) bolus doses of 50 mg/kg MPL and 20 mg/kg MPN and upon i.v. infusion of MPL and MPN at 0.3, 3, and 10 mg/h per kg. The concentrations of MPL and MPN were simultaneously measured. A comprehensive physiologically based pharmacokinetic (PBPK) model was applied to describe the plasma and tissue profiles and estimate PK parameters of the MPL/MPN interconversion system. Both dosed and formed MPL and MPN were in rapid equilibrium or achieved steady-state rapidly in plasma and tissues. MPL tissue partitioning was nonlinear, with highest capacity in liver (322.9 ng/ml) followed by kidney, heart, intestine, skin, spleen, bone, brain, muscle, and lowest in adipose (2.74 ng/ml) and displaying high penetration in lung. The tissue partition coefficient of MPN was linear but widely variable (0.15∼5.38) across most tissues, with nonlinear binding in liver and kidney. The conversion of MPL to MPN occurred in kidney, lung, and intestine with total clearance of 429 ml/h, and the back conversion occurred in liver and kidney at 1342 ml/h. The irreversible elimination clearance of MPL was 789 ml/h from liver and that of MPN was 2758 ml/h with liver accounting for 44%, lung 35%, and kidney 21%. The reversible metabolism elevated MPL exposure in rats by 13%. This highly complex PBPK model provided unique and comprehensive insights into the disposition of a major corticosteroid. SIGNIFICANCE STATEMENT: Our dual physiologically based pharmacokinetic (PBPK) study and model of methylprednisolone/methylprednisone (MPL/MPN) with multiple complexities reasonably characterized and parameterized their disposition, and provided greater insights into the interpretation of their pharmacodynamics in rats. Drug knowledge gained in this study may be translatable to higher-order species to appreciate the clinical utility of MPL. The complex model itself is instructive for advanced PBPK analysis of drugs with reversible metabolism and/or nonlinear tissue partitioning features.

Efficient noncollinear optical parametric chirped-pulse amplification in oversaturation region

Optical parametric chirped pulse amplification (OPCPA) is the workhorse to generate intense ultrashort pulses across a broad wavelength range. Typically, OPCPA operates in the saturation region, but barely in the oversaturation region due to efficiency drop caused by back conversion. Through numerical simulations, we reveal the potential of noncollinear OPCPA to achieve significantly higher conversion efficiency in the oversaturation regime compared to the recognized saturation efficiency. This enhancement stems from the suppression of back conversion facilitated by noncollinearity-induced idler dissipation. Besides offering high efficiency and robustness, the oversaturated noncollinear OPCPA also exhibits acceptable spatial and temporal properties, as well as spatiotemporal coupling properties. These findings hold promise for enhancing the final stage of a noncollinear OPCPA system, where a high conversion efficiency is essential.

Development of an in-situ ortho-to-parahydrogen fraction measurement system for the ESS cryogenic moderator system

At the European Spallation Source (ESS) ERIC, the liquid hydrogen moderator development is undertaken for its predominantly high parahydrogen fraction, which helps to attain a higher neutron intensity at a very high brightness. The Cryogenic Moderator System (CMS) is equipped with a catalyst to convert hydrogen from the ortho to the parastate to keep desirably high parahydrogen fractions of more than 99.5% in the cold moderators, which is required to deliver high brightness cold neutron beams to the neutron instruments. An in-situ measurement system for the ortho and para fractions of liquid hydrogen (OPMS) has been developed using a Raman spectroscopy to detect any undesirable shift towards a high orthohydrogen fraction caused by neutron scattering driven para-to-ortho back conversion. A Raman optics system was installed into a mock-up OPMS vacuum chamber and its performance evaluation tests have been conducted by flowing liquid hydrogen. It was verified that the developed Raman optics system succeeded in measuring the parahydrogen fraction with an accuracy of 0.1%, which met the requirement.

Miniaturized on-spot protein denaturation/microwave-assisted extraction for spectrofluorimetric determination of favipiravir in dried plasma: Application to real human sample and inclusive incurred sample reanalysis study

The development of high-throughput sample preparation methods is a key step for upgrading the throughput of classical analytical techniques. In this work, a miniaturized on-spot protein denaturation coupled with microwave-assisted extraction sample treatment method was developed for extraction and subsequent spectrofluorimetric determination of favipiravir (FAV) in human plasma spots. Dried plasma spotting was performed using only 10 µL of plasma on filter paper discs followed by on-spot protein denaturation using 10 µL methanol. Maximum extraction efficiency was achieved using water: methanol (1:1) as extraction solvent with 50 % microwave power for 60 sec. The fluorescence intensity of extracted FAV was measured at 432 nm after excitation at 361 nm. According to the International Council for Harmonization of Technical Requirements for Pharmaceuticals for Human Use (ICH -M10) guidelines for bioanalytical method validation, spiked plasma samples showed very good linearity between 100 and 1000 ng/mL. The accuracy and precision of the developed method were indicated by mean recovery (%) within 100 ± 15 % for all tested concentrations levels. The obtained results were further compared with a reported protein precipitation method using both F-test and t-test revealing no significant difference between either method. Moreover, the method was successfully applied for FAV determination in real human samples for an incurred sample reanalysis study revealing no metabolite back conversion. The developed method showed superior green performance using analytical Eco-scale, Green Analytical Procedure Index (GAPI), and Analytical Greenness Metric Approach (AGREE) tools compared to a classical protein precipitation method. According to Blue Applicability Grade Index (BAGI), and whiteness tools, the developed method outperformed all reported methods for FAV determination in plasma in terms of practicality and analytical functionality. Compared to reported sample treatment methods, this method exhibited excellent analytical performance, increased throughput, hundred-fold reduction of sample volume (10 μL), significant reduction of organic solvent consumption (260 μL methanol) and produced negligible wastes. Thus, it can be adopted for routine work in pharmacokinetics and clinical trial studies.

Solution Structures of Two Different FRP-OCP Complexes as Revealed via SEC-SANS.

Photosynthetic organisms have established photoprotective mechanisms in order to dissipate excess light energy into heat, which is commonly known as non-photochemical quenching. Cyanobacteria utilize the orange carotenoid protein (OCP) as a high-light sensor and quencher to regulate the energy flow in the photosynthetic apparatus. Triggered by strong light, OCP undergoes conformational changes to form the active red state (OCPR). In many cyanobacteria, the back conversion of OCP to the dark-adapted state is assisted by the fluorescence recovery protein (FRP). However, the exact molecular events involving OCP and its interaction with FRP remain largely unraveled so far due to their metastability. Here, we use small-angle neutron scattering combined with size exclusion chromatography (SEC-SANS) to unravel the solution structures of FRP-OCP complexes using a compact mutant of OCP lacking the N-terminal extension (∆NTEOCPO) and wild-type FRP. The results are consistent with the simultaneous presence of stable 2:2 and 2:1 FRP-∆NTEOCPO complexes in solution, where the former complex type is observed for the first time. For both complex types, we provide ab initio low-resolution shape reconstructions and compare them to homology models based on available crystal structures. It is likely that both complexes represent intermediate states of the back conversion of OCP to its dark-adapted state in the presence of FRP, which are of transient nature in the photocycle of wild-type OCP. This study demonstrates the large potential of SEC-SANS in revealing the solution structures of protein complexes in polydisperse solutions that would otherwise be averaged, leading to unspecific results.

Borate speciation and structural studies of vanadium ion doping in borate bioglass

Different glasses in the system, xV2O5-(45–x)B2O3–24.5Na2O–24.5CaO–6P2O5, (x = 0, 3, 6, 9, 12, 15, 18, 20 and 25 Wt%) were prepared through melt quenching method. X-ray diffraction (XRD) patterns have revealed that the amorphous structure is the dominant type. There is no tendency for crystallization even with higher vanadium content. Crystallization occurred utilizing treating the glasses thermally. FTIR spectral absorption data showed the presence of both BO3 and BO4 structural groups in combination with the presence of VO4 and VO5 structural building units. The deconvolution analysis technique (DAT) was adopted to retrace the conversion progressions of the coordinated boron. At low V2O5 content (up to 10 wt%), it entered as a glass modifier as well as both Na2O and CaO. The high content of the glass modifier (Na2O + CaO + V2O5) could destroy some of the well-formed BO4 units which are transformed into asymmetric BO3. The back conversion of BO4 to asymmetric or loose BO3 can simply reduce the fraction of tetrahedral units (N4). When V2O5 entered as a glass former (> 10 wt%), the N4 fraction increased. The change in the measured densities and estimated molar volumes may assigned to the formation of BO4 units resulting from increasing vanadium oxide content.

Primary emissions or environmental persistence contribute to the present DDTs: Evidence from sediment records in Tibetan lakes

Dichlorodiphenyltrichloroethane (DDT) compounds are still circulating the global environment even though the technical DDT has been restricted in agriculture since the last century. The persistent presence of DDTs worldwide remains uncertain, as it is unclear whether their existence is primarily due to ongoing use or the prolonged persistence in soils and sediments that result in continuous reemission into the atmosphere. The present study applied a sequential extraction procedure to determine the DDT concentrations in rapid desorption, slow desorption, and bound residue fractions in the dated sediment cores from distinct regions of Tibet. The temporal variation of total DDTs (sum of three fractions) in sediments from southern and eastern Tibet respectively revealed the different DDT usage histories in India and China mainland. Nevertheless, the current application volumes of DDT-containing products in these regions were found to decrease significantly. The reversible transformations among three fractions of DDTs with aging time was observed along sediment profile, including the back conversion from bound residue. This process may be the key driver to prolong the half-life of sediment p,p'-DDT, resulting in the persistence of secondary sources of this persistent organic pollutant in the global environment for a longer duration than previously expected.

Molecular Cloning, Subcellular Localization, and Abiotic Stress Induction Analysis of a Polyamine Oxidase Gene from Oryza sativa

Abiotic stress is a major bottleneck for crop productivity. To counter abiotic stresses, plants have developed several strategies, and the accumulation of polyamine (PA) serving as an osmolyte is one of them. The cellular pool of PAs is primarily regulated by polyamine oxidases (PAOs) either by terminal catabolism or by back conversion (BC) of polyamines. The role of PAO in abiotic stress tolerance has also been reported. Polyamine oxidases are primarily localized in the cytosol, cell wall, and apoplastic regions; however, lately, their peroxisomal localization has also been demonstrated. In this study, we reported the detection of polyamine oxidase isoform 3 from Oryza sativa (OsPAO3) in peroxisome as early as 12 h post-transformation under in vitro conditions using fluorescent microscopy. The gene was also found to be significantly upregulated by salinity, dehydration, cold, and heat stress. We have also demonstrated that the expression of OsPAO3 gene was mediated by a second messenger, calcium. The upregulation of OsPAO3 by salinity, dehydration, cold, and heat stresses suggests that it could be a suitable candidate for providing tolerance to plants against abiotic stress combination or stress matrix, which is a common feature in agricultural field conditions. Furthermore, the data provided here would be valuable in understanding the abiotic stress-mediated signal transduction network of PAOs.

The Prevalence of Several Treatments in Preventing the Back Conversion of Acyl Glucuronide Metabolites in Abbreviated New Drug Applications.

The bioanalysis of drugs that undergo acyl glucuronidation presents an analytical challenge due to poor stability of acyl glucuronide metabolites in biological matrices. The objective of this study was to investigate the impact of back conversion of acyl glucuronide metabolites on drug concentration measurement in bioequivalence (BE) studies submitted to Abbreviated New Drug Applications (ANDAs). The prevalence of several treatments for preventing the back conversion of acyl glucuronide metabolites and the results of incurred sample reanalysis (ISR) were analyzed. In total, 322 ANDAs for 26 drugs known to generate acyl glucuronide metabolites were surveyed. Many studies have applied multiple preventive treatments during the clinical and bioanalytical phases. More than two-thirds (67.2%) of the studies utilized procedures of lowering the temperature for sample collection during clinical phase. Fewer studies have utilized procedures for lowering the pH of plasma samples (12.3%) or adding enzyme inhibitors (4.4%) in the clinical phase. A small fraction (16.9%) validated the pre-study method in the presence of the acyl glucuronide metabolites. The majority (62.2%) of the studies employed the procedure of lowering the pH during the sample extraction process in the bioanalytical phase. Among the studies that had significantly higher (p-value < 0.01 by sign test) ISR results than the corresponding original concentration values, 41 BE studies did not carry out any preventive treatments during the bioanalysis phase, suggesting that back conversion of acyl glucuronide metabolites to parent drugs may be present in these studies. The awareness of appropriate treatments of study samples for possible back-conversions of acyl glucuronide metabolites is expected to assist generic drug applicants in improving the quality of their future applications.

Mid-infrared quasi-parametric chirped-pulse amplification based on Sm:LGN crystals.

We numerically demonstrate highly efficient mid-infrared quasi-parametric chirped-pulse amplification (QPCPA) based on a recently developed Sm3+-doped La3Ga5.5Nb0.5O14 (Sm:LGN) crystal. At pump wavelength around 1 µm, the broadband absorption of Sm3+ on idler pulses can enable QPCPA for femtosecond signal pulses centered at 3.5 or 5 µm, with a conversion efficiency approaching the quantum limit. Due to suppression of back conversion, such mid-infrared QPCPA exhibits robustness against phase-mismatch and pump-intensity variation. The Sm:LGN-based QPCPA will provide an efficient approach for converting currently well-developed intense laser pulses at 1 µm to mid-infrared ultrashort pulses.

Comparison of back conversion and power differential in extra-cavity multi-optical parametric oscillator using MgO:APLN

The extra-cavity multi-optical parametric oscillator (MOPO) using MgO-doped aperiodically poled lithium niobite (MgO:APLN) is a technique to generate multi-wavelength tunable laser output, in which the back conversion and power differential can reduce the output power and conversion efficiency. A comparison of the back conversion and power differential between the two methods is presented in this paper. One approach is to adjust the mirror transmittance to change the parametric light's power density involved in the oscillation. With 1.47 μm transmittance of 20 % and 3.30 μm transmittance of 60 %, the 3.30 μm output power is 0.95 W, the 3.84 μm output power is 0.94 W, and the power ratio is 1.01. The other approach is to add two electro-optical polarization mode converters (EO PC) to change the parametric light's polarization. When the electric fields of two EO PCs are 66 V/mm and 15 V/mm, the 3.30 μm and 3.84 μm output powers are 2.54 W and 2.49 W, the conversion efficiencies are 10.3 % and 10.0 %, and the power ratio is 1.02. The comparison results confirm that both methods have the capability of back conversion suppression and power differential reduction. Compared with the adjusting transmittance, adding EO PCs has higher output power and conversion efficiency, which is the first reported method for better balanced multi-wavelength laser output.

Identification of homogeneous chemical kinetic regimes of methane-air ignition

Sensitivity analysis results for ignition delay time (IDT) may be very different depending on the initial temperature, pressure and equivalence ratio φ, but similar in some regions of these variables. This phenomenon was investigated systematically by carrying out ignition simulations and local sensitivity calculations of methane−air mixtures using the Aramco-II-2016 mechanism at 14,417 combinations of initial temperature (changed between 500 and 3000 K), initial pressure (0.05−500 atm) and φ (0.05−8.0) values. The cluster analysis of the sensitivity vectors identified five large kinetically homogeneous regions. Each region has well defined borders in the (T, p φ) space and can be characterized by different sets of important reactions. The related kinetic scheme is very different in each region. Regions 1 and 2 are dominated by catalytic cycles based on species CH3O2/CH3O2H and HO2/H2O2/CH3O, respectively. In regions 3, 4, and 5 the H atoms are converted to CH3 in an identical chain branching sequence, but the back conversion is via three different routes. Literature experimental data on the IDTs of methane−air mixtures were sorted according to these five regions. Regions 1 to 5 contain 214, 328, 3, 0, and 237 experimental data points, respectively. In regions 1, 2 and 5 the data points are well reproduced by the Aramco-II-2016 mechanism, but little or no experimental information is available about kinetic regions 3 and 4. Further experimental exploration of the ignition of methane−air mixtures may aim the study of these regions. A similar approach can be used for the characterization of other combustion systems and sorting the related experimental data.

327 Parameter Updates in the Davis Growth Model for Growth, Intake, and Composition of Modern Angus-Cross Cattle

Abstract The Davis Growth Model is a dynamic model used to estimate body composition and growth in beef cattle by simulating total body DNA and protein turnover. Since model development and parametrization in the 1980s, the model has been re-structured to account for previous rate of protein accretion and prior nutrition. Original parameter estimates for alpha (maintenance constant, where net energy for maintenance is alpha x shrunk body weight0.75; 0.08406) and K2 (protein synthesis rate constant; 0.0444) may not fit modern, heavier, more productive cattle. Angus-cross steers (n = 24; initial body weight 402 ± 12 kg) were fed using automated feed weight stations in group pens (8 steers/pen). Steers were fed a high energy ration twice daily, at 10% greater than the intake from the previous day. Steers were measured for hip height, body weight (BW), and ultrasonic measurements for ribeye area and back fat every 28 d until harvest (d 128). These measurements were used to calculate empty BW, empty body fat, and empty percent body fat for alpha and K2 estimates. Parameter estimates (± SD) were 0.12661 (0.01587) and 0.04919 (0.00220) for alpha and K2, respectively. Parameter estimates in the current study reflect a large increase in apparent maintenance. Maintenance requirements were moderately correlated with back fat thickness and feed conversion efficiency. Protein turnover had very strong correlations with ribeye area and feed conversion efficiency. Average feed conversion efficiency in the current study was 0.17. To evaluate parameter estimates, the model was re-run using the new values for alpha and K2. On average, the model underpredicted final empty body weight by 0.08 kg and empty body fat percent by 0.01%-units. Considering the relatively large variation among observed alpha values and the magnitude of increase compared with those previously reported, further research is required to determine an accurate alpha.

Amino Acid Conjugated Spiropyrans: Synthesis and Photoisomerization Studies

Enantiopure alanine and phenyl alanine derivatized spiropyran syntheses were accomplished. It was found that chiroptical signal was not observed for the chiral merocyanine dyes for all compounds. Nevertheles, the photoisomerization of diastereomeric compounds revealed that the merocyanine -phenyl alanine derived compound has a faster kinetics to spiropyran than merocyanine-alanine derived compound.

Fe2O3 within Na2O–Al2O3– B2O3 glasses to study the structural and optical features changes

This paper aims to study the structural and optical properties of the glass system 75B2O3 + 5Al2O3 + (20-x)Na2O + (x)Fe2O3; (x = 0, 1, 3 and 5 mol. %). The melt quenching approach was utilized to prepare all the glass samples. The Fourier transform infrared (FTIR) results confirmed the back conversion of the BO4 units into BO3 units with a steady increase in nonbridging oxygen content. The absorbance of all the samples was determined in wavelength range (300–650 nm). The overlap between the real absorption edge and an absorption band at about 370 nm produces a pseudo absorption edge accompanied by an error in calculating the optical band gap. To overcome this error, a deconvolution process is performed. The bands from 417 to 469 nm confirm the presence of trivalent iron cations (Fe3+) within the glass matrix. These Fe3+ cations have a distorted octahedral symmetry originating from d-d transitions. The densities (ρemp and ρexp), molar volume (Vm) optical band gap (EOpt), refractive index (n0) and nonlinear refractive index (n2) were determined. The ρemp, ρexp,Vm, n0 and n2 of the prepared glasses show an increasing behavior, with further Fe2O3 doping, while EOpt shows a decreasing one. Further, the addition of Fe2O3 produced an increment in Racah parameters (B and C) values, which in turn reflects the more stability of the bonds between Fe cations and their complexes.

Hybrid Organic–Inorganic Perovskite Semiconductor-Based High-Flux Neutron Detector with BN Converter

Neutrons are analyzed in various fields such as space exploration, neutron radiography, and medicine. When neutrons are employed, a neutron detector is required to control the exposure dose. However, issues such as detector radiation tolerance, response linearity, and γ-ray noise limit the development of effective neutron detectors. Metal halide perovskite based direct conversion radiation detectors exhibit attractive characteristics such as being solution-processable at low temperatures and possessing tunable band gaps, low trap density, high charge carrier mobility, high radiation tolerance, and fast responses. The perovskite device’s potential for high-flux neutron applications has not been greatly determined; however, only related research has been conducted thus far. Here, we demonstrate a hybrid organic–inorganic perovskite semiconductor based neutron detector that satisfies all high-flux neutron detection requirements. The perovskite device was designed to possess a structure similar to that of solar cells and could be driven solely by the built-in potential, without an applied voltage. Using this perovskite device, a neutron detector was designed to maximize the efficiency of the back side conversion configuration and minimize sensitivity variations. Experiments on irradiation with the spectrum neutrons and calculations of the reaction rates revealed a 25 meV neutron sensitivity of 6.0 × 10–17 A n–1 cm–2 and a detection limit of 106 n cm–2 s–1. Further, an optical response test showed that a dynamic detection range with 6–7 orders of magnitude was realized. The detection characteristics for high-flux neutrons indicated a stable operation with no degradation during neutron irradiation at a fluence of −1012 cm–2. Moreover, noise from γ-rays had an insignificant effect on the accuracy of the neutron flux measurements. These results highlight that the proposed neutron detector based on a perovskite solar cell is a suitable monitoring sensor for high-flux neutrons.

Design of an in-situ measurement system for ortho and para liquid hydrogen fractions at ESS

The Cryogenic Moderator System (CMS) is equipped with a catalyst to convert hydrogen from the ortho state to the para state, to keep desirably high parahydrogen fractions in the cold moderators, which is required to deliver a high brightness cold neutron beams to the scientific instruments using neutron scattering. An in-situ measurement system for the ortho and para fractions of liquid hydrogen (OPMS) where a Raman spectroscopy will be used is being developed. The required measurement precision is 0.1% to detect an undesirable shift towards a high orthohydrogen fraction caused by neutron scattering driven para-to-ortho back conversion. The dedicated OPMS sampling line has been designed and is placed in a bypass line from and to the CMS to minimize the hydrogen inventory and to make it physically isolated from the CMS if a sapphire window failure happens. Accident analysis for a hydrogen leak due to the sapphire window failure was carried out using an inhouse-developed simulation code, and the required safety relief size has been determined.

O2 Loaded Germanosilicate Optical Fibers: Experimental In Situ Investigation and Ab Initio Simulation Study of GLPC Evolution under Irradiation

In this work we present a combined experimental and ab initio simulation investigation concerning the Germanium Lone Pair Center (GLPC), its interaction with molecular oxygen (O2), and evolution under irradiation. First, O2 loading has been applied here to Ge-doped optical fibers to reduce the concentration of GLPC point defects. Next, by means of cathodoluminescence in situ experiments, we found evidence that the 10 keV electron irradiation of the treated optical fibers induces the generation of GLPC centers, while in nonloaded optical fibers, the irradiation causes the bleaching of the pre-existing GLPC. Ab initio calculations were performed to investigate the reaction of the GLPC with molecular oxygen. Such investigations suggested the stability of the dioxagermirane (DIOG) bulk defect, and its back conversion into GLPC with a local release of O2 under irradiation. Furthermore, it is also inferred that a remarkable portion of the O2 passivated GLPC may form Ge tetrahedra connected to peroxy bridges. Such structures may have a larger resistance to the irradiation and not be back converted into GLPC.