Search

We report oxygen, calcium, titanium and 26 Al– 26 Mg isotope systematics for spinel-hibonite inclusions (SHIBs), a class of calcium–aluminum-rich inclusions (CAI) common in CM chondrites. In contrast to previous studies, our analyses of 33 SHIBs and four SHIB-related objects obtained with high spatial resolution demonstrate that these CAIs have a uniform Δ 17 O value of approximately −23‰, similar to many other mineralogically pristine CAIs from unmetamorphosed chondrites (e.g., CR, CV, and Acfer 094). Five SHIBs studied for calcium and titanium isotopes have no resolvable anomalies beyond 3 σ uncertainties. This suggests that nucleosynthetic anomalies in the refractory elements had been significantly diluted in the environment where SHIBs with uniform Δ 17 O formed. We established internal 26 Al– 26 Mg isochrons for eight SHIBs and found that seven of these formed with uniformly high levels of 26 Al (a multi-CAI mineral isochron yields an initial 26 Al/ 27 Al ratio of ∼4.8 × 10 −5 ), but one SHIB has a smaller initial 26 Al/ 27 Al of ∼ 2.5 × 10 −5 , indicating variation in 26 Al/ 27 Al ratios when SHIBs formed. The uniform calcium, titanium and oxygen isotopic characteristics found in SHIBs with both high and low initial 26 Al/ 27 Al ratios allow for two interpretations. (1) If subcanonical initial 26 Al/ 27 Al ratios in SHIBs are due to early formation, as suggested by Liu et al. (2012), our data would indicate that the CAI formation region had achieved a high degree of isotopic homogeneity in oxygen and refractory elements before a homogeneous distribution of 26 Al was achieved. (2) Alternatively, if subcanonical ratios were the result of 26 Al– 26 Mg system resetting, the clustering of SHIBs at a Δ 17 O value of ∼−23‰ would imply that a 16 O-rich gaseous reservoir existed in the nebula until at least ∼0.7 Ma after the formation of the majority of CAIs. [ABSTRACT FROM AUTHOR]

The SHELS velocity filter originated upon reconstruction of the VASSILISSA electrostatic separator used for investigations of heavy nuclei produced in complete fusion reactions. The goals of this modernization were to increase the transmission of products of asymmetric reactions and to extend the region of reactions to be investigated up to symmetric combinations. The first tests of the set-up were performed with the beams of accelerated 22 Ne, 40 Ar, 48 Ca, and 50 Ti ions. [ABSTRACT FROM AUTHOR]

We report the results of the deepest Galactic plane (|b| < 17. . 5) survey in the 67.9 and 78.4 keV nuclear de-excitation lines of titanium-44 (44Ti) performed using the data acquired with the IBIS/ISGRI instrument onboard the INTEGRAL satellite during 12 yr of operation. The peak sensitivity of our survey reached an unprecedented level of 4.8 ? 10-6 ph cm-2 s-1 (3σ) that improves the sensitivity of the survey done by Compton Gamma-Ray Observatory/COMPTEL by a factor of ~5. As a result, constraining upper limits for all sources from the catalogue of Galactic supernova remnants (SNRs; Green 2014) are derived. These upper limits can be used to estimate the exposure needed to detect 44Ti emission from any known SNR using existing and prospective X- and gamma-ray telescopes. Among the youngest Galactic SNRs, only Cas A shows significant 44Ti emission flux in good agreement with the NuSTAR measurements. We did not detect any other sources of titanium emission in the Galactic plane at significance level higher than 5σ confirming previous claims of the rarity of such 44Ti-producing SNRs. [ABSTRACT FROM AUTHOR]

Background: No data on the fusion excitation function of 48Ti + 58Fe in the energy region near the Coulomb barrier existed prior to the present work, while fusion of 58Ni + 54Fe was investigated in detail some years ago, down to very low energies, and clear evidence of fusion hindrance was noticed at relatively high cross sections. 48Ti and 58Fe are soft and have a low-lying quadrupole excitation lying at ≈800-900 keV only. Instead, 58Ni and 54Fe have a closed shell (protons and neutrons, respectively) and are rather rigid. Purpose: We aim to investigate (1) the possible influence of the different structures of the involved nuclei on the fusion excitation functions far below the barrier and, in particular, (2) whether hindrance is observed in 48Ti + 58Fe, and to compare the results with current coupled-channels models. Methods: 48Ti beams from the XTU Tandem accelerator of INFN-Laboratori Nazionali di Legnaro were used. The experimental setup was based on an electrostatic beam separator, and fusion-evaporation residues (ERs) were detected at very forward angles. Angular distributions of ERs were measured. Results: Fusion cross sections of 48Ti + 58Fe have been obtained in a range of nearly six orders of magnitude around the Coulomb barrier, down to ≲2 μb. The sub-barrier cross sections of 48Ti + 58Fe are much larger than those of 58Ni + 45Fe. Significant differences are also observed in the logarithmic derivatives and astrophysical S factors. No evidence of hindrance is observed, because coupled-channels calculations using a standard Woods- Saxon potential are able to reproduce the data in the whole measured energy range. Analogous calculations for 58Ni + 45Fe predict clearly too large cross sections at low energies. The two fusion barrier distributions are wide and display a complex structure that is only qualitatively fit by calculations. Conclusions: It is pointed out that all these different trends originate from the dissimilar low-energy nuclear structures of the involved nuclei. In particular, the strong quadrupole excitations in 48Ti and 58Fe produce the relative cross section enhancement and make the barrier distribution ≈ 2 MeV wider, thus probably pushing the threshold for hindrance below the measured limit. [ABSTRACT FROM AUTHOR]

In the present work, novel isolated Ti-SBA-15-spherical and Ti-KIT-6 (Si/Ti = 200, 100 and 50) photocatalysts have been synthesized; optimized through N 2 -adsorption/desorption, SEM, EDX, UV–Vis, FT-IR, XPS and TEM analysis techniques; and explored for the photocatalytic reduction of greenhouse gas CO 2 to renewable fuels. The Ti-KIT-6 (Si/Ti = 100) showed better CH 4 production rate (4.15 μmol gcat. −1 h −1 ) than the corresponding Ti-KIT-6-dried (2.63 μmol gcat. −1 h −1 ) and the Ti-SBA-15-calcined/dried (1.85, 3.45 μmol gcat. −1 h −1 , respectively) in the initial optimization reactions. CH 3 OH, CO, and H 2 are the other main fuel products produced by the Ti-KIT-6-calcined (Si/Ti = 100). The increased surface concentration of OH groups found in the Ti-KIT-6-calcined (Si/Ti = 100) than the other two ratios (Si/Ti = 200, 50), the presence of more accessible surface reaction active sites due to the lower number of Ti–O–Ti or TiO 2 agglomerates, and the more isolated Ti species which are uniformly dispersed on the 3-D KIT-6 mesoporous silica support without collapsing the mesoporous structure, have boosted the higher activity, which is even higher than the best commercial Aeroxide P25 TiO 2 . The reaction has been preceded by the competitive adsorption of CO 2 and H 2 O vapors. The UV light source/intensity, H 2 O/CO 2 ratios and catalyst shapes are the key factors that influence the performance of the catalyst, and therefore, these parameters have been optimized to boost the fuel products. [ABSTRACT FROM AUTHOR]

The nuclear root-mean-square charge radii and nuclear density distributions have been calculated in the framework of relativistic self-consistent mean-field models based on density-dependent meson-exchange relativistic energy density functional for even isotopes of Ti (A = 44-56). The calculations agree well with available laser spectroscopic measurements for 44,46,48,50Ti, and results for neutron-rich isotopes are reported. The semimicroscopic proton optical potentials for 44-56Ti have been derived by folding the target matter density with the extended Jeukenne-Lejeune-Mahaux energy- and density-dependent intemucleon interaction and are used to calculate the differential elastic scattering and reaction cross sections at 65 MeV. The calculated differential cross sections reproduce the corresponding experimental values for stable even isotopes, and predictions are presented for 44,52,54,56Ti. The calculations reveal a prominent kink at the N = 28 shell closure observed in the variation of reaction cross sections, consistent with mean-square charge radii systematics in the Ti isotopic chain. [ABSTRACT FROM AUTHOR]

Decay spectroscopy of 184Tl has been performed at the CERN Isotope Separator On-Line (ISOLDE) facility. An excitation energy of 506.1(1) keV and a half-life of 47.1(7) ms of the intruder based (10-) state have been extracted. The internal decay characteristics of this state are determined and discussed, extending the systematics of such states in the even-mass thallium nuclei below neutron midshell at N = 104. The retardation factors of the isomeric M2 and E3 transitions are deduced and compared with retardation factors in neighboring odd-mass and even-mass thallium isotopes. The new information is combined with a review of hindered and unhindered a-decay data of Bi187-192 populating levels in daughter nuclei 183-188Tl and supports the interpretation of the intruder character of the (10-) state in 184Tl. [ABSTRACT FROM AUTHOR]

Thermodynamic quantities of 46 Ti have been calculated in the framework of the BCS model with inclusion of modified nuclear pairing gap (MPBCS) that was proposed in our previous publication. Using modified paring gap results in an S-shaped heat capacity curve at critical temperature with a smooth behavior instead of singular behavior of the same curve in the BCS calculations. In addition the thermal quantities have been extracted within the framework of a canonical ensemble according to the new experimental data on nuclear level densities measured by the Oslo group. Comparison shows a good agreement between our calculations in MPBCS and the extracted quantities in the canonical ensemble framework. [ABSTRACT FROM AUTHOR]

The space radiation environment consists of multiple species of charged particles, including 28Si, 48Ti and protons that may impact cognition, but their damaging effects have been poorly defined. In mouse studies, C57Bl6/J homozygous wild-type mice and genetic mutant mice on a C57Bl6/J background have typically been used for assessing effects of space radiation on cognition. In contrast, little is known about the radiation response of mice on a heterozygous background. Therefore, in the current study we tested the effects of 28Si, 48Ti and proton radiation on hippocampus-dependent contextual fear memory and hippocampus-independent cued fear memory in C57Bl6/J × DBA2/J F1 (B6D2F1) mice three months after irradiation. Contextual fear memory was impaired at a 1.6 Gy dose of 28Si radiation, but not cued fear memory. 48Ti or proton irradiation did not affect either type of memory. Based on earlier space radiation cognitive data in C57Bl6/J mice, these data highlight the importance of including different genetic backgrounds in studies aimed at assessing cognitive changes after exposure to space radiation. [ABSTRACT FROM AUTHOR]

The photodisintegration of titanium isotopes in the giant-dipole-resonance energy region is studied by the photon-activation method. Bremsstrahlung photons whose spectrum has the endpoint energy of 55 MeV is used. The yields and integrated cross sections are determined for photoproton reactions on the titanium isotopes Ti. The respective experimental results are compared with their counterparts calculated on the basis of the TALYS code and a combined photonucleon-reaction model. The TALYS code disregards the isospin structure of the giant dipole resonance and is therefore unable to describe the yield of photoproton reactions on the heavy titanium isotopes Ti. [ABSTRACT FROM AUTHOR]

A portable fiber-optic laser-induced breakdown spectroscopy (FO-LIBS) system was developed and employed to quantitatively analyze Mn and Ti elements in pig iron. The ablated craters produced by FO-LIBS are shallower with flatter bottom surfaces as compared with those produced by a conventional LIBS system without using optical fibers to deliver the laser pulses. This is beneficial on the special occasions requiring shallower destruction. The time-resolved images of plasma plumes were obtained and compared using both LIBS systems. Plasmas with lower temperature and electron density generated by the FO-LIBS system were thinner and more uniform, which means a lower self-absorption. Using the FO-LIBS system, the coefficients of determination (R2 factors) of calibration curves for Mn and Ti elements were 0.997 and 0.998, respectively. The leave-one-out cross-validation (LOOCV) method was used to evaluate the detection accuracy. The root-mean-square errors of cross-validation (RMSECV) for Mn (concentration range 0.072–2.06 wt%) and Ti (concentration range 0.006–0.399 wt%) elements were 0.0501 and 0.0054 wt%, respectively. These results are comparable with or even slightly better than those obtained by conventional LIBS. Furthermore, the FO-LIBS system is more compact and cost effective, more suitable for harsh environments, and hence more promising for industrial applications. [ABSTRACT FROM AUTHOR]

A systematic study of the Raman spectra of Pb(Zr1-xTix)O3 (PZT) ceramics has been performed in a broad temperature interval (10-600 K) and a broad Ti/Zr concentration range around the morphotropic phase boundary (x = 0.25-0.70). The number of the spectral components was estimated by a standard fitting procedure with damped harmonic oscillators as well as by counting the number of peaks and shoulders with the help of a purposely designed mathematical analysis based on frequency derivatives of the Raman spectra. This last method proves to be very useful to study Raman spectra of disordered materials. For the case of PZT, the comparison with the Raman modes of PbTiO3 allows us to assign the phonon bands on both sides of the morphotropic phase boundary, and the crossover from the tetragonal to rhombohedral phase spectra is clearly visible. However, there are no indications of a systematic splitting of the JS-symmetry modes into monoclinic A'-A" doublets in the morphotropic samples. Detailed adjusting of the response function to the spectrum requires to assume additional Raman-active modes, but this holds for a much broader concentration range than that of the anticipated monoclinic phase. In particular, the lowest frequency transverse optic mode of E-symmetry (soft mode of the ferroelectric phase transition) is split into two components, a THz frequency anharmonic (central modelike) component and a resonant component (at ω ~ 80 cm-1), both related to the same normal coordinate. The additional Raman band appearing in this frequency range (ω ~ 65 cm-1) at low temperatures is rather associated with the antiphase tilt vibrations of the oxygen octahedra. [ABSTRACT FROM AUTHOR]