A Theoretical Study of ãA2 CH2

The potential energy surface and dipole moment surfaces of the ã⁴A₂ electronic state of CH₂⁺ are calculated ab initio using an augmented correlation-consistent polarized valence quadruple-ζ (aug-cc-pVQZ) basis set, with the incorporation of dynamical correlation using the coupled cluster method with single and double excitations and perturbatively connected triple excitations [CCSD(T)]. We use these surfaces in the MORBID program system to calculate rotation and rotation-vibration term values for ã-state CH₂⁺, CD⁺₂, and CHD⁺ and to simulate the rotation and rotation-vibration absorption spectrum of CH₂⁺ in the ã⁴A₂ electronic state. Our work is motivated by studies of CH₂⁺ that use the Coulomb explosion imaging technique and by the goal of predicting spectra that may be obtained from discharge sources. Although the ã state is the lowest-lying excited state above the X?/Ã ground state pair, it turns out to be relatively high-lying, and we determine that T_e(ã)=30447.5 cm⁻¹. The equilibrium bond angle for ã-state CH₂⁺ is only 77.1°; as a result the asymmetric top κ value is close to 0, and the molecule is equally far from the oblate and prolate symmetric top limits in this electronic state.     

Assessment of interstitial water content of articular cartilage with T1 relaxation

The interstitial water content typically increases in the early degeneration of articular cartilage. Previously, T₂ relaxation has been related to water content, yet it is known to be strongly affected by the collagen orientation. Articular cartilage plugs from the bovine patella, femur and tibia (N=20) were mapped for T₁ and T₂ at 9.4 T to test the ability of T₁ relaxation to reflect cartilage water content. As a reference, water and proteoglycan (PG) contents were determined. Significant (P<.01) linear associations were demonstrated between the relaxation rates and tissue water content (R₁: r=−.81, R₂: r=−.60) and PG content (R₁: r=.75). After adjustment for the tissue water content, partial correlation analysis did not show significant associations between the relaxation rates and tissue PG content. After the effect of PGs was removed, significant (P<.05) linear correlation between the relaxation rates and tissue water content (R₁: r=−.48, R₂: r=−.50) was observed. Thus, the spin-lattice relaxation rate is proposed to provide a biomarker for water content in articular cartilage.     

Improved in vivo human carotid artery wall T2 estimation

T₂^? quantification has been shown to noninvasively and accurately estimate tissue iron content in the liver and heart; applying this to thin-walled carotid arteries introduces a new challenge to the estimation process. With most imaging voxels in a vessel being along its boundaries, errors in parameter estimation may result from partial volume mixing and misregistration due to motion in addition to noise and other common error sources. To minimize these errors, we propose a novel technique to reliably estimate T₂^? in thin regions of vessel wall. The technique weights data points to reduce the influence of expected error sources. It uses neighborhoods of data to increase the number of points for fitting and to assess lack of fit for automated outlier detection and deletion. The performance of this method was observed in simulations, phantom and in vivo patient studies and compared to results obtained using a pixelwise linear least squares estimation of T₂^?. The new proposed method showed a closer match to the expected results, and a 4.2-fold decrease in interobserver variability for in vivo studies. This increased confidence in estimation should improve the ability to reliably quantify iron noninvasively in the arterial wall.     

Observation of the K2 4Δg state by cw perturbation-facilitated optical-optical double resonance spectroscopy

This paper reports for the first time both, an experimental observation and theoretical calculations of the K₂ 4³Δ_g state. For the experiment we used cw perturbation-facilitated optical-optical double resonance (PFOODR) spectroscopy. A single mode Ti-sapphire laser and a dye laser served as the pump and probe lasers, respectively. A total of 55 PFOODR signals have been assigned to the 4³Δ_g ← b³Π_u transitions. Absolute vibrational numbering was determined by using quantum defect analysis combined with comparing observed intensities with calculated Franck-Condon factors (FCF). For the former we used known parameters from the 2³Δ_g state since the 2³Δ_g and the 4³Δ_g states belong to the same Rydberg series. We report here our experimental and calculated spectroscopic constants, the corresponding RKR potential energy curve, the Franck-Condon table for the 4³Δ_g ↔ b³ Π_u system, as well as a comparison with the theoretical potential energy curve. The T_e value is found to be 28408.938(52) cm⁻¹.     

MBE growth and properties of T′-La2CuO4 thin films

We prepared thin films of T′-La₂CuO₄, which usually crystallizes in the T structure, by MBE, and investigated their properties while systematically changing the post-reduction conditions with a view towards obtaining superconductivity along the lines of the parent compound superconductors we have recently reported (O. Matsumoto et al., Phys. Rev. B 79 (2009) 100508(R)). The results indicate that the optimal reduction window is very narrow, near which metallic conductivity is obtained down to 50 K. The resistivity of the T′-La₂CuO₄ films is in the range of 10⁻²–10⁻³ Ω cm, which is several orders of magnitude lower than that of the counterpart T-La₂CuO₄, the implication of which is briefly discussed from the viewpoint of the difference in electronic structure induced by different oxygen coordination.     

Measurement and correction of stimulated echo contamination in T2-based iron quantification

The purpose of this study was to characterize the effects of stimulated echo contamination on MR-based iron measurement derived from quantitative T₂ images and develop a method for retrospective correction. Two multiple spin-echo (MSE) pulse sequences were implemented with different amounts of stimulated echo contamination. Agarose-based phantoms were constructed that simulate the relaxation and susceptibility properties of tissue with different concentrations of dispersed (ferritin-like) and aggregated (hemosiderin-like) iron. Additionally, myocardial iron was assessed in nine human subjects with transfusion iron overload. These data were used to determine the influence of stimulated echoes on iron measurements made by an MR-based iron quantification model that can separately measure dispersed and aggregated iron. The study found that stimulated echo contamination caused an underestimation of dispersed (ferritin-like) iron and an overestimation of aggregated (hemosiderin-like) iron when applying this model. The relationship between the measurements made with and without stimulated echo appears to be linear. The findings suggest that while it is important to use MSE sequences with minimal stimulated echo in T₂-based iron quantification, it appears that data acquired with sub-optimal sequences can be retrospectively corrected using the methodology described here.     

Spectroscopy of X2Y4 (D2h) molecules: tensorial formalism adapted to the O(3)⊃D2h chain, Hamiltonian and transition moment operators

A tensorial formalism adapted to the case of the X₂Y₄ molecules with D_2h symmetry has been developed in the same way as in the previous works on XY₄ (T_d) and XY₆ (O_h) spherical tops and XY₅Z (C_4v) symmetric tops. Here, we use the O(3)⊃D_2h group chain. All the coupling coefficients and formulas for the computation of matrix elements are given for this chain and used in the case of the Hamiltonian and transition moment operators.     

The structural and magnetic properties of Ni2Mn1−xBxGa Heusler alloys

The influence of the substitution of manganese by boron on the crystal structure and magnetic properties of Ni₂Mn_1−xB_xGa Heusler alloys with 0?x?0.5 has been investigated using X-ray diffraction, thermal expansion, resistivity, and magnetization measurements. The samples with concentrations x<0.25 were found to be of single phase and belonged to the cubic L2₁ crystal structure at room temperature. Crystal cell parameters of the alloys decreased from 5.830 to 5.825 Å with increasing boron concentration (x) from 0 to 0.25. The alloys were ferromagnetically ordered at 5 K and the saturation magnetization decreased with increasing boron concentration. The ferromagnetic ordering and structural transition temperatures for 0?x?0.3 have been observed and the phase (x−T) diagram of the Ni₂Mn_1−xB_xGa system was constructed. The phase (x−T) diagram indicates that the ground state of Ni₂Mn_1−xB_xGa alloys belongs to ferromagnetic martensitic, premartensitic, and austenitic phases in x?0.12, 0.12<x?0.18, and 0.18<x?0.3, respectively. The relative influence of cell parameters and electron concentrations on the phase diagram is discussed.     

High-resolution FTIR measurement of the ν4 band of methylene fluoride-d2

A high-resolution (0.002 cm⁻¹) infrared absorption spectrum of methylene fluoride-d₂ (CD₂F₂) of the lowest fundamental mode ν₄ in the region from 460 to 610 cm⁻¹ has been measured on a Bruker IFS 120-HR Fourier transform infrared spectrometer. More than 3500 transitions have been assigned in this B-type band centered at 521.9 cm⁻¹. The data have been combined with upper state pure rotational measurements in a weighted least-squares fit to obtain molecular constants for the upper state resulting in an overall standard deviation of 0.00018 cm⁻¹. Accurate value for the band origin (521.9578036 cm⁻¹) has been obtained and inclusion of transitions with very high J (?60) and K_a (?34) values has resulted in improved precision for sextic centrifugal distortion constants, in particular D_K, H_KJ, and H_K.     

具有介孔结构的MnSiO3@Fe3O4@C纳米粒子的制备以及作为pH响应的T1-T2*双模MRI造影剂的研究应用

本文通过一个简单的、温和的方案制备了平均尺寸为120 nm,介孔结构的纳米粒子MnSiO₃@Fe₃O₄@C. 粒子的细胞毒性微小,可以用作T₁-T₂^*双模MRI造影剂. 酸性条件下MnSiO₃@Fe₃O₄@C释放出大量的Mn²⁺缩短T₁弛豫时间,提高成像分辨率. 超顺磁性的Fe₃O₄可以增强T₂对比成像,检测病变组织. 类似于肿瘤微环境/细胞器的酸性PBS(pH=5.0)中Mn²⁺的释放率达到31.66%,约为中性条件(pH=7.4)下的7倍. 释放的Mn²⁺通过内吞作用被细胞摄取,经肾脏排出,细胞毒性实验表明,MnSiO₃@Fe₃O₄@C具有低的细胞毒性,即使高浓度的200 ppm MnSiO₃@Fe₃O₄@C对HeLa细胞的毒性也相对较小. 对荷瘤小鼠静脉注射定量MnSiO₃@Fe₃O₄@C后,可以观察到一个快速增强的对比成像,给药24 h后,T₁MRI信号显著增强,达到132%,而T₂信号则明显降低至53.8%,活体MR成像证明了MnSiO₃@Fe₃O₄@C可以同时作为阳性和阴性造影剂. 此外,得益于介孔MnSiO₃优秀的酸敏感性,MnSiO₃@Fe₃O₄@C可以作为一种潜在的药物载体,实现肿瘤的诊疗一体化.     

External cavity tunable diode laser spectra of the ν1 + 2ν4 stretch-bend combination bands of NH3 and NH3

The ammonia ν₁ + 2ν₄ perpendicular stretch-bend combination band has been investigated in spectra of ¹⁴NH₃ and ¹⁵NH₃ recorded in the 6400-6800 cm⁻¹ region with an external cavity tunable diode laser (ECTDL) spectrometer. For ¹⁴NH₃, new assignments were determined initially by extrapolating from published low-J jet-cooled beam results up to transitions of higher J and K. Corresponding ν₁ + 2ν₄ transitions for the ¹⁵NH₃ species were then found by identifying similar patterns of lines with a characteristic downshift of approximately 9.7 cm⁻¹. Assignments were confirmed employing ground-state combination differences. Term values, a-s inversion splittings, l-doubling energies and parameter estimates from simple single-state fits are reported for the two ammonia species.     

Feasibility of similarity coefficient map in improving morphological evaluation of T2* weighted MRI for renal cancer

The purpose of this paper is to investigate the feasibility of similarity coefficient map (SCM) in improving morphological evaluation of T₂^* weighted (T₂^*W) magnatic resonance imaging (MRI) for renal cancer. Simulation studies and in vivo 12-echo T₂^*W experiments for renal cancers were performed for this purpose. The results of the first simulation study suggest that SCM can reveal small structures which are hard to be distinguished from the background tissue in T₂^*W images and the corresponding T₂^* map. The capability of improving morphological evaluation is likely due to the improvement in signal to noise ratio (SNR) and carrier to noise ratio (CNR) by SCM technique. Compared with T₂^*W images, SCM can improve SNR by a factor ranging from 1.87 to 2.47. Compared with T₂^* maps, SCM can improve SNR by a factor ranging from 3.85 to 33.31. Compared with T₂^*W images, SCM can improve CNR by a factor raging from 2.09 to 2.43. Compared with T₂^* maps SCM can improve CNR by a factor raging from 1.94 to 8.14. For a given noise level, the improvements of SNR and CNR depend mainly on the original SNRs and CNRs in T₂^*W images, respectively. In vivo experiments confirmed the results of the first simulation study. The results of the second simulation study suggest that more echoes are used to generate SCM, and higher SNR and CNR can be achieved in SCM. In conclusion, SCM can provide improved morphological evaluation of T₂^*W MR images for renal cancer by unveiling fine structures which are ambiguous or invisible in the corresponding T₂^*W MR images and T₂^* maps. What is more, in practical application, for a fixed total sampling time, one should increase the number of echoes as much as possible to achieve SCMs with better SNR and CNR.     

Current-induced effect on resistivity and magnetoresistance of La0.67Ba0.33MnO3 manganite

The influence of dc biasing current on temperature dependence of resistivity and low-field magnetoresistance (MR) of La_0.67Ba_0.33MnO₃ bulk sample is reported. A prominent finding is the change in resistivity around the insulator-to-metal transition temperature (T_IM) and the change in MR around the ferromagnetic transition temperature (T_C). The decrease in MR around T_C at higher biasing current indicates a strong interaction between carrier spin and spin of Mn ions resulting in a higher alignment of Mn ion spins. Change in resistivity around T_IM is interpreted in the framework of percolative conduction model based on the mixed phase of itinerant electrons and localized magnetic polarons.     

Magnetic phase transitions in Nd7Rh3 single crystal

Magnetic phase transitions in rare earth intermetallic compound Nd₇Rh₃ have been investigated using a single crystal. Measurement results of magnetization, magnetic susceptibility, specific heat, and electrical resistivity reveal that Nd₇Rh₃ has two magnetic phase transitions at T_N=34 K, T_t2=9.1 K and a change of the magnetic feature at T_t1=6.8 K in the absence of an external magnetic field. Antiferromagnetic orderings exist in all the three magnetic states; a large magnetic anisotropy between the c-axis and the c-plane is observed. In the magnetic phase below T_t2, an irreversible field-induced magnetic phase transition takes place in the c-plane; after removing external magnetic field, a coexistence state of ferro- and antiferromagnetic ordering or a ferrimagnetic state having a remanent magnetization M_R is stabilized. The M_R decays to a certain value for several hours after the first process; a magnetic field cooling effect was also observed in the c-plane below T_t2. In the antiferromagentic state above T_t2, the irreversibility disappears and an ordinary antiferromagnetic state takes place. As the origin of this phenomenon, a kind of martensitic structural transition that is observed in Gd₅Ge₄ can be considered.     

Structure and magnetostriction of Tb0.2Pr0.8(Fe0.4Co0.6)1.93−xCx intermetallic compounds

The structure and magnetostriction of Tb_0.2Pr_0.8(Fe_0.4Co_0.6)_1.93−xC_x intermetallic compounds were studied by X-ray diffraction and magnetic measurements. Almost a single cubic Laves phase forms in the alloys for x ≤0.20, and a small amount of C can inhibit the formation of the 1:3 phase. The lattice parameter increases when 0≤x≤0.15, while the T_c and the spontaneous magnetization decreases with increasing x. The lattice parameter decreases slowly when 0.15≤x≤0.30, while the T_c decreases evidently with increasing x. The magnetostriction λ_a (=λ_∥-λ_⊥) is improved at low magnetic fields at room temperature for the compounds with 0.05≤x≤0.10, indicating that these C-containing compounds are promising magnetostrictive materials.     

On the ferromagnetism of AlFe2B2

Based on extensive Mossbauer effect (ME) and magnetization measurements, the orthorhombic AlFe₂B₂ was characterized as a ferromagnet (FM) because this character is evident as an onset of a FM transition at T_c=320 K and characteristic magnetizations isotherms below T_c. At liquid helium temperatures, the magnetization saturates to μ_sat≈1μ_B per Fe atom; a value which is half the one reported for the iron metal indicating a relatively more filled 3d band. The ME analysis revealed a hyperfine field H(0) of 88(2) kOe, an isomer shift (relative to Fe) of 0.50(2) mm/s, and a quadrupole parameter of 0.02 mm/s: all parameters extrapolated to zero Kelvin. The itinerant character of the magnetic moment will be discussed.     

Exchange coupling behavior in bimagnetic CoFe2O4/CoFe2 nanocomposite

In this work we report a study of the magnetic behavior of ferrimagnetic oxide CoFe₂O₄ and ferrimagnetic oxide/ferromagnetic metal CoFe₂O₄/CoFe₂ nanocomposite. The latter compound is a good system to study hard ferrimagnet/soft ferromagnet exchange coupled. Two steps were followed to synthesize the bimagnetic CoFe₂O₄/CoFe₂ nanocomposite: (i) first, preparation of CoFe₂O₄ nanoparticles using a simple hydrothermal method, and (ii) second, reduction reaction of cobalt ferrite nanoparticles using activated charcoal in inert atmosphere and high temperature. The phase structures, particle sizes, morphology, and magnetic properties of CoFe₂O₄ nanoparticles were investigated by X-Ray diffraction (XRD), Mossbauer spectroscopy (MS), transmission electron microscopy (TEM), and vibrating sample magnetometer (VSM) with applied field up to 3.0 kOe at room temperature and 50 K. The mean diameter of CoFe₂O₄ particles is about 16 nm. Mossbauer spectra revealed two sites for Fe³⁺. One site is related to Fe in an octahedral coordination and the other one to the Fe³⁺ in a tetrahedral coordination, as expected for a spinel crystal structure of CoFe₂O₄. TEM measurements of nanocomposite showed the formation of a thin shell of CoFe₂ on the cobalt ferrite and indicate that the nanoparticles increase to about 100 nm. The magnetization of the nanocomposite showed a hysteresis loop that is characteristic of exchange coupled systems. A maximum energy product (BH)_max of 1.22 MGOe was achieved at room temperature for CoFe₂O₄/CoFe₂ nanocomposites, which is about 115% higher than the value obtained for CoFe₂O₄ precursor. The exchange coupling interaction and the enhancement of product (BH)_max in nanocomposite CoFe₂O₄/CoFe₂ are discussed.     

The analysing powers iT11, T20, T21 and T22 in deuteron-deuteron elastic scattering between 6 and 11.5 MeV

The angular distributions of the analysing powers iT₁₁(θ), T₂₀(θ), T₂₁(θ) and T₂₂(θ) of the elastic scattering of polarized deuterons on deuterons have been measured at deuteron energies of 6.0, 8.0, 10.0 and 11.5 MeV. The vector component has small but non-zero values which change sign between 6.0 and 10.0 MeV. The tensor components have increasing values with increasing energy. The results are discussed in respect of resonances in ⁴He and a term scheme is proposed for a complete phase-shift analysis.     

Retrospective correction for T1-weighting bias in T2 values obtained with various spectroscopic spin-echo acquisition schemes

Localized tissue transverse relaxation time (T₂) is obtained by fitting a decaying exponential to the signals from several spin-echo experiments at different echo times (TE). Unfortunately, time constraints in magnetic resonance spectroscopy (MRS) often mandate in vivo acquisition schemes at short repetition times (TR), that is, comparable with the longitudinal relaxation constant (T₁). This leads to different T₁-weighting of the signals at each TE. Unaccounted for, this varying weighting causes systematic underestimation of the T₂'s, sometimes by as mush as 30%. In this article, we (i) analyze the phenomenon for common MRS spin-echo T₂ acquisition schemes; (ii) propose a general post hoc T₁-bias correction for any (TR, TE) combination; (iii) show that approximate knowledge of T₁ is sufficient, since a 20% uncertainty in T₁ leads to under 3% bias in T₂; and consequently, (iv) efficient, precision-optimized short TR spin-echo T₂ measurement protocols can be designed and used without risk of accuracy loss. Tables of correction for single-refocusing (conventional) spin-echo and double refocusing, such as, PRESS acquisitions, are provided.     

Specific heat of EuIn2P2 at high magnetic fields

We have carried out specific heat measurements on EuIn₂P₂ at high magnetic fields perpendicular to the c-axis in the hexagonal crystal structure in order to understand its thermal properties. The temperature dependence of the specific heat exhibits a clear λ-type anomaly due to a magnetic transition at , indicating that the magnetic transition is of second-order. The λ-type anomaly becomes markedly broader with increasing the magnetic field. This remarkable field-dependence is consistent with the results of previous magnetization measurements which suggest that Eu²⁺ magnetic moments align ferromagnetically perpendicular to the c-axis below T_C. In addition, a hump in the specific heat is observed around 7 K, which can be ascribed to the Zeeman splitting of the Eu²⁺ multiplet by internal magnetic fields.