Overcoming depolarizing resonances with dual helical partial Siberian snakes

Acceleration of polarized protons in the energy range of 5 to 25 GeV is challenging. In a medium energy accelerator, the depolarizing spin resonances are strong enough to cause significant polarization loss but full Siberian snakes cause intolerably large orbit excursions and are also not feasible since straight sections usually are too short. Recently, two helical partial Siberian snakes with double pitch design have been installed in the Brookhaven Alternating Gradient Synchrotron (AGS). With a careful setup of optics at injection and along the energy ramp, this combination can eliminate the intrinsic and imperfection depolarizing resonances otherwise encountered during acceleration to maintain a high intensity polarized beam in medium energy synchrotrons. The observation of partial snake resonances of higher than second order will also be described.     

High-resolution FTIR spectroscopy of HCFC-31 in the 950−1160 cm−1 region: rovibrational analysis and resonances in the ν4, ν9 and ν5+ν6 bands of CH235ClF

The FTIR spectrum of CH₂ClF (natural isotopic mixture) was investigated in the ν₄, ν₉ and ν₅+ν₆ band region between 950 and 1160 cm^?1 at the resolution of 0.004 cm^?1. The ν₄ and ν₅+ν₆ vibrations of A′ symmetry give rise to a/b hybrid bands with a predominant a-type component. The ν₉ vibration of A^″ symmetry, expected with a c-type band contour, shows an intense Coriolis-induced parallel component (ΔK_a = 0, ΔK_c = 0) derived from mixing with the v₄ = 1 vibrational state. The high-resolution spectra of ν₉ and ν₅+ν₆ have been analyzed for the first time, while the assignments of the ν₄ band, previously investigated, have been extended to higher J and K_a values in the b-type component. The spectral analysis resulted in the identification of 1508, 809 and 349 transitions for the ν₄, ν₉ and ν₅+ν₆ bands of CH₂³⁵ClF, respectively. Besides the strong first-order a- and b-type Coriolis resonances between ν₄ and ν₉, the ν₅+ν₆ vibration was found to interact through a c-type Coriolis with the ν₄ and 3ν₆. High-order anharmonic resonance (ΔK_a = ±2) between ν₄ and ν₅+ν₆ was also established. All the assigned data were simultaneously fitted using the Watson's A-reduction Hamiltonian in the I^r representation and the relevant perturbation operators. The model employed includes five types of resonances within the tetrad ν₄/ν₉/ν₅+ν₆/3ν₆. Α set of spectroscopic constants for ν₄, ν₉ and ν₅+ν₆ bands as well as parameters for the dark state 3ν₆ and seven coupling terms have been determined. The simulations performed in different spectral regions satisfactorily reproduce the experimental data.     

On the mechanism of the broadening of the proton vibrational IR band in weak hydrogen bonds. Double adiabatic approximation

It is proposed that broadening of the ν_s (AH) IR band is due to the ν_s (AH) and ν_σ (AH…B) mode coupling and to the stochastic variation of the equilibrium distance R_e (A…B) modulating the proton vibration. The R_e disordering variation is caused by a coupling of the ν_σ mode with the low frequency oscillators (ν_Q) of the medium and of the complex as such. Besides, the (ν_σ, ν_Q) and (ν_s, ν_σ) couplings cause a ν_s frequency shift. Both the band broadening and the frequency shift increase with higher force constants responsible for (ν_σ, ν_Q) mode coupling. Furthermore the Q_i low frequency stochastic vibrations directly modulate the ν_σ (AH…B) vibration and the free AH groups stretching vibration (ν^o_s) causing some broadening at their bands which is however several times smaller than the ν_s band broadening in the complex. Several examples are reported to confirm the proposed model.     

Polarized proton collisions at 205 GeV at RHIC

The Brookhaven Relativistic Heavy Ion Collider (RHIC) has been providing collisions of polarized protons at a beam energy of 100 GeV since 2001. Equipped with two full Siberian snakes in each ring, polarization is preserved during acceleration from injection to 100 GeV. However, the intrinsic spin resonances beyond 100 GeV are about a factor of 2 stronger than those below 100 GeV making it important to examine the impact of these strong intrinsic spin resonances on polarization survival and the tolerance for vertical orbit distortions. Polarized protons were first accelerated to the record energy of 205 GeV in RHIC with a significant polarization measured at top energy in 2005. This Letter presents the results and discusses the sensitivity of the polarization survival to orbit distortions.     

Cold attractive spin polarized Fermi lattice gases and the doped positive U Hubbard model

Experiments on polarized fermion gases performed by trapping ultracold atoms in optical lattices allow the study of an attractive Hubbard model for which the strength of the on-site interaction is tuned by means of a Feshbach resonance. Using a well-known particle-hole transformation we discuss how results obtained for this system can be reinterpreted in the context of a doped repulsive Hubbard model. In particular, we show that the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state corresponds to the striped state of the two-dimensional doped positive U Hubbard model. We then use the results of numerical studies of the striped state to relate the periodicity of the FFLO state to the spin polarization. We also comment on the relationship of the d(x(2)-y(2)) superconducting phase of the doped 2D repulsive Hubbard model to a d-wave spin density wave state for the attractive case.     

Quantification of regional intrapulmonary oxygen partial pressure evolution during apnea by (3)He MRI

We present a new method to determine in vivo the temporal evolution of intrapulmonary oxygen concentrations by functional lung imaging with hyperpolarized (3)Helium ((3)He-->). Single-breath, single-bolus visualization of (3)He--> administered to the airspaces is used to analyze nuclear spin relaxation caused by the local oxygen partial pressure p(O(2))(t). We model the dynamics of hyperpolarization in the lung by rate equations. Based hereupon, a double acquisition technique is presented to separate depolarization by RF pulses and oxygen induced relaxation. It permits the determination of p(O(2)) with a high accuracy of up to 3% with simultaneous flip angle calibration using no additional input parameters. The time course of p(O(2)) during short periods of breathholding is found to be linear in a pig as well as in a human volunteer. We also measured the wall relaxation time in the lung and deduced a lower limit of 4.3 min.     

Common energy scale for magnetism and superconductivity in underdoped cuprates: a muon spin resonance investigation of (Ca(x)La(1-x)) (Ba(1.75-x)La(0.25+x))Cu3O(y)

We characterize the spontaneous magnetic field, and determine the associated temperature T(g), in the superconducting state of (Ca(x)La(1-x)) (Ba(1.75-x)La(0.25+x)) Cu(3)O(y) using zero and longitudinal field muon spin resonance measurements for various values of x and y. Our major findings are (i) T(g) and T(c) are controlled by the same energy scale, (ii) the phase separation between hole poor and hole rich regions is a microscopic one, and (iii) spontaneous magnetic fields appear gradually with no moment size evolution.     

Electromagnetic behaviors in a bilayered metal helical structure

We studied both numerically and experimentally electromagnetic behaviors of a bilayered metal helical structure in the microwave-frequency. Two resonances are found in the transmission spectrum of the circularly polarized wave which has the same handedness with the helices. The resonance frequencies are almost independent on the distance between the two layers. In addition, the center frequency of full width at half-maximum (FWHM) in the transmission spectrum is approximately inversely proportional to the distance between the two layers.     

High resolution infrared study of the 2ν9 and ν4 bands of 10BF2OH and 11BF2OH: evidence of large amplitude effects for the OH-torsion and OH-bending modes in the 92 and 41 excited states

High resolution (2–3?×?10^?3?cm^?1) Fourier transform infrared spectra of gas phase ¹⁰B and ¹¹B enriched and natural samples of BF₂OH (difluoroboric acid) were recorded at Wuppertal and Richland. Starting from the results of previous studies, it was possible to perform the first rovibrational analysis of the 2ν₉ (first overtone of ν₉, the OH torsion) and ν₄ (BOH bending) bands located at about 1043.9 and 961.7?cm^?1 and 1042.9 and 961.5?cm^?1 for the ¹⁰BF₂OH and ¹¹BF₂OH isotopic species, respectively. Numerous ‘classical’ perturbations were observed in the analysis of the 2ν₉ and ν₄ bands. The energy levels of the 9² bright state are indeed involved in a B-type Coriolis resonance with those of the 6¹9¹ dark state. The 4¹ levels are perturbed by a B-type Coriolis resonance and by an anharmonic resonance with the levels of the 7¹9¹ and the 6¹7¹ dark states, respectively. In addition large amplitude effects were observed for the 2ν₉ and also, more surprisingly, the ν₄ bands. This results in splittings of the energy levels of about 0.005 and 0.0035?cm^?1 for the 9² and 4¹ states, respectively, which are easily observable in the P and R branches for both bands. The theoretical model used to reproduce the experimental levels accounts for the classical vibration–rotation resonances. Also the large amplitude torsional (or bending) effects are accounted for within the frame of the IAM (Internal Axis Method)-like approach. The Coriolis resonances between the two torsional (or bending) substates are taken into account by {J_x,?J_z} non orthorhombic terms in the v-diagonal blocks. This means that the z-quantification axis deviates from the a inertial axis by an axis switching effect of ～35° for the {9²,?6¹9¹} system and of ～16.6° for the {4¹,?7¹9¹,?6¹7¹} system of interacting vibrational states. The calculation of the relative line intensities for the 2ν₉ and ν₄ bands accounts for these axis switching effects as well as for the intensity alternation which is due to the nuclear spin statistical weights since the OH large amplitude torsion and/or bending motion results indeed in an exchange of the two fluorine nuclei.     

二苯基亚砜、苯甲酸与轻稀土高氯酸四元配合物的合成表征及光致发光

合成并表征了高氯酸稀土与二苯基亚砜、苯甲酸的四种四元配合物。经元素分析、稀土络合滴定、摩尔电导率及差热-热重分析,表明四元配合物组成为[REL5L′(ClO4)] (ClO4) (RE= La,Pr,Nd,Eu;L=C6H5SOC6H5,L′=C6H5COO-)。在红外光谱中,第一配体二苯基亚砜的νS O的特征吸收峰出现在1 037cm-1处,而各稀土配合物的νS O向低波数移动到984 ～989 cm-1,红移50 cm-1左右,表明稀土离子与亚砜基团的氧原子之间发生配位作用。第二配体苯甲酸钠的反对称伸缩振动吸收峰νas(COO -)出现在1 550 cm-1,对称伸缩振动吸收峰νs(COO -)出现在1 416 cm-1处,羧基伸缩振动吸收频率差Δn[νas(COO -)-νs(COO -)]值为134cm-1;在所有配合物的红外光谱图中νas(COO -)向高波数方向发生了位移,而νs(COO -)向低波数方向发生了位移,并且Δn值均大于钠盐的Δn值,由此可以认为配合物中羧基是通过单齿方式与稀土离子配位。测定了配合物在丙酮溶液中的摩尔电导率,根据配合物在常见有机溶剂中的摩尔电导率与正负离子的关系结合配合物的红外光谱中高氯酸根离子的四条特征吸收带,表明配合物为1:1型电解质,两个ClO4-无机抗衡阴离子,其中一个在外界,一个进入内界与稀土离子配位。配合物的荧光发射光谱表明,四元配合物的荧光强度比二苯基亚砜高氯酸稀土二元配合物的荧光强度提高469%。磷光光谱表明苯甲酸三重态能级的下限和二苯亚砜三重态能级的上限重叠,导致三重态能级范围扩大,由此可见第二配体的加入提高了配体的三重态能级与Eu3 离子5D0能级的匹配程度。同时在配合物的荧光发射光谱中还可以看到铕离子的电偶极跃迁强度大于磁偶极跃迁,表明稀土离子不处于晶体场的对称中心。在四元配合物中,由于第二配体的加入,往往会降低配合物的对称性,从而增强稀土离子的荧光强度。本文合成的稀土配合物具有良好的荧光性能,而且在室温下稳定,溶解性好,分解温度较高。     

Solution-state dynamics of sugar-connected spin probes in sucrose solution as studied by multiband (L-, X-, and W-band) electron paramagnetic resonance

A multiband (L-band, 0.7GHz; X-band, 9.4GHz; and W-band, 94GHz) electron paramagnetic resonance (EPR) study was performed for two glycosidated spin probes, 4-(alpha,beta-D-glucopyranosyloxy)-TEMPO (Glc-TEMPO) and 4-(alpha,beta-D-lactopyranosyloxy)-TEMPO (Lac-TEMPO), and one non-glycosylated spin probe, 4-hydroxy-TEMPO (TEMPOL), where TEMPO=2,2,6,6-tetramethyl-1-piperidinyloxyl, to characterize fundamental hydrodynamic properties of sugar-connected spin probes. The linewidths of these spin probes were investigated in various concentrations of sucrose solutions (0-50wt%). The multiband approach has allowed full characterization of the linewidth parameters, providing insights into the molecular shapes of the spin probes in sucrose solution. The analysis based on the fast-motional linewidth theory has yielded anisotropy parameters of rho(x) approximately 2.6 and rho(y) approximately 0.9 for Glc-TEMPO, and rho(x) approximately 4.2 and rho(y) approximately 0.9 for Lac-TEMPO. These values indicate that the glycosidated spin probes have a prolate-type molecular shape elongated along the x-axis (NO(rad) axis) with Lac-TEMPO elongated more remarkably, consistent with their molecular structures. The interaction parameters k (the ratios of the effective hydrodynamic volumes to the real ones) corrected for the difference in molecular shape have been estimated and found to have the relation k(TEMPOL)相似文献   

Energy-resolved spin filtering effect and thermoelectric effect in topological-insulator junctions with anisotropic chiral edge states

Topological edge states have crucial applications in the future nano spintronics devices. In this work, circularly polarized light is applied on the zigzag silicene-like nanoribbons resulting in the anisotropic chiral edge modes. An energy-dependent spin filter is designed based on the topological-insulator (TI) junctions with anisotropic chiral edge states. The resonance transmission has been observed in the TI junctions by calculating the local current distributions. And some strong Fabry−Perot resonances are found leading to the sharp transmission peaks. Whereas, the weak and asymmetric resonance corresponds to the broad transmission peaks. In addition, a qualitative relation between the resonant energy separation T_R and group velocity v_f is derived: T_R=πhv_fn/L, that indicated T_R is proportional to v_f and inversely proportional to the length L of the conductor. The different T_R between the spin-up and spin-down cases results in the energy-resolved spin filtering effect. Moreover, the intensity of the circularly polarized light can modulate the group velocity v_f. Thus, the intensity of circularly polarized light, as well as the conductor-length, play very vital roles in designing the energy-dependent spin filter. Since the transmission gap root in the Fabry−Perot resonances, the thermoelectric (TE) property can be enhanced by adjusting the gap. A schedule to enhance the TE performance in the TI-junction is proposed by modulating the electric field (E_z). The TE dependence on E_z in the nanojunction is investigated, where the appropriate E_z leads to a very high spin thermopower and spin figure of merit. These TI junctions have potential usages in the nano spintronics and thermoelectric devices.     

Enhanced suppression of residual water in a "270" WET sequence

In certain water suppression experiments, the residual water, which comes from a region away from the center of the RF coil and experiences a much smaller flip angle than the designed one, may appear. The residual water in the WET sequence can be reduced significantly by using a composite 90(x)( degrees )90(y)( degrees )90(-x)( degrees )90(-y)( degrees ) pulse, which de-excites molecules experiencing a small flip angle. The composite pulse, however, has two null excitation points near on resonance, causing a severe loss of spectrum intensity and baseline distortion toward the null points. Since the residual water experiences a very small flip angle, it can be treated as a linear spin system; i.e., the intensity of the residual water is proportional to the pulse strength and width. Based on this principle, the residual water can be reduced dramatically by replacing the 90 degrees pulse in the "270" WET sequence with a 270 degrees pulse for one out of every four scans, without noticeable loss of intensity and baseline distortion.     

Artifacts in T1 rho-weighted imaging: compensation for B(1) and B(0) field imperfections

The origin of spin locking image artifacts in the presence of B(0) and B(1) magnetic field imperfections is shown theoretically using the Bloch equations and experimentally at low (omega(1) < Delta omega(0)), intermediate (omega(1) approximately Delta omega(0)) and high (omega(1) > Delta omega(0)) spin locking field strengths. At low spin locking fields, the magnetization is shown to oscillate about an effective field in the rotating frame causing signature banding artifacts in the image. At high spin lock fields, the effect of the resonance offset Deltao mega(0) is quenched, but imperfections in the flip angle cause oscillations about the omega(1) field. A new pulse sequence is presented that consists of an integrated spin echo and spin lock experiment followed by magnetization storage along the -z-axis. It is shown that this sequence almost entirely eliminates banding artifacts from both types of field inhomogeneities at all spin locking field strengths. The sequence was used to obtain artifact free images of agarose in inhomogeneous B(0) and B(1) fields, off-resonance spins in fat and in vivo human brain images at 3 T. The new pulse sequence can be used to probe very low frequency (0-400 Hz) dynamic and static interactions in tissues without contaminating B(0) and B(1) field artifacts.     

CH4分子ν1模拉曼诱导克尔效应谱与受激拉曼光声光谱峰形的比较

以气相甲烷分子ν₁模Q支的拉曼光谱为例，采用拉曼诱导克尔效应谱(RIKES)进行峰形测量，并将其与同时测量的受激拉曼光声光谱(PARS)的峰形进行了比较.结果表明，在pump光和Stokes光均为线偏振的情况下，两者存在着差异；在拉曼共振峰的低频端，RIKES谱强度略高；而高频端则恰好相反.从信号产生机制出发，对此进行了合理解释. 关键词： 拉曼诱导克尔效应谱 受激拉曼光声光谱 峰形     

Generation of an axially super-resolved quasi-spherical focal spot using an amplitude-modulated radially polarized beam

An axially super-resolved quasi-spherical focal spot can be generated by focusing an amplitude-modulated radially polarized beam through a high numerical aperture objective. A method based on the unique depolarization properties of a circular focus is proposed to design the amplitude modulation. The generated focal spot shows a ratio of x:y:z=1:1:1.48 for the normalized FWHM in three dimensions, compared to that of x:y:z=1:0.74:1.72 under linear polarization (in the x direction) illumination. Moreover, the focusable light efficiency of the designed amplitude-modulated beam is 65%, which is more than 3 times higher than the optimized case under linear polarization and thus make the amplitude-modulated radial polarization beam more suitable for a wide range of applications.     

Ferromagnetic resonance spin pumping in CoFeB with highly resistive non-magnetic electrodes

The relative contribution of spin pumping and spin rectification from the ferromagnetic resonance of CoFeB/non-magnetic bilayers was investigated as a function of non-magnetic electrode resistance. Samples with highly resistive electrodes of Ta or Ti exhibit a stronger spin rectification signal, which may result in over-(or under-) estimation of the spin Hall angle of the materials, while those with low resistive electrodes of Pt or Pd show the domination of the inverse spin Hall effect from spin pumping. By comparison with samples of single FM layer and an inverted structure, we provide a proper analysis method to extract spin pumping contribution.     

Improved proton spectroscopic U-FLARE imaging for the detection of coupled resonances in the rat brain in vivo

Modifications of the pulse sequence for spectroscopic U-FLARE imaging are discussed to detect not only the predominant singlet signals of N-acetylaspartate, total creatine, and choline containing compounds or the doublet signal of lactate, but also the coupled resonances of glutamate, glutamine, taurine and myo-inositol. Effective homonuclear decoupling is achieved by use of constant time chemical shift encoding. A maximum signal-to-noise ratio (SNR) can be obtained for a certain coupled resonance of interest by optimizing the evolution period t(c) of the J modulated spin echo. Good reproducibility and a high SNR were achieved by combining several methods for water suppression and by using the displaced variant of U-FLARE. Measurements of a 3 mm slice of the rat brain were performed in vivo within 4 min, giving a nominal voxel size of 1.5 x 1.5 x 3.0 mm3 or 1.5 x 0.75 x 3.0 mm3. Thus, optimized spectroscopic U-FLARE is a powerful tool for proton spectroscopic imaging with high spectral, spatial and temporal resolution.