Theory of NMR multiple echoes in solid hydrogen

We have examined the theory of NMR multiple echoes developed for solid³He to determine whether multiple echoes could be observed in solid hydrogen. We were particularly interested in the possibility of testing for low frequency quantum tunneling motions in solid hydrogen by the observation of multiple echoes. We find that for easily accessible nuclear spin polarizations, P > 12%, multiple echoes would be observed for HD impurities in solid parahydrogen if motional narrowing is effective in increasing the HD nuclear spin-spin relaxation time T₂ to the order of 1 msec. These values for T₂, which have been observed for HD impurity concentrations of the order of 1%, are larger than the calculated rigid lattice values and can be attributed to quantum tunneling at frequencies of the order of 1kHz.     

Kinetic analysis of daily hemofiltration

Background: Daily hemofiltration (D‐HF) is a new treatment modality that shows unique solute removal characteristics and possibly provides a high quality of life for patients with end‐stage renal disease. We evaluated solute removal characteristics of D‐HF for five patients by kinetic modeling analysis. Methods: Five patients treated with normal 3 × 4 hr/week hemodialysis (HD) were switched to D‐HF (6 × 2 hr/week). Ultrafiltration rates (Q_F) or small‐solute clearances ranged from 63 to 106 mL/min. All the necessary kinetic parameters were determined from patients' physical data and HD portion of the clinical measurements. The two‐compartment kinetic model predicted the concentration changes after switching from normal HD to D‐HF. Results: Concentrations of small solutes such as urea nitrogen (UN) increased, whereas that of β₂‐microglobulin (β₂‐MG) decreased after switching from normal HD to D‐HF in all five patients. Predicted solute concentrations and clinical measurements for UN and β₂‐MG were in good agreement with mean error less than 10%. The model predicted that Q_F = 155 mL/min may be necessary for time‐averaged concentration (TAC) of UN to be unchanged. The model also predicted that the 7 times/week D‐HF should not increase the pretreatment concentration of UN, expecting even much lower β₂‐MG concentration after switching from normal HD to D‐HF. Conclusion: D‐HF is superior to normal HD for removing larger solutes but may increase the TAC of small solutes. Seven‐day (7 times/week) D‐HF may improve the solute removal capacity of small solutes.     

Half-lives of atomic tritium and free triton determined from the chemical shift of the beta decay time constant

Data on the chemical shift of the beta decay time constant were used to determine the experimentally justified half-lives of atomic tritium (t _1/2)_a=12.264±0.018 year and free triton (t _1/2)_t=12.238±0.020 year.     

Pulsed NMR in solid D2. II. Stimulated echo

A study of the NMR stimulated echo resulting from an r.f. three-pulse sequence is presented for hcp D₂ with para-D₂ concentrations X between 0.06 and 0.49 and over the temperature range 0.07 < T < 1.5 K. The echo has two components, a sharp one on top of a broad one, which are the signals of the I = I (p-D₂) and the I= 2 (o-D₂) spins respectively. The echo widths reflect the different degrees of molecular orientational ordering. The echo amplitudes are studied as a function of the experimental parameters in the r.f. pulse sequence. The temperature dependence of the amplitude shows the expected Curie law behavior for the I = 2 spins, but a strong deviation from this law for the I = 1 spins. This anomalous behavior is consistent with that found for the I = 1 solid echo signal. The echo decay time _E is found to be very different for both spin systems, both in magnitude and in temperature dependence. The comparison of the I=1 spin results in D₂ with those in H₂, where the molecular orientational ordering is also from quadrupolar interaction, shows substantial differences. These are discussed in terms of the spin diffusion within each NMR line, and of the cross-relaxation between the two I = 1 and I = 2 spin systems.     

Axisymmetric damped natural frequencies in a slowly spinning cylindrical container filled with viscous liquid

The axisymmetric fundamental natural damped frequency of the free surface in a slowly rotating cylindrical container is determined for incompressible viscous liquid. It was found that with increasing liquid height ratio h/a oscillation frequencies and decay magnitude both exhibit increased values. The influence of the surface tension parameter σ*=σa/?ν² shows for increasing magnitude increasing oscillation frequencies and decreasing decay magnitudes. For increasing Bond number Bo the oscillation frequency increases while the decay magnitude decreases. The effect of increasing the spin parameter ω₀=Ω₀ a ²/ν is manifested by an increase of the oscillation frequency and decay magnitude, i.e. for faster spin a liquid disturbance decays faster with larger oscillation frequency.     

Magnetic Resonance Studies of Impurity-Helium Solids Containing Hydrogen and Deuterium Impurities

Impurity-Helium Solids (Im-He) produced by injecting a mixed beam of helium and impurity gases into superfluid ⁴He have been investigated by electron spin resonance (ESR) and nuclear magnetic resonance (NMR) techniques. NMR signals from deuterium molecules in a D₂-He solid have been studied. Only samples prepared from gaseous mixtures containing high concentrations of D₂ molecules gave observable signals. The ESR experiments were performed on H and/or D atomic impurities in Im-He solids containing H, D, H₂, and D₂ in various combinations. The exchange tunneling reactions D+H₂HD+H and D+HDD₂+H were used to generate high concentrations of H atoms (10¹⁷/cm³) in Im-He samples.     

Quantum spin dynamics of the transverse Ising model in two dimensions

We use the method of recurrence relations to obtain the time-dependent spin correlation function of the Ising model in a transverse field in 2D. We find that the correlation function decays algebraically at long times as t_– where 2.2. This is to be contrasted with the 1D case where the decay is Gaussian. We expect that in 3D the dynamical correlation will also exhibit a power law decay. Our results can be used to understand the experimental shape functions for the induced moment in LiTb_pY _1–pF ₄ .     

Electron Spin Coherence of Phosphorus Donors in Isotopically Purified <Superscript>29</Superscript>Si

We investigate spin coherence time of electrons bound to phosphorus donors in silicon single crystals, employing a pulsed electron paramagnetic resonance technique. The samples were isotopically controlled so that they may possess different concentrations (about 5% and 100%) of ²⁹Si, which is the only non-zero-spin (spin-1/2) stable isotope of Si. Both ²⁹Si-concentration dependence and orientation dependence of the electron spin coherence time demonstrate that the decoherence is caused by spectral diffusion due to mutual flip-flops of the environmental nuclear spins. The detail analysis of spin echo decay curves enables the unique assignment of the host sites responsible for electron spin echo envelope modulation.     

Electron Spin Coherence of Phosphorus Donors in Isotopically Purified 29Si

We investigate spin coherence time of electrons bound to phosphorus donors in silicon single crystals, employing a pulsed electron paramagnetic resonance technique. The samples were isotopically controlled so that they may possess different concentrations (about 5% and 100%) of ²⁹Si, which is the only non-zero-spin (spin-1/2) stable isotope of Si. Both ²⁹Si-concentration dependence and orientation dependence of the electron spin coherence time demonstrate that the decoherence is caused by spectral diffusion due to mutual flip-flops of the environmental nuclear spins. The detail analysis of spin echo decay curves enables the unique assignment of the host sites responsible for electron spin echo envelope modulation.     

Decay of 2 - Anions in Solid Parahydrogen via Two-Stage Quantum Tunneling Diffusion Processes

Decay mechanism of H ₂ ^- anions in X()-irradiated solid para-H₂ (p-H ₂ ) has been studied using high-resolution ESR spectroscopy in the temperature range between 1.3–6.6 K. The results are summarized as follows. First,the decay rate constant of the ₂ ^- anions is not proportional to initial yields of reactive species such as cations and H atoms but proportional to the concentration of less-reactive species of HD molecules in p-H₂ . This result shows that the decay of the ₂ ^- anion is due to the reaction neither with cations nor H atoms but with HD molecules originally contained in the p-H₂ sample at natural abundance. Second,the decay rate constant of the ₂ ^- anions increases proportionally with the increase in temperature below 3 K and decreases with the increase in temperature between 3–5 K,although it increases exponentially with the increase in temperature above 5 K. This result indicates that the decay rate constant of the ₂ ^- anions is controlled by the rate constant for the diffusion of the ₂ ^- anions via one-phonon assisted quantum tunneling below 3 K,two-phonon scattered or assisted quantum tunneling between 3–5 K,and thermally-activated process above 5 K.     

Optical and scintillation properties of SrI2:Yb2+

The luminescence and scintillation properties of SrI₂:0.5%Yb²⁺ have been investigated. SrI₂:Yb single crystals were grown by the vertical Bridgeman method from the melt. They showed a light yield of 38,400 ph/MeV and energy resolution of 12.5% for the 662 keV full absorption peak. Yb²⁺ photoluminescence intensity and decay time were studied between 78 and 600 K. Two emission bands centered at 418 and 446 nm were observed and ascribed to spin-allowed and spin-forbidden Yb²⁺ 5d-4f transitions, respectively. Their corresponding room-temperature decay time constants are 710 ns and 77 μs. Both, the emission intensities and the decay time constants vary with temperature. The obtained results were interpreted using a model of self-absorption of Yb²⁺ emission and a model of non-radiative relaxation of the electron from the low spin to the high spin 4f¹³5d Yb²⁺ excited states. The radiative lifetime of the low spin Yb²⁺ excited state was determined as 400 ns.     

Pulsed NMR study in nuclear ordered solid3He

The nuclear spin dynamics in nuclear spin ordered solid³He in low magnetic fields on the melting curve has been studied by pulsed NMR down to 0.6 mK. The free induction decay signals (FID) were measured in single crystals of solid³He at three operating frequencies of 920, 1380, and 1840 kHz. The FIDs were nonexponential and dependent on the rf pulse strength _p H ₁ t _w , where is the gyromagnetic ratio,H ₁ is the rf field strength, andt _w is the pulse width. At small _p they decayed almost linearly in time with a small exponential tail at the end. When _p was further increased they became shorter and neither exponential nor linear in time. At large _p they decayed very rapidly and sometimes could not be observed at all because of the dead time of the NMR detection system. Such behavior of the FID was observed in many different single crystals in the given temperature range at 920 kHz. Tsubota and Tsuneto have shown by solving the nonlinear equations of motion numerically that the motion of the nuclear spin becomes chaotic when the tipping angle exceeds a critical value. Comparing their result with our experimental results, we concluded that some of the results of the rapid decay of the FID at large _p might be attributed to the onset of the chaotic motion. At 1840 kHz it is expected that the nonlinear effects in the equations of motion become less effective than that at 920 kHz. In fact, at this operating frequency the FIDs even at large _p and the tipping angle-dependent frequency shift could be observed. These frequency shifts were in rather good agreement with Namaizawa's theory provided an effective tipping angle was taken into account.     

Functional iron deficiency in hemodialysis patients with high ferritin

Although functional iron deficiency (FID) may be present in hemodialysis (HD) patients with high serum ferritin levels (>800 ng/mL), current protocols often preclude the use of intravenous (IV) iron in these patients. However, it has not been demonstrated that iron supplementation during erythropoietin therapy is ineffective or unsafe in increasing hemoglobin (Hb) levels in patients with high serum ferritin. This report describes the hematologic efficacy and safety of ferric gluconate (FG) therapy in patients with serum ferritin >800 ng/mL. A retrospective analysis was performed on HD patients at a single California dialysis center from January 1 to December 31, 2003. Patients classified as having high ferritin levels (serum ferritin >800 ng/mL on at least 66% of routine monthly measurements and transferrin saturation [TSAT] <25% on at least 1 occasion) were stratified as follows: patients in Group I were suspected of having FID and received FG > or =250 mg IV over a 3-month period when Hb was <11 g/dL, and patients in Group II were thought not to have FID and received <250 mg FG over a 3-month period. Both groups received standard recombinant human erythropoietin therapy as per the unit's protocol. Of 496 patients, 95 exhibited high ferritin and of these, 39 patients had sufficient data for analysis. Group I patients (n=14) showed a significant increase in Hb levels compared with Group II (n=25). There was no increase in ferritin levels in response to iron administration. No significant differences in hospitalizations or infections were observed between groups. Hemodialysis patients with high ferritin levels may have FID, and IV iron therapy safely improves FID in some patients. A larger randomized trial examining the optimal management of iron administration in HD patients with high ferritin levels is warranted.     

Quantitative analysis of low-field NMR signals in the time domain

Two novel methods are described for direct quantitative analysis of NMR free induction decay (FID) signals. The methods use adaptations of the generalized rank annihilation method (GRAM) and the direct exponential curve resolution algorithm (DECRA). With FID-GRAM, the Hankel matrix of the sample signal is compared with that of a reference mixture to obtain quantitative data about the components. With FID-DECRA, a single-sample FID matrix is split into two matrices, allowing quantitative recovery of decay constants and the individual signals in the FID. Inaccurate results were obtained with FID-GRAM when there were differences between the frequency or transverse relaxation time of signals for the reference and test samples. This problem does not arise with FID-DECRA, because comparison with a reference signal is unnecessary. Application of FID-DECRA to 19F NMR data, which contained overlapping signals from three components, gave concentrations comparable to those derived from partial least squares (PLS) analysis of the Fourier transformed spectra. However, the main advantage of FID-DECRA was that accurate (<5% error) and precise (2.3% RSD) results were obtained using only one calibration sample, whereas with PLS, a training set of 10 standard mixtures was used to give comparable accuracy and precision.     

Interpretation of1H NMR results of HD impurities in solid H2. I. Spin-spin relaxation

Previous¹H NMR results on HD impurities in solid H₂ samples of low ortho concentration (X0.01) are reexamined, resulting in a different interpretation of the spin-spin relaxation timeT ₂. The relaxation time is found to be measured by using short rf pulses rather than the long (100–120 µsec) pulses used previously for the spin-echo pulse sequences. This is due to the fact that the nuclear spin dipolar flip-flop interactions between the HD and ortho-H₂ molecules are effectively quenched because of the large intramolecular dipolar splittings of the H₂ molecules. The measured spin-spin relaxation times for the HD impurities in a sample ofX0.01 are found to be consistent with those from statistical theory, revealing no appreciable motional narrowing, which was invoked previously.     

Effect of the pinning layer thickness on the linewidth of spin wave resonance modes

The dependence of the linewidth 2ΔH _n of the spin wave resonance (SWR) modes on the thickness h ₂ of a pinning layer in two-layer garnet ferrite films is sharply different for the perpendicular and parallel orientations of an external magnetic field relative to the film plane. The increase in 2ΔH _n with decreasing h ₂ in the case of the perpendicular field orientation is related to the growth in the relative contribution of the region of exponential decay to the total dissipation of the spin wave energy. The periodic variation of 2ΔH _n observed for the parallel field orientation is explained by special features of the spin wave configuration in the pinning layer.     

Pulse Electron Spin Resonance Studies of H and D Atoms in Impurity-Helium Solids

We have performed measurements of the two-pulse ESEEM (electron spin echo envelope modulation) spectra of H and D atoms within impurity-helium solids. The local environments of the atoms were determined from the modulation of the ESEEM signal by neighboring D₂ and HD molecules. We have measured changes in the atom environments due to coalescence of the nanoclusters within the impurity-helium solids and due to the tunneling exchange chemical reaction D+HD→H+D₂.      

The carbon footprints of home and in‐center maintenance hemodialysis in the United Kingdom

Climate change presents a global health threat. However, the provision of healthcare, including dialysis, is associated with greenhouse gas emissions. The aim of this study was to determine the carbon footprints of the differing modalities and treatment regimes used to deliver maintenance hemodialysis (HD), in order to inform carbon reduction strategies at the level of both individual treatments and HD programs. This was a component analysis study adhering to PAS2050. Emissions factors were applied to data that were collected for building energy use, travel and procurement. Thrice weekly in‐center HD has a carbon footprint of 3.8 ton CO₂ Eq per patient per year. The majority of emissions arise within the medical equipment (37%), energy use (21%), and patient travel (20%) sectors. The carbon footprint of providing home HD varies with the regime. For standard machines: 4 times weekly (4 days, 4.5 hours), 4.3 ton CO₂ Eq; 5 times weekly (5 days, 4 hours), 5.1 ton CO₂ Eq; short daily (6 days, 2 hours), 5.2 ton CO₂ Eq; nocturnal (3 nightly, 7 hours), 3.9 ton CO₂ Eq; and nocturnal (6 nightly, 7 hours), 7.2 ton CO₂ Eq. For NxStage equipment: short daily (5.5 days, 3 hours), 1.8 t CO₂ Eq; 6 nightly nocturnal (2.1 ton CO₂ Eq). The carbon footprint of HD is influenced more by the frequency of treatments than by their duration. The anticipated rise in the prevalence of home HD patients, dialyzing more frequently and for longer than in‐center patients, will increase the emissions associated with HD programs (despite reductions in patient travel emissions). Emerging technologies, such as NxStage, might offer a solution to this problem.     

Distillation of hydrogen isotopes for polarized HD targets

We have developed a new cryogenic distillation system to purify Hydrogen-Deuteride (HD) gas for polarized HD targets in LEPS experiments at SPring-8. A small amount of ortho-H₂ (∼0.01%) in the HD gas plays an important role in efficiently polarizing the HD target. Since there are 1-5% impurities of H₂ and D₂ in commercially available HD gases, it is necessary to purify the HD gas up to ∼99.99%. The distillation system is equipped with a cryogenic distillation unit filled with many small stainless steel cells called “Heli-pack”. The distillation unit consists of a condenser part, a rectification part, and a reboiler part. The unit is kept at the temperature of 17-21 K. The Heli-pack has a large surface area that makes a good contact between gases and liquids. An amount of 5.2 mol of commercial HD gas is fed into the distillation unit. Three trials were carried out to purify the HD gas by changing temperatures (17.5 K and 20.5 K) and gas extraction speeds (1.3 ml/min and 5.2 ml/min). The extracted gas was analyzed using a gas analyzer system combining a quadrupole mass spectrometer with a gas chromatograph. One mol of HD gas with a purity better than 99.99% has been successfully obtained for the first time. The effective NTP (Number of Theoretical Plates), which is an indication of the distillation performances, is obtained to be 37.2±0.6. This value is in good agreement with a designed value of 37.9. The HD target is expected to be efficiently polarized under a well-controlled condition by adding an optimal amount of ortho-H₂ to the purified HD gas.     

3He Anomalously High Spin Diffusion in Solid Para-Hydrogen

NMR measurements of ³He spin diffusion coefficient in solid para-H₂ are carried out at the temperatures 0.45–1.5 K. The crystals have been grown under constant pressure 20–130 bar. The ³He concentrations in the initial para-H₂–³He gas mixtures were 0.1% and 0.3%. It is found out that the decay of echo amplitude vs both magnetic field gradient G and time interval τ between RF pulses is of non-exponential character, typical of one-dimensional diffusion in restricted geometry. The values of true spin-diffusion coefficient D _S measured are found to be ∼10⁻⁴ cm²/s at 20 bar. At 108 bar D _S value is one order of magnitude less. D _S does not depend on temperature. Such spin diffusion coefficient values seem to be anomalously high in comparison with well-known values of D _S =10⁻⁵ cm²/s for bulk liquid ³He at 27 bar and D _S =10⁻⁸ cm²/s for bulk solid ³He at 108 bar. The special experiments with the crystal annealing make it clear that the high spin diffusion here is connected with fast diffusion along dislocation lines.