Paramagnetic contribution of serum iron to the spin-spin relaxation rate (1/T 2) measured by MRI

Spin-spin relaxation timeT ₂ values of serum with and without iron were measured by magnetic resonance imaging (MRI) to find the proton relaxivity of Fe(III) in serum.T ₂ values in serum containing definite amounts of added iron were also measured before and after addition of ascorbic acid. The difference in the 1/T ₂ of serum with and without ascorbic acid was used for recalculation of the added iron values. Recalculated iron values confirm that the difference in healthy serum is caused by iron only. In addition, in order to find the paramagnetic contribution of serum iron,T ₂ values of iron-deficient, healthy and iron-overloaded serum were measured before and after addition of ascorbic acid. The difference in the 1/T ₂ values was then applied to the calculation of the serum iron values. The consistency of iron values determined from the difference to those by autoanalyzer suggests that the differences in diseased serum also represent the paramagnetic contribution of serum iron. The data imply that serum iron content in healthy, iron-deficient and iron-overloaded serum may be assessed by MRI.     

Carrier concentration dependence and temperature dependence of mobility in silicon (100) N-channel inversion layers at low temperatures

The carrier concentration (N_s) dependence of electron mobility in Si (100) inversion layers has been measured at temperatures T = 1.5?70K for high- and low-mobility MOSFETs. An extrinsic term is observed in the T-dependent part of the scattering probability, τ^?1_T. At T = 4.4 K, τ^?1_T depends on N_s as N^?1.9_s in low mobility samples. In high-mobility samples, τ^?1_T increases with increasing N_s in high N_s region while τ^?1_T ∝ N^?1.6_s in low N_s region. The N_s-dependence of τ^?1_T becomes weaker with increasing T in both of low- and high-mobility samples. At N_s = 3 × 10¹² cm^?2, τ^?1_T depends on T as T^1.8 in low-mobility samples and τ^?1_T ∝ T^2.0 in high- mobility samples at T 5 K.     

A monte-carlo/molecular dynamics study of the diffusional recombination kinetics of C(a) + O(a) → CO(g) on Pt(111)

The diffusion constants for C and O adsorbates on Pt(111) surfaces have been calculated with Monte-Carlo/Molecular Dynamics techniques. The diffusion constants are determined to be D_C(T)=(3.4 × 10^?3e^{$\text{?13156}\text{T}$})cm²s^?1 for carbon and D_O(T) = (1.5×10^?3 e^{$\text{?9089}\text{T}$}) cm² s^?1 for oxygen. Using a recently developed diffusion model for surface recombination kinetics an approximate upper bound to the recombination rate constant of C and O on Pt(111) to produce CO_(g) is found to be (9.4×10^?3 e^{$\text{?9089}\text{T}$}) cm² s^?1.     

Two-photon exchange in p⊆)p→ℓ+ℓ−X and a comparison with QCD

A thorough study of lepton-pair production from two-photon annihilation in p?)p collisions is presented. The differential cross section is calculated over a large range of energies (27?√s?800 GeV as a function of the dilepton mass M as well as the dilepton transverse momentum Q_T and the Feynman variable x_F. No kinematical approximations (such as the equivalent photon approximation) are made. For Q_T ≈ 0 the two-photon mechanism represents an important fraction of the pp→e⁺e^?X cross section already at ISR energies, whereas at ISABELLE energies it dramatically dominates in the interval 0?Q_T?1 GeV. At ISR energies these conclusions follow from a direct comparison of the two-photon contribution with pp→e⁺e^?X data. For the ISABELLE energy range the expected O(α_s) QCD contribution to pp→?⁺?^?X, corrected for soft gluon radiation to all orders (in leading bilogarithmic approximation), was taken as a reference. At larger Q_T and ISR energies the γγ contribution is negligible, whereas at √s = 800 GeV γγ/QCD? 10–20% almost everywhere. Furthermore, two-photon candidate events from the ISR are shown to be in reasonable agreement with theory. A decomposition of the γγ cross section into contributions from both proton vertices being elastic, inelastic and of mixed configuration is given. The results provide important clues for a future isolation of the two-photon mechanism.     

Anomalies in the surface impedance penetration depth in ferromagnetic superconductors

We have investigated the surface impedance penetration depth, Λ, of ErRh₄B₄ and Er_0.5Ho_0.5Rh₄B₄ both experimentally and theoretically. For ErRh₄B₄, owing to the critical spin fluctuations just above T_s ( > T_c2), the critical temperature at which surface ferromagnetism appears, Λ^?1 decreases smoothly as T decreases toward T_s. For Er_0.5Ho_0.5Rh₄B₄, the decrease in Λ^?1 owing to spin fluctuations for T ? T_c2 is very small, and Λ^?1 decreases abruptly at T_c2. Theoretical values of Λ^?1 are in good agreement with the data.     

Spin relaxation parameters in recombining radical ion pair (diphenylsulfide-d10)+/(p-Terphenyl-d14)− obtained by OD ESR and quantum beats techniques

Parameters of paramagnetic relaxation were determined by OD ESR and quantum beats techniques for a recombining pair of radical ions (DPS-d₁₀)⁺/(PTP-d₁₄)^? inn-hexane, isooctane,cis-decalin, and squalane solutions. TheT ₂ relaxation time determined by quantum beats technique is independent of solvent viscosity and magnetic field strength in the range 170–9600 G. These data are in agreement with the results obtained by OD ESR technique assuming fastT ₁ relaxation for radical cation. Neglecting the contribution of radical anion relaxation, we obtainedT _1c=T _2c?50 ns for (DPS-d₁₀)⁺.     

Changes in metal specificity due to iron ligand substitutions in reaction centers fromRhodobacter sphaeroides

Bacterial reaction centers have a single nonheme iron that is located between two bound quinones, Q_A and Q_B, which are the primary and secondary electron acceptors during photosynthesis, respectively. InRhodobacter sphaeroides, the iron is coordinated by four nitrogen atoms, contributed by histidines at L190, L230, M219, and M266, and two oxygen atoms, contributed by Glu at M234. The roles of these ligands in determining the metal-binding specificity and electron transfer properties of the quinones were investigated by mutagenesis. Each of the four His ligands was changed to Glu, Gln, and Cys, whereas Glu was changed to His, Gln, Cys, and Asp. All mutants supported photosynthetic growth except for those with substitutions of Glu or Cys at L190 or M219. The metal specificity of isolated mutant RCs was determined by measurements using atomic absorption and 35 GHz electron paramagnetic resonance spectroscopy. The M234 mutants had a lesser iron specificity than the wild type with a mole fraction of 0.7 to 0.8 iron but retained a total metal content of 1.0. All His mutants had an even lower iron content with mole fractions of 0.04 to 0.16. The His to Cys at M266 mutant had a significantly greater amount of bound zinc that was further enhanced when the strain was grown in zinc-supplemented media. The charge recombination rates from Q _B ^?. , which ranged from 0.5 to 1 s^?1 in the mutants, were comparable to the 1 s^?1 value for the wild type. Charge recombination from Q _A ^?. showed complex kinetics, with rates of 15 to 30 s^?1 for the L190, L230, and M234 mutants and 200 s^?1 for the M266 mutants compared with 8 s^?1 for the wild type. The faster rates in the mutants most likely reflected a smaller free energy difference between Q _A ^?. and Φ _A ^? , a nearby bacteriopheophytin, with the smaller energy difference facilitating indirect recombination. All of the mutants transferred electrons to the secondary quinone, with rates (1200 to 4700 s^?1) comparable to that of the native (3700 s^?1). The data demonstrate that neither the ligands nor the bound metal play a critical role in the electron transfer processes at the acceptor side.     

Effect of Ce impurities on superconductivity and nuclear spin-lattice relaxation in La1−cCecAl2

In the superconducting state of La_1?cCe_cAl₂ alloys ¹³⁹La spin-lattice relaxation times T_1s for relatively high c were found to agree with theory based on weak exchange coupling between conduction electrons and paramagnetic impurities. But for a dilute specimen the measured values of T_1s are significantly longer than expected. These results are tentatively attributed to the existence of a localized impurity band within the superconducting energy gap.     

Resonant phonon scattering due to crystal-field-split paramagnetic levels of Pr ions in PrTe1.46

The lattice heat conductivity κ_ph of PrTe_1.46 and LaTe_1.46 has been measured within the 2-to 100-K interval. The quantity ?Δκ_res(T), the decrease in the heat conductivity caused by resonant phonon scattering due to crystal-field-split paramagnetic levels of Pr, was derived from experimental data using the relation $ - \Delta \kappa _{res} (T) = \kappa _{ph(PrTe_{1.46} )} (T) - \kappa _{ph(LaTe_{1.46} )} (T)$ . The energy of the first split paramagnetic level of Pr, Δ₁ was calculated from the Δκ_res(T) relation for T<T _res. It was found that Δ₁ depends on the nature of the nearest neighbor environment of Pr ions in the lattice. The temperature dependence Δκ_res(T) has been determined to be Δκ_res(T) (Δκ_res～T ^?0.5) for T>T _res.     

Temperature and concentration quenching of mid-IR photoluminescence in iron doped ZnSe and ZnS laser crystals

Concentration dependences of the mid-IR kinetic of luminescence at ⁵E?⁵T₂ transition in Fe:ZnSe and Fe:ZnS laser samples were studied in 14–300 K temperature ranges. Radiation lifetime in Fe:ZnSe samples measured using low doped samples with iron concentration 0.1×10¹⁸ cm^?3 was estimated to be 57 μs. The magnetic susceptibility for higher doped (C_Fe=38 and 112×10¹⁸ cm^?3) Fe:ZnSe samples was found to consist of a paramagnetic Curie–Weiss behavior arising from the weakly interacting Fe²⁺ ions and a diamagnetic ZnSe contribution plus a temperature-independent, field-dependent contribution possibly arising from very small amounts of aggregated Fe.     

Synthesis and characterisation of the Fe(II–III) hydroxy-formate green rust

A new methodology was envisioned in order to prepare green rust compounds build on organic anions that could intervene in microbiologically influenced corrosion processes of iron and steel. The formate ion was chosen as an example. The formation of rust was simulated by the oxidation of aqueous suspensions of Fe(OH)₂ precipitated from Fe(II) lactate and sodium hydroxide, in the presence of sodium formate to promote the formation of the corresponding green rust. The evolution of the precipitate with time was followed by transmission Mössbauer spectroscopy at 15 K. It was observed that the initial hydroxide was transformed into a new GR compound. Its spectrum is composed of three quadrupole doublets, D ₁ (δ?=?1.28 mm s^?1, Δ?=?2.75 mm s^?1) and D ₂ (δ?=?1.28 mm s^?1, Δ?=?2.48 mm s^?1) that correspond to Fe(II) and D ₃ (δ?=?0.49 mm s^?1, Δ?=?0.37 mm s^?1) that corresponds to Fe(III). The relative area of D ₃, close to the proportion of Fe(III) in the GR, was found at 28.5?±?1.5% (～2/7). Raman spectroscopy confirmed that the intermediate compound was a Fe(II–III) hydroxy-formate, GR(HCOO^?).     

Low temperature1H NMR study of electronic structure parameters (T 1e T) in zirconium dihydride

Measurements of the proton-spin-lattice relaxation times (T ₁) are reported for zirconium dihydrides: ZrH_1.87, ZrH_1.93 and ZrH_2.00 at nominal frequency of 41 MHz, with emphasis on the low temperature (4.2–25 K) behaviour of theT ₁. The dominant contributions are originated from the hyperfine interactions of the protons with the conduction electrons and the paramagnetic impurities. The (T _1e T)^–1/2 values determined from the low temperature range (4.2–25 K) agree with those obtained in the extended range (4.2–300 K) as well as with the values reported by the other researches. The paramagnetic impurity contribution is found to be small and teperature independent.     

Intermediate electronic relaxation betweenS=3/2 andS=1/2 states in Fe(J-mph)NO with a jäger-type ligand J-mph

The incomplete spin transition between the low-spin (LS) (S=1/2) and the intermediate-spin (IS) (S=3/2) states in the iron (III) complex Fe(J-mph)NO (mph=4-methyl-o-phenylene), centered atT _c≈212 K, has been studied with⁵⁷Fe Mössbauer spectroscopy and magnetic susceptibility measurements between 80 K and 320 K. The lineshape of the Mössbauer spectra is well reproduced by a two state stochastic relaxation model resulting in values of about 2·10⁶ s^?1 to 7·10⁶ s^?1 for the IS→LS transition rate constantk _IL. The kinetics of this spin transition can be described by an Arrhenius equation yielding activation energiesE _IL=1.1 (2) kJ/mol andE _LI=6.1 (2) kJ/mol for the IS→LS and LS→IS conversion, respectively.     

An influence of deposition temperature on structural,optical and electrical properties of sprayed ZnO thin films of identical thickness

Nanocrystalline ZnO thin films were deposited at different temperatures (T_s = 325 °C–500 °C) by intermittent spray pyrolysis technique. The thickness (300 ± 10 nm) independent effect of T_s on physical properties was explored. X-Ray diffraction analysis revealed the growth of wurtzite type polycrystalline ZnO films with dominant c-axis orientation along [002] direction. The crystallite size increased (31 nm–60 nm) and optical band-gap energy decreased (3.272 eV–3.242 eV) due to rise in T_s. Scanning electron microscopic analysis of films deposited at 450 °C confirmed uniform growth of vertically aligned ZnO nanorods. The films deposited at higher T_s demonstrated increased hydrophobic behavior. These films exhibited high transmittance (>91%), low dark resistivity (～10^?2 Ω-cm), superior figure of merit (～10^?3 Ω^?1) and low sheet resistance (～10² Ω/□). The charge carrier concentration (η -/cm³) and mobility (μ – cm²V^?1s^?1) are primarily governed by crystallinity, grain boundary passivation and oxygen desorption effects.     

Nuclear magnetic relaxation by self-diffusion in solid lithium:T 1-frequency dependence

We report on measurements of the⁷Li nuclear spin relaxation timeT ₁ in solid lithium as a function of temperature (?170°C≦T≦+180°C) and Larmor frequency (450kHz≦v _Li≦31.5 MHz). Using a relaxation model developed by Wolf and Cavelius and combining it with Seeger's diffusion formalism, the diffusion parameters for mono-and divacancy migration were evaluated by a least squares fit to the newly obtainedT ₁ data as well as to previousT _1? measurements. The result for the self-diffusion coefficientD ^SD is given byD ^SD=D ₁₀·exp(?Q ₁/RT)·[1+D ₂₁·exp(?Q ₂₁/RT)], withD ₁₀=0.038 cm²s^?1,Q ₁=12.0 kcal mol^?1,D ₂₁=250,Q ₂₁=4 kcal mol^?1 andR=1.98₅·10^?3 kcal mol^?1 degree^?1. Due to the flexibility of Seeger's formula, which contrasts with the standard Arrhenius interpretation of diffusion, discrepancies between earlier high- and low-frequency NMR investigations were eliminated. Furthermore, an excellent agreement with available results from tracer experiments was achieved by taking into account the theoretical predictions of the isotope effect and the vacancy correlation factor.     

Spin dynamics in strongly coupled spin-correlated radical pairs: Stochastic modulation of the exchange interaction and ST−1 mixing in different magnetic fields

We investigate the effect of stochastic modulation of the exchange interaction J_ex on singlet (S)-triplet (T) transitions in radical pairs. These transitions limit the lifetime of the photo-generated radical pairs in covalently linked porphyrin-quinone systems that have been developed for biomimetic modeling of photosynthetic electron transfer processes. In order to explain transient electron paramagnetic resonance (EPR) results in different magnetic fields, i.e., with X-band ((0.34 T)/ (9.5 GHz)) and W-band ((3.4 T)/(95 GHz)) time-resolved EPR, we have to assume that J_ex is modulated over a range of 20000 G, which is wide enough that S is temporarily almost degenerate with T₀ as well as with T_?1. This large modulation of J_ex is caused by restricted rotational diffusion of the quinone subunit with respect to the porphyrin subunit. However, because of the small interradical distance of about 1.0–1.4 nm, the radical pair is continuously kept in the strong coupling limit and, therefore, we observe only EPR transition between the triplet sublevels. We find an approximation to solve the stochastic Liouville equation valid for rotational diffusion on an intermediate time scale, i.e., the diffusion rate D_R is smaller than the singlet electron recombination rate K_S ～ 10⁹ s^?1, but larger than the ST transition rates κ₀, κ_?1 < 10⁶ s^?1.     

Green function theory of Curie and order—order transitions in ferromagnetic systems

Dipolar critical temperatures in ferromagnetic systems with isotropic bilinear and biquadratic exchange are investigated by means of the Green function technique. Expressions are found for both the familiar Curie temperature, T_c, and the less well known order-order transition temperature, T_o, at which, under appropriate conditions, the magnetic ordering undergoes a change between fully aligned and canted ferromagnetism. At T = 0, a fully aligned state has <s_i^z = s for spin s and all lattice sites i, while a canted state has 〈s_i^z〉<s. It is shown independently of the Green function analysis that the T = 0 ground state is fully aligned if α, the ratio of biquadratic to bilinear exchange integrals, obeys ?[2s(s?1)]^?1<α< [2s²?2s+1]^?1. The region below the lower limit is identified as the range in which canted ferromagnetism can occur and is a range that does not appear to have been considered previously via the Green function formalism.The temperature dependence of the magnetic ordering is investigated by means of the double-time temperature-dependent Green function formalism. A new decoupling scheme is derived and used to reduce higher order Green functions to lowest order. It is found that a canted state, occuring at low temperatures, undergoes a transition to a fully aligned state at a temperature T₀ and subsequently becomes disordered at temperature T_c. Transitions to paramagnetism are found to be second order for α<α_c and first order for α?α_c where α_c is a critical value that depends on the atomic spin and weakly on the lattice structure. A phase diagram is given to illustrate the results, and a comparison is made with the corresponding results found in mean field theory.     

Nuclear magnetic resonance studies of CePd2In and LaPd2In at low temperatures

We report on In nuclear magnetic resonance (NMR) and nuclear quadrupolar resonance (NQR) measurements on the new heavy-electron compound CePdZIn over a wide temperature range, from 45 mK up to 30 K. CePd₂In undergoes an antiferromagnetic (AF) phase transition at T _N = 1.23 K involving small localised Ce moments of 0.11 μ_B. In zero field, the spin-lattice relaxation rate T ₁ ^?1 (T) shows remarkable changes in its temperature dependence. Above 3 K, T ₁ ^?1 is constant and 850 sec^?1. Between T _N and 2T _N, (T ₁ T)^?1 = 330 (Ksec)^?1, but rapidly decreases below T _N. A Korringatype relaxation, characteristic for simple metals at low temperatures, with (T ₂ T)^?1 = 17(Ksec)¹ is resumed below 0.6 K. This value is an order of magnitude larger than (T ₁ T)^?1 for LaPd₂In and therefore is associated with low-energy excitations of the itinerant charge carriers with 4f symmetry. The T ₁ ^?1 data at various non-zero magnetic fields fall on a single curve when plotted as a function of (T/H) if H exceeds 3.5 T. Thus the AF ordering, the 4f moment fluctuations and the Kondo screening are drastically suppressed by the application of fields H of the order of 3.5 T.     

Structural and magnetic studies of the alloy system GdInxAg1-x

The structural and magnetic studies below room temperature of the alloy system GdIn_xAg_1-x(0?x?1) are reported. It has been found that alloys with x?0.5 crystallize in CsCl type cubic structure, but the distortion of the unit cell starts for alloys with x#62;0.5 and for these alloys the unit cell becomes tetragonal. No phase change is evident from the low temperature (295-8 K) structural studies. However, a break appears in the X^-1_m vs. T linear plot of each alloy of this system at a specific temperature (designated as break temperature T_B). The variation of T_B with x is similar to the variation of phase transition temperature with x reported for LaIn_xAg_1-x. Close agreement has been found in the values of effective magneton number (p), magnetic ordering [Néel (T_N) or Curie (T_C)] and paramagnetic Curie (θ_p) temperature for materials studied by us and earlier workers. The variation of magnetization with applied field strength (2.5-65)×10⁵ Am^-1) at 4.2 K has also been reported for ferromagnetic of this system. It has been concluded that alloys with 0.4?x?0.6 are simple ferromagnets with parallel alignment of magnetic moment in the ground state. The angular arrangement of the magnetic moment starts appearing in the ground state for alloys with x?0.4 for x#62;0.6 and continues till x becomes closure to 0.17 or 0.84. The alloys with x=0.17 or x=0.84 have θ_p and T_C equal to zero and appear paramagnetic. Angular arrangement in spins again appear for alloys with x?0.17 or x#62;0.84, however all materials with 0?x?0.17 or 0.84?x?1 remain antiferromagnetic.