In Vivo Relaxation Time Measurements in the Human Placenta Using Echo Planar Imaging at 0.5 T

This paper presents the first in vivo measurements of the nuclear magnetic resonance relaxation times T₁ and T₂ at 0.5 T in the human placenta from 20 weeks gestational age until term, in both normal and compromised pregnancies. T₁ measurements were performed by using both an inversion recovery sequence and the Look-Locher echo planar imaging (EPI) sequence on a total of 41 women with normal pregnancies and 11 women with compromised pregnancies. T₂ measurements were performed by using a spin-echo EPI sequence on 36 women with normal pregnancies and 14 women with compromised pregnancies. In normal pregnancies, both the T₁ values measured with the inversion recovery sequence and the T₂ values were found to decrease with gestational age, the linear regression results gave T₁=−9.1t+1538 r²=0.23 p=0.03 T₂=−4.0t+338 r²=0.47 p=4 10⁻⁶ where t is the gestational age in weeks, and T₁ and T₂ are the relaxation times in milliseconds. T₁ values measured very rapidly with the Look-Locher EPI sequence, but, therefore, with a much lower signal-to-noise ratio, showed no significant trends.The T₁ values measured in the abnormal group were significantly lower than those measured in the normal group. Four out of eight patients with compromised pregnancies had placental T₁ values lying outside the 90% confidence limits for the normal population based about the regression line, significantly more than expected by chance (p = 0.005). Ten out of fourteen of the T₂ measurements in the abnormal group were below the regression line established for the normal group, with 4 lying below the 90% confidence interval, although these trends were only just significant (p = 0.06 and p = 0.03).     

Large angle spin-echo imaging

A study was undertaken to assess the use of excitation flip angles greater than 90° for T₁ weighted spin-echo (SE) imaging with a single 180° refocusing pulse and short TR values. Theoretical predictions of signal intensity for SE images with excitation pulse angles of 90–180° were calculated based on the Bloch equations and then measured experimentally from MR images of MnCl₂ phantoms of various concentrations. Liver signal-to-noise ratios (SNR) and liver-spleen contrast-to-noise ratios (CNR) were measured from breathhold MR images of the upper abdomen in 16 patients using 90 and 110° excitation flip angles. The theoretical predictions showed significant improvements in SNR with excitation flip angles >90°, which were more pronounced at small TR values. The phantom studies showed reasonably good agreement with the theoretical predictions in correlating the excitation pulse angle with signal intensity. In the human imaging studies, the 110° excitation pulse angle resulted in a 7.4% (p < .01) increase in liver SNR and an 8.2% (p = .2) increase in liver-spleen CNR compared to the 90° pulse angle at TR = 275 ms. Increased signal intensity resulting from the use of large flip angle excitation pulses with a single echo SE pulse sequence was predicted and confirmed experimentally in phantoms and humans.     

Dynamic critical scattering near the smectic-A—nematic phase transition in CBOOA

High resolution neutron quasielastic scattering has been applied to a study on the critical dynamics near the smectic-A—nematic phase transition in CBOOA. A line narrowing is observed for a certain value of the momentum transfer. We interpret this narrowing as a critical slowing down of the smectic order parameter fluctuations near the transition temperature T_SN. The relaxation times vary between 10^-8 and 10^-7 sec for a temperature interval of 2 K below T_SN.     

Tensor interaction in heavy-ion scattering: (I). The turning-point model

The Heidelberg shape-effect model for heavy-ion tensor interactions is reformulated and generalized using the Hooton-Johnson formulation. The generalized semiclassical model (the turning-point model) predicts that the components of the tensor analysing power $\text{T}{}_{\mathrm{2q}}$ have certain relations with each other for each type of tensor interaction (T_R, T_P and T_L types). The predicted relations between the $\text{T}{}_{\mathrm{2q}}$ are very simple and have a direct connection with the properties of the tensor interaction at the turning point. The model predictions are satisfied in quantum-mechanical calculations for ⁷Li and ²³Na elastic scattering from ⁵⁸Ni in the Fresnel-diffraction energy region. As a consequence of this model, it becomes possible to single out effects from a T_P? or T_L-type tensor interaction in polarized heavy-ion scattering. The presence of a T_P-type tensor interaction is suggested by measured $\text{T}{}_{20}\text{/}\text{T}{}_{22}$ ratios for ⁷Li+⁵⁸Ni scattering. In the turning-point model the three types of tensor operator are not independent, and this is found to be true also in a quantum-mechanical calculation. The model also predicts relations between the components of higher-rank tensor analysing power in the presence of a higher-rank tensor interaction. The rank-3 tensor case is discussed in detail.     

L 1 subshell yields atZ=63

TheL x ray fluorescence yield Ω₁ (= 0.06±0.02) and the Coster-Kronig yieldsf ₁₂ (=0.26 ±0.10) andf ₁₃ (=0.27±0.03) are measured for Europium (Z=63) by observing EuL x rays and 21.54 keV gammas in coincidence with 174.68 keV gammas in the electron capture decay of¹³¹Gd. In addition the total conversion coefficient α _T for 21.54 keV transition is measured to be 27.5±1.5.     

On two-dimensional finite amplitude electro-convection in a dielectric liquid induced by a strong unipolar injection

The hydrodynamic stability of a dielectric liquid subjected to strong unipolar injection is numerically investigated. We determined the linear criterion T_c (T being the electric Rayleigh number) and finite amplitude one T_f over a wide range of the mobility parameter M. A noticeable discrepancy is shown for T_f between our numerical prediction and the value predicted by stability analysis, which is due to the velocity field used in stability analysis. Recent studies revealed a transition of the flow structure from one cell to two with an increase in T. We demonstrate that this transition results in a new subcritical bifurcation.     

Electron spinT 2 of a nitroxyl radical at 250 MHz measured by rapid-scan EPR

Rapid-scan electron paramagnetic resonance (EPR) was used to measure the room temperature spin-spin relaxation timeT ₂ for the per-deuterated nitroxyl radical, 4-oxo-2,2,6,6-tetramethylpiperidin-1-oxyl-d₁₆ in water at 250 MHz. Signals were recorded on a locally constructed system using either sinusoidal or triangular magnetic field scans. Values ofT ₂ were obtained by simulation of the rapid-scan response and were systematically shorter for the high-field line (m ₁=?1) than for them ₁=0 or +1 lines. Form ₁=+1, the value ofT ₂ increased from 0.41±0.03 μs at 0.5 mM to 0.53±0.03 μs at 0.1 or 0.2 mM. Form ₁=?1,T ₂ increased from 0.35±0.03 μs at 0.5 mM to 0.42±0.03 μs at 0.1 or 0.2 mM. These values put lower bounds on the values ofT ₁ for this nitroxyl at 250 MHz.     

Critical current behavior in locally illuminated superconducting lead strips

We have used guided optical waves to locally illuminate superconducting thin lead strips and measured the critical current as a function of optical power. The measured results resemble the predictions of a simple heating model more closely than the Parker T¹ model in the temperature range investigated (5.5 K to T_c) and several possible reasons for this behavior are discussed.     

Transverse momentum of jets in electroproduction from quantum chromodynamics

Detailed predictions of QCD on transverse momentum distributions of jets in leptoproduction are presented. The average p_⊥² is found to be asymptotically proportional to W² (the hadronic invariant mass squared) with a coefficient function that depends little on x and y. Contributions from gluons in the nucleon are relatively smaller than for σ_L/σ_T.     

A comparative study at 3 T of sequence dependence of T2 quantitation in the knee

Objective

T₂ mapping has been used widely in detecting cartilage degeneration in osteoarthritis. Several scanning sequences have been developed in the determination of T₂ relaxation times of tissues. However, the derivation of these times may vary from sequence to sequence. This study seeks to evaluate the sequence-dependent differences in T₂ quantitation of cartilage, muscle, fat and bone marrow in the knee joint at 3 T.

Methods

Three commercial phantoms and 10 healthy volunteers were studied using 3 T MR. T₂ relaxation times of the phantoms, cartilage, muscle, subcutaneous fat and marrow were derived using spin echo (SE), multiecho SE (MESE), fast SE (FSE) with varying echo train length (ETL), spiral and spoiler gradient (SPGR) sequences. The differences between these times were then evaluated using Student's t test. In addition, the signal-to-noise ratio (SNR) efficiency and coefficient of variation of T₂ from each sequence were calculated.

Results

The average T₂ relaxation time was 36.38±5.76 ms in cartilage and 34.08±6.55 ms in muscle, ranging from 27 to 45 ms in both tissues. The times for subcutaneous fat and marrow were longer and more varying, ranging from 41 to 143 ms and from 42 to 160 ms, respectively. In FSE acquisition, relaxation time significantly increases as ETL increases (P<.05). In cartilage, the SE acquisition yields the lowest T₂ values (27.52±3.10 ms), which is significantly lower than those obtained from other sequences (P<.002). T₂ values obtained from spiral acquisition (38.27±6.45 ms) were higher than those obtained from MESE (34.35±5.62 ms) and SPGR acquisition (31.64±4.53 ms). These differences, however, were not significant (P>.05).

Conclusion

T₂ quantification can be a valuable tool for the diagnosis of degenerative disease. Several different sequences exist to quantify the relaxation times of tissues. Sequences range in scan time, SNR efficiency, reproducibility and two- or three-dimensional mapping. However, when choosing a sequence for quantitation, it is important to realize that several factors affect the measured T₂ relaxation time.     

Properties of the Ising magnet confined in a corner geometry

The properties of Ising square lattices with nearest neighbor ferromagnetic exchange confined in a corner geometry, are studied by means of Monte Carlo simulations. Free boundary conditions at which boundary magnetic fields ±h are applied, i.e., at the two boundary rows ending at the lower left corner a field +h acts, while at the two boundary rows ending at the upper right corner a field −h acts. For temperatures T less than the critical temperature T_c of the bulk, this boundary condition leads to the formation of two domains with opposite orientation of the magnetization direction, separated by an interface which for T larger than the filling transition temperature T_f(h) runs from the upper left corner to the lower right corner, while for T<T_f(h) this interface is localized either close to the lower left corner or close to the upper right corner. It is shown that for T=T_f(h) the magnetization profile m(z) in the z-direction normal to the interface simply is linear and the interfacial width scales as w∝L, while for T>T_f(h) it scales as . The distribution P(?) of the interface position ? (measured along the z-direction from the corners) decays exponentially for T<T_f(h) from either corner, is essentially flat for T=T_f(h), and is a Gaussian centered at the middle of the diagonal for T>T_f(h). Unlike the findings for critical wetting in the thin film geometry of the Ising model, the Monte Carlo results for corner wetting are in very good agreement with the theoretical predictions.     

Aspects of the acoustical design and properties of Christchurch Town Hall,New Zealand

The Christchurch Town Hall (2650 seats) is the major hall in a complex which includes a 986 seat theatre. It was opened on 30 September 1972 and was designed primarily as a choral symphony hall. Reverberation time (125 Hz to 2 kHz) in excess of 2·2 seconds with the hall full is provided by a volume of 20 500 m³ and reflective surfaces. The basic design aim, provision of relatively strong early lateral reflections, is achieved by large interior oblique reflectors which hang free from the boundaries of the reverberant volume. The resulting early lateral energy and long R.T. gives the hall a combination of reverberance, envelopment and clarity. The paper gives an account of design aims and studies including a ray tracing computer program with an interactive graphics output. Measurements of T₆₀, T₁₅ and integrated early energy have been carried out in the hall. Echograms and other measured data are presented. Clarity has been measured by a speech intelligibility test with the Hall empty except for 40 participants. With T₆₀ at 500 Hz 2·7 seconds, the intelligibility was better than the Peutz criterion for public address systems.     

Frequency-dependent spin-lattice relaxation study of transport processes in superionic conductors

The sensitivity of the¹⁹F spin-lattice relaxation dispersion, T₁,(ω), to motional disorder in crystalline superionic conductors of the type La_1?xSr_xF_3?x (x = 0; 0.03) is shown. T₁ times are measured in the frequency range from 90 kHz to 370 MHz using standard techniques in combination with field-cycling. The relaxation dispersion shows qualitative differences from the standard Bloembergen-Purcell-Pound behavior. At low frequencies a relaxation model using a distribution of correlation times for diffusing ions is found to be consistent with the experimental results. At frequencies higher than 50 MHz another process of the Debye type which is not induced by ionic hopping dominates the relaxation.     

Messung der Lebensdauer angeregter Kernniveaus von Gd155

Using two different experimental arrangements, the halflife of the following excited nuclear states in Gd¹⁵⁵ have been measured by the method of delayed coincidences: 60.0 keV-level:T _1/2=(2.4±0.6) · 10^?10 sec, 86.5 keV-level:T _1/2=(6.35±0.09) · 10^?9 sec, 105.3 keV-level:T _1/2=(1.14±0.03) · 10^?9 sec. These results are discussed and compared with the predictions of the collective model.     

Surface and volume phase states of Fe<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Ga<Subscript>x</Subscript>BO<Subscript>3</Subscript> crystals in the vicinity of the Néel point

The behavior of the magnetic system of a surface layer of macroscopic Fe_1?xGa_xBO₃ crystal (x=0, 0.3) in the vicinity of the Néel temperature T_N was studied. The studies were made by a method involving simultaneous gamma, x-ray, and electron Mössbauer spectroscopy that made it possible to obtain information simultaneously from surface layers and from the bulk of a macroscopic crystal. It was found that the temperature T_N(L) at which a thin layer at a depth L from the surface switches to a disordered state is lower than T_N for the bulk and is lower the closer this layer is to the surface. In the vicinity of T_N, a nonuniform state is observed in which the bulk of the crystal is magnetically ordered and the surface layer is disordered. The transition temperature T_N(L) decreases from T_N to its surface value within a surface layer of a “critical” thickness.     

Sound velocity in single crystals of synthetic opals

The [111] longitudinal sound velocity (v _L) in a single-crystal synthetic opal has been measured at a frequency of 10 MHz in the temperature range 4.2–300 K. At 300 K, v _L=2.1×10⁵ cm/s. The quantity dv _L/v _{300 K}(T) (where v _T,K?v_{300 K}) in the ranges 4.2–200 and 200–300 K behaves in the way typical of amorphous and crystalline solids, respectively.     

X-ray production by 1.5–11 MeV protons

K-shell ionization andL x-ray production cross-sections by proton impact have been determined from measurements ofK x-ray yields from thin targets of Ti, Fe, Co, Cu, Ni and Ag and ofL x-ray yields from Au and Pb. The proton energies varied from 1.5 to 11 MeV. A Si(Li) semiconductor detector recorded the x-rays. The total error in the measured cross-sections is mostly less than 5%.K _β /K _α ratios andL _l,β,γ /L _α ratios have been determined. Ionization cross-sections have been compared with predictions of the plane-wave Born approximation (PWBA) and the binary-encounter approximation (BEA). Both theories describe the ionization quite well: PWBA is, however, better for higher proton energies whereas BEA is superior for lower energies. An empirical formula for ionization cross-sections is derived.     

Current-conducting properties of paper consisting of multiwall carbon nanotubes

Electrical conductivity σ(T) of the paper consisting of multiwalled carbon nanotubes (MWCNTs) is studied in the temperature range 4.2-295 K, and its magnetoresistivity ρ(B) at various temperatures in magnetic fields up to 9 T is analyzed. The temperature dependence of the paper electrical conductivity σ(T) exhibits two-dimensional quantum corrections to the conductivity below 10 K. The dependences of negative magnetoresistivity ρ(B) measured at various temperatures are used to estimate the wavefunction phase breakdown length L _φ of conduction electrons and to obtain the temperature dependence L _φ = constT ^?p/2, where p ≈ 1/3. Similar dependences of electrical conductivity σ(T), magnetoresistivity ρ(B), and phase breakdown length L _φ(T) are detected for the initial MWCNTs used to prepare the paper.     

Understanding higher twist: operator approach to power corrections

A thorough discussion of perturbative QCD for twist-4 is presented from a practical point of view. Misleading uses of intrinsic transverse momentum and mass terms are criticized and corrected in the complete expressions relevant for a model-independent experimental test of power corrections which is proposed. Upper and lower bounds for the twist-4 scale are deduced from a theoretically-consistent analysis of present DIS data with a simplified assumption on twist-4, from which a power-dominatedR=σ _L /R=σ _T is predicted.     

Lewis number effects on laminar and turbulent expanding flames of NH3/H2/air mixtures at elevated pressures

This study clarifies the effects of Lewis number (Le) on laminar and turbulent expanding flames of NH₃/H₂/air mixtures. The laminar burning velocity (S_L) and turbulent burning velocity (S_T) were measured using a medium-scale, fan-stirred combustion chamber with ammonia/hydrogen molar ratio (NH₃/H₂) of 50/50 and 80/20 under the maximum pressures of 5 atm. The lean laminar flame with NH₃/H₂ = 50/50 is significantly accelerated by the diffusional–thermal instability, which dominated the trend of S_T,c=0.1 with the equivalence ratio (ϕ). The lean normalized turbulent burning velocity (S_T/S_L) increases with the decrease of hydrogen content due to the weakening effects of S_L. However, the S_T/S_L reaches peak with hydrogen volumetric content less than 20% due to effects made by diffusional–thermal instability than S_L did. The turbulent flame of NH₃/H₂/air mixtures is characterized by self-similar acceleration propagation, and propagation with Le < 1 is faster. A modified correlation considering the effects of Le was proposed, as (d<r>/dt)/σS_L = 0.118(Re_T,flameLe⁻²)^0.57, which was able to predict not only the self-similar propagation of NH₃/H₂/air but also the previous syngas/air flames. The Kobayashi correlations modified by three kinds of Le power exponents were used to clarify the effects of Le by comparing their fitting parameters and predictive powers on experimental data and literature data. Similar pre-factors, power exponents and the goodness of fit (R²) were obtained with Le ranging from 0.58 to 1.62, which suggested that the determination of Le power exponent had no significant effect on the prediction accuracy of the S_T/S_L trend with data of Le near unity. This might be attributed to the fact that the variation ranges of the dimensionless number that characterizes the experimental conditions is much larger than that of the Le.