Reaction of bulk protons with a mitochondrial inner membrane preparation: time-resolved measurements and their analysis

The laser-induced proton pulse technique [Gutman, M. (1986) Methods Enzymol. 127, 522-538] was applied on suspensions of submitochondrial vesicles, and the exchange of protons between the bulk and the mitochondrial membranes was measured in the time-resolved domain with a submicrosecond resolution. The protons were discharged by photoexcitation of pyranine (8-hydroxypyrene-1,3,6-trisulfonate) by a short laser pulse, and the reprotonation of the pyranine anion was monitored at 457.8 nm. In parallel, the protonation of the membrane was followed at 496.5 nm, looking at the transient absorbance of fluorescein, covalently attached to the M side of the membrane. The analysis of the relaxation dynamics was carried out by a simulation procedure that reconstructs the observed dynamics of the two chromophores. The analysis revealed the presence of the membrane indigenous buffering moieties. The low-pK buffer (pK 4.1) was present in a quantity of 100 +/- 20 nmol/mg of protein, and its kinetics indicate that it appears in multianionic clusters bearing a negative electric charge. The medium-pK buffer (pK 6.9) was present in a larger quantity (200 +/- 20 nmol/mg), and its kinetic parameter indicated clustering into positively charged domains. Both types of indigenous buffer reacted with the proton and pyranine anion in unhindered diffusion-controlled reactions. On the other hand, the exchange of protons between the indigenous buffer moieties was rather slow. No evidence was found for the presence of sites capable of retaining a proton, secluded from the bulk, for a time frame longer than 100 microseconds as required by the models of localized proton gradient.     

Classification of hemodynamic changes in renal artery stenosis using cine magnetic resonance phase contrast flow measurements

PURPOSE: To evaluate the use of high-temporal resolution cine MR phase-contrast flow measurements for assessment of flow dynamics in renal artery stenosis (RAS). MATERIAL AND METHODS: In a dog model, cine MR flow measurements were validated by comparing the MR flow data to an invasive transit-time ultrasound reference technique for different degrees of RAS. Cardiac-gated MR flow curves were recorded in 56 renal arteries of 28 patients with a temporal resolution of at least 32 ms. In all cases RAS was confirmed by digital subtraction angiography (DSA). Abnormalities of flow dynamics were assessed in the calculated flow curves using the MR parameters mean flow, maximum velocity, and time to systolic maximum. RESULTS: By means of the MR blood flow parameters high-grade stenoses (> 50%, n = 23) were detected with sensitivity of 100% and specificity of 94% with reference to DSA. The overall differentiation between stenoses (n = 37) and non-stenosed vessels (n = 19) revealed a sensitivity of 87% and a specificity of 100%. CONCLUSION: Analysis of cardiac-gated MR flow curves provides a non-invasive method to assess the hemodynamic significance of RAS and thus allows a functional evaluation in relation to the morphologic characteristics of the stenosis.     

Structure and magnetic properties of bulk nanocrystalline Nd-Fe-B permanent magnets prepared by hot pressing and hot deformation

Structure and magnetic properties were studied for bulk nanocrystalline Nd-Fe-B permanent magnets that were prepared at 650 °C for 3 min under 300 MPa using the SPS-3.20-MK-V sintering machine and the hot pressed magnets were then submitted to hot deformation with height reduction of 50%,60%,70%,80%,and 85%.Effects of height reduction(HR) and deformation temperature on the structure and magnetic properties of the magnets were investigated.The crystal structure was evaluated by means of X-ray diffraction(XRD) and the microstructure was observed by transmission electron microscopy(TEM).The magnetic properties of the magnets were investigated by vibrating sample magnetometer(VSM).As the height reduction increased,the remanence(B r) of the magnets increased first,peaks at 1.3 T with HR=60%,then decreased again,and the coercivity(H ci) of the magnets decreased monotonically.On the other hand,as the deformation temperature increased,the B r of the magnets increased first,peaks at 1.36 T with HR=60%,then decreased again,and the H ci of the magnets decreased monotonically.Under optimal conditions,the hot deformed magnet possessed excellent magnetic properties as B r =1.36 T,H ci =1143 kA/m,and(BH) max =370 kJ/m 3,suggesting the good potential of the magnets in practical applications.     

An analysis of the formation of bulk amorphous silicon from the melt

The possibility of forming bulk amorphous silicon from the undercooled liquid is analyzed by calculations of the rates for homogeneous nucleation of the amorphous and crystalline phases, the rate of heterogeneous nucleation of the crystalline phase on the liquid-amorphous interface, and the possibility of crystallization of the amorphous phase in the solid state. It appears that bulk formation of the amorphous phase may be possible in appropriately seeded millimeter-sized samples. A new lower limit for the amorphous-liquid interfacial tension is presented as well. This article is based on a presentation made in the “Structure and Properties of Bulk Amorphous Alloys” Symposium as part of the 1997 Annual Meeting of TMS at Orlando, Florida, February 10–11, 1997, under the auspices of the TMS-EMPMD/SMD Alloy Phases and MDMD Solidification Committees, the ASM-MSD Thermodynamics and Phase Equilibria, and Atomic Transport Committees, and sponsorship by the Lawrence Livermore National Laboratory and the Los Alamos National Laboratory.     

Estimating cochlear filter response properties from distortion product otoacoustic emission (DPOAE) phase delay measurements in normal hearing human adults

This study examined cochlear filter response properties derived from f1- and f2-sweep phase delay difference measures in 60 normal hearing human adults. Seven different f2 frequencies ranging from 1.1 to 9.2 kHz were presented (f2/f1 ratios of 1.1-1.3). F2 intensity level was varied in 5 dB steps from 30 to 50 dB SPL (the level of f1 was 15 dB above the level of f2). DPOAE delay estimates in a f2-sweep paradigm are longer than in a f1-sweep paradigm at the same frequency and intensity. This indicates that the f2-sweep DPOAE phase delay is composed of a greater proportion of the filter response time at the site of DPOAE generation than the f1-sweep delay. This proportion was isolated by subtracting f1-sweep DPOAE delays from f2-sweep delays at similar f2 frequencies and intensities. Under the assumption of linearity and minimum phase the impulse response of the filter at each f2 stimulus level was calculated from the mean phase delay difference. Frequency response properties were calculated by Fourier transformation of the impulse response at each f2 frequency and intensity. High frequency low intensity impulse responses had longer response times and narrower frequency bandwidths than low frequency high intensity responses. The Q10dB values of DPOAE derived tuning curves ranged from 2.4 (1.5 kHz) to 7.3 (8.5 kHz).     

The importance of slice location on the accuracy of aortic regurgitation measurements with magnetic resonance phase velocity mapping

Although several methods have been used clinically to evaluate the severity of aortic regurgitation, there is no purely quantitative approach for aortic regurgitant volume (ARV) measurements. Magnetic resonance phase velocity mapping can be used to quantify the ARV, with a single imaging slice in the ascending aorta, from through-slice velocity measurements. To investigate the accuracy of this technique, in vitro experiments were performed with a compliant model of the ascending aorta. Our goals were to study the effects of slice location on the reliability of the ARV measurements and to determine the location that provides the most accurate results. It was found that when the slice was placed between the aortic valve and the coronary ostia, the measurements were most accurate. Beyond the coronary ostia, aortic compliance and coronary flow negatively affected the accuracy of the measurements, introducing significant errors. This study shows that slice location is important in quantifying the ARV accurately. The higher accuracy achieved with the slice placed between the aortic valve and the coronary ostia suggests that this slice location should be considered and thoroughly examined as the preferred measurement site clinically.     

精密合金3J1棒材制造工艺技术与性能浅析

本文介绍3J1合金棒材制造的工艺技术及性能浅析。通过合理控制真空感应炉冶炼各个阶段的参数和工艺要点,从而为电渣炉冶炼出优质的母材。电渣炉冶炼出的电渣锭经不同锻造比锻造后再经热处理得出相应的力学性能。     

Computation of thermodynamic properties of liquid ferrous alloys from structural measurements

Relation between X-ray scattering intensities, mean square thermal fluctuations and thermodynamic properties. High temperature X-ray diffraction study of liquid Fe-Ni and Fe-Si alloys using reflection and transmission geometries. Calculation of the structure factor as a function of wave vector. Extrapolation to zero wave vector. Calculation of the concentration-concentration correlation function defined by A. B. Bhatia and D. E. Thorton. Computation of thermodynamic quantities of mixing ΔG, ΔH and ΔS for the binary alloys. Comparison with direct thermodynamic measurements reported in the literature.