Al-Cl-N-H体系化学气相淀积AIN粉末的热力学研究

给出了Al-Cl-N-H体系的一组关联反应,探讨了化学气相淀积过程的关联反应热力学特性。根据Gibbs自由焓最小的原则,研究了Al-Cl-N-H体系的平衡组成。Al-Cl-N-H体系合成AlN超细粒子粉末的最佳温度为600～1200℃,AlN平衡得率和体系的初始组成有关,AlCl_2和AlCl的平衡得率随温度的升高而增大。     

Continuous measurement of the heat-induced changes in the optical properties (at 1,064 nm) of rat liver

The radiative transfer optical properties (absorption coefficient, scattering coefficient, and anisotropy of scattering) of slowly heated rat liver have been measured at 1,064 nm. Continuous measurements were made using double-integrating spheres and collimated illumination of the sample for up to 5,000 seconds heating with equilibrium temperatures of 48°, 52°, and 58°C. Generally, the scattering increased, and the absorption and anistropy decreased at rates dependent on the heating temperatures. However, there was a large variability between samples. © 1994 Wiley-Liss, Inc.     

Elasticity changes in the large arteries of human limbs in response to cycle ergometry performed with upper and lower limbs

Summary At rest and after cycle ergometry the elastic properties of the large arteries of limbs of healthy men were examined using an original non-invasive quantitative oscillometric method. It has been shown that in response to muscle work performed with the legs there is a decrease of the effective inner radius, and an increase of the characteristic impedance modulus and bulk modulus and of the elastic resistance of the intact and relaxed wall in the large arteries in the upper limbs. All these changes testify to an increase of vascular tension in the upper limbs. In response to work performed with the hands, there is an increase of the effective inner radius of large arteries of the upper limbs, a large increase of the pulsatile blood volume increment of the intact vessels and a decrease of the characteristic impedance modulus, of the bulk modulus and of the elastic resistance of the intact arterial wall. These changes indicate a decrease of the vascular tension of these arteries. In response to work performed either with the legs or with the hands a decrease of the effective inner radius of large arteries and an increase of the elastic resistance of the relaxed arterial wall were observed in the lower limbs, all these changes indicating relatively small changes in tone of these vessels. It is concluded that the wall tension of large arteries supplying blood to the muscles of non-working limbs is increased. Vascular tension changes in the arteries in working limbs are accounted for by the superimposition of centrally originating vasoconstriction with local vasodilatation, which also affects large arteries.     

Quantitative Analysis of Concealed Conduction into Accessory Atrioventricular Pathways in Wolff-Parkinson-White Syndrome

Concealed conduction is demonstrated to occur in an accessory AV pathway (AP). To test the hypothesis that anterograde and retrograde concealed conduction in the AP would have different characteristics, 35 consecutive patients with single APs were studied. The anterograde or retrograde ERP of the AP could be determined in 23 of those patients. Anterograde concealed conduction in the AP was assessed in the first 13 patients with retrograde AP conduction (8 APs with retrograde conduction only and 5 with both directions) (group A). Retrograde concealed conduction in the AP was evaluated in the remaining 10 patients with anterograde AP conduction (6 APs with anterograde conduction only and 4 with both directions) (group B). The concealed conduction in the AP was quantified by determining the ERP of the AP using a “probe” extrastimulus (S_p) introduced in the opposite chamber. The ERP was determined both during conventional extrastimulus (S₁S₂ method; ERP_c) and during that with an S_p (S₁S_pS₂ method; ERP_p). The S_p was delivered before or after the last S₁ with various S₁S_p intervals. The ERP_p was determined at each S₁S_p interval. Three distinct patterns in concealed conduction in the AP were noted. In the first pattern, the ERP_p was always shorter than the ERP_c, whereas the reverse relation was noted in the second pattern. The third pattern showed a combination of the two. In group A, only the first pattern was noted. In group B, the first, second, and third patterns were noted in 4, 2, and 4 patients, respectively. The first pattern was noted only in septal APs and the second and third were seen only in left free-wall APs. The second pattern was seen in patients with retrograde AP conduction, whereas the third one was mainly noted in patients without retrograde AP conduction. These observations indicate that anterograde and retrograde concealed conduction in the AP have different characteristics. Shortening of the ERP_p might be due to the “peeling back” phenomenon, and its lengthening might be caused by the presence of the inhomogeneous refractory periods of the AP. (PACE 1997; 20[Pt. I]:1342-1353)     

Relationship Between Different Recovery Curves Representing Rate-Dependent AV Nodal Function in Rabbit Heart

Nodal Function and Recovery Measures. Introduction: The rate-dependent changes in atrioventricular (AV) nodal conduction time show different characteristics depending upon whether the conduction times are plotted against the atrial interval (AA-recovery curve) or His-atrial interval (HA-recovery curve). This study characterizes these differences in the context of controlled changes of nodal functional properties, determines their functional significance, and tests the hypothesis that they are related solely to the nodal conduction time of the last beat (last conduction time) before the premature beat.
Methods and Results; Premature nodal conduction times obtained in isolated rabbit heart preparations under various steady-state and transient conditions were plotted as a function of the corresponding HA and AA intervals, as well as the AA interval corrected for the last conduction time. Under all conditions, the corrected AA-recovery curve was indistinguishable in shape from the HA-recovery curve, and as such reflected similar underlying nodal functional properties. Moreover, a selective increase in the last conduction time, induced in the absence of time-dependent effects associated with the functional property of fatigue, shifted the AA-recovery but not the HA-recovery curve upward with respect to the control curve.
Conclusion: The last conduction time accounts entirely for differences between AA-recovery and HA-recovery curves that otherwise reflect the same underlying nodal functional state. Thus, a consistent assessment of rate-dependent changes in nodal function can be achieved with either measure of recovery time.     

Electrophysiological and morphological measurements in cat gastrocnemius and soleus α-motoneurones

Intracellular recording and staining with HRP was used to study the electrical properties and anatomical size of medial gastrocnemius (MG) and soleus (SOL) alpha-motoneurones in curarized cats. The MG motoneurones were divided into two groups on the basis of their input resistance (RN), namely low-resistance MG-LR cells (RN less than 1.0 M omega) and high-resistance MG-HR cells (RN greater than 1.0 M omega). Analysis of the voltage transients following applied current pulses indicated that the SOL neurones had longer membrane time constants (tau o) than the MG-LR cells, while the MG-HR group exhibited intermediate values. Using Rall's equivalent cylinder model, a difference in specific membrane resistivity (Rm) between the MG-LR (low Rm) and SOL (high Rm) cells was obtained. This difference was observed also in neurones of similar anatomical size, and was consistent with the observed difference in tau o. In two neurones Rm was in addition calculated directly from anatomy and input resistance according to the general solution for a continuous neurone model with arbitrary geometry given by Rall. The latter method was found to yield significantly lower values for Rm, although the observed difference between the neurone types remained similar. Also the values for electrotonic length (L) were found to differ considerably between the calculations based on voltage transient analysis and those obtained from combined physiological and anatomical measurements. The observed variations in results are discussed in relation to possible sources of error in the experimental techniques and/or in the theoretical assumptions, particularly that of Rm being uniform over the entire soma-dendritic membrane. It is suggested that Rm might be larger in the dendritic regions than in the soma. A crude approximation of the dendrite to soma conductance ratio (Q) indicated that most cells (80%) had Q greater than 5.     

Mechanical properties of human skeletal muscle fromin vitro studies of biopsies

The steady-state and small-scale dynamic mechanical properties of human rectus abdominis and intercostal muscle have been investigated by testing small biopsiesin vitro, taken during normal surgery. It has proved possible to obtain valid data on the tension/length/stimulation-rate relationship at body temperature for up to 24 hours after removal. The twitch and tetanus parameters, i.e. maximum tension, rise time and decay time, show comparability with those found by other workersin vivo. The steady-state tension/length/stimulation-rate relationship is similar to those found for other mammalian muscles; the tension/stimulation-rate relationship being dependent on muscle length. The responses to small-scale dynamic inputs show the importance of dynamic properties at physiological rates of change of parameters. Responses to single-parameter inputs appear to add when both inputs are applied simultaneously.     

The principal projection pathway between the olfactory bulb and the prepyriform cortex in the cat

The anatomy and neuroelectric properties of the lateral olfactory tract (LOT) were investigated in the cat. Electron micrographs were obtained from sampled areas across the rostro-caudal projection of the pathway. Fiber diameters were estimated and axon spectra were obtained from three regions corresponding to penduncle, mid-LOT, and caudal-LOT. The mean inside diameter for all measured axons was 1.13 ± 0.53 μm. The greatest number was found in the peduncle (approximately 600,000 axons). Mid-LOT and caudal-LOT each contained approximately 250,000 axons. Unmyelinated processes were estimated to be more numerous than the myelinated axons. Synaptic structures were also observed in the LOT. Crosssectional area measurements of the LOT were obtained from tissue repared for light microscopy. The area decreased from about 0.3 to 0.2 mm² across the projection from olfactory bulb to cortex. The anatomical data were used to predict the conduction properties of transmission over the LOT. The olfactory bulb mitral cells were stimulated electrically and conduction velocity and temporal dispersion were evaluated in the tract. The strength-duration and stimulus-response curves and the potential profile during stimulation were also obtained. The time constant for LOT axons was 0.3 msec. The stimulus-response curve was sigmoidal in shape for both presynaptic and postsynaptic responses. The relationship between input (the action potentials) and output (cortical postsynaptic potentials) was linear up to 90 times threshold. Action potentials were conducted at 20 m/sec across the pathway over the peduncle and decreased to about 10 m/sec in caudal aspects. The potential profile for action potentials decayed exponentially into the depths of the cortex whereas the synaptic potential was a surface negative dipole field. The axon spectra were convolved with the electrophysiological properties of the LOT Yto mathematically reconstruct action potentials. The empirically derived monoand biphasic curves fitted reasonably well with experimentally derived data under various stimulus conditions.     

Membrane properties of preganglionic fibers occurred in bullfrog lumbar sympathetic ganglion

Membrane propeties of preganglionic fibers in the bullfrog lumbar sympathetic ganglion were studied using a conventional intracellular microelectrode technique. Charging or discharging electrotonus of the preganglionic fibers were found to be slow. The slow and fast time constants were around 62 and 15 msec, respectively. An inward-going rectification was activated in the potential range below –8mV. These electrophysiological properties differed from those observed in a principal neuron and suggested a close resemblance between the sympathetic preganglionic fibers and thick myelinated fibers.     

High-strength dental gypsum prepared by cold isostatic pressing

Powder of a dental plaster (Moldabaster^R, Bayer) was compacted by cold isostatic pressing (CIP) at 300 MPa for 10 min and immersed in water for 1 h. The compressive strength of the CIP-processed material was compared with that of conventionally processed material. The green block of plaster before water immersion was carvable with a green density and green strength of 50% and 5 MPa, respectively. The compressive strength of the CIP-processed gypsum after 24 h was three times higher than that of conventionally processed, 103 compared with 29 MPa, and the microhardness (Vickers hardness number, VHN) of CIP-processed materials was 40 compared with 12VHN. An increase of density was also recorded. It seems that the CIP process produced a dense and pore-free gypsum with a composite-like structure. The high-strength gypsum processed by CIP may extend the applications of this material in the medical field as implant materials.