Jumping Distance Research Articles

Jump rate and linear distance of vacancy on the structure and electrical conductivity of Ni 0.65Zn 0.35Cu xFe 2− xO 4 ferrites

Ferrite compositions of Ni 0.65Zn 0.35Cu x Fe 2− x O 4 (0⩽ x<1) were examined using X-ray analysis. The effect of the linear distance of vacancy jumping on the lattice parameter was studied. The jump rate of vacancy increased with increasing Cu concentration. The increase of jump rate of vacancy enhanced the linear distance which increased the conductivity and mobility of the charge carriers. The majority of charge carriers of our systems are holes. The estimated linear distance of each jump was 2.86×10 −7 m. The decrease of thermal conductivity was attributed to the increase of the jump rate and also the linear distance. The formation of oxygen vacancies during the substitution of Cu 2+ ions for Fe 3+ ions helped the internal stress to decrease the lattice parameter. Because the ionic radius of O 2− (0.136 nm) is larger than that of Fe 3+ (0.067 nm) ion.

Comparative Effects of Deep Versus Shallow Squat and Leg-Press Training on Vertical Jumping Ability and Related Factors

Young, previously untrained healthy men (n = 10) and women (n = 8) completed 9 weeks of periodized, machine-based squat training to determine if manipulating range of motion would have a differential effect on vertical jumping ability and related measures. Subjects were pretested and then randomly assigned to 1 of 3 groups: (a) deep squats (n = 6), (b) shallow squats (n = 6), and (c) controls (n = 6). Training took place 3 days per week. Pre-and posttesting included standing (RVJ) and depth (DVJ) vertical jumps for distance; machine deep and shallow squats for 1RM (1 repetition maximum) relative strength; and velocity-controlled squats at 0.51 m·s−1 for relative peak force and at 1.43 m·s−1 for relative peak power. Based on ANCOVA posttest results, the training protocols were ineffective in eliciting improved performance (p > 0.05) in VJ, slow-velocity squatting force, and moderately fast squatting power when performance was compared with the performance of control subjects. Conversely, the group training with deep squats was the only group to perform significantly (p <0.05) better than controls for 1RM shallow squats and significantly (p <0.05) better than both shallow-squat and control groups for 1RM deep squats. Furthermore, the coefficient of transfer for deep squats to both RVJ (2.32) and DVJ (1.68) was substantially greater than for shallow squats (0.31 and 0.11, respectively). It was concluded that deep-squat training appears to elicit the best improvement for both shallow-and deep-squatting performance. However, 9 weeks of machine-based, periodized squat training, regardless of depth, does not appear to appreciably enhance slow-velocity squatting force, moderately fast squatting power, or vertical jumping distance in previously untrained men and women.

Allometric Scaling Relationships of Jumping Performance in the Striped Marsh Frog Limnodynastes Peronii

We constructed a force platform to investigate the scaling relationships of the detailed dynamics of jumping performance in striped marsh frogs (Limnodynastes peronii). Data were used to test between two alternative models that describe the scaling of anuran jumping performance; Hill's model, which predicts mass- independence of jump distance, and Marsh's model, which predicts that jump distance increases as M(0.2), where M is body mass. From the force platform, scaling relationships were calculated for maximum jumping force (F(max)), acceleration, take-off velocity (U(max)), mass-specific jumping power (P(max)), total jumping distance (D(J)) and total contact time for 75 L. peronii weighing between 2.9 and 38. 4 g. F(max) was positively correlated with body mass and was described by the equation F(max)=0.16M(0.61), while P(max) decreased significantly with body mass and was described by the equation P(max)=347M(-)(0.46). Both D(J) and U(max) were mass-independent over the post-metamorph size range, and thus more closely resembled Hill's model for the scaling of locomotion. We also examined the scaling relationships of jumping performance in metamorph L. peronii by recording the maximum jump distance of 39 animals weighing between 0.19 and 0.58 g. In contrast to the post-metamorphic L. peronii, D(J) and U(max) were highly dependent on body mass in metamorphs and were described by the equations D(J)=38M(0.53) and U(max)=1.82M(0.23), respectively. Neither model for the scaling of anuran jumping performance resembled data from metamorph L. peronii. Although the hindlimbs of post-metamorphic L. peronii scaled geometrically (body mass exponent approximately 0.33), the hindlimbs of metamorphs showed greater proportional increases with body mass (mass exponents of 0.41-0.42).

Scaling of Jumping Performance in Anuran Amphibians

-Theories on the scaling of saltatory locomotion were examined using data of anuran jump performance. We explored whether take-off speed in geometrically similar animals would be the same regardless of body mass (an energy output model), or whether it would scale with mass0?11 (a power output model). Two frog species in central Panama, Eleutherodactylus fitzingeri (powerful jumpers, 0.14-8.65 g) and Bufo typhonius (slow hoppers; 0.16-11.60 g), were used for morphometric and take-off potential measurements. Like those of other species, our frog species showed isometric body shape in general in terms of muscle mass, hindlimb length, and interilial width. Scaling exponents for take-off speed were 0.16-0.17 for the two species and were not statistically deviated from those predicted by the power output approach. This conclusion would be supported by the fact that burst-type locomotion relies on the rate of energy release, not the total amount of energy released, by jumping muscles. A theory on scaling of saltatory locomotion postulates that geometrically similar animals exhibit the same jump capacity (height, distance, speed) regardless of size, because the energy output per muscle mass required for takeoff is essentially the same among these animals (Hill, 1950). This theory, however, has been challenged by empirical tests on various anuran species where results showed that jump distance scaled with body mass to the power of 0.2-0.3 (Zug, 1978; Emerson, 1978; Miller et al., 1993). Deviations of the empirical results from theoretical predictions led us to consider an alternative model for the scaling problem. BennetClark (1977) and Gabriel (1984) emphasized that power output (rate of energy release), rather than energy availability, produced by jumping muscles would be the major factor determining the locomotory scaling in relatively small animals. The present study revisits the theoretical bases of the two approaches, and uses the power output approach to try to explain how jump capacity scales allometrically with body mass. Theories associated with take-off speed Energy output approach.-This theory is based on the concept that the specific work done by the jumping muscle is the same among isometric animals (Hill, 1950). At maximal jumping, all extensor muscles of frog hindlimbs contract simultaneously. The average muscle force (F,) and the length (1) by which the muscles shorten yield energy output (work) for the take-off. Because force is proportional to cross-sectional area (A) and muscle shortening to the initial * To whom correspondence should be addressed. muscle length (L), the work (E) should be proportional to muscle mass and thus to body mass (m). E = F 1 cx A L x m, and so E/m = constant. Eq. (1) This work is converted into kinetic energy that is used by the frog to create its takeoff velocity (v). E = mv2/2, or E/m O v2 = constant. Eq. (2) Jump distance (D) can be defined with (v), takeoff angle (0), and the gravitational constant (g) as follows. D = v2sin20 /g. Eq. (3) If take-off angle is assumed to be similar among the animals, combining the above equations gives D oc E/m = constant. Eq. (4) Equations (2) and (4) confirm that take-off capacity by isometric animals is the same regardless of size. Power output approach.-This theory is based on the concept that the jump power of a whole animal (P,) is proportional to mechanical power (Pm) of its extensor muscles (Lutz and Rome, 1994). Because power is a product of force multiplied by velocity, Pi c Pm, and thus F, v x F,, V, Eq. (5) where Fj is the ground reaction force exerted by the hindlimbs at take-off and V is the average shortening velocity of extensors. Fi is given by Fi = mv'/2s, or F,i mv2/LH. Eq. (6) Here, s and LH are the acceleration distance and This content downloaded from 157.55.39.123 on Mon, 18 Jul 2016 06:01:23 UTC All use subject to http://about.jstor.org/terms SCALING OF ANURAN TAKE-OFF PERFORMANCE the hindlimb length, respectively. From equations (5) and (6), v oc (Fm V)/(mv2/LH), or v3 cc (F, V)/(m/LH). Eq. (7) As Fm is proportional to muscle cross-sectional area and V is proportional to muscle length, Pm is proportional to muscle mass and thus body mass (m). Equation (7) can be re-written as

Comparative Effects of Deep Versus Shallow Squat and Leg-Press Training on Vertical Jumping Ability and Related Factors

Young, previously untrained healthy men (n = 10) and women (n = 8) completed 9 weeks of periodized, machine-based squat training to determine if manipulating range of motion would have a differential effect on vertical jumping ability and related measures. Subjects were pretested and then randomly assigned to 1 of 3 groups: (a) deep squats (n = 6), (b) shallow squats (n = 6), and (c) controls (n = 6). Training took place 3 days per week. Pre-and posttesting included standing (RVJ) and depth (DVJ) vertical jumps for distance; machine deep and shallow squats for 1RM (1 repetition maximum) relative strength; and velocity-controlled squats at 0.51 m·s−1 for relative peak force and at 1.43 m·s−1 for relative peak power. Based on ANCOVA posttest results, the training protocols were ineffective in eliciting improved performance (p > 0.05) in VJ, slow-velocity squatting force, and moderately fast squatting power when performance was compared with the performance of control subjects. Conversely, the group training with deep squats was the only group to perform significantly (p <0.05) better than controls for 1RM shallow squats and significantly (p <0.05) better than both shallow-squat and control groups for 1RM deep squats. Furthermore, the coefficient of transfer for deep squats to both RVJ (2.32) and DVJ (1.68) was substantially greater than for shallow squats (0.31 and 0.11, respectively). It was concluded that deep-squat training appears to elicit the best improvement for both shallow-and deep-squatting performance. However, 9 weeks of machine-based, periodized squat training, regardless of depth, does not appear to appreciably enhance slow-velocity squatting force, moderately fast squatting power, or vertical jumping distance in previously untrained men and women.

Dynamics of the long jump

A mechanical model is proposed which quantitatively describes the dynamics of the centre of gravity (c.g.) during the take-off phase of the long jump. The model entails a minimal but necessary number of components: a linear leg spring with the ability of lengthening to describe the active peak of the force time curve and a distal mass coupled with nonlinear visco-elastic elements to describe the passive peak. The influence of the positions and velocities of the supported body and the jumper's leg as well as of systemic parameters such as leg stiffness and mass distribution on the jumping distance were investigated. Techniques for optimum operation are identified: (1) There is a minimum stiffness for optimum performance. Further increase of the stiffness does not lead to longer jumps. (2) For any given stiffness there is always an optimum angle of attack. (3) The same distance can be achieved by different techniques. (4) The losses due to deceleration of the supporting leg do not result in reduced jumping distance as this deceleration results in a higher vertical momentum. (5) Thus, increasing the touch-down velocity of the jumper's supporting leg increases jumping distance.

Predicting depth vertical jumping distance

If independent variables collectively account for each person's ability to vertically jump, then appropriate manipulations of any or all of these factors would be expected to improve jumping performance. Furthermore, if training may elicit the desired manipulations, then the identification of specific weaknesses would enable clinicians and scientists to individualize interventions so as to maximize the effects. In the present exploratory investigation, equations were developed predicting depth vertical jumping (DVJ) distance, a technique roughly simulating the myriad of scenarios in which a rapidly decelerated linear movement precedes vertical jumping. To accomplish this, body composition and 32 variables generated during the performance of concentric-only velocity-spectrum squats were obtained using 52 men and 50 women. At each of four different squatting velocities four force and four power variables met conservative reliability standards for selection as potential predictors of jumping performance. Two explanatory regression equations generated via a forward stepwise approach yielded R-values of 0.89 and 0.90 and SEE ranging from 0.059 to 0.060 meters (2.32 to 2.36 inches). Relative peak power (peak-power-to-body-weight ratio) during squatting exercises performed at 1.43 meters.sec -1 as well as at each individual's optimal velocity for power production were significant predictors of DVJ distance. The predicted distance was also significantly attenuated if subjects were female. Based upon the variables assessed in this investigation, it appears that for young adults, the higher the relative peak squatting power at moderately fast velocities the greater the DVJ performance, and being female negatively impacts this type of jumping.

Determination of The Diffusion Mechanism by A Method with New Possibilities: Nuclear Scattering of Synchrotron Radiation

ABSTRACTThe elementary diffusion jump in crystalline solids can be determined by methods derived from nuclear physics. With these methods not only diffusion rate(s) but also diffusion vector(s), i.e. the complete diffusion mechanism can be deduced. We report on a new method for probing the elementary diffusion jumps in crystalline lattices on an atomistic scale and demonstrate its potential by a study of 57Fe diffusion in different intermetallic alloys. Compared to the results of conventional tracer (macroscopic) technique, the new method provides clear and doubtless statements concerning the direction and distance of elementary jumps. One can also determine (though less precisely than with tracer diffusion), iron diffusion coefficients.

Jump distance of dance landings influencing internal joint forces: II. Shear forces.

Little is known about shear loading patterns during dance movements. The purpose of the study was to investigate the effect of jumping distance (JD) on contributors of ankle and knee shear forces (SF) generated during the landing phase of traveling jumps. Six female dancers performed 10 trials each at 30, 60, and 90% maximum jump distance (JD) and 15 jumps ranging from 35 to 100% JD. A sagittal view of the right leg landing onto a force platform was filmed using a high-speed cine camera. Greater ankle and knee joint reaction shear forces (JRSF) and quadriceps SF (QuadSF) were observed (P < 0.05) at increased JD. Although the triceps surae SF (TriSurSF) also increased at greater JD for all but one participant, the effect on minimizing the increase in the ankle SF was minor. The peak QuadSF magnitude and rate of loading were always greater than the corresponding knee JRSF variables. However, the increased QuadSF that occurred at longer jumps led to increased knee SF for only half of the participants.

Jump distance of dance landings influencing internal joint forces: I. Axial forces.

Knowledge of the magnitude and rate of applying axial forces (AF) during actual dance movements is necessary for understanding the etiology of chronic injuries and osteoarthritis. The purpose of this study was to investigate the effect of jumping distance on component ankle and knee joint AFs generated during the landing phase of traveling jumps. Six female dancers performed 10 jumps each at 30, 60, and 90% maximum jump distance (JD) and 15 jumps ranging from 35 to 100% JD. A sagittal view of the right leg landing onto a force platform was filmed. Greater ground reaction force maxima, knee flexion, knee and ankle flexion velocity, tibial landing angle, net ankle and knee joint moment maxima, ankle and knee joint reaction AFs, and quadriceps AFs (QuadAF) peak magnitudes and rates of AF application (dFmax/dt) were observed (P < 0.05) at increased JD. The QuadAF was a more important determinant of knee AF than joint reaction AF. Increased quadriceps force was useful for accommodating impact forces but served to increase its contribution to Knee AF, particularly during the later portion of the impact phase. High impact situations create significant magnitudes (e.g., 14 BW) and dFmax/dt of muscle AFs which could contribute to excessive joint wear.

PREDICTION EQUATION FOR STANDING VERTICAL JUMPING DISTANCE: CROSS VALIDATION ANALYSES 587

In this investigation, the validity of a regression equation predictive of restricted standing vertical jumping distance (RVJ) was assessed. This jump eliminates arm swing and antero-posterior torso motion in order to isolate the legs and hips. The estimation sample (X1) included 52 men and 50 women. However, due to the small number of subjects per potential predictor (≈3), cross validity analyses using a holdout sample were not performed. A new validation sample (X2) was acquired including 31 men and 32 women with characteristics similar to those of the original group: age ([horizontal bar over]X1 = 23.0 yrs, [horizontal bar over]X2 = 23.9 yrs), body weight ([horizontal bar over]X1 = 72.4 kg, [horizontal bar over]X2 = 70.9 kg),% fat ([horizontal bar over]X1 = 16.6,[horizontal bar over]X2 = 15.5), and RVJ ability ([horizontal bar over]X1 =.32 m, [horizontal bar over]X2 =.28 m). The original equation for RVJ was:.2494 +.009074 (Relative Peak Squatting Power @ 1.43 m· sec.-1) -.004417 (Relative Peak Squatting Force @ 0.51 m· sec.-1) -.001480 (% Fat). The multiple correlation was.83 and SE was.0452, suggesting the equation accounted for 69% of the variability in jumping performance. To assess validity, residuals were compared for X1 and X2 samples using an independent t-test, correlations between predicted and actual RVJ distances were calculated for the X2 sample, and both the original equation and a new one generated from the hold-out sample were evaluated for parallelism and coincidence of slopes. Residuals were smaller (p <.001) for X2. The correlation between predicted and actual RVJ's for X2 was high (r =.84, p <.001). Slopes for the original equation and a new one based on the X2 sample were parallel (p>.91 for relative peak power and force, and% fat) and coincident (p >.82 for relative peak force and power, and% fat). This suggests the original equation is predictive of RVJ for young, healthy men and women although it tends to slightly under predict. Therefore, it appears that increasing moderately fast relative peak squatting power and reducing both slow-velocity relative peak force and excessive body fat will enhance RVJ performance.

Cation distribution and mechanism of electrical conduction in nickel-copper manganite spinels

With the view of understanding the electrical conduction mechanism in the nickel-copper manganite spinels, the cation distribution and the ionic configurations of these compounds have been established by associating powder neutron diffraction, thermogravimetric measurements and XPS spectroscopy analysis. Neutron diffraction measurements allow us to reach the scattering lengths in both tetrahedral and octahedral sites. From this information we deduce lower and upper limits for the different cation fractions in both sites. The XPS spectroscopy analysis shows a predominately divalent copper, localized in tetrahedral sites. The monovalent copper is also present, but at a much smaller content. The additional information supplied by Mn 2+ tetrahedral thermogravimetric measurements resolves the cation distribution in these compounds. Finally, the discussion of the electrical properties using these structural formulas has shown that the presence of copper probably induces a mean-range hopping, the average distance of jumps being estimated to ≈ 9 Å.

Variation in jump force production within an instar of the grasshopper Schistocerca americana

Jumping ability varies by two‐fold within an instar during the moult cycle in the grasshopper, Schistocerca americana (Acrididae: Cyrtacanthacridinae). Changes in jump distance could result from deviations in jump angle away from the optimum during development, a change in jump energy and/or a change in body mass. Body mass has already been shown to vary by over two‐ fold within an instar (Queathem, 1991). In the present study, jump angle remained near the optimum of 43° during the time course of maximal jumps throughout the instar. Jump energy was correlated with ground reaction force production because energy lost to backward rotation and drag was small. Ground reaction force production varied by nearly four‐fold over the period of the instar. Within instar six, force production and body mass accounted for 85% of the variation in jump distance. Their patterns of change relative to one another explain the four functional stages we define for within instar performance. Jump distance increased early within instar six (Stage I, days 0–2) because force production increased. In Stage II (days 3–8), jump distance remained at its peak because an increase in body mass was offset by an equal increase in force production. Jump distance decreased in Stage III (days 8–11) because body mass continued to increase while force production levelled off. Force production decreased to a greater extent than body mass during Stage IV (days 11–13), resulting in a further decline in jump distance during the three days preceding the moult to adulthood. Our results suggest that further examination of the musculo‐skeletal system could provide a causal explanation for this change in jumping ability within an instar. The present study illustrates the remarkable physiological and mechanical changes that affect locomotion within a single instar, and highlights developmental differences between arthropods and vertebrates. Arthropod development is by its very nature a discontinuous process separated by periods of continuous, parabolic changes, and this pattern of growth is reflected in locomotor performance through ontogeny.

Can Children with Mild Mental Retardation Perceive Affordances for Action?

Recent evidence utilizing an ecological approach to perception (Gibson, 1979; Warren, 1984) suggests that children acquire the ability to distinguish what movement an environment “affords” soon after they acquire motor skills (e.g., Gibson et al., 1987; Palmer, 1989; Ulrich, Thelen, &amp; Niles, 1991). However, it is still unclear whether or not children with cognitive disabilities can accurately perceive affordances (see Burton, 1987, 1990). The purpose of this study was to determine if boys with mild mental retardation could perceive affordances for the skill of jumping distances (standing long jump). Boys with mild mental retardation were asked to judge whether or not various distances could be jumped across by use of a two-footed takeoff and landing. Perceptual judgment was then compared to actual maximum jumping distance. Results indicate that boys with mental retardation were able to accurately perceive the affordance for jumping distance. Results were explained via an ecological perspective.

スキージャンプの踏み切り直後の動作

This paper presents a model of ski jumping movement after the take-off phase. The flight distance of ski jumping is dependent on the aerodynamic forces. We measure the aerodynamic forces using a scale model of a ski jumper for three flight styles (Normal Style, V Style, Flat V Style) and in addition measure the aerodynamic forces present after the take-off motion. The longest flight distance is achieved with Flat V Style. Considering style transition, we calculate the optimal Changing Time (CT) from Normal Style to V Style or Flat V Style to V Style with computer flight simulation. The relation between the initial angular velocity of a rigid body model of a ski jumper on the sagittal plane and flight distance is clearly explained. In the take-off phase a significant fraction of jumpers initiate upward motion by rotating the upper body. But others complete this movement with small rotation of the upper body to decrease drag. We performe computer simulations for these two cases from takeoff to 0.4sec after take-off. Linear velocity is greatly decreased with the first jumping technique. The second technique however does not suffer from this velocity decrease.

Analysis of athletic performance with prophylactic ankle devices

We evaluated the effect of different ankle support devices on athletic performance. Thirty varsity college athletes were tested with both ankles supported by taping, Swede-O brace, Kallassy brace or left unsupported. The athletes performed four events: broad jump, vertical leap, 10 yard shuttle run, and 40 yard sprint. The events and appliances were randomized to prevent bias by fatigue. Compared to the results when no support was used, ankle taping resulted in a significant decreased performance in the vertical jump (4%), shuttle run (1.6%), and sprint (3.5%) (P less than 0.05). Use of the Swede-O brace decreased performance in the vertical jump (4.6%), broad jump (3.6%), and time of the sprint (3.2%). Results using the Kallassy brace showed a decrease in the vertical jump (3.4%) when compared to no support. The test results of the shuttle run with taping were slower than the Kallassy brace (P less than 0.05). Wearing the Swede-O brace caused the athletes' broad jump distance to decrease more than the Kallassy brace (P less than 0.05). Subjective questionnaires supported the Kallassy brace as the most comfortable support and the one that decreased performance the least. Taping of the ankles is universally accepted for ankle prophylaxis. This study has shown a decrease in performance when ankles are taped compared to ankles with no protection. Since the decreases in performance caused by ankle braces are minor, this should not be used as a criterion for selection of prophylactic support compared to taping.

Basic Study on the Teaching in the Running Long Jump

The present study was made to elucidate some factors which seemed to be involved in variable jumped distances of the running long jump by age and sex, and also to clarify age changes in these factors.Six hundred and thirty school children aged 8-12 years (second-sixth graders) were asked to perform the running long jump from an arbitrary approach distance. Out of these 630, 526 presented an ordinary movement pattern of taking-off on one leg and landing on both legs and were employed as experimental subjects. Fourteen factors were found by motion analysis to be involed in the jumped distance; 2 factors were by the physical structure of each child. These 16 factors were analyzed in terms of multiple regression.The results obtained here are as follows:1) Except for the 9-year-old children, approach velocity, jumping height, and angle of landing were found to be factors generally responsible for deciding the jumped distances.2) Generally, approach velocity tended to contribute more highly to the jumped distance than either the jumping height or the angle of landing.3) However, approach velocity tended to contribute less and jumping height tended to contribute more to the jump distance respectively, when both the male and female subjects were 10 years old or older. Approach velocity showed a tendency to contribute increasingly to the jumped distance and the angle of landing to contribute decreasingly to the jumped distance until the male subjects became 10 years old.4) In the 11-and 12-year-old males tested, the angle of the knee joint in the free leg at the moment of the take-off was found to be responsible for the jumped distance. In the 11-and 12-year-old females tested, on the other hand, the angle of the hip joint-toe line from the horizontal plane in the take-off and the angle of the both thighs in the touch-down were involved in the jumped distance.

Fatigue Parameters of Lead Zirconate Titanate Thin Films

AbstractTemperature and voltage dependence of fatigue parameters were studied for PZT thin film capacitors on the basis of our fatigue model. It was found that the coefficient of dielectric viscosity of PZT and initial internal field difference of PZT capacitors play a key role in determining fatigue rate. Jump distance was calculated from voltage dependence of decay constant, and it turned out to be essentially the same as the lattice parameter. This result indicates that vacancies (oxygen vacancies, mainly) move parallel to the polarization direction during fatigue. Activation energy was calculated from the temperature dependence of the decay constant. It was confirmed that activation energy for domain wall movement determines fatigue rate at various temperatures. This fatigue model can be used to predict the fatigue behavior and can be extended to develop an accelerated test for fatigue.

Dislocation jump distances during creep of pure and doped NaCl single crystals using nuclear magnetic resonance pulse techniques

Jump distances of dislocations are determined from the spin-lattice relaxation rates in a rotating frame [1/T1ρ] using in situ nuclear magnetic resonance pulse techniques during creep of pure and doped NaCl single crystals. Effects of divalent impurity and solid solution are investigated by doping with Ca and LiCl, respectively. Compression creep tests were performed at 10–30 MPa at 473 K. Relaxation rates were evaluated from spin-echo heights following π/2, locking, and 64° pulse sequence. The amplitude of the spin echo decreased as soon as the load was applied following which it increased until the steady-state creep was reached, at which point a saturation value was observed. Mean jump distance of the mobile dislocations decreased with strain during the transient creep reaching a constant value at the onset and during the secondary creep. While the addition of 0.01 Ca has negligible influence on the jump distance, a solid solution with 0.01 LiCl resulted in about a four-fold increase. The results are compared and correlated with various microstructural parameters.

The dynamics of bipyramidal ions in magnetoplumbite-like hexagonal ferrite systems revisited

The dynamics of the bipyramidal 4e−Fe ions in the M-type hexagonal ferrite La0.7Na0.3Fe12O19 single crystal, is investigated by using Mossbauer spectroscopy. We show that a photon self-interference phenomenon can be used to explain the available experimental data. From this model we have deduced the jumping distance of the Fe(4e) ions. This model can also be succesfully used to investigate the existing data on the isomorphous CaAl11FeO19 and BaFe12O19 oxides. In all cases, the calculated jumping distances are in a excellent agreement with X-ray diffraction results. For CaAl11FeO19 and BaFe12O19 we have deduced the thermal dependence of the jumping distance. Any evidence of an atomic freezing is not found in the temperature range 80–300 K.