Active axial stress in mouse aorta

The study verifies the development of active axial stress in the wall of mouse aorta over a range of physiological loads when the smooth muscle cells are stimulated to contract. The results obtained show that the active axial stress is virtually independent of the magnitude of pressure, but depends predominately on the longitudinal stretch ratio. The dependence is non-monotonic and is similar to the active stress-stretch dependence in the circumferential direction reported in the literature. The expression for the active axial stress fitted to the experimental data shows that the maximum active stress is developed at longitudinal stretch ratio 1.81, and 1.56 is the longitudinal stretch ratio below which the stimulation does not generate active stress. The study shows that the magnitude of active axial stress is smaller than the active circumferential stress. There is need for more experimental investigations on the active response of different types of arteries from different species and pathological conditions. The results of these studies can promote building of refined constrictive models in vascular rheology.     

Pressure changes induced by whole body acceleration shocks

In the present paper pressure changes induced by sudden body acceleration are studied "in vivo" on the dog and compared to the results obtainable with a recently developed mathematical model. A dog was fixed to a movable table, which was accelerated by a compressed air piston for less than 1 s. Acceleration was varied by changing the air pressure in the piston. Pressure was measured during the experiment at different points along the vascular bed. However, only data obtained in the carotid artery and abdominal aorta are presented here. The results demonstrated that impulse body accelerations cause significant pressure peaks in the vessel examined (about + 25 mmHg in the carotid artery with body acceleration of g/2). Moreover, pressure changes are rapidly damped, with a time constant of about 0.1s. From the present results it may be concluded that, according to the prediction of the mathematical model, body accelerations such as those occurring in normal life can induce pressure changes well beyond the normal pressure value.     

Eye movements induced by linear acceleration in humans.

The otolith-function study is remarkably behind the semicanal-function study. In the present paper, we introduced briefly our on-going studies on eye movements including nystagmic elicitation during lateral (Gy) linear acceleration with step and sinusoidal modes using a sled-type accelerator. The eye movements were recorded by EOGs (DC) from subjects who looked at an imaginary target of their straight ahead in darkness during G-loading up to 0.5 G. Corresponding to the +Gy and -Gy segments, nystagmus and/or deviation in eye position were frequently induced in some subjects, but none or slightly in the other. The nystagmus changed the beating direction dependently on the Gy direction, while the eye-deviation could be either direction of compensatory or anticompensatory. In half of subjects, nystagmus elicitation was absent or low at 0.3 G, while it tended to increase above 0.3 G. The nystagmic elicitation was similar to each other between the both modes of acceleration, and directional preponderance (DP) was observed in some subjects. There was no correlation between the DP and the nystagmic slow-phase velocity. Functional meanings of these findings were discussed.     

Inhibition and acceleration of erythrocyte aggregation induced by small macromolecules

The aggregation (especially the 'rouleau' formation) of human erythrocytes induced by polysaccharide and polyglutamic acid was quantitatively examined by using a low-shear rheoscope combined with a television image analyzer and a computer. (1) The morphological characteristics of rouleaux induced by these macromolecules are presented. (2) Polysaccharides with high molecular weights of 70 400 and 494 000 and poly(glutamic acids) with weights of 50 000 and 66 000 formed the rouleaux (then the three-dimensional aggregates). But polysaccharides with the low molecular weights of 10 300 and 42 500 and poly(glutamic acids) with weights of 8000 and 20 000 did not. The dependences of the velocity of rouleau formation on the macromolecule concentration and on the shear rate are shown. (3) The erythrocyte aggregation induced by high-molecular-weight polysaccharides was inhibited by low-molecular-weight polysaccharides and glucose, but was not affected by low-molecular-weight poly(glutamic acids). (4) The aggregation induced by high-molecular-weight poly(glutamic acids) was inhibited by poly(glutamic acid) with a molecular weight of 8000, but was accelerated by that of 20 000. The poly(glutamic acid)-induced aggregation was not affected by low-molecular-weight polysaccharides. (5) The stereochemical structure-dependent interaction (or the mode of bridging) of macromolecules with erythrocytes was stressed for the mechanism of erythrocyte aggregation.     

Electron acceleration by Langmuir waves excited by a laser pulse in a semi-infinite plasma

Results are presented from a theoretical investigation of the acceleration of test electrons by a Langmuir wave excited by a short laser pulse at half the electron plasma frequency. Such a pulse penetrates into the plasma over a distance equal to the skin depth and efficiently excites Langmuir waves in the resonant interaction at the second harmonic of the laser frequency. It is shown that the beam of electrons accelerated by these waves is modulated into a train of electron bunches, but because of the initial thermal spread of the accelerated electrons, the bunches widen and begin to overlap, with the result that, at large distances, the electron beam becomes unmodulated.     

Transmission characteristics of axial waves in blood vessels

The elastic behavior of blood vessels can be quantitatively examined by measuring the propagation characteristics of waves transmitted by them. In addition, specific information regarding the viscoelastic properties of the vessel wall can be deduced by comparing the observed wave transmission data with theoretical predictions. The relevance of these deductions is directly dependent on the validity of the mathematical model for the mechanical behavior of blood vessels used in the theoretical analysis. Previous experimental investigations of waves in blood vessels have been restricted to pressure waves even though theoretical studies predict three types of waves with distinctly different transmission characteristics. These waves can be distinguished by the dominant displacement component of the vessel wall and are accordingly referred to as radial, axial and circumferential waves. The radial waves are also referred to as pressure waves since they exhibit pronounced pressure fluctuations. For a thorough evaluation of the mathematical models used in the analysis it is necessary to measure also the dispersion and attenuation of the axial and circumferential (torsion) waves.

To this end a method has been developed to determine the phase velocities and damping of sinusoidal axial waves in the carotid artery of anesthetized dogs with the aid of an electro-optical tracking system. For frequencies between 25 and 150 Hz the speed of the axial waves was between 20 and 40 m/sec and generally increased with frequency, while the natural pressure wave travelled at a speed of about 10 m/sec. On the basis of an isotropic wall model the axial wave speed should however be approximately 5 times higher than the pressure wave speed. This discrepancy can be interpreted as an indication for an anisotropic behavior of the carotid wall. The carotid artery appears to be more elastic in the axial than in the circumferential direction.     

Stochastic electron acceleration in plasma waves driven by a high-power subpicosecond laser pulse

The mechanism of stochastic electron acceleration and heating by a picosecond laser pulse in underdense plasma is studied using particle-in-cell simulations and theoretical models. The formation of wide electron energy spectra in the simultaneously acting laser and plasma fields is analyzed. It is shown that electron scattering by turbulent plasma fluctuations excited through stimulated forward Raman scattering plays a governing role in the formation of high-energy tails in the electron distribution function.     

Trapping of high-energy electrons into regime of surfatron acceleration by electromagnetic waves in space plasma

The phenomenon of trapping of weakly relativistic charged particles (with kinetic energies on the order of mc ²) into a regime of surfatron acceleration by an electromagnetic wave that propagates in plasma across a weak external magnetic field has been studied using nonlinear numerical calculations based on a solution of the relativistic equations of motion. Analysis showed that, for the wave amplitude above a certain threshold value and the initial wave phase outside the interval favorable for the surfing regime, the trajectory of a charged particle initially corresponds to its cyclotron rotation in the external magnetic field. For the initial particle energies studied, the period of this rotation is relatively short. After a certain number (from several dozen to several thousand and above) of periods of rotation, the wave phase takes a value that is favorable for trapping of the charged particle on its trajectory by the electromagnetic wave, provided the Cherenkov resonance conditions are satisfied. As a result, the wave traps the charged particle and imparts it an ultrarelativistic acceleration. In momentum space, the region of trapping into the regime of surfing on an electromagnetic wave turns out to be rather large.     

Solitary waves in soybean induced by localized thermal stress

Action potentials in higher plants are believed to be the information carriers in intercellular and intracellular communication in the presence of an environmental stressor. Plant electrophysiologists have recorded long distance electrical signaling in higher plants during the last two hundred years. Reproducing the duration, speed of propagation, and the shape of the action potential is challenging. Early measurements revealed that the speed of action potential propagation in plants is extremely slow - from 0.1 mm/s to 20 cm/s, although many faster plant responses to stress have been recorded as well. We hypothesized that this discrepancy is most likely due to the artifacts of aliasing from slow registration systems. In this study, we employ real time measurements using modern data acquisition techniques to detect ultra fast action potentials in green plants induced by localized heat stress. Thermal shock or heat stress is the most common environmental stress. Based on more sophisticated measuring techniques, we show that plants transmit solitary waves and that the speed of action potential propagation in green plants is similar to the speed of action potentials in mammalians, varying from a few meters per second up to 105 m/s. Possible pathways for electrical signal propagation in vascular plants are discussed.Key words: Action potential, plant electrophysiology, electrical signaling, localized heat stress, excitability     

Distinct signalling pathways regulate sprouting angiogenesis from the dorsal aorta and the axial vein

Angiogenesis, the formation of new blood vessels from pre-existing vessels, is critical to most physiological processes and many pathological conditions. During zebrafish development, angiogenesis expands the axial vessels into a complex vascular network that is necessary for efficient oxygen delivery. Although the dorsal aorta and the axial vein are spatially juxtaposed, the initial angiogenic sprouts from these vessels extend in opposite directions, indicating that distinct cues may regulate angiogenesis of the axial vessels. We found that angiogenic sprouts from the dorsal aorta are dependent on vascular endothelial growth factor A (Vegf-A) signalling, and do not respond to bone morphogenetic protein (Bmp) signals. In contrast, sprouts from the axial vein are regulated by Bmp signalling independently of Vegf-A signals, indicating that Bmp is a vein-specific angiogenic cue during early vascular development. Our results support a paradigm whereby different signals regulate distinct programmes of sprouting angiogenesis from the axial vein and dorsal aorta, and indicate that signalling heterogeneity contributes to the complexity of vascular networks.     

Exencephaly and axial skeletal dysmorphogenesis induced by maternal exposure to cadmium in the mouse

To investigate the axial skeletal dysmorphogenesis associated with exencephaly and facial abnormalities, two doses of cadmium chloride (4 mg/kg and 6 mg/kg) were administered subcutaneously to MF1 mice on day 7 of gestation (sperm-positive day = day 0). Fetuses were collected on day 18. Gross examination revealed a very high incidence of cranioschisis aperta with exencephaly, maxillary and mandibular hypoplasia, low-set microtia, edema, and growth retardation of fetuses in both treatment groups. Alizarin red S-stained and cleared skeletal preparations of these embryos revealed hypoplasia of the premaxilla, maxilla, nasal bone, zygoma, and mandible of the facial skeleton. The orbital plate represented the frontal bone. The vault of the skull was conspicuously absent. In cranioschisis, the exoccipitals had splayed and fused with the atlas. The basicranial bones were hypoplastic and crowded, thus reducing the cranial cavity. The vertebral bodies were more affected than the arches. Hemivertebrae and longitudinal fusion of centra and arches were also noted. The ribs were usually rudimentary. Agenesis, fusion, and forking of ribs were frequently observed. The sternebrae were rudimentary, bipartite, or longitudinally fused. These data clearly establish the association between neural tube and axial mesodermal abnormalities and emphasize the interdependence of the neurectoderm and mesoderm in normal morphogenesis.     

An induced acceleration index for examining joint couplings

A muscle produces moments at the joints it crosses, but these moments can also cause accelerations at joints not crossed by the muscle. This phenomenon, the acceleration of a joint caused by a muscle not crossing the joint, is referred to as induced acceleration. For a system of rigid bodies this study examines how system configuration, and segmental inertial properties dictate the potential of one joint to cause the acceleration of other joints in the system. From the equations of motion for a series of rigid bodies, an induced acceleration index (IAI) was developed. The IAI permits quantification of the relative potential of moments produced at joints in the kinematic chain to accelerate other joints in the kinematic chain. The IAI is a function of system orientation, segment lengths, and inertial properties. The IAI was used to examine the roles of the ankle and hip joints in quiet standing. The ankle joint had over 12 times the ability to accelerate the hip joint, than the hip had to accelerate the ankle joint. These results in part explain the relative merits of the two strategies predominantly used to maintain upright stance: the ankle and hip strategies. This index permits an understanding of how the induced accelerations are dependent on system configuration and inertial properties. The IAI is also useful in situations where the inertial properties of the system under investigation changes, for example due to the fitting of a new prostheses to a trans-tibial amputee.     

Excitation of plasma waves by nonlinear currents induced by a high-frequency electromagnetic pulse

Excitation of plasma waves by nonlinear currents induced by a high-frequency electromagnetic pulse is analyzed within the kinetic approach. It is shown that the most efficient source of plasma waves is the nonlinear current arising due to the gradient of the energy density of the high-frequency field. Generation of plasma waves by the drag current is usually less efficient but not negligibly small at relatively high frequencies of electron–ion collisions. The influence of electron collisions on the excitation of plasma waves by pulses of different duration is described quantitatively.