Inferences concerning anatomy and physiology of the human brain based on its magnetic field

Summary Research in the evoked magnetic field reported in the last two years is reviewed. The studies have shown that the magnetic technique may be used 1) to reveal complementary aspects of the current sources common to evoked potential, 2) to identify the organization of the cerebral cortex and subcortical areas of the brain and 3) to measure functional properties of the active neural areas whose locations are identified. Paper presented at the ?IV International Workshop on Biomagnetism?, held in Rome, September 14–16, 1982.     

Variations of the 1H spin-lattice relaxation in a fatty liver model as compared to normal liver

We report the results of an in vitro study on ethionine-injected rat liver (EI) and on normal rat liver (C) performed analyzing with iterative fitting procedures the 1H spin-lattice relaxation curves detected by IR pulse sequence at 20 MHz and at 37 degrees C on fresh excised samples. Single-exponential functions did not adequately describe the experimental curves both in EI and in C group. The analysis of the curves by two-exponential hypothesis showed a small portion of the signal characterizable by a time constant of about 80 ms, common both to EI and to C samples. A slowing of about 30% in the relaxation characterized the remaining portion of the curve (90-95%) in EI as compared to C samples. The hypothesis that the 1H of the triglycerides vacuoles present in EI livers had a relaxation curve additional to the remaining signal was checked by three-exponential analysis. The results were not in contrast with the known value of the triglycerides percentage content and with the spin-lattice relaxation time of the -CH2 group 1H obtained in different experimental conditions in the same fatty liver model. The negative results of the three-exponential analysis on normal liver curves as well as the favorable controls performed to test the analysis procedure supported further this hypothesis. The remaining signal after subtraction of the triglycerides contribution showed still the small fast portion and the increase of the relaxation time of the major portion (from approximately 300 ms up to approximately 400 ms) as compared to C samples.(ABSTRACT TRUNCATED AT 250 WORDS)     

The 38 K transition in TTF-TCNQ viewed as a percolation phenomenon

The d.c. conductivity, static dielectric constant and thermopower of TTF-TCNQ have been calculated for temperatures below 54 K within a self-consistent effective medium approximation. TTF-TCNQ is assumed to consist of small regions which are semiconducting and others which are highly conducting. The conducting regions have a large negative dielectric constant, a large d.c. conductivity and a negative thermopower; the semiconducting portions have a large positive dielectric constant, an activated d.c. conductivity and a large positive thermopower. The volume fraction of conductor increases from zero at T = 0 to unity at 54 K. The model is the first to reproduce the observed metal-insulator transition (e.g. the d.c. conductivity anomaly) near 38 K. The dielectric constant is calculated to rise initially with temperature and then become negative as the temperature increases above 38 K. The thermopower changes sign below 54 K and increases very rapidly at 38 K.     

Variations in substitution rate in human and mouse genomes

We present a method to quantify spatial fluctuations of the substitution rate on different length scales throughout genomes of eukaryotes. The fluctuations on large length scales are found to be predominantly a consequence of a coarse-graining effect of fluctuations on shorter length scales. This is verified for both the mouse and the human genome. We also found that the relative standard deviation of fluctuations in substitution rate is about a factor three smaller in mouse than in human. The method allows furthermore to determine time-resolved substitution rate maps of the genomes, where the corresponding autocorrelation functions quantify the velocity of spatial chromosomal reorganization.     

Many paths to dewetting of thin films: anatomy and physiology of surface instability

The role of essential, real life thin film complexities such as antagonistic (attractive and repulsive) interactions, retardation of van der Waals force, substrate and film heterogeneities, slippage and visco-elasticity are critically examined. It is argued that several factors that are usually overlooked within the framework of the most widely used simple theory can conspire to produce similar length and time scalings and morphologies. Further it is shown with examples that the precise details of the preparation conditions and materials, which also determine the initial physico-chemical roughness of the interfaces, can have profound influences in the Density Variation Induced Instability, Defect Sensitive Spinodal Regime, as well as in the True Nucleation Regime.Received: 1 August 2003PACS: 68.15. + e Liquid thin films - 68.55.-a Thin film structure and morphology - 47.20.Ma Interfacial instability     

Electronic effects in multibridged cyclophanes as viewed by the indices of excitation

[2.2]Paracyclophane and its multibridged analogs containing 3 to 6 bridges [3(1,2,3), 3(1,2,4), 3(1,3,5), 4(1,2,3,4), 4(1,2,3,5), 4(1,2,4,5), 5 and 6] were characterized by the indices of excitation expressed as localization of excitation numbers and charge transfer numbers based on the analysis of the transition density matrix. The MO theory, in supermolecule approximation, was applied together with the PPP CI-1 method. The σ-π orbitals interactions between bridges and rings were also considered. With regard to the first UV absorption band at 33000 ± 1000 cm⁻¹, the relatively low transition energies for 3(1,3,5) and 4(1,2,4,5) resulted from the lowest degree of localization of excitation on the aromatic rings and the highest transannular interaction. For 3(1,2,3) and 4(1,2,3,4), the opposite conclusion was reached. The 3(1,3,5) cyclophane was distinguished not only by neglecting the linear correlation between the transition energies E(S₀→ S₂) and the localization numbers that are valid for other cyclophanes, but also by the stronger transannular interaction appearing in the 2¹A' state connected with the third absorption band.     

Charged particle orbits in Kerr geometry with electromagnetic fields as viewed from locally non-rotating frames

The charged particle orbits in electromagnetic fields on Kerr background as viewed from a locally non-rotating frame do not exhibit non-gyrating bound orbits, which was an essential feature in the earlier study of Prasanna and Vishveshwara, thus showing the non gyration to be due to the effect of dragging of inertial frames produced by the rotating black hole.     

Molecular theory of nematic liquid crystals viewed as effect of collective excitation in ferromagnetic systems

We develop a microscopic theory of the nematic phase with consideration of the effect of the collective excitation on properties of nematic liquid crystals. The model is based on the Heisenberg's exchange model of the ferromagnetic materials. Since the orientation of the molecular long axis and the angular momentum of the molecule rotating around its long axis have the same direction, operators can be introduced to research the nematic liquid crystals. Using the lattice model and the Holstein--Primakoff transformation, the Hamiltonian of the system can be obtained, which has the same form as that of the ferromagnetic substance. The relation between the order parameter and reduced temperature can be gotten. It is in good agreement with the experimental results in the low temperature region, the accordance is better than that of the molecular field theory and the computer simulation. In high temperature region close to the transition point, by considering the effect of the higher-order terms in the Hamiltonian, theoretical prediction is in better agreement with the experiment. That indicates the many-body effect is important to nematic liquid crystals.     

Narrow-band AP latencies in normal and recruiting human ears.

Derived narrow-band action potential latencies increase monotonically with decreasing central frequency, and can be interpreted as reflecting the traveling wave delay in the cochlea. It was found that, for recruiting human ears with average flat hearing losses around 40 dB, this accumulating latency increase was smaller than for normal ears. A comparison of 15 normal ears and 37 recruiting ears showed, however, that in only half of the recruiting ears this difference was significant. These recruiting ears were therefore divided in two groups based on the waveform of the narrow-band action potential AP, which correlated well with the subdivision according to latency. The findings have been explained on the basis that latency of the narrow-band APs is not determined solely by the mechanical traveling-wave delay, but also by the response time of the (second?) cochlear filter. When this filter broadens, one expects a decrease in its impulse response time. Since this impulse response time. Since this impulse response depends on the sum of the high- and low-frequency slope values of the cochlear filter, one expects only a latency decrease when the steep high-frequency slope also becomes more shallow. A support for the influence of the response times of the cochlear filter is found in the narrow-band AP latencies for restricted cochlear losses (e.g., in a 4-kHz noise dip). It appears that the latency in that area actually is shorter than for the higher central frequencies, a fact which cannot be explained solely on the basis of a traveling wave phenomenon.     

Aharonov-Bohm shift as a shift in normal coordinates

The Aharonov-Bohm shift in a closed system is considered. The solenoid is a charged, rotating cylinder which is electrically neutral. This model of Henneberger and Opatrny has a Hamiltonian which is a quadratic form. This quadratic form is transformed to normal coordinates, so that the stationary states become self-evident. It is shown that, in the original system, it is the kinetic angular momentum which is quantized. Solutions of the problem for an electron inside the solenoid are discussed. It is shown that the rotating cylinder exhibits different behavior if the electron is in the magnetic field or if it is in the external region. An external field approximation which replaces the cylinder by a constant magnetic field therefore cannot yield a correct solution of the Schrödinger equation which is continuous at the surface of the solenoid.     

次声试验系统及次声对人体生理功能影响的试验方法

研制了一种在试验室内可提供次声环境的次声舱,测量的次声波特性曲线和其空间均匀性表明,在6~20Hz频率范围内的试验结果是令人满意的。设计的次声对人体生理功能影响的试验研究方法具有可行性。     

Anisotropy of ultrasonic velocity and elastic properties in normal human myocardium.

Measurements of ultrasonic quasilongitudinal velocity were made in the muscle fiber plane of excised human myocardium. Multiple adjacent planes across the left ventricular wall were interrogated to assess the transmural dependence of velocity. For each measurement plane, data were obtained in 2-deg increments through the full 360 deg relative to the myofibers. An approximate 1.3% magnitude of anisotropy was observed with maximum velocity along the muscle fibers and minimum velocity perpendicular to the muscle fibers. The known transmural shift in myofiber orientation was evidenced in the anisotropy of velocity as angular shifts between plots obtained from adjacent transmural planes within the same specimen. Measured values of velocity and density were used to estimate the effective C33 and C11 elastic constants of a thin layer of normal myocardium.     

Sources of T1 variance in normal human white matter

The major factors contributing to T1 variance at 0.5 T in white matter were studied in healthy people. Anatomical location of the white matter sampled and differences between individuals contributed 74% of the total variance in serial measurements of the same subjects. There was also significant change over time within an individual subject that could not be attributed to machine drift. This information permitted estimates to be made concerning adequate sample size in future studies that examine for pathological white matter T1 change.     

Raman spectroscopic identification of normal and malignant human stomach cells

Micro-Raman spectroscopy is employed to identify the normal and malignant human stomach cells. For the cancer cell, the reduced intensity of the Raman peak at 1250 cm-1 indicates that the protein secondary structure transforms from β-sheet or disordered structures to α-helical, while the increased intensity of the symmetric PO2 stretching vibration mode at 1094 cm-1 shows the increased DNA content.     

Nonlinear time series analysis of normal and pathological human walking

Characterizing locomotor dynamics is essential for understanding the neuromuscular control of locomotion. In particular, quantifying dynamic stability during walking is important for assessing people who have a greater risk of falling. However, traditional biomechanical methods of defining stability have not quantified the resistance of the neuromuscular system to perturbations, suggesting that more precise definitions are required. For the present study, average maximum finite-time Lyapunov exponents were estimated to quantify the local dynamic stability of human walking kinematics. Local scaling exponents, defined as the local slopes of the correlation sum curves, were also calculated to quantify the local scaling structure of each embedded time series. Comparisons were made between overground and motorized treadmill walking in young healthy subjects and between diabetic neuropathic (NP) patients and healthy controls (CO) during overground walking. A modification of the method of surrogate data was developed to examine the stochastic nature of the fluctuations overlying the nominally periodic patterns in these data sets. Results demonstrated that having subjects walk on a motorized treadmill artificially stabilized their natural locomotor kinematics by small but statistically significant amounts. Furthermore, a paradox previously present in the biomechanical literature that resulted from mistakenly equating variability with dynamic stability was resolved. By slowing their self-selected walking speeds, NP patients adopted more locally stable gait patterns, even though they simultaneously exhibited greater kinematic variability than CO subjects. Additionally, the loss of peripheral sensation in NP patients was associated with statistically significant differences in the local scaling structure of their walking kinematics at those length scales where it was anticipated that sensory feedback would play the greatest role. Lastly, stride-to-stride fluctuations in the walking patterns of all three subject groups were clearly distinguishable from linearly autocorrelated Gaussian noise. As a collateral benefit of the methodological approach taken in this study, some of the first steps at characterizing the underlying structure of human locomotor dynamics have been taken. Implications for understanding the neuromuscular control of locomotion are discussed. (c) 2000 American Institute of Physics.     

Investigating acoustic correlates of human vocal fold vibratory phase asymmetry through modeling and laryngeal high-speed videoendoscopy

Vocal fold vibratory asymmetry is often associated with inefficient sound production through its impact on source spectral tilt. This association is investigated in both a computational voice production model and a group of 47 human subjects. The model provides indirect control over the degree of left-right phase asymmetry within a nonlinear source-filter framework, and high-speed videoendoscopy provides in vivo measures of vocal fold vibratory asymmetry. Source spectral tilt measures are estimated from the inverse-filtered spectrum of the simulated and recorded radiated acoustic pressure. As expected, model simulations indicate that increasing left-right phase asymmetry induces steeper spectral tilt. Subject data, however, reveal that none of the vibratory asymmetry measures correlates with spectral tilt measures. Probing further into physiological correlates of spectral tilt that might be affected by asymmetry, the glottal area waveform is parameterized to obtain measures of the open phase (open/plateau quotient) and closing phase (speed/closing quotient). Subjects' left-right phase asymmetry exhibits low, but statistically significant, correlations with speed quotient (r=0.45) and closing quotient (r=-0.39). Results call for future studies into the effect of asymmetric vocal fold vibration on glottal airflow and the associated impact on voice source spectral properties and vocal efficiency.     

Nonlinear dynamics in pulsatile secretion of parathyroid hormone in normal human subjects

In many biological systems, information is transferred by hormonal ligands, and it is assumed that these hormonal signals encode developmental and regulatory programs in mammalian organisms. In contrast to the dogma of endocrine homeostasis, it could be shown that the biological information in hormonal networks is not only present as a constant hormone concentration in the circulation pool. Recently, it has become apparent that hormone pulses contribute to this hormonal pool, which modulates the responsiveness of receptors within the cell membrane by regulation of the receptor synthesis, movement within the membrane layer, coupling to signal transduction proteins and internalization. Phase space analysis of dynamic parathyroid hormone (PTH) secretion allowed the definition of a (in comparison to normal subjects) relatively quiet "low dynamic" secretory pattern in osteoporosis, and a "high dynamic" state in hyperparathyroidism. We now investigate whether this pulsatile secretion of PTH in healthy men exhibits characteristics of nonlinear determinism. Our findings suggest that this is conceivable, although on the basis of presently available data and techniques, no proof can be established. Nevertheless, pulsatile secretion of PTH might be a first example of nonlinear deterministic dynamics in an apparently irregular hormonal rhythm in human physiology. (c) 1995 American Institute of Physics.