On the origin of apparently negative minimum susceptibility of hematite single crystals calculated from low-field anisotropy of magnetic susceptibility

SUMMARY As shown in the literature several times, the calculation of the anisotropy of magnetic susceptibility (AMS) of hematite single crystals using standard linear AMS theory reveals that the calculated minimum principal susceptibility is parallel to the crystallographic c-axis, but is negative, which is however not due to diamagnetism as evidenced by direct measurements of susceptibility along the principal directions. Susceptibility of a few hematite single crystals from Minas Gerais, Brazil, was measured in 320 directions using a special 3-D rotator and the measurements were processed through AMS calculation by means of standard linear theory and through constructing contour diagrams in equal-area projection. In addition, the susceptibility was in detail measured in three perpendicular planes approximately passing through the main crystallographic directions. The crystals show extremely high anisotropy, the susceptibility measured along the basal plane is several hundred times higher than that along the c-axis and the AMS ellipsoids are very oblate. The contour diagrams show relatively simple patterns of directional susceptibilities, similar to those of the second-rank tensor. Fitting tensor to measured hematite grains results in small but negative minimum principal susceptibility. Nevertheless, summation of many oriented grains filters out the non-tensorial parts of the grain susceptibility in multicrystal assemblages, the AMS of which is well represented by a tensor.

On the origin of apparently negative minimum susceptibilities of hematite single crystals calculated from low-field anisotropy of magnetic susceptibility

<p>As shown in the literature several times, the calculation of the anisotropy of magnetic susceptibility (AMS) of hematite single crystals using standard linear AMS theory reveals that the calculated minimum principal susceptibility is parallel to the crystallographic c-axis, but is negative, which is however not due to diamagnetism as evidenced by direct measurements of susceptibility along the principal directions.</p><p>Susceptibility of a few hematite single crystals from Minas Gerais, Brazil, was measured in 320 directions using a special 3D rotator and the measurements were processed through AMS calculation by means of standard linear theory and through constructing contour diagram in equal-area projection. In addition, the deviations of the measured directional susceptibilities from the directional susceptibilities calculated from the fitted AMS tensor were calculated. The crystals show extremely high anisotropy, the susceptibility measured along the basal plane is several hundred to several thousand times higher than that along the c-axis and the AMS ellipsoids are very oblate, nearly rotational. The contour diagrams show relatively simple patterns of directional susceptibilities, similar to those of the second-rank tensor. However, the calculated AMS ellipsoids are slightly more eccentric than is the surface connecting the directional susceptibility values. The present study is assessing whether, realizing that the susceptibility along the c-axis is about three orders lower than that along the basal plane and taking into account the directional distribution of the fitting errors, one can ascribe the existence of the negative minimum susceptibilities calculated through standard linear theory to imperfect techniques of second-rank tensor fitting rather than to complicated magnetization mechanisms.  </p>

Effects of different sources and levels of dietary iron and selenium on the postprandial net portal appearance of these minerals in growing pigs

The present study compares the net portal appearance of dietary iron (Fe) and selenium (Se) after meals containing different sources and levels of these minerals. Twelve pigs (55.1 ± 3.7 kg) were used in a cross-over design to assess the 11-h net portal-drained viscera (PDV) flux of serum Fe and Se after ingestion of boluses containing inorganic (I) or organic (O) dietary Fe and Se at industry average (A; 200 and 0.6 mg, respectively) or high (H; 400 and 1.2 mg, respectively) levels. Arterial serum Fe concentrations increased by an average of 158% within 6 h post-meal and gradually decreased thereafter (P < 0.001). Values were greater (P < 0.001) for I than for O until 6 h post-meal and greater (P ≤ 0.001) for A than for H from 4 to 8 h post-meal. For the whole post-prandial period (11 h), arterial serum Fe concentrations tended (P = 0.06) to be greater for I than for O and were lowest for HO (P ≤ 0.03). Net PDV flux of Fe tended to be greater for AI than for AO (P ≥ 0.07). Cumulative appearance of Fe in PDV serum (% of dietary intake) was greater for I than for O (2.43 vs. −0.76%; P = 0.02) and A tended to be greater than H (1.96 vs. −0.29 %; P = 0.09) until 3 h post-meal, but these effects further faded out (P ≥ 0.43). Arterial serum Se concentration decreased for all treatments (average of 7%) from premeal values (P < 0.001), and this was more pronounced for O than for I (P = 0.03). Irrespective of treatment, net PDV flux of Se was positive (different from 0, P ≤ 0.03) during the first 90 min post-meal, decreased to negative minimum values (different from 0, P = 0.03) at 5 h post-meal, and was not different from 0 thereafter (P ≥ 0.11). Cumulative appearance of Se in PDV serum (% of dietary intake) was greater for I than for O (20.0 vs. −3.8%; P = 0.04) only at 45 min post-meal. In conclusion, both dietary Fe and Se absorption are limited to the early post-meal period. Whereas for Fe, the level effect is in accordance with the known negative correlation between its dietary concentration and percentage of intestinal absorption, this was not the case for dietary Se. The postabsorptive availability of dietary I was greater than O for both minerals and, particularly for Fe, at low levels.

ECG body surface mapping (BSM) in type 1 diabetic patients

Diabetes mellitus is a risk factor of cardiovascular diseases. ECG of patients with diabetes mellitus type 1 (DM 1) shows tachycardia (block of parasympathetic innervation) and abnormal repolarization (increased QT interval and QT dispersion (QTd)) indicating a risk of ventricular tachycardia and sudden death in young people with DM 1. The aim of the present report was to measure 145 parameters of the heart electric field in 22 patients (14 men, 8 women) with DM 1 without complications (mean age 32.8+/-11.4 years) and in 22 controls (11 men, 11 women, mean age 30.1+/-3.4 years). The duration of diabetes was 13.9+/-7.8 years. The parameters were registered by the diagnostic system Cardiag 112.2 and statistically evaluated by the Student and Mann-Whitney test. Tachycardia (86.3+/-2.7 beats.min(-1)), shortening of both QRS (79.9+/-1.6 ms) and QT (349.0+/-5.9 ms) and increased QT dispersion (115+/-36 ms) were observed in DM 1 when compared with the controls (75.0+/-2.1 beats. min.(-1), QRS 89.9+/-2.7 ms, QT 374.0+/-4.4 ms, QTd 34.0+/-12.0 ms, p<0.01). The QTc was 415.2+/-4.1 ms in DM 1 and 401.4+/-6.6 ms in controls (NS). Other significant findings in DM 1 were: higher maximum of depolarization isopotential maps (DIPMmax) in the initial phase of QRS and less positive in the terminal phase, more negative minimum (DIPMmin) during QRS similarly as the minimum in depolarization isointegral maps (DIIMmin) and the minimum in isointegral map of the Q wave (Q-IIMmin), lower maximum in repolarization isopotential maps (RIPMmax) and less negative minimum (RIPMmin), more negative amplitude of Q wave (Q-IPMAM) and more pronounced spread of depolarization (activation time). Our results confirmed a decreased parasympathetic to sympathetic tone ratio (tachycardia, shortening of the activation time) and revealed different depolarization and repolarization patterns in DM 1. The differences in heart electric field parameters measured by the BSPM method in DM 1 and in the controls indicate the importance of ECG examination of diabetic patients type 1 in the prevention of cardiovascular diseases.

INFLATION AND COMPACTIFICATION DERIVED FROM DUALITY INVARIANT GAUGINO CONDENSATION

Recently it has been demonstrated that the breaking of space-time supersymmetry in the context of string-induced effective actions may be realized in a duality invariant way using gaugino condensates. Although generically the ground state is a negative minimum, we present a toy model of a Hawking-Moss type inflation by invoking a one-loop Casimir effect and adjusting the cosmological constant to zero. This can only be justified a posteriori since we obtain inflation and compactification of the target space albeit fine-tuning is necessary.

Interaction between secretory leucocyte proteinase inhibitor and bronchial mucins or glycopeptides. Physiopathological implications for the protection of mucins against proteolysis by human leucocyte elastase

The interaction of secretory leucocyte proteinase inhibitor with bronchial mucins and glycopeptides was studied by means of c.d. spectroscopy. The interaction with mucins was characterized by an increase in organized structure of alpha-helical type, as evidenced by the appearance in the difference spectra of two positive bands at 208 and 218 nm. This phenomenon was correlated with the amount of inhibitor present in the mixtures, suggesting that the change was inherent to the inhibitor. Surprisingly, when the inhibitor was mixed with acid glycopeptides, difference c.d. spectra showed a decrease in organized structure, characterized by a negative minimum at 196 nm. Glycopeptides treated with neuraminidase gave similar profiles of difference spectra in three different mixtures, indicating that the interaction was smaller. The interaction between the inhibitor and mucins was also studied for its ability to modify in vitro the proteolytic activity of human leucocyte elastase. Mucins alone were degraded by that proteinase into glycopeptides of Mr 400,000-500,000, whereas mucins mixed with inhibitor before adding elastase were proteolysed to a lesser extent. These data demonstrate that the secretory leucocyte proteinase inhibitor interacts with mucins and consequently is capable of protecting the mucins against proteolysis by elastase.

Viscous and Nuclei Effects on Hydrodynamic Loadings and Cavitation of a NACA 66 (MOD) Foil Section

A series of experiments has been conducted on a two-dimensional NACA 66 (MOD) foil to examine the effects of viscosity and nuclei on cavitation inception. In this paper the main discussions center on two foil angles having different types of pressure loadings to represent a propeller blade section operating at design and off-design conditions. At one degree design angle of attack the foil experiences a rooftop-type gradually varying pressure distribution. At three degrees off-design angle of attack the foil experiences a sharp suction pressure peak near the leading edge. Cebeci’s viscid/inviscid interactive code is used to compute the viscous scale effects on the development of the boundary layer, lift, drag and pressure distribution on the foil. Chahine’s multibubble interaction code is used to compute the effect of nuclei, test speeds, foil size and foil surface on traveling bubble cavitation. Both computer codes are found to agree satisfactorily with the experimental measurements reported here. Two assumptions commonly used to predict full scale surface cavitation from model tests are examined experimentally and theoretically. The first assumption states that cavitation inception occurs when the static pressure reaches the vapor pressure. On the contrary, the experiments showed that the water flowing over the foil surface sustained significant amounts of tension during inception of midchord bubble cavitation as well as leading edge sheet cavitation. The second assumption states that there is no scale effect on the values of negative minimum pressure coefficient. In the case of a rooftop-type pressure loading, the second assumption is supported by the pressure numerical calculations. However, in the case of a pressure loading with a strong suction peak near the leading edge the value of negative minimum pressure coefficient is as much as 12 to 15 percent lower on a model than at full scale.