This paper presents an analytic model of a read head with shields of finite length and width, suitable for replay at 1 Tb/in 2 . The model determines the shield potential by iterative solution of the ...equations governing the Fourier coefficients, given an initial guess. The model is used to demonstrate the effect of varying the length and width of the shields. The paper gives results for the shield potential, equipotentials, vertical head field, and spectral response function. A head with shields that are the same length as the semi-shield - shield gap offers an almost constant magnitude response over a broad range of along-track frequencies, and the use of sufficiently wide side shields is advantageous.
To examine persisting effects of depolarizing rises in extracellular potassium concentration (K
+
o) on synapses, we depolarized cells to simulate ischemia-like rises in K
+
o. Elevated K
+
o for ...1–16 hr severely depressed glutamate signaling, while mildly depressing GABA transmission. The glutamate-specific changes were plastic over several hours and involved a decrease in the size of the pool of releasable vesicles. Rather than a reduction of the number of vesicles per release site, the change involved functional elimination of release sites. This change was clearly dissociable from a second effect, depressed probability of transmitter release, which was common to both glutamate and GABA transmission. Thus, while other recent evidence links alteration of the releasable pool size with changes in
p
r, our results suggest the two can be independently manipulated. Selective depression of glutamate release may provide an adaptive mechanism by which neurons limit excitotoxicity.
Infinite series involving associated Legendre functions of general degree and order are used to describe the scalar potential in the vicinity of a cubic corner. The method of analysis closely follows ...methods used to describe the magnetic field in the gap of a ring head for magnetic recording and the degree of the Legendre functions can be approximated when the determinant of the derived matrix vanishes. We solve with both Dirichlet and Neumann boundary conditions, but study symmetric and antisymmetric solutions separately. Other geometries considered are the two-dimensional straight edge and the quarter-plane. We also discuss the degeneracy of higher order eigenvalues.
We investigated the effects of transition curvature on T 50 and V p-p for a shielded giant magnetoresistive (GMR) element reading a single, isolated transition recorded on a perpendicular medium in ...the presence of a soft magnetic underlayer. We considered displacement and rotation of the read head relative to the recorded track and a range of read head geometries. The curvature of the transition adversely affects T 50 , which also increases with azimuth angle. Both T 50 and V p-p decrease as either the GMR element or the element-side shield spacing is reduced
The expected increase in areal density in hard drives will require very narrow tracks. Tracks which are of a similar width to the read head and which are not separated by guardbands normally suffer ...from large inter-track interference (ITI) or crosstalk. Here, we show that it is possible to read from tracks which are not separated by guardbands and that are narrower than the head. In addition to the significant increase in areal density obtainable by reducing the unrecorded area of the disk and narrowing the tracks, such a system would also lead to a decrease in data retrieval times. We have identified across-track magnetization constraints for future coding across three adjacent tracks so that it will be possible to read from tracks which are only 73% as wide as the read head. Reading from tracks not separated by guardbands which have been written under these constraints yields an increase in track density of at least 47% greater than that possible in conventional drives.
We investigated conditions that promote basal and activity-dependent neuronal apoptosis in postnatal rat hippocampal cultures. Low-density mixed cultures of astrocytes and neurons exhibited lower ...sensitivity than high-density cultures to basal neuronal death and activity-sensitive neuronal death, induced with glutamate receptor blockers, sodium channel blockers, or calcium channel blockers. Although elevations of Ca
2+
i protect neurons from apoptosis, low-density microcultures and mass cultures exhibited only minor differences in resting Ca
2+
i and Ca
2+ current density, suggesting that these variables are unlikely to explain differences in susceptibility. Astrocytes, rather than neurons, were implicated in the neuronal loss. Several candidate molecules implicated in other astrocyte-dependent neurotoxicity models were excluded, but heat inactivation experiments suggested that a heat-labile factor is critically involved. In sum, our results suggest the surprising result that astrocytes can be negative modulators of neuronal survival during development and when the immature nervous system is challenged with drugs that dampen electrical excitability.
In a move to extend the storage capabilities of magnetic storage systems beyond 1 Tb/in/sup 2/, the use of patterned media has often been cited. Here, recorded domains are constrained by the geometry ...of the magnetic island and not the geometry of the recording head. Conventional two-dimensional readout modeling techniques, using the reciprocity integral, rely on the assumption that the across-track medium magnetization is uniform under the giant magnetoresistive replay head. However, in the case of a geometrically constrained medium this is not the case. This work investigates the effect that the island geometry has on the characteristics of the replay signal in perpendicular patterned magnetic media storage through the extension of the reciprocity integral to three dimensions. The paper describes replay pulses that offer different characteristics from those obtained by conventional two-dimensional techniques. The origins of these differences are explained by the variation in medium magnetization across the track.
The in vivo effects of administration of the synthetic, functional biomimetic cation Cr(3)O(O(2)CCH(2)CH(3))(6)(H(2)O)(3)(+) to healthy and type I and type II diabetic model rats are described. In ...contrast to current chromium-containing nutrition supplements, which only serve as sources of absorbable chromium, the trinuclear cation has been shown in in vitro assays to interact with the insulin receptor, activating its kinase activity, presumably by trapping the receptor in its active conformation. Thus, treatment of rats with the trinuclear cation would be expected to result in changes in lipid and carbohydrate metabolism related to insulin action. After 24 weeks of intravenous administration (0-20 micro g Cr/kg body mass), the cation results in a concentration-dependent lowering of levels of fasting blood plasma LDL cholesterol, total cholesterol, triglycerides, and insulin and of 2-h plasma insulin and glucose levels after a glucose challenge; these results confirm a previous 12-week study examining the effect of the synthetic cation on healthy rats and are in stark contrast to those of administration of other forms of Cr(III) to rats, which have no effect on these parameters. The cation has little, if any, effect on rats with STZ-induced diabetes (a type I diabetes model). However, Zucker obese rats (a model of the early stages of type II diabetes) after 24 weeks of supplementation (20 micro g/kg) have lower fasting plasma total, HDL, and LDL cholesterol, triglycerides, and insulin levels and lower 2-h plasma insulin levels. The lowering of plasma insulin concentrations with little effect on glucose concentrations suggests that the supplement increases insulin sensitivity.
By matching a singular function approximation to the Fourier solution at the air-bearing surface (ABS), we have derived a three-dimensional (3-D) analytic model of a shielded giant magnetoresistive ...(GMR) head, with side shields, for perpendicular replay. We present an explicit expression for the potential in the ABS and give values for the parameters in that expression for a range of practical head dimensions. Using only a few terms of this singular potential model, we show that the vertical field is accurate to within 1% of the sensor potential in the region of the medium for the majority of head dimensions suitable for magnetic recording.
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