Granular vortex spin-torque nano oscillator for reservoir computing.

In this paper, we investigate the granularity in the free layer of the magnetic tunnel junctions (MTJ) and its potential to function as a reservoir for reservoir computing where grains act as oscillatory neurons while the device is in the vortex state. The input of the reservoir is applied in the form of a magnetic field which can pin the vortex core into different grains of the device in the magnetic vortex state. The oscillation frequency and MTJ resistance vary across different grains in a non-linear fashion making them great candidates to be served as the reservoir's outputs for classification objectives. Hence, we propose an experimentally validated area-efficient single granular vortex spin-torque nano oscillator (GV-STNO) device in which pinning sites work as random reservoirs that can emulate neuronal functions. We harness the nonlinear oscillation frequency and resistance exhibited by the vortex core granular pinning of the GV-STNO reservoir computing system to demonstrate waveform classification.

High power and low critical current density spin transfer torque nano-oscillators using MgO barriers with intermediate thickness.

Reported steady-state microwave emission in magnetic tunnel junction (MTJ)-based spin transfer torque nano-oscillators (STNOs) relies mostly on very thin insulating barriers [resulting in a resistance × area product (R × A) of ~1 Ωµm2] that can sustain large current densities and thus trigger large orbit magnetic dynamics. Apart from the low R × A requirement, the role of the tunnel barrier in the dynamics has so far been largely overlooked, in comparison to the magnetic configuration of STNOs. In this report, STNOs with an in-plane magnetized homogeneous free layer configuration are used to probe the role of the tunnel barrier in the dynamics. In this type of STNOs, the RF modes are in the GHz region with integrated matched output powers (P out ) in the range of 1-40 nW. Here, P o u t values up to 200 nW are reported using thicker insulating barriers for junctions with R × A values ranging from 7.5 to 12.5 Ωµm2, without compromising the ability to trigger self-sustained oscillations and without any noticeable degradation of the signal linewidth (Γ). Furthermore, a decrease of two orders of magnitude in the critical current density for spin transfer torque induced dynamics (J STT ) was observed, without any further change in the magnetic configuration.

Mutual synchronization of spin torque nano-oscillators through a long-range and tunable electrical coupling scheme.

The concept of spin-torque-driven high-frequency magnetization dynamics, allows the potential construction of complex networks of non-linear dynamical nanoscale systems, combining the field of spintronics and the study of non-linear systems. In the few previous demonstrations of synchronization of several spin-torque oscillators, the short-range nature of the magnetic coupling that was used has largely hampered a complete control of the synchronization process. Here we demonstrate the successful mutual synchronization of two spin-torque oscillators with a large separation distance through their long range self-emitted microwave currents. This leads to a strong improvement of both the emitted power and the linewidth. The full control of the synchronized state is achieved at the nanoscale through two active spin transfer torques, but also externally through an electrical delay line. These additional levels of control of the synchronization capability provide a new approach to develop spin-torque oscillator-based nanoscale microwave-devices going from microwave-sources to bio-inspired networks.

Spin-torque resonant expulsion of the vortex core for an efficient radiofrequency detection scheme.

It has been proposed that high-frequency detectors based on the so-called spin-torque diode effect in spin transfer oscillators could eventually replace conventional Schottky diodes due to their nanoscale size, frequency tunability and large output sensitivity. Although a promising candidate for information and communications technology applications, the output voltage generated from this effect has still to be improved and, more pertinently, reduces drastically with decreasing radiofrequency (RF) current. Here we present a scheme for a new type of spintronics-based high-frequency detector based on the expulsion of the vortex core in a magnetic tunnel junction (MTJ). The resonant expulsion of the core leads to a large and sharp change in resistance associated with the difference in magnetoresistance between the vortex ground state and the final C-state configuration. Interestingly, this reversible effect is independent of the incoming RF current amplitude, offering a fast real-time RF threshold detector.

The use of Lee and co-workers' index to assist a risk adjusted audit of perioperative cardiac outcome.

Lee and co-workers' revised cardiac risk index was used to study the perioperative cardiac outcome of 296 patients. The index uses a history of ischaemic heart disease, congestive cardiac failure, diabetes treated with insulin, a creatinine greater than 180 micromol/l, cerebrovascular disease and high risk surgery as the risk factors involved in predicting a perioperative cardiac event. It was derived on the basis of data from patients over the age of 50 years undergoing elective, noncardiac surgery with an expected inpatient stay of two or more days. The presence of one, two and three or more risk factors predicted a risk of a major cardiac event of 1.3% (95% confidence interval [CI] 0.7 to 2.1), 3.6% (95% CI 2.1 to 5.6) and 9% (95% CI 5.5 to 13.8) respectively in Lee's derivation group of 2,893 patients. In our audit of 296 patients we observed a cardiac event rate of 0.8% (95% CI 0 to 2.3%), 6.7% (95% CI 1.6 to 10%) and 2% (95% CI 0 to 5.9%), in patients with one, two and three or more risk factors respectively. The more frequent use of ECGs and troponin levels in the routine postoperative care of high risk patients undergoing major noncardiac surgery is recommended on the basis of the frequency of a positive result and the impact of a positive result on a patient's management.

The influence of calciotrophic hormones on lymphocyte transformation and interleukin-2 production in human mononuclear cells.

Peripheral blood mononuclear cells (PBMC) display receptors for parathyroid hormone (PTH) and calcitonin (CT) and, when activated, express receptors for 1,25 dihydroxyvitamin D3 (1,25(OH)2D3). The role of these receptors in unclear. It is well established that 1,25 dihydroxyvitamin D3 (1,25(OH)2D3) has a significant effect on lymphocyte transformation and interleukin-2 (IL-2) activity in PBMC's. We have proceeded to compare the effects of the calciotrophic hormones, 1,25(OH)2D3, 24,25 dihydroxyvitamin D3 (24,25(OH)2D3), 25 dihydroxyvitamin D3 (25(OH)D3), bovine (1-35)PTH (b(1-35)PTH) and salmon CT on both lymphocyte transformation and IL-2 activity in PBMC's from normal human volunteers. We have also sought an indication as to which subset of cells is responsible for the 1,25(OH)2D3 effect. Unlike the other calciotrophic hormones 1,25(OH)2D3 inhibited the proliferation of phytohemagglutinin (PHA), concanavalin A (ConA) and pokeweed mitogen (PWM) stimulated cells. 1,25(OH)2D3 had a significantly greater effect on PHA induced cell proliferation and only inhibited cells with the T-helper/inducer (TH, CD4 + ve) phenotype, this suggested that 1,25(OH)2D3 may act selectively on the cells with CD4 + ve phenotype. In addition, of the calciotrophic hormones, 1,25(OH)2D3 had a greater effect on IL-2 activity. These findings indicate that 1,25(OH)2D3 and not the other calciotrophic hormones has a significant immunomodulatory effect.

Effect on embryo survival of short-term exposure to the uterine environment of two selected lines of mice.

Two genetic lines of mice (Mus musculus), one selected for high embryo survival (Line E) and the other for small litter size (Line CN-), were used as models to study preimplantation embryo survival. The two lines displayed similar ovulation rates, but significantly lower embryo survival to implantation was observed in Line CN- females (P less than 0.01). The effect of the uterine environment on embryo survival was examined by incubating embryos in pseudopregnant host females for 26 hours beginning at 1500 hours on day 2 (day of copulatory plug = day 0). Embryos were then removed from the host and transferred to recipient uteri of the same genetic line as the embryos for development to term. Survival of embryos was significantly greater after exposure to Line E hosts (P less than 0.01). Survival of Line E embryos was reduced from 71% in Line E hosts to 28% in Line CN- hosts. Survival of Line CN- embryos increased from 17% in Line CN- hosts to 70% in Line E hosts. Embryos also were cultured in vitro in uterine flushings collected from each line. More Line E embryos developed to the blastocyst stage than did Line CN- embryos (P less than 0.01). Development of Line CN- (P less than 0.01) embryos, but not Line E embryos, was affected by the line from which uterine flushings were collected. These lines of mice provide a useful model for the study of the physiological basis for differences in embryo survival due to genetic selection.

Malignancy-associated hypercalcaemia: relationship between mechanisms of hypercalcaemia and response to antihypercalcaemic therapy.

The pathophysiological mechanisms of hypercalcaemia were assessed in 50 rehydrated patients with cancer-associated hypercalcaemia. Surprisingly, renal tubular calcium reabsorption appeared to increase progressively as serum calcium rose, suggesting that the nomogram used for the calculation may have been inaccurate, in absolute terms, probably due to its failure to take account of the levels of urinary sodium excretion. There were significant differences in the mechanisms of hypercalcaemia in different patient subgroups, however, independent of differences in urinary sodium excretion. In those with few or no bone metastases, increased renal tubular calcium reabsorption was the principal cause of hypercalcaemia, often in association with increased bone resorption. These abnormalities were thought to reflect the renal and skeletal actions of a tumour-associated humoral mediator. The main cause of hypercalcaemia in those with extensive metastatic bone disease was increased bone resorption, with contributions from impairment of glomerular filtration rate and, to a minor extent, increased renal tubular calcium reabsorption. These abnormalities were thought to reflect a mainly local-osteolytic mechanism of hypercalcaemia with secondary impairment of GFR. Of all the biochemical variables assessed pre-treatment, the renal tubular component of hypercalcaemia correlated most strongly with post-treatment serum calcium values (r = 0.61, P less than 0.001). Because of their generally lower levels of renal tubular calcium reabsorption, patients with extensive skeletal metastases also had significantly lower post treatment calcium values than patients with few or no metastases (P less than 0.05). These data indicate that the pathophysiological mechanisms of hypercalcaemia are a major determinant of the calcium lowering response after antihypercalcaemic treatment. This should be taken into account during comparative studies of antihypercalcaemic therapy in patients with malignancy.

Comparison of aminohydroxypropylidene diphosphonate, mithramycin, and corticosteroids/calcitonin in treatment of cancer-associated hypercalcaemia.

Thirty-nine patients with cancer-associated hypercalcaemia were randomly allocated to receive aminohydroxypropylidene diphosphonate (APD), mithramycin, or corticosteroids and salmon calcitonin. Corticosteroids/calcitonin had the fastest calcium-lowering effect, owing mainly to an acute reduction in renal tubular calcium reabsorption; continued therapy over 9 days failed to suppress accelerated bone resorption, however, and most patients remained hypercalcaemic. Mithramycin also substantially reduced serum calcium within 24 h. A further dose on day 2 generally controlled hypercalcaemia until day 6 by reducing both bone resorption and renal tubular calcium reabsorption. By day 9, however, about 50% of the mithramycin-treated patients had started to relapse as bone resorption increased again. With APD serum calcium levels fell more slowly but progressively owing to effective suppression of bone resorption; by day 9 the control of hypercalcaemia was significantly better than in the other treatment groups. Symptoms of hypercalcaemia were greatly relieved, especially by APD.

Predictive value of derived calcium figures based on the measurement of ionised calcium.

The algorithms used in this hospital to assess calcium status are calculated ionised serum calcium and the serum calcium concentration adjusted for albumin. In order to establish their clinical usefulness, they were compared with the ionised calcium concentration measured on the Nova 2 instrument in patients with various calcium and protein abnormalities. Good correlation was found between the measured and calculated values. The predictive values for the calculated results and for total serum calcium concentrations are presented. In this series, the derived values were useful in predicting the serum ionised calcium concentration of the patients studied.

Preparation of material to control precision of calcium selective electrodes.

A simple procedure is described for the preparation of a stable precision quality control material for use in the measurement of level of ionised calcium in serum at or near the reference range. Repeat analyses on a Nova 2 ionised calcium analyser of serum pools stored at different temperatures over a period of three months showed coefficients of variation less of less than 4%.