Incubation Delay Research Articles

Nanosecond magnetization dynamics during spin Hall switching of in-plane magnetic tunnel junctions

We present a study of the magnetic dynamics associated with nanosecond scale magnetic switching driven by the spin Hall effect in 3-terminal nanoscale magnetic tunnel junctions (MTJs) with in-plane magnetization. Utilizing fast pulse measurements in a variety of material stacks and detailed micromagnetic simulations, we demonstrate that this unexpectedly fast and reliable magnetic reversal is facilitated by the self-generated Oersted field, and that the short-pulse energy efficiency can be substantially enhanced by spatial non-uniformity in the initial magnetization of the magnetic free layer. The sign of the Oersted field is essential for this enhancement—in simulations in which we artificially impose a field-like torque with a sign opposite to the effect of the Oersted field, the result is a much slower and stochastic switching process that is reminiscent of the so-called incubation delay in conventional 2-terminal spin-torque-switched MTJs.

Radiation-induced segregation on defect clusters in single-phase concentrated solid-solution alloys

A group of single-phase concentrated solid-solution alloys (SP-CSAs), including NiFe, NiCoFe, NiCoFeCr, as well as a high entropy alloy NiCoFeCrMn, was irradiated with 3 MeV Ni2+ ions at 773 K to a fluence of 5 × 1016 ions/cm2 for the study of radiation response with increasing compositional complexity. Advanced transmission electron microscopy (TEM) with electron energy loss spectroscopy (EELS) was used to characterize the dislocation loop distribution and radiation-induced segregation (RIS) on defect clusters in the SP-CSAs. The results show that a higher fraction of faulted loops exists in the more compositionally complex alloys, which indicate that increasing compositional complexity can extend the incubation period and delay loop growth. The RIS behaviors of each element in the SP-CSAs were observed as follows: Ni and Co tend to enrich, but Cr, Fe and Mn prefer to deplete near the defect clusters. RIS level can be significantly suppressed by increasing compositional complexity due to the sluggish atom diffusion. According to molecular static (MS) simulations, “disk” like segregations may form near the faulted dislocation loops in the SP-CSAs. Segregated elements tend to distribute around the whole faulted loop as a disk rather than only around the edge of the loop.

Stability and optimal control of a delayed HIV model

We propose and investigate a delayed model that studies the relationship between HIV and the immune system during the natural course of infection and in the context of antiviral treatment regimes. Sufficient criteria for local asymptotic stability of the infected and viral free equilibria are given. An optimal control problem with time delays both in state variables (incubation delay) and control (pharmacological delay) is then formulated and analyzed, where the objective consists to find the optimal treatment strategy that maximizes the number of uninfected CD4 + T cells as well as cytotoxic T lymphocyte immune response cells, keeping the drug therapy as low as possible. Copyright © 2016 John Wiley & Sons, Ltd.

Yolk steroids in great tit Parus major eggs: variation and covariation between hormones and with environmental and parental factors.

Avian mothers can potentially alter the phenotypes of their offspring by varying the concentration of steroid hormones in their eggs. We explored variation in androstenedione (A4), testosterone (T), 5α-dihydrotestosterone (DHT), 17β-estradiol (E2), and corticosterone (CORT) in the yolks of 12 free-living great tit Parus major clutches. We analyzed variation and covariation in greater detail than previous studies, using models for variation with laying sequence that take into account variable clutch size and comparing correlations between pairs of hormones at the within- and between-clutch levels. We also investigated relationships between hormone levels and various environmental, life history, and parental traits. For three of the five steroids, we found no significant correlates, but based on individual statistical tests (a) DHT varied between clutches with male age (1 year old vs older); (b) DHT and CORT were negatively correlated within clutches with the average temperature on the day (DHT and CORT) or 3 days (DHT only) preceding laying; and (c) DHT in the last egg of the clutch relative to the clutch mean was positively correlated with the interval between clutch completion and the onset of incubation (incubation delay). Relationships with ambient temperature and incubation delay have not previously been reported for any yolk hormone in birds. Intriguingly, the three relationships for DHT are consistent with more DHT being transferred to eggs in situations that could be more energetically challenging for the female. More research is needed to determine the generality of the patterns we found and to understand their functional significance.Significance statementThe yolks of birds’ eggs contain steroid hormones produced by the mother which can affect the development and behavior of the resultant chicks. We analyzed five steroid hormones in the yolks of wild great tits and show for the first time that yolk hormone levels are related to ambient temperature in the day(s) just before laying and, in the last-laid egg, with the day it is laid relative to the onset of incubation, and that the concentrations of pairs of yolk hormones can vary with each other in a different way between and within clutches. These results contribute insights into the ways in which yolk hormones may adaptively modify the chicks or may reflect physiological processes occurring in the mother.Electronic supplementary materialThe online version of this article (doi:10.1007/s00265-016-2107-1) contains supplementary material, which is available to authorized users.

Switching from simple to complex dynamics in a predator–prey–parasite model: An interplay between infection rate and incubation delay

Parasites play a significant role in trophic interactions and can regulate both predator and prey populations. Mathematical models might be of great use in predicting different system dynamics because models have the potential to predict the system response due to different changes in system parameters. In this paper, we study a predator–prey–parasite (PPP) system where prey population is infected by some micro parasites and predator–prey interaction occurs following Leslie–Gower model with type II response function. Infection spreads following SI type epidemic model with standard incidence rate. The infection process is not instantaneous but mediated by a fixed incubation delay. We study the stability and instability of the endemic equilibrium point of the delay-induced PPP system with respect to two parameters, viz., the force of infection and the length of incubation delay under two cases: (i) the corresponding non-delayed system is stable and (ii) the corresponding non-delayed system is unstable. In the first case, the system populations coexist in stable state for all values of delay if the force of infection is low; or show oscillatory behavior when the force of infection is intermediate and the length of delay crosses some critical value. The system, however, exhibits very complicated dynamics if the force of infection is high, where the system is unstable in absence of delay. In this last case, the system shows oscillatory, stable or chaotic behavior depending on the length of delay.

Complexity in a predator-prey-parasite model with nonlinear incidence rate and incubation delay

This paper is concerned with a predator-prey-parasite model with nonlinear infection rate and incubation delay. To explore the system dynamics, we study the distribution of roots of the characteristic equation of the Jacobian matrix of the system which has delay-dependent coefficients. The dynamics displayed by the system can exhibit some of the key features observed in the natural systems, such as appearance and disappearance of cycles in succession. It is shown that the switching phenomenon between stable coexistence and oscillatory coexistence of interior equilibrium as well as of predator-free equilibrium is an interplay of three system parameters, viz. the crowding coefficient, the prey consumption rate and the length of incubation delay. We also discuss the stability of the delayed-system when the non-delayed system is assumed to be unstable.

Cannibalistic Predator–Prey Model with Disease in Predator — A Delay Model

In this paper, we propose and analyze a cannibalistic predator–prey model with a transmissible disease in the predator population. The disease can be transmitted through contacts with infected individuals as well as the cannibalism of an infected predator. We also consider incubation delay in disease transmission, where the incubation period represents the time in which the infectious agent develops in the host. Local stability analysis of the system around the biologically feasible equilibria is studied. Bifurcation analysis of the system around interior equilibrium is also studied. Applying the normal form theory and central manifold theorem, the direction of Hopf bifurcation, the stability and the period of bifurcating periodic solutions are derived. Under appropriate conditions, the permanence of the system with time delay is proved. Our results suggest that incubation delay destabilizes the system and can produce chaos. We also observe that cannibalism can control disease and population oscillations. Extensive numerical simulations are performed to support our analytical results.

(Invited) Low Power Stt-Mram and Its Application to Normally-Off Processor

Reduction of the power consumption of mobile electronic devices is one of the principal issues in current and future electronics technology. In particular, reducing the power consumption of the processor is critical because it increases as the processor’s performance improves. Normally-off computing is one of the solutions. Standby power of a cache memory while the device power is on but the memory is idle accounts for a large proportion of the processor’s power consumption, which can be eliminated by shutting down the cache memory during the idle time and turning it on instantly when the memory becomes active. The key technology for the normally-off processor to reduce power effectively is a fast, low-power, non-volatile memory for the cache memory to replace the current SRAM cache memory. Among the various non-volatile memories, Spin Transfer Torque Magnetoresistive Random Access Memory (STT-MRAM) is the most promising candidate for the cache memory of the normally-off processor because of its potential performance in terms of fast switching and scalability. A magnetic tunnel junction (MTJ) storage element having perpendicular magnetization (p-MTJ) reduces the writing current of the STT-MRAM, which enables scaling of the STT-MRAM. However, for power saving of the normally-off processor, small write current and short write pulse duration time must be achieved simultaneously. In other words, write charge, which is write current multiplied by write pulse width, is a key parameter for power saving. Toshiba demonstrated STT switching of the p-MTJ with write charge of 90 fC whose write pulse width was 1 ns and write current was 90 uA. Simulation of the processor’s power consumption with this STT MRAM showed good power saving. Landau–Lifshitz–Gilbert (LLG) micromagnetic simulation of spin-transfer torque shows that a coherent precession of the spin plays an important role for fast switching of the p-MTJ. Initially, when the write current is applied to the p-MTJ, each spin precesses independently and the spin stays in the initial direction. It corresponds to incubation delay time. Immediately after the precession of each spin is synchronized and rotates coherently, switching of the spin begins. Therefore, the coherency of the spin precession needs to be controlled for further improvement of the fast switching of the p-MTJ. A part of this work was supported by NEDO.

Magnetic non‐volatile flip‐flop with spin‐Hall assistance

A novel multi‐bit non‐volatile flip‐flop (NVFF) written by spin‐Hall‐assisted spin‐transfer torque (STT) is proposed. This NVFF employs perpendicular‐anisotropy MTJs and requires an STT current combined with a spin‐Hall current to write the data. Thanks to the assistance of spin‐Hall effect (SHE), the incubation delay required by the conventional STT switching can be eliminated to achieve fast operation. Our proposed NVFF uses multi‐bit architecture and shows high‐density and low‐energy advantages over hybrid NV/volatile FFs in the application of the NV register file. Sim‐ulation results show that the proposed spin‐Hall‐assisted NVFF saves ∼31% storage density and ∼32% energy dissipation compared with the conventional STT‐NVFF. Moreover, the reliability of MTJ barrier is enhanced due to the reduction of the write voltage. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)

Domino-Style Spin–Orbit Torque-Based Spin Logic

We propose a new spin–orbit torque-based domino-style spin logic (SOT-DSL) that operates in a sequence of preset and evaluation modes of operation. During the preset mode, the output magnet is clocked to its hard axis using spin-Hall effect. In the evaluation mode, the clocked output magnet is switched by a spin current from the preceding stage. The nanomagnets in SOT-DSL are always driven by orthogonal spins rather than collinear spins, which in turn eliminates the incubation delay and allows fast magnetization switching. Based on our simulation results, SOT-DSL shows up to 50% improvement in energy consumption compared to all-spin logic. Moreover, SOT-DSL relaxes the requirement for buffer insertion between long spin channels and significantly lowers the design complexity.

Significant Reduction in Rate of Indeterminate Results of the QuantiFERON-TB Gold In-Tube Test by Shortening Incubation Delay

The QuantiFERON-TB Gold In-Tube (QFT-G IT) test (Cellestis Inc., Valencia, CA) is one of the gamma interferon release assays (IGRAs) that are promising tools for diagnosing active or latent Mycobacterium tuberculosis infections. We investigated the clinical and laboratory factors that affect the rate of indeterminate QFT-G IT test results. We also suggest a workflow strategy for achieving optimized test results using the QFT-G IT test for the diagnosis of active tuberculosis (TB) or latent TB infection. We performed statistical analysis using data from a retrospective review of medical records. The first phase included 683 QFT-G IT test results from 676 patients tested between January 2008 and May 2008, and the second phase included an additional 663 QFT-G IT test results from 653 patients tested between January 2008 and December 2008 at Samsung Medical Center, a tertiary care hospital in South Korea. Immunosuppressive drug therapy, underlying diseases, bedridden status, and hypoalbuminemia were significantly associated with indeterminate QFT-G IT test results. With reduction of the incubation delay during the test procedure from an average of 9.82 h to an average of 2.70 h with changes in the workflow, the frequency of indeterminate QFT-G IT test results was significantly reduced from 11.4% to 2.7%. With >6 h of incubation delay, however, the frequency of indeterminate QFT-G IT test results was increased in a statistically significant manner. This study demonstrates that not only clinicopathological factors but also laboratory factors, such as incubation delay, significantly affect the rate of indeterminate QFT-G IT test results; therefore, optimization of the test procedure may contribute to reductions in the rate of indeterminate QFT-G IT test results, which delay the diagnosis of TB.

Effects of Nest Reuse and Onset of Incubation on Microbial Growth and Viability of Wood Duck Eggs

Abstract. In many birds, egg viability declines the longer that eggs remain unincubated (i.e., incubation delay), possibly because of increased levels of microbial infection. Reuse of nests is common in cavity-nesting species and may also increase exposure of eggs to microbes. Starting incubation before the clutch is complete may help protect early-laid eggs from microbial infection. In this study, we tested the effects of nest cleaning, length of incubation delay, and onset of night incubation on growth of microbes on Wood Duck (Aix sponsa) eggshells and examined the effect of microbial infection on hatching success. We used nest boxes that had been cleaned or not cleaned of previous nesting materials and sampled microbes on eggshells during early and mid egg laying and after the start of night incubation. We detected levels of eggshell microbes (101 colony forming units [CFU] egg-1) lower than at more tropical locations (103–4 CFU egg-1). Levels of heterotrophic bacteria were 2.2 times greater in unclea...

A Study of the Spawning Ecology and Early Life History Survival of Bonneville Cutthroat Trout

AbstractWe completed a large‐scale field experiment in four tributaries of the Logan River, Utah, where the largest metapopulation of imperiled Bonneville cutthroat troutOncorhynchus clarkii utahpersists. We documented the spatial and temporal distributions of spawners, quantified substrate use versus substrate availability, and evaluated differences in hatch and emergence fry success between and among sites in relation to habitat characteristics. We observed considerable variability in the timing, magnitude, and duration of spawning among study areas (streams), in part as a function of a variable, multipeaked hydrograph. Nevertheless, across study areas, >70% of redds were constructed on the final descending limb of the hydrograph. Despite large differences in the amount of spawning substrate available, Bonneville cutthroat trout utilized a narrow range of substrate and sizes (3–80 mm) similar to that utilized by other subspecies of cutthroat trout, albeit biased towards larger sizes. Water temperatures generally remained below the recommended range (6–17°C) for spawning; however, the viability of this metapopulation of cutthroat trout suggests that the recommended temperature range for spawning is overestimated for this subspecies and (or) does not account for local thermal adaptation. Hatch varied from 43% to 77% and emergence survival from 39% to 65% among streams, and within‐stream variability was substantial; both survival rates declined significantly as a function of increased fine sediment concentrations. Egg development rates were nearly 50% greater in a high‐elevation tributary where redd counts were also lowest. In high, mountain systems with short growing seasons, this incubation delay likely presents a significant growth disadvantage for age‐0 trout. Our research enhances our understanding of Bonneville cutthroat trout spawning ecology and early survival and provides critical information for aiding in the development of benchmarks for their recovery. Effective conservation efforts should be directed towards minimizing anthropogenic activities that result in excess sedimentation in their critical spawning tributaries.Received April 15, 2011; accepted February 7, 2012

Effects of incubation delay on viability and microbial growth of Wood Duck (Aix sponsa) eggs

Egg viability in birds declines with increasing length of the delay in the start of incubation (i.e., incubation delay) and may be influenced by microbial infection and exposure of eggs to temperatures above physiological zero (>24°C). Onset of incubation during egg laying results in developmental asynchrony of embryos but may help to maintain viability of early-laid eggs. We manipulated incubation delay of Wood Duck (Aix sponsa) eggs and tested for effects of incubation delay and ambient temperature on egg viability and microbial infection. We also examined onset of incubation by egg-laying females. Hatching success declined slowly with increasing length of incubation delay and was very weakly affected by increasing exposure to temperatures >24°C. On average, females began incubation at night 7 days after nest initiation, but egg viability had declined only 8.6% (95% confidence interval: 4.3–15.2) by day 7. Microbial infection of eggshells was not related to length of incubation delay or mean daily temperature of the exposure period. Clutch size declined as the breeding season progressed, and nocturnal incubation began earlier in the laying sequence with declining clutch sizes. Laying females, regardless of clutch size, incubated for 3 nights before starting full incubation. We suggest that early onset of incubation may be more important in reducing incubation period and predation risk than in maintaining viability of early-laid eggs.

Effect of crystalline structure of TiO2 substrates on initial growth of atomic layer deposited Ru thin films

Ru thin films were grown on polymorphic TiO2 thin film substrates at 230 and 250°C by atomic layer deposition using 2,4-(dimethylpentadienyl)(ethylcyclopentadienyl)Ru and an O2 gas. While the Ru films grown on amorphous and rutile TiO2 substrates showed a relatively long incubation cycle number of approximately 350 and 100 at 230 and 250°C, respectively, the Ru films grown on anatase TiO2 substrates exhibited a significantly shorter incubation delay which was attributed to the catalytic activity of anatase TiO2. This difference in the incubation cycle affected the surface morphology of the Ru films on different TiO2 substrates.

Thermal effects on spin-torque-driven switching in high-tunneling-magnetoresistance magnetic tunnel junctions

This paper presents a micromagnetic study of the spin-transfer torque induced, thermally assisted switching, in magnetic tunnel junctions. Having performed numerous repeated simulations, we confirm that temperature fluctuations facilitate reversal processes. In particular, different averaging procedures were employed in order to separate pure thermal effects from other contributions. The results indicate that the finite temperature introduces well-defined pre and postswitching oscillation modes and thus, the “incubation delay” is not observed for the simulated device. Detailed analysis of the preswitching oscillations, for both the antiparallel to parallel and parallel to antiparallel transitions, reveals that the oscillations in the center of the sample are the dominating mode. The excitation of these central modes is the main mechanism leading to earlier switching, especially at current densities below the critical ones computed at T=0 K.

Immediate Incubation Reduces Indeterminate Results for QuantiFERON-TB Gold In-Tube Assay

In vitro gamma interferon release assays (IGRAs) are increasingly used as an alternative to the traditional tuberculin skin test for the diagnosis of latent Mycobacterium tuberculosis infection. Evaluation of the QuantiFERON-TB Gold in-tube assay (QFT-IT) prior to large-scale implementation at the Stanford Hospital and Clinics for a health care worker screening program revealed a critical preanalytical factor affecting the results. We found that incubation delay significantly increased the frequency of indeterminate results. In this study, QFT-IT was performed with samples from healthy volunteers, and replicate tubes were incubated at 37 degrees C either immediately or after a delay at room temperature for 6 and 12 h. No indeterminate results (0/41) were seen when the assay was performed with immediate incubation. Incubation delays of 6 and 12 h yielded indeterminate results at rates of 10% (2/20) (P = 0.10) and 17.1% (7/41) (P = 0.01), respectively. The increased rate of indeterminate results was due to a decrease in the mean values for the mitogen-nil tubes when incubation was delayed for 6 h (P = 0.004) and 12 h (P < 0.001). The rates of concordance of positive or negative results obtained following immediate incubation and following 6- and 12-h delays were 77.8% (14/18) and 79.4% (27/34), respectively. Subsequent implementation of the immediate incubation procedure in our screening program for 14,830 health care workers yielded an indeterminate result rate of 0.36% over a period of 12 months, a significant improvement over the reported rates of 5 to 40% for QFT-IT. We conclude that immediate incubation of QFT-IT tubes is an effective way to minimize indeterminate results. The effect of incubation delay on the accuracy of QFT-IT remains to be determined.

Macrospin model to explain the absence of preswitching oscillations in magnetic tunnel junctions: Fieldlike spin-transfer torque

We show that the absence of preswitching oscillations (``incubation delay'') in magnetic tunnel junctions can be explained within the macrospin model by a sizable fieldlike component of the spin-transfer torque. It is further suggested that measurements of the voltage dependence of tunnel junction switching time in the presence of external easy axis magnetic fields can be used to determine the magnitude and voltage dependence of the fieldlike torque.

Impacts of Incubation Delay on the Dynamics of an Eco-Epidemiological System—A Theoretical Study

Parasite and predator play significant role in trophic interaction, productivity and stability of an ecosystem. In this paper, we have studied a host-parasite-predator interaction that incorporates incubation delay. How the qualitative and quantitative behaviors of the system alter with the incubation delay have been discussed both from mathematical and biological point of views. It is observed that for a lower infection rate, the system is stable for all delays; but for a higher infection rate, there exists a threshold value of the delay above which the system is unstable and below which the system is stable leading to the persistence of all the species. Also, the instability arising from the incubation delay may be controlled if somehow the growth rate of predator population is increased. Numerical studies have also been performed to illustrate different analytical findings.

Electrical time-domain observation of magnetization switching induced by spin transfer in magnetic nanostructures (invited)

We have measured the distribution of switching times in spin-transfer switching induced by fast current pulses in two pillar-shaped systems: (i) spin valves and (ii) MgO-based magnetic tunnel junctions. (i) Spin valves can sustain high currents, such that the application of pulsed currents of amplitude a few times that of the static switching threshold is possible. This makes subnanosecond switching within reach. In that limit, the pulse durations leading to switching follow a multiply stepped distribution at 300K and a regular distribution at 40K. At 300K, this reflects the precessional nature of the switching, which proceeds through a small number of precession cycles. The switching time distribution can be modeled from the thermal variance of the initial magnetization orientations. At 40K, nonuniform magnetization switching occurs. (ii) In MgO-based tunnel junctions, we could follow individual time-resolved switching events with a 13GHz bandwidth. The switching proceeds through a nanosecond-scale random incubation delay during which the resistance is quiet, followed by a sudden (400ps duration) transition terminated by a pronounced ringing that is damped within 1.5ns. While the incubation delay is probabilistic, the following time dependence of the resistance is reproducible.