High Initial Susceptibility Research Articles

Mechanisms of replacement of circulating viruses by seasonal and pandemic influenza A viruses

Seasonal influenza causes annual epidemics by the accumulation of antigenic changes. Pandemic influenza occurs through a major antigenic change of the influenza A virus, which can originate from other hosts. Although new antigenic variants of the influenza A virus replace formerly circulating seasonal and pandemic viruses, replacement mechanisms remain poorly understood. A stochastic individual-based SEIR (susceptible-exposed-infectious-recovered) model with two viral strains (formerly circulating old strain and newly emerged strain) was developed for simulations to elucidate the replacement mechanisms. Factors and conditions of virus and host populations affecting the replacement were identified. Replacement is more likely to occur in tropical regions than temperate regions. The magnitude of the ongoing epidemic by the old strain, herd immunity against the old strain, and timing of appearance of the new strain are not that important for replacement. It is probable that the frequency of replacement by a pandemic virus is higher than a seasonal virus because of the high initial susceptibility and high basic reproductive number of the pandemic virus. The findings of this study on replacement mechanisms could lead to a better understanding of virus transmission dynamics and may possibly be helpful in establishing an effective strategy to mitigate the impact of seasonal and pandemic influenza.

Susceptibility of Nilaparvata lugens (Hemipteran: Delphacidae) populations in the Philippines to insecticides

Development of field resistance among Asian brown planthopper populations to insecticides contributes significantly towards the overall problem caused by the brown planthopper in rice production. We evaluated the susceptibility of brown planthoppers collected in the Philippines to the insecticides imidacloprid, fipronil and fenobucarb insecticides. Additionally we documented the changes in the populations' susceptibilities to the same insecticides when reared in insecticide-free environments. We found that brown planthopper populations collected in the Philippines between 2009 and 2010 were relatively susceptible to the tested insecticides when compared to historical data. Our findings provide baseline data for future studies. We also found that in populations characterized by high initial susceptibility to insecticides, the continued absence of insecticide selection pressure generally resulted in a slight decrease or no change in the populations' insecticide susceptibility.

Long-term effect of pegylated liposomal doxorubicin in recurrent platinum-resistant ovarian cancer: а clinical case

Despite the high initial susceptibility of ovarian cancer (OC) to chemotherapy, the vast majority of patients with Stages III–IV of the disease have its recurrences. Chemotherapy is a main treatment for recurrent OC. In Russia, the rate of platinum-resistant recurrences after first-line chemotherapy is more than 50 %, which may be due to the high extent of a tumor process at the moment of diagnosis, to the low rate of optimal cytoreductive interventions, and to non-optimal treatment. Many oncologists refuse to treat patients with recurrent platinum-resistant OC since the existing Russian and foreign guidelines point to the low efficiency of current chemotherapy for this type of recurrences. At the same time, whether chemotherapy should be used to treat platinum-resistant recurrences must be decided by taking into account a set of clinical factors that along with the duration of a platinum-free interval are also predictors for the efficiency of chemotherapy. These predictors should include mainly the histological pattern of a tumor; an immediate response to previous lines of chemotherapy; the number of previously used anticancer drugs; a patient’s general condition; and her existing factors that can influence the tolerability of chemotherapy. This paper describes a clinical case of a long-term survival in an OC patient who has developed a platinum-resistant recurrence just after first-line chemotherapy. Incomplete cross-resistance of the tumor to other drugs when a platinum-resistance recurrence develops, as well as its high susceptibility to the re-use of platinum-resistant derivatives possibly due to the artificial increase of a platinum-free interval should be identified among the factors that have influenced the prediction of treatment in this patient.

Relation between Initial Magnetization Curve and Grain Size of Nanocrystalline NdFeB Magnets

The volume fraction of the single domain size particles can be directly estimated from the initial magnetization of thermally demagnetized magnets. Multi-domain grains present initial magnetization curve with high initial susceptibility, whereas single-domain grains present low susceptibility initial magnetization curve. In the case of single domain size particles, the coercivity mechanism is coherent rotation and the Stoner-Wohlfarth (SW) model can be applied. From the initial magnetization curve of magnets, the volume fraction of grains with diameter less than 0.3 micrometers can be estimated in NdFeB magnets. This is possible because the Nd2Fe14B phase is single domain below 0.3 micrometers.

Effect of Al incorporation for Co on the gamma-beta phase boundary of rapidly solidified CoNiAl ferromagnetic shape memory alloys

The alloys Co64−xNi36Alx(at%, X=23,24,26 and 28) prepared through melt spinning technique revealed β- and γ-phase structure at room temperature. A monotonous increase in β-phase and simultaneous decrease in γ-phase has been observed with increasing Al content. The synergistic competition between β- and γ-phase influence β(B2)→L10 martensitic transformation. Therefore transformation broadening has been observed with Al content. Consequently, martensitic transformation temperature decreases and austenite transformation temperature increases. The γ-rich alloys showed magnetically soft phase, with high initial susceptibility and enhanced saturation magnetization. These alloys also revealed large magneto-strain values which are also supported by micro-structural morphology.

Structural and magnetic properties of uniform magnetite nanoparticles prepared by hightemperature decomposition of organic precursors

Magnetite nanoparticles (Fe3O4) of three different sizes below the limit for single domain magnetic behaviour have beenobtained by thermal decomposition of an iron precursor in an organic medium in thepresence of a surfactant. Good agreement between mean particle size obtained by TEM,crystal size calculated from x-ray diffraction and magnetic diameter calculated frommagnetization curves measured at room temperature shows that the samples consist ofuniform, crystalline and isolated magnetite nanoparticles with sizes between 5 and 11 nm.High saturation magnetization and high initial susceptibility values have been found, thelatter decreasing as the particle size decreases. The main contribution to the anisotropy ismagnetocrystalline and shape anisotropy, since surface anisotropy is suppressed by theoleic acid molecules which are covalently bonded to the nanoparticle surface.

Effect of Co addition on the microstructure and magnetic properties of FeCuNbSiB alloy

The microstructure and magnetic properties of Fe 73.5Cu 1Nb 3Si 13.5B 9 and Fe 66.5Co 7Cu 1Nb 3Si 13.5B 9 alloys were investigated. It was found that the addition of Co atoms enhances the effective hyperfine field at 57Fe nuclei and accelerates the crystallization process. Additionally, Fe 66.5Co 7Cu 1Nb 3Si 13.5B 9 ribbons exhibit low disaccommodation intensity and high initial susceptibility.

Microstructure and some magnetic properties of high-silicon FeSi sheets

The microstructure and some magnetic properties of Fe-6.42 wt% Si alloy in the as-received state and after annealing at 773 K for 1–31 h have been studied. From Mössbauer spectroscopy it was found that in all investigated samples the magnetization vector is almost randomly distributed. In the temperature range 200–400 K the intensity of the magnetic susceptibility disaccommodation is very low. Moreover, this alloy exhibits very low coercivity and high initial susceptibility.

Sm2Fe17 interstitial magnets (invited)

Various processing routes for making permanent magnets based on interstitially modified Sm2Fe17 have been recently developed. Zn bonding of coarse grained Sm2Fe17N3 gives coercivities μ0JHc as high as 2.2 T. Effective methods to prepare highly coercive Sm2Fe17N3 powders for polymer bonding are mechanical alloying and rapid quenching. With the very simple method of additional milling of coarse grained nitrided powders we achieved μ0JHc≊1.5 T. A coercivity up to 3.5 T has been achieved by a modified HDDR procedure, reducing the particle size of the starting material by milling prior to the hydrogenation–disproportionation–desorption–recombination (HDDR) treatment. This is attributed to a better control of two critical parameters, namely grain size and the amount of unrecombined α-Fe accompanying the intermediate TbCu7 structure-type phase. Resin bonded HDDR-Sm2Fe17N3 magnets show an unexpected high initial susceptibility. This may be due to a strong magnetic interaction of the grains. To develop coercivity in Sm2Fe17Cy≳1 obtained by gas–solid reactions of Sm2Fe17 the same methods as those applied to Sm2Fe17N3 can be successfully used. Fully dense magnets with a coercivity up to 1.5 T were made from the interstitially as well as substitutionally modified compound Sm2Fe15Ga2C2 by hot pressing of highly coercive powders.

The Effect of Heat Treatment on the Magnetic Properties of the Old Red Sandstone

Summary Magnetic methods of analysis have been used to identify and determine the grain size of minerals deposited in rocks of the Old Red Sandstone from South Wales. Changes in magnetic properties occur when the rock is heated in air to temperatures between 500 and 1OOOC. Three distinct processes, deduced from measurements of the low field reversible susceptibility, operate in successively higher temperature ranges. The first process is characterized by an increase in susceptibility over the range 500-700°C; the second involves a decrease in susceptibility over the range 700-850°C; the third process is responsible for a very large susceptibility increase above 850 C. The first process, operating over geological time, may be largely responsible for the production of a relatively high initial susceptibility in the virgin rock and of a secondary magnetization superposed on the original. Production of magnetite on heating is the interpretation given to the mechanism responsible for the increases in susceptibility.