Stability and Hopf Bifurcation for a Delayed SLBRS Computer Virus Model

By incorporating the time delay due to the period that computers use antivirus software to clean the virus into the SLBRS model a delayed SLBRS computer virus model is proposed in this paper. The dynamical behaviors which include local stability and Hopf bifurcation are investigated by regarding the delay as bifurcating parameter. Specially, direction and stability of the Hopf bifurcation are derived by applying the normal form method and center manifold theory. Finally, an illustrative example is also presented to testify our analytical results

Bifurcation analysis for a delayed food chain system with two functional responses

A delayed three-species food chain system with two types of functional response, Holling type and Beddington-DeAngelis type, is investigated. By analyzing the distribution of the roots of the associated characteristic equation, we get the sufficient conditions for the stability of the positive equilibrium and the existence of Hopf bifurcation. In particular, using the normal form theory and center manifold theorem, the properties of Hopf bifurcation such as direction and stability are determined. Finally, numerical simulations are given to substantiate the theoretical results

Carbon gas concentrations and fluxes in Lake Vesijärvi : possible effects of artificial aeration

Lakes play an important role in both global and regional carbon cycling, especially, the role of lakes is pronounced in the boreal zone, where lakes cover up to 20% of the land area. Allochthonous carbon is discharged mainly from terrestrial processes, but also through anthropogenic eutrophication. The role of allochthonous carbon load in lacustrine ecosystems is important, which can have far-reaching effects on lacustrine biogeochemistry in general and especially on carbon cycling. Part of dissolved organic carbon is transformed to carbon dioxide (CO2) and methane (CH4) in biological processes that result in carbon gas concentrations in water that increase above atmospheric equilibrium, thus making boreal lakes serve as sources of the important greenhouse gases. Lake Vesijärvi is renowned for its clear-water, but it has suffered eutrophication for a long history. The severely affected Enonslkä lake basin is the most eutrophic part since it surrounded mainly by urban area (28%) and forests (31%). To improve the water quality, large scale aeration in the autumn 2009 was started with the Mixox-oxygenerators. Aeration is used to weaken thermal stratification and recharge oxygen by increasing vertical flow circulation within the water columns. This leads to most chemical cocnetrations become more homogenous with depth and concentrations of reduced forms decrease in the hypolimnion. The aeration units were operated on campaign basis in summer 2013. One aim here was to investigate carbon gas concentrations and fluxes from the urban boreal lake basin, and examine the impacts of artificial aeration on greenhouse gases during the open water period in 2013. Besides CO2 and CH4 concentrations and fluxes, I measured also the water temperature and dissolved oxygen concentration of the water columns for monitoring the efficiency of artificial aeration. All gas samples were analyzed at the Lammi Biological Station of University of Helsinki with gas chromatography using the head space technique. As background data I used the information on temperature and oxygen profiles collected from the measuring platform on Lake Vesijärvi, and a reference study on CO2 and CH4 concentrations and fluxes dating back to 2005 when there was no aeration going on. In 2013, the studied lake basin was a source of CO2 to the atmosphere during the open water period, although the lake basin showed uptake of CO2 from the atmosphere for short times. The lake acted as a steady source of CH4 to the atmosphere throughout the measuring period. The mean CO2 flux was 34.1 mmol m-2 d-1, which was over 2.5 times higher than in the reference year 2005 when there was no the aeration yet. During the campaigns, the CO2 fluxes were higher from aerated than non-aerated water column and from the longer aerations as well. Therefore, aeration mixed stratified water columns and thus enhanced release of gases such as CO2 from surface water to the atmosphere. The mean CH4 flux was 0.2 mmol m-2 d-1. The CH4 fluxes from the Enonselkä basin were slightly decreased in 2013. These decreased CH4 fluxes in Enonselkä basin can be attributed to the limited CH4 production and high rate of CH4 oxidation in the oxygenated hypolimnion and surface of sediment. The daily CH4 fluxes fluxes during the long time aerated operations decreased. The significance of aeration to carbon cycling processes dpended on the residual CH4 concentrations in the water column

Laser-enhanced cavitation during high intensity focused ultrasound: An in vivo study

This is the published version.Laser-enhanced cavitation during high intensity focused ultrasound (HIFU) was studied in vivo using a small animal model. Laser light was employed to illuminate the sample concurrently with HIFU radiation. The resulting cavitation was detected with a passive cavitation detector. The in vivo measurements were made under different combinations of HIFU treatment depths, laser wavelengths, and HIFU durations. The results demonstrated that concurrent light illumination during HIFU has the potential to enhance cavitation effect by reducing cavitation threshold in vivo

Generation of nonparaxial self-accelerating beams using pendant droplets

We propose and demonstrate the effectual generation and control of nonparaxial self-accelerating beams by using UV-resin pendant droplets. We show that the geometrical shape of the hanging droplets formed as a result of the interplay between surface tension and gravity offers a natural curvature enabling the generation of nonparaxial self-accelerating beams. By simply adjusting the tilt angle of the surface where the droplets reside, a passing light beam is set to propagate along different curved trajectories, bending into large angles with non-diffracting features superior to a conventional Airy beam. Such self-accelerating beams are directly traced experimentally through the scattered light in yeast-cell suspensions, along with extensive ray tracing and numerical simulations. Furthermore, by modifying the shape of uncured pendant resin droplets in real time, we showcase the dynamical trajectory control of the self-accelerating beams. Our scheme and experimental method may be adopted for droplet-based shaping of other waves such as microfluidic jets and surface acoustic waves.Comment: 8 pages, 8 figures, research articl

The effect of corporate credit rating changes on UK common stock returns

Credit ratings play an essential role in the UK financial market, and their changes can convey information to affect the stock returns. This paper studies the impact of corporate credit rating changes on UK stock returns instead of bond rating revisions. We adopt the event study method to analyze 283 samples of corporate credit rating revisions by Standard & Poor`s and Moody`s from 1999 to 2020. Results indicate that significant negative abnormal returns exist in downgrade changes, while the upgrades only have insignificant abnormal returns. The multiple-step and contaminated rating reviews result in a more incredible market reaction than the others. Cross-sectional regressions are launched to investigate whether the switch to and within the investment and speculative category would affect the abnormal returns but only get an insignificant result

DETERMINATION OF DESIGN PARAMETERS OF ASPHALT PAVEMENT BASED ON PG TECHNOLOGY

The design parameters are one of the important factors to ensure the quality of asphalt pavement design. In “Highway Asphalt Pavement Design Specification” (JTGD50-2017), the stander of China, used the asphalt mixture anti-pressure resilience modulus at a single temperature of 20 ℃ as the design metrics. However, asphalt mixture, as a sticky-bullet plastic material, shows different mechanical properties at different temperatures. China is a vast territory, and there are great differences between the high and low temperature value (m and n) of each region. Therefore, it is unreasonable to design asphalt pavement only with the asphalt mixture anti-pressure resilience modulus value at 20 ℃. Studies show that the design parameters using PG technology can improve the high temperature anti-rutting and low temperature cracking performance of asphalt pavement

Dynamical Analysis of a Viral Infection Model with Delays in Computer Networks

This paper is devoted to the study of an SIRS computer virus propagation model with two delays and multistate antivirus measures. We demonstrate that the system loses its stability and a Hopf bifurcation occurs when the delay passes through the corresponding critical value by choosing the possible combination of the two delays as the bifurcation parameter. Moreover, the direction of the Hopf bifurcation and the stability of the bifurcating periodic solutions are determined by means of the center manifold theorem and the normal form theory. Finally, some numerical simulations are performed to illustrate the obtained results