Multimodal oscillations in systems with strong contraction

One- and two-parameter families of flows in $R^3$ near an Andronov-Hopf bifurcation (AHB) are investigated in this work. We identify conditions on the global vector field, which yield a rich family of multimodal orbits passing close to a weakly unstable saddle-focus and perform a detailed asymptotic analysis of the trajectories in the vicinity of the saddle-focus. Our analysis covers both cases of sub- and supercritical AHB. For the supercritical case, we find that the periodic orbits born from the AHB are bimodal when viewed in the frame of coordinates generated by the linearization about the bifurcating equilibrium. If the AHB is subcritical, it is accompanied by the appearance of multimodal orbits, which consist of long series of nearly harmonic oscillations separated by large amplitude spikes. We analyze the dependence of the interspike intervals (which can be extremely long) on the control parameters. In particular, we show that the interspike intervals grow logarithmically as the boundary between regions of sub- and supercritical AHB is approached in the parameter space. We also identify a window of complex and possibly chaotic oscillations near the boundary between the regions of sub- and supercritical AHB and explain the mechanism generating these oscillations. This work is motivated by the numerical results for a finite-dimensional approximation of a free boundary problem modeling solid fuel combustion

Clinical, epidemiological and virological features of acute hepatitis B in Italy

Purpose To evaluate the association of hepatitis B virus (HBV) genotypes, basal core promoter (BCP)/precore (PC) and S gene mutations with the clinical-epidemiological characteristics of acute hepatitis B (AHB) in Italy. Methods During July 2005–January 2007, 103 symptomatic AHB patients were enrolled and prospectively followed up at 15 national hospitals. HBV genotypes, BCP/ PC and S gene variants were determined by nested-PCR and direct sequence analysis. Results Genotype D, A and F were detected in 49, 45 and 6 % of patients, respectively. BCP, PC, and BCP plus PC variants were found in 3.1, 11.3 and 7.2 % of patients, respectively. At enrollment, 68.3 % of patients were hepatitis B e antigen (HBeAg)-positive and 31.7 % HBeAg-negative. BCP/PC mutations were more common in HBeAg-negative than in HBeAg-positive patients (p < 0.0001). Compared to genotype D patients, those harboring non-D genotypes were more frequently males (p = 0.023), HBeAg-positive (p < 0.001), had higher bilirubin (p = 0.014) and viremia (p = 0.034) levels and less frequently carried BCP/PC mutations (p < 0.001). Non-D genotype patients more often were from Central Italy (p = 0.001) and reported risky sexual exposure (p = 0.021). Two patients had received vaccination before AHB: one harbored genotype F; the other showed a S gene mutation. Four patients developed fulminant AHB; mutations were found in 2 of 3 patients who underwent BCP/ PC sequencing. After a 6-month follow-up, only 2 (2.8 %) patients developed persistent infection. Conclusion AHB by non-D genotypes is increasing in Italy and is associated with risky sexual exposure. The ability of some genotypes to cause persistent and/or severe infection in Italy warrants larger studies for clarificatio

Chaos at the border of criticality

The present paper points out to a novel scenario for formation of chaotic attractors in a class of models of excitable cell membranes near an Andronov-Hopf bifurcation (AHB). The mechanism underlying chaotic dynamics admits a simple and visual description in terms of the families of one-dimensional first-return maps, which are constructed using the combination of asymptotic and numerical techniques. The bifurcation structure of the continuous system (specifically, the proximity to a degenerate AHB) endows the Poincare map with distinct qualitative features such as unimodality and the presence of the boundary layer, where the map is strongly expanding. This structure of the map in turn explains the bifurcation scenarios in the continuous system including chaotic mixed-mode oscillations near the border between the regions of sub- and supercritical AHB. The proposed mechanism yields the statistical properties of the mixed-mode oscillations in this regime. The statistics predicted by the analysis of the Poincare map and those observed in the numerical experiments of the continuous system show a very good agreement.Comment: Chaos: An Interdisciplinary Journal of Nonlinear Science (tentatively, Sept 2008

Synthesis of AMBA AHB from formal specification: A case study

The standard hardware design flow involves: (a) design of an integrated circuit using a hardware description language, (b) extensive functional and formal verification, and (c) logical synthesis. However, the above-mentioned processes consume significant effort and time. An alternative approach is to use a formal specification language as a high-level hardware description language and synthesize hardware from formal specifications. Our work is a case study of the synthesis of the widely and industrially used AMBA AHB protocol from formal specifications. Bloem et al. presented the first formal specifications for the AMBA AHB Arbiter and synthesized the AHB Arbiter circuit. However, in the first formal specification some important assumptions were missing. Our contributions are as follows: (a) We present detailed formal specifications for the AHB Arbiter incorporating the missing details, and obtain significant improvements in the synthesis results (both with respect to the number of gates in the synthesized circuit and with respect to the time taken to synthesize the circuit), and (b) we present formal specifications to generate compact circuits for the remaining two main components of AMBA AHB, namely, AHB Master and AHB Slave. Thus with systematic description we are able to automatically and completely synthesize an important and widely used industrial protocol

Sugar preference and the importance of viscosity in Apis cerana, the Asian honeybee

The Asian honeybee, Apis cerana java (AHB) is a tropical bee species that recently breached quarantine in northern Australia. It is classed as an invasive pest with the potential to detrimentally impact upon Australian beekeeping and other agricultural industries. New research is investigating the behaviour and ecotoxicology of AHB with the aim of developing and optimising trapping stations to impede colony spread. Whilst sugar feeding preferences in the temperate species Apis mellifera have been extensively investigated, preferences in AHB are much less known. This information is crucial to the design of an efficient AHB trapping station. Here, we investigate the sugar solution preferences of AHB using the sugars most common found in nectar. We tested glucose and fructose (hexose sugars), sucrose (a disaccharide sugar) and various mixtures. We also used manipulated solution viscosity through the addition of tylose. We found that, as for Apis mellifera, AHB displayed a strong preference for equicaloric solutions of sucrose over hexose solutions, with both hexoses equally attractive. However, whilst Apis mellifera displayed a strong preference for glucose-fructose- sucrose over an equicaloric sucrose solution, AHB displayed no preference between equicaloric solutions of sucrose, glucose-fructose and glucose-fructose-sucrose. In addition, when sucrose concentrations were fixed and viscosity was manipulated using tylose, AHB showed a preference for more viscous solutions than was predicted by a recently published model of nectar-feeding. We discuss these results in light of this model and the ecology of AHB

Implementation of AMBA AHB protocol using verilog HDL

Advanced Microcontroller Bus Architecture (AMBA) is a series of bus protocols provided by ARM. These include AHB, APB and ASB. AMBA provides an on-chip communication standard for these buses to be used in high performance microcontrollers. In this paper we have implemented the AMBA AHB (Advanced High-Performance Bus) which is used for high performance transfers among different modules of the microcontroller. AHB supports efficient connection of processor, on chip memory, DMA and off chip external memories. AMBA AHB system bus supports multiple bus masters and slaves. The design is implemented using Verilog HDL and simulated using ModelSim 6.4a. Synthesis for the design is done using Xilinx ISE 14.4

Tenofovir as rescue therapy following clinical failure to lamivudine in severe acute hepatitis B

Acute hepatitis B (AHB) is a self-limiting condition in more than 95% of cases. Treatment is however recommended in patients with severe AHB (<1% of cases), aiming to prevent liver failure and death. Various nucleos(t)ide analogues (NA) have been found to be effective in severe AHB, although NA-resistant strains causing AHB have been also recently reported. The use of tenofovir in severe AHB has only been described in 3 cases (1 adult and 1 infant with HBV mono-infection, 1 adult with HBV/HIV co-infection). We hereby report a 47-year-old treatment-naïve male, who developed severe AHB and was initially treated with lamivudine (LMV). Initial rapid biochemical response was followed by biochemical breakthrough after 9 days, suggesting LMV resistance. Rescue therapy with ‘add-on’ tenofovir brought about a sustained improvement in biochemical, serological and virological markers until HBsAg was lost after 4 months. Thus, this is the second adult HBV mono-infected patient, who responded successfully to tenofovir in severe AHB.peer-reviewe

Parameterized Synthesis Case Study: AMBA AHB (extended version)

We revisit the AMBA AHB case study that has been used as a benchmark for several reactive syn- thesis tools. Synthesizing AMBA AHB implementations that can serve a large number of masters is still a difficult problem. We demonstrate how to use parameterized synthesis in token rings to obtain an implementation for a component that serves a single master, and can be arranged in a ring of arbitrarily many components. We describe new tricks -- property decompositional synthesis, and direct encoding of simple GR(1) -- that together with previously described optimizations allowed us to synthesize the model with 14 states in 30 minutes.Comment: Moved to appendix some not very important proofs. To section 'optimizations: added the model for 0-process. Extended version of the paper submitted to SYNT 201

Dynamic changes of cytotoxic T lymphocytes (CTLs), natural killer (NK) cells, and natural killer T (NKT) cells in patients with acute hepatitis B infection

<p>Abstract</p> <p><b>Background</b></p> <p>The goal of this study is to observe changes in HBcAg-specific cytotoxic T lymphocytes (CTLs), natural killer (NK) and natural killer T (NKT) cells from peripheral blood and to relate such changes on viral clearance and liver injury in patients with acute hepatitis B (AHB).</p> <p><b>Methods</b></p> <p>Dynamic profiles on the frequency of HLA-A0201-restricted HBcAg18-27 pentamer complex (MHC-Pentamer)-specific CTLs and lymphocyte subsets in AHB patients were analyzed in addition to liver function tests, HBV serological markers, and HBV DNA levels. ELISPOT was used to detect interferon-gamma (INF-γ) secretion in specific CTLs stimulated with known T cell epitope peptides associated with HBV surface protein, polymerase, and core protein.</p> <p><b>Results</b></p> <p>HBV-specific CTL frequencies in AHB patients were much higher than in patients with chronic hepatitis B (CHB) (p < 0.05). HBeAg and HBV DNA disappeared earlier in AHB patients with a high frequency of HBV-specific CTLs compared with those with a low frequency of HBV-specific CTLs (p = 0.001 and 0.024, respectively). INF-γ spots of effector cells stimulated by Pol575-583, Env348-357, or Core18-27 epitope peptides were significantly greater in AHB patients than in CHB patients (p < 0.01). CD3⁺CD8⁺T cell numbers in AHB patients was more than observed in the healthy control group from the first to the fourth week after admission (p <it>= </it>0.008 and 0.01, respectively); the number of CD3⁺CD8⁺T cells and frequency of HBcAg18-27-specific CTLs in AHB patients reached peak levels at the second week after admission. NK and NKT cell numbers were negatively correlated with the frequency of HBcAg-specific CTLs (<it>r </it>= -0.266, p = 0.05).</p> <p><b>Conclusions</b></p> <p>Patients with AHB possess a higher frequency of HBcAg-specific CTLs than CHB patients. The frequency of specific CTLs in AHB patients is correlated with HBeAg clearance indicating that HBV-specific CTLs play an important role in viral clearance and the self-limited process of the disease. Furthermore, NK and NKT cells are likely involved in the early, non-specific immune response to clear the virus.</p