Cardiovascular risk assessment

Cardiovascular disease remains the leading cause of mortality in the Westernised world. Lifestyle changes and drug therapy can reduce cardiovascular risk. Many interventions such as lipid-lowering therapy reduce relative risk to the same extent irrespective of baseline risk, but the absolute benefit is still highest in those with the highest absolute risk. Cardiovascular risk assessment is a tool to determine absolute cardiovascular risk in asymptomatic patients and to select those most likely to benefit from intervention. Conventional risk assessment (Framingham) requires age, gender, blood pressure, smoking status, total cholesterol and high-density lipoprotein cholesterol (HDLC) to determine risk. This is usually expressed as the 10-year risk of coronary heart disease. The accuracy and predictive ability of conventional risk assessment have limitations. Many biomarkers, genetic tests and vascular imaging procedures correlate statistically with vascular risk. Adding these tests to conventional risk assessment (expanded risk assessment) may therefore improve our ability to predict risk. It has, however, been difficult to conclusively demonstrate that expanded risk assessment outperforms conventional risk assessment. Many tests and procedures require further validation before they become part of routine clinical practice. Additional testing may be useful in patients with intermediate risk or where risk is difficult to determine for other reasons

Statins: Adherence and side-effects

Many patients either do not adhere to, or fail to persist with, long-term lipid-lowering therapy. This unfavourable medication utilisation behaviour compromises potential treatment benefit. In retrospective studies, patients aged 50-65 had the highest adherence rates, while both younger and older patients had lower rates. Patients with pre-existing cardiovascular disease adhere better than those in primary prevention. Financial barriers may impair adherence. At the individual patient level, health beliefs, perceptions of own cardiovascular risk and need for medication, concerns about side-effects and inconvenience of treatment may influence adherence. In clinical trials, regular reminders to patients have been shown to improve adherence, but each patient will require an individually tailored treatment strategy. Myopathy is the most common clinically relevant adverse effect of statins. The clinical severity of statin myopathy is highly variable, ranging from mild muscle ache to rare instances of rhabdomyolysis. Risk factors for statin myopathy include age, statin dose, hypothyroidism, medications that inhibit statin metabolism, combined statin and fibrate therapy, and renal impairment. Alternative causes of myopathy should be excluded before muscular symptoms are ascribed to statins. The management of statin myopathy is guided by the severity of symptoms and the creatine kinase level. Potential management strategies include statin dechallenge and rechallenge, statin dose reduction, statin switching, non-daily dosing and use of alternative lipid-lowering agents, such as ezetimibe. Statins rarely cause severe liver disease. Mild liver enzyme elevations are seen relatively frequently in patients starting statins, but are usually not clinically important. Patients with persistently elevated liver enzymes should be investigated to determine the cause of liver disease. Patients with stable, well-compensated liver disease can be prescribed statins, provided they are closely monitored

Familial hypercholesterolaemia

amilial hypercholesterolaemia (FH) is a monogenic disorder of low-density lipoprotein (LDL) metabolism. It is characterised by markedly elevated LDL cholesterol, autosomal dominant inheritance, premature cardiovascular disease and tendon xanthomata. FH is a genetically heterogeneous disorder, but the most common underlying molecular cause is mutation of the LDL receptor gene. The worldwide prevalence of FH is 1:500. South Africa has three founder populations in which the prevalence of FH may be as high as 1:70. FH is diagnosed clinically, but the diagnosis can be confirmed by DNA analysis. DNA testing cannot always identify the causative mutation because there are several genes to examine and more than 1 500 different mutations have been identified in the LDL receptor alone. Statins are the treatment of choice for patients with FH. Ezetimibe or cholestyramine can be added if additional LDL lowering is required, or if patients are unable to tolerate high statin doses

A functional central limit theorem for a Markov-modulated infinite-server queue

The production of molecules in a chemical reaction network is modelled as a Poisson process with a Markov-modulated arrival rate and an exponential decay rate. We analyze the distributional properties of $M$, the number of molecules, under specific time-scaling; the background process is sped up by $N^{\alpha}$, the arrival rates are scaled by $N$, for $N$ large. A functional central limit theorem is derived for $M$, which after centering and scaling, converges to an Ornstein-Uhlenbeck process. A dichotomy depending on $\alpha$ is observed. For $\alpha\leq1$ the parameters of the limiting process contain the deviation matrix associated with the background process.Comment: 4 figure

Optically activated ZnO/Sio2/Si cantilever beams

The photomechanical effect induced by periodically varying sub-bandgap illumination in thin ZnO films deposited on oxidized Si has been demonstrated for the first time. The efficiency of this effect is at least one order of magnitude higher as compared to the photothermal activation of Si. Thus it can be considered as a powerful optical drive for resonant sensors. A phenomenological model of the mechanisms involved in the process is proposed. The optomechanical effect can also be used as a complementary method in determination of the surface state parameters of ZnO films

Interviewer Effects on Nonresponse

In face-to-face surveys interviewers play a crucial role in making contact with and gaining cooperation from sample units. While some analyses investigate the influence of interviewers on nonresponse, they are typically restricted to single-country studies. However, interviewer training, contacting and cooperation strategies as well as survey climates may differ across countries. Combining call-record data from the European Social Survey (ESS) with data from a detailed interviewer questionnaire on attitudes and doorstep behavior we find systematic country differences in nonresponse processes, which can in part be explained by differences in interviewer characteristics, such as contacting strategies and avowed doorstep behavior.

Strain rate effect on the mechanical behaviour of a textile reinforced cement composite

The static tensile behaviour of Textile Reinforced Cement Composites is known and can be modeled adequately. However, using these static material properties under dynamic loadings such as impact and seismic loadings, can cause over- or underestimation of the material due to effects of strain rate. This work focuses on the strain rate dependency of a specific textile reinforced cement composite under tensile loadings at strain rates equivalent to quasi static applications towards low velocity impacts. It was found that the main damage mechanisms of this material stay the same. However cracking of the cement matrix is delayed to higher stress levels

Exact solution of the Zeeman effect in single-electron systems

Contrary to popular belief, the Zeeman effect can be treated exactly in single-electron systems, for arbitrary magnetic field strengths, as long as the term quadratic in the magnetic field can be ignored. These formulas were actually derived already around 1927 by Darwin, using the classical picture of angular momentum, and presented in their proper quantum-mechanical form in 1933 by Bethe, although without any proof. The expressions have since been more or less lost from the literature; instead, the conventional treatment nowadays is to present only the approximations for weak and strong fields, respectively. However, in fusion research and other plasma physics applications, the magnetic fields applied to control the shape and position of the plasma span the entire region from weak to strong fields, and there is a need for a unified treatment. In this paper we present the detailed quantum-mechanical derivation of the exact eigenenergies and eigenstates of hydrogen-like atoms and ions in a static magnetic field. Notably, these formulas are not much more complicated than the better-known approximations. Moreover, the derivation allows the value of the electron spin gyromagnetic ratio $g_s$ to be different from 2. For completeness, we then review the details of dipole transitions between two hydrogenic levels, and calculate the corresponding Zeeman spectrum. The various approximations made in the derivation are also discussed in details.Comment: 18 pages, 4 figures. Submitted to Physica Script

On the Nature of MeV-blazars

Broad-band spectra of the FSRQ (flat-spectrum-radio quasars) detected in the high energy gamma-ray band imply that there may be two types of such objects: those with steep gamma-ray spectra, hereafter called MeV-blazars, and those with flat gamma-ray spectra, GeV-blazars. We demonstrate that this difference can be explained in the context of the ERC (external-radiation-Compton) model using the same electron injection function. A satisfactory unification is reachable, provided that: (a) spectra of GeV-blazars are produced by internal shocks formed at the distances where cooling of relativistic electrons in a jet is dominated by Comptonization of broad emission lines, whereas spectra of MeV-blazars are produced at the distances where cooling of relativistic electrons is dominated by Comptonization of near-IR radiation from hot dust; (b) electrons are accelerated via a two step process and their injection function takes the form of a double power-law, with the break corresponding to the threshold energy for the diffusive shock acceleration. Direct predictions of our model are that, on average, variability time scales of the MeV-blazars should be longer than variability time scales of the GeV-blazars, and that both types of the blazar phenomenon can appear in the same object.Comment: Accepted for publication in the Astrophysical Journa

Ultimate performance of polymer:fullerene bulk heterojunction tandem solar cells

We present the model calculations to explore the potential of polymer:fullerene tandem solar cells. As an approach we use a combined optical and electrical device model, where the absorption profiles are used as starting point for the numerical current-voltage calculations. With this model a maximum power efficiency of 11.7% for single cells has been achieved as a reference. For tandem structures with a ZnO/poly(3,4-ethylenedioxythiophene)/ poly(styrenesulphonic acid) middle electrode an ultimate efficiency of 14.1% has been calculated. In the optimum configuration the subcell with the narrowest band gap is placed closest to the incoming light. Consequently, tandem structures are expected to enhance the performance of optimized single cells by about 20%. © 2011 American Institute of Physics