Variational Principles for Stochastic Soliton Dynamics

We develop a variational method of deriving stochastic partial differential equations whose solutions follow the flow of a stochastic vector field. As an example in one spatial dimension we numerically simulate singular solutions (peakons) of the stochastically perturbed Camassa-Holm (CH) equation derived using this method. These numerical simulations show that peakon soliton solutions of the stochastically perturbed CH equation persist and provide an interesting laboratory for investigating the sensitivity and accuracy of adding stochasticity to finite dimensional solutions of stochastic partial differential equations (SPDE). In particular, some choices of stochastic perturbations of the peakon dynamics by Wiener noise (canonical Hamiltonian stochastic deformations, or CH-SD) allow peakons to interpenetrate and exchange order on the real line in overtaking collisions, although this behaviour does not occur for other choices of stochastic perturbations which preserve the Euler-Poincar\'e structure of the CH equation (parametric stochastic deformations, or P-SD), and it also does not occur for peakon solutions of the unperturbed deterministic CH equation. The discussion raises issues about the science of stochastic deformations of finite-dimensional approximations of evolutionary PDE and the sensitivity of the resulting solutions to the choices made in stochastic modelling.Comment: 21 pages, 15 figures -- 2nd versio

Structure, (governance) and health: An unsolicited response

Background: In a recently published article, it was suggested that governance was the significant structural factor affecting the epidemiology of HIV. This suggestion was made notwithstanding the observed weak correlation between governance and HIV prevalence (r = .2). Unfortunately, the paper raised but left unexamined the potentially more important questions about the relationship between the broader health of populations and structural factors such as the national economy and physical infrastructure. Methods: Utilizing substantially the same data sources as the original article, the relationship between population health (healthy life expectancy) and three structural factors (access to improved water, GDP per capita, and governance) were examined in each of 176 countries. Results: Governance was found to be significantly correlated with population health, as were GDP per capita, and access to improved water. They were also found to be significantly correlated with each other. Conclusion: The findings are discussed with reference to the growing interest in structural factors as an explanation for population health outcomes, and the relatively weak relationship between governance and HIV prevalence

Update on medication-overuse headache and its treatment

OPINION STATEMENT: Medication-overuse headache-i.e., a too-frequent consumption of acute headache medications leading to increased headache frequency and reduced effectiveness of acute and preventive treatments-is a serious medical condition whose pathophysiology still remains incompletely known, which is reflected into a lack of mechanism-based treatments. The first mandatory step in the therapeutic strategy remains withdrawal of the abused drug, preferably abrupt, in concomitance with a detoxification pharmacological regimen to lessen withdrawal symptoms. Intravenous hydration, antiemetics, corticosteroids (prednisone), tranquilizers (benzodiazepine), neuroleptics, and rescue medication (another analgesic than the overused) should be delivered in various combinations, on an inpatient (hospitalization and day hospital) basis or outpatient basis, depending on the characteristics of the specific patient and type of overuse. Inpatient withdrawal should be preferred in barbiturate and opioid overuse, in concomitant depression, or, in general, in patients who have difficulty in stopping the overused medication as outpatients. In contrast, in overuse limited to simple analgesics in highly motivated patients, without high levels of depression and/or anxiety, home detoxification should be chosen. Re-prophylaxis should immediately follow detoxification, ideally with local injections of onabotulinumtoxinA every 3 months or topiramate orally for at least 3 months. Adequate information to patients about the risks of a too-frequent consumption of symptomatic headache medications is essential and should constantly parallel treatment to help preventing relapse after detoxification and re-prophylaxis

Precise service level agreements

SLAng is an XML language for defining service level agreements, the part of a contract between the client and provider of an Internet service that describes the quality attributes that the service is required to possess. We define the semantics of SLAng precisely by modelling the syntax of the language in UML, then embedding the language model in an environmental model that describes the structure and behaviour of services. The presence of SLAng elements imposes behavioural constraints on service elements, and the precise definition of these constraints using OCL constitutes the semantic description of the language. We use the semantics to define a notion of SLA compatibility, and an extension to UML that enables the modelling of service situations as a precursor to analysis, implementation and provisioning activities

Quantum splines

A quantum spline is a smooth curve parameterised by time in the space of unitary transformations, whose associated orbit on the space of pure states traverses a designated set of quantum states at designated times, such that the trace norm of the time rate of change of the associated Hamiltonian is minimised. The solution to the quantum spline problem is obtained, and is applied in an example that illustrates quantum control of coherent states. An e cient numerical scheme for computing quantum splines is discussed and implemented in the examples

MC2: A framework and service for MPEG-7 content-modelling communities

This article is available open access through the publisher’s website through the link below. Copyright @ The Author 2012.Harnessing the power of Web communities, the effort on creating metadata can be greatly reduced. Collaborative communities can create, update and maintain content models for multimedia resources more effectively than single users working alone. This paper presents MC2, a framework for MPEG-7 content-modelling communities. MC2 is based on the challenges to collaborative multimedia content modelling reported in the research literature and the results of an experiment undertaken to investigate user behaviour in collaborative content modelling. An MC2 service has also been implemented as a proof of concept for this framework, which is evaluated with a population of users and against the challenges.EPSR

Structural and dynamic changes associated with beneficial engineered single-amino-acid deletion mutations in enhanced green fluorescent protein.

Single-amino-acid deletions are a common part of the natural evolutionary landscape but are rarely sampled during protein engineering owing to limited and prejudiced molecular understanding of mutations that shorten the protein backbone. Single-amino-acid deletion variants of enhanced green fluorescent protein (EGFP) have been identified by directed evolution with the beneficial effect of imparting increased cellular fluorescence. Biophysical characterization revealed that increased functional protein production and not changes to the fluorescence parameters was the mechanism that was likely to be responsible. The structure EGFP(D190Δ) containing a deletion within a loop revealed propagated changes only after the deleted residue. The structure of EGFP(A227Δ) revealed that a `flipping mechanism was used to adjust for residue deletion at the end of a β-strand, with amino acids C-terminal to the deletion site repositioning to take the place of the deleted amino acid. In both variants new networks of short-range and long-range interactions are generated while maintaining the integrity of the hydrophobic core. Both deletion variants also displayed significant local and long-range changes in dynamics, as evident by changes in B factors compared with EGFP. Rather than being detrimental, deletion mutations can introduce beneficial structural effects through altering core protein properties, folding and dynamics, as well as function

Failure of dideoxynucleosides to inhibit human immunodeficiency virus replication in cultured human macrophages.

Primary human monocyte-derived macrophages (MDM) were shown to have diminished deoxynucleoside kinase activities compared to T lymphoblasts, and a reduced ability to phosphorylate dideoxynucleosides with anti-human immunodeficiency virus (HIV) activity. These drugs, azidothymidine (AZT), dideoxycytidine (ddC), and dideoxyadenosine (ddA), which are potent anti-HIV agents in CD4 lymphocytes, did not inhibit HIV replication in MDM, even at concentrations of 100 microM. This drug concentration of AZT is approximately 100-fold higher than the levels attained in the serum of treated patients and the levels required to inhibit HIV replication in lymphocytes. These observations may explain the failure of AZT therapy to clear viremia, consistent with the presence of a drug-resistant reservoir of infected cells in vivo. New therapeutic approaches to inhibit the replication of HIV in MDM may be needed

Stigma, social reciprocity and exclusion of HIV/AIDS patients with illicit drug histories: A study of Thai nurses' attitudes

Background: Stigma is a key barrier for the delivery of care to patients living with HIV/AIDS (PLWHA). In the Asia region, the HIV/AIDS epidemic has disproportionately affected socially marginalised groups, in particular, injecting drug users. The effect of the stigmatising attitudes towards injecting drug users on perceptions of PLWHA within the health care contexts has not been thoroughly explored, and typically neglected in terms of stigma intervention. Methods: Semi-structured interviews were conducted with a group of twenty Thai trainee and qualified nurses. Drawing upon the idea of 'social reciprocity', this paper examines the constructions of injecting drug users and PLWHA by a group of Thai nurses. Narratives were explored with a focus on how participants' views concerning the high-risk behaviour of injecting drug use might influence their attitudes towards PLWHA. Results: The analysis shows that active efforts were made by participants to separate their views of patients living with HIV/AIDS from injecting drug users. While the former were depicted as patients worthy of social support and inclusion, the latter were excluded on the basis that they were perceived as irresponsible 'social cheaters' who pose severe social and economic harm to the community. Absent in the narratives were references to wider socio-political and epidemiological factors related to drug use and needle sharing that expose injecting drug users to risk; these behaviours were constructed as individual choices, allowing HIV positive drug users to be blamed for their seropositive status. These attitudes could potentially have indirect negative implications on the nurses' opinions of patients living with HIV/AIDS more generally. Conclusion: Decreasing the stigma associated with illicit drugs might play crucial role in improving attitudes towards patients living with HIV/AIDS. Providing health workers with a broader understanding of risk behaviours and redirecting government injecting drug policy to harm reduction are discussed as some of the ways for stigma intervention to move forward