Authentication of Quantum Messages

Authentication is a well-studied area of classical cryptography: a sender S and a receiver R sharing a classical private key want to exchange a classical message with the guarantee that the message has not been modified by any third party with control of the communication line. In this paper we define and investigate the authentication of messages composed of quantum states. Assuming S and R have access to an insecure quantum channel and share a private, classical random key, we provide a non-interactive scheme that enables S both to encrypt and to authenticate (with unconditional security) an m qubit message by encoding it into m+s qubits, where the failure probability decreases exponentially in the security parameter s. The classical private key is 2m+O(s) bits. To achieve this, we give a highly efficient protocol for testing the purity of shared EPR pairs. We also show that any scheme to authenticate quantum messages must also encrypt them. (In contrast, one can authenticate a classical message while leaving it publicly readable.) This has two important consequences: On one hand, it allows us to give a lower bound of 2m key bits for authenticating m qubits, which makes our protocol asymptotically optimal. On the other hand, we use it to show that digitally signing quantum states is impossible, even with only computational security.Comment: 22 pages, LaTeX, uses amssymb, latexsym, time

Phase-field crystal study of grain-boundary premelting

We study the phenomenon of grain-boundary premelting for temperatures below the melting point in the phase-field crystal model of a pure material with hexagonal ordering in two dimensions. We investigate the structures of symmetric tilt boundaries as a function of misorientation for two different inclinations and compute in the grand canonical ensemble the disjoining potential V(w) that governs the fundamental interaction between crystal-melt interfaces as a function of the premelted layer width w. The results reveal qualitatively different behaviors for high-angle grain boundaries that are uniformly wetted, with w diverging logarithmically as the melting point is approached from below, and low-angle boundaries that are punctuated by liquid pools surrounding dislocations, separated by solid bridges. This qualitative difference between high and low angle boundaries is reflected in the w-dependence of the disjoining potential that is purely repulsive (V'(w)<0 for all w) above a critical misorientation, but switches from repulsive at small w to attractive at large w for low angles. In the latter case, V(w) has a minimum that corresponds to a premelted boundary of finite width at the melting point. Furthermore, we find that the standard wetting condition (the grain boundary energy is equal to twice the solid-liquid free energy) gives a much too low estimate of the critical misorientation when a low-temperature value of the grain boundary energy is used. In contrast, a reasonable estimate is obtained if the grain boundary energy is extrapolated to the melting point, taking into account both the elastic softening of the material at high temperature and local melting around dislocations.Comment: 24 pages, 13 figures, some figure files with reduced resolution because of submission size limitations. In the 2nd version, some parts (and figures) have been modified, especially in Sec. V (discussion

Synthesis and characterisation of biologically compatible TiO2 nanoparticles

Peer reviewedPublisher PD

Changes in 2-fluoro-2-deoxy-D-glucose incorporation, hexokinase activity and lactate production by breast cancer cells responding to treatment with the anti-HER-2 antibody trastuzumab

Peer reviewedPublisher PD

Why Should I Provide Social Support? A Social Capital Perspective of Individual Helping Behavior in Healthcare Virtual Support Communities

The phenomenon of online social support has been studied for years. However, little is known about the factors that drive individual online helping behavior. While the Information systems literature provides rich insights into the determinants of online social support, the emphasis has been exclusively on the provision of informational help. By contending the need to expand our investigation to different types of support, this paper studies individual provisions of both informational and emotional social support in healthcare virtual support communities (HVSCs). Drawing on social capital theory, the structural, relational, and cognitive dimensions of social capital are conceptualized as the social support determinants. The results show that the social capital dimensions can be both facilitators and inhibitors of the two types of social support. This study can contribute not only to the literature on HVSCs, but also to studies of other types of virtual communities such as electronic networks of practice

Discovery of ram-pressure stripped gas around an elliptical galaxy in Abell 2670

Studies of cluster galaxies are increasingly finding galaxies with spectacular one-sided tails of gas and young stars, suggestive of intense ram-pressure stripping. These so-called "jellyfish" galaxies typically have late-type morphology. In this paper, we present MUSE observations of an elliptical galaxy in Abell 2670 with long tails of material visible in the optical spectra, as well as blobs with tadpole-like morphology. The spectra in the central part of the galaxy reveals a stellar component as well as ionized gas. The stellar component does not have significant rotation, while the ionized gas defines a clear star-forming gas disk. We argue, based on deep optical images of the galaxy, that the gas was most likely acquired during a past wet merger. It is possible that the star-forming blobs are also remnants of the merger. In addition, the direction and kinematics of the one-sided ionized tails, combined with the tadpole morphology of the star-forming blobs, strongly suggests that the system is undergoing ram pressure from the intracluster medium. In summary, this paper presents the discovery of a post-merger elliptical galaxy undergoing ram pressure stripping.Comment: 6 pages, 5 figures, accepted for publication in ApJ

Post-reproductive Longevity in a Natural Fertility Population

Fertility patterns may be useful markers for rates of biological aging. Based on evolutionary and socio-demographic approaches to historical data from the population of Québec (taken from the Registre de population du Québec ancien at the University of Montreal), we examine the effects of reproduction on longevity. Using Cox hazard models on about 2,000 couples married in the colony before 1740, we show that women bearing their last child late in life had longer post-reproductive lives, suggesting that late menopause is associated with an overall slower rate of aging. Increased parity had an opposite, detrimental effect on women’s post-reproductive survival. On the other hand, husband’s longevity was less sensitive to parity and reproductive history. For husbands increased effective family size (EFS; the number of children who survived up to age 18) in a “compressed” reproductive time-span meant higher chances for survival past age 60. Children may serve as strong economical assets on farmstead during colonization, which would mostly benefit fathers. In a collaborative effort to unveil post-reproductive aging patterns in historical populations, the results are compared to previous analyses conducted on the Utah population database and evolutionary and socio-demographic theories addressed in light of the results

Niche modelling the distributions of large Acacia nigrescens and Sclerocarya birrea trees.

Thesis (M.Sc.)-University of KwaZulu-Natal, Westville, 2011.MaxEnt modelling uses only the known locations of a species to predict the overall distribution of a species. Large trees are important for the functioning of savanna ecosystems, bringing nutrients to the surface, providing shelter to animals and providing a number of ecological functions. Large trees have been identified as declining in density in many southern African reserves, making the conservation of large trees within reserves an issue in park management, such as in Kruger National Park (KNP) and Hluhluwe iMfolzi Parks (HiP). Two species of primary concern are Acacia nigrescens and Sclerocarya birrea, which have similar distributions in Southern Africa. Effective management of large trees requires understanding their distribution within reserves and any potential distribution changes. By determining the current locations of a species, and using GIS layers of environmental variables to predict the extent of habitats that could support the species, niche models can predict species distribution. Maximum Entropy techniques evaluate the probability of finding the species in raster squares, with values for environmental factors controlling distribution. For this study, the locations of A. nigrescens and S. birrea trees higher than 5 m were recorded in KNP and HiP, and were used in conjunction with MaxEnt to produce distribution probability maps for both species in each reserve. In HiP, the distribution map was compared with an independent existing data set to determine if the predicted distributions were accurate. The factors effecting their distribution were compared between HiP and KNP to determine why the species were found together in KNP but not in HiP. MaxEnt could predict the locations of the species within HiP, but predictions were better for A. nigrescens than S. birrea. In both Reserves, rainfall was the best predictor of tree location, along with elevation. The niche overlap was higher in KNP, where both species are well within their total species range, than in HiP where A. nigrescens was at the edge of its distribution. These variables that are limiting distribution at a reserve scale will have an influence on the overall distribution of the species. Niche models can be used to inform the establishment of botanical reserves or other management strategies that can help preserve large trees within reserves

Simulation of the cost-effectiveness of malaria vaccines

<p>Abstract</p> <p>Background</p> <p>A wide range of possible malaria vaccines is being considered and there is a need to identify which vaccines should be prioritized for clinical development. An important element of the information needed for this prioritization is a prediction of the cost-effectiveness of potential vaccines in the transmission settings in which they are likely to be deployed. This analysis needs to consider a range of delivery modalities to ensure that clinical development plans can be aligned with the most appropriate deployment strategies.</p> <p>Methods</p> <p>The simulations are based on a previously published individual-based stochastic model for the natural history and epidemiology of <it>Plasmodium falciparum </it>malaria. Three different vaccine types: pre-erythrocytic vaccines (PEV), blood stage vaccines (BSV), mosquito-stage transmission-blocking vaccines (MSTBV), and combinations of these, are considered each delivered via a range of delivery modalities (Expanded Programme of Immunization – EPI-, EPI with booster, and mass vaccination combined with EPI). The cost-effectiveness ratios presented are calculated for four health outcomes, for assumed vaccine prices of US$2 or US$ 10 per dose, projected over a 10-year period.</p> <p>Results</p> <p>The simulations suggest that PEV will be more cost-effective in low transmission settings, while BSV at higher transmission settings. Combinations of BSV and PEV are more efficient than PEV, especially in moderate to high transmission settings, while compared to BSV they are more cost-effective in moderate to low transmission settings. Combinations of MSTBV and PEV or PEV and BSV improve the effectiveness and the cost-effectiveness compared to PEV and BSV alone only when applied with EPI and mass vaccinations. Adding booster doses to the EPI is unlikely to be a cost-effective alternative to delivering vaccines via the EPI for any vaccine, while mass vaccination improves effectiveness, especially in low transmission settings, and is often a more efficient alternative to the EPI. However, the costs of increasing the coverage of mass vaccination over 50% often exceed the benefits.</p> <p>Conclusion</p> <p>The simulations indicate malaria vaccines might be efficient malaria control interventions, and that both transmission setting and vaccine delivery modality are important to their cost-effectiveness. Alternative vaccine delivery modalities to the EPI may be more efficient than the EPI. Mass vaccination is predicted to provide substantial health benefits at low additional costs, although achieving high coverage rates can lead to substantial incremental costs.</p