Efficient computation of hashes

The sequential computation of hashes at the core of many distributed storage systems and found, for example, in grid services can hinder efficiency in service quality and even pose security challenges that can only be addressed by the use of parallel hash tree modes. The main contributions of this paper are, first, the identification of several efficiency and security challenges posed by the use of sequential hash computation based on the Merkle-Damgard engine. In addition, alternatives for the parallel computation of hash trees are discussed, and a prototype for a new parallel implementation of the Keccak function, the SHA-3 winner, is introduced

Frequency selective reflection and transmission at a layer composed of a periodic dielectric

The feasibility of using a periodic dielectric layer, composed of alternating bars having dielectric constants epsilon sub 1 and epsilon sub 2, as a frequency selective subreflector in order to permit feed separation in large aperture reflecting antenna systems was examined. For oblique incidence, it is found that total transmission and total reflection can be obtained at different frequencies for proper choices of epsilon sub 1, epsilon 2, and the geometric parameters. The frequencies of total reflection and transmission can be estimated from wave phenomena occurring in a layer of uniform dielectric constant equal to the average for the periodic layers. About some of the frequencies of total transmission, the bandwidth for 90% transmission is found to be 40%. However, the bandwidth for 90% reflection is always found to be much narrower; the greatest value found being 2.5%

The Impossible Quest – Problems with Diligent Search for Orphan Works

Digital technologies allow unprecedented preservation and sharing of world-wide cultural heritage. Public and private players are increasingly entering the scene with mass digitisation projects that will make this possible. In Europe, legislative action has been taken to allow cultural institutions to include in their online collections copyright works whose owners are either unknown or non-locatable (“orphan works”). However, according to the Orphan Works Directive, cultural institutions must attempt to locate the owner of a work before using it. This is the so-called “diligent search” requirement. This paper provides an empirical analysis of the conditions under which a diligent search can feasibly be carried out. The United Kingdom, the Netherlands, and Italy, all of which have implemented the Orphan Works Directive, have been selected as case studies. For each jurisdiction, this analysis determines what the requirements for a diligent search to locate copyright holders are, what the authoritative sources and databases to be consulted are in practice and, most importantly, to what extent these are freely accessible online. In doing so, our analysis provides insights into the two main issues affecting cultural heritage institutions: (1) how much legal certainty does the implementation provide, and (2) what is the practical burden of a diligent search. The analysis reveals that the jurisdictions have given different meanings to the term “diligent”. While the UK’s extensive guidance makes it unlikely that a search would not be deemed diligent, the search burden is onerous. On the other hand, Italy and especially the Netherlands have a lighter search burden, but in the absence of clear, definite guidance, the likelihood of accidental infringement by failing to meet the diligence standard is greater. In addition, all three jurisdictions have so far failed to take the accessibility of the sources into account, making the searches even more onerous than the numbers suggest at first sight. Therefore, it will be difficult for cultural institutions to clear the rights for their collections while fully complying with the requirements of the legislation. This article concludes that legislative action, official guidelines, or jurisprudence are needed to establish a different legal value of sources for a diligent search, with various degrees of optionality depending on data relevance and accessibility

Hysteresis and spin phase transitions in quantum wires in the integer quantum Hall regime

We demonstrate that a split-gate quantum wire in the integer quantum Hall regime can exhibit electronic transport hysteresis for up- and down-sweeps of a magnetic field. This behavior is shown to be due to phase spin transitions between two different ground states with and without spatial spin polarization in the vicinity of the wire boundary. The observed effect has a many-body origin arising from an interplay between a confining potential, Coulomb interactions and the exchange interaction. We also demonstrate and explain why the hysteretic behavior is absent for steep and smooth confining potentials and is present only for a limited range of intermediate confinement slopes.Comment: submitted to PR

Effect of quasi-bound states on coherent electron transport in twisted nanowires

Quantum transmission spectra of a twisted electron waveguide expose the coupling between traveling and quasi-bound states. Through a direct numerical solution of the open-boundary Schr\"odinger equation we single out the effects of the twist and show how the presence of a localized state leads to a Breit-Wigner or a Fano resonance in the transmission. We also find that the energy of quasi-bound states is increased by the twist, in spite of the constant section area along the waveguide. While the mixing of different transmission channels is expected to reduce the conductance, the shift of localized levels into the traveling-states energy range can reduce their detrimental effects on coherent transport.Comment: 8 pages, 9 color figures, submitte

Spray congealing: An emerging technology to prepare solid dispersions with enhanced oral bioavailability of poorly water soluble drugs

The low and variable oral bioavailability of poorly water soluble drugs remains a major concern for the pharmaceutical industry. Spray congealing is an emerging technology for the production of solid dispersion to enhance the bioavailability of poorly soluble drugs by using low-melting hydrophilic excipients. The main advantages are the absence of solvents and the possibility to obtain spherical free-flowing microparticles (MPs) by a relatively inexpensive, simple, and one-step process. This review aims to fully describe the composition, structure, physico-chemical properties, and characterization techniques of spray congealed-formulations. Moreover, the influence of these properties on the MPs performance in terms of solubility and dissolution enhancement are examined. Following, an overview of the different spray congealed systems developed to increase the oral drug bioavailability is provided, with a focus on the mechanisms underpinning the bioavailability enhancement. Finally, this work gives specific insights on the main factors to be considered for the rational formulation, manufacturing, and characterization of spray congealed solid dispersions

Targeting a therapeutic LIF transgene to muscle via the immune system ameliorates muscular dystrophy.

Many potentially therapeutic molecules have been identified for treating Duchenne muscular dystrophy. However, targeting those molecules only to sites of active pathology is an obstacle to their clinical use. Because dystrophic muscles become extensively inflamed, we tested whether expressing a therapeutic transgene in leukocyte progenitors that invade muscle would provide selective, timely delivery to diseased muscle. We designed a transgene in which leukemia inhibitory factor (LIF) is under control of a leukocyte-specific promoter and transplanted transgenic cells into dystrophic mice. Transplantation diminishes pathology, reduces Th2 cytokines in muscle and biases macrophages away from a CD163+/CD206+ phenotype that promotes fibrosis. Transgenic cells also abrogate TGFβ signaling, reduce fibro/adipogenic progenitor cells and reduce fibrogenesis of muscle cells. These findings indicate that leukocytes expressing a LIF transgene reduce fibrosis by suppressing type 2 immunity and highlight a novel application by which immune cells can be genetically modified as potential therapeutics to treat muscle disease