Mechanics of the Ski-Snow Contact

Two outstanding questions of the ski-snow friction are considered: the deformation mode of the snow and the real contact area. The deformation of hard, well sintered snow in a short time impact has been measured with a special linear friction tester. Four types of deformations have been identified: brittle fracture of bonds, plastic deformation of ice at the contact spots, elastic and delayed elastic deformation of the snow matrix. The latter is the dominant deformation in the ski-snow contact. Based on the measured loading curves the mechanical energy dissipation of snow deformation in skiing on hard snow has been determined and found negligible compared to the thermal energy dissipation. A mechanical model consisting of ice spheres supported by rheological elements (a non-linear spring in series with a Kelvin element) is proposed to model the deformation of snow in the ski-snow contact. The model can describe the delayed elastic behaviour of snow. Coupled with the complete topographical description of the snow surface obtained from X-ray micro computer tomography measurements, the model predicts the number and area of contact spots between ski and snow. An average contact spot size of 110μm, and a relative real contact area of 0.4% has been foun

Site-specific C-terminal and internal loop labeling of proteins using sortase-mediated reactions

Methods for site-specific modification of proteins should be quantitative and versatile with respect to the nature and size of the biological or chemical targets involved. They should require minimal modification of the target, and the underlying reactions should be completed in a reasonable amount of time under physiological conditions. Sortase-mediated transpeptidation reactions meet these criteria and are compatible with other labeling methods. Here we describe the expression and purification conditions for two sortase A enzymes that have different recognition sequences. We also provide a protocol that allows the functionalization of any given protein at its C terminus, or, for select proteins, at an internal site. The target protein is engineered with a sortase-recognition motif (LPXTG) at the place where modification is desired. Upon recognition, sortase cleaves the protein between the threonine and glycine residues, facilitating the attachment of an exogenously added oligoglycine peptide modified with the functional group of choice (e.g., fluorophore, biotin, protein or lipid). Expression and purification of sortase takes ∼3 d, and sortase-mediated reactions take only a few minutes, but reaction times can be extended to increase yields.National Institutes of Health (U.S.) (Grant RO1 AI08787

Esociformes: Esocidae, Pikes, and Umbridae (Mudminnows)

The order Esociformes (Pikes and Mudminnows) comprises two families, Esocidae (Pikes) and Umbridae (Mudminnows). The Pikes are a small Holarctic (Northern Hemisphere) family, that includes large, elongate predators with duckbill-like snouts full of sharp teeth. Popular with sport fishers, the largest Pikes fight fiercely on hook and line. As piscivorous, voracious, ambush predators, the Pikes play an important functional role in the trophic ecology and fish assemblage structure of many aquatic systems, especially in northern lakes. Other esocids, such as the Olympic Mudminnow, Novumbra hubbsi, and Blackfishes, genus Dallia, are interesting because of their tolerance of low dissolved oxygen and pH. The Alaska Blackfish, Dallia pectoralis, and the Northern Pike, Esox lucius, can also withstand the extremely cold conditions of the Arctic and subarctic waters of Canada, Alaska, and Siberia. The name Esocidae is derived from Linnaeus’s (1758) generic name for Pike, Esox, from the Latin word esox meaning Pike, which came originally from the Greek isox or possibly the Gaelic eog, ehawe (salmon) (Boschung & Mayden 2004)

Site-specific protein modification using immobilized sortase in batch and continuous-flow systems

Transpeptidation catalyzed by ​sortase A allows the preparation of proteins that are site-specifically and homogeneously modified with a wide variety of functional groups, such as fluorophores, PEG moieties, lipids, glycans, bio-orthogonal reactive groups and affinity handles. This protocol describes immobilization of ​sortase A on a solid support (Sepharose beads). Immobilization of ​sortase A simplifies downstream purification of a protein of interest after labeling of its N or C terminus. Smaller batch and larger-scale continuous-flow reactions require only a limited amount of enzyme. The immobilized enzyme can be reused for multiple cycles of protein modification reactions. The described protocol also works with a Ca²⁺-independent variant of ​sortase A with increased catalytic activity. This heptamutant variant of ​sortase A (7M) was generated by combining previously published mutations, and this immobilized enzyme can be used for the modification of calcium-senstive substrates or in instances in which low temperatures are needed. Preparation of immobilized ​sortase A takes 1–2 d. Batch reactions take 3–12 h and flow reactions proceed at 0.5 ml h⁻¹, depending on the geometry of the reactor used.United States. National Institutes of Health (RO1 AI087879

Alternative infill strategies for expensive multi-objective optimisation

This is the author accepted manuscript. The final version is available from ACM via the DOI in this record.Many multi-objective optimisation problems incorporate computationally or financially expensive objective functions. State-of-the-art algorithms therefore construct surrogate model(s) of the parameter space to objective functions mapping to guide the choice of the next solution to expensively evaluate. Starting from an initial set of solutions, an infill criterion — a surrogate-based indicator of quality — is extremised to determine which solution to evaluate next, until the budget of expensive evaluations is exhausted. Many successful infill criteria are dependent on multi-dimensional integration, which may result in infill criteria that are themselves impractically expensive. We propose a computationally cheap infill criterion based on the minimum probability of improvement over the estimated Pareto set. We also present a range of set-based scalarisation methods modelling hypervolume contribution, dominance ratio and distance measures. These permit the use of straightforward expected improvement as a cheap infill criterion. We investigated the performance of these novel strategies on standard multi-objective test problems, and compared them with the popular SMS-EGO and ParEGO methods. Unsurprisingly, our experiments show that the best strategy is problem dependent, but in many cases a cheaper strategy is at least as good as more expensive alternatives.This research was supported by the Engineering and Physical Sciences Research Council [grant number EP/M017915/1]

In planta expression of human polyQ-expanded huntingtin fragment reveals mechanisms to prevent disease-related protein aggregation

In humans, aggregation of polyglutamine repeat (polyQ) proteins causes disorders such as Huntington’s disease. Although plants express hundreds of polyQ-containing proteins, no pathologies arising from polyQ aggregation have been reported. To investigate this phenomenon, we expressed an aggregation-prone fragment of human huntingtin (HTT) with an expanded polyQ stretch (Q69) in Arabidopsis thaliana plants. In contrast to animal models, we find that Arabidopsis sp. suppresses Q69 aggregation through chloroplast proteostasis. Inhibition of chloroplast proteostasis diminishes the capacity of plants to prevent cytosolic Q69 aggregation. Moreover, endogenous polyQ-containing proteins also aggregate on chloroplast dysfunction. We find tha

Slingshot: a PiggyBac based transposon system for tamoxifen-inducible ‘self-inactivating’ insertional mutagenesis

We have developed a self-inactivating PiggyBac transposon system for tamoxifen inducible insertional mutagenesis from a stably integrated chromosomal donor. This system, which we have named ‘Slingshot’, utilizes a transposon carrying elements for both gain- and loss-of-function screens in vitro. We show that the Slingshot transposon can be efficiently mobilized from a range of chromosomal loci with high inducibility and low background generating insertions that are randomly dispersed throughout the genome. Furthermore, we show that once the Slingshot transposon has been mobilized it is not remobilized producing stable clonal integrants in all daughter cells. To illustrate the efficacy of Slingshot as a screening tool we set out to identify mediators of resistance to puromycin and the chemotherapeutic drug vincristine by performing genetrap screens in mouse embryonic stem cells. From these genome-wide screens we identified multiple independent insertions in the multidrug resistance transporter genes Abcb1a/b and Abcg2 conferring resistance to drug treatment. Importantly, we also show that the Slingshot transposon system is functional in other mammalian cell lines such as human HEK293, OVCAR-3 and PE01 cells suggesting that it may be used in a range of cell culture systems. Slingshot represents a flexible and potent system for genome-wide transposon-mediated mutagenesis with many potential applications

Jejunum free flap in hypopharynx reconstruction: Case series

BACKGROUND: Surgical treatment of hypopharyngeal cancers with extension to the retrocricoid region generally requires a circumferential pharyngolaryngectomy followed by a reconstruction of the removed segment of the upper digestive tract. Historically, many techniques have been used in order to achieve a safe and functional reconstruction. Jejunum interposition is generally considered the best reconstructive technique. METHODS: This study examines the details of the surgical technique, the complications, the oncological and the functional results in a series of 29 consecutive patients submitted to circumferential pharyngoesophageal resection for advanced hypopharyngeal cancer followed by reconstruction with a free flap of jejunum. RESULTS: Three of the transplants failed because of venous thrombosis. The overall success rate was 90%. There were no general complications. A good swallowing has been preserved in all our patients. All our patients where a phonatory prosthesis was positioned (20/29) were able to achieve speech following speech therapy and all were satisfied with their own capacity to communicate. CONCLUSIONS: The prognosis of hypopharyngeal tumours (18–40% at 5 years) remains poor, but jejunum autografts are being shown to be an excellent choice for the reconstruction of the cervical hypopharyngo-oesophagus offering the patient fast rehabilitation and a reasonable quality of survival. Our experience confirm that this kind of reconstruction is safe with a good results in improving oncologic controls and restoring a good quality of life