698 research outputs found
Dynamics beyond dynamic jam; unfolding the Painlev\'e paradox singularity
This paper analyses in detail the dynamics in a neighbourhood of a
G\'enot-Brogliato point, colloquially termed the G-spot, which physically
represents so-called dynamic jam in rigid body mechanics with unilateral
contact and Coulomb friction. Such singular points arise in planar rigid body
problems with slipping point contacts at the intersection between the
conditions for onset of lift-off and for the Painlev\'e paradox. The G-spot can
be approached in finite time by an open set of initial conditions in a general
class of problems. The key question addressed is what happens next. In
principle trajectories could, at least instantaneously, lift off, continue in
slip, or undergo a so-called impact without collision. Such impacts are
non-local in momentum space and depend on properties evaluated away from the
G-spot. The results are illustrated on a particular physical example, namely
the a frictional impact oscillator first studied by Leine et al.
The answer is obtained via an analysis that involves a consistent contact
regularisation with a stiffness proportional to . Taking a
singular limit as , one finds an inner and an outer
asymptotic zone in the neighbourhood of the G-spot. Two distinct cases are
found according to whether the contact force becomes infinite or remains finite
as the G-spot is approached. In the former case it is argued that there can be
no such canards and so an impact without collision must occur. In the latter
case, the canard trajectory acts as a dividing surface between trajectories
that momentarily lift off and those that do not before taking the impact. The
orientation of the initial condition set leading to each eventuality is shown
to change each time a certain positive parameter passes through an
integer
Setting up and initiating patient public involvement (PPI) as a collaborative process benefits research in its early stages
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Characterisation of microRNAs from apple (Malus domestica 'Royal Gala') vascular tissue and phloem sap
<p>Abstract</p> <p>Background</p> <p>Plant microRNAs (miRNAs) are a class of small, non-coding RNAs that play an important role in development and environmental responses. Hundreds of plant miRNAs have been identified to date, mainly from the model species for which there are available genome sequences. The current challenge is to characterise miRNAs from plant species with agricultural and horticultural importance, to aid our understanding of important regulatory mechanisms in crop species and enable improvement of crops and rootstocks.</p> <p>Results</p> <p>Based on the knowledge that many miRNAs occur in large gene families and are highly conserved among distantly related species, we analysed expression of twenty-one miRNA sequences in different tissues of apple (<it>Malus </it>x <it>domestica </it>'Royal Gala'). We identified eighteen sequences that are expressed in at least one of the tissues tested. Some, but not all, miRNAs expressed in apple tissues including the phloem tissue were also detected in the phloem sap sample derived from the stylets of woolly apple aphids. Most of the miRNAs detected in apple phloem sap were also abundant in the phloem sap of herbaceous species. Potential targets for apple miRNAs were identified that encode putative proteins shown to be targets of corresponding miRNAs in a number of plant species. Expression patterns of potential targets were analysed and correlated with expression of corresponding miRNAs.</p> <p>Conclusions</p> <p>This study validated tissue-specific expression of apple miRNAs that target genes responsible for plant growth, development, and stress response. A subset of characterised miRNAs was also present in the apple phloem translocation stream. A comparative analysis of phloem miRNAs in herbaceous species and woody perennials will aid our understanding of non-cell autonomous roles of miRNAs in plants.</p
Familial multiple myeloma. Two more families
The authors report on two multiple myeloma sibling pairs. In the absence of a known disease-specific marker one can only speculate on an explanation: is it because of inherited errors or is it related to the same environmental exposure, or both? In this study HLA typing and metabolizing enzyme polymorphism studies have been carried out with the aim of finding inherited similarities in the siblings or characteristics that might differ from the average population. Sibling pair 1 shared an HLA haplotype. Sibling pair 2 shared only HLA-B51, DR4, DRw53, DQ3. Sibling 1/1 was GSTT1/GSTM1 null and GSTP1 Ile105Val; sibling 1/2 was a GSTT1/GSTM1 heterozygote and GSTP1 Ile105Val; sibling 2/1 and 2/2 were GSTT1 heterozygotes and shared GSTM1 null/GSTP1 Ile105Ile. The siblings had identical light chain or heavy chain secretion, or both. The similarities found in the inherited factors together with the same environmental exposure in the siblings' first 20 years of life imply that the development of the same disease cannot be a coincidence
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