5,252 research outputs found
Are All Particles Identical?
We consider the possibility that all particles in the world are fundamentally
identical, i.e., belong to the same species. Different masses, charges, spins,
flavors, or colors then merely correspond to different quantum states of the
same particle, just as spin-up and spin-down do. The implications of this
viewpoint can be best appreciated within Bohmian mechanics, a precise
formulation of quantum mechanics with particle trajectories. The implementation
of this viewpoint in such a theory leads to trajectories different from those
of the usual formulation, and thus to a version of Bohmian mechanics that is
inequivalent to, though arguably empirically indistinguishable from, the usual
one. The mathematical core of this viewpoint is however rather independent of
the detailed dynamical scheme Bohmian mechanics provides, and it amounts to the
assertion that the configuration space for N particles, even N
``distinguishable particles,'' is the set of all N-point subsets of physical
3-space.Comment: 12 pages LaTeX, no figure
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Molybdenum Disubstituted Alkylidene Complexes
Through relatively straightforward techniques that begin with Mo(NAr)(CH-t-Bu)[OCMe(CF3)2]2 (Ar = 2,6-i-Pr2C6H3), we have prepared Mo(NAr)(CMePh)(OMesityl)2, [Mo(NAr)(CMePh)(OC6F5)2]2, Mo(NAr)(CMePh)(OC6F5)2(MeCN), Mo(NAr)(CMePh)(OC6F5)2(bipyridyl), Mo(NAr)(CMePh)(Cl)2(bipyridyl), Mo(NAr)(CMePh)(Cl)(OHMT)(MeCN) (OHMT = O-2,6-(2,4,6-Me3C6H2)2C6H3), and Mo(NAr)(CMePh)(Pyrrolide)(OHMT). X-ray studies reveal that in five compounds the alkylidene isomer (A) is that in which the phenyl group in the alkylidene points toward the imido nitrogen. In Mo(NAr)(CMePh)(OC6F5)2(MeCN) the isomer in which the methyl group points toward the imido nitrogen (isomer B) has cocrystallized with isomer A (12%). In two 14e compounds that contain isomer A, the Mo═C-C angles differ by 30-36°, consistent with a Mo...C-Hβ agostic interaction. Several of the complexes reported here react readily with ethylene, 1-decene, or cyclooctene to give the expected products, thus confirming their viability as initiators or intermediates in metathesis reactions
A new method for isolating turbulent states in transitional stratified plane Couette flow
We present a new adaptive control strategy to isolate and stabilize turbulent states in transitional, stably stratified plane Couette flow in which the gravitational acceleration (non-dimensionalized as the bulk Richardson number) is adjusted in time to maintain the turbulent kinetic energy (TKE) of the flow. We demonstrate that applying this method at various stages of decaying stratified turbulence halts the decay process and allows a succession of intermediate turbulent states of decreasing energy to be isolated and stabilized. Once the energy of the initial flow becomes small enough, we identify a single minimal turbulent spot, and lower-energy states decay to laminar flow. Interestingly, the turbulent states which emerge from this process have very similar time-averaged, but TKE levels different by an order of magnitude. The more energetic states consist of several turbulent spots, each qualitatively similar to the minimal turbulent spot. This suggests that the minimal turbulent spot may well be the lowest-energy turbulent state which forms a basic building block of stratified plane Couette flow. The fact that a minimal spot of turbulence can be stabilized, so that it neither decays nor grows, opens up exciting opportunities for further study of spatiotemporally intermittent stratified turbulence.The EPSRC grant EP/K034529/1 entitled ‘Mathematical Underpinnings of Stratified Turbulence’ is gratefully acknowledged for supporting the research presented here.This is the author accepted manuscript. The final version is available from Cambridge University Press via https://doi.org/10.1017/jfm.2016.62
Disruption of SorCS2 reveals differences in the regulation of stereociliary bundle formation between hair cell types in the inner ear
Behavioural anomalies suggesting an inner ear disorder were observed in a colony of transgenic mice. Affected animals were profoundly deaf. Severe hair bundle defects were identified in all outer and inner hair cells (OHC, IHC) in the cochlea and in hair cells of vestibular macular organs, but hair cells in cristae were essentially unaffected. Evidence suggested the disorder was likely due to gene disruption by a randomly inserted transgene construct. Whole-genome sequencing identified interruption of the SorCS2 (Sortilin-related VPS-10 domain containing protein) locus. Real-time-qPCR demonstrated disrupted expression of SorCS2 RNA in cochlear tissue from affected mice and this was confirmed bySorCS2 immuno-labelling. In all affected hair cells, stereocilia were shorter than normal, but abnormalities of bundle morphology and organisation differed between hair cell types. Bundles on OHC were grossly misshapen with significantly fewer stereocilia than normal. However, stereocilia were organised in rows of increasing height. Bundles on IHC contained significantly more stereocilia than normal with some longer stereocilia towards the centre, or with minimal height differentials. In early postnatal mice, kinocilia (primary cilia) of IHC and of OHC were initially located towards the lateral edge of the hair cell surface but often became surrounded by stereocilia as bundle shape and apical surface contour changed. In macular organs the kinocilium was positioned in the centre of the cell surface throughout maturation. There was disruption of the signalling pathway controlling intrinsic hair cell apical asymmetry. LGN and Gαi3 were largely absent, and atypical Protein Kinase C (aPKC) lost its asymmetric distribution. The results suggest that SorCS2 plays a role upstream of the intrinsic polarity pathway and that there are differences between hair cell types in the deployment of the machinery that generates a precisely organised hair bundle
Spectral analysis of the biharmonic operator subject to Neumann boundary conditions on dumbbell domains
We consider the biharmonic operator subject to homogeneous boundary
conditions of Neumann type on a planar dumbbell domain which consists of two
disjoint domains connected by a thin channel. We analyse the spectral behaviour
of the operator, characterizing the limit of the eigenvalues and of the
eigenprojections as the thickness of the channel goes to zero. In applications
to linear elasticity, the fourth order operator under consideration is related
to the deformation of a free elastic plate, a part of which shrinks to a
segment. In contrast to what happens with the classical second order case, it
turns out that the limiting equation is here distorted by a strange factor
depending on a parameter which plays the role of the Poisson coefficient of the
represented plate.Comment: To appear in "Integral Equations and Operator Theory
Characterizing human vestibular sensory epithelia for experimental studies: new hair bundles on old tissue and implications for therapeutic interventions in ageing.
Balance disequilibrium is a significant contributor to falls in the elderly. The most common cause of balance dysfunction is loss of sensory cells from the vestibular sensory epithelia of the inner ear. However, inaccessibility of inner ear tissue in humans severely restricts possibilities for experimental manipulation to develop therapies to ameliorate this loss. We provide a structural and functional analysis of human vestibular sensory epithelia harvested at trans-labyrinthine surgery. We demonstrate the viability of the tissue and labeling with specific markers of hair cell function and of ion homeostasis in the epithelium. Samples obtained from the oldest patients revealed a significant loss of hair cells across the tissue surface, but we found immature hair bundles present in epithelia harvested from patients >60 years of age. These results suggest that the environment of the human vestibular sensory epithelium could be responsive to stimulation of developmental pathways to enhance hair cell regeneration, as has been demonstrated successfully in the vestibular organs of adult mice
Bell-Type Quantum Field Theories
In [Phys. Rep. 137, 49 (1986)] John S. Bell proposed how to associate
particle trajectories with a lattice quantum field theory, yielding what can be
regarded as a |Psi|^2-distributed Markov process on the appropriate
configuration space. A similar process can be defined in the continuum, for
more or less any regularized quantum field theory; such processes we call
Bell-type quantum field theories. We describe methods for explicitly
constructing these processes. These concern, in addition to the definition of
the Markov processes, the efficient calculation of jump rates, how to obtain
the process from the processes corresponding to the free and interaction
Hamiltonian alone, and how to obtain the free process from the free Hamiltonian
or, alternatively, from the one-particle process by a construction analogous to
"second quantization." As an example, we consider the process for a second
quantized Dirac field in an external electromagnetic field.Comment: 53 pages LaTeX, no figure
Connexin30-mediated intercellular communication plays an essential role in epithelial repair in the cochlea.
A role for connexin (Cx)30 in epithelial repair following injury was examined in the organ of Corti, the sensory epithelium of the cochlea. In this tissue, lesions caused by loss of the sensory hair cells are closed by the supporting cells that surround each one. Gap junctions in which Cx30 is the predominant connexin are large and numerous between supporting cells. In mice carrying a deletion in the gene (Gjb6) that encodes Cx30, the size and number of gap junction plaques, and the extent of dye transfer, between supporting cells was greatly reduced compared with normal animals. This corresponded with unique peculiarities of the lesion closure events during the progressive hair cell loss that occurs in these animals in comparison with other models of hair cell loss, whether acquired or as a result of a mutation. Only one, rather than all, of the supporting cells that contacted an individual dying hair closed the lesion, indicating disturbance of the co-ordination of cellular responses. The cell shape changes that the supporting cells normally undergo during repair of the organ of Corti did not occur. Also, there was disruption of the migratory activities that normally lead to the replacement of a columnar epithelium with a squamous-like one. These observations demonstrate a role for Cx30 and intercellular communication in regulating repair responses in an epithelial tissue
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