992 research outputs found
Surface Roughness and Effective Stick-Slip Motion
The effect of random surface roughness on hydrodynamics of viscous
incompressible liquid is discussed. Roughness-driven contributions to
hydrodynamic flows, energy dissipation, and friction force are calculated in a
wide range of parameters. When the hydrodynamic decay length (the viscous wave
penetration depth) is larger than the size of random surface inhomogeneities,
it is possible to replace a random rough surface by effective stick-slip
boundary conditions on a flat surface with two constants: the stick-slip length
and the renormalization of viscosity near the boundary. The stick-slip length
and the renormalization coefficient are expressed explicitly via the
correlation function of random surface inhomogeneities. The effective
stick-slip length is always negative signifying the effective slow-down of the
hydrodynamic flows by the rough surface (stick rather than slip motion). A
simple hydrodynamic model is presented as an illustration of these general
hydrodynamic results. The effective boundary parameters are analyzed
numerically for Gaussian, power-law and exponentially decaying correlators with
various indices. The maximum on the frequency dependence of the dissipation
allows one to extract the correlation radius (characteristic size) of the
surface inhomogeneities directly from, for example, experiments with torsional
quartz oscillators.Comment: RevTeX4, 14 pages, 3 figure
Atom capture by nanotube and scaling anomaly
The existence of bound state of the polarizable neutral atom in the inverse
square potential created by the electric field of single walled charged carbon
nanotube (SWNT) is shown to be theoretically possible. The consideration of
inequivalent boundary conditions due to self-adjoint extensions lead to this
nontrivial bound state solution. It is also shown that the scaling anomaly is
responsible for the existence of bound state. Binding of the polarizable atoms
in the coupling constant interval \eta^2\in[0,1) may be responsible for the
smearing of the edge of steps in quantized conductance, which has not been
considered so far in literature.Comment: Accepted in Int.J.Theor.Phy
CMB constraints on noncommutative geometry during inflation
We investigate the primordial power spectrum of the density perturbations
based on the assumption that spacetime is noncommutative in the early stage of
inflation. Due to the spacetime noncommutativity, the primordial power spectrum
can lose rotational invariance. Using the k-inflation model and slow-roll
approximation, we show that the deviation from rotational invariance of the
primordial power spectrum depends on the size of noncommutative length scale
L_s but not on sound speed. We constrain the contributions from the spacetime
noncommutativity to the covariance matrix for the harmonic coefficients of the
CMB anisotropies using five-year WMAP CMB maps. We find that the upper bound
for L_s depends on the product of sound speed and slow-roll parameter.
Estimating this product using cosmological parameters from the five-year WMAP
results, the upper bound for L_s is estimated to be less than 10^{-27} cm at
99.7% confidence level.Comment: 8 pages, 1 figure, References added, Accepted for publication in EPJC
(submitted version
Moments of Nucleon Light Cone Quark Distributions Calculated in Full Lattice QCD
Moments of the quark density, helicity, and transversity distributions are
calculated in unquenched lattice QCD. Calculations of proton matrix elements of
operators corresponding to these moments through the operator product expansion
have been performed on lattices for Wilson fermions at using configurations from the SESAM collaboration and at
using configurations from SCRI. One-loop perturbative renormalization
corrections are included. At quark masses accessible in present calculations,
there is no statistically significant difference between quenched and full QCD
results, indicating that the contributions of quark-antiquark excitations from
the Dirac Sea are small. Close agreement between calculations with cooled
configurations containing essentially only instantons and the full gluon
configurations indicates that quark zero modes associated with instantons play
a dominant role. Naive linear extrapolation of the full QCD calculation to the
physical pion mass yields results inconsistent with experiment. Extrapolation
to the chiral limit including the physics of the pion cloud can resolve this
discrepancy and the requirements for a definitive chiral extrapolation are
described.Comment: 53 Pages Revtex, 26 Figures, 9 Tables. Added additional reference and
updated referenced data in Table I
MicroRNA clusters integrate evolutionary constraints on expression and target affinities : the miR-6/5/4/286/3/309 cluster in Drosophila
This research was supported by the Hong Kong Research Grant Council GRF Grant (14103516), The Chinese University of Hong Kong Direct Grant (4053248), and TUYF Charitable Trust (6903957) (JHLH).A striking feature of microRNAs is that they are often clustered in the genomes of animals. The functional and evolutionary consequences of this clustering remain obscure. Here, we investigated a microRNA cluster miR-6/5/4/286/3/309 that is conserved across drosophilid lineages. Small RNA sequencing revealed expression of this microRNA cluster in Drosophila melanogaster leg discs, and conditional overexpression of the whole cluster resulted in leg appendage shortening. Transgenic overexpression lines expressing different combinations of microRNA cluster members were also constructed. Expression of individual microRNAs from the cluster resulted in a normal wild-type phenotype, but either the expression of several ancient microRNAs together (miR-5/4/286/3/309) or more recently evolved clustered microRNAs (miR-6-1/2/3) can recapitulate the phenotypes generated by the whole-cluster overexpression. Screening of transgenic fly lines revealed down-regulation of leg patterning gene cassettes in generation of the leg-shortening phenotype. Furthermore, cell transfection with different combinations of microRNA cluster members revealed a suite of downstream genes targeted by all cluster members, as well as complements of targets that are unique for distinct microRNAs. Considered together, the microRNA targets and the evolutionary ages of each microRNA in the cluster demonstrates the importance of microRNA clustering, where new members can reinforce and modify the selection forces on both the cluster regulation and the gene regulatory network of existing microRNAs.PostprintPeer reviewe
The ExaVolt Antenna: A Large-Aperture, Balloon-embedded Antenna for Ultra-high Energy Particle Detection
We describe the scientific motivation, experimental basis, design
methodology, and simulated performance of the ExaVolt Antenna (EVA) mission,
and planned ultra-high energy (UHE) particle observatory under development for
NASA's suborbital super-pressure balloon program in Antarctica. EVA will
improve over ANITA's integrated totals - the current state-of-the-art in UHE
suborbital payloads - by 1-2 orders of magnitude in a single flight. The design
is based on a novel application of toroidal reflector optics which utilizes a
super-pressure balloon surface, along with a feed-array mounted on an inner
membrane, to create an ultra-large radio antenna system with a synoptic view of
the Antarctic ice sheet below it. Radio impulses arise via the Askaryan effect
when UHE neutrinos interact within the ice, or via geosynchrotron emission when
UHE cosmic rays interact in the atmosphere above the continent. EVA's
instantaneous antenna aperture is estimated to be several hundred square meters
for detection of these events within a 150-600 MHz band. For standard
cosmogenic UHE neutrino models, EVA should detect of order 30 events per flight
in the EeV energy regime. For UHE cosmic rays, of order 15,000 geosynchrotron
events would be detected in total, several hundred above 10 EeV, and of order
60 above the GZK cutoff energyComment: 20 pages, 14 figures; introductory section shortened; additional
horizontal polarization simulation results included. In final review for
Astroparticle Physic
Search for direct production of charginos and neutralinos in events with three leptons and missing transverse momentum in √s = 7 TeV pp collisions with the ATLAS detector
A search for the direct production of charginos and neutralinos in final states with three electrons or muons and missing transverse momentum is presented. The analysis is based on 4.7 fb−1 of proton–proton collision data delivered by the Large Hadron Collider and recorded with the ATLAS detector. Observations are consistent with Standard Model expectations in three signal regions that are either depleted or enriched in Z-boson decays. Upper limits at 95% confidence level are set in R-parity conserving phenomenological minimal supersymmetric models and in simplified models, significantly extending previous results
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