24,431 research outputs found
Scanning probe microscopy imaging of metallic nanocontacts
We show scanning probe microscopy measurements of metallic nanocontacts
between controlled electromigration cycles. The nanowires used for the thinning
process are fabricated by shadow evaporation. The highest resolution obtained
using scanning force microscopy is about 3 nm. During the first few
electromigration cycles the overall slit structure of the nanocontact is
formed. The slit first passes along grain boundaries and then at a later stage
vertically splits grains in the course of consuming them. We find that first
the whole wire is heated and later during the thinning process as the slit
forms the current runs over several smaller contacts which needs less power.Comment: 4 pages, 4 figure
Nuclear magnetic resonance spectroscopy: Abnormal splitting of ethyl groups due to molecular asymmetry
Nuclear magnetic resonance (n.m.r.) spectroscopy provides an excellent means for qualitative identification of ethyl groups by use of the familiar three-four pattern of spin-spin splitting (1). It has been observed previously (2) that the methylene protons of systems of the type R-CH2-CR1R2R3 (where R1 can be the same as R or different) may be magnetically nonequivalent and display AB rather than A2-type spectra (3). We now wish to report several examples of this type of behavior with ethyl groups, particularly ethoxy groups, knowledge of which could be important to anyone using n.m.r. for organic qualitative analysis
Universal measurement of quantum correlations of radiation
A measurement technique is proposed which, in principle, allows one to
observe the general space-time correlation properties of a quantized radiation
field. Our method, called balanced homodyne correlation measurement, unifies
the advantages of balanced homodyne detection with those of homodyne
correlation measurements.Comment: 4 pages, 4 figures, small misprints were corrected, accepted to Phys.
Rev. Let
Mass Hierarchy Resolution in Reactor Anti-neutrino Experiments: Parameter Degeneracies and Detector Energy Response
Determination of the neutrino mass hierarchy using a reactor neutrino
experiment at 60 km is analyzed. Such a measurement is challenging due to
the finite detector resolution, the absolute energy scale calibration, as well
as the degeneracies caused by current experimental uncertainty of . The standard method is compared with a proposed Fourier
transformation method. In addition, we show that for such a measurement to
succeed, one must understand the non-linearity of the detector energy scale at
the level of a few tenths of percent.Comment: 7 pages, 6 figures, accepted by PR
Production of radioactive isotopes through cosmic muon spallation in KamLAND
Radioactive isotopes produced through cosmic muon spallation are a background for rare-event detection in ν detectors, double-β-decay experiments, and dark-matter searches. Understanding the nature of cosmogenic backgrounds is particularly important for future experiments aiming to determine the pep and CNO solar neutrino fluxes, for which the background is dominated by the spallation production of ^(11)C. Data from the Kamioka liquid-scintillator antineutrino detector (KamLAND) provides valuable information for better understanding these backgrounds, especially in liquid scintillators, and for checking estimates from current simulations based upon MUSIC, FLUKA, and GEANT4. Using the time correlation between detected muons and neutron captures, the neutron production yield in the KamLAND liquid scintillator is measured to be Y_n=(2.8±0.3)×10^(-4) μ^(-1) g^(-1) cm^2. For other isotopes, the production yield is determined from the observed time correlation related to known isotope lifetimes. We find some yields are inconsistent with extrapolations based on an accelerator muon beam experiment
Measurement of neutrino oscillation with KamLAND: Evidence of spectral distortion
We present results of a study of neutrino oscillation based on a 766 ton/year exposure of KamLAND to reactor antineutrinos. We observe 258 v_e candidate events with energies above 3.4 MeV compared to 365.2±23.7 events expected in the absence of neutrino oscillation. Accounting for 17.8±7.3 expected background events, the statistical significance for reactor v_e over bar (e) disappearance is 99.998%. The observed energy spectrum disagrees with the expected spectral shape in the absence of neutrino oscillation at 99.6% significance and prefers the distortion expected from v_e oscillation effects. A two-neutrino oscillation analysis of the KamLAND data gives Δm^2=7.9_(-0.5)^(+0.6)x10^(-5) eV^2. A global analysis of data from KamLAND and solar-neutrino experiments yields
Δm^2=7.9_(-0.5)^(+0.6)x10^(-5) eV^2 and tan^2θ=0.40_(-0.07)^(+0.10), the most precise determination to date
Search for the Invisible Decay of Neutrons with KamLAND
The Kamioka Liquid scintillator Anti-Neutrino Detector is used in a search for single neutron or two-neutron intranuclear disappearance that would produce holes in the s-shell energy level of ^(12)C nuclei. Such holes could be created as a result of nucleon decay into invisible modes (inv), e.g., n→3ν or nn→2ν. The deexcitation of the corresponding daughter nucleus results in a sequence of space and time-correlated events observable in the liquid scintillator detector. We report on new limits for one- and two-neutron disappearance: τ(n→inv) > 5.8 × 10^(29) years and τ(nn→inv) > 1.4 × 10^(30) years at 90% C.L. These results represent an improvement of factors of ~3 and > 10^4 over previous experiments
Kinetostatic Analysis and Solution Classification of a Planar Tensegrity Mechanism
Tensegrity mechanisms have several interesting properties that make them
suitable for a number of applications. Their analysis is generally challenging
because the static equilibrium conditions often result in complex equations. A
class of planar one-degree-of-freedom (dof) tensegrity mechanisms with three
linear springs is analyzed in detail in this paper. The kinetostatic equations
are derived and solved under several loading and geometric conditions. It is
shown that these mechanisms exhibit up to six equilibrium configurations, of
which one or two are stable. Discriminant varieties and cylindrical algebraic
decomposition combined with Groebner base elimination are used to classify
solutions as function of the input parameters.Comment: 7th IFToMM International Workshop on Computational Kinematics, May
2017, Poitiers, France. 201
Herschel-Bulkley rheology from lattice kinetic theory of soft-glassy materials
We provide a clear evidence that a two species mesoscopic Lattice Boltzmann
(LB) model with competing short-range attractive and mid-range repulsive
interactions supports emergent Herschel-Bulkley (HB) rheology, i.e. a power-law
dependence of the shear-stress as a function of the strain rate, beyond a given
yield-stress threshold. This kinetic formulation supports a seamless transition
from flowing to non-flowing behaviour, through a smooth tuning of the
parameters governing the mesoscopic interactions between the two species. The
present model may become a valuable computational tool for the investigation of
the rheology of soft-glassy materials on scales of experimental interest.Comment: 5 figure
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