6,409 research outputs found
Coherence of Nitrogen-Vacancy Electronic Spin Ensembles in Diamond
We present an experimental and theoretical study of electronic spin
decoherence in ensembles of nitrogen-vacancy (NV) color centers in bulk
high-purity diamond at room temperature. Under appropriate conditions, we find
ensemble NV spin coherence times (T_2) comparable to that of single NVs, with
T_2 > 600 microseconds for a sample with natural abundance of 13C and
paramagnetic impurity density ~10^15 cm^(-3). We also observe a sharp decrease
of the coherence time with misalignment of the static magnetic field relative
to the NV electronic spin axis, consistent with theoretical modeling of NV
coupling to a 13C nuclear spin bath. The long coherence times and increased
signal-to-noise provided by room-temperature NV ensembles will aid many
applications of NV centers in precision magnetometry and quantum information.Comment: 5 pages, 3 figures; v2 minor correction
Experimental Line Parameters of the b^(1)Σ^(+)_g ← X^(3)Σ^(-)_g Band of Oxygen Isotopologues at 760 nm Using Frequency-Stabilized Cavity Ring-Down Spectroscopy
Positions, intensities, self-broadened widths, and collisional narrowing coefficients of the oxygen isotopologues ^(16)O^(18)O, ^(16)O^(17)O, ^(17)O^(18)O, and ^(18)O^(18)O have been measured for the b^(1)Σg + ← X^(3)Σg − (0,0) band using frequency-stabilized cavity ring-down spectroscopy. Line positions of 156 P-branch transitions were referenced against the hyperfine components of the ^(39)K D_1 (4s ^(2)S_(1/2) → 4p ^(2)P_(1/2)) and D_2 (4s ^(2)S_(1/2) → 4p ^(2)P_(3/2)) transitions, yielding precisions of ~0.00005 cm^(−1) and absolute accuracies of 0.00030 cm^(−1) or better. New excited b^(1)Σg + state molecular constants are reported for all four isotopologues. The measured line intensities of the ^(16)O^(18)O isotopologue are within 2% of the values currently assumed in molecular databases. However, the line intensities of the ^(16)O^(17)O isotopologue show a systematic, J-dependent offset between our results and the databases. Self-broadening half-widths for the various isotopologues are internally consistent to within 2%. This is the first comprehensive study of the line intensities and shapes for the ^(17)O^(18)O or ^(18)O_2 isotopologues of the b^(1)Σg + ← X^(3)Σg − (0,0) band of O_2. The ^(16)O_2, ^(16)O^(18)O, and ^(16)O^(17)O line parameters for the oxygen A-band have been extensively revised in the HITRAN 2008 database using results from the present study
A solution for estimating the tensile yield strength from small specimens
The small punch test is an innovative test that utilises small disc-shaped specimens to assess the mechanical behaviour of materials. The main advantage is the relatively small specimen size. In this article, a modified analytical solution for the small punch maximum bend strength is proposed that is based on classical plate theory. A clear linear relationship is observed between the tensile yield strength σYS and the small punch maximum bend strength σy for both alloys and metal matrix composites. Copyright by ASTM Int'l (all rights reserved)
Structural Routability of n-Pairs Information Networks
Information does not generally behave like a conservative fluid flow in
communication networks with multiple sources and sinks. However, it is often
conceptually and practically useful to be able to associate separate data
streams with each source-sink pair, with only routing and no coding performed
at the network nodes. This raises the question of whether there is a nontrivial
class of network topologies for which achievability is always equivalent to
routability, for any combination of source signals and positive channel
capacities. This chapter considers possibly cyclic, directed, errorless
networks with n source-sink pairs and mutually independent source signals. The
concept of downward dominance is introduced and it is shown that, if the
network topology is downward dominated, then the achievability of a given
combination of source signals and channel capacities implies the existence of a
feasible multicommodity flow.Comment: The final publication is available at link.springer.com
http://link.springer.com/chapter/10.1007/978-3-319-02150-8_
Fast Domain Growth through Density-Dependent Diffusion in a Driven Lattice Gas
We study electromigration in a driven diffusive lattice gas (DDLG) whose
continuous Monte Carlo dynamics generate higher particle mobility in areas with
lower particle density. At low vacancy concentrations and low temperatures,
vacancy domains tend to be faceted: the external driving force causes large
domains to move much more quickly than small ones, producing exponential domain
growth. At higher vacancy concentrations and temperatures, even small domains
have rough boundaries: velocity differences between domains are smaller, and
modest simulation times produce an average domain length scale which roughly
follows , where varies from near .55 at 50% filling
to near .75 at 70% filling. This growth is faster than the behavior
of a standard conserved order parameter Ising model. Some runs may be
approaching a scaling regime. At low fields and early times, fast growth is
delayed until the characteristic domain size reaches a crossover length which
follows . Rough numerical estimates give and simple theoretical arguments give . Our conclusion that
small driving forces can significantly enhance coarsening may be relevant to
the YBCuO electromigration experiments of Moeckly {\it et
al.}(Appl. Phys. Let., {\bf 64}, 1427 (1994)).Comment: 18 pages, RevTex3.
Information capacity in the weak-signal approximation
We derive an approximate expression for mutual information in a broad class
of discrete-time stationary channels with continuous input, under the
constraint of vanishing input amplitude or power. The approximation describes
the input by its covariance matrix, while the channel properties are described
by the Fisher information matrix. This separation of input and channel
properties allows us to analyze the optimality conditions in a convenient way.
We show that input correlations in memoryless channels do not affect channel
capacity since their effect decreases fast with vanishing input amplitude or
power. On the other hand, for channels with memory, properly matching the input
covariances to the dependence structure of the noise may lead to almost
noiseless information transfer, even for intermediate values of the noise
correlations. Since many model systems described in mathematical neuroscience
and biophysics operate in the high noise regime and weak-signal conditions, we
believe, that the described results are of potential interest also to
researchers in these areas.Comment: 11 pages, 4 figures; accepted for publication in Physical Review
Evolution of speckle during spinodal decomposition
Time-dependent properties of the speckled intensity patterns created by
scattering coherent radiation from materials undergoing spinodal decomposition
are investigated by numerical integration of the Cahn-Hilliard-Cook equation.
For binary systems which obey a local conservation law, the characteristic
domain size is known to grow in time as with n=1/3,
where B is a constant. The intensities of individual speckles are found to be
nonstationary, persistent time series. The two-time intensity covariance at
wave vector can be collapsed onto a scaling function , where and . Both analytically and numerically, the covariance
is found to depend on only through in the
small- limit and in the large-
limit, consistent with a simple theory of moving interfaces that applies to any
universality class described by a scalar order parameter. The speckle-intensity
covariance is numerically demonstrated to be equal to the square of the
two-time structure factor of the scattering material, for which an analytic
scaling function is obtained for large In addition, the two-time,
two-point order-parameter correlation function is found to scale as
, even for quite large
distances . The asymptotic power-law exponent for the autocorrelation
function is found to be , violating an upper bound
conjectured by Fisher and Huse.Comment: RevTex: 11 pages + 12 figures, submitted to PR
Coalitions in International Litigation: A Network Perspective
We apply network science principles to analyze the coalitions formed by
European Union (EU) nations and institutions during litigation proceedings at
the European Court of Justice. By constructing Friends and Foes networks, we
explore their characteristics and dynamics through the application of cluster
detection, motif analysis, and duplex analysis. Our findings demonstrate that
the Friends and Foes networks exhibit disassortative behavior, highlighting the
inclination of nodes to connect with dissimilar nodes. Furthermore, there is a
correlation among centrality measures, indicating that member states and
institutions with a larger number of connections play a prominent role in
bridging the network. An examination of the modularity of the networks reveals
that coalitions tend to align along regional and institutional lines, rather
than national government divisions. Additionally, an analysis of triadic binary
motifs uncovers a greater level of reciprocity within the Foes network compared
to the Friends network.Comment: 13 pages 11 figures, style and bibtex files include
Phase Separation Kinetics in a Model with Order-Parameter Dependent Mobility
We present extensive results from 2-dimensional simulations of phase
separation kinetics in a model with order-parameter dependent mobility. We find
that the time-dependent structure factor exhibits dynamical scaling and the
scaling function is numerically indistinguishable from that for the
Cahn-Hilliard (CH) equation, even in the limit where surface diffusion is the
mechanism for domain growth. This supports the view that the scaling form of
the structure factor is "universal" and leads us to question the conventional
wisdom that an accurate representation of the scaled structure factor for the
CH equation can only be obtained from a theory which correctly models bulk
diffusion.Comment: To appear in PRE, figures available on reques
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