44,907 research outputs found
Ultrabright Linearly Polarized Photon Generation from a Nitrogen Vacancy Center in a Nanocube Dimer Antenna
We demonstrate an exceptionally bright photon source based on a single
nitrogen- vacancy center (NV-center) in a nanodiamond (ND), placed in the
nanoscale gap between two monocrystalline silver cubes in a dimer
configuration. The system is operated near saturation at a stable photon rate
of 850 kcps, while we further achieve strongly polarized emission and high
single photon purity, evident by the measured auto-correlation with a
g(2)(0)-value of 0.08. These photon source features are key parameters for
quantum technological applications, such as secure communication based on
quantum key distribution. The cube antenna is assembled with an atomic force
microscope, which allows us to predetermine the dipole orientation of the
NV-center and optimize cube positioning accordingly, while also tracking the
evolution of emission parameters from isolated ND to the 1 and 2 cube
configuration. The experiment is well described by finite element modelling,
assuming an instrinsic quantum efficiency of 0.35. We attribute the large
photon rate of the assembled photon source, to increased quantum efficiency of
the NV-center and high antenna efficiency
Exact spin-orbital separation in a solvable model in one dimension
A one-dimensional model of coupled spin-1/2 spins and pseudospin-1/2 orbitals
with nearest-neighbor interaction is rigorously shown to exhibit spin-orbital
separation by means of a non-local unitary transformation. On an open chain,
this transformation completely decouples the spins from the orbitals in such a
way that the spins become paramagnetic while the orbitals form the soluble XXZ
Heisenberg model. The nature of various correlations is discussed. The more
general cases, which allow spin-orbital separation by the same method, are
pointed out. A generalization for the orbital pseudospin greater than 1/2 is
also discussed. Some qualitative connections are drawn with the recently
observed spin-orbital separation in Sr2CuO3.Comment: 5 page
A High Reliability Asymptotic Approach for Packet Inter-Delivery Time Optimization in Cyber-Physical Systems
In cyber-physical systems such as automobiles, measurement data from sensor
nodes should be delivered to other consumer nodes such as actuators in a
regular fashion. But, in practical systems over unreliable media such as
wireless, it is a significant challenge to guarantee small enough
inter-delivery times for different clients with heterogeneous channel
conditions and inter-delivery requirements. In this paper, we design scheduling
policies aiming at satisfying the inter-delivery requirements of such clients.
We formulate the problem as a risk-sensitive Markov Decision Process (MDP).
Although the resulting problem involves an infinite state space, we first prove
that there is an equivalent MDP involving only a finite number of states. Then
we prove the existence of a stationary optimal policy and establish an
algorithm to compute it in a finite number of steps.
However, the bane of this and many similar problems is the resulting
complexity, and, in an attempt to make fundamental progress, we further propose
a new high reliability asymptotic approach. In essence, this approach considers
the scenario when the channel failure probabilities for different clients are
of the same order, and asymptotically approach zero. We thus proceed to
determine the asymptotically optimal policy: in a two-client scenario, we show
that the asymptotically optimal policy is a "modified least time-to-go" policy,
which is intuitively appealing and easily implementable; in the general
multi-client scenario, we are led to an SN policy, and we develop an algorithm
of low computational complexity to obtain it. Simulation results show that the
resulting policies perform well even in the pre-asymptotic regime with moderate
failure probabilities
Muon anomaly and a lower bound on higgs mass due to a light stabilized radion in the Randall-Sundrum model
We investigate the Randall-Sundrum model with a light stabilized radion
(required to fix the size of the extra dimension) in the light of muon
anomalous magnetic moment . Using the recent data
(obtained from the E821 experiment of the BNL collaboration) which differs by
from the Standard Model result, we obtain constraints on radion
mass \mphi and radion vev \vphi. In the presence of a radion the beta
functions \beta(\l) and of higgs quartic coupling (\l) and
top-Yukawa coupling () gets modified. We find these modified beta
functions. Using these beta functions together with the anomaly constrained
\mphi and \vphi, we obtain lower bound on higgs mass . We compare our
result with the present LEP2 bound on .Comment: Version to be appeared in IJMP
Elucidating the structural composition of a Fe-N-C catalyst by nuclear and electron resonance techniques
FeâNâC catalysts are very promising materials for fuel cells and metalâair batteries. This work gives fundamental insights into the structural composition of an FeâNâC catalyst and highlights the importance of an inâdepth characterization. By nuclearâ and electronâresonance techniques, we are able to show that even after mild pyrolysis and acid leaching, the catalyst contains considerable fractions of αâiron and, surprisingly, iron oxide. Our work makes it questionable to what extent FeN4 sites can be present in FeâNâC catalysts prepared by pyrolysis at 900â°C and above. The simulation of the iron partial density of phonon states enables the identification of three FeN4 species in our catalyst, one of them comprising a sixfold coordination with endâon bonded oxygen as one of the axial ligands
Alpha decay chains study for the recently observed superheavy element Z=117 within the Isospin Cluster Model
The recently observed -decay chains were produced by
the fusion reactions with target and projectile at Dubna
in Russia. The reported cross-sections for the mentioned reaction are
pb and =1.3(+1.5,-0.6) at and
, respectively. The Q-values of -decay and the half-lives
(s) are calculated for the -decay chains of
nuclei, within the framework of Isospin Cluster Model (ICM). In
the ICM model the proximity energy is improved by using the isospin dependent
radius of parent, daughter and alpha particle. The binding energy (i=1,2) of any nucleus of mass number A and atomic number Z was
obtained from a phenomenological and more genaralized BW formula given by
\cite{samanta02}. The calculated results in ICM are compared with the
experimental results and other theoretical Macro-Microscopic(M-M), RMF(with NL3
and SFU Gold forces parameter) model calculations. The estimated values of
-decay half-lives are in good agreement with the recent data. The ICM
calculation is in favor of the persence of magic number at N=172
Statistical model of the powder flow regulation by nanomaterials
Fine powders often tend to agglomerate due to van der Waals forces between
the particles. These forces can be reduced significantly by covering the
particles with nanoscaled adsorbates, as shown by recent experiments. In the
present work a quantitative statistical analysis of the effect of powder flow
regulating nanomaterials on the adhesive forces in powders is given. Covering
two spherical powder particles randomly with nanoadsorbates we compute the
decrease of the mutual van der Waals force. The dependence of the force on the
relative surface coverage obeys a scaling form which is independent of the used
materials. The predictions by our simulations are compared to the experimental
results.Comment: 18 pages, 9 figures, 1 table, LaTeX; reviewed version with minor
changes, published (Powder Technology
P Wave Meson Spectrum in a Relativistic Model with Instanton Induced Interaction
On the basis of the phenomenological relativistic harmonic models for quarks
we have obtained the masses of P wave mesons. The full Hamiltonian used in the
investigation has Lorentz scalar + vector confinement potential, along with one
gluon exchange potential (OGEP) and the instanton-induced quark-antiquark
interaction (III). A good agreement is obtained with the experimental masses.
The respective role of III and OGEP for the determination of the meson masses
is discussed.Comment: Corrected typo
Effect of isospin dependent cross-section on fragment production in the collision of charge asymmetric nuclei
To understand the role of isospin effects on fragmentation due to the
collisions of charge asymmetric nuclei, we have performed a complete
systematical study using isospin dependent quantum molecular dynamics model.
Here simulations have been carried out for , where n
varies from 47 to 59 and for , where m varies from 14
to 23. Our study shows that isospin dependent cross-section shows its influence
on fragmentation in the collision of neutron rich nuclei
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