5,478 research outputs found
Spectral reflectance measurements of a virus host model
A technique has been developed to detect the characteristic spectral signatures of healthy and infected St. Augustine grass. It is possible to predict the coverage of the infected area provided ground truth coverage shows positive St. Augustine grass turf. Qualitative measurements from photographs of plants in the blue and red regions with polarization show that light reflected from healthy plants is more strongly polarized than that from diseased plants. Photographs taken through the blue Wratten 47 filter in conjuction with a polarizer show an excellent differentiation. A large photographic difference also appears in the red region. Much smaller differences were noted in the 540 to 550 nm region. Although the intensity in the near-IR region is much higher than the visible region of the spectrum, differences in the healthy and diseased plants' reflectance were quite small
Magnetic phenomena at and near nu =1/2 and 1/4: theory, experiment and interpretation
I show that the hamiltonian theory of Composite Fermions (CF) is capable of
yielding a unified description in fair agreement with recent experiments on
polarization P and relaxation rate 1/T_1 in quantum Hall states at filling nu =
p/(2ps+1), at and near nu = 1/2 and 1/4, at zero and nonzero temperatures. I
show how rotational invariance and two dimensionality can make the underlying
interacting theory behave like a free one in a limited context.Comment: Latex 4 pages, 2 figure
Magnetotransport of Dirac Fermions on the surface of a topological insulator
We study the properties of Dirac fermions on the surface of a topological
insulator in the presence of crossed electric and magnetic fields. We provide
an exact solution to this problem and demonstrate that, in contrast to their
counterparts in graphene, these Dirac fermions allow relative tuning of the
orbital and Zeeman effects of an applied magnetic field by a crossed electric
field along the surface. We also elaborate and extend our earlier results on
normal metal-magnetic film-normal metal (NMN) and normal metal-barrier-magnetic
film (NBM) junctions of topological insulators [Phys. Rev. Lett. {\bf 104},
046403 (2010)]. For NMN junctions, we show that for Dirac fermions with Fermi
velocity , the transport can be controlled using the exchange field
of a ferromagnetic film over a region of width . The
conductance of such a junction changes from oscillatory to a monotonically
decreasing function of beyond a critical which leads to the
possible realization of magnetic switches using these junctions. For NBM
junctions with a potential barrier of width and potential , we find
that beyond a critical , the criteria of conductance maxima
changes from to for
integer . Finally, we compute the subgap tunneling conductance of a normal
metal-magnetic film-superconductor (NMS) junctions on the surface of a
topological insulator and show that the position of the peaks of the zero-bias
tunneling conductance can be tuned using the magnetization of the ferromagnetic
film. We point out that these phenomena have no analogs in either conventional
two-dimensional materials or Dirac electrons in graphene and suggest
experiments to test our theory.Comment: 11 pages, 12 figures; v
Tuning the conductance of Dirac fermions on the surface of a topological insulator
We study the transport properties of the Dirac fermions with Fermi velocity
on the surface of a topological insulator across a ferromagnetic strip
providing an exchange field over a region of width . We show
that the conductance of such a junction changes from oscillatory to a
monotonically decreasing function of beyond a critical . This
leads to the possible realization of a magnetic switch using these junctions.
We also study the conductance of these Dirac fermions across a potential
barrier of width and potential in the presence of such a
ferromagnetic strip and show that beyond a critical , the
criteria of conductance maxima changes from
to for integer . We point out that these novel phenomena
have no analogs in graphene and suggest experiments which can probe them.Comment: v1 4 pages 5 fig
Selection bias in dynamically-measured super-massive black hole samples: consequences for pulsar timing arrays
Supermassive black hole -- host galaxy relations are key to the computation
of the expected gravitational wave background (GWB) in the pulsar timing array
(PTA) frequency band. It has been recently pointed out that standard relations
adopted in GWB computations are in fact biased-high. We show that when this
selection bias is taken into account, the expected GWB in the PTA band is a
factor of about three smaller than previously estimated. Compared to other
scaling relations recently published in the literature, the median amplitude of
the signal at yr drops from to
. Although this solves any potential tension between
theoretical predictions and recent PTA limits without invoking other dynamical
effects (such as stalling, eccentricity or strong coupling with the galactic
environment), it also makes the GWB detection more challenging.Comment: 6 pages 4 figures, submitted to MNRAS letter
A stable Algebraic Spin Liquid in a Hubbard model
We show the existence of a stable Algebraic Spin Liquid (ASL) phase in a
Hubbard model defined on a honeycomb lattice with spin-dependent hopping that
breaks time-reversal symmetry. The effective spin model is the Kitaev model for
large on-site repulsion. The gaplessness of the emergent Majorana fermions is
protected by the time reversal (TR) invariance of this model. We prove that the
effective spin model is TR invariant in the entire Mott phase thus ensuring the
stability of the ASL. The model can be physically realized in cold atom systems
and we propose experimental signals of the ASL.Comment: Published in PR
Rotating fermions in two dimensions: Thomas Fermi approach
Properties of confined mesoscopic systems have been extensively studied
numerically over recent years. We discuss an analytical approach to the study
of finite rotating fermionic systems in two dimension. We first construct the
energy functional for a finite fermionic system within the Thomas-Fermi
approximation in two dimensions. We show that for specific interactions the
problem may be exactly solved. We derive analytical expressions for the
density, the critical size as well as the ground state energy of such systems
in a given angular momentum sector.Comment: Latex 15 pages, 3 ps. figures. Poster in SCES-Y2K, held at SAHA
Institute of Nuclear Physics,Calcutta,October (2000
Performance analysis and comparison of m x n zero forcing and MMSE equalizer based receiver for mimo wireless channel
Wireless transmission is affected by fading and interference effects which can be combated with equalizer.The useof MIMO system promises good improvement in terms of spectral efficency,link relaibility andSignal to Noise Ratio (SNR).The effect of fading and interference always causes an issue for signal recovery in wireless communication. Equalizationcompensates for Intersymbol Interference (ISI) created by multipath within time dispersive channels. This paper analyses theperformance of Zeroforcing and MMSE equalizer for MIMO wireless chaneels. The simulation results are obtained usingMatLab tool box version 7.0 at RF signal processing lab.The Bit Error Rate (BER) characteristics for the various transmittingand receiveing antennna is simulated in matlab tool box and many advantages and disdvantagesof the system is descrbed.The simulation results show that the equalizer based zero forcing receiver is good for noise free channel and is successfulin remving ISI,but MMSE is a better choice than ZF in terms of BER charateristics and under Noise performance
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