52,852 research outputs found
Secure thermal infrared communications using engineered blackbody radiation
The thermal (emitted) infrared frequency bands, from 20â40â
THz and 60â100â
THz, are best known for applications in thermography. This underused and unregulated part of the spectral range offers opportunities for the development of secure communications. The âTHz Torch' concept was recently presented by the authors. This technology fundamentally exploits engineered blackbody radiation, by partitioning thermally-generated spectral noise power into pre-defined frequency channels; the energy in each channel is then independently pulsed modulated and multiplexing schemes are introduced to create a robust form of short-range secure communications in the far/mid infrared. To date, octave bandwidth (25â50â
THz) single-channel links have been demonstrated with 380â
bps speeds. Multi-channel âTHz Torch' frequency division multiplexing (FDM) and frequency-hopping spread-spectrum (FHSS) schemes have been proposed, but only a slow 40â
bps FDM scheme has been demonstrated experimentally. Here, we report a much faster 1,280â
bps FDM implementation. In addition, an experimental proof-of-concept FHSS scheme is demonstrated for the first time, having a 320â
bps data rate. With both 4-channel multiplexing schemes, measured bit error rates (BERs) of < 10(â6) are achieved over a distance of 2.5â
cm. Our approach represents a new paradigm in the way niche secure communications can be established over short links
A novel approach to modelling and simulating the contact behaviour between a human hand model and a deformable object
A deeper understanding of biomechanical behaviour of human hands becomes fundamental for any human hand-operated Q2 activities. The integration of biomechanical knowledge of human hands into product design process starts to play an increasingly important role in developing an ergonomic product-to-user interface for products and systems requiring high level of comfortable and responsive interactions. Generation of such precise and dynamic models can provide scientific evaluation tools to support product and system development through simulation. This type of support is urgently required in many applications such as hand skill training for surgical operations, ergonomic study of a product or system developed and so forth. The aim of this work is to study the contact behaviour between the operatorsâ hand and a hand-held tool or other similar contacts, by developing a novel and precise nonlinear 3D finite element model of the hand and by investigating the contact behaviour through simulation. The contact behaviour is externalised by solving the problem using the bi-potential method. The human bodyâs biomechanical characteristics, such as hand deformity and structural behaviour, have been fully modelled by implementing anisotropic hyperelastic laws. A case study is given to illustrate the effectiveness of the approac
Correlation Between the Halo Concentration (c) and the Virial Mass (Mvir) Determined from X-ray Clusters
Numerical simulations of structure formation have suggested that there exists
a good correlation between the halo concentration c (or the characteristic
density delta_c) and the virial mass Mvir for any virialized dark halo
described by the Navarro, Frenk & White (1995) density profile. In this Letter,
we present an observational determination of the c-Mvir (or delta_c-Mvir)
relation in the mass range of 10^14< Mvir <10^16 (solar mass) using a sample of
63 X-ray luminous clusters. The best-fit power law relation, which is roughly
independent of the values of Omega_M and Lambda, is c propto Mvir^(-0.5) or
delta_c propto Mvir^(-1.2), indicating n=-0.7 for a scale-free power spectrum
of the primordial density fluctuations. We discuss the possible reasons for the
conflict with the predictions by typical CDM models such as SCDM, LCDM and
OCDM.Comment: 13 pages, 1 figure, two tables. Accepted for publication in ApJ
Calculations of polarizabilities and hyperpolarizabilities for the Be ion
The polarizabilities and hyperpolarizabilities of the Be ion in the
state and the state are determined. Calculations are performed
using two independent methods: i) variationally determined wave functions using
Hylleraas basis set expansions and ii) single electron calculations utilizing a
frozen-core Hamiltonian. The first few parameters in the long-range interaction
potential between a Be ion and a H, He, or Li atom, and the leading
parameters of the effective potential for the high- Rydberg states of
beryllium were also computed. All the values reported are the results of
calculations close to convergence. Comparisons are made with published results
where available.Comment: 18 pp; added details to Sec. I
Symmetric multiparty-controlled teleportation of an arbitrary two-particle entanglement
We present a way for symmetric multiparty-controlled teleportation of an
arbitrary two-particle entangled state based on Bell-basis measurements by
using two Greenberger-Horne-Zeilinger states, i.e., a sender transmits an
arbitrary two-particle entangled state to a distant receiver, an arbitrary one
of the agents via the control of the others in a network. It will be
shown that the outcomes in the cases that is odd or it is even are
different in principle as the receiver has to perform a controlled-not
operation on his particles for reconstructing the original arbitrary entangled
state in addition to some local unitary operations in the former. Also we
discuss the applications of this controlled teleporation for quantum secret
sharing of classical and quantum information. As all the instances can be used
to carry useful information, its efficiency for qubits approaches the maximal
value.Comment: 9 pages, 3 figures; the revised version published in Physical Review
A 72, 022338 (2005). The detail for setting up a GHZ-state quantum channel is
adde
Probabilistic teleportation of unknown two-particle state via POVM
We propose a scheme for probabilistic teleportation of unknown two-particle
state with partly entangled four-particle state via POVM. In this scheme the
teleportation of unknown two-particle state can be realized with certain
probability by performing two Bell state measurements, a proper POVM and a
unitary transformation.Comment: 5 pages, no figur
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