12,662 research outputs found
Arrays of optical vortices formed by "fork" holograms
Singular light beams with optical vortices (OV) are often generated by means
of thin binary gratings with groove bifurcation ("fork holograms") that produce
a set of diffracted beams with different OV charges. Usually, only single
separate beams are used and investigated; here we consider the whole set of
diffracted OV beams that, at certain conditions, are involved in efficient
mutual interference to form a characteristic pattern where the ring-like
structure of separate OV beams is replaced by series of bright and dark lines
between adjacent diffraction orders. This pattern, well developed for high
diffraction orders, reflects the main spatial properties of the diffracted
beams as well as of the fork grating used for their generation. In particular,
it confirms the theoretical model for the diffracted beams (Kummer beam model)
and enables to determine the sign and the absolute value of the phase
singularity embedded in the hologram.Comment: 9 pages, 8 figure
High-Rate Space-Time Coded Large MIMO Systems: Low-Complexity Detection and Channel Estimation
In this paper, we present a low-complexity algorithm for detection in
high-rate, non-orthogonal space-time block coded (STBC) large-MIMO systems that
achieve high spectral efficiencies of the order of tens of bps/Hz. We also
present a training-based iterative detection/channel estimation scheme for such
large STBC MIMO systems. Our simulation results show that excellent bit error
rate and nearness-to-capacity performance are achieved by the proposed
multistage likelihood ascent search (M-LAS) detector in conjunction with the
proposed iterative detection/channel estimation scheme at low complexities. The
fact that we could show such good results for large STBCs like 16x16 and 32x32
STBCs from Cyclic Division Algebras (CDA) operating at spectral efficiencies in
excess of 20 bps/Hz (even after accounting for the overheads meant for pilot
based training for channel estimation and turbo coding) establishes the
effectiveness of the proposed detector and channel estimator. We decode perfect
codes of large dimensions using the proposed detector. With the feasibility of
such a low-complexity detection/channel estimation scheme, large-MIMO systems
with tens of antennas operating at several tens of bps/Hz spectral efficiencies
can become practical, enabling interesting high data rate wireless
applications.Comment: v3: Performance/complexity comparison of the proposed scheme with
other large-MIMO architectures/detectors has been added (Sec. IV-D). The
paper has been accepted for publication in IEEE Journal of Selected Topics in
Signal Processing (JSTSP): Spl. Iss. on Managing Complexity in Multiuser MIMO
Systems. v2: Section V on Channel Estimation is update
The Stable Manifold Theorem for Stochastic Differential Equations
We formulate and prove a {\it Local Stable Manifold Theorem\/} for stochastic
differential equations (sde's) that are driven by spatial Kunita-type
semimartingales with stationary ergodic increments. Both Stratonovich and
It\^o-type equations are treated. Starting with the existence of a stochastic
flow for a sde, we introduce the notion of a hyperbolic stationary trajectory.
We prove the existence of invariant random stable and unstable manifolds in the
neighborhood of the hyperbolic stationary solution. For Stratonovich sde's, the
stable and unstable manifolds are dynamically characterized using forward and
backward solutions of the anticipating sde. The proof of the stable manifold
theorem is based on Ruelle-Oseledec multiplicative ergodic theory
NOVEL METHODS FOR SOLVING THE CONFORMABLE WAVE EQUATION
In this paper, a two-dimensional conformable fractional wave equation describing a circular membrane undergoing axisymmetric vibrations is formulated. It was found that the analytical solutions of the fractional wave equation using the conformable fractional formulation can be easily and efficiently obtained using separation of variables and double Laplace transform methods. These solutions are compared with the approximate solution obtained using the differential transform method for certain cases
Separation And Determination Of Benzoylated Polyamines (Spermidine Andspermine) Using Hplc Techniqe
A simple and sensitive reversed-phase high performance liquid chromatography (Rp -HPLC) was developed for separation and determination of polyamines (Spermidine and Spermine). Derivatization of polyamines was improved by dissolving benzoyl chloride in methanol to increase the detection of UV-Visible detector at ? max. 254 nm. The benzoylated polyamines eluted by Rp- HPLC using methanol : water (52 : 48) as mobile phase. The detection limited of this method is (50ng/ml) .The separation was performed on BDS-DB (250 x 4.6 mm I.D) column at flow rate 1 ml/ min. using standard solutions. The retention time of two compounds (Spermidine and Spermine) were (7.7 , 8.5 min.) respectively, this method suggested that monitoring the Spermidine and Spermine compounds could play an important role in diagnosis of different types of carcinoma and fallow up chemo and radiotherapy treatments
Separation and Determination of Benzoylated Polyamines (Spermidine Andspermine) using HPLC Techniqe
A simple and sensitive reversed-phase high performance liquid chromatography (Rp -HPLC) was developed for separation and determination of polyamines (Spermidine and Spermine). Derivatization of polyamines was improved by dissolving benzoyl chloride in methanol to increase the detection of UV-Visible detector at ? max. 254 nm. The benzoylated polyamines eluted by Rp- HPLC using methanol : water (52 : 48) as mobile phase. The detection limited of this method is (50ng/ml) .The separation was performed on BDS-DB (250 x 4.6 mm I.D) column at flow rate 1 ml/ min. using standard solutions. The retention time of two compounds (Spermidine and Spermine) were (7.7 , 8.5 min.) respectively, this method suggested that monitoring the Spermidine and Spermine compounds could play an important role in diagnosis of different types of carcinoma and fallow up chemo and radiotherapy treatments
- …