90 research outputs found
A Novel Encryption Method for Dorsal Hand Vein Images on a Microcomputer
In this paper, a Lorenz-like chaotic system was developed to encrypt the dorsal hand patterns on a microcomputer. First, the dorsal hand vein images were taken from the subjects via an infrared camera. These were subjected to two different processes called contrast enhancement and segmentation of vein regions. Second, the pre- and post-processed images were encrypted with a new encryption algorithm in the microcomputer environment. For the encryption process, random numbers were generated by the chaotic system. These random numbers were subjected to NIST-800-22 test which is the most widely accepted statistical test suite. The speeded up robust feature (SURF) matching algorithm was utilized in the initial condition sensitivity analysis of the encrypted images. The results of the analysis have shown that the proposed encryption algorithm can be used in identification and verification systems. The encrypted images were analyzed with histogram, correlation, entropy, pixel change rate (NPCR), initial condition sensitivity, data loss, and noise attacks which are frequently used for security analyses in the literature. In addition, the images were analyzed after noise attacks by means of peak signal-to-noise ratio (PSNR), mean square error (MSE), and the structural similarity index (SSIM) tests. It has been shown that the dorsal hand vein images can be used in identification systems safely with the help of the proposed method on microcomputers.This work was supported by the Qatar National-LibraryScopu
Stability analysis of second order pulsed Raman laser in dispersion managed systems
8siWavelength tunable synchronous pulse sources are highly desirable for spectroscopy and optical diagnostics. The common method to generate short pulses in the fiber is the use of nonlinear induced spectral broadening which result in soliton shaping in anomalous dispersion regime. However, to generate ultra-short pulses, broadband gain mechanism is also required. In recent years, Raman fiber lasers have retrieved strong interest due to their capability of serving as pump sources in gain-flattened amplifiers for optical communication systems. The fixed-wavelength Raman lasers have been widely studied in the last years, but recently, much focus has been on the multi wavelength tunable Raman fiber lasers which generate output Stokes pulses in a broad wavelength range by so called cascaded stimulated Raman scattering. In this paper we investigate synchronous 1st and 2nd order pulsed Raman lasers that can achieve frequency spacing of up to 1000cm-1 that is highly desired for CARS microscopy. In particular, analytical and numerical analysis of pulsed stability derived for Raman lasers by using dispersion managed telecom fibers and pumped by 1530nm fiber lasers. We show the evolution of the 1st and 2nd order Stokes signals at the output for different pump power and SMF length (determines the net anomalous dispersion) combinations. We investigated the stability of dispersion managed synchronous Raman laser up to second order both analytically and numerically. The results show that the stable 2nd order Raman Stokes pulses with 0.04W to 0.1W peak power and 2ps to 3.5ps pulse width can be achieved in dispersion managed systemopenopenS. K. Kalyoncu; S. Gao; E.K. Tien; Y. Huang; D. Yildirim; E. Adas; S. Wabnitz; O. BoyrazS. K., Kalyoncu; S., Gao; E. K., Tien; Y., Huang; D., Yildirim; E., Adas; Wabnitz, Stefan; O., Boyra
On-chip two-octave supercontinuum generation by enhancing self-steepening of optical pulses
Dramatic advances in supercontinuum generation have been made recently using
photonic crystal fibers, but it is quite challenging to obtain an
octave-spanning supercontinuum on a chip, partially because of strong
dispersion in high-index-contrast nonlinear integrated waveguides. We show by
simulation that extremely flat and low dispersion can be achieved in silicon
nitride slot waveguides over a wavelength band of 500 nm. Different from
previously reported supercontinua that were generated either by higher-order
soliton fission in anomalous dispersion regime or by self phase modulation in
normal dispersion regime, a two-octave supercontinuum from 630 to 2650 nm (360
THz in total) can be generated by greatly enhancing self-steepening in
nonlinear pulse propagation in almost zero dispersion regime, when an optical
shock as short as 3 fs is formed, which enables on-chip ultra-wide-band
applications
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Immunity of nanoscale magnetic tunnel junctions with perpendicular magnetic anisotropy to ionizing radiation
Spin transfer torque magnetic random access memory (STT-MRAM) is a promising candidate for next generation memory as it is non-volatile, fast, and has unlimited endurance. Another important aspect of STT-MRAM is that its core component, the nanoscale magnetic tunneling junction (MTJ), is thought to be radiation hard, making it attractive for space and nuclear technology applications. However, studies on the effects of ionizing radiation on the STT-MRAM writing process are lacking for MTJs with perpendicular magnetic anisotropy (pMTJs) required for scalable applications. Particularly, the question of the impact of extreme total ionizing dose on perpendicular magnetic anisotropy, which plays a crucial role on thermal stability and critical writing current, remains open. Here we report measurements of the impact of high doses of gamma and neutron radiation on nanoscale pMTJs used in STT-MRAM. We characterize the tunneling magnetoresistance, the magnetic field switching, and the current-induced switching before and after irradiation. Our results demonstrate that all these key properties of nanoscale MTJs relevant to STT-MRAM applications are robust against ionizing radiation. Additionally, we perform experiments on thermally driven stochastic switching in the gamma ray environment. These results indicate that nanoscale MTJs are promising building blocks for radiation-hard non-von Neumann computing
Terahertz All-Optical Modulation in a Silicon-Polymer Hybrid System
Although Gigahertz-scale free-carrier modulators have been previously
demonstrated in silicon, intensity modulators operating at Terahertz speeds
have not been reported because of silicon's weak ultrafast optical
nonlinearity. We have demonstrated intensity modulation of light with light in
a silicon-polymer integrated waveguide device, based on the all-optical Kerr
effect - the same ultrafast effect used in four-wave mixing. Direct
measurements of time-domain intensity modulation are made at speeds of 10 GHz.
We showed experimentally that the ultrafast mechanism of this modulation
functions at the optical frequency through spectral measurements, and that
intensity modulation at frequencies in excess of 1 THz can be obtained in this
device. By integrating optical polymers through evanescent coupling to
high-mode-confinement silicon waveguides, we greatly increase the effective
nonlinearity of the waveguide for cross-phase modulation. The combination of
high mode confinement, multiple integrated optical components, and high
nonlinearities produces all-optical ultrafast devices operating at
continuous-wave power levels compatible with telecommunication systems.
Although far from commercial radio frequency optical modulator standards in
terms of extinction, these devices are a first step in development of
large-scale integrated ultrafast optical logic in silicon, and are two orders
of magnitude faster than previously reported silicon devices.Comment: Under consideration at Nature Material
âBrowningâ the cardiac and peri-vascular adipose tissues to modulate cardiovascular risk
Excess visceral adiposity, in particular that located adjacent to the heart and coronary arteries is associated with increased cardiovascular risk. In the pathophysiological state, dysfunctional adipose tissue secretes an array of factors modulating vascular function and driving atherogenesis. Conversely, brown and beige adipose tissues utilise glucose and lipids to generate heat and are associated with improved cardiometabolic health. The cardiac and thoracic perivascular adipose tissues are now understood to be composed of brown adipose tissue in the healthy state and undergo a brown-to-white transition i.e. during obesity which may be a driving factor of cardiovascular disease. In this review we discuss the risks of excess cardiac and vascular adiposity and potential mechanisms by which restoring the brown phenotype i.e. âre-browningâ could potentially be achieved in clinically relevant populations
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