Properties Of Bits Research Articles

Improving chaos-based pseudo-random generators in finite-precision arithmetic

One of the widely-used ways in chaos-based cryptography to generate pseudo-random sequences is to use the least significant bits or digits of finite-precision numbers defined by the chaotic orbits. In this study, we show that the results obtained using such an approach are very prone to rounding errors and discretization effects. Thus, it appears that the generated sequences are close to random even when parameters correspond to non-chaotic oscillations. In this study, we confirm that the actual source of pseudo-random properties of bits in a binary representation of numbers can not be chaos, but computer simulation. We propose a technique for determining the maximum number of bits that can be used as the output of a pseudo-random sequence generator including chaos-based algorithms. The considered approach involves evaluating the difference of the binary representation of two points obtained by different numerical methods of the same order of accuracy. Experimental results show that such estimation can significantly increase the performance of the existing chaos-based generators. The obtained results can be used to reconsider and improve chaos-based cryptographic algorithms.

Atomistic simulation of static magnetic properties of bit patterned media

In this work we present a new design of Co based bit pattern media with out-of-plane uni-axial anisotropy induced by interface effects. Our model features the inclusion of magnetic impurities in the non-magnetic matrix. After the material model was refined during three iterations using Monte Carlo simulations, further simulations were performed using an atomistic integrator of Landau–Lifshitz–Gilbert equation with Langevin dynamics to study the behavior of the system paying special attention to the super-paramagnetic limit. Our model system exhibits three magnetic phase transitions, one due to the magnetically doped matrix material and the weak magnetic interaction between the nano-structures in the system. The different magnetic phases of the system as well as the features of its phase diagram are explained.

Photoluminescence and ferroelectric properties in Eu doped Bi4Ti3O12–SrBi4Ti4O15 intergrowth ferroelectric ceramics

Photoluminescence excitation (PLE) spectra monitored at 614 nm and photoluminescence (PL) spectra excited at 464 nm of BIT–SBTi: x Eu 3+ with x = 0.7 at room temperature. The left inset of this Figure shows a polarization–electric field ( P–E ) hysteresis loop of x = 0.7. The right inset of this Figure gives a luminescence photograph of x = 0.7 under the excitation of a blue light. • Photoluminescence of the BIT–SBTi: x Eu 3+ ceramics were first reported. • Bright red emission excited by blue light has been observed at room temperature. • Enhanced ferroelectric and dielectric properties were obtained for BIT–SBTi: x Eu 3+ . A series of Eu 3+ doped intergrowth Bi 4 Ti 3 O 12 –SrBi 4 Ti 4 O 15 (BIT–SBTi: x Eu 3+ ) (0.0 ⩽ x ⩽ 4) ceramics were prepared through a solid-state reaction method. Contrast with conventional ferroelectric (FE) research, here, we report the photoluminescence (PL) properties of BIT–SBTi: x Eu 3+ system for the first time. Bright red emission was observed at room temperature. It should be noted that the red emission of BIT–SBTi: x Eu 3+ can be excited by both blue light and near ultraviolet (NUV) radiation. Optimized emission intensity was obtained when x = 2 for BIT–SBTi: x Eu 3+ . Moreover, the FE and dielectric properties of BIT–SBTi: x Eu 3+ were also investigated. BIT–SBTi: x Eu 3+ with x = 0.7 ceramic exhibits optimized FE and dielectric behavior. The multifunctional properties of BIT–SBTi: x Eu 3+ ceramics were confirmed in this work.

PKP simulation of size effect on interaction field distribution in highly ordered ferromagnetic nanowire arrays

Abstract Perpendicular structured nanowire arrays interaction field distributions (IFDs), as revealed from first-order reversal curves (FORC) diagrams, are related to the presence of the demagnetizing field in the system. Despite the similarity between the geometric properties of bit patterned media and mentioned nanowire arrays, FORC diagrams of these two types of systems are not similar essentially due to the different number of magnetic entities influencing the switch of an individual element. We show that one Preisach–Krasnosel'skii–Pokrovskii (PKP) symmetrical hysteron can be representative of an ideal infinite nanowire array when the field is applied along the wires. Starting from this observation, we present a very simple model based on PKP symmetrical hysterons that can be applied to real finite ferromagnetic nanowire arrays, and is able to describe a wide class of experimentally observed FORC distributions, revealing features due to size effects. We also present IFDs modeled for different geometric characteristics such as array size, interwire distance, and nanowire dimensions, and an identification procedure for the proposed model.

Synthesis, Structure, Thermal and Electrical Behavior of La-Doped Bismuth Titanate Ceramics

In this paper, we report the properties of bismuth titanate (Bi4Ti3O12, BIT) based nano powders with variation of La content synthesized by well known conventional solid state reaction method. These BIT based ceramic samples sintered above 1000°C had density in the range of 95 to 98% of the theoretical density. The effect of La-doping on structural, thermal and electrical properties of BIT has been studied. The results of XRD, TGA-DSC showed the presence of La-content which shifts the peaks to higher level. The change of dielectric constant, dc conductivity of BIT ceramics were observed as increase in the La concentration from x = 0 to 0.45.

Enhanced Magnetic Properties of Bit Patterned Magnetic Recording Media by Trench-Filled Nanostructure

The structure and properties of nanoscale magnetic island arrays for bit patterned media (BPM) have been studied. A periodic Si nano-island array was fabricated by nano-imprint-lithography (NIL), with the trenchfilling and flattening achieved by resist spin coating followed by reactive ion back-etching. A Co/Pd multilayer magnetic media with a perpendicular anisotropy was then sputtered and lifted-off so that the processed nanostructure array now has the magnetic material only on the top of the pillars. This process significantly improved the magnetic characteristics of BPM. A planarization by hydrogen silsesquioxane filling reduced the tribological interference of the protruding nanoisland heights in BPM.

Magnetization reversal processes of single nanomagnets and their energy barrier

Micromagnetic simulations were performed to investigate the influence of geometry and magnetic anisotropy constant on energy barrier and magnetization reversal mechanism of individual bits important for the bit patterned media concept in magnetic data storage. It is shown that dependency of the energy barrier on magnetic and geometric properties of bits can be described by an analytical approach in the case of quasi-coherent magnetization rotation process. However, when the bit size exceeds a critical size, for which an incoherent magnetization reversal is preferred, the analytical approach becomes invalid and no self-consistent theory is available. By systematically investigating the influence of bit size on the magnetization reversal mode, it was found that the transition from quasi-coherent to incoherent magnetization reversal mode can still be described analytically if an activation volume is considered instead of the bit volume. In this case, the nucleation volume is an important parameter determining thermal stability of the bit. If the volume of the bit is larger than twice the activation volume, the energy barrier stays nearly constant; with further increase in bit size, no gain in thermal stability can be achieved.

Simulation Study of Bit Patterned Media With Weakly Inclined Anisotropy

Recording properties of bit patterned media with weakly inclined anisotropy were studied by simulation. When a shielded planar head was used, a recording system with an areal density of 2.6 Tbit/in2 was expected for 30-degree inclined anisotropy media. Relatively large tolerance of around 4% in the anisotropy field and 7 degrees in orientation dispersion as well as write margins in down- and cross-track directions would be expected. Recording densities would be extended to 4 Tbit/in2 with additional exchange coupling between the dots. It is expected that bit patterned media with weakly inclined anisotropy is one of promising media for ultra high density recording.

Pseudorandom rounding for truncated multipliers

An economical, unbiased, overflow-free rounding scheme for multiplication of multiple-precision floating-point numbers is proposed. The scheme, called pseudorandom rounding, saves multiplications of lower bits and makes use of statistical properties of bits around the least significant bit of products in order to compensate for truncated parts. The method is deterministic, and inputs are commutable. The validity of the rounding is verified by numerical simulation. >