Meir Danino

Ising lattices with four-spin interactions

Abstract A derivation is given of the magnetic ground states for the spin- 1 2 Ising model with pure four spin interaction on cubic lattices with infinite order parameter dimensionality. The results depend on the periodic boundary conditions that must be used in infinite systems. A new type of boundary condition is thus suggested which enables us to calculate the order parameter dimensionality, with no further assumptions. This system is simpler and gives lower values than those found previously.

Anomalous electron-electron scattering contribution to the electrical resistivity of lithium

The electron-electron scattering contribution to the electrical resistivity of Li has been measured. The coefficient of the T2 term was found to be 3.0+or-0.1 p Omega cm K-2, which is more than an order of magnitude larger than the value for Na and K. The anomalously large value for Li is attributed to the anisotropy of the electron relaxation time.

Uncooled infrared sensor technology for hostile fire indication systems

An evolving combat arena poses an ever-growing hostile fire threat for various ground and airborne targets. Protecting both static posts and moving military platforms against these threats require high performance and affordable solutions, favoring uncooled sensing alert technologies. By analyzing accumulated target and clutter data using new algorithmic and hardware building blocks we establish improved hostile fire indication system configurations. The paper will review new system demonstrations harnessing uncooled IR sensors technology alongside empirical field testing results.

The average number of kinks of a short polyelectrolyte chain : a Monte Carlo study

An interesting connection between the mean straight length 〈ls〉 and the defined average number of kinks 〈nkink〉 in a polyelectrolyte chain configuration is found and described. 〈nkink〉 is found to be the dominant parameter throughout the entire range of the Bjerrum length λ and very sensitive to salt concentration. Identification of λm where (nkink values for various chain lengths coincide, as a percolation threshold is suggested. Considering the kink as a bond, it is found to be much more significant than the contacts described in a previous article as a new type of bonds. It is shown that the family of the physical statistical bonds includes not only contacts but also kinks. The kink fraction in a chain and the effective screening of 〈nkink〉 are defined and described for various values of λ. Through the use of these new parameters, pronounced size effects appear clearly. A connection between polymer systems and molecular cluster systems is proposed.

All optical modulator based on silicon resonator

In this paper we present an all-optical silicon modulator, where a silicon slab (450 μm) thick is coated on both sides to get a Fabry-Perot resonator for laser beam at wavelength of 1550nm. Most of the modulators discussed in literature, are driven by electrical field rather than by light. We investigate new approaches regarding the dependence of the absorption of the optical signal on the control laser pulse at 532 nm having 5nm pulse width. Our silicon based Fabry-Perot resonator increases the intrinsic c-Si finesse to >10, instead of the uncoated silicon with natural finesse of 2.5. The improved finesse is shown to have significant effect on the modulation depth using a pulsed laser. A modulation of 12dB was attained. The modulation is ascribed to two different effects - The Plasma Dispersion Effect (PDE) and the Thermo- Optic Effect (TOE). The PDE causes increase in the signal absorption in silicon via the absorption of the control laser light. On top of that, the transmission of the signal can decrease dramatically in high finesse resonators due to change in the refractive index due to TOE. The changes in the signals absorption coefficient and in the refractive index are the result of incremental change in the concentration of free carriers. The TOE gives rise to higher refractive index as opposed to the PDE which triggers a decrease in the refractive index. Finally, tradeoff considerations are presented on how to modify one effect to counter the other one, leading to an optimal device having reduced temperature dependence.

IRST test standardization for panoramic IR sensors

Infrared staring sensors used in a large field of view (panoramic) applications such as IRST and MWS are still in need for specialized figures of merit to bridge the gap between feasible laboratory measurements and specification and actual performance. Imaging applications has so far dominated the industry attention and so the need to examine the applicability of conventional analyzing concepts and testing procedures for the new applications was overlooked. In this paper we present a universal test station for panoramic MWS/IRST sensors, designed by Elisra and built by CI-Systems Inc. Following the description of the test station configuration, a set of measurable figures of merit and corresponding test procedures that were devised by the authors to support a panoramic sensor specification are introduced. The figures of merit, replacing conventional resolution, sensitivity and pointing accuracy mapping concepts are suggested and explained as viable alternative to the analogous imaging sensors measurement concepts.

New mechanism for the quenching of phonon drag in the alkali metals

A new mechanism is proposed for the quenching of phonon drag in the electrical resistivity of the alkali metals. The mechanism is based on the anisotropy of electron-dislocation scattering, and is thus appropriate to strained samples. The theory is applied to the low-temperature resistivity data for strained samples of potassium.

Phonon-dislocation scattering and the phonon-drag contribution to the electrical resistivity of the alkali metals

A calculation is presented of the temperature dependence of the electron-phonon scattering contribution to the electrical resistivity of the alkali metals as a function of the dislocation density present in the sample. Explicit account is taken of the partial quenching of phonon drag by phonon-dislocation scattering. The calculated results are compared with the recent low-temperature resistivity data for a strained sample of potassium. Excellent agreement is found between the calculated values and the measured data.

SWAD: small arms fire warning and direction finding system: a passive IR concept

A passive IR approach for stationary system is introduced providing protection to high value infrastructure and strategic areas by detecting and warnings against fire shot from rifles, carbines, sub-machines and various other small arms - SWAD. SWAD provides protected surroundings in which it remotely detects small arms fire. By analyzing their patterns, including duration and intensity, SWAD classifies the type of weapon being used.

Fractals in Monte Carlo simulations of a short polyelectrolyte

Fractal dimensionalities, , for charged polymers are calculated over a continuous range of Bjerrum length for chains with various numbers of beads, N. Drastically decreasing values of , characteristic of a phase transition, are found as increases from zero in the range A. The fractal dimensionality approaches unity as predicted by de Gennes et al (de Gennes P-G, Pincus P, Valesco R M and Brochard F 1976 J. Physique 37 1461) close to the onset of order. A newly developed smoothing algorithm yields a substantial improvement in the MC results and reveals an interesting fan-shaped behaviour of exponents and prefactor components at slightly above zero. It also enables discernment of a non-monotonic behaviour of versus N at and close to zero. Differences found in bending between short and long chains may provide an additional explanation for the stability of benzene and the low stability of conjugated rings of N>6. Based on fractal concepts, monomer densities are derived at various and it is suggested that the drastic density changes at A are evidence of the first-order nature of this phase transition.