Algorithm and architecture for a Galois field multiplicative arithmetic processor

We present a new algorithm for generic multiplicative computations of the form ab/c in GF(p/sup m/), including multiplication, inversion, squaring, and division. The algorithm is based on solving a sequence of congruences that are derived from the theory of Grobner bases in modules over the polynomial ring GF(p)[x]. Its corresponding hardware and software architectures can be successfully used in applications such as error control coding and cryptography. We describe a versatile circuit associated with the algorithm for the most important case p=2. The same hardware can be used for a range of field sizes thus permitting applications in which different levels of error control or of security are required by different classes of user. The operations listed are all performed by the hardware in the same number of clock cycles, which prevents certain side-channel attacks. The loss in performance by having 2m iterations for multiplication is compensated by the full parameterization of the Galois field and the ability to perform division and multiplication in parallel.     

Preparation of ferroelectric Ba(Ti/sub 0.85/Sn/sub 0.15/)O/sub 3/ thin films by metal-organic decomposition

Ferroelectric Ba(Ti/sub 0.85/Sn/sub 0.15/)O/sub 3/ (BTS/sub 15/) thin film is newly prepared on the Pt/Ti/SiO/sub 2//Si substrate by metal-organic decomposition. The firing condition is determined by thermogravimetric and differential thermal analysis. The BTS/sub 15/ thin film with a flat surface and uniform thickness is obtained by spin coating in N/sub 2/ atmosphere that avoids moisture. The BTS/sub 15/ film has a perovskite phase and a preferential [110] texture. It is also found that the crystalline structure is cubic at 24/spl deg/C with a lattice constant of 4.01 /spl Aring/, and a grain size of about 30 nm was estimated by Scherrer equation and SEM image. From P-E hysteresis loop at 20/spl deg/C, the polarization at E=0 and the electric field at P=0 are found to be 1.07 /spl mu/C/cm/sup 2/ and 24.0 kV/cm, respectively. It is observed that the dielectric constant decreases monotonously from about 830 to 630 with increasing temperature ranging from 20/spl deg/C to 50/spl deg/C. Finally, it is found that the BTS/sub 15/ thin film shows a sufficient ferroelectricity and is an attractive material for functional ferroelectric devices, such as thermal-type infrared sensors.     

Laser-Enhanced Gas Phase Surface Modifications of Teflon AF1600 for Increased Copper Adhesion

Multilevel interconnect devices, made of alternating layers of a low permittivity polymer (e.g., Teflon AF1600^TM) and a low resistivity metal (e.g., copper), are increasingly being used in microelectronics in order to decrease the RC signal transmission time delay. The mechanical stability of the multilevel interconnects is related to the adhesion developed at the metal-dielectric interface. Since Cu/Teflon AF1600 adhesion is moderate and may not satisfy the requirements of the microelectronics industry, new treatments of the fluoropolymer surface are needed to improve it. In this note, we present several surface modifications, such as the formation of reactive sites during intense X-ray exposure, and S- or N-grafting, activated by UV radiation in the presence of H₂S and NH₃; copper is well known to react with both thiols (R—SH) and amines (R—NH₂) to form strong bonds. Both X-ray exposure and N-grafting lead to enhanced adhesion.     

Effect of the composition on the bandgap width of high-κ MexTiyOz (Me = Hf, Ta, Sr) layers

To explore the possibility of bandgap engineering in Ti-oxide based insulators, we investigated the effect of added cations of another kind (Hf, Ta, Sr) on the optical absorption and photoconductivity of thin titanate films. A bandgap of 3.1-3.4 eV, typical for pure polycrystalline TiO₂, was found in crystallized Sr_xTi_yO_z of different composition as well as in amorphous Ta₂Ti₃O_z. By contrast, the gap width of Hf titanates increases starting from 3.5 eV for 30% Hf/(Hf + Ti) to 4.2 eV for 84% Hf/(Hf + Ti). We suggest that this gap widening is associated with reduced interaction between electron states of neighboring Ti cations as influenced by a wide-gap (E_g = 5.6 eV) HfO₂ sub-network.     

West Nile encephalitis epidemic in southeastern Romania

BACKGROUND: West Nile fever (WNF) is a mosquito-borne flavivirus infection endemic in Africa and Asia. In 1996, the first major WNF epidemic in Europe occurred in Romania, with a high rate of neurological infections. We investigated the epidemic to characterise transmission patterns in this novel setting and to determine its origin. METHODS: Hospital-based surveillance identified patients admitted with acute aseptic meningitis and encephalitis in 40 Romanian districts, including Bucharest. Infection was confirmed with IgM capture and indirect IgG ELISAs. In October, 1996, we surveyed outpatients in Bucharest and seven other districts to estimate seroprevalence and to detect infected patients not admitted to hospital. We also measured the rates of infection and seropositivity in mosquitoes and birds, respectively. RESULTS: Between July 15 and Oct 12, we identified 393 patients with serologically confirmed or probable WNF infection, of whom 352 had acute central-nervous-system infections. 17 patients older than 50 years died. Fatality/case ratio and disease incidence increased with age. The outbreak was confined to 14 districts in the lower Danube valley and Bucharest (attack rate 12.4/100000 people) with a seroprevalence of 4.1%. The number of mild cases could not be estimated. WN virus was recovered from Culex pipiens mosquitoes, the most likely vector, and antibodies to WN virus were found in 41% of domestic fowl. INTERPRETATION: The epidemic in Bucharest reflected increased regional WNF transmission in 1996. Epidemics of Cx pipiens-borne WNF could occur in other European cities with conditions conducive to transmission.     

Hollow-cathode discharge in magnetic field

In order to study the effect of a transverse magnetic field on a hollow-cathode discharge, voltage/current measurements have been made for Ne in a cylindrical geometry and for N2 in a plane-parallel geometry at approximately 1 mmHg pressure. Current-density amplifications of more than 104 have been obtained.     

New TiO2/MgAl-LDH nanocomposites for the photocatalytic degradation of dyes

In this study we report the synthesis of a series of composite nanostructures comprising LDH and TiO2 phases. The materials characterization showed that the LDH crystallites are encapsulated inside the TiO2 matrix after the anatase seeds are deposited on MgxAl-LDHs. The structure in which LDH phase is embedded into anatase matrix is unique bringing important advantages to the photocatalytic performances of the nanocomposites. The photocatalytic activity of the prepared nanocomposites was tested on the degradation of the methylene blue (MB) in aqueous solution. The photocatalytic activities of the nanocomposites were compared with commercial TiO2 nanoparticles Degussa P25. The nanocomposites exhibited superior photocatalytic activity in basic environment because the negatively charged surface of TiO2 nanoparticles at high pH attracts the positively charged methylene blue species.