M. M. Radwan

Influence of composition and heat treatment on the structure of Se-Te films

Abstract Thin films of Se 1 − x Te x (composition x = 0, 0.2, 0.4, 0.6 and 0.8) were obtained by direct thermal evaporation of the bulk compounds. X-ray diffraction and electron diffraction microscopy investigations were carried out on Se 1 − x Te x films. From X-ray analysis and electron diffraction measurements it was found that the films with x x > 0.6 the as-deposited films were crystalline and the crystallinity increased with increasing Te content. It has been reported that the binary system Se 1− x Te x has a hexagonal structure. The lattice parameters a and c and the grain size for the annealed films of Se 1 − x Te x are calculated.

Structural characterization of diglycol carbonate and polycarbonate SSNTDs irradiated with infrared laser pulses

Abstract Samples of solid-state nuclear track detectors (SSNTDs) CR-39 diglycol carbonate and Makrofol polycarbonate polymers were exposed to infrared laser pulses with different exposure doses ranging from 0.0 to 7.5 J / cm 2 . The development of the noncrystalline phase in the semicrystalline polymers and the effect of laser pulses on the degree of ordering in these two polymers were investigated through X-ray scattering and infrared region spectra studies. The results indicate that similar changes in short-range order take place in both polymers upon laser irradiation. The noncrystalline phase content in the two detectors increases on increasing the laser dose up to 1.5 J / cm 2 and then decreases when increasing laser dose up to 7.5 J / cm 2 . Infrared absorbance measurements show that different deformation in molecular microstructure takes place in the two polymers when exposed to laser irradiation and that Makrofol polycarbonate polymer may be used as a sensor for infrared laser irradiation.

Structural studies of glassy and crystalline selenium-sulphur compounds

X-ray diffraction studies revealed that the compositional dependence of the glassy structure of the binary selenium-sulphur system conforms to and can be explained by structure variations in corresponding crystalline compounds. For up to ∼28% S, sulphur atoms are accommodated in the structure based on the selenium matrix and distorting it. As the percentage of sulphur reaches 50%, complete phase transitions take place. The discontinuity observed in the lattice parameters of crystalline selenium-sulphur compounds is interpreted in terms of the interatomic and inter-molecular forces. The crystallization process of the sample SSe20 was studied, where sulphur clusters were likely to be formed during the growth of selenium crystals, but sulphur atoms were accommodated in the fully crystalline selenium matrix so that no sulphur phase was formed.

Optical studies of (NH4)2SO4 single crystal in the paraelectric phase

Abstract Transmittance and absorbance spectra of (NH 4 ) 2 SO 4 single crystals along [010] direction were measured at different temperatures (296, 308, 318, 328 and 348 K) in the paraelectric phase. The absorption coefficient was computed and the analysis of the data revealed the existence of two optical transitions in (NH 4 ) 2 SO 4 single crystals. The direct and indirect band gaps were shifted towards the longer wavelength with increasing temperature. The data on the allowed indirect transition was analyzed and interpreted in terms of two valence bands originated by spin orbit interaction and crystal field splitting. The momenta E p were calculated as the difference between E g1 , the first valence to conduction band, and E g2 for the second valence band at different temperatures. The results of extinction coefficient ( k ), the refractive index ( n ), and dielectric constants ( e ) were also discussed and calculated as a function of wave length ( λ ). The heat treatment of the crystals proved that the variations of these optical parameters can be consequence of the internal microstructure changes caused by annealing.

Fibre and molecular structure of thymidylyl-3′,5′-deoxyadenosine

Abstract X-ray diffraction and molecular model building studies of an ordered structure of thymidylyl-3′,5′-deoxyadenosine which gives fibre-type diffraction patterns, are consistent with a seven-residues per turn, left-handed structure in which the adenine of one molecule and the thymine of the next are linked together by Hoogsteen type of hydrogen bonds. The structure thus resembles a macromolecule in which units are linked together by hydrogen bonds and stabilized by base stocking. Both nucleosides in the basic molecule are in the anti conformation and both sugar rings have C3′-endo puckers. The C5′-05′ bond of the deoxyadenosine is trans relative to C4′-C3′ and the conformations about the P-03′ and P-05′ bond are gauche−, trans.

Structure and optical investigation of the effect of laser radiation in stabilized poly (vinyl chloride)

Structure and optical property studies using IR & UV spectroscopy, refractive index measurement and X-ray diffraction were performed on poly (vinyl chloride), PVC, stabilized by para-ethyl carboxy N-phenyl maleimide (PEC-NPMI) additive. The effect of addition of the stabilizer PEC-NPMI, with different concentrations, was studied. The results indicate that the addition of PEC-NPMI with 0.01 r g/1 r g PVC enhances the isotropic nature of the PVC polymer. Furthermore the effect of laser radiation on the optical properties of the 0.01 r g PEC-NPMI/1 r g PVC polymer was studied. The study shows that the PVC stabilized with 0.01 r g PEC-NPMI/1 r g PVC and irradiated with 4.27 r J/cm 2 infrared laser radiation is most suitable for applications requiring PVC of high absorbance value in the IR and UV regions.

Diffraction Studies of Tulip Virus X Particles

Summary X-ray diffraction from oriented tulip virus X (TVX) particles and optical diffraction from electron micrographs show that the virus particles have a helical structure with a pitch of about 3.25 nm and a true repeat in five turns of the helix. Both X-ray and optical diffraction indicate that the number of subunits in the repeat period is 5q + 4, where q is an integer. The X-ray diffraction patterns suggest that 9 ⩾ q ⩾ 6, and the optical diffraction patterns suggest that q is probably 7 or 8. The X-ray diffraction patterns indicate that there is a marked feature in the virus particle at a radial position of about 3.3 nm, which is probably the RNA. The equatorial diffraction further suggests that the virus has an axial hole of about 1.5 nm radius.

Fragment‐Based Drug Discovery in the Bromodomain and Extra‐Terminal Domain Family

Bromodomain and extra‐terminal domain (BET) inhibition has emerged recently as a potential therapeutic target for the treatment of many human disorders such as atherosclerosis, inflammatory disorders, chronic obstructive pulmonary disease (COPD), some viral infections, and cancer. Since the discovery of the two potent inhibitors, I‐BET762 and JQ1, different research groups have used different techniques to develop novel potent and selective inhibitors. In this review, we will be concerned with the trials that used fragment‐based drug discovery (FBDD) approaches to discover or optimize BET inhibitors, also showing fragments that can be further optimized in future projects to reach novel potent BET inhibitors.

Structural studies of amorphous and crystalline Tl-As-Se compounds

X-ray diffraction and microstructure studies for amorphous samples of composition (As2Se3)1−xTlx, wherex varies between 0 and 0.7, show that up tox=0.25 the short-range order is similar to that of As2Se3. A change in the structure is observed asx increases. Diffraction from samples crystallized by annealing confirms that a thallium content up tox=0.25 is not enough to alter a characteristic matrix similar to crystalline As2Se3; however, it results in a decrease of crystallization tendency. Forx>0.25 up to 0.7 the structural matrix features are almost similar to those of crystalline TlAsSe2. The observed structural changes could rationalize reported changes in the electrical and thermal transport properties of the amorphous ternary system compounds.

A sub-2dB noise figure, 200–3700 MHz receiver for LTE-A applications

A wideband low-noise amplifier (LNA) with an inherent active-balun and a wideband Downconversion Mixer are proposed in this work. For the LNA, a combination of a common-gate (CG) stage and a common-source (CS) stage is used to acquire the differential output signal out of a single-ended input while still maintaining acceptable output balancing. A positive feedback loop is added to increase the degree of freedom in choosing the design parameters. This leads to decreasing the overall noise figure (NF) without affecting the input matching performance. The LNA shows a NF below 1.86dB, gain of 25.9dB, and IIP3 of -8dBm across all band (200-3700 MHz). A minimum NF of 1.75dB was achieved at 400-1500 MHz band. For the Mixer, A dual current bleeding technique is used to maintain the linear operation at high input amplitudes to achieve high linearity reaching a maximum IIP3 value of 9.66dBm. The Mixer shows a NF of 13dB and gain 6dB. The front-end is designed in 0.13μm standard CMOS process. A total minimum NF of 1.9dB was achieved with a gain of 31.9dB.