A solution of the DGLAP equation for gluon at low x

We obtain a solution of the DGLAP equation for the gluon at low x first by expanding the gluon in a Taylor series and then using the method of characteristics. We test its validity by comparing it with that of Glück, Reya and Vogt. The convergence criteria of the approximation used are also discussed. We also calculate εF ₂(x,Q)²/ε In Q ² using its approximate relations with the gluon distribution at low x. The predictions are then compared with the HERA data.     

Overtone spectroscopy of some benzaldehyde derivatives

Overtone spectrum of o, m and p-nitrobenzaldehydes and p-chlorobenzaldehyde has been studied in 2000–12000 cm⁻¹ region. Vibrational frequencies and anharmonicity constants for aryl as well as alkyl CH stretch vibrations have been determined. We have also determined the internuclear distances for the aryl CH bond in the different molecules. The small variation observed in these distances is an indication of the substitution effect. It is observed that in the case of p-disubstituted benzens, the shift in aryl CH bond is proportional to sum of the Hammet σ of the substituents. However in the case of o-disubstituted benzenes it is only 80% of the para-substituted shift.     

Hydrogen generation by hangman metalloporphyrins

A cobalt(II) hangman porphyrin with a xanthene backbone and a carboxylic acid hanging group catalyzes the electrochemical production of hydrogen from benzoic and tosic acid in acetonitrile solutions. We show that Co(II)H is exclusively involved in the generation of H(2) from weak acids. In a stronger acid, a Co(III)H species is observed electrochemically, but it still needs to be further reduced to Co(II)H before H(2) generation occurs. Overpotentials for H(2) generation are lowered as a result of the hangman effect.     

Multiple ionization of argon in coincidence with projectile ions in 60–120 MeV Si q+-Ar collisions

A projectile ion-recoil ion coincidence technique has been employed to study the multiple ionization and the charge transfer processes in collisions of 60–120 MeV Si ^q+ (q = 4−14) ions with neutral argon atoms. The relative contribution of different ionization channels, namely; direct ionization, electron capture and electron loss leading to the production of slow moving multiply charged argon recoil ions have been investigated. The data reported on the present collision system result from a direct measurement in the considered impact energy for the first time. The total ionization cross-sections for the recoil ions are shown to scale as q ^1.7/E _p ^0.5 , where E _p is the energy in MeV of the projectile and q its charge state. The recoil fractions for the cases of total- and direct ionizations are found to decrease with increasing recoil charge state j. The total ionization fractions of the recoils are seen to depend on q and to show the presence of a ‘shell-effect’ of the target. Further, the fractions are found to vary as 1/j ² upto j = 8+. The average recoil charge state 〈j〉 increases slowly with q and with the number of lost or captured electrons from or into the projectile respectively. The projectile charge changing cross-sections σ _qq′ are found to decrease with increasing q for loss ionization and to increase with q for direct-and capture ionization processes respectively. The physics behind various scaling rules that are found to follow our data for different ionization processes is reviewed and discussed.     

Microwave absorption studies of MgB2 superconductor

Microwave absorption studies have been carried out on MgB₂ superconductor using a standard X-band EPR spectrometer. The modulated low-field microwave absorption signals recorded for polycrystalline (grain size ∼ 10 μm) samples suggested the absence of weak-link character. The field dependent direct microwave absorption has been found to obey a ✓H dependence with two different slopes, which indicated a transition from strongly pinned lattice to flux flow regime.     

Effect of substrate temperature on electrical and magnetic properties of epitaxial La1−x Pb x MnO3 films

Epitaxial La_1−x Pb _x MnO₃ (LPMO) thin films, grown on (100) SrTiO₃ substrates by laser ablation technique at different temperatures between 600 and 850°C, have been characterized for electrical and magnetic properties. The temperature dependence of resistivity showed that the metal-insulator transition temperature (T _MI) decreases with increasing substrate temperature, which has been attributed to decrease in Pb content in the filsm. The YBa₂Cu₃O _x /La_1−x MnO₃ heterostructures, exhibiting both superconductivity and ferromagnetism, have been fabricated.     

Rational or statistical routes from 1-acyldipyrromethanes to meso-substituted porphyrins. Distinct patterns, multiple pyridyl substituents, and amphipathic architectures

New methodology is described for the synthesis of porphyrins bearing four (A 4, cis-A 2B 2, cis-ABC 2, trans-A 2B 2) or fewer (A, cis-AB, cis-A 2, trans-A 2) meso substituents. The method entails condensation of two 1-acyldipyrromethanes in the presence of a metal salt (MgBr 2, 3 mol equiv) and a noncoordinating base (DBU, 10 mol equiv) in a noncoordinating solvent (toluene) with heating (conventional or microwave irradiation) and exposure to air. The rational synthesis of trans-A 2B 2- or trans-A 2-porphyrins was achieved via condensation of two identical 1-acyldipyrromethanes. The statistical synthesis of various meso-substituted porphyrins was achieved via condensation of two nonidentical 1-acyldipyrromethanes. Both routes possess attractive features including (1) no scrambling, (2) good yield (up to 60%) at high concentration (100 mM) for the macrocycle-forming step, (3) reasonable scope (aryl, heteroaryl, alkyl, or no substituent), (4) short reaction time ( approximately 2 h) via microwave irradiation, (5) magnesium porphyrins as the products, which easily undergo demetalation, and (6) facile chromatographic purification. A key advantage of the statistical route is to obtain a cis-substituted porphyrin without the corresponding trans isomer. For example, reaction of an A/B-substituted 1-acyldipyrromethane and the fully unsubstituted 1-formyldipyrromethane gave the magnesium chelates of three porphyrins: the trans-A 2B 2-porphyrin, the "hybrid" cis-AB-porphyrin, and porphine (no trans-AB-porphyrin can form), which were readily demetalated and separated as the free base species. Altogether 26 1-acyldipyrromethanes and 26 target porphyrins have been prepared, including many with two different pyridyl substituents. One set of amphipathic porphyrins includes cis-A 2B 2- or cis-A 2BC-porphyrins wherein A = pentyl and B/C = pyridyl ( o-, m-, p-). Taken together, the rational and statistical routes enable facile conversion of readily available 1-acyldipyrromethanes to diverse porphyrins bearing 1-4 meso substituents for which access is limited via other methods.     

Xanthene-modified and hangman iron corroles

Iron corroles modified with a xanthene scaffold are delivered from easily available starting materials in abbreviated reaction times. These new iron corroles have been spectroscopically examined with particular emphasis on defining the oxidation state of the metal center. Investigation of their electronic structure using (57)Fe Mo?ssbauer spectroscopy in conjunction with density functional theory (DFT) calculations reveals the non-innocence of the corrole ligand. Although these iron corroles contain a formal Fe(IV) center, the deprotonated corrole macrocycle ligand is one electron oxidized. The electronic ground state of these complexes is best described as an intermediate spin S = 3/2 Fe(III) site strongly antiferromagnetically coupled to the S = 1/2 of the monoradical dianion corrole [Fe(III)Cl-corrole(+?)]. We show here that iron corroles as well as xanthene-modified and hangman xanthene iron corroles are redox active and catalyze the disproportionation of hydrogen peroxide via the catalase reaction, and that this activity scales with the oxidation potential. The meso position of corrole macrocycle is susceptible toward nucleophilic attack during catalase turnover. The reactivity of peroxide within the hangman cleft reported here adds to the emerging theme that corroles are good at catalyzing two-electron activation of the oxygen-oxygen bond in a variety of substrates.     

Studies on the valence electronic structure of Fe and Ni in Fe x Ni1−x alloys

K _β-to-K _α X-ray intensity ratios of Fe and Ni in pure metals and in Fe _x Ni_1−x alloys (x=0.20, 0.50, 0.58) exhibiting similar crystalline structure have been measured following excitation by 59.54 keV γ-rays from a ²⁴¹Am point source, to understand as to why the properties of permalloy Fe_0.2Ni_0.8 is distinct from other alloy compositions. It is observed that the valence electronic structure of Fe_0.2Ni_0.8 alloy is totally different from other alloys which may be attributed to its special magnetic properties.