Transverse momentum of charged hadrons observed in deep inelastic muon scattering

The transverse momenta of charged hadrons produced in high energy muon-proton scattering have been studied. The average squared transverse momentum 〈p²_⊥〉 shows a strong dependence on z = E_h/v characteristic of intrinsic momentum effects and a significant rise as a function of s = W². The W², q², x and z dependences of the data are compared with the predictions of a perturbative QCD model.     

Enthalpies of sublimation and fusion for N-acetyl substituted glycine,L-alanine,and D-leucine amides

Enthalpies and entropies of sublimation for N-acetylglycine amide (NAGA), N-acetyl-L-alanine amide (L-NAAA), and N-acetyl-D-leucine amide (D-NALA) were determined from the dependence of their vapour pressures on temperature, as measured by the torsion-effusion method. Enthalpies and temperatures of fusion were measured by differential scanning calorimetry (DSC) and entropies of fusion were derived. No solid-to-solid transitions were detected from r.t. to fusion. Enthalpies of sublimation and fusion were combined to evaluate enthalpies of vaporization of the melts. The experimental results decreased inversely to the molecular mass. An interpretation of this trend in terms of the crystalline structure of these compounds is proposed.     

Effect of fungal degradation on mechanical properties of cellophane

Changes in dynamic mechanical properties of cellophane films due either to fungal attack or to hydrochloric acid hydrolysis have been measured. It appears that damage caused by cellulase enzymes that are released from a fungal overgrowth is localized in noncrystalline regions. These effects include a substantial reduction in elastic modulus, a reduction in temperature at which relaxation processes involving chain segmental mobility occur, and a broadening of loss tangent peaks due to segmental mobility and to rotations of methylol groups. Comparing results obtained from cellulase hydrolysis with those obtained from acid hydrolysis, it is clear that enryme attack proceeds by a characteristic and selective process. Implications regarding the embrittlement often seen to accompany biodegradation are discussed.     

Sul minimo di funzionali definiti sullo spazio delle funzioni di variazione limitata inn dimensioni

Summary Given a proper normal integrand we define a functional on the space of functions of bounded variations inR ⁿ; sufficient conditions which assure the existence of the minimum of this functional are given.

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Entrata in Redazione il 27 aprile 1977.

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Lavoro eseguito nell'ambito dell'attività del Laboratorio per la Matematica Applicata.     

Calculation of the average energy and the energy distribution function of chemically activated species

Equations for the average energy of chemically activated species are developed, and uncertainties in the various energy quantities involved are discussed. Various approaches to the energy distribution function of chemically activated species are discussed. Trial calculations on methylcyclobutane are presented.     

Recommendations for measuring second-order rate constants and kinetic solvent isotope effects on acid-catalyzed reactions

Kinetic solvent isotope effects (KSIE) were measured for the hydrolyses of acetals of benzaldehydes in aqueous solutions covering the pH (pD) range of 1–6. For p-methoxybenzaldehyde diethyl acetal, k/k = 1.8–3.1, depending on the procedure used to calculate the KSIE and on the pH (pD) range used as the basis for k(k). It is shown that this variation is an experimental artifact, and is a characteristic of KSIE measurements in general. It is recommended that k be calculated from a least-squares fit of data to the equation k_obs = k[L⁺], and that the KSIE be reported as k/k. The limitation remains, however, that the KSIE measured for a variety of substances over quite different pH (pD) ranges may not be comparable to more than ?20%. The source of these observations is discussed in terms of small changes in the activity coefficient ratios (a specific salt effect), including the solvent isotope effect on the activity coefficient ratio [eq. (3)].     

Vertex-linked ZnO2S2 tetrahedra in the oxysulfide BaZnOS: a new coordination environment for zinc in a condensed solid

The wide-band-gap semiconductor BaZnOS adopts a high-symmetry modification of the SrZnO2 structure type and contains layers of vertex-linked ZnO2S2 tetrahedra, which represent a novel coordination environment for zinc in the solid state. BaZnOS: orthorhombic, space group Cmcm; a = 3.9619(2) angstroms, b = 12.8541(7) angstroms, c = 6.1175(4) angstroms, Z = 4. Diffuse-reflectance spectroscopy measurements reveal a direct band gap of 3.9(3) eV, consistent with the white color and the results of band structure calculations. The band gap is larger than those observed in ZnO and ZnS, consistent with the more ionic nature of BaZnOS. Attempts to dope this compound electronically have so far not proved possible.     

The combined effect of silanols and the reversed-phase ligand on the retention of positively charged analytes

The nature of the interaction of positively charged analytes with the surface of reversed-phase bonded phases has been investigated as a function of both pH and volume fraction of organic modifier. Studies of the combined effect of both the parameters have been previously reported by us, and the data presented here further demonstrate a multiplicative interaction between pH and the concentration of organic modifier in the mobile phase. Fitting of the data as functions of pH and eluent composition clearly shows that the hydrophobically assisted ion-exchange process dominates over a purely reversed-phase or a pure ion-exchange retention mechanism. The underlying theory is developed in detail, and the mechanism is elucidated using several reversed-phase packings of substantially different character.     

Role of ion pairing in anionic additive effects on the separation of cationic drugs in reversed-phase liquid chromatography

Mobile phase additives can significantly affect the separation of cationic drugs in reversed-phase liquid chromatography (RPLC). Although there are many applications for anionic additives in RPLC separations, the retention mechanism of basic drugs in the presence of inorganic and highly hydrophilic anionic species in the mobile phase is not at all well understood. Two major retention mechanisms by which anionic additives can influence the retention of cations are: (1) ion pair formation in the mobile phase with subsequent retention of the neutral ion pair; (2) pre-sorption of anionic additives on the stationary phase followed by "dynamic ion-exchange" or "electrostatic interaction" with the analytes. Because the use of ion pair chromatography in the separation of proteins, peptides, and basic drugs is rapidly increasing, understanding the retention mechanism involved is becoming more important, especially for the smaller commonly used hydrophilic anionic additives (e.g., formate HCOO, chloride Cl-, trifluoroacetate CF3COO-, perchlorate ClO4-, and hexafluorophosphate PF6-). In this work, we compared various anionic additives in light of their effects on the retention of basic drugs. As did many others we found that the addition of anionic additives (Cl-, CF3COO-, ClO4-, PF6-) profoundly influences the retention of basic drugs. In order to explain the data and differentiate the mechanisms by which the anionic additives perturb the chromatography, we used ion pair formation constants independently measured by capillary electrophoresis (CE) under the mobile phase conditions (pH, solvent composition) identical to those used in chromatography. Agreement between the predicted and experimental chromatographic data under various conditions was evaluated. Under specific circumstances (e.g., pH, stationary phase, and nature of anionic additive), we conclude that the ion pair mechanism is more important than the dynamic ion-exchange and at other conditions it remains a significant contribution.