Priming and aging: an electrophysiological investigation of N400 and recall

Twenty young (20.5 years) and 20 middle-aged academics (57.2 years) performed a priming-recall task which was presented in three blocks. In each block, participants read 40 word pairs after which a recall task had to be carried out. Half of the word pairs were highly associated while the others were low associated. Targets showed the N400 of the middle-aged group to be both delayed and smaller in amplitude for low-associated items. N400 of primes, however, showed no age-related latency difference but was smaller for the middle-aged group due to a positive shift. It is argued that this shift possibly indicates age differences in semantic activation or buildup of context. A reanalysis showed individual differences in word pair processing to depend on recall performance. In general, high recallers were found to show a much larger differentiation between low- and high-associated targets. This resulted from a much larger N400 component elicited by low-associated targets and a more positive ERP in the N400-region for the high-associated targets. It is suggested that the middle-aged subjects activated the expected target word to a level at least equivalent to the younger subjects, but that the activated network itself was larger/less selective particularly in subjects showing a low recall.     

Sliding friction behaviour of polymer-polymer material combinations

The intermolecular bonding energies of polymeric materials can be employed in the evaluation of sliding under conditions determined predominantly by adhesion. The effect at the interface of these energies can be evaluated by reference to the surface energy and to its polar and dispersion-related components. Wetting angle measurements were used to determine the work of adhesion for a group of polymer-polymer material combinations. An exponential relationship exists between the work of adhesion and the coefficients of friction of these combinations, these coefficients of friction being determined primarily by adhesion.     

The role of attribution processes in conformity and dissent: Revisiting the Asch situation.

In an investigation of S. E. Asch's (1955) findings regarding the role of attribution processes in mediating conformity and dissent, 160 undergraduates listened to 24 pairs of tones and after each pair judged which tone was longer in duration. In a control condition, Ss simply wrote private judgments after hearing each pair of tones. As predicted, the majority's impact was minimal when differences in judgment could readily be attributed to corresponding differences in potential payoffs. The majority's influence increased when the only satisfactory explanation for disagreement demanded the postulation of differences between the "priorities" of the dissenter and those of the group. Conformity pressures became most intense when there was no satisfactory explanation and dissent could be attributed only to serious perceptual incapacity on the part of the dissenter or of the majority. (24 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Heat transfer during fluidized-bed coating

A fully implicit numerical method for linear parabolic free boundary problems with coupled and integral boundary conditions is described. The partial differential equation and the boundary conditions are time discretized with the method of lines. An auxiliary function is introduced to remove the coupled and integral boundary conditions from the resulting free boundary problem for ordinary differential equations. Once separated boundary conditions are obtained, invariant imbedding is used to solve the free boundary problem numerically. The method is illustrated by solving the heat transfer equations for the fluidized-bed coating of a thin-walled cylinder.     

On the complexity of deciding avoidability of sets of partial words

Blanchet-Sadri et al. have shown that Avoidability, or the problem of deciding the avoidability of a finite set of partial words over an alphabet of size k≥2, is NP-hard [F. Blanchet-Sadri, R. Jungers, J. Palumbo, Testing avoidability on sets of partial words is hard, Theoret. Comput. Sci. 410 (2009) 968-972]. Building on their work, we analyze in this paper the complexity of natural variations on the problem. While some of them are NP-hard, others are shown to be efficiently decidable. Using some combinatorial properties of de Bruijn graphs, we establish a correspondence between lengths of cycles in such graphs and periods of avoiding words, resulting in a tight bound for periods of avoiding words. We also prove that Avoidability can be solved in polynomial space, and reduces in polynomial time to the problem of deciding the avoidability of a finite set of partial words of equal length over the binary alphabet. We give a polynomial bound on the period of an infinite avoiding word, in the case of sets of full words, in terms of two parameters: the length and the number of words in the set. We give a polynomial space algorithm to decide if a finite set of partial words is avoided by a non-ultimately periodic infinite word. The same algorithm also decides if the number of words of length n avoiding a given finite set of partial words grows polynomially or exponentially with n.     

Velocity of detonation,charge diameter and critical diameter in unconfined RDX-driven heterogeneous explosives

Abstract

The relationship between the experimentally-determined velocity of detonation of unconfined, cylindrical charges of RDX-driven PBXs and composite explosives, V(d), and charge diameter, d, has been examined critically. It has been found that, for many formulations, the data can be fitted more satisfactorily to an elliptical relationship between V(d) and (1/d) than to a linear relationship but this depends, at least in part, on the particle size distribution and shape of the RDX used in the formulation. It has also been observed that the experimentally-determined critical diameter of the formulation, d_c, can be directly related to the linear coefficient in the elliptical V(d) / d relationship, a*, by the equation, d_c = 2.208 a*. This leads to a practical outcome, namely:- that the critical diameter of an explosive formulation may be estimated without the need to prepare a large number of charges, very close to or less than the expected d_c.     

Design of Cyclic Peptides Featuring Proline Predominantly in the cis Conformation under Physiological Conditions

Turns are secondary‐structure elements that are omnipresent in natively folded polypeptide chains. A large variety of four‐residue β‐turns exist, which differ mainly in the backbone dihedral angle values of the two central residues i+1 and i+2. The βVI‐type turns are of particular biological interest because the i+2 residue is always a proline in the cis conformation and might thus serve as target of peptidyl prolyl cis/trans isomerases (PPIases). We have designed cyclic hexapeptides containing two proline residues that predominantly adopt the cis conformation in aqueous solution. NMR data and MD calculations indicated that the cyclic peptide sequences c‐(‐D Xaa‐Ser‐Pro‐D Xaa‐Lys‐Pro‐) result in highly symmetric backbone structures when both prolines are in the cis conformation and the D ‐amino acids are either alanine or phenylalanine residues. Replacement of the serine residue either by phosphoserine or by tyrosine compromises this symmetry, but further increases the cis conformation content of both prolines. As a result, we obtained a cyclic hexapeptide that exists almost exclusively as the cis‐Pro/cis‐Pro conformer but shows no cis/trans interconversion even in the presence of the PPIase Pin1, apparently due to an energetically quite favorable but highly restricted conformational space.     

Identification of late-stage glycosylation steps in the biosynthetic pathway of the anthracycline nogalamycin

Nogalamycin is an anthracycline antibiotic that has been shown to exhibit significant cytotoxicity. Its biological activity requires two deoxysugar moieties: nogalose and nogalamine, which are attached at C7 and C1, respectively, of the aromatic polyketide aglycone. Curiously, the aminosugar nogalamine is also connected through a C-C bond between C2 and C5'. Despite extensive molecular genetic characterization of early biosynthetic steps, nogalamycin glycosylation has not been investigated in detail. Here we show that expression of the majority of the gene cluster in Streptomyces albus led to accumulation of three new anthracyclines, which unexpectedly included nogalamycin derivatives in which nogalamine was replaced either by rhodosamine with the C-C bond intact (nogalamycin R) or by 2-deoxyfucose without the C-C bond (nogalamycin F). In addition, a monoglycosylated intermediate-3',4'-demethoxynogalose-1-hydroxynogalamycinone-was isolated. Importantly, when the remaining biosynthetic genes were introduced into the heterologous host by using a two-plasmid system, nogalamycin could be isolated from the cultures, thus indicating that the whole gene cluster had been identified. We further show that one of the three glycosyltransferases (GTs) residing in the cluster-snogZ-appears to be redundant, whereas gene inactivation experiments revealed that snogE and snogD act as nogalose and nogalamine transferases, respectively. The substrate specificity of the nogalamine transferase SnogD was demonstrated in vitro: the enzyme was able to remove 2deoxyfucose from nogalamycin F. All of the new compounds were found to inhibit human topoisomerase I in activity measurements, whereas only nogalamycin R showed minor activity against topoisomerase II.