The effect of Magic Angle Spinning on proton spin-lattice relaxation times in some organic solids

Proton spectra of solids are usually broadened by strong proton homonuclear dipolar interactions. However, substantial line narrowing may be achieved by Magic Angle Spinning (MAS) in systems of low proton density or in systems in which rapid molecular motions occur. In such conditions, T1(H) measurements are often used to characterise the dynamics of each resolved proton site. We show that T1(H) values measured for solid organic compounds with high proton abundance, such as adamantane and glycine, may be strongly dependent on the spinning rate employed, so that care is required when values are compared. The effects of molecular motion and proton density on T1(H) and its dependence on spinning rate were investigated. We found that an increase in molecular motion leads to an increase of T1(H) at higher spinning rates. The opposite is found for systems with low proton densities which show relatively lower T1(H), at higher spinning rates. A possible interpretation is suggested in terms of the reduced spin diffusion efficiency at higher spinning rates.     

The memory enhancement effect of emotion is absent in conceptual implicit memory.

Memory for emotional stimuli is superior to memory for neutral stimuli. This study investigated whether this memory advantage is present in implicit memory. Memory was tested with a test of explicit memory (associate cued recall) and a test of conceptual implicit memory (free association) identical in all respects apart from the retrieval instructions. After studying emotional and neutral paired associates, participants saw the first member of the pair, the cue; in the test of explicit memory participants were instructed to recall the associate; in the test of implicit memory participants were instructed to generate the first word coming to mind associated to the word. Depth of study processing dissociated performance in the tests, confirming that the free-association test was not contaminated by an intentional retrieval strategy. Emotional pairs were better recalled than neutral pairs in the test of explicit memory but not in the equivalent test of implicit memory. The absence of an emotion effect in implicit memory implies that emotional material does not have a privileged global mnemonic status; intentional retrieval is necessary for observing the emotion-related memory advantage. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The enhancement effect in letter detection: Further evidence for the structural model of reading.

According to the structural model of reading (A. Koriat and S. N. Greenberg; 1994), the extraction of structure leads the way to the analysis of meaning. Consistent with this model, previous letter-detection studies have documented an inordinately high rate of letter omissions in function morphemes, suggesting that the cognitive representation of function morphemes is diminished once they have been utilized to set phrase structure. The present study revealed a new and complementary enhancement effect: Letter detection in content morphemes that immediately followed functors was superior to that of content morphemes positioned elsewhere in the text. Together these effects suggest an on-line figure–ground representation of text in which structural elements recede as semantic elements are pushed to the foreground. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The effect of ultrahigh magnetic fields on dopant distribution in CZ systems: A modeling study and comparison with asymptotic solutions

A mathematical representation is developed to describe the velocity, temperature, and dopant concentration fields in a magnetically-damped axisymmetric Czochralski (CZ) crystal growing system. Particular attention is paid to the near-field conditions, that is, to the dopant concen-tration profiles in the vicinity of the crystal surface, to the transient dopant distribution, and to the effect of very high magnetic fields up to 80 kilogauss.     

The rates of adhesion development and the effects of crystalloid solutions on adhesion development in pelvic surgery

OBJECTIVE: To document rates of adhesion development after abdomino-pelvic surgery, stratified by adhesion type, access method, and use of crystalloid solution instillates. DESIGN: Reports from a MEDLINE search (1/1/1966-12/18/1996) detailing rates of adhesion development and meeting the inclusion criteria were subjected to meta-analysis. SETTING: Meta-analysis. PATIENT(S): Patients undergoing abdomino-pelvic surgery. INTERVENTION(S): Intraperitoneal crystalloid solution instillates. MAIN OUTCOME MEASURE(S): Percentage adhesion-free outcome in patients ("patients") or surgical sites ("sites"). RESULT(S): Adhesion-free outcome (sites) was lowest for reformed (26.3% laparotomy; 14.3% laparoscopy), higher for de novo 1b (direct trauma) (45.2% laparotomy, 37.2% laparoscopy), and highest for de novo 1a (indirect trauma) adhesions (82.4% laparoscopy). Crystalloid solution instillates reduced adhesion-free outcome at sites (45.2% versus 20% de novo 1b adhesions in laparotomy) and in patients (43.5% versus 19.9% reformed, laparotomy; 71.7% versus 25% de novo 1b, laparoscopy). CONCLUSION(S): Adhesion-free outcome was lowest for reformed, higher for de novo 1b, and highest for de novo 1a adhesions. Surprisingly, it was lower in laparoscopy than in laparotomy for de novo 1b and reformed adhesions. Crystalloid instillates did not increase adhesion-free outcome. Although limited by the retrospective and heterogeneous nature of the data, these conclusions nonetheless provide a basis on which to formulate future hypotheses.     

The compact form of DNA in solution. V. The heat effect preceding compactization of double-chained DNA in PEG containing water-salt solutions]

The half-life of antipyrine has been estimated from saliva samples in ten subjects by a gas chromatographic method. Half-life, apparent volume of distribution and total body clearance estimated from saliva and plasma concentrations of antipyrine are not significantly different. The concentration of antipyrine in saliva is independent of flow rate within the range expected in healthy subjects in response to mechanical and sapid stimuli. Antipyrine estimation in saliva could facilitate many areas of phaamacokinetic research limited by the difficulty of obtaining serial plasma samples.     

Biochemical changes in Pinus pinea seeds. III. The effect of growth substances and steroidal hormones on nucleic acids

The effects of exogenous growth factors (indolacetic acid, gibberellic acid and kinetin and steroidal hormones (estrone, estradiol and testosterone on the germination pattern of Pinus pinea seeds were studied. Nucleic acids metabolism during the stages before germination, has also been investigated. Seeds sown in the presence of all these substances, showed a higher growth rate and a higher germination degree than their respective controls; kinetin and estradiol were the most active factors. The level of total nucleic acids was studied in seeds after one day soaking and on the 1rst, 3rd, 5th, and 7th day after sowing. Megagametophytes contained a higher amount of acids when growth factors and steroidal hormones were present, specially after one day soaking. In embryos; after the 3rd day, a similar result was obtained. The RNA fraction increased the most.     

Binding of tissue plasminogen activator to endothelial cells. The effect on functional properties. Localization of a ligand in the B-chain of tPA

The binding of 125I-labelled tissue plasminogen activator (tPA), the tPA A- or B-chain to endothelial cells (EC) were studied in suspensions of cultured human umbilical vein EC (HUVEC) or immortalized microvascular EC (HMEC). By determinations of the concentration-dependent binding it was shown that both the A-chain and the B-chain, which were isolated after partial reduction of two-chain tPA, contain ligands for binding to EC. The affinity for the B-chain was much higher than for the A-chain according to Scatchard analysis (Kd 24 and 515 nM, respectively), whereas the number of binding sites was higher for the A-chain than for the B-chain (Bmax 8 x 10(5) and 1.2 x 10(5), respectively). There were no cross interactions between the A- and B-chains and their binding sites. The binding of tPA to EC induced an almost 100-fold increase of the activation rate when compared to the same amount of enzyme in free solution, which in contrast to the fibrin-induced stimulation was not inhibited by antibodies against fibrin. The enzymatic activity of the B-chain was much less affected by the association to the cells. Both tPA and the tPA B-chain were largely protected against inhibition by an excess plasminogen activator type-1 (PAI-1) when bound to EC, whereas the same amount of free tPA was totally inactivated. The competition studies strongly indicated that an N-terminal segment in the B-chain, AKHRRSPGER, may be the ligand part of the B-chain. It is interesting to note that this polypeptide segment also participates in a binding site for PAI-1, necessary for effective inhibition. This implies a possible competition between PAI-1 and a tPA-receptor for binding of tPA. High molecular weight urokinase had no quenching effect on the binding of the B-chain to EC.     

The role of mass transport in the stress-corrosion cracking mechanism of Cu-25 At. Pct Au single crystals in chloride solutions

Available crack growth rate data obtained during discontinuous and continuous propagation of stresscorrosion cracks in Cu-25 at. pct Au single crystals in chloride solutions have been used to investigate the role of mass transport in the mechanism of transgranular stress-corrosion (TSCC) cracking. The results of calculations suggest that during discontinuous crack growth the stage of rapidly increasing crack extension will lead to the formation of a salt film near the crack tip, ultimately resulting in crack arrest. Also, during continuous cracking, the crack growth rate appears to be controlled by the formation of a salt film at the crack tip.     

The rat approximates an ideal detector of changes in rates of reward: Implications for the law of effect.

Rats responded on 2 levers delivering brain stimulation reward on concurrent variable interval schedules. Following many successive sessions with unchanging relative rates of reward, subjects adjusted to an eventual change slowly and showed spontaneous reversions at the beginning of subsequent sessions. When changes in rates of reward occurred between and within every session, subjects adjusted to them about as rapidly as they could in principle do so, as shown by comparison to a Bayesian model of an ideal detector. This and other features of the adjustments to frequent changes imply that the behavioral effect of reinforcement depends on the subject's perception of incomes and changes in incomes rather than on the strengthening and weakening of behaviors in accord with their past effects or expected results. Models for the process by which perceived incomes determine stay durations and for the process that detects changes in rates are developed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

An age comparison of the rates of acquisition and forgetting of spatial information in relation to long-term enhancement of hippocampal synapses.

Compared age differences in the rates of acquisition and forgetting of a spatial memory problem with corresponding differences in the rates of increase and decay of long-term synaptic enhancement (LTE) of hippocampal synapses, induced by high-frequency stimulation of perforant path fibers, in 45 young (12 mo of age) and 45 old (27 mo of age) male Fischer 344 rats. Results indicate that old Ss approached their final asymptotic performance levels more slowly than did the young Ss and exhibited faster rates of forgetting of the problem. Similarly, LTE reached its maximum more slowly in the old Ss and decayed more quickly. Although the absolute rates of behavioral acquisition and forgetting were different from the corresponding rates of increase and decay of LTE, the relative differences between age groups were similar. This was particularly true for the comparison of forgetting with LTE decay. The relation of these data to the hypotheses that LTE underlies spatial learning and memory is discussed. (38 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)