scholarly journals Picosecond Laser Chemistry in Supersonic Jet Beams

1983 ◽  
Vol 2 (3-4) ◽  
pp. 55-76 ◽  
Author(s):  
Ahmed H. Zewail
Keyword(s):  
Supersonic Jet ◽  
Picosecond Laser ◽  
Threshold Effect ◽  
Quantum Beats ◽  
Energy Redistribution ◽  
Laser Chemistry ◽  
Large Molecules ◽  
Rrkm Calculation ◽  
Statistical Behavior

In this review we describe the development and the applications of the picosecond-jet technique, which utilizes a picosecond laser and a supersonically-cold jet beam of large molecules. The applications include studies of coherence (quantum beats), photodissociation, isomerization, and partial solvation. The results emphasize the role of intramolecular energy redistribution, and provide evidence for intramolecular threshold effect for rates vs. excess molecular energy. Simple theory for this redistribution of energy among certain modes in molecules is given, and comparison with RRKM calculation is also made to assess the nature of the statistical behavior for the redistribution.

scholarly journals The Effect of Octapeptide Repeats on Prion Folding and Misfolding

2021 ◽  
Vol 22 (4) ◽  
pp. 1800
Author(s):  
Kun-Hua Yu ◽  
Mei-Yu Huang ◽  
Yi-Ru Lee ◽  
Yu-Kie Lin ◽  
Hau-Ren Chen ◽  
...  
Keyword(s):  
Amyloid Fibrils ◽  
Age Of Onset ◽  
Prion Diseases ◽  
Critical Role ◽  
Threshold Effect ◽  
Central Feature ◽  
Terminal Domain ◽  
Amyloid Aggregates

Misfolding of prion protein (PrP) into amyloid aggregates is the central feature of prion diseases. PrP has an amyloidogenic C-terminal domain with three α-helices and a flexible tail in the N-terminal domain in which multiple octapeptide repeats are present in most mammals. The role of the octapeptides in prion diseases has previously been underestimated because the octapeptides are not located in the amyloidogenic domain. Correlation between the number of octapeptide repeats and age of onset suggests the critical role of octapeptide repeats in prion diseases. In this study, we have investigated four PrP variants without any octapeptides and with 1, 5 and 8 octapeptide repeats. From the comparison of the protein structure and the thermal stability of these proteins, as well as the characterization of amyloids converted from these PrP variants, we found that octapeptide repeats affect both folding and misfolding of PrP creating amyloid fibrils with distinct structures. Deletion of octapeptides forms fewer twisted fibrils and weakens the cytotoxicity. Insertion of octapeptides enhances the formation of typical silk-like fibrils but it does not increase the cytotoxicity. There might be some threshold effect and increasing the number of peptides beyond a certain limit has no further effect on the cell viability, though the reasons are unclear at this stage. Overall, the results of this study elucidate the molecular mechanism of octapeptides at the onset of prion diseases.

The role of the correlation coefficient on the statistical behavior of a simple band ratio

2008 ◽  
Author(s):  
Georgios Aim. Skianis ◽  
Konstantinos G. Nikolakopoulos ◽  
Dimitrios A. Vaiopoulos
Keyword(s):  
Correlation Coefficient ◽  
Band Ratio ◽  
Statistical Behavior

scholarly journals Correction to: Threshold Effect of Globalization on Democracy: the Role of Demography

2020 ◽  
Vol 11 (4) ◽  
pp. 1708-1708
Author(s):  
Houda Haffoudhi ◽  
Rihab Bellakhal
Keyword(s):  
Threshold Effect

Threshold Effect of Globalization on Democracy: the Role of Demography

2020 ◽  
Vol 11 (4) ◽  
pp. 1690-1707
Author(s):  
Houda Haffoudhi ◽  
Rihab Bellakhal
Keyword(s):  
Threshold Effect

scholarly journals On the role of the runoff coefficient in the mapping of rainfall to flood return periods

2009 ◽  
Vol 13 (5) ◽  
pp. 577-593 ◽  
Author(s):  
A. Viglione ◽  
R. Merz ◽  
G. Blöschl
Keyword(s):  
Monte Carlo ◽  
Return Period ◽  
Threshold Effect ◽  
Flood Frequency ◽  
Runoff Coefficient ◽  
Return Periods ◽  
Runoff Generation ◽  
Design Storm ◽  
Shed Light

Abstract. While the correspondence of rainfall return period TP and flood return period TQ is at the heart of the design storm procedure, their relationship is still poorly understood. The purpose of this paper is to shed light on the controls on this relationship examining in particular the effect of the variability of event runoff coefficients. A simplified world with block rainfall and linear catchment response is assumed and a derived flood frequency approach, both in analytical and Monte-Carlo modes, is used. The results indicate that TQ can be much higher than TP of the associated storm. The ratio TQ /TP depends on the average wetness of the system. In a dry system, TQ can be of the order of hundreds of times of TP. In contrast, in a wet system, the maximum flood return period is never more than a few times that of the corresponding storm. This is because a wet system cannot be much worse than it normally is. The presence of a threshold effect in runoff generation related to storm volume reduces the maximum ratio of TQ /TP since it decreases the randomness of the runoff coefficients and increases the probability to be in a wet situation. We also examine the relation between the return periods of the input and the output of the design storm procedure when using a pre-selected runoff coefficient and the question which runoff coefficients produce a flood return period equal to the rainfall return period. For the systems analysed here, this runoff coefficient is always larger than the median of the runoff coefficients that cause the maximum annual floods. It depends on the average wetness of the system and on the return period considered, and its variability is particularly high when a threshold effect in runoff generation is present.

Role of the porous structure of the hemosorbent in the sorption of large molecules

1987 ◽  
Vol 21 (2) ◽  
pp. 149-152
Author(s):  
N. M. Kaznacheeva ◽  
S. I. Surinova ◽  
S. P. Valueva ◽  
B. S. �l'tsefon ◽  
G. S. Golovina
Keyword(s):  
Porous Structure ◽  
Large Molecules

Antibonding σ* orbitals in molecular spectroscopy

1985 ◽  
Vol 63 (7) ◽  
pp. 2032-2043 ◽  
Author(s):  
M. B. Robin
Keyword(s):  
Ground State ◽  
Molecular Spectroscopy ◽  
Atomic Spectroscopy ◽  
High Symmetry ◽  
Giant Resonances ◽  
Molecular Absorption ◽  
Large Molecules ◽  
The Past ◽  
Bond Strengths

This paper discusses the role of σ* antibonding valence MO's in the electronic spectra of large molecules. Using the term value and antishielding concepts, molecular absorption patterns terminating at σ* MO's are systematized and rationalized; the frequencies of such excitations correlate with the ground-state bond strengths of the bonds giving rise to the σ* MO's. In unsaturated systems, the π → σ* and np → σ* excitations can be distinguished on the basis of their term values. Confusion in the past regarding the existence of excitations to σ* relates to the fact that σ* MO's often can be totally mixed into the surrounding sea of Rydberg levels of the same symmetry, and for all practical purposes can cease to exist except as perturbations on the Rydberg levels. For nonpenetrating Rydberg manifolds there is little or no mixing with σ* MO's of the same symmetry, setting the stage for the appearance of valence-shell excitations to σ* in high-symmetry molecules which are analogous to the d → f inner-well giant resonances of atomic spectroscopy.

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