The use of laser desorption/ionization mass spectrometry in the analysis of inks in questioned documents

Determination of the age of a handwritten or ink printed questioned document can be an important consideration in forensic cases. Most often the age of a document is determined by the chemical behavior of the dyes that make up the ink. Exposure of the dyes to environmental factors such as oxygen and ultraviolet or visible light cause them to degrade. Often this degradation can be correlated to the time since the exposure of the ink to the elements began. A number of methods have been used to track the aging of inks on paper. This paper reports the use of laser desorption mass spectrometry as a valuable tool in not only elucidating the structures of dyes used in inks but tracking the change in their chemistry as they age. This study also explores methods for artificially aging documents using ultraviolet and visible light.     

Rearrangement ions—II: Mass spectra of the C-13 labeled 2-methyl-2-hydroxy-propanes and 2-methyl-2-aminopropanes

The mass spectra of 2-methyl-2-hydroxypropane (I) and 2-methyl-2-aminopropane (II) exhibit fragment ions which suggest skeletal rearrangement processes. The C-13 analogs of I and II, labeled in the 1- and 2-positions, were prepared in order to determine the most probable mechanistic pathways for fragmentation. Label retentions in major fragment ions indicate that I and II decompose into common fragments through structurally similar intermediates.     

A decoding problem in dynamics and in number theory

Given a homeomorphism f of the circle, any splitting of this circle in two semiopen arcs induces a coding process for the orbits of f, which can be determined by recording the successive arcs visited by the orbit. The problem of describing these codes has a two hundred year history (that we briefly recall) in the particular case when the arcs are limited by a point and its image; in modern language, it is the kneading theory of such maps, and as such is relevant for our understanding of dynamical problems involving oscillations. This paper deals with questions attached to the general case, a problem considered by many mathematicians in the 50's and 60's in the case where f is a rotation, and which has recently found some applications in physiology. We show that, except for trivial cases, any code determines the rotation number, up to the orientation, of the homeomorphism which generates it. In the case the code is periodic, we can also determine whether or not it can be generated in this way. An equivalent problem in arithmetic consists of finding +/-p, knowing a collection of classes in Z/qZ of the form {m,m+p,.,m+(k-1)p}, where 2相似文献   

An approach to renormalization on the n-torus

The coding theory of rotations (by inspecting closely their relation to flows) and the continued fractions algorithm (by considering even two-coloring of the integers with a given proportion of, say, blue and red) are revisited. Then, even n-coloring of the integers is defined. This allows one to code rotations on the (n-1)-torus by considering linear flows on the n-torus and yields a simple geometric approach to renormalization on tori by first return maps on the coding regions.