A Sedimentological Continuum Occurring through Geologic Time: A Study for students

Exponential decrease in grain size with linear distance of sediment transport is expressed as a variation of Sternberg's Law. This variation is Y = Yoe-ax in which Y0 is the initial diameter of a particle, Y is the diameter of the particle after Travelling a distance X, and a is the slope of the curve. This slope was designated the coefficient of size reduction by Sternberg, Determination of paleoslope attitude, and paleocurrent direction, and sedimentary anisotropy were achieved from the field measurements on vectoral properties of foreset beds and current ripples, and from the examination of sedimentologic-stratigraphic maps such as grain size distribution, isopachs, and facies. The basic equation (Y = Yoe-ax) is applied to grain diameters of sediment samples from Arctic rivers, thus representing sedimentation on the modern temporal plane. Next, the mathematical operations carried out on both scalar and vectoral entities are applied to the upper and lower parts of a Silurian member (the Grimeby Sandstone in the Niagara Peninsula) of Ontario, in order to illustrate the persistence of the exponential law through a small interval of geologic time. Superposition of the size-distance curves representing top and bottom beds show parallelism of slope. The operations applied across two members (the Grimsby and overlying Thorold sandstone) show a similar parallelism of size-distance curves. The operations applied across several formations representing almost an entire geologic period (the Triassic sandstones of northeastern British Columbia - Toad, Liard, and Grey Beds) yield a family of negative, exponential, size-distance curves, drawn from the textural analyses. Finally, the operations are applied to formations representing a long interval of geologic time (the conglomerates of the lower Mississippian Pocono and lower Pennsylvanian Pottsville). Size-distance curves based on textural variations along a sampling line trending northwesterly across Pennsylvania were constructed and superposed on the same graph. The resulting relationship demonstrates that under prograding conditions a natural law of growth for sedimentary clastic bodies exists and persists over long periods, being expressed in the form of a family of negative exponential curves. Also, this law together with sedimentary anisotropy and progradation constitute a sedimentologic continuum operating through this different but successive interval of geologic time

Transport of Cosmic Rays in Chaotic Magnetic Fields

The transport of charged particles in disorganised magnetic fields is an important issue which concerns the propagation of cosmic rays of all energies in a variety of astrophysical environments, such as the interplanetary, interstellar and even extra-galactic media, as well as the efficiency of Fermi acceleration processes. We have performed detailed numerical experiments using Monte-Carlo simulations of particle propagation in stochastic magnetic fields in order to measure the parallel and transverse spatial diffusion coefficients and the pitch angle scattering time as a function of rigidity and strength of the turbulent magnetic component. We confirm the extrapolation to high turbulence levels of the scaling predicted by the quasi-linear approximation for the scattering frequency and parallel diffusion coefficient at low rigidity. We show that the widely used Bohm diffusion coefficient does not provide a satisfactory approximation to diffusion even in the extreme case where the mean field vanishes. We find that diffusion also takes place for particles with Larmor radii larger than the coherence length of the turbulence. We argue that transverse diffusion is much more effective than predicted by the quasi-linear approximation, and appears compatible with chaotic magnetic diffusion of the field lines. We provide numerical estimates of the Kolmogorov length and magnetic line diffusion coefficient as a function of the level of turbulence. Finally we comment on applications of our results to astrophysical turbulence and the acceleration of high energy cosmic rays in supernovae remnants, in super-bubbles, and in jets and hot spots of powerful radio-galaxies.Comment: To be published in Physical Review D, 20 pages 9 figure

Development of an X-band Photoinjector at SLAC

As part of a National Cancer Institute contract to develop a compact source of monoenergetic X-rays via Compton backscattering, we have completed the design and construction of a 5.5 cell Photoinjector operating at 11.424 GHz. Successful completion of this project will result in the capability of generating a monoenergetic X-ray beam, continuously tunable from 20 - 85 KeV. The immediate goal is the development of a Photoinjector producing 7 MeV, 0.5 nC, sub-picosecond electron bunches with normalized RMS emittances of approximately 1 pi-mm-mR at repetition rates up to 60 Hz. This beam will then be further accelerated to 60 MeV using a 1.05 m accelerating structure. This Photoinjector is somewhat different than the traditional 1.5 cell design both because of the number of cells and the symmetrically fed input coupler cell. Its operating frequency is also unique. Since the cathode is non-removable, cold-test tuning was somewhat more difficult than in other designs. We will present results of "bead-drop" measurements used in tuning this structure. Initial beam measurements are currently in progress and results will be presented as well as results of RF conditioning to high gradients at X-band. Details of the RF system, emittance-compensating solenoid, and cathode laser system as well as PARMELA simulations will also be presented.Comment: 3 pages, 6 figures, 1 Table, LINAC 200