10,193 research outputs found
Mercury in the environs of the north slope of Alaska
The analysis of Greenland ice suggests that the flux of mercury from the continents
to the atmosphere has increased in recent times, perhaps partly as a result of the many of
man’s activities that effect an alteration of terrestrial surfaces. Upon the exposure of fresh
crustal matter, the natural outgassing of mercury vapor from the earth’s surface could be
enhanced.
Accordingly, mercury was measured in a variety of environmental materials gathered
from the North Slope of Alaska to provide background data prior to the anticipated increase
of activity in this environment. The materials were collected during the U. S. Coast Guard
WEBSEC 72-73 cruises as well as through the facilities provided by Naval Arctic Research
Laboratory in the spring of 1973.
The method of measurement depended upon radioactivation of mercury with neutrons
and the subsequent quantification of characteristic gamma radiations after radiochemical
purification.
Mercury concentrations in seawater at several locations in the vicinity of 151°W,
71°N averaged 20 parts per trillion. The waters from all stations east of this location showed
a significantly smaller concentration. This difference may relate to penetration o f Bering-
Chukchi Sea water into the southern Beaufort Sea to 151°W. Marine sediments on the shelf
and slope between 143°W and 153°W contained about 100 parts per billion mercury, except
for those on the continental shelf between Barter Island and the Canning River, where the
concentration was less than half this value. These results are consistent with sediment input
from the respective rivers when their mercury content and mineralogy are considered. The
mercury content of river waters was 18 ppt and in reasonable agreement with the average of
snow samples (13 ppt). The burden of mercury in plankton was 37 ppb.This work was supported by the office of Naval Research under grant N R 083-290
Dyadic Green's Functions and Guided Surface Waves for a Surface Conductivity Model of Graphene
An exact solution is obtained for the electromagnetic field due to an
electric current in the presence of a surface conductivity model of graphene.
The graphene is represented by an infinitesimally-thin, local and isotropic
two-sided conductivity surface. The field is obtained in terms of dyadic
Green's functions represented as Sommerfeld integrals. The solution of
plane-wave reflection and transmission is presented, and surface wave
propagation along graphene is studied via the poles of the Sommerfeld
integrals. For isolated graphene characterized by complex surface conductivity,
a proper transverse-electric (TE) surface wave exists if and only if the
imaginary part of conductivity is positive (associated with interband
conductivity), and a proper transverse-magnetic (TM) surface wave exists when
the imaginary part of conductivity is negative (associated with intraband
conductivity). By tuning the chemical potential at infrared frequencies, the
sign of the imaginary part of conductivity can be varied, allowing for some
control over surface wave properties.Comment: 9 figure
Mechanical vaccum pumps
This presentation gives an overview of the technology of contemporary primary and secondary mechanical vacuum pumps. For reference a brief history of vacuum and a summary of important and basic vacuum concepts are first presented
Recursion relations for generalized Fresnel coefficients: Casimir force in a planar cavity
We emphasize and demonstrate that, besides using the usual recursion
relations involving successive layers, generalized Fresnel coefficients of a
multilayer can equivalently be calculated using the recursion relations
involving stacks of layers, as introduced some time ago [M. S. Tomas, Phys.
Rev. A 51, 2545 (1995)]. Moreover, since the definition of the generalized
Fresnel coefficients employed does not imply properties of the stacks, these
nonstandard recursion relations can be used to calculate Fresnel coefficients
not only for local systems but also for a general multilayer consisting of
various types (local, nonlocal, inhomogeneous etc.) of layers. Their utility is
illustrated by deriving a few simple algorithms for calculating the
reflectivity of a Bragg mirror and extending the formula for the Casimir force
in a planar cavity to arbitrary media.Comment: 5 pages, 2 figures, slightly expande
The Riemann Surface of a Static Dispersion Model and Regge Trajectories
The S-matrix in the static limit of a dispersion relation is a matrix of a
finite order N of meromorphic functions of energy in the plane with
cuts . In the elastic case it reduces to N functions
connected by the crossing symmetry matrix A. The scattering of
a neutral pseodoscalar meson with an arbitrary angular momentum l at a source
with spin 1/2 is considered (N=2). The Regge trajectories of this model are
explicitly found.Comment: 5 pages, LaTe
Bistability and chaos at low-level of quanta
We study nonlinear phenomena of bistability and chaos at a level of few
quanta. For this purpose we consider a single-mode dissipative oscillator with
strong Kerr nonlinearity with respect to dissipation rate driven by a
monochromatic force as well as by a train of Gaussian pulses. The quantum
effects and decoherence in oscillatory mode are investigated on the framework
of the purity of states and the Wigner functions calculated from the master
equation. We demonstrate the quantum chaotic regime by means of a comparison
between the contour plots of the Wigner functions and the strange attractors on
the classical Poincar\'e section. Considering bistability at low-limit of
quanta, we analyze what is the minimal level of excitation numbers at which the
bistable regime of the system is displayed? We also discuss the formation of
oscillatory chaotic regime by varying oscillatory excitation numbers at ranges
of few quanta. We demonstrate quantum-interference phenomena that are assisted
hysteresis-cycle behavior and quantum chaos for the oscillator driven by the
train of Gaussian pulses as well as we establish the border of
classical-quantum correspondence for chaotic regimes in the case of strong
nonlinearities.Comment: 10 pages, 14 figure
Phase-locking at low-level of quanta
We discuss phase-locking phenomena at low-level of quanta for parametrically
driven nonlinear Kerr resonator (PDNR) in strong quantum regime. Oscillatory
mode of PDNR is created in the process of a degenerate down-conversion of
photons under interaction with a train of external Gaussian pulses. We
calculate the Wigner functions of cavity mode showing two-fold symmetry in
phase space and analyse formation of phase-locked states in the regular as well
as the quantum chaotic regime.Comment: 6 pages, 4 figure
The scattering of a cylindrical invisibility cloak: reduced parameters and optimization
We investigate the scattering of 2D cylindrical invisibility cloaks with
simplified constitutive parameters with the assistance of scattering
coefficients. We show that the scattering of the cloaks originates not only
from the boundary conditions but also from the spatial variation of the
component of permittivity/permeability. According to our formulation, we
propose some restrictions to the invisibility cloak in order to minimize its
scattering after the simplification has taken place. With our theoretical
analysis, it is possible to design a simplified cloak by using some peculiar
composites like photonic crystals (PCs) which mimic an effective refractive
index landscape rather than offering effective constitutives, meanwhile
canceling the scattering from the inner and outer boundaries.Comment: Accepted for J. Phys.
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