1,775 research outputs found
Analysis of the theory of high energy ion transport
Procedures for the approximation of the transport of high-energy ions are discussed on the basis of available data on ion nuclear reactions. A straightahead approximation appears appropriate for space applications. The assumption that the secondary-ion-fragment velocity is equal to that of the fragmenting nucleus is inferior to straightahead theory but is of sufficient accuracy if the primary ions display a broad energy spectrum. An iterative scheme for the solution of the inhomogenous integral transport equations holds promise for practical calculation. A model calculation shows that multiple charged ion fragments penetrate to greater depths in comparison with the free path of a primary heavy ion
Interfacing single photons and single quantum dots with photonic nanostructures
Photonic nanostructures provide means of tailoring the interaction between
light and matter and the past decade has witnessed a tremendous experimental
and theoretical progress in this subject. In particular, the combination with
semiconductor quantum dots has proven successful. This manuscript reviews
quantum optics with excitons in single quantum dots embedded in photonic
nanostructures. The ability to engineer the light-matter interaction strength
in integrated photonic nanostructures enables a range of fundamental
quantum-electrodynamics experiments on, e.g., spontaneous-emission control,
modified Lamb shifts, and enhanced dipole-dipole interaction. Furthermore,
highly efficient single-photon sources and giant photon nonlinearities may be
implemented with immediate applications for photonic quantum-information
processing. The review summarizes the general theoretical framework of photon
emission including the role of dephasing processes, and applies it to photonic
nanostructures of current interest, such as photonic-crystal cavities and
waveguides, dielectric nanowires, and plasmonic waveguides. The introduced
concepts are generally applicable in quantum nanophotonics and apply to a large
extent also to other quantum emitters, such as molecules, nitrogen vacancy
ceters, or atoms. Finally, the progress and future prospects of applications in
quantum-information processing are considered.Comment: Updated version resubmitted to Reviews of Modern Physic
Fundamental limits to optical response in absorptive systems
At visible and infrared frequencies, metals show tantalizing promise for
strong subwavelength resonances, but material loss typically dampens the
response. We derive fundamental limits to the optical response of absorptive
systems, bounding the largest enhancements possible given intrinsic material
losses. Through basic conservation-of-energy principles, we derive
geometry-independent limits to per-volume absorption and scattering rates, and
to local-density-of-states enhancements that represent the power radiated or
expended by a dipole near a material body. We provide examples of structures
that approach our absorption and scattering limits at any frequency, by
contrast, we find that common "antenna" structures fall far short of our
radiative LDOS bounds, suggesting the possibility for significant further
improvement. Underlying the limits is a simple metric, for a material with susceptibility , that enables
broad technological evaluation of lossy materials across optical frequencies.Comment: 21 pages and 6 figures (excluding appendices, references
Millimeter wave propagation modeling of inhomogeneous rain media for satellite communications systems
A theoretical propagation model that represents the scattering properties of an inhomogeneous rain often found on a satellite communications link is presented. The model includes the scattering effects of an arbitrary distribution of particle type (rain or ice), particle shape, particle size, and particle orientation within a given rain cell. An associated rain propagation prediction program predicts attenuation, isolation and phase shift as a function of ground rain rate. A frequency independent synthetic storm algorithm is presented that models nonuniform rain rates present on a satellite link. Antenna effects are included along with a discussion of rain reciprocity. The model is verified using the latest available multiple frequency data from the CTS and COMSTAR satellites. The data covers a wide range of frequencies, elevation angles, and ground site locations
Spatially-controlled complex molecules and their applications
The understanding of molecular structure and function is at the very heart of
the chemical and molecular sciences. Experiments that allow for the creation of
structurally pure samples and the investigation of their molecular dynamics and
chemical function have developed tremendously over the last few decades,
although "there's plenty of room at the bottom" for better control as well as
further applications.
Here, we describe the use of inhomogeneous electric fields for the
manipulation of neutral molecules in the gas-phase, \ie, for the separation of
complex molecules according to size, structural isomer, and quantum state. For
these complex molecules, all quantum states are strong-field seeking, requiring
dynamic fields for their confinement. Current applications of these controlled
samples are summarised and interesting future applications discussed.Comment: Accepted by Int. Rev. Phys. Che
Study of resonance light scattering for remote optical probing
Enhanced scattering and fluorescence processes in the visible and UV were investigated which will enable improved remote measurements of gas properties. The theoretical relationship between scattering and fluorescence from an isolated molecule in the approach to resonance is examined through analysis of the time dependence of re-emitted light following excitation of pulsed incident light. Quantitative estimates are developed for the relative and absolute intensities of fluorescence and resonance scattering. New results are obtained for depolarization of scattering excited by light at wavelengths within a dissociative continuum. The experimental work was performed in two separate facilities. One of these utilizes argon and krypton lasers, single moded by a tilted etalon, and a 3/4 meter double monochromator. This facility was used to determine properties of the re-emission from NO2, I2 and O3 excited by visible light. The second facility involves a narrow-line dye laser, and a 3/4 meter single monochromator. The dye laser produces pulsed light with 5 nsec pulse duration and 0.005 nm spectral width
Effects of motion on jet exhaust noise from aircraft
The various problems involved in the evaluation of the jet noise field prevailing between an observer on the ground and an aircraft in flight in a typical takeoff or landing approach pattern were studied. Areas examined include: (1) literature survey and preliminary investigation, (2) propagation effects, (3) source alteration effects, and (4) investigation of verification techniques. Sixteen problem areas were identified and studied. Six follow-up programs were recommended for further work. The results and the proposed follow-on programs provide a practical general technique for predicting flyover jet noise for conventional jet nozzles
Application of moderate resolution band models to the prediction of heat transfer from rocket exhaust plumes
Computer program for resolution band model prediction of heat transfer from rocket exhaust plume
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