Navigation Using Orthogonal Frequency Division Multiplexed Signals of Opportunity

The global positioning system (GPS) provides high-accuracy position measurements anywhere in the world. However, a limitation of this system is that a line of sight to multiple satellites is required; therefore, it is unsuitable to use indoors or in urban canyons. Also, in the presence of radio-frequency interference or jamming, GPS may be unavailable. Alternative methods of navigation and positioning are need to either compliment GPS as a backup or for use in areas unreachable by satellites. This research analyzes a feature-based correlation approach for determining reception differences between two Orthogonal Frequency Division receivers for the purpose of TDOA calculations. Multicarrier signals have a very defined signal structure which allows for non-cooperative symbol detection techniques. Simulations are conducted with different correlation windows sizes, SNR values, and eight different statistical features. Out of the eight features tested the symbol mean and average symbol phase proved to be the most promising because they are able to achieve accurate symbol difference estimations at SNR values below 0 dB

Influence of generalized focusing of few-cycle Gaussian pulses in attosecond pulse generation

In contrast to the case of quasi-monochromatic waves, a focused optical pulse in the few-cycle limit may exhibit two independent curved wavefronts, associated with phase and group retardations, respectively. Focusing optical elements will generally affect these two wavefronts differently, thus leading to very different behavior of the pulse near focus. As limiting cases, we consider an ideal diffractive lens introducing only phase retardations and a perfect non-dispersive refractive lens (or a curved mirror) introducing equal phase and group retardations. We study the resulting diffraction effects on the pulse, finding both strong deformations of the pulse shape and shifts in the spectrum. We then show how important these effects can be in highly nonlinear optics, by studying their role in attosecond pulse generation. In particular, the focusing effects are found to affect substantially the generation of isolated attosecond pulses in gases from few-cycle fundamental optical fields.Comment: 8 pages and 6 figure

Optical emission investigation of laser-produced MgB2 plume expanding in an Ar buffer gas

Optical emission spectroscopy is used to study the dynamics of the plasma generated by pulsed-laser irradiation of a MgB2 target, both in vacuum and at different Ar buffer gas pressures. The analysis of the time-resolved emission of selected species shows that the Ar background gas strongly influences the plasma dynamics. Above a fixed pressure, plasma propagation into Ar leads to the formation of blast waves causing both a considerable increase of the fraction of excited Mg atoms and a simultaneous reduction of their kinetic flux energy. These results can be particularly useful for optimizing MgB2 thin film deposition processes.Comment: 11 pages,4 figures, Applied Physics Letters in pres

EFFECTS OF LEG DOMINANCE ON THE SINGLE LEG HOP FUNCTIONAL TEST IN NON-INJURED ADULTS

The purpose of this study was to determine the effects of leg dominance on the single leg hop (SLH) functional test used in ACL rehabilitation. Twenty-two subjects performed four manipulative, and two standing balance tests to determine leg dominance; and three trials of a standing broad jump and the single leg hop test on both lower limbs. Ground reaction forces were measure using two force platforms (AMTI) and the distance jumped were recorded. T-tests for dependent measure (SPSS) were used to determine difference between dominant and non-dominant limb. Subjects were able to significantly jump farther, produce more vertical and horizontal ground reaction forces when using the dominant leg, except when they jumped from both legs. Clinicians should take in consideration the effects of leg dominance on the single leg hop test results

EFFECTS OF LEG DOMINANCE ON THE SINGLE LEG HOP FUNCTIONAL TEST IN NON-INJURED ADULTS

The purpose of this study was to determine the effects of leg dominance on the single leg hop (SLH) functional test used in ACL rehabilitation. Twenty-two subjects performed four manipulative, and two standing balance tests to determine leg dominance; and three trials of a standing broad jump and the single leg hop test on both lower limbs. Ground reaction forces were measure using two force platforms (AMTI) and the distance jumped were recorded. T-tests for dependent measure (SPSS) were used to determine difference between dominant and non-dominant limb. Subjects were able to significantly jump farther, produce more vertical and horizontal ground reaction forces when using the dominant leg, except when they jumped from both legs. Clinicians should take in consideration the effects of leg dominance on the single leg hop test results

Single isolated attosecond pulse from multicycle lasers

n/

Navigation and Position Determination with a Multicarrier Modulation Signal of Opportunity

A multicarrier modulation position determination method that includes deploying at least one known receiver with a known location and a second receiver with an unknown location. At least two signals of opportunity with different locations are obtained by both the receiver and the second receiver. The signals having a plurality of block data, the block data having block boundaries. The block boundaries including a beginning block boundary and an end block boundary. The block data further including a cyclic prefix at the beginning block boundary. Acquiring a plurality of data samples for at least a portion of the block data and correlating the attained signal of opportunity between the receivers. The correlating process includes the calculation of a time difference of arrival between the known receiver and the second receiver. The time difference of arrival is calculated by aligning the block boundaries and computing a single scalar statistical feature associated with each block. The location of the second receiver is calculated by using a plurality of single scalar statistical features

Interference effects in high-order harmonic generation with molecules

Published versio

Experimental and Theoretical Analysis of Non-linear Vibrational Relaxation of Polyatomic Molecules Strongly Excited by Resonant Laser Radiation

We present a very simple theoretical model aimed at the analysis of non-linear relaxation processes in molecular gases in the presence of partial molecular dissociation induced by vibrational–vibrational exchange between highly excited molecules. The model has a phenomenological character, since it analyzes the behavior of a system of anharmonic diatomic molecules, which is a very rough approximation of a polyatomic molecule such as SF6. Nonetheless, it provides an interesting key for the interpretation of a number of peculiar features characterizing our experimental observation, with which a comparison is made. In particular, the model takes realistic account of the influence of dissociation processes on the relaxation time

RELATIONSHIP BETWEEN LEG DOMINANCE TESTS AND TYPE OF TASK

The purpose of this study was to determine the relationships between common leg dominance tests and the type of tasks performed. Twenty-two subjects performed 4 manipulative and 2 standing balance tests. Leg preference was determined for each of the tests. Kendal tau correlations were used to establish the relationships between the tests. Significant correlations were found between the manipulative types of tests whereas the majority of the subjects used the right leg as the preferred leg. There were significant correlations between the two balance tests but little or no correlation between the balance and manipulative tests. This finding was the result of more than 50% of the subjects switching the preferred leg during the balance tests. Leg preference maybe an adaptation that depends on the nature of the tests required to perform