Intensity Modulation (intensity + modulation)

Distribution by Scientific Domains


Selected Abstracts


Intensity modulation of TMS-induced cortical excitation: Primary motor cortex

HUMAN BRAIN MAPPING, Issue 6 2006
Peter T. Fox
Abstract The intensity dependence of the local and remote effects of transcranial magnetic stimulation (TMS) on human motor cortex was characterized using positron-emission tomography (PET) measurements of regional blood flow (BF) and concurrent electromyographic (EMG) measurements of the motor-evoked potential (MEP). Twelve normal volunteers were studied by applying 3 Hz TMS to the hand region of primary motor cortex (M1hand). Three stimulation intensities were used: 75%, 100%, and 125% of the motor threshold (MT). MEP amplitude increased nonlinearly with increasing stimulus intensity. The rate of rise in MEP amplitude was greater above MT than below. The hemodynamic response in M1hand was an increase in BF. Hemodynamic variables quantified for M1hand included value-normalized counts (VNC), intensity (z-score), and extent (mm3). All three hemodynamic response variables increased nonlinearly with stimulus intensity, closely mirroring the MEP intensity-response function. VNC was the hemodynamic response variable which showed the most significant effect of TMS intensity. VNC correlated strongly with MEP amplitude, both within and between subjects. Remote regions showed varying patterns of intensity response, which we interpret as reflecting varying levels of neuronal excitability and/or functional coupling in the conditions studied. Hum Brain Mapp, 2005. © 2005 Wiley-Liss, Inc. [source]


On the design of bandwidth efficient signalling for indoor wireless optical channels

INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 3 2005
Steve HranilovicArticle first published online: 15 MAR 200
Abstract It is well known that indoor wireless optical channels are limited not only in transmitted optical power, but also in signalling bandwidth. This bandwidth constraint arises due to multipath dispersion in indoor settings as well as due to response time limitations of optoelectronic components. This paper presents an overview of theoretical and practical issues in the design of signalling for bandwidth constrained intensity modulated, direct detection wireless optical channels. A brief overview of the salient qualities of the wireless optical channel are presented to highlight the amplitude constraints which arise. A survey of modulation design is then presented which includes the review of a general technique to represent optical intensity modulation in a signal space and to construct optical intensity lattice codes. Results on the channel capacity of indoor wireless optical channels are surveyed and particular emphasis is placed on recently derived asymptotically exact bounds. The use of multiple emitters and receivers in wireless optical channels is also presented and particular emphasis is placed on techniques which exploit spatial dimensions to improve spectral performance. The paper concludes with some remarks regarding the status of the research area and suggestions for future work. Copyright © 2005 John Wiley & Sons, Ltd. [source]


Application of general formulas for the correction of a lattice-translocation defect in crystals of a lentiviral integrase in complex with LEDGF

ACTA CRYSTALLOGRAPHICA SECTION D, Issue 9 2009
Stephen Hare
The symmetry inherent to many biological macromolecular assemblies has been implicated in a range of crystal pathologies, including lattice-translocation defects (LTDs). Crystals suffering from classic LTDs contain two lattices that are shifted with respect to each other but nonetheless remain within the length of coherent interference. LTD introduces an undesirable intensity modulation into diffraction data, resulting in scrambled or partially scrambled electron densities. In this report, LTD theory is extended and a new general method for determining defect fractions is developed based on the heights of the non-origin peaks observed in native Patterson maps. The application of this method to crystals of lentiviral integrase in complex with its cofactor, where the observed translocation vector does not equal a small integral fraction of a unit-cell edge, is reported and its general application to all classic LTD cases is predicted. [source]


Experimental observation of a strange temporal oscillation of X-ray Pendellösung fringes

JOURNAL OF SYNCHROTRON RADIATION, Issue 5 2009
Jun-ichi Yoshimura
As a strange property not explained by existing theories, it has been known from experiment that X-ray moiré and Pendellösung interference fringes show a small spatial oscillation in the beam path in free space that the diffraction image carrying those fringes is propagated after emerging from the crystal. In connection with the investigation into this strange fringe oscillation, it has been found, by an experiment successively recording Pendellösung-fringe topographs using an X-ray CCD camera, that X-ray Pendellösung fringes also show a small temporal oscillation. Characteristics of this temporal Pendellösung-fringe oscillation, namely irregularities in the fringe profile, the manner of fringe oscillation and a reciprocal correlation between oscillation amplitude and fringe contrast, are shown to be very similar to those of the previously reported spatial oscillation of moiré and Pendellösung fringes. Therefore this temporal oscillation is supposed to have the same origin as the spatial oscillation, revealing another section of the same phenomenon. This discovery of the temporal oscillation advances a step nearer to the full understanding of this strange phenomenon, while disclosing a new property of Pendellösung fringes. As well as the above, a three-dimensional profile representation (surface plot) is given of the image of Pendellösung fringes, to make it clear that unidentified fine intensity modulations, called subfringes in this paper, are produced superposed on the main fringe system. Overall inspection of the intensity profiles of the fringe-imaged topographs suggests that temporal intensity oscillations also occur on a more global scale than the extension of individual fringes, as an unidentified action of the wavefield. [source]