Bulletin of the American Physical Society
74th Annual Meeting of the Southeastern Section
Volume 52, Number 13
Thursday–Saturday, November 8–10, 2007; Nashville, Tennessee
Session HB: General Physics (Posters) |
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Chair: David Haase, North Carolina State University Room: Scarritt-Bennett Center Laskey C |
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HB.00001: Resonance structure of the photoelectron $\beta_{nl}$ parameter versus autoionizing resonance minima in partial $\sigma_{nl\pm 1}$ cross sections: A model of ``complete'' experiments with \textit{fewer} measurements Valeriy Dolmatov, Emre Guler The relationship between the structure of the autoionizing resonance minima in partial photoionization cross sections $\sigma_{nl \pm 1}$ and the resonance profile of the dipole photoelectron angular distribution parameter $\beta_{nl}$ in the vicinity of the resonance is established. From this, the information can be extracted (from known $\beta_{nl}$ alone) on the energy positions and ordering of autoionizing resonance minima in $\sigma_{l\pm1}$, the energies at which $\sigma_{l+1}$ and $\sigma_{l-1}$ are equal, signs and magnitudes of relative phase shifts of the photoionization amplitudes $D_{l\pm1}$ through the autoionizing resonance energy region, and the magnitudes of $D_ {l\pm1}$ at extreme points in $\beta_{nl}$; no tedious experimentation with electron spin polarization or light polarization is required. The established relationship expands our previously developed, so to speak ``point'' model of ``complete'' photoionization experiments with \textit{fewer} measurements [V.K. Dolmatov and S.T. Manson, PRA \textbf{58}, R2635 (1998)] onto a broader energy region [V.K. Dolmatov, E. Guler, S.T. Manson, PRA (submitted)]. [Preview Abstract] |
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HB.00002: Simulating the Interactions of the Sagittarius Dwarf Galaxy and the Milky Way Mary Rusthoven, Jeannette Myers, Bart Snyder, Lih-Sin The, Dieter Hartmann The Sagittarius Dwarf Galaxy is one of the satellite galaxies interacting with the Milky Way. Discovered to be located just below the galactic center; this galaxy is currently being tidally disrupted as it approaches the Milky Way disk. We performed a series of four N-body simulations of the interaction between Sagittarius and the Milky Way over a 1 Gyr time period leading up to today's position. Two of the simulations were designed to test the initial conditions used for the Milky Way model. The other two simulations were designed to test what happens when the Milky Way is treated as a static system with only the Sagittarius system evolving with time. [Preview Abstract] |
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HB.00003: Analysis of the Sagittarius Dwarf Galaxy Tidal Tails Bart Snyder, Jeannette Myers, Mary Rusthoven, Lih-Sin The, Dieter Hartmann The Sagittarius Dwarf Galaxy is one of the satellite galaxies interacting with the Milky Way. Discovered to be located just below the galactic center; this galaxy is currently being tidally disrupted as it approaches the Milky Way disk. We performed a series of N-body simulations of the interaction between Sagittarius and the Milky Way over a 1 Gyr time period leading up to today's position. Here we present our analysis of the tidal tails and compare them to the known tidal structures we observe today. [Preview Abstract] |
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HB.00004: Energetics and transport coherence in a two-state shifting ratchet Ronald Benjamin We study the efficiency and coherence of transport of a two-state shifting ratchet in the underdamped regime. [Preview Abstract] |
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HB.00005: Adsorption Studies with AFM of Human Plasma Fibrinogen on Silicon Surfaces Sheena Gause, Wendy Kong, J.E. (Jack) Rowe Fibrinogen (FGN) plays an important role in the clotting of blood. Human plasma fibrinogen (HPF) is a protein that readily adsorbs on biomaterial surfaces. The purpose of this experiment was to use the Atomic Force Microscope to study the adsorption of HPF molecules or FGN onto several silicon surfaces with different orientations and resistivities. The size of the FGN molecules found to be somewhat different of Si(111), (100) and (110) were compared to the size of the FGN molecules in solution (45 nm in length, the end dynodes measures to be 6.5 nm in diameter, and the middle dynode measures to be 5 nm in diameter. For this study, the CPR (Thermo-microscope) Atomic Force Microscope (AFM) was used to observe the amount of fibrinogen molecules adsorbed by Si (111) with a resistance of .0281-.0261 $\Omega $ \textbullet cm, Si (111) with a resistance of 1 $\Omega $ \textbullet cm, Si (100), and Si (110) surfaces. In finding any single fibrinogen molecules, the appropriate image scans and measurements were taken. After collection and analysis of the data, it was found from AFM that the fibrinogen molecules found on Si (110) mostly resembled fibrinogen molecules found in solution. The other images showed that the fibrinogen molecules adsorbed on Silicon substrates is significantly greater ($\sim $10-20 {\%}) than those in solution. [Preview Abstract] |
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HB.00006: Three-dimensional theory of the Smith-Purcell free-electron laser Jonathan Jarvis, Heather Andrews We present an analytic theory for the operation of a Smith-Purcell free-electron laser (SPFEL) that includes transverse diffraction of the optical beam. For the case of an infinitely wide electron beam, this theory agrees with previous two-dimensional analyses. When the electron beam is narrow compared to the mode, the gain (amplifier regime) is substantially reduced by diffraction, while its dependence on the beam current is increased due to gain guiding. A 5/2-power dispersion relation replaces the conventional cubic dispersion relation. The number and location of the physically allowed roots depends on the electron-beam energy. For low beam energies, an estimate of the start current (oscillator regime) of the device is obtained by satisfying the appropriate boundary conditions on the beam axis. [Preview Abstract] |
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HB.00007: Measurement of Silver Nanoparticles on Periodically Poled Lithium Niobate (PPLN) Surfaces Sarah Earl, James Perkins, Dong Wu, J.E. (Jack) Rowe Atomic force microscopy (AFM) was used to measure the size and shape of silver nanoparticles which were deposited photochemically on PPLN surfaces. These nanoparticles form patterns of nanowires on PPLN surfaces which may be useful in new applications. Metallic nanowires are necessary for the advancement of nanoscale devices, and better methods of fabricating these wires are needed. An AFM uses a cantilever that moves across a given surface to provide measurements on the size and shape of nanoscale features on a surface. The AFM used was calibrated using a standardized grating sample. Different tips were analyzed to determine the best tip for imaging. AFM was then applied to the PPLN surfaces. PPLN consists of striped (positive and negative) domains that are between 10 and 14 micrometers in width. Silver nanowires, typically about 65nm in width, can be formed by depositing silver in aqueous solution under ultraviolet light on PPLN surfaces. The nanowires form along the edges or boundaries of these domains. Multiple PPLN samples of different deposition times are analyzed. These samples are compared by measuring the volume of silver in the wires and by measuring the amount of silver deposited on the different domains. [Preview Abstract] |
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HB.00008: Variable temperature conducting tip atomic force microscopy of cobalt silicide on n-type Si(111):7$\times $7 and n-type Si(100):2$\times $1 Joseph Tedesco, J.E. (Jack) Rowe, Robert Nemanich Cobalt silicide (CoSi$_{2})$ nanoislands have been formed by ultrahigh vacuum deposition of thin films ($\sim $0.3 -- 1.0 $\pm $ 0.1 nm) of cobalt on clean n-type Si(111) and n-type Si(100) surfaces followed by annealing to $\sim $900$^{\circ}$C. Contact areas of the nanoislands were found to range from $\sim $50 $\times $ 10$^{3}$ -- 450 $\times $ 10$^{3}$ nm$^{2}$ when grown on Si(111) and from $\sim $100 $\times $ 10$^{3}$ -- 700 $\times $ 10$^{3}$ nm$^{2}$ when grown on Si(100). Conducting tip atomic force microscopy ($c$-AFM) has been used to record current-voltage (I-V) curves from the nanoislands at several temperatures between room temperature and $\sim $-200$^{\circ}$C. The I-V curves are analyzed using thermionic emission theory to determine the Schottky barrier height, $\Phi _{B}$, and the ideality factor, n, of the nanoislands. Room temperature values of $\Phi_{B}$ and n are found to be in the range of 0.35 -- 0.63 eV and 1.1 -- 1.8, respectively. Comparisons of $\Phi_{B}$ and n are performed for nanoislands of different shapes, and the temperature dependence of both $\Phi_{B}$ and n is analyzed. Richardson plots for the nanoislands are created and found to be non-linear at low temperature. The nanoislands were etched off the silicon surface using \textit{ex} \textit{situ} hydrofluoric acid (HF) etching and AFM was used to examine the shape of the nanoisland-substrate interfaces, and nanoisland properties are that shape. [Preview Abstract] |
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HB.00009: TiO2 Films on Si(111) by Dilute Aqueous Chemical Bath Deposition J.F. Anderson, Erie Morales, Aaron Hamilton, Ulrike Diebold Dilute Aqueous Chemical Bath Deposition (CBD) from highly acidic (pH $<$ 1) TiCl$_{3}$ HCl solutions at room temperature and slightly higher (23$^{o}$C -- 40$^{o}$C) produced thin titanium dioxide films on clean Si(111). We report initial results of X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy (SEM), and X-ray Diffraction (XRD). The films thicknesses varied from 300 nm to $\sim $ 1 $\mu$m. It was found that the films required annealing to ensure adherence to the Si(111) substrate. XRD showed that the rutile structure was present in the TiO$_{2}$. [Preview Abstract] |
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HB.00010: Effects of laser excitation saturation in measurements of biomolecule binding by FCS. You Li, Guoqing Shen, Lloyd M. Davis Fluorescence Correlation Spectroscopy (FCS) is a technique developed by physicists in the 1970's that is now widely used for determination of the nanomolar concentrations of fluorescently-labeled biomolecules within microliter-sized droplets of solutions. The conventional theory, which dates from the early papers, states that the amplitude of the autocorrelation function of fluctuations in the fluorescence signal is inversely proportional to the mean number of fluorescent molecules in the focused laser beam. However, we have recently shown that excitation saturation causes dependence of the autocorrelation function on laser power even in the limit of infinitesimal laser power, and thereby a bias in the determined concentration. Here we use computer simulations to investigate the effects of such bias on two-species concentration determinations for application to measurements of molecular binding in pharmaceutical drug discovery. [Preview Abstract] |
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HB.00011: Multiple Incidence Media in Ellipsometry to Determine Both Refractive Index `n' and Thickness `d' of Very Thin Dielectric Layers. Douglas Ngatunyi, Jeremy Peters, Hans Hallen Ellipsometry is a powerful technique for measuring thin film thickness and index of refraction, widely used in both industry and research. A limitation of the technique is found with ultrathin samples, for which errors in the derived values permit measurement of only one of the thickness or index of refraction, rather than both as for thicker samples. A value for the other must be assumed. We investigate the use of multiple input media to allow measurement of both parameters, the index of refraction and the thickness, of ultrathin films. In particular, air, water, and hexadecane were used as media. Standard ellipsometric analysis failed, but we determined both thickness and index with a modified method that minimizing the variation of the thickness over the measurements in all media. Samples used were PEDA and SiO$_{2}$. [Preview Abstract] |
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HB.00012: Characterization of 4-foci pulse-interleaved two-photon fluorescence confocal microscope for particle tracking and trapping James Germann, Alexander Terekhov, Guoqing Shen, Lloyd Davis Single fluorescent biomolecules may be readily detected in a confocal fluorescence microscope as they are transported through a tightly focused laser beam. For many applications, two-photon excitation by femtosecond laser pulses provides a key advantage in that the sample excitation is confined to the center of the focal spot. We are examining means to extend the confocal microscope to provide information on the position and trajectory of particles as they traverse the probe volume. We have set up a femtosecond Ti-Sapphire laser, dispersion pre-compensation optics, and double Michelson interferometer to create four beams of temporally interleaved pulses, which enter a confocal microscope so as to produce four foci centered at the vertices of a tetrahedron. We report experiments to adjust and measure the irradiance profile produced by each beam, and the net irradiance from the combination. A 3-D piezoelectric nano-translation stage under LabView control is used to translate a target through the laser foci. Fluorescence, or scattered light, may be imaged to a camera, or to a single-photon counting module. We explain how time-resolved photon counting may be used with maximum-likelihood analysis to determine the position of a particle as it is translated through the probe volume. [Preview Abstract] |
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HB.00013: Angle-resolved spatial and compositional variations in pulsed- electron-beam deposited thin films Andrew Steigerwald, Richard Mu Pulsed electron deposition (PED) is a novel thin film growth technique that utilizes short, high-energy electron pulses to ablate material at a target surface. We report experimental evidence of angular dependent variations in particle-flux and composition within the ablated plume. These results are discussed within the framework of a model for a similar technique, pulsed laser deposition. Film thickness profiles are fitted to $Cos(\theta )^p$ and $A\cdot (1+k^2\cdot Tan(\theta )^2)^{-(3/2)}$ curves, representing effusive source models and an adiabatic expansion model, respectively. Similarities between the PED and PLD processes are highlighted. Understanding plume dynamics and its consequences on local film structure will lead to higher quality films, increased innovation in deposition techniques, and advancement of PED as a promising candidate for industrial thin film growth. [Preview Abstract] |
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HB.00014: Kirchhoff's Rule and the Two Capacitor Paradox H.L. Neal We demonstrate that Kirchhoff's rules are not applicable when considering the two capacitor paradox, where initially one capacitor is charged and the other is uncharged before the combination is discharged through a resistor. We also consider the general problem of analyzing $RC$ circuits where the capacitors are initially in different states of arbitrary charge. [Preview Abstract] |
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HB.00015: Polarization engineering of collected fluorescence for improved determination of the molecular emission dipole orientation in single-molecule spectroscopy Zbigniew Sikorski, Lloyd Davis In some single-molecule spectroscopy experiments we would like to target our measurements to molecules of specific orientation. We propose and numerically investigate phase and polarization engineering of the collected fluorescence field in a high numerical aperture confocal microscope to enable unambiguous detection of a specific molecule orientation. If the molecule is located within a fraction of a wavelength from a planar interface, such as a microscope cover-glass, then emission occurs preferentially into the interface at angles above the critical angle. This so-called forbidden light is in general elliptically polarized. Moreover, the field varies in phase and polarization across the pupil of the lens, no matter what the orientation of the emitting dipole may be. However, spatial light modulators may be used to transform the phase and polarization of the field so that for a selected molecule orientation the polarization becomes spatially homogeneous and linear. A polarizing beam splitter and two detectors are used to determine the polarization of the field. For the selected molecule emission dipole orientation, all photons will pass to one detector, while for other orientations photons will be statistically divided between the detectors. [Preview Abstract] |
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HB.00016: Characterization of Single-Photon Avalanche Diodes for Time-Resolved Single-Molecule Spectroscopy Jason King, Guoqing Shen, Lloyd Davis Experiments in single-molecule spectroscopy often use single-photon avalanche diodes that provide high quantum efficiency ($>$60{\%}) for detection of red fluorescence. However, current-model photon detector modules exhibit a count-rate dependent shift in the photon timing and a broadened single-photon timing distribution. Because the fluorescence photon emission rates in single-molecule experiments can rapidly shift from 10 to 10$^{6}$ photons/second, these timing errors can significantly deteriorate single-molecule measurements that are dependent on use of pulsed lasers and accurate photon timing. As the problem stems largely from the current design of active quenching circuits, new circuits and modified photon detector modules are under development to counteract this issue and minimize shifts, all while maintaining the required high quantum efficiency. Here, we describe an apparatus developed in our lab for testing and comparing several of these detectors over a wide range of count rates, and we report on ongoing measurements in order to better understand their timing characteristics. [Preview Abstract] |
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HB.00017: Multi-channel digital correlator and hardware simulator for fluorescence correlation spectroscopy, dynamic light scattering and multichannel photon time stamping Isaac Lescano, Lloyd Davis In fluorescence correlation spectroscopy and dynamic light scattering, digital correlators acquire the autocorrelation function of detected photons to measure diffusional dynamics of biomolecules and small particles. Multi-channel data from different wavelengths or scattering angles provides increased information for resolving multiple species. Similarly, in single-molecule spectroscopy and in experiments on photon entanglement, there is a need to acquire time stamps of photons from multiple detectors. To enable such advances, we have developed a cost-effective 16-channel correlator, and also a hardware simulator for a 16-channel photon detector for testing digital correlators, each based on a National Instruments R-series reconfigurable digital i/o card. The correlator scans 16 digital inputs each 6.25 ns for photon detector pulses and sends the photon time stamp and channel data to the host PC via a FIFO and 3 DMA channels, allowing $>$10$^{7}$ counts/s among the 16 channels. The PC calculates all autocorrelation and cross-correlations for logarithmically spaced delays in a real-time algorithm. The hardware simulator works in reverse: Simulated time stamp and channel data are sent by DMA to the card, which generates TTL pulses for the 16 digital outputs as though they came from 16 real photon detectors. [Preview Abstract] |
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HB.00018: X-Ray Fluorescence With a Krypton Gas Proportional Counter David Peterson X-Ray fluorescence analysis of potential meteorites can provide evidence of the typical iron and nickel content of certain classes of meteorites. The resolution of a Krypton-Carbon Dioxide filled proportional counter is sufficient to resolve the K X-rays of these low Z elements. The detector operates at room temperature, and the associated electronic circuit is simple and can be assembled quickly. [Preview Abstract] |
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HB.00019: Studying magnetic molecules with quantum Monte Carlo simulations Larry Engelhardt The term ``magnetic molecules'' refers to materials that contain a huge number ($\sim $10$^{22})$ of identical molecules that do not interact with one another, and which each exhibit magnetic properties of a distinctly quantum character. While the theory to describe such systems has been established for many decades, the computational complexity of the subsequent calculations still provides a significant challenge today. The typical computational approach involves diagonalizing matrices, whose sizes grow \textit{exponentially} with the size of the corresponding molecules. Because these matrices become extremely large, this approach cannot be applied to large molecules, even using the most advanced computers. We have avoided this obstacle by instead implementing a quantum Monte Carlo technique. We have used this technique to successfully model many recently synthesized magnetic molecules, even though, in some cases, the associated matrices would have been larger than 10$^{18}$ rows by 10$^{18}$ columns! Both the computational method and the subsequent analysis of physical systems will be summarized. [Preview Abstract] |
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HB.00020: Large Scale Computer Simulation of Erthocyte Membranes Cameron Harvey, Joel Revalee, Mohamed Laradji The cell membrane is crucial to the life of the cell. Apart from partitioning the inner and outer environment of the cell, they also act as a support of complex and specialized molecular machinery, important for both the mechanical integrity of the cell, and its multitude of physiological functions. Due to its relative simplicity, the red blood cell has been a favorite experimental prototype for investigations of the structural and functional properties of the cell membrane. The erythrocyte membrane is a composite quasi two-dimensional structure composed essentially of a self-assembled fluid lipid bilayer and a polymerized protein meshwork, referred to as the cytoskeleton or membrane skeleton. In the case of the erythrocyte, the polymer meshwork is mainly composed of spectrin, anchored to the bilayer through specialized proteins. Using a coarse-grained model, recently developed by us, of self-assembled lipid membranes with implicit solvent and using soft-core potentials, we simulated large scale red-blood-cells bilayers with dimensions $\sim $ 10$^{-1} \mu $m$^{2}$, with explicit cytoskeleton. Our aim is to investigate the renormalization of the elastic properties of the bilayer due to the underlying spectrin meshwork. [Preview Abstract] |
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HB.00021: Magnetic properties of ball milled Mn nanoparticles John Griffis, Sanjay Mishra, M. Khan, N. Ali, G. Marasingh Here in we report detail structural and magnetic properties of antiferromagnetic Mn nanoparticles prepared via mechanical ball milling. The surface defects in particle are induced by reducing the particle size and strain induced by ball milling. The x-ray diffraction measurement along with DSC suggests presence of Mn3O4 phase in the sample, a ferrimagnetic phase which increases with the milling time. Upon ball milling a decrease in the Curie temperature of Mn3O4 phase (Tc 42K) to a value Tc 35 K has been observed. A large coercive field at 25K and shifted hysteresis loops along the field and magnetization direction clearly indicates that the overall magnetic properties of the system are governed by surface defects on the particles. [Preview Abstract] |
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HB.00022: Force Production of \emph{Mastigocladus laminosus} Hormogonia W. Brad Robinson The cyanobacterium \textit{Mastigocladus laminosus }is a colonial bacterium living near hot springs in densely packed filaments of cells. Under certain conditions, some of these filaments break off and move away from the main body. These motile filaments, or \textit{hormogonia}, can move through extremely viscous environments by extruding slime out of nozzles in a process reminiscent of the gliding motility exhibited by some myxobacteria. The slime-producing nozzles of these hormogonia are apparently very powerful nano-scale motors. Through TEM, we have observed these 9nm diameter nozzles spaced at 21nm intervals arranged in concentric rings along the septa separating hormogonial cells. Assuming theis arrangement to be ubiquitous and that all anzzles are active, we were able to approximate the number of active nozzles per hormogonium (typically 10-100 thousand). We then observed hormogonia embedded in and moving through tremendously viscous 1-4{\%} agar solutions, and maintaining an average velocity of 0.5 microns per second. We then found the viscosities of these agar solutions at low shear rates appropriate for a gliding hormogonium and determined that the average force per nozzle was incredibly high, 71pN in 3{\%} agar, and 126pN in 4{\%}. [Preview Abstract] |
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HB.00023: Frontiers of Magnetism, Electric Field and Electron Studies Richard DeSantis There is evidence that does not support the idea that electrons are responsible for voltage. For example: current causes voltage in a resistor, but current does not change point charge concentration within the resistor. Therefore voltage is not point charge concentration. A Wimshurst generator provides evidence that voltage is fundamentally different than force between point charges. Stretching and compressing voltage gradients in a Wimshurst generator increases both voltage and current. Stretching and compressing the distance between point charges does not similarly increase both voltage and current. By definition, an electron volt is the amount of increase in electron kinetic energy that results when an electron passes though an electric field of one volt. The conversion is irreversible if point charge concentration energy is not voltage gradient energy. Irreversible conversion of voltage gradient energy to point charge kinetic energy means that atoms do not contain point charges. Atoms that contain point charges cannot store voltage gradient energy. All atoms have relative permittivity $>$1, thus can store voltage gradient energy. Point charges irreversibly deplete voltage gradient energy. If point charge repulsion energy completely converts to electron acceleration, nothing is left to convert to magnetic energy. If part of the electron acceleration energy converts to magnetic energy, electron velocity resulting from acceleration energy would be less than predicted. [Preview Abstract] |
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HB.00024: On the Microwave Signal at the Second Lagrange Point. Pierre-Marie Robitaille, Larissa Borissova, Dmitri Rabounski It has been proposed that the 2.7 K Penzias-Wilson monopole is of oceanic origin. Under this scenario, the signal should be powerful near the Earth and rapidly fall in power away from our planet. As a result, the Penzias and Wilson signal is not expected to have any significant intensity at the second Lagrange point. In July 2008, the ESA will launch the PLANCK mission to this location. The low Frequency Instrument (LFI) on PLANCK is operating as a group of pseudo-correlation receivers. Since the 2.7 K signal will not be found at L2, an analytical analysis of the PLANCK LFI reveals that the knee frequency of the radiometers will rise to $\sim $50 mHz, well above the 3-7 mHz levels expected by the PLANCK team and substantially above the satellite spin frequency of $\sim $17 mHz. This will result in the production of significant stripes in the raw maps generated, potentially impacting the harvest from PLANCK. Calculations reveal that little difference exists in the intensity of the 2.7 K field, either at the position of a U2 plane (25 km), or in the COBE orbit (900 km). However, the density of the energy of the field drops to $\sim $10$^{-7}$ of these near Earth values at the L2 point, rendering detection improbable. Since the LFI on PLANCK can operate either in absolute or difference mode and since the HFI operate as bolometers, PLANCK should unequivocally ascertain the origin of the 2.7K monopole. [Preview Abstract] |
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