Laser vibrometry on solid surfaces : the effects of laser speckle

This letter discusses the phase and amplitude modulation of Doppler signals generated in laser Doppler velocimetry (LDV) systems with reference to the paper entitled 'Dynamic laser Doppler velocimetry on solid surfaces' by Rajadhyaksha and Stevenson (Vol. 4 No. 2). In particular, transit time and velocity gradient frequency broadenings are described in terms of the speckle pattern behavior on the photodetector and this approach is reconciled with the scattering element approach adopted by Rajadhyaksha and Stevenson. Furthermore, it is described how the frequency components of the Doppler phase noise can coincide with the vibration components of interest, thereby introducing ambiguity in interpretation of data. As a consequence, the reduction of Doppler phase noise by averaging is not generally acceptable. It is concluded that consideration of the dynamic speckle pattern is more appropriate to the investigation of Doppler phase noise since the speckle pattern itself has the ultimate influence on the LDV performance

The role of intermolecular coupling in the photophysics of disordered organic semiconductors: Aggregate emission in regioregular polythiophene

We address the role of excitonic coulping on the nature of photoexcitations in the conjugated polymer regioregular poly(3-hexylthiophene). By means of temperature-dependent absorption and photoluminescence spectroscopy, we show that optical emission is overwhelmingly dominated by weakly coupled H-aggregates. The relative absorbance of the 0-0 and 0-1 vibronic peaks provides a powerfully simple means to extract the magnitude of the intermolecular coupling energy, approximately 5 and 30 meV for films spun from isodurene and chloroform solutions respectively.Comment: 10 pages, 4 figures, published in Phys. Rev. Let

Ultra Low Momentum Neutron Catalyzed Nuclear Reactions on Metallic Hydride Surfaces

Ultra low momentum neutron catalyzed nuclear reactions in metallic hydride system surfaces are discussed. Weak interaction catalysis initially occurs when neutrons (along with neutrinos) are produced from the protons which capture ``heavy'' electrons. Surface electron masses are shifted upwards by localized condensed matter electromagnetic fields. Condensed matter quantum electrodynamic processes may also shift the densities of final states allowing an appreciable production of extremely low momentum neutrons which are thereby efficiently absorbed by nearby nuclei. No Coulomb barriers exist for the weak interaction neutron production or other resulting catalytic processes.Comment: 4 pages, ReVTeX forma

Polarization dependence of four-wave mixing in a degenerate two-level system

Nearly degenerate four-wave mixing (NDFWM) within a closed degenerate two-level atomic transition is theoretically and experimentally examined. Using the model presented by A. Lezama et al [Phys. Rev. A 61, 013801 (2000)] the NDFWM spectra corresponding to different pump and probe polarization cases are calculated and discussed. The calculated spectra are compared to the observation of NDFWM within the $6S_{1/2}(F=4)\to 6P_{3/2}(F=5)$ transition of cesium in a phase conjugation experiment using magneto optically cooled atomsComment: 10 pages, 13 figures; submitted to Phys. Rev.

The Globular Cluster Systems around NGC 3311 and NGC 3309

We present extensive new photometry in (g',i') of the large globular cluster (GC) system around NGC 3311, the central cD galaxy in the Hydra cluster. Our GMOS data cover a 5.5' field of view and reach a limiting magnitude i' = 26, about 0.5 magnitude fainter than the turnover point of the GC luminosity function. We find that NGC 3311 has a huge population of ~16, 000 GCs, closely similar to the prototypical high specific frequency Virgo giant M87. The color-magnitude distribution shows that the metal-poor blue GC sequence and the metal-richer red sequence are both present, with nearly equal numbers of clusters. Bimodal fits to the color distributions confirm that the blue sequence shows the same trend of progressively increasing metallicity with GC mass that has previously been found in many other large galaxies; the correlation we find corresponds to a scaling of GC metallicity with mass of Z ~ M^0.6 . By contrast, the red sequence shows no change of mean metallicity with mass, but it shows an upward extension to much higher than normal luminosity into the UCD-like range, strengthening the potential connections between massive GCs and UCDs. The GC luminosity function, which we measure down to the turnover point at M_I = -8.4, also has a normal form like those in other giant ellipticals. Within the Hydra field, another giant elliptical NGC 3309 is sitting just 100" from the cD NGC 3311. We use our data to solve simultaneously for the spatial structure and total GC populations of both galaxies at once. Their specific frequencies are S_N (NGC 3311) = 12.5 +/- 1.5 and S_N (NGC 3309) = 0.6 +/-0.4. NGC 3311 is completely dominant and entirely comparable with other cD-type systems such as M87 in Virgo.Comment: 15 pages, 15 figures. Accepted to the Astrophysical Journal. Version with higher resolution figures is available at http://www.thewehners.net/astro/papers/wehner_n3311_highres.pd

On laser vibrometry of rotating targets: effects of torsional and in-plane motion

Vibration measurements on rotating surfaces are often referred to in ·the commercial literature as a major application of laser Doppler vibration transducers. This paper examines such use of these instruments and shows how the presence of a velocity component due to the rotation itself leads to spurious measurement dependence on both torsional vibration and motion perpendicular to the line of incidence of the laser beam. In addition, the scale of this dependence increases with both rotation speed and perpendicular distance between the line of incidence and a parallel line through the centre of rotation. These phenomena are investigated theoretically and excellent agreement is found when compared with experimental data. Two solutions are suggested; the first involves careful alignment of the laser beam whereas the second requires two simultaneous, orthogonal measurements to be made. If neither method is adopted it is entirely conceivable that the intended solid body vibration measurement may be masked at many frequencies of interest

Emission-Line Galaxies from the Hubble Space Telescope Probing Evolution and Reionization Spectroscopically (PEARS) Grism Survey. II: The Complete Sample

We present a full analysis of the Probing Evolution And Reionization Spectroscopically (PEARS) slitess grism spectroscopic data obtained with the Advanced Camera for Surveys on HST. PEARS covers fields within both the Great Observatories Origins Deep Survey (GOODS) North and South fields, making it ideal as a random survey of galaxies, as well as the availability of a wide variety of ancillary observations to support the spectroscopic results. Using the PEARS data we are able to identify star forming galaxies within the redshift volume 0< z<1.5. Star forming regions in the PEARS survey are pinpointed independently of the host galaxy. This method allows us to detect the presence of multiple emission line regions (ELRs) within a single galaxy. 1162 Ha, [OIII] and/or [OII] emission lines have been identified in the PEARS sample of ~906 galaxies down to a limiting flux of ~1e-18 erg/s/cm^2. The ELRs have also been compared to the properties of the host galaxy, including morphology, luminosity, and mass. From this analysis we find three key results: 1) The computed line luminosities show evidence of a flattening in the luminosity function with increasing redshift; 2) The star forming systems show evidence of disturbed morphologies, with star formation occurring predominantly within one effective (half-light) radius. However, the morphologies show no correlation with host stellar mass; and 3) The number density of star forming galaxies with M_* > 1e9} M_sun decreases by an order of magnitude at z<0.5 relative to the number at 0.5<z<0.9 in support of the argument for galaxy downsizing.Comment: Submitted. 48 pages. 19 figures. Accepted to Ap

Analysis of paediatric prescribing profiles in two health-funding systems

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Evidence for Excimer Photoexcitations in an Ordered {\pi}-Conjugated Polymer Film

We report pressure-dependent transient picosecond and continuous-wave photomodulation studies of disordered and ordered films of 2-methoxy-5-(2-ethylhexyloxy) poly(para-phenylenevinylene). Photoinduced absorption (PA) bands in the disordered film exhibit very weak pressure dependence and are assigned to intrachain excitons and polarons. In contrast, the ordered film exhibits two additional transient PA bands in the midinfrared that blueshift dramatically with pressure. Based on high-order configuration interaction calculations we ascribe the PA bands in the ordered film to excimers. Our work brings insight to the exciton binding energy in ordered films versus disordered films and solutions. The reduced exciton binding energy in ordered films is due to new energy states appearing below the continuum band threshold of the single strand.Comment: 5.5 pages, 5 figure