Sample records for attenuation coefficient lac

  1. Attenuation coefficients of Rayleigh and Lg waves

    Microsoft Academic Search

    Igor B. Morozov

    2010-01-01

    Analysis of the frequency dependence of the attenuation coefficient leads to significant changes in interpretation of seismic\\u000a attenuation data. Here, several published surface-wave attenuation studies are revisited from a uniform viewpoint of the temporal\\u000a attenuation coefficient, denoted by ?. Theoretically, ?( f) is expected to be linear in frequency, with a generally non-zero intercept ??=??(0) related to the variations of

  2. Measurements of Gamma-Ray Attenuation Coefficients

    Microsoft Academic Search

    B. Goswami; N. Chaudhuri

    1973-01-01

    Measurements have been made to determine gamma-ray attenuation coefficients very accurately by using an extremely-narrow-collimated-beam transmission method which effectively excluded corrections due to small-angle and multiple scattering of photons. The measured mass attenuation coefficients with maximum errors less than 3% for 34 elements in the range from hydrogen to lead are given.

  3. Gamma-Ray Attenuation Coefficient Measurements

    Microsoft Academic Search

    S. Gopal; B. Sanjeevaiah

    1973-01-01

    In an earlier paper, published by the authors elsewhere, it was shown that for 661.6-keV gamma rays the measurements of gamma-ray attenuation coefficients would greatly improve if one uses the counting sequence of Conner et al. together with a new criterion mut<1, where mu is the gamma-ray attenuation coefficient and t is the thickness of the sample. In this paper

  4. Measurement of $gamma$-ray attenuation coefficients

    Microsoft Academic Search

    Christmas

    1974-01-01

    Gamma-ray attenuation coefficients have been determined for aluminum, ; copper, tin, platinum and lead (elements with Z between 13 and 82) using gamma -; rays with energies between 295 and 2440 keV from a sealed Ra-226 source. A ; lithium-drifted germanium detector was employed without collimation or shielding. ; The average standard error of the experimental results was 1%. (auth)

  5. Unbiased Estimation of Atmosphere Attenuation Coefficient

    Microsoft Academic Search

    G. D. Dikic; Z. M. Djurovic

    2007-01-01

    According to the passive sensors’ nature, only the azimuth and elevation angles are used for the target state estimation.\\u000a In some scenarios, additional information like the irradiances generated by the passive sensors must be introduced to improve\\u000a the estimation process. On the other hand, irradiances are strongly dependent on the atmosphere properties that may be described\\u000a by attenuation coefficient. An

  6. Linear attenuation coefficients for compensator based imrt

    Microsoft Academic Search

    T. Bartrum; M. Bailey; V. Nelson; M. Grace

    2007-01-01

    With rapid technological improvements in computer driven 3-D radiotherapy treatment planning systems (RTPS) the use of compensating\\u000a filters for intensity modulated radiation therapy (IMRT) will dramatically increase the ease of treatment. The procedure for\\u000a commissioning .decimal™ (Sanford, Florida) compensators involved the measurement of the effective linear attenuation coefficients\\u000a for aluminium and brass. Field sizes to be measured vary from small

  7. Gamma-Ray Attenuation-Coefficient Measurements

    Microsoft Academic Search

    A. L. Conner; H. F. Atwater; Elizabeth H. Plassmann; J. H. McCrary

    1970-01-01

    Total gamma-ray attenuation coefficients have been measured at nine energies in the range of 88 keV to 2.75 MeV for the following elements: Be, C, Mg, Al, S, Ti, Fe, Ni, Cu, Zn, Zr, Nb, Mo, Ag, Sn, La, Gd, Hf, W, Au, Pb, Th, U, and Pu. Radioactive isotopes were used as sources of monoenergetic gamma radiation in a

  8. Gamma-ray attenuation coefficients for human tissues

    Microsoft Academic Search

    P S Rao; E C Gregg

    1974-01-01

    The diagnosis of soft tissue disease such as cancer by radiographic means depends to some extent on the difference in the attenuation of gamma -rays in healthy and diseased tissues. Since devices for imaging very small changes in attenuation are now being introduced, a more exact knowledge of such attenuation coefficients in various tissues would be of help in the

  9. Gamma Ray Attenuation Coefficient of Microalloyed Stainless Steel

    Microsoft Academic Search

    I. Akkurt; H. Aky?ld?r?m; A. Calik; O. B. Aytar; N. Uçar

    2011-01-01

    Gamma ray attenuation coefficients of microalloyed steel have been investigated. For this purposes the linear attenuation\\u000a coefficients of steel have been measured at the photon energy of 0.662, 1.173 and 1.332 MeV and the results were compared\\u000a with the calculation at the photon energy of 1–105 MeV obtained using XCOM.

  10. Optical attenuation coefficient in individual ZnO nanowires.

    PubMed

    Little, Anree; Hoffman, Abigail; Haegel, Nancy M

    2013-03-11

    Attenuation coefficient measurements for the propagation of bandedge luminescence are made on individual ZnO nanowires by combining the localized excitation capability of a scanning electron microscope (SEM) with near-field scanning optical microscopy (NSOM) to record the distribution and intensity of wave-guided emission. Measurements were made for individual nanostructures with triangular cross-sections ranging in diameter from 680 to 2300 nm. The effective attenuation coefficient shows an inverse dependence on nanowire diameter (d(-1)), indicating scattering losses due to non-ideal waveguiding behavior. PMID:23482201

  11. Measurement of Acoustic Attenuation and Absorption Coefficients using Thermometry

    Microsoft Academic Search

    Hugh Morris; Ian Rivens; Adam Shaw; Gail Ter Haar

    2007-01-01

    Accurate knowledge of both the attenuation and the absorption coefficient of tissue are required when planning an optimal high intensity focused ultrasound treatment. A novel technique for simple measurement of this parameters has been developed in which a thin-film thermocouple (TFT) is placed between two layers of tissue of different thicknesses. The sample can be rotated about an axis through

  12. Gamma-ray attenuation coefficients in bismuth borate glasses

    Microsoft Academic Search

    Kulwant Singh; Harvinder Singh; Vishal Sharma; Rohila Nathuram; Atul Khanna; Rajesh Kumar; Surjit Singh Bhatti; Hari Singh Sahota

    2002-01-01

    Mass attenuation coefficients of glasses in the system: xBi2O3(1?x)B2O3 (x=0.30, 0.35, 0.40, 0.45 and 0.55) were determined at 356, 662, 1173 and 1332 keV photon energies using a narrow beam transmission method. Appreciable variations were observed in these coefficients due to changes in the chemical composition of glasses. These coefficients were then used to determine effective atomic numbers of glass

  13. Gamma ray attenuation coefficient measurement for neutron-absorbent materials

    Microsoft Academic Search

    Majid Jalali; Ali Mohammadi

    2008-01-01

    The compounds Na2B4O7, H3BO3, CdCl2 and NaCl and their solutions attenuate gamma rays in addition to neutron absorption. These compounds are widely used in the shielding of neutron sources, reactor control and neutron converters. Mass attenuation coefficients of gamma related to the four compounds aforementioned, in energies 662, 778.9, 867.38, 964.1, 1085.9, 1173, 1212.9, 1299.1,1332 and 1408keV, have been determined

  14. Simultaneous estimation of ultrasonic wave speed, sample thickness, attenuation coefficient, and reflection coefficient

    NASA Astrophysics Data System (ADS)

    Kinzie, Aaron Wagner

    Acoustic wave speed, sample thickness, acoustic attenuation coefficient, and acoustic reflection coefficient are routinely estimated for materials characterization and flaw detection. Previous work at MU yielded a new technique to estimate the wave speed and sample thickness simultaneously. Prior work at MU has also lead to a new approach for simultaneous estimation of attenuation and reflection coefficients given prior knowledge of the sample wave speed and thickness. The research reported in this thesis shows that the simultaneous wave speed and sample thickness estimation technique can be combined with the simultaneous attenuation and reflection coefficient estimation approach. Once the wave speed and Reflection coefficient are estimated the material density can also be estimated. This study shows that without prior knowledge of a sample's properties, it is possible to estimate thickness, acoustic wave speed, acoustic attenuation coefficient, and acoustic reflection coefficient. This is shown theoretically and demonstrated experimentally. The models used are for an isotropic material with a sample of plate type geometry. This is a single sided approach using pulse-echo ultrasonic techniques. The technique utilizes axial scans to find equal diffraction points of interface reflections. The knowledge of the location in the water path length of the equal diffraction points of the interface reflections allows for the estimation of the wave speed and thickness of the sample. Data at the equal diffraction points is then used to calculate the attenuation and reflection coefficients simultaneously. Validity of the combined approach is demonstrated experimentally. Measurement procedures and data processing methods are detailed. Results are given for plastic, copper, and quartz samples. These results are shown with different broadband focused transducers with nominal center frequencies of 5, 10, and 15MHz.

  15. Changes in the linear attenuation coefficient of canine appendicular bone following intravenous infusion of strontium lactate, measured using gamma-ray computed tomography

    Microsoft Academic Search

    Thomas R. Overton; Richard E. Snyder; Thomas N. Hangartner; Safwat Girgis; Robert J. Audette; David C. Secord

    1992-01-01

    Changes in the average linear attenuation coefficient (LAC) within a fixed measurement volume in the proximal end of the dog tibia, which contains trabecular bone and associated soft tissues (the trabecular bone “space”), were monitored continuously using gamma-ray computed tomography (?-CT) prior to, during, and following intravenous infusion of strontium (Sr) lactate. An infusion of 1.3–4.7 g of Sr over

  16. Investigations of the attenuation coefficient of a narrow-bandwidth pulsed laser beam in water

    Microsoft Academic Search

    Jianhui Bai; Juan Liu; Yi Huang; Yinan Liu; Lu Sun; Dahe Liu; E. S. Fry

    2007-01-01

    The attenuation coefficient of a pulsed laser beam in water is investigated experimentally. It is found that the attenuation coefficient is dependent on the pulse energy and the linewidth of the laser, rather than a constant. The attenuation coefficient for a narrow linewidth laser can exceed that of a broad linewidth laser due to stimulated Brillouin scattering when the laser

  17. Temporal Variations of Seismic Coda: Attenuation-Coefficient View

    NASA Astrophysics Data System (ADS)

    Morozov, I. B.

    2010-12-01

    When monitoring spatial or temporal variations of the subsurface, it is important to use properties that objectively exist and are insensitive to observational uncertainties. Although the frequency-dependent seismic coda quality factor, Qc is often found to change prior and following relation to major earthquakes and volcanic eruptions, it does not represent such a property. Qc is strongly dependent on the assumed theoretical models, which are usually insufficiently accurate for constraining the actual relationships between the geometrical spreading, anelastic dissipation, and scattering of seismic waves. This inaccuracy often leads to significant exaggeration of attenuation effects, and particularly to interpretations of temporal variations in Qc as related to changes in lithospheric scattering. To overcome this bias, we use an approach based on the temporal attenuation-coefficient, ?(f), instead of Q(f) for describing coda attenuation. Several attenuation case studies suggest that ?(f) typically linearly depends on f, with both the intercept ? = ?(0) and slope d?(f)/df = ?Qe-1 being sensitive to the physical state of the subsurface. Two published examples of temporal variations of local-earthquake coda Q are revisited: non-volcanic (near Stone Canyon in central California) and volcanic (Mt. St. Helens, Washington). In both cases, linear ?(f) patterns are found, with the effects of geometrical spreading (?) on coda attenuation being significantly stronger than those of Qe-1. At Stone Canyon, ? values ranged from 0.035 to 0.06 s-1 and Qe varies from 3000 to 10000, with ? increasing and Qe decreasing during the winter season. At Mt. St. Helens, ? ? 0.18 s-1, and Qe changed from 400 before the eruption to 750 after it. The observed temporal variations are explained by near-surface effects (seasonal variations in the non-volcanic case and gas-, magma-, and geothermal-system related in the volcanic case),which mostly affect the geometrical spreading and anelastic attenuation. Scattering does not appear to be a significant attenuation factor in these areas, or otherwise it may be indistinguishable from the intrinsic attenuation in the data.

  18. Apparent Linear Attenuation Coefficients in Phase Contrast X-Ray Tomography

    PubMed Central

    Yan, Aimin; Wu, Xizeng

    2011-01-01

    In the inline phase contrast x-ray tomography the reconstructed apparent linear attenuation coefficient values may be greatly larger than sample’s linear attenuation coefficients or even be negative. In this work we present a general formula to quantitatively relate the apparent linear attenuation coefficient values in cone-beam phase contrast tomography to sample’s linear attenuation coefficients and refractive indices. This formula overcomes the gross inaccuracy of the existing formula in the literature in analyzing high-resolution phase contrast tomography, and it will be useful for correctly interpreting and quantifying the apparent linear attenuation coefficients in cone-beam x-ray phase contrast tomography. PMID:21691420

  19. Measurement of Acoustic Attenuation and Absorption Coefficients using Thermometry

    NASA Astrophysics Data System (ADS)

    Morris, Hugh; Rivens, Ian; Shaw, Adam; ter Haar, Gail

    2007-05-01

    Accurate knowledge of both the attenuation and the absorption coefficient of tissue are required when planning an optimal high intensity focused ultrasound treatment. A novel technique for simple measurement of this parameters has been developed in which a thin-film thermocouple (TFT) is placed between two layers of tissue of different thicknesses. The sample can be rotated about an axis through the junction of the TFT so that it can be insonated from either side leaving the tissue adjacent to the junction unchanged, but changing the overlying thickness. The attenuation and absorption coefficients can be calculated from the heating curves measured in the two orientations. Experiments have been carried out in both tissue mimicking material (TMM) and in ex vivo liver tissue. Weakly focused transducers, resonant at 1.05 MHz, 2.4 MHz and 3.55 MHz were used at free-field spatial peak intensities of 9-14 W/cm2. The temperature rise was measured as a function of time using a TFT. These thermocouples are not subject to the viscous heating artefact that is common to other thermocouple devices and so are advantageous for this purpose. Alignment was achieved with a 3D automated gantry system, which was controlled with specialised software. Timing and data acquisition were also controlled with this software. All experiments were carried out in degassed water. Results for TMM and degassed excised bovine liver are presented.

  20. PET attenuation coefficients from CT images: experimental evaluation of the transformation of CT into PET 511keV attenuation coefficients

    Microsoft Academic Search

    C. Burger; G. Goerres; S. Schoenes; A. Buck; A. Lonn; G. von Schulthess

    2002-01-01

    The CT data acquired in combined PET\\/CT studies provide a fast and essentially noiseless source for the correction of photon attenuation in PET emission data. To this end, the CT values relating to attenuation of photons in the range of 40-140 keV must be transformed into linear attenuation coefficients at the PET energy of 511 keV. As attenuation depends on

  1. Uranium soft x-ray total attenuation coefficients

    SciTech Connect

    Del Grande, N.K.; Oliver, A.J.

    1981-01-01

    Uranium total attenuation coefficients were measured continuously from 0.84 to 6.0 keV and at selected higher energies using a vacuum single crystal diffractometer and flow-proportional counter. Statistical fluctuations ranged from 0.5% to 2%. The overall accuracy was 3%. Prominent structure was measured within 20 eV of the M/sub 5/ (3.552 keV) and M/sub 4/ (3.728 keV) edges. Jump ratios were determined from log-log polynomial fits to data at energies apart from the near-edge regions. These data were compared with calculations based on a relativistic HFS central potential model and with previously tabulated data.

  2. Representative Elementary Length to Measure Soil Mass Attenuation Coefficient

    PubMed Central

    Borges, J. A. R.; Pires, L. F.; Costa, J. C.

    2014-01-01

    With increasing demand for better yield in agricultural areas, soil physical property representative measurements are more and more essential. Nuclear techniques such as computerized tomography (CT) and gamma-ray attenuation (GAT) have been widely employed with this purpose. The soil mass attenuation coefficient (?s) is an important parameter for CT and GAT analysis. When experimentally determined (?es), the use of suitable sized samples enable to evaluate it precisely, as well as to reduce measurement time and costs. This study investigated the representative elementary length (REL) of sandy and clayey soils for ?es measurements. Two radioactive sources were employed (241Am and 137Cs), three collimators (2–4?mm diameters), and 14 thickness (x) samples (2–15?cm). Results indicated ideal thickness intervals of 12–15 and 2–4?cm for the sources 137Cs and 241Am, respectively. The application of such results in representative elementary area (REA) evaluations in clayey soil clods via CT indicated that ?es average values obtained for x?>?4?cm and source 241Am might induce to the use of samples which are not large enough for soil bulk density evaluations (?s). As a consequence, ?s might be under- or overestimated, generating inaccurate conclusions about the physical quality of the soil under study. PMID:24672338

  3. Representative elementary length to measure soil mass attenuation coefficient.

    PubMed

    Borges, J A R; Pires, L F; Costa, J C

    2014-01-01

    With increasing demand for better yield in agricultural areas, soil physical property representative measurements are more and more essential. Nuclear techniques such as computerized tomography (CT) and gamma-ray attenuation (GAT) have been widely employed with this purpose. The soil mass attenuation coefficient (?(s)) is an important parameter for CT and GAT analysis. When experimentally determined (?(es)), the use of suitable sized samples enable to evaluate it precisely, as well as to reduce measurement time and costs. This study investigated the representative elementary length (REL) of sandy and clayey soils for ?(es) measurements. Two radioactive sources were employed ((241)Am and (137)Cs), three collimators (2-4 mm diameters), and 14 thickness (x) samples (2-15 cm). Results indicated ideal thickness intervals of 12-15 and 2-4 cm for the sources (137)Cs and (241)Am, respectively. The application of such results in representative elementary area (REA) evaluations in clayey soil clods via CT indicated that ?(es) average values obtained for x > 4 cm and source (241)Am might induce to the use of samples which are not large enough for soil bulk density evaluations (?(s)). As a consequence, ?(s) might be under- or overestimated, generating inaccurate conclusions about the physical quality of the soil under study. PMID:24672338

  4. EVALUATION OF SATELLITE DERIVED SPECTRAL DIFFUSE ATTENUATION COEFFICIENTS

    Microsoft Academic Search

    T. Suresh; Madhubala Talaulikar; Elgar Desa; Antonio Mascaranhas; S. G. Prabhu

    2007-01-01

    Spectral diffuse attenuation Kd(?) is an important apparent optical property that provide information about the attenuation of the spectral downwelling solar irradiance with depth in water. Here we have compared the spectral Kd(?) at ?= 412, 443, 490, 510, 555 and 670 nm derived from the ocean color satellite sensor, SeaWiFS with the in-situ measured values from the Arabian Sea.

  5. Monitoring changes of optical attenuation coefficients of acupuncture points during laser acupuncture by optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Huang, Yimei; Yang, Hongqin; Wang, Yuhua; Zheng, Liqin; Xie, Shusen

    2010-11-01

    The physical properties of acupuncture point were important to discover the mechanism of acupuncture meridian. In this paper, we used an optical coherence tomography to monitor in vivo the changes of optical attenuation coefficients of Hegu acupuncture point and non-acupuncture point during laser irradiation on Yangxi acupuncture point. The optical attenuation coefficients of Hegu acupuncture point and non-acupuncture point were obtained by fitting the raw data according to the Beer-Lambert's law. The experimental results showed that the optical attenuation coefficient of Hegu acupuncture point decreased during the laser acupuncture, in contrast to a barely changed result in that of non-acupuncture point. The significant change of optical attenuation coefficient of Hegu acupuncture point indicated that there was a correlation between Hegu and Yangxi acupuncture points to some extent.

  6. NXcom – A program for calculating attenuation coefficients of fast neutrons and gamma-rays

    Microsoft Academic Search

    A. M. El-Khayatt

    2011-01-01

    This work is concerned with a construction and use of NXcom computer program for calculating the removal and attenuation coefficients of transmitted fast neutrons and ?-rays, respectively, through mixtures, composites, concretes and compounds. The program uses only one input data file for neutrons and ?-rays calculations. For ?-ray attenuation, the program predictions were tested by comparing them with the well-known

  7. Measurement of atomic number and mass attenuation coefficient in magnesium ferrite

    Microsoft Academic Search

    R. H. Kadam; S. T. Alone; G. K. Bichile; K. M. Jadhav

    2007-01-01

    Pure magnesium ferrite sample was prepared by standard ceramic technique and characterized by X-ray diffraction method. XRD pattern revealed that the sample possess single-phase cubic spinel structure. The linear attenuation coefficient (mu), mass attenuation coefficient (mu\\/rho), total atomic cross-section (sigma_{tot}), total electronic cross-section (sigma_{ele}) and the effective atomic number (Z_{eff}) were calculated for pure magnesium ferrite (MgFe_{2}O_{4}). The values of

  8. A Precision Measurement of some Attenuation Coefficients for 1.33 MeV Gamma Rays

    Microsoft Academic Search

    A-M Roux

    1976-01-01

    Measurements of some mass attenuation coefficients for 1.33 MeV ? radiation of 60Co have been performed in excellent narrow beam collimated geometry. The mass attenuation coefficient of aluminum was determined from the experimental transmission curve with a good accuracy (less than 2 × 10-3) and the value obtained was then used as a reference for other elements or compounds: copper,

  9. A method to determine the gamma-ray linear attenuation coefficient

    Microsoft Academic Search

    C. Celiktas

    2011-01-01

    In this work, gamma-ray linear attenuation coefficients of the materials such as Pb, Fe, Cu and Al were determined by means of traditional energy method and the developed timing detection technique. 1.33MeV-energy radiation emitted from 60Co radioisotope was used in the experiments. The gamma-ray linear attenuation coefficient values of the materials were calculated by using Xcom code, and the experimental

  10. A Precision Measurement of some Attenuation Coefficients for 1.33 MeV Gamma Rays

    Microsoft Academic Search

    A.-M. Roux

    1976-01-01

    Measurements of some mass attenuation coefficients for 1.33 MeV gamma radiation of 60Co have been performed in excellent narrow beam collimated geometry. The mass attenuation coefficient of aluminum was determined from the experimental transmission curve with a good accuracy (less than 2 × 10-3) and the value obtained was then used as a reference for other elements or compounds: copper,

  11. Study of effective atomic numbers and mass attenuation coefficients in some compounds

    Microsoft Academic Search

    K. Singh; Rajinderjit Kaur; Vandana Kumar; Vijay Kumar

    1996-01-01

    The effective atomic numbers and mass attenuation coefficients of some different compounds for total and partial photon interactions have been calculated in the energy range 10?2–105 MeV. The effective atomic numbers and mass attenuation coefficients have also been determined experimentally in the energy range 123–1132 keV by a transmission method. Experimental and theoretical values are in good agreement. The values

  12. ATTENUATION COEFFICIENTS FOR GAMMA RAYS FROM Co⁶°

    Microsoft Academic Search

    S. S. R. Sastry; S. Jnanananda

    1958-01-01

    Attention coefficients in seven different alloys and in Perspex for the ; 1.1715 and 1.3316 Mev gamma radiations from a 17 mc Co⁶° source have been ; estimated by the method of least squares, employing the narrow beam geometry of ; Davisson and Evans with provision for accurate collimation. The experimental ; values for the coefficients and the theoretical values,

  13. FREQUENCY DEPENDENT ULTRASONIC ATTENUATION COEFFICIENT ASSESSMENT IN FRESH

    E-print Network

    Illinois at Urbana-Champaign, University of

    states that the Langevin radiation pressure on a perfectly absorbing target in an open vessel is 2-PL the speed of sound in the medium (1). Multiplying Langevin radiation pressure by the area of the sound beam. Multiplying that force by the speed of sound yields total acoustic power. Attenuation measurements can be made

  14. Comparison of RNFL thickness and RPE-normalized RNFL attenuation coefficient for glaucoma diagnosis

    NASA Astrophysics Data System (ADS)

    Vermeer, K. A.; van der Schoot, J.; Lemij, H. G.; de Boer, J. F.

    2013-03-01

    Recently, a method to determine the retinal nerve fiber layer (RNFL) attenuation coefficient, based on normalization on the retinal pigment epithelium, was introduced. In contrast to conventional RNFL thickness measures, this novel measure represents a scattering property of the RNFL tissue. In this paper, we compare the RNFL thickness and the RNFL attenuation coefficient on 10 normal and 8 glaucomatous eyes by analyzing the correlation coefficient and the receiver operator curves (ROCs). The thickness and attenuation coefficient showed moderate correlation (r=0.82). Smaller correlation coefficients were found within normal (r=0.55) and glaucomatous (r=0.48) eyes. The full separation between normal and glaucomatous eyes based on the RNFL attenuation coefficient yielded an area under the ROC (AROC) of 1.0. The AROC for the RNFL thickness was 0.9875. No statistically significant difference between the two measures was found by comparing the AROC. RNFL attenuation coefficients may thus replace current RNFL thickness measurements or be combined with it to improve glaucoma diagnosis.

  15. Mathematical approach to determine the linear attenuation coefficient without collimator in gamma-ray spectrometry.

    PubMed

    Kim, Chang-Jong; Cho, Yoon-Hae; Byun, Jong-In; Yun, Ju-Yong

    2013-07-01

    The linear attenuation coefficient is an important factor in the correction of self-attenuation. In this study, a cone beam from a source of ?1 ?Ci was utilised, not equipped with the collimator, and a complete geometric configuration was mathematically modelled. Samples of NaCl, Na2CO3 and (NH4)2SO4 were used to verify the mathematical model. The linear attenuation coefficient can be calculated within ?4 % of difference in the cylindrical sample at energies of 59.5, 121.8, 244.7, 344.2 and 444.0 keV. PMID:23230217

  16. TOTAL ATTENUATION COEFFICIENTS OF 5-11 Mev GAMMA RAYS

    Microsoft Academic Search

    Barlett

    1963-01-01

    The attenuation of neutron-capture gamma rays in Be, Al, Cu, Sn, and ; Pb was measured at energies of 5.44, 6.40, 7.73, and 10.83 Mev. Absorption of ; thermal neutrons frora a reactor by different elements, with the subsequent ; emission of photons, provided the monoenergetic gamma -ray source. An intense ; well-collimated photon beam allowed uncertainties to be held

  17. Modeling spectral diffuse attenuation, absorption, and scattering coefficients in a turbid estuary

    Microsoft Academic Search

    CHARLES L. GALLEGOS; DAVID L. CORRELL; J. W. PIERCE

    1990-01-01

    Spectral diffuse attenuation coefficients were measured in the Rhode River and Chesapeake Bay, Maryland, on 28 occasions in 1988 and 1989. The model of Kirk was used to extract scattering and absorption coefficients from the measurements in waters considerably more turbid than those in which the model was previously applied. Estimated scattering coefftcients were linearly related to mineral suspended solids.

  18. Beam hardening: Analytical considerations of the effective attenuation coefficient of x-ray tomography

    SciTech Connect

    Alles, J.; Mudde, R. F. [Kramers Laboratorium voor Fysische Technology, Department of Multi-Scale Physics, Delft University of Technology, Pr. Bernhardlaan 6, 2628 Delft (Netherlands)

    2007-07-15

    Polychromatic x-ray beams traveling though material are prone to beam hardening, i.e., the high energy part of the incident spectrum gets over represented when traveling farther into the material. This study discusses the concept of a mean attenuation coefficient in a formal way. The total energy fluence is one-to-one related to the traveled distance in case of a polychromatic beam moving through a given, inhomogeneous material. On the basis of this one-to-one relation, it is useful to define a mean attenuation coefficient and study its decrease with depth. Our results are based on a novel parametrization of the energy dependence of the attenuation coefficient that allows for closed form evaluation of certain spectral integrals. This approach underpins the ad hoc semianalytical expressions given in the literature. An analytical model for the average attenuation coefficient is proposed that uses a simple fit of the attenuation coefficient as a function of the photon energy as input. It is shown that a simple extension of this model gives a rather good description of beam hardening for x-rays traveling through water.

  19. Reconstruction of Ultrasonic Sound Velocity and Attenuation Coefficient Using Linear Arrays: Clinical Assessment

    Microsoft Academic Search

    Chen-Han Chang; Sheng-Wen Huang; Hsin-Chia Yang; Yi-Hong Chou; Pai-Chi Li

    2007-01-01

    The aim of this study was to determine the efficacy of using sound velocity and tissue attenuation to clinically discriminate breast cancer from healthy tissues. The methods for reconstructing the sound-velocity and attenuation-coefficient distributions were previously proposed and tested on tissue-mimicking phantoms. The methods require only raw channel data acquired by a linear transducer array and can therefore be implemented

  20. X-Ray Attenuation Coefficients from 13 to 80 Mev for Hydrogen, Carbon, Water, and Aluminum

    Microsoft Academic Search

    J. M. Wyckoff; H. W. Koch

    1960-01-01

    The x-ray attenuation coefficients for hydrogen, carbon, water, and aluminum have been measured in the energy range from 13 to 80 Mev by placing varying lengths of attenuators in a 90-Mev bremsstrahlung beam in a good geometry experiment using a large sodium-iodide total-absorption spectrometer as the detector. In the hydrogen case, a difference method employing cyclohexane (C6H12) and graphite was

  1. Linear attenuation coefficient and build up factor of MCP-96 alloy for radiation shielding and protection

    Microsoft Academic Search

    Deidre Hopkins; Muhammad Maqbool; Mohammed Islam

    2009-01-01

    Build-up factors and linear attenuation coefficients of MCP-96 alloy are determined for radiation shielding and protection, using ^60Co and ^137Cs gamma emitters. A narrow collimated beam of gamma-rays is passed through various thicknesses of MCP-96 alloy and the attenuation in the intensity of the beam is determined. The thickness of the 4 x 4 cm^2 blocks varies from 0.5 cm

  2. IEEE TRANSACTIONSON SONICS ANDULTRASONICS, VOL. SU-32,NO. 2, MARCH 1985 259 Attenuation Coefficient Measurement Technique at

    E-print Network

    Illinois at Urbana-Champaign, University of

    is the ultrasonic attenuation coefficient, which is the de- crease in energy of the sound wavewhenit propagates throughamaterial. The attenuation includes absorption and scattering.Absorption represents the loss of energy

  3. Measurement of the linear attenuation coefficients of breast tissues by synchrotron radiation computed tomography

    NASA Astrophysics Data System (ADS)

    Chen, R. C.; Longo, R.; Rigon, L.; Zanconati, F.; De Pellegrin, A.; Arfelli, F.; Dreossi, D.; Menk, R.-H.; Vallazza, E.; Xiao, T. Q.; Castelli, E.

    2010-09-01

    The measurement of the linear attenuation coefficients of breast tissues is of fundamental importance in the field of breast x-ray diagnostic imaging. Different groups have evaluated the linear attenuation coefficients of breast tissues by carrying out direct attenuation measurements in which the specimens were thin and selected as homogeneous as possible. Here, we use monochromatic and high-intensity synchrotron radiation computed tomography (SR CT) to evaluate the linear attenuation coefficients of surgical breast tissues in the energy range from 15 to 26.5 keV. X-ray detection is performed by a custom digital silicon micro-strip device, developed in the framework of the PICASSO INFN experiment. Twenty-three human surgical breast samples were selected for SR CT and histological study. Six of them underwent CT, both as fresh tissue and after formalin fixation, while the remaining 17 were imaged only as formalin-fixed tissues. Our results for fat and fibrous tissues are in good agreement with the published values. However, in contrast to the published data, our measurements show no significant differences between fibrous and tumor tissues. Moreover, our results for fresh and formalin-fixed tissues demonstrate a reduction of the linear attenuation coefficient for fibrous and tumor tissues after fixation.

  4. Measurement of atomic number and mass attenuation coefficient in magnesium ferrite

    Microsoft Academic Search

    R H Kadam; S T Alone; G K Bichile; K M Jadhav

    2007-01-01

    Pure magnesium ferrite sample was prepared by standard ceramic technique and characterized by X-ray diffraction method. XRD\\u000a pattern revealed that the sample possess single-phase cubic spinel structure. The linear attenuation coefficient (µ), mass attenuation coefficient (µ\\/?), total atomic cross-section (?\\u000a tot), total electronic cross-section (?\\u000a ele) and the effective atomic number (Z\\u000a eff) were calculated for pure magnesium ferrite (MgFe2O4).

  5. Remote sensing algorithm of particle attenuation coefficient in East China Sea

    NASA Astrophysics Data System (ADS)

    Bai, Yan; He, Xianqiang; Pan, Delu; Hao, Zengzhou; Song, Qingjun; Lei, Hui

    2008-10-01

    China coastal sea is characteristic of the high concentration of suspended matter which has complex components of mineral particles, organic detritus and phytoplankton, etc. The similarity of spectrum characters of mineral particles and organic particles in backscattering coefficient, and the organic detritus and color dissolve organic matters (CDOM) in absorption coefficient makes the information inverse of coastal ocean color become a very difficult work. In this paper, based on the in situ data of optical investigation in East China Sea in the spring of 2003, including the absorption coefficients of CDOM and de-pigment particles from laboratory spectrophotometer measurement, and the field measurement with ac-9 (WET labs, Inc.), the optical properties of suspended particles were studied. And then, a semi-analysis algorithm of particle attenuation coefficient (Cp) in ECS was developed. There are two key steps in this algorithm, one is the estimation of the ratio of particle backscattering coefficient to the total scattering coefficient; and the other is the retrieval of absorption coefficient of CDOM. With this inversion algorithm of Cp and the input of remote sensing reflectance obtained from the underwater profiler radiometer (Satlantic. Inc.), the particle attenuation coefficient was inversed, which was consistent well with the in situ data of Cp . In the high turbid water, the scattering signal is dominant in the Cp values, so the modeled-Cp was less than the in situ data due to the underestimation of backscattering coefficient in IOPs semi-analysis algorithms. The modeled -Cp at 660nm wavelength has the R2 of 0.84 and RMSE=0.22 compared with the attenuation coefficient at 650nm measured by the ac-9, in which the absorption coefficient of CDOM is neglect. The semi-analysis algorithms of Cp developed in this paper showed a good potential to estimate the biogeochemical parameters, like POC, but the further study should be focused on the distinguish of the sub-division materials with more in situ data set.

  6. Linear attenuation coefficient and build up factor of MCP-96 alloy for radiation shielding and protection

    NASA Astrophysics Data System (ADS)

    Hopkins, Deidre; Maqbool, Muhammad; Islam, Mohammed

    2009-10-01

    Build-up factors and linear attenuation coefficients of MCP-96 alloy are determined for radiation shielding and protection, using ^60Co and ^137Cs gamma emitters. A narrow collimated beam of ?-rays is passed through various thicknesses of MCP-96 alloy and the attenuation in the intensity of the beam is determined. The thickness of the 4 x 4 cm^2 blocks varies from 0.5 cm to 6 cm. Plotting the thickness of the alloy and the corresponding intensity of the beam allowed us to determine its linear attenuation coefficient. The narrow beam geometry is then replaced by broad beam geometry by removing the collimator and the radiation beam is able to interact with the MCP-96 alloy at all possible positions facing the radiation source. Additional radiations obtained by the detector as a result from the scattering of radiation develops the build-up factor. The buildup factor is then calculated using the attenuated beam received by the detector in the broad beam geometry and in the narrow beam geometry. The buildup factor is found to be dependent on the thickness of the MCP-96 attenuator, the beam energy and the source to attenuator distance. These values are providing ways for dose correction in radiation oncology and radiation shielding and protection when MCP-96 is used as tissue compensator or for radiation protection purposes.

  7. Gamma ray attenuation coefficient measurements at 1115, 1173, and 1332 keV

    Microsoft Academic Search

    S. Gopal; B. Sanjeevaiah

    1977-01-01

    Gamma ray attenuation coefficients in C, Al, Cu, Zr, Sn and Pb were measured for gamma ray energies 1115, 1173 and 1330 keV using the technique employed earlier by the authors for similar measurements at lower energies. The results will be presented here and discussed.

  8. Two media method for gamma ray attenuation coefficient measurement of archaeological ceramic samples

    Microsoft Academic Search

    R. M Cunha e Silva; C. R Appoloni; P. S Parreira; F. R Espinoza-Quiñones; M. M Coimbra; P. H. A Aragão

    2000-01-01

    This work reports the application of an alternative methodology for the linear attenuation coefficient determination of irregular shape samples, in such a way that it is not necessary to know the sample thickness. Based on this method, indigenous archaeological ceramic fragments from the region of Londrina, north of Parana State in Brazil, were studied. On the other hand, theoretical mass

  9. Improvements in the two media method for measurements of gamma-ray linear attenuation coefficients

    Microsoft Academic Search

    Elimoel A. Elias

    2003-01-01

    The two media method has been previously presented as a solution to the problem of measuring gamma-ray attenuation coefficients of odd-shaped samples. We propose that air is chosen as one of the two media. We theoretically demonstrate that this choice simplifies the equation used, as well as the laboratory work, and also reduces some of the terms associated with experimental

  10. Modeling the vertical distributions of downwelling plane irradiance and diffuse attenuation coefficient in optically deep waters

    Microsoft Academic Search

    Xiaoju Pan; Richard C. Zimmerman

    2010-01-01

    The diffuse attenuation coefficient (Kd) is critical to understand the vertical distribution of underwater downwelling irradiance (Ed). Theoretically Ed is composed of the direct solar beam and the diffuse sky irradiance. Applying the statistical results from Hydrolight radiative transfer simulations, Kd is expressed into a mathematical equation (named as PZ06) integrated from the contribution of direct solar beam and diffuse

  11. Total photon attenuation coefficients in some rare earth elements using selective excitation method

    NASA Astrophysics Data System (ADS)

    SitaMahalakshmi, N. V.; Kareem, M. A.; Premachand, K.

    2015-01-01

    The total mass attenuation coefficients were measured in the elements La, Nd, Sm, Gd and Dy belonging to rare earth region in the energy range 30-55 keV by employing the selective excitation method. This method facilitates selection of excitation energies near the K edge. The present experimental results were compared with the theoretical values due to Chantler and XCOM.

  12. Estimate of attenuation coefficient for ultrasonic tissue characterization using time-varying state-space model.

    PubMed

    Shih, L Y; Barnes, C W; Ferrari, L A

    1988-04-01

    The images generated from ultrasound pulse-echo signals have long been used to aid clinical diagnosis. Recently, there has been a growing interest in quantitatively determining the acoustic parameters of the tissue as a means of classification and diagnosis. For example, the frequency-dependent attenuation is known to be correlated with different diseases in the liver. In this paper we introduce a new technique for estimating the attenuation coefficient. The effect of attenuation on an interrogating signal with a gaussian-shaped spectrum can be obtained by studying the Wigner distribution of reflected rf data based on a one-dimensional signal model. We show that under the condition that the attenuation varies linearly with frequency, the spectral mean of the reflected signal decreases linearly with time. The estimation algorithm models the pulse-echo signal as the output of a second-order time-varying state-space innovations model driven by white noise. The state coupling matrix A and the output coupling vector C vary with time in a known fashion; moreover, they are also functions of an unknown constant parameter theta. The attenuation coefficient, which is one of the elements of theta, can be estimated directly using a recursive system identification algorithm. The algorithm was verified using both computer-generated synthetic data and in-vivo liver data of known diagnosis. The results show correlation between the estimated parameter and the pathological state of the tissue. PMID:3057715

  13. Determination of attenuation coefficient for self-absorption correction in routine gamma ray spectrometry of environmental bulk sample

    Microsoft Academic Search

    K. Satoh; N. Ohashi; H. Higuchi; M. Noguchi

    1984-01-01

    A simple method to determine -ray attenuation coefficients using Ba-133 -rays has been developed and applied to self-absorption correction in routine -ray spectrometry for environmental samples composed of unknown matrix elements. Experimental values of the mass attenuation coefficient obtained by the method agree well with calculated values for samples of known elemental composition which was determined by means of chemical

  14. A generalized method of converting CT image to PET linear attenuation coefficient distribution in PET/CT imaging

    NASA Astrophysics Data System (ADS)

    Wang, Lu; Wu, Li-Wei; Wei, Le; Gao, Juan; Sun, Cui-Li; Chai, Pei; Li, Dao-Wu

    2014-02-01

    The accuracy of attenuation correction in positron emission tomography scanners depends mainly on deriving the reliable 511-keV linear attenuation coefficient distribution in the scanned objects. In the PET/CT system, the linear attenuation distribution is usually obtained from the intensities of the CT image. However, the intensities of the CT image relate to the attenuation of photons in an energy range of 40 keV-140 keV. Before implementing PET attenuation correction, the intensities of CT images must be transformed into the PET 511-keV linear attenuation coefficients. However, the CT scan parameters can affect the effective energy of CT X-ray photons and thus affect the intensities of the CT image. Therefore, for PET/CT attenuation correction, it is crucial to determine the conversion curve with a given set of CT scan parameters and convert the CT image into a PET linear attenuation coefficient distribution. A generalized method is proposed for converting a CT image into a PET linear attenuation coefficient distribution. Instead of some parameter-dependent phantom calibration experiments, the conversion curve is calculated directly by employing the consistency conditions to yield the most consistent attenuation map with the measured PET data. The method is evaluated with phantom experiments and small animal experiments. In phantom studies, the estimated conversion curve fits the true attenuation coefficients accurately, and accurate PET attenuation maps are obtained by the estimated conversion curves and provide nearly the same correction results as the true attenuation map. In small animal studies, a more complicated attenuation distribution of the mouse is obtained successfully to remove the attenuation artifact and improve the PET image contrast efficiently.

  15. Quantitative RNFL attenuation coefficient measurements by RPE-normalized OCT data

    NASA Astrophysics Data System (ADS)

    Vermeer, K. A.; van der Schoot, J.; Lemij, H. G.; de Boer, J. F.

    2012-03-01

    We demonstrate significantly different scattering coefficients of the retinal nerve fiber layer (RNFL) between normal and glaucoma subjects. In clinical care, SD-OCT is routinely used to assess the RNFL thickness for glaucoma management. In this way, the full OCT data set is conveniently reduced to an easy to interpret output, matching results from older (non- OCT) instruments. However, OCT provides more data, such as the signal strength itself, which is due to backscattering in the retinal layers. For quantitative analysis, this signal should be normalized to adjust for local differences in the intensity of the beam that reaches the retina. In this paper, we introduce a model that relates the OCT signal to the attenuation coefficient of the tissue. The average RNFL signal (within an A-line) was then normalized based on the observed RPE signal, resulting in normalized RNFL attenuation coefficient maps. These maps showed local defects matching those found in thickness data. The average (normalized) RNFL attenuation coefficient of a fixed band around the optic nerve head was significantly lower in glaucomatous eyes than in normal eyes (3.0mm-1 vs. 4.9mm-1, P<0.01, Mann-Whitney test).

  16. Total attenuation coefficient of intralipid dilutions for discrete laser wavelengths between 405 and 1315 nm

    NASA Astrophysics Data System (ADS)

    Dreischuh, Tanja N.; Gurdev, Ljuan L.; Vankov, Orlin I.; Avramov, Lachezar A.; Stoyanov, Dimitar V.

    2015-01-01

    The experimental investigations on different aspects of optical tomography require the knowledge of the optical parameters of tissues and tissue-like phantoms in order to unambiguously interpret the experimental data and specify characteristic inhomogeneities in tissue diagnostics. The main optical parameters of interest are the absorption coefficient, the scattering, backscattering, and reduced-scattering coefficients, the total attenuation (extinction) coefficient and the anisotropy factor. In this work, we extend our investigations of the optical properties of tissuemimicking phantoms, such as Intralipid-20% fat emulsion, using an approach we have developed recently based on the peculiarities of laser radiation beams propagating through semi-infinite turbid media. The dependence of the total attenuation coefficient on the Intralipid concentration, for laser radiation wavelengths ?=405, 672, 850, and 1314 nm, is studied, by using a set of phantoms consisting of different dilutions of Intralipid in distilled water. The experimental results for the extinction are in agreement with our previous results and with empiric formulae found by other authors concerning the wavelength dependence of the scattering coefficient of Intralipid -10% and Intralipid - 20%. They are also in agreement with known data of the water absorptance. As a whole, the results obtained in this work confirm the consideration of the experimental phantoms as semi-infinite media. They also confirm and extend theoretical and experimental results obtained previously, and reveal advantages of using longer wavelengths for deeper diagnostics of tissues and mimic turbid media.

  17. Measurement of photon mass attenuation coefficients of plutonium from 60 to 2615 keV

    Microsoft Academic Search

    M. Rettschlag; R. Berndt; P. Mortreau

    2007-01-01

    Measurements have been made to determine plutonium photon mass attenuation coefficients by using a collimated-beam transmission method in the energy range from 60 to 2615keV. These experimental results were compared with previous experimental and theoretical data. Good agreements are observed in the 240–800keV energy range, whereas differences up to maximum 10% are observed out of these limits.

  18. Measurement of mass attenuation coefficients of biological materials by energy dispersive X-ray fluorescence spectrometry

    Microsoft Academic Search

    N. Ekinci; N. Astam

    2007-01-01

    The mass attenuation coefficients for cornea taken from keratitis patient and soft contact lens (-1.75, -3.75, -4 dioptres), leiomyomata uteri and uterus were measured in the X-ray energy (5.9keV) using a SiLi detector and Fe55 annular source. Full details of the experimental method, experimental set up, the procedure of sample preparation and the results within estimated error are presented. Energy

  19. Comparison of measured and satellite-derived spectral diffuse attenuation coefficients for the Arabian Sea

    Microsoft Academic Search

    Suresh Thayapurath; Madhubala Talaulikar; Elgar Desa; S. G. P. Matondkar; Antonio Mascarenhas

    2011-01-01

    We present here the results of our study comparing the spectral diffuse attenuation coefficients Kd(?) measured in the Arabian Sea with those derived from the Sea-Viewing Wide Field-of-View Sensor (SeaWiFS) using three algorithms, of which two are empirical-data-driven and one is semi-analytical. The measurements were carried out in all water types and the mean values of the measured spectral Kd(?)

  20. Gamma-ray attenuation coefficients of some building materials available in Egypt

    Microsoft Academic Search

    M. E. Medhat

    2009-01-01

    Mass attenuation coefficients of various types of building materials were measured using a high-resolution HPGe spectrometer detector. Samples were irradiated by gamma-rays emitted from point sources of 241Am, 133Ba, 60Co and 137Cs. The results are in good agreement with the theoretical calculations of XCOM code. The effectiveness of building materials in shielding were determined over the range 50–3000keV. Finally, the

  1. Determination of attenuation coefficients, thicknesses and effective atomic numbers for CuInSe 2 semiconductor

    Microsoft Academic Search

    Hasan Baltas; Ahmet Çelik; Emin Bacaksiz

    2006-01-01

    The X-rays attenuation coefficients for Cu, In and Se in elemental state and the semiconductor CuInSe2 were measured at 15 different energies from 11.9 to 37.3keV by using the secondary excitation method. Monochromatic photons were obtained using the following secondary targets: Br, Sr, Mo, Cd, Te and Ba. 59.5keV gamma rays emitted from an annular 241Am radioactive source were used

  2. Diffuse attenuation coefficient of downwelling irradiance: An evaluation of remote sensing methods

    Microsoft Academic Search

    Zhong-Ping Lee; Miroslaw Darecki; Kendall L. Carder; Curtiss O. Davis; Dariusz Stramski; W. Joseph Rhea

    2005-01-01

    The propagation of downwelling irradiance at wavelength ? from surface to a depth (z) in the ocean is governed by the diffuse attenuation coefficient, $\\\\bar{K}_{d}$(?). There are two standard methods for the derivation of $\\\\bar{K}_{d}$(?) in remote sensing, which both are based on empirical relationships involving the blue-to-green ratio of ocean color. Recently, a semianalytical method to derive $\\\\bar{K}_{d}$(?) from

  3. Observations of the vertical structure of the diffuse attenuation coefficient spectrum

    NASA Astrophysics Data System (ADS)

    Siegel, D. A.; Dickey, T. D.

    1987-04-01

    Profiles of the diffuse attenuation coefficient spectrum for downwelling spectral irradiance ( Kd( z, ?)) were determined using data taken during the autumn of 1982 in the eastern North Pacific Ocean as part of the Optical Dynamics Experiment (ODEX). The near-surface Kd(5 m, ?) was consistent with Jerlov water types IA or IB and did not show any significant variations with sun altitude angle or cloud amount, supporting the notion that Kd( z, ?) is a "quasi-inherent" optical property. Vertical profiles of Kd( z, ?) showed significant structures with amplitudes that decrease with increasing wavelength. The observed depth-wavelength distribution may be divided into a blue-green group (400-500 nm) with a vertical structure similar to the vertical distribution of chlorophyll pigments and a green-yellow group (500-575 nm) with little vertical variation. For wavelengths >575 nm, the values of Kd( z, ?) decreased with depth apparently because of limitations of the irradiance sensors. The mean vertical distribution of Kd( z, ?) for the blue-green group was well-correlated with the mean in situ fluorescence (correlation coefficient r ˜ 0.94-0.99) and with the mean total pigment concentration ( r ˜ 0.90-0.95). The correlation coefficients relating Kd( z, ?) with the phaeopigment concentration ( r ˜ 0.84-0.92) were higher than those relating the chlorophyll a concentration ( r ˜ 0.63-0.90), indicating the contributions of detrital materials. The mean beam attenuation coefficient at 660 nm was not significantly correlated with Kd( z, ?). The total pigment specific diffuse attenuation coefficient spectrum was similar to spectra determined from previous studies, with departures only in the blue region of the spectrum ( ? < 440 nm). The differences may be attributed to detrital effects.

  4. Gamma-ray attenuation coefficients in some heavy metal oxide borate glasses at 662 keV

    Microsoft Academic Search

    A. Khanna; S. S. Bhatti; K. J. Singh; K. S. Thind

    1996-01-01

    The linear attenuation coefficient (mu) and mass attenuation coefficients (mu\\/rho) of glasses in three systems: xPbO(1-x)B2O3, 0.25PbO.xCdO(0.75-x)B2O3 and xBi2O3(1-x)B2O3 were measured at 662 keV. Appreciable variations were noted in the attenuation coefficients due to changes in the chemical composition of glasses. In addition to this, absorption cross-sections per atom were also calculated. A comparison of shielding properties of these glasses

  5. Gamma-ray attenuation coefficients in some heavy metal oxide borate glasses at 662 keV

    Microsoft Academic Search

    Atul Khanna; S. S. Bhatti; K. J. Singh; K. S. Thind

    1996-01-01

    The linear attenuation coefficient (?) and mass attenuation coefficients (??) of glasses in three systems: xPbO(1 ? x)B2O3, 0.25PbO · xCdO(0.75 ? x)B2O3 and xBi2O3(1 ? x)B2O3 were measured at 662 keV. Appreciable variations were noted in the attenuation coefficients due to changes in the chemical composition of glasses. In addition to this, absorption cross-sections per atom were also calculated.

  6. Simultaneous reconstruction of emission activity and attenuation coefficient distribution from TOF data, acquired with external transmission source

    NASA Astrophysics Data System (ADS)

    Panin, V. Y.; Aykac, M.; Casey, M. E.

    2013-06-01

    The simultaneous PET data reconstruction of emission activity and attenuation coefficient distribution is presented, where the attenuation image is constrained by exploiting an external transmission source. Data are acquired in time-of-flight (TOF) mode, allowing in principle for separation of emission and transmission data. Nevertheless, here all data are reconstructed at once, eliminating the need to trace the position of the transmission source in sinogram space. Contamination of emission data by the transmission source and vice versa is naturally modeled. Attenuated emission activity data also provide additional information about object attenuation coefficient values. The algorithm alternates between attenuation and emission activity image updates. We also proposed a method of estimation of spatial scatter distribution from the transmission source by incorporating knowledge about the expected range of attenuation map values. The reconstruction of experimental data from the Siemens mCT scanner suggests that simultaneous reconstruction improves attenuation map image quality, as compared to when data are separated. In the presented example, the attenuation map image noise was reduced and non-uniformity artifacts that occurred due to scatter estimation were suppressed. On the other hand, the use of transmission data stabilizes attenuation coefficient distribution reconstruction from TOF emission data alone. The example of improving emission images by refining a CT-based patient attenuation map is presented, revealing potential benefits of simultaneous CT and PET data reconstruction.

  7. Determination of Mass Attenuation Coefficients for CuInSe2 and CuGaSe2 Semiconductors

    Microsoft Academic Search

    Emin Bacaksiz

    2007-01-01

    This work presents mass attenuation coefficients values of CuInSe2 and CuGaSe2 semiconductor thin films commonly used in photovoltaic devices. The mass attenuation coefficients were measured at different energies from 11.9 to 37.3 keV by using the secondary excitation method. Monochromatic photons were obtained using the Br, Sr, Mo, Cd, Te, Ba and Nd secondary targets. 59.5 keV gamma rays emitted

  8. Retrieval of diffuse attenuation coefficient in the Chesapeake Bay and turbid ocean regions for satellite ocean color applications

    Microsoft Academic Search

    Menghua Wang; SeungHyun Son; Lawrence W. Harding Jr

    2009-01-01

    There are several empirical and semianalytical models for the satellite-based estimation of the diffuse attenuation coefficient for the downwelling spectral irradiance at the wavelength 490 nm, Kd(490), or the diffuse attenuation coefficient for the downwelling photosynthetically available radiation (PAR), Kd(PAR). An empirical algorithm has been used to routinely produce NASA standard Kd(490) product from the Moderate Resolution Imaging Spectroradiometer (MODIS).

  9. Measurement of mass attenuation coefficients and effective atomic numbers for MgB 2 superconductor using X-ray energies

    Microsoft Academic Search

    H. Balta?; ?. Çelik; U. Çevik; E. Yanmaz

    2007-01-01

    The powder and bulk MgB2 superconductors sintered in different Ar gas pressures were investigated using X-ray diffraction patterns, mass density and mass attenuation coefficient measurements. During the sintering process, 2, 4, 6, 8 and 10bar argon pressures were used to minimize the evaporation of Mg from the compound. Mass attenuation coefficients (?\\/?) of powder and bulk samples were determined by

  10. Evaluation of Compton scattering and self-attenuation coefficient after ? -ray analysis of naturally occurring radioactive elements in environmental samples

    Microsoft Academic Search

    A. A. El-Sayed

    2007-01-01

    Comparison of Compton scattering and Compton scattering cross section with self-attenuation coefficient were explained based\\u000a on the kinematic equation and Klein-Nishina formula. Naturally occurring elements, 238U (226Ra), 40K, 232Th (228Ra) and 137Cs were determined in sediments and water from Ismailia canal in Egypt which were found in the range of permissible level.\\u000a Self-attenuation coefficients, K, the ratio between photopeak detection

  11. Dynamic changes of integrated backscatter, attenuation coefficient and bubble activities during high-intensity focused ultrasound (HIFU) treatment.

    PubMed

    Zhang, Siyuan; Wan, Mingxi; Zhong, Hui; Xu, Cheng; Liao, Zhenzhong; Liu, Huanqing; Wang, Supin

    2009-11-01

    This paper simultaneously investigated the transient characteristics of integrated backscatter (IBS), attenuation coefficient and bubble activities as time traces before, during and after HIFU treatment, with different HIFU parameters (acoustic power and duty cycle) in both transparent tissue-mimicking phantoms and freshly excised bovine livers. These dynamic changes of acoustic parameters and bubble activities were correlated with the visualization of lesion development selected from photos, conventional B-mode ultrasound images and differential IBS images over the whole procedure of HIFU treatment. Two-dimensional radiofrequency (RF) data were acquired by a modified diagnostic ultrasound scanner to estimate the changes of mean IBS and attenuation coefficient averaged in the lesion region, and to construct the differential IBS images and B-mode ultrasound images simultaneously. Bubble activities over the whole procedure of HIFU treatment were investigated by the passive cavitation detection (PCD) method and the changes in subharmonic and broadband noise were correlated with the transient characteristics of IBS and attenuation coefficient. When HIFU was switched on, IBS and attenuation coefficient increased with the appearance of bubble clouds in the B-mode and differential IBS image. At the same time, the level of subharmonic and broadband noise rose abruptly. Then, there was an initial decrease in the attenuation coefficient, followed by an increase when at lower HIFU power. As the lesion appeared, IBS and attenuation coefficient both increased rapidly to a value twice that of normal. Then the changes in IBS and attenuation coefficient showed more complex patterns, but still showed a slower trend of increases with lesion development. Violent bubble activities were visible in the gel and were evident as strongly echogenic regions in the differential IBS images and B-mode images simultaneously. This was detected by a dramatic high level of subharmonic and broadband noise at the same time. These bubble activities caused fluctuations in IBS and attenuation coefficient during HIFU treatment. After HIFU, IBS and attenuation coefficient decreased gradually accompanied by the fadeout of bright hyperechoic spot in the B-mode and differential IBS image, but were still higher than normal when they were stable. The increases of IBS and attenuation coefficient were greater when using higher acoustic power or a higher duty cycle of the therapeutic emission. These experiments indicated that the bubble activities had the dominant effects on the transient characteristics of IBS and attenuation. This should be taken into consideration when using the dynamic acoustic-property changes for the potentially real-time monitoring imaging of HIFU treatment. PMID:19716225

  12. Estimating dynamic changes of tissue attenuation coefficient during high-intensity focused ultrasound treatment

    PubMed Central

    2013-01-01

    Background This study investigated the dynamic changes of tissue attenuation coefficients before, during, and after high-intensity focused ultrasound (HIFU) treatment at different total acoustic powers (TAP) in ex vivo porcine muscle tissue. It further assessed the reliability of employing changes in tissue attenuation coefficient parameters as potential indicators of tissue thermal damage. Methods Two-dimensional pulse-echo radio frequency (RF) data were acquired before, during, and after HIFU exposure to estimate changes in least squares attenuation coefficient slope (??) and attenuation coefficient intercept (??0). Using the acquired RF data, ?? and ??0 images, along with conventional B-mode ultrasound images, were constructed. The dynamic changes of ?? and ??0, averaged in the region of interest, were correlated with B-mode images obtained during the HIFU treatment process. Results At a HIFU exposure duration of 40 s and various HIFU intensities (737–1,068 W/cm2), ?? and ??0 increased rapidly to values in the ranges 1.5–2.5 dB/(MHz.cm) and 4–5 dB/cm, respectively. This rapid increase was accompanied with the appearance of bubble clouds in the B-mode images. Bubble activities appeared as strong hyperechoic regions in the B-mode images and caused fluctuations in the estimated ?? and ??0 values. After the treatment, ?? and ??0 values gradually decreased, accompanied by fade-out of hyperechoic spots in the B-mode images. At 10 min after the treatment, they reached values in ranges 0.75–1 dB/(MHz.cm) and 1–1.5 dB/cm, respectively, and remained stable within those ranges. At a long HIFU exposure duration of around 10 min and low HIFU intensity (117 W/cm2), ?? and ??0 gradually increased to values of 2.2 dB/(MHz.cm) and 2.2 dB/cm, respectively. This increase was not accompanied with the appearance of bubble clouds in the B-mode images. After HIFU treatment, ?? and ??0 gradually decreased to values of 1.8 dB/(MHz.cm) and 1.5 dB/cm, respectively, and remained stable at those values. Conclusions ?? and ??0 estimations were both potentially reliable indicators of tissue thermal damage. In addition, ?? and ??0 images both had significantly higher contrast-to-speckle ratios compared to the conventional B-mode images and outperformed the B-mode images in detecting HIFU thermal lesions at all investigated TAPs and exposure durations. PMID:25516802

  13. Linear attenuation coefficients of tissues from 1 keV to 150 keV

    NASA Astrophysics Data System (ADS)

    Böke, Aysun

    2014-09-01

    The linear attenuation coefficients and three interaction processes have been computed for liver, kidney, muscle, fat and for a range of x-ray energies from 1 keV to 150 keV. Molecular photoelectric absorption cross sections were calculated from atomic cross section data. Total coherent (Rayleigh) and incoherent (Compton) scattering cross sections were obtained by numerical integration over combinations of F2m(x) with the Thomson formula and Sm(x) with the Klein-Nishina formula, respectively. For the coherent (Rayleigh) scattering cross section calculations, molecular form factors were obtained from recent experimental data in the literature for values of x<1 Å-1 and from the relativistic modified atomic form factors for values of x?1 Å-1. With the inclusion of molecular interference effects in the coherent (Rayleigh) scattering, more accurate knowledge of the scatter from these tissues will be provided. The number of elements involved in tissue composition is 5 for liver, 47 for kidney, 44 for muscle and 3 for fat. The results are compared with previously published experimental and theoretical linear attenuation coefficients. In general, good agreement is obtained. The molecular form factors and scattering functions and cross sections are incorporated into a Monte Carlo program. The energy distributions of x-ray photons scattered from tissues have been simulated and the results are presented.

  14. Influence Of Scattering On The Diffuse Attenuation Coefficient In The Asymptotic Region

    NASA Astrophysics Data System (ADS)

    Tanis, Fred J.; Kattawar, George W.; Hickman, G. Daniel

    1986-08-01

    In a homogeneous ocean that both scatters and absorbs the radiance decreases with depth and the angular dependence of the radiance becomes independent of depth and of the incident distribution at the surface. In the diffusion region the asymptotic radiance distribution is only dependent on the inherent properties of the medium including the scattering phase function. Under these conditions an exact integral equation can be derived for the asymptotic radiance. A numerical calculation of the asymptotic radiance was made with Lobatto quadrature resulting in a precise estimate of the diffuse attenuation coefficient for selected values of the single scattering albedo. Calculations were made using estimated single scattering phase functions derived from scattering measurements made for a wide variety of marine and freshwater water types. A two parameter empirical expression was derived from these model calculations relating the diffuse attenuation coefficient and the single scattering albedo. Predictions are made over the entire range of single scattering albedos and are compared to those given by other investigators. The predictability of this relationship and the influence of the scattering phase function are evaluated for each of the scattering phase functions examined. Individual derived relationships are able to predict the diffusion exponent with RMS errors of less than one percent. The overall variation in determining the two parameters is approximately 3 and 18 percent using samples which varied optically from very clear waters of Sargasso Sea to the turbid waters of Lake Erie.

  15. Anisotropy of intrinsic attenuation in the Earth's inner core: quantitative models from normal mode splitting function coefficients

    NASA Astrophysics Data System (ADS)

    Makinen, A.; Deuss, A. F.; Redfern, S. A.

    2013-12-01

    Seismic normal mode and body wave studies find that the Earth's inner core is characterized by strong, large-scale average, cylindrically symmetric velocity anisotropy: compressional waves traversing the inner core in the North-South (polar) direction propagate faster than those travelling in the equatorial plane. Compressional body wave studies also suggest that the inner core exhibit anisotropy of attenuation, finding that compressional waves are also more strongly attenuated in the fast direction. This relationship between anisotropy of velocity and attenuation in the metallic inner core is the reverse of that observed in the silicate mantle; thus far, the existing body wave observations of anisotropic attenuation have been interpreted almost exclusively in terms of anisotropic scattering attenuation. However, body waves cannot distinguish between attenuation by intrinsic (anelastic) mechanisms and by scattering, which prevents us from understanding the physical origin of the attenuation anisotropy. Here, we elucidate attenuation anisotropy using normal modes, the low-frequency free oscillations of the planet as a whole. Due to their very long wavelengths, normal modes are transparent to scattering from small-scale heterogeneities; this makes them a particularly valuable tool for probing the intrinsic component of attenuation, and its possible anisotropy. They are also simultaneously sensitive to both compressional and shear wave properties of the inner core, unlike the various inner core body wave phases. Here, we invert our recently measured anelastic normal mode splitting function coefficients of inner core sensitive normal modes and present a new model of attenuation anisotropy of the Earth's inner core. Our model reveals that the intrinsic attenuation is anisotropic, and confirms that for compressional waves, attenuation anisotropy is indeed correlated with velocity anisotropy, with the fast direction being also more attenuating. Such anisotropy of intrinsic attenuation has the characteristics of anisotropic Zener-like relaxations within single iron crystals due to the reorientation of pairs of solute atoms, and confirms the necessity of incorporating a few per cent of light elements into the solid inner core.

  16. Determination of mass attenuation coefficients for threshold contrast evaluation in digital mammography

    NASA Astrophysics Data System (ADS)

    Hummel, Johann; Semturs, Friedrich; Menhart, Susanne; Figl, Michael

    2010-04-01

    According to the 'European protocol for the quality control of the physical and technical aspects of mammography screening' (EPQC) image quality digital mammography units has to be evaluated at different breast thicknesses. At the standard thickness of 50 mm polymethyl methacrylate (PMMA) image quality is determined by the analysis of CDMAM contrast detail phantom images where threshold contrasts are calculated for different gold disc diameters. To extend these results to other breast thicknesses contrast-to-noise ratios (CNR) and threshold contrast (TC) visibilities have to be calculated for all required thicknesses. To calculate the latter the mass attenuation coefficient (MAC) of gold has to be known for all possible beam qualities in the tube voltage range between 26 and 32 kV. In this paper we first determined the threshold contrast visibility using the CDMAM phantom with the same beam quality at different current-time products (mAs). We can derive from Rose theory that CNR • CT • ? = const, where ? is the diameter of the gold cylinder. From this the corresponding attenuation coefficients can be calculated. This procedure was repeated for four different beam qualities (Mo/Mo 27kV, Rh/Rh 29kV, Rh/Rh 31 kV, and W/Rh 29 kV)). Next, we measured the aluminium half value layer (HVL) of all x-ray spectra relevant for mammography. Using a first order Taylor expansion of MAC as a function of HVL, all other desired MAC can be calculated. The MAC as a function of the HVL was derived to MAChvl = -286.97 * hvl+186.03 with R2 = 0.997, where MAChvl indicates the MAC for all specific x-ray spectrum defined by its aluminium half value layer. Based on this function all necessary MACs needed for quality assurance (QA) were calculated. The results were in good agreement with the data found in the protocol.

  17. Dependence of optical attenuation coefficient and mechanical tension of irradiated human cartilage measured by optical coherence tomography.

    PubMed

    Martinho Junior, A C; Freitas, A Z; Raele, M P; Santin, S P; Soares, F A N; Herson, M R; Mathor, M B

    2015-03-01

    As banked human tissues are not widely available, the development of new non-destructive and contactless techniques to evaluate the quality of allografts before distribution for transplantation is very important. Also, tissues will be processed accordingly to standard procedures and to minimize disease transmission most tissue banks will include a decontamination or sterilization step such as ionizing radiation. In this work, we present a new method to evaluate the internal structure of frozen or glycerol-processed human cartilages, submitted to various dosis of irradiation, using the total optical attenuation coefficient retrieved from optical coherence tomography (OCT) images. Our results show a close relationship between tensile properties and the total optical attenuation coefficient of cartilages. Therefore, OCT associated with the total optical attenuation coefficient open a new window to evaluate quantitatively biological changes in processed tissues. PMID:24322969

  18. Noninvasive monitoring of photodynamic therapy on skin neoplastic lesions using the optical attenuation coefficient measured by optical coherence tomography.

    PubMed

    Goulart, Viviane P; dos Santos, Moisés O; Latrive, Anne; Freitas, Anderson Z; Correa, Luciana; Zezell, Denise M

    2015-05-01

    Photodynamic therapy (PDT) has become a promising alternative for treatment of skin lesions such as squamous cell carcinoma. We propose a method to monitor the effects of PDT in a noninvasive way by using the optical attenuation coefficient (OAC) calculated from optical coherence tomography (OCT) images. We conducted a study on mice with chemically induced neoplastic lesions and performed PDT on these lesions using homemade photosensitizers. The response of neoplastic lesions to therapy was monitored using, at the same time, macroscopic clinical visualization, histopathological analysis, OCT imaging, and OCT-based attenuation coefficient measurement. Results with all four modalities demonstrated a positive response to treatment. The attenuation coefficient was found to be 1.4 higher in skin lesions than in healthy tissue and it decreased after therapy. This study shows that the OAC is a potential tool to noninvasively assess the evolution of skin neoplastic lesions with time after treatment. PMID:25415566

  19. Determination of the mass attenuation coefficients for X-ray fluorescence measurements correction by the Rayleigh to Compton scattering ratio

    NASA Astrophysics Data System (ADS)

    Conti, C. C.; Anjos, M. J.; Salgado, C. M.

    2014-09-01

    X-ray fluorescence technique plays an important role in nondestructive analysis nowadays. The development of equipment, including portable ones, enables a wide assortment of possibilities for analysis of stable elements, even in trace concentrations. Nevertheless, despite of the advantages, one important drawback is radiation self-attenuation in the sample being measured, which needs to be considered in the calculation for the proper determination of elemental concentration. The mass attenuation coefficient can be determined by transmission measurement, but, in this case, the sample must be in slab shape geometry and demands two different setups and measurements. The Rayleigh to Compton scattering ratio, determined from the X-ray fluorescence spectrum, provides a link to the mass attenuation coefficient by means of a polynomial type equation. This work presents a way to construct a Rayleigh to Compton scattering ratio versus mass attenuation coefficient curve by using the MCNP5 Monte Carlo computer code. The comparison between the calculated and literature values of the mass attenuation coefficient for some known samples showed to be within 15%. This calculation procedure is available on-line at www.macx.net.br.

  20. Comparison of Chang's with Sorenson's Attenuation Correction Method by Varying Linear Attenuation Coefficient Values in Tc99m SPECT Imaging

    Microsoft Academic Search

    Inayatullah Shah Sayed; Ahmed Zakaria; Norhafiza Nik

    2007-01-01

    Attenuation (scattering and absorption) of gamma photons in the patient’s body is one of the major limitations among the others\\u000a in single photon emission computed tomography (SPECT). It reduces quantitative accuracy of measured radioactivity concentration\\u000a and causes hot rim artifacts in reconstructed images if not corrected for. A variety of approximate attenuation correction\\u000a methods has been developed or proposed by

  1. Linear attenuation coefficient and buildup factor of MCP-96 alloy for dose accuracy, beam collimation, and radiation protection.

    PubMed

    Hopkins, Deidre N; Maqbool, Muhammad; Islam, Mohammed S

    2012-07-01

    The linear attenuation coefficients and buildup factor of MCP-96 alloy were determined for (60)Co, (54)Mn, and (137)Cs gamma emitters and a NaI detector. The thickness of the MCP-96 attenuator was varied from 1 to 4 cm. A collimated beam of gamma rays was allowed to pass through various thicknesses of the MCP-96 alloy. The attenuated beam was detected by a NaI detector, and data were recorded by a multichannel analyzer. The run was repeated without the collimator for broad-beam geometry. For each run, the attenuated beam intensity was normalized by the intensity of the unattenuated incident beam obtained by removing the attenuators. Linear attenuation coefficients were determined by plotting of the intensity of the collimated beam against the attenuator thickness. For every thickness of the alloy, the ratio of the attenuated to the unattenuated beam was found to be higher in broad-beam geometry as compared to the same ratio in narrow-beam geometry. We used the difference in these ratios in broad and narrow-beam geometries to calculate the buildup factor. The buildup factor was found to increase with beam energy and attenuator thickness. Variation in the source-to-detector distance gave a lower value of the buildup factor for a small and a large distance and a higher value for an intermediate distance. The buildup factor was found to be greater than 1 in all cases. We conclude that the buildup factor must be calculated and incorporated for dose correction and precision when the MCP-96 alloy is used for tissue compensation or radiation shielding and protection purposes. PMID:22585280

  2. Diffuse Attenuation Coefficient of Downwelling Irradiance: An Evaluation of Remote Sensing Methods

    NASA Technical Reports Server (NTRS)

    Lee, Zhong-Ping; Darecki, Miroslaw; Carder, Kendall L.; Davis, Curtiss O.; Stramski, Dariusz; Rhea, W. Joseph

    2005-01-01

    The propagation of downwelling irradiance at wavelength lambda from surface to a depth (z) in the ocean is governed by the diffuse attenuation coefficient, K(sup -)(sub d)(lambda). There are two standard methods for the derivation of K(sup -)(sub d)(lambda) in remote sensing, which both are based on empirical relationships involving the blue-to-green ratio of ocean color. Recently, a semianalytical method to derive K(sup -)(sub d)(lambda) from reflectance has also been developed. In this study, using K(sup -)(sub d)(490) and K(sup -)(sub d)(443) as examples, we compare the K(sup -)(sub d)(lambda) values derived from the three methods using data collected in three different regions that cover oceanic and coastal waters, with K(sup -)(sub d)(490) ranging from approximately 0.04 to 4.0 per meter. The derived values are compared with the data calculated from in situ measurements of the vertical profiles of downwelling irradiance. The comparisons show that the two standard methods produced satisfactory estimates of K(sup -)(sub d)(lambda) in oceanic waters where attenuation is relatively low but resulted in significant errors in coastal waters. The newly developed semianalytical method appears to have no such limitation as it performed well for both oceanic and coastal waters. For all data in this study the average of absolute percentage difference between the in situ measured and the semianalytically derived K(sup -)(sub d) is approximately 14% for lambda = 490 nm and approximately 11% for lambda = 443 nm.

  3. Prediction of the light attenuation coefficient through the Secchi disk depth: empirical modeling in two large Neotropical ecosystems

    Microsoft Academic Search

    André Andrian Padial; Sidinei Magela Thomaz

    2008-01-01

    The easiest way to evaluate water transparency is from the Secchi disk depth (SD). The behavior of radiation passing through\\u000a water can also be quantified by the light attenuation coefficient (k) of photosynthetically active radiation (PAR), measured using quanta meters. Due to the high costs of quanta meters, k is usually predicted from SD. This prediction can be made using

  4. Precise measurement of attenuation coefficients of gamma rays in the 7.5 MeV region

    Microsoft Academic Search

    R. Moreh; D. Salzmann; Y. Wand

    1969-01-01

    A new technique utilising nuclear resonance scattering of gamma rays was used for measuring total attenuation coefficients of 15 elements between Be and U. The gamma-ray energies were 7.279 and 7.646 MeV, and the results were found to be generally higher than the calculated values.

  5. Evaluation of moisture-related attenuation coefficient and water diffusion velocity in human skin using optical coherence tomography.

    PubMed

    Lee, Cheng-Kuang; Tsai, Meng-Tsan; Chang, Feng-Yu; Yang, Chih-Hsun; Shen, Su-Chin; Yuan, Ouyang; Yang, Chih-He

    2013-01-01

    In this study, time-resolved optical coherence tomography (OCT) scanning images of the process of water diffusion in the skin that illustrate the enhancement in the backscattered intensities due to the increased water concentration are presented. In our experiments, the water concentration in the skin was increased by soaking the hand in water, and the same region of the skin was scanned and measured with the OCT system and a commercial moisture monitor every three minutes. To quantitatively analyze the moisture-related optical properties and the velocity of water diffusion in human skin, the attenuation coefficients of the skin, including the epidermis and dermis layers, were evaluated. Furthermore, the evaluated attenuation coefficients were compared with the measurements made using the commercial moisture monitor. The results demonstrate that the attenuation coefficient increases as the water concentration increases. Furthermore, by evaluating the positions of center-of mass of the backscattered intensities from OCT images, the diffusion velocity can be estimated. In contrast to the commercial moisture monitor, OCT can provide three-dimensional structural images of the skin and characterize its optical property, which together can be used to observe morphological changes and quantitatively evaluate the moisture-related attenuation coefficients in different skin layers. PMID:23529149

  6. Radiation dose estimation and mass attenuation coefficients of cement samples used in Turkey.

    PubMed

    Damla, N; Cevik, U; Kobya, A I; Celik, A; Celik, N; Van Grieken, R

    2010-04-15

    Different cement samples commonly used in building construction in Turkey have been analyzed for natural radioactivity using gamma-ray spectrometry. The mean activity concentrations observed in the cement samples were 52, 40 and 324 Bq kg(-1) for (226)Ra, (232)Th and (40)K, respectively. The measured activity concentrations for these radionuclides were compared with the reported data of other countries and world average limits. The radiological hazard parameters such as radium equivalent activities (Ra(eq)), gamma index (I(gamma)) and alpha index (I(alpha)) indices as well as terrestrial absorbed dose and annual effective dose rate were calculated and compared with the international data. The Ra(eq) values of cement are lower than the limit of 370 Bq kg(-1), equivalent to a gamma dose of 1.5 mSv y(-1). Moreover, the mass attenuation coefficients were determined experimentally and calculated theoretically using XCOM in some cement samples. Also, chemical compositions analyses of the cement samples were investigated. PMID:20018450

  7. Single-experiment simultaneous-measurement of elemental mass-attenuation coefficients of hydrogen, carbon and oxygen for 0.123–1.33 MeV gamma rays

    Microsoft Academic Search

    M. T. Teli; R. Nathuram; C. S. Mahajan

    2000-01-01

    As it is inconvenient to use elements like hydrogen, carbon and oxygen in pure forms for measurement of their gamma mass-attenuation coefficients, the measurements are to be done indirectly, by using compounds of the elements or a mixture of them. We give here a simple method of measuring the total mass-attenuation coefficients ?\\/? of the elements in a compound simultaneously

  8. The precise measurement of the attenuation coefficients of various IR optical materials applicable to immersion grating

    NASA Astrophysics Data System (ADS)

    Kaji, Sayumi; Sarugaku, Yuki; Ikeda, Yuji; Kobayashi, Naoto; Nakanishi, Kenshi; Kondo, Sohei; Yasui, Chikako; Kawakita, Hideyo

    2014-07-01

    Immersion grating is a next-generation diffraction grating which has the immersed the diffraction surface in an optical material with high refractive index of n > 2, and can provide higher spectral resolution than a classical reflective grating. Our group is developing various immersion gratings from the near- to mid-infrared region (Ikeda et al.1, 2, 3, 4, Sarugaku et al.5, and Sukegawa et al.6). The internal attenuation ?att of the candidate materials is especially very important to achieve the high efficiency immersion gratings used for astronomical applications. Nevertheless, because there are few available data as ?att < 0.01cm-1 in the infrared region, except for measurements of CVD-ZnSe, CVD-ZnS, and single-crystal Si in the short near-infrared region reported by Ikeda et al.7, we cannot select suitable materials as an immersion grating in an aimed wavelength range. Therefore, we measure the attenuation coefficients of CdTe, CdZnTe, Ge, Si, ZnSe, and ZnS that could be applicable to immersion gratings. We used an originally developed optical unit attached to a commercial FTIR which covers the wide wavelength range from 1.3?m to 28?m. This measurement system achieves the high accuracy of (triangle)?att ~ 0.01cm-1. As a result, high-resistivity single-crystal CdZnTe, single-crystal Ge, single-crystal Si, CVD-ZnSe, and CVD-ZnS show ?att < 0.01cm-1 at the wavelength range of 5.5 - 19.0?m, 2.0 - 10.5?m, 1.3 - 5.4?m, 1.7 - 13.2?m, and 1.9 - 9.2?m, respectively. This indicates that these materials are good candidates for high efficiency immersion grating covering those wavelength ranges. We plan to make similar measurement under the cryogenic condition as T <= 10K for the infrared, especially mid-infrared applications.

  9. Using water quality variables to predict light attenuation coefficient: case study in Shihmen Reservoir

    Microsoft Academic Search

    Wen-Cheng Liu; Ray-Shyan Wu; Edward Ming-Yang Wu; Yu-Pei Chang; Wei-Bo Chen

    2010-01-01

    The amount of photosynthetically active radiation (PAR) in the water column is of fundamental importance in determining the\\u000a growth of aquatic plant and aquatic primary production. Light attenuation in aquatic ecosystems has important ecological implication\\u000a and water quality applications. In the present study, the light attenuation through the water column in the Shihmen Reservoir,\\u000a Taiwan was measured. A light attenuation

  10. Calibration of a turbidity meter for making estimates of total suspended solids concentrations and beam attenuation coefficients in field experiments

    NASA Technical Reports Server (NTRS)

    Usry, J. W.; Whitlock, C. H.

    1981-01-01

    Management of water resources such as a reservoir requires using analytical models which describe such parameters as the suspended sediment field. To select or develop an appropriate model requires making many measurements to describe the distribution of this parameter in the water column. One potential method for making those measurements expeditiously is to measure light transmission or turbidity and relate that parameter to total suspended solids concentrations. An instrument which may be used for this purpose was calibrated by generating curves of transmission measurements plotted against measured values of total suspended solids concentrations and beam attenuation coefficients. Results of these experiments indicate that field measurements made with this instrument using curves generated in this study should correlate with total suspended solids concentrations and beam attenuation coefficients in the water column within 20 percent.

  11. Derivation of total diffuse attenuation coefficient from water column temperature data and meteorological water surface fluxes: A simple management tool

    Microsoft Academic Search

    Sri Adiyanti; Jörg Imberger

    2007-01-01

    The total diffuse attenuation coefficient of Photosynthetically Available Radiation (Kd(PAR)) is derived by optimising the solution of a surface layer model to match temperature profiles measured with a precision thermistor chain; a non?linear least?squares Levenberg?Marquardt scheme is applied to optimize Kd(PAR). The method was validated in Lake Kinneret (Israel) over 10 days in summer to early winter 2001, Valle de

  12. Measurement of the mass attenuation coefficients of Ge and BGO for high-energy gamma-rays

    Microsoft Academic Search

    Hideo Harada; Fumito Kitatani; Kaoru Y. Hara; Hiroyuki Toyokawa; Takeshi Kaihori; Hiroaki Utsunomiya

    2007-01-01

    The gamma-ray mass attenuation coefficients of important materials for gamma-ray detection have been measured using the laser-Compton backscattering gamma-rays (LCS gamma-rays) and the high-resolution high-energy photon spectrometer (HHS). The preliminary results performed for materials (Ge and BGO) are presented for gamma-ray energy of 5.1 MeV. The measured data are compared with tabulated theoretical calculations.

  13. Determination of mass attenuation coefficients of some boron ores at 59.54keV by using scintillation detector.

    PubMed

    Demir, Faruk

    2010-01-01

    The mass attenuation coefficients of the 59.54keV radiation of (241)Am point source in boron ores such as tincal, ulexite and colemanite were determined experimentally by a scintillation detector and theoretically. Since boron ores contain boron, hydrogen, and a lot of elements, they may be used as shielding against neutrons and gammas simultaneously, e.g. for shielding (241)Am/Be neutron sources, as they emit both gammas and neutrons. PMID:19800806

  14. Improved Algorithms for Accurate Retrieval of UV - Visible Diffuse Attenuation Coefficients in Optically Complex, Inshore Waters

    NASA Technical Reports Server (NTRS)

    Cao, Fang; Fichot, Cedric G.; Hooker, Stanford B.; Miller, William L.

    2014-01-01

    Photochemical processes driven by high-energy ultraviolet radiation (UVR) in inshore, estuarine, and coastal waters play an important role in global bio geochemical cycles and biological systems. A key to modeling photochemical processes in these optically complex waters is an accurate description of the vertical distribution of UVR in the water column which can be obtained using the diffuse attenuation coefficients of down welling irradiance (Kd()). The Sea UV Sea UVc algorithms (Fichot et al., 2008) can accurately retrieve Kd ( 320, 340, 380,412, 443 and 490 nm) in oceanic and coastal waters using multispectral remote sensing reflectances (Rrs(), Sea WiFS bands). However, SeaUVSeaUVc algorithms are currently not optimized for use in optically complex, inshore waters, where they tend to severely underestimate Kd(). Here, a new training data set of optical properties collected in optically complex, inshore waters was used to re-parameterize the published SeaUVSeaUVc algorithms, resulting in improved Kd() retrievals for turbid, estuarine waters. Although the updated SeaUVSeaUVc algorithms perform best in optically complex waters, the published SeaUVSeaUVc models still perform well in most coastal and oceanic waters. Therefore, we propose a composite set of SeaUVSeaUVc algorithms, optimized for Kd() retrieval in almost all marine systems, ranging from oceanic to inshore waters. The composite algorithm set can retrieve Kd from ocean color with good accuracy across this wide range of water types (e.g., within 13 mean relative error for Kd(340)). A validation step using three independent, in situ data sets indicates that the composite SeaUVSeaUVc can generate accurate Kd values from 320 490 nm using satellite imagery on a global scale. Taking advantage of the inherent benefits of our statistical methods, we pooled the validation data with the training set, obtaining an optimized composite model for estimating Kd() in UV wavelengths for almost all marine waters. This optimized composite set of SeaUVSeaUVc algorithms will provide the optical community with improved ability to quantify the role of solar UV radiation in photochemical and photobiological processes in the ocean.

  15. Measurement of X-ray mass attenuation coefficients in biological and geological samples in the energy range of 7-12keV.

    PubMed

    Trunova, Valentina; Sidorina, Anna; Kriventsov, Vladimir

    2014-10-17

    Information about X-ray mass attenuation coefficients in different materials is necessary for accurate X-ray fluorescent analysis. The X-ray mass attenuation coefficients for energy of 7-12keV were measured in biological (Mussel and Oyster tissues, blood, hair, liver, and Cabbage leaves) and geological (Baikal sludge, soil, and Alaskite granite) samples. The measurements were carried out at the EXAFS Station of Siberian Synchrotron Radiation Center (VEPP-3). Obtained experimental mass attenuation coefficients were compared with theoretical values calculated for some samples. PMID:25464176

  16. Photon attenuation coefficients of Heavy-Metal Oxide glasses by MCNP code, XCOM program and experimental data: A comparison study

    NASA Astrophysics Data System (ADS)

    El-Khayatt, A. M.; Ali, A. M.; Singh, Vishwanath P.

    2014-01-01

    The mass attenuation coefficients, ?/?, total interaction cross-section, ?t, and mean free path (MFP) of some Heavy Metal Oxides (HMO) glasses, with potential applications as gamma ray shielding materials, have been investigated using the MCNP-4C code. Appreciable variations are noted for all parameters by changing the photon energy and the chemical composition of HMO glasses. The numerical simulations parameters are compared with experimental data wherever possible. Comparisons are also made with predictions from the XCOM program in the energy region from 1 keV to 100 MeV. Good agreement noticed indicates that the chosen Monte Carlo method may be employed to make additional calculations on the photon attenuation characteristics of different glass systems, a capability particularly useful in cases where no analogous experimental data exist.

  17. Measurements of the thermal coefficient of optical attenuation at different depth regions of in vivo human skins using optical coherence tomography: a pilot study

    PubMed Central

    Su, Ya; Yao, X. Steve; Li, Zhihong; Meng, Zhuo; Liu, Tiegen; Wang, Longzhi

    2015-01-01

    We present detailed measurement results of optical attenuation’s thermal coefficients (referenced to the temperature of the skin surface) in different depth regions of in vivo human forearm skins using optical coherence tomography (OCT). We first design a temperature control module with an integrated optical probe to precisely control the surface temperature of a section of human skin. We propose a method of using the correlation map to identify regions in the skin having strong correlations with the surface temperature of the skin and find that the attenuation coefficient in these regions closely follows the variation of the surface temperature without any hysteresis. We observe a negative thermal coefficient of attenuation in the epidermis. While in dermis, the slope signs of the thermal coefficient of attenuation are different at different depth regions for a particular subject, however, the depth regions with a positive (or negative) slope are different in different subjects. We further find that the magnitude of the thermal coefficient of attenuation coefficient is greater in epidermis than in dermis. We believe the knowledge of such thermal properties of skins is important for several noninvasive diagnostic applications, such as OCT glucose monitoring, and the method demonstrated in this paper is effective in studying the optical and biological properties in different regions of skin. PMID:25780740

  18. Multi-frequency characterization of the speed of sound and attenuation coefficient for longitudinal transmission of freshly excised human skulls

    PubMed Central

    Pichardo, Samuel; Sin, Vivian W; Hynynen, Kullervo

    2011-01-01

    For medical applications of ultrasound inside the brain, it is necessary to understand the relationship between the apparent density of skull bone and its corresponding speed of sound and attenuation coefficient. Although there have been previous studies exploring this phenomenon, there is still a need to extend the measurements to cover more of the clinically relevant frequency range. The results of measurements of the longitudinal speed of sound and attenuation coefficient are presented for specimens of human calvaria. The study was performed for the frequencies of 0.27, 0.836, 1.402, 1.965 and 2.525 MHz. Specimens were obtained from fresh cadavers through a protocol with the Division of Anatomy of the University of Toronto. The protocol was approved by the Research Ethics Board of Sunnybrook Health Sciences Centre. The specimens were mounted in polycarbonate supports that were marked for stereoscopic positioning. Computer tomography (CT) scans of the skulls mounted on their supports were performed, and a three-dimensional skull surface was reconstructed. This surface was used to guide a positioning system to ensure the normal sound incidence of an acoustic signal. This signal was produced by a focused device with a diameter of 5 cm and a focal length of 10 cm. Measurements of delay in time of flight were carried out using a needle hydrophone. Measurements of effective transmitted energy were carried out using a radiation force method with a 10 ?g resolution scale. Preliminary functions of speed of sound and attenuation coefficient, both of which are related to apparent density, were established using a multi-layer propagation model that takes into account speed of sound, density and thickness of the layer. An optimization process was executed from a large set of random functions and the best functions were chosen for those ones that closest reproduced the experimental observations. The final functions were obtained after a second pass of the optimization process was executed, but this time using a finite-difference time-difference solution of the Westervelt equation, which is more precise than the multi-layer model but much more time consuming for computation. For six of seven specimens, measurements were carried out on five locations on the calvaria, and for the other specimen three measurements were made. In total, measurements were carried out on 33 locations. Results indicated the presence of dispersion effects and that these effects are different according to the type of bone in the skull (cortical and trabecular). Additionally, both the speed of sound and attenuation showed dependence on the skull density that varied with the frequency. Using the optimal functions and the information of density from the CT scans, the average values (±s.d.) of the speed of sound for cortical bone were estimated to be 2384(±130), 2471(±90), 2504(±120), 2327(±90) and 2053(±40) m s?1 for the frequencies of 270, 836, 1402, 1965 and 2526 kHz, respectively. For trabecular bone, and in the same order of frequency values, the speeds of sound were 2140(±130), 2300(±100), 2219(±200), 2133(±130) and 1937(±40) m s?1, respectively. The average values of the attenuation coefficient for cortical bone were 33(±9), 240(±9) and 307(±30) Np m?1 for the frequencies of 270, 836, and 1402, respectively. For trabecular bone, and in the same order of frequency values, the average values of the attenuation coefficient were 34(±13), 216(±16) and 375(±30) Np m?1, respectively. For frequencies of 1.965 and 2.525 MHz, no measurable radiation force was detected with the setup used. PMID:21149950

  19. Multi-frequency characterization of the speed of sound and attenuation coefficient for longitudinal transmission of freshly excised human skulls

    NASA Astrophysics Data System (ADS)

    Pichardo, Samuel; Sin, Vivian W.; Hynynen, Kullervo

    2011-01-01

    For medical applications of ultrasound inside the brain, it is necessary to understand the relationship between the apparent density of skull bone and its corresponding speed of sound and attenuation coefficient. Although there have been previous studies exploring this phenomenon, there is still a need to extend the measurements to cover more of the clinically relevant frequency range. The results of measurements of the longitudinal speed of sound and attenuation coefficient are presented for specimens of human calvaria. The study was performed for the frequencies of 0.27, 0.836, 1.402, 1.965 and 2.525 MHz. Specimens were obtained from fresh cadavers through a protocol with the Division of Anatomy of the University of Toronto. The protocol was approved by the Research Ethics Board of Sunnybrook Health Sciences Centre. The specimens were mounted in polycarbonate supports that were marked for stereoscopic positioning. Computer tomography (CT) scans of the skulls mounted on their supports were performed, and a three-dimensional skull surface was reconstructed. This surface was used to guide a positioning system to ensure the normal sound incidence of an acoustic signal. This signal was produced by a focused device with a diameter of 5 cm and a focal length of 10 cm. Measurements of delay in time of flight were carried out using a needle hydrophone. Measurements of effective transmitted energy were carried out using a radiation force method with a 10 µg resolution scale. Preliminary functions of speed of sound and attenuation coefficient, both of which are related to apparent density, were established using a multi-layer propagation model that takes into account speed of sound, density and thickness of the layer. An optimization process was executed from a large set of random functions and the best functions were chosen for those ones that closest reproduced the experimental observations. The final functions were obtained after a second pass of the optimization process was executed, but this time using a finite-difference time-difference solution of the Westervelt equation, which is more precise than the multi-layer model but much more time consuming for computation. For six of seven specimens, measurements were carried out on five locations on the calvaria, and for the other specimen three measurements were made. In total, measurements were carried out on 33 locations. Results indicated the presence of dispersion effects and that these effects are different according to the type of bone in the skull (cortical and trabecular). Additionally, both the speed of sound and attenuation showed dependence on the skull density that varied with the frequency. Using the optimal functions and the information of density from the CT scans, the average values (±s.d.) of the speed of sound for cortical bone were estimated to be 2384(± 130), 2471(± 90), 2504(± 120), 2327(± 90) and 2053(± 40) m s-1 for the frequencies of 270, 836, 1402, 1965 and 2526 kHz, respectively. For trabecular bone, and in the same order of frequency values, the speeds of sound were 2140(± 130), 2300(± 100), 2219(± 200), 2133(± 130) and 1937(± 40) m s-1, respectively. The average values of the attenuation coefficient for cortical bone were 33(± 9), 240(± 9) and 307(± 30) Np m-1 for the frequencies of 270, 836, and 1402, respectively. For trabecular bone, and in the same order of frequency values, the average values of the attenuation coefficient were 34(± 13), 216(± 16) and 375(± 30) Np m-1, respectively. For frequencies of 1.965 and 2.525 MHz, no measurable radiation force was detected with the setup used.

  20. Characterization of the ultrasonic attenuation coefficient and its frequency dependence in a polymer gel dosimeter

    Microsoft Academic Search

    Remo A. Crescenti; Jeffrey C. Bamber; Mike Partridge; Nigel L. Bush; Steve Webb

    2007-01-01

    Research on polymer-gel dosimetry has been driven by the need for three-dimensional dosimetry, and because alternative dosimeters are unsatisfactory or too slow for that task. Magnetic resonance tomography is currently the most well-developed technique for determining radiation-induced changes in polymer structure, but quick low-cost alternatives remain of significant interest. In previous work, ultrasound attenuation and speed of sound were found

  1. Spectral modification of Beer's law and relation to the humidity attenuation coefficient in atmospheric maritime mist

    NASA Astrophysics Data System (ADS)

    Vul'fson, A. N.

    2000-12-01

    Similarity theory and dimensional analysis are applied to the construction of a relationship for the spectral aerosol extinction coefficient in the visible atmospheric window 0.48 (DOT) 10-4 cm < (lambda) < 0.76 (DOT) 10-4 cm. For maritime mist the results allow one to compare the dependence of the spectral extinction coefficient on humidity as determined in situ with known laboratory observations on the variation in the radius of aerosol particle in moist air. Raoult's modified law is used to show that the variation in the optical properties of soluble aerosol is entirely determined by the variation in the average radius of particles depending on humidity.

  2. Gamma Ray Attenuation Coefficient Measurement in Energies 1172 keV and 1332 keV for Neutron Absorbent Saturated Solutions

    Microsoft Academic Search

    Jalali; Majid

    2006-01-01

    The compounds, NaBO, HBO, CdCl and NaCl and their solutions, attenuate gamma rays in addition to neutron absorption. These compounds are widely used in shielding of neutron sources, reactor control and neutron converters. Mass attenuation coefficients of gamma related to saturated solutions of the above four compounds, in energies 1172 keV and 1332 keV have been measured by NaI detector

  3. Determination of photon attenuation coefficient, porosity and field capacity of soil by gamma-ray transmission for 60, 356 and 662 keV gamma rays

    Microsoft Academic Search

    D. Demir; A. Ün; M. Özgül; Y. ?ahin

    2008-01-01

    Gamma-ray transmission methods have been used accurately for the study of the properties of soil in the agricultural purposes. In this study, photon attenuation coefficient, porosity and field capacity of soil are determined by using gamma-ray transmission method. To this end, the soil sample was collected from Erzurum and a 2×2 in NaI (Tl) scintillation detector measured the attenuation of

  4. New consistency tests for high-accuracy measurements of X-ray mass attenuation coefficients by the X-ray extended-range technique

    SciTech Connect

    Chantler, C.T.; Islam, M.T.; Rae, N.A.; Tran, C.Q.; Glover, J.L.; Barnea, Z. (La Trobe); (Melbourne)

    2012-09-25

    An extension of the X-ray extended-range technique is described for measuring X-ray mass attenuation coefficients by introducing absolute measurement of a number of foils - the multiple independent foil technique. Illustrating the technique with the results of measurements for gold in the 38-50 keV energy range, it is shown that its use enables selection of the most uniform and well defined of available foils, leading to more accurate measurements; it allows one to test the consistency of independently measured absolute values of the mass attenuation coefficient with those obtained by the thickness transfer method; and it tests the linearity of the response of the counter and counting chain throughout the range of X-ray intensities encountered in a given experiment. In light of the results for gold, the strategy to be ideally employed in measuring absolute X-ray mass attenuation coefficients, X-ray absorption fine structure and related quantities is discussed.

  5. Functional relations between total scattering and backscattering for retrieving the profile of the attenuation coefficient in the atmosphere from lidar-sensing data

    SciTech Connect

    Kovalev, V.A. (A.I. Voeikov Main Geophysical Observatory, St. Petersburg (Russian Federation))

    1992-05-01

    The possibility of using a variable along a sensing path backscattering phase function in lidar data processing with the goal of increasing the accuracy of retrieving the profile of the attenuation coefficient in the inhomogeneous atmosphere is analyzed. Approximated dependences of the total aerosol scattering an aerosol backscattering are given based on the published experimental data. By way of example, the model profiles of the attenuation coefficient are given retrieved with the use of the scattering phase functions being constant and variable along the sensing path. 12 refs., 5 figs.

  6. Tables of X-ray mass attenuation coefficients and mass energy-absorption coefficients 1 keV to 20 MeV for elements Z=1 to 92 and 48 additional substances of dosimetric interest

    Microsoft Academic Search

    J. H. Hubbell; Stephen M Seltzer

    1995-01-01

    Tables and graphs of the photon mass attenuation coefficient mu\\/rho and the mass energy-absorption coefficient mu(en)\\/rho are presented for all of the elements Z=1 to 92, and for 48 compounds and mixtures of radiological interest. The tables cover energies of the photon (x ray, gamma ray, bremsstrahlung) from 1 keV to 20 MeV. The mu\\/rho values are taken from the

  7. Retrieval of phytoplankton biomass from simultaneous inversion of reflectance, the diffuse attenuation coefficient, and Sun-induced fluorescence in coastal waters

    Microsoft Academic Search

    Yannick Huot; Catherine A. Brown; John J. Cullen

    2007-01-01

    A model has been developed to retrieve phytoplankton absorption, a proxy for phytoplankton biomass, from observations of reflectance (R) and the diffuse attenuation coefficient (K d) collected by moored radiometers in coastal waters, where high concentrations of chromophoric dissolved organic matter (CDOM) confound conventional ocean color algorithms. The inversion uses simultaneously two forward models: (1) a look-up table (LUT) that

  8. Retrieval of phytoplankton biomass from simultaneous inversion of reflectance, the diffuse attenuation coefficient, and Sun-induced fluorescence in coastal waters

    Microsoft Academic Search

    Yannick Huot; Catherine A. Brown; John J. Cullen

    2007-01-01

    A model has been developed to retrieve phytoplankton absorption, a proxy for phytoplankton biomass, from observations of reflectance (R) and the diffuse attenuation coefficient (Kd) collected by moored radiometers in coastal waters, where high concentrations of chromophoric dissolved organic matter (CDOM) confound conventional ocean color algorithms. The inversion uses simultaneously two forward models: (1) a look-up table (LUT) that accounts

  9. Seasonal variability in the vertical attenuation coefficient at 490 nm (K490) in waters around Puerto Rico and US Virgin Islands

    Microsoft Academic Search

    William J. Hernandez; Fernando Gilbes

    Satellite sensors provide a valuable tool in understanding the seasonal variability of ocean color properties. The vertical diffuse attenuation coefficient (Kd) was evaluated for the waters around Puerto Rico and the US Virgin Islands. The MODIS K490 of Band 3 Level82 daily images were processed with a resolution of 1 kilometer for the year 2008. The images were projected to

  10. Study of variance and covariance terms in linear attenuation coefficient measurements of irregular samples through the two media method by gamma-ray transmission

    Microsoft Academic Search

    Renato Yoichi Ribeiro Kuramoto; Carlos Roberto Appoloni

    2002-01-01

    The two media method permits the application of Beer's law (Thesis (Master Degree), Universidade Estadual de Londrina, PR, Brazil, pp. 23) for the linear attenuation coefficient determination of irregular thickness samples by gamma-ray transmission. However, the use of this methodology introduces experimental complexity due to the great number of variables to be measured. As consequence of this complexity, the uncertainties

  11. Measurement of the x-ray mass attenuation coefficients of gold in the 38?50-keV energy range

    SciTech Connect

    Islam, M.T.; Rae, N.A.; Glover, J.L.; Barnea, Z.; de Jonge, M.D.; Tran, C.Q.; Wang, J.; Chantler, C.T. (Melbourne)

    2010-11-12

    We used synchrotron x rays to measure the x-ray mass attenuation coefficients of gold at nine energies from 38 to 50 keV with accuracies of 0.1%. Our results are much more accurate than previous measurements in this energy range. A comparison of our measurements with calculated mass attenuation coefficients shows that our measurements fall almost exactly midway between the XCOM and FFAST calculated theoretical values, which differ from one another in this energy region by about 4%, even though the range includes no absorption edge. The consistency and accuracy of these measurements open the way to investigations of the x-ray attenuation in the region of the L absorption edge of gold.

  12. MODIS-based retrieval of suspended sediment concentration and diffuse attenuation coefficient in Chinese estuarine and coastal waters

    NASA Astrophysics Data System (ADS)

    Sokoletsky, Leonid; Yang, Xianping; Shen, Fang

    2014-11-01

    Radiative transfer modelling in atmosphere, water, and on the air-water surface was used to create an algorithm and computer code for satellite monitoring Chinese estuarine and coastal waters. The atmospheric part of the algorithm is based on the Reference Evaluation of Solar Transmittance (REST) model for calculation of optical properties of the atmosphere from the top of the atmosphere to the target; for modelling optical properties from target towards satellite's sensor, an optical reciprocity principle has been used. An algorithm uses estimates derived from three different sources: 1) the MODIS-based software; 2) radiative transfer equations, and 3) well-known empirical relationships between measured parameters and optical depths and transmittances for such atmospheric components as molecules, aerosols, ozone, nitrogen dioxide, precipitable water vapor and uniformly mixed gases. Using this model allowed us to derive a reliable relationship relating an important parameter, the diffuse-to-global solar incoming irradiance ratio, to the aerosol optical thickness, solar zenith angle and wavelength. The surface and underwater parts of the algorithm contained theoretical and semi-empirical relationships between inherent (such as absorption, scattering and backscattering coefficients) and apparent (remote-sensing reflectance and diffuse attenuation coefficient, Kd) optical properties, and suspended sediment concentration (SSC) measured in the Yangtze River Estuary and its adjacent coastal area. The first false colour maps of SSC and Kd demonstrated a well accordance with the multi-year field observations in the region, and suggest promise for use of this algorithm for the regular monitoring of Chinese and worldwide natural waters.

  13. K-shell absorption jump factors and jump ratios in elements between Tm ( Z = 69) and Os ( Z = 76) derived from new mass attenuation coefficient measurements

    Microsoft Academic Search

    Necati Kaya; Engin Tirasoglu; Gökhan Apaydin; Volkan Aylikci; Erhan Cengiz

    2007-01-01

    The K-shell absorption jump factors and jump ratios were derived from new mass attenuation coefficients measured using an energy dispersive X-ray fluorescence (EDXRF) spectrometer for Tm, Yb elements being Tm2O3, Yb2O3 compounds and pure Lu, Hf, Ta, W, Re and Os. The measurements, in the region 56–77keV, were done in a transmission geometry utilizing the K?1, K?2, K?1 and K?2

  14. Measurements of the X-ray linear attenuation coefficient for low atomic number materials at energies 32–66 and 140 keV

    Microsoft Academic Search

    S. M. Midgley

    2005-01-01

    The X-ray linear attenuation coefficient was measured for materials containing elements hydrogen to calcium. Characteristic X-rays with energies 32–66keV were produced by X-ray fluorescence using a secondary target system, and 140keV gamma rays were obtained from an unsealed 99mTc source. The photon beams were highly collimated and recorded using energy dispersive detection. A high-purity germanium detector was utilised to distinguish

  15. Measurement of attenuation coefficients for bone, muscle, fat and water at 140, 364 and 662 keV gamma-ray energies

    Microsoft Academic Search

    A. Akar; H. Baltas; U. Çevik; F. Korkmaz; N. T. Okumusoglu

    2006-01-01

    The half-value thicknesses, linear and mass attenuation coefficients of biological samples such as bone, muscle, fat and water have been measured at 140, 364 and 662 keV gamma-ray energies by using the ATOMLABTM-930 medical spectrometer. The gamma-rays were obtained from 99mTc, 131I and 137Cs gamma-ray point sources. Also theoretical calculations have been performed in order to obtain the half-value thicknesses

  16. Measurement of x-ray attenuation coefficients for elements in the range 79 less than or equal to Z less than or equal to 92

    Microsoft Academic Search

    N. S. Saleh; M. A. Sharif; K. A. Al-Saleh

    2009-01-01

    A method for measuring the X-ray attenuation coefficients for elements with 79 less than or equal to Z less than or equal to 92 at the excitation energy of 121.9 keV (Gamma-rays emitted by Co-57 radioisotope source) is described. The accuracy is greatly improved by intensity ratio measurements of infinitely thin and thick targets; thus the uncertainties in the fundamental

  17. Measurements of the X-ray linear attenuation coefficient for low atomic number materials at energies 32-66 and 140keV

    Microsoft Academic Search

    S. M. Midgley

    2005-01-01

    The X-ray linear attenuation coefficient was measured for materials containing elements hydrogen to calcium. Characteristic X-rays with energies 32-66keV were produced by X-ray fluorescence using a secondary target system, and 140keV gamma rays were obtained from an unsealed 99mTc source. The photon beams were highly collimated and recorded using energy dispersive detection. A high-purity germanium detector was utilised to distinguish

  18. Use of Electromagnetic Acoustic Resonance Method to Detect Micro-Voids Via Evaluation of Ultrasonic Wave Attenuation Coefficient of SUS304 Steel Fabricated by Hot Isostatic Press

    Microsoft Academic Search

    Hidetaka Nishida; Hiroshi Yamaguchi; Masashi Yoshida

    2001-01-01

    Creep damage in SUS304 steel samples fabricated by a hot isostatic press (HIP) at 1050°C was evaluated using the electromagnetic acoustic resonance (EMAR), noise energy and ultrasonic spectroscopy (first moment) methods. The coefficients of attenuation of 1.1 to 5.4 MHz electromagnetically excited acoustic waves in the samples were investigated. By reducing diffraction loss and the loss to the electromagnetic acoustic

  19. Effect of sample thickness on the measured mass attenuation coefficients of some compounds and elements for 59.54, 661.6 and 1332.5 keV \\/gamma-rays

    Microsoft Academic Search

    M. A. Abdel-Rahman; E. A. Badawi; Y. L. Abdel-Hady; N. Kamel

    2000-01-01

    Measurements have been made to determine \\/gamma-rays attenuation coefficients very accurately by using an extremely narrow-collimated-beam transmission method. The effect of the sample thickness on the measured values of the mass attenuation coefficients (mu\\/rho)cm2\\/g of perspex, bakelite, paraffin, Al, Cu, Pb and Hg have been investigated at three different \\/gamma-ray energies (59.54, 661.6 and 1332.5 keV). It is seen that

  20. Measurement of the mass attenuation coefficients and electron densities for BiPbSrCaCuO superconductor at different energies

    Microsoft Academic Search

    U. Çevik; H. Baltas

    2007-01-01

    The mass attenuation coefficients for Bi, Pb, Sr, Ca, Cu metals, Bi2O3, PbO, SrCO3, CaO, CuO compounds and solid-state forms of Bi1.7Pb0.3Sr2Ca2Cu3O10 superconductor were determined at 57.5, 65.2, 77.1, 87.3, 94.6, 122 and 136keV energies. The samples were irradiated using a 57Co point source emitted 122 and 136keV ?-ray energies. The X-ray energies were obtained using secondary targets such as

  1. X-ray attenuation coefficients of Fe compounds in the Kedge region at different energies and the validity of the mixture rule

    Microsoft Academic Search

    U. Turgut; E. Buyukkasap; O. ?im?ek; M. Ertugrul

    2005-01-01

    The total mass attenuation coefficients for element Fe and compounds FeF3, Fe2O3, FeCl2·4H2O, FeCl32NH4Cl·H2O were measured at different energies between 4.508–17.443keV range by using secondary excitation method. Ti, V, Cr, Ni, Cu, Zn, As, Se, Br, Rb, Sr, Y, Zr, Nb, Mo were chosen as secondary exciter. 59.5keV gamma rays emitted from an 241Am annular source were used to excite

  2. Simultaneous evaluation of the linear and quadratic electro-optic coefficients of the nonlinear optical polymer by attenuated-total-reflection technique

    NASA Astrophysics Data System (ADS)

    Zhu, Xiaohui; Deng, Xiaoxu; Li, Honggen; Cao, Zhuangqi; Shen, Qishun; Wei, Wei; Liu, Feng

    2011-05-01

    A method of simultaneously evaluating the linear electro-optic and quadratic electro-optic coefficients of the nonlinear polymer poly (9,9-dioctyl-2,7-fluorene-co-benzo[c][1,2,5]thiadiazole-co-9-hexyl-3, 6-carbazole) (PF8-BT-CZ) was proposed based on the attenuated-total-reflection (ATR) technique. The measurement was sensitively carried out without the lock-in amplifier due to the prism-waveguide configuration of the sample and only one single optical path was applied, which simplified the experimental setup.

  3. Measurement of mass attenuation coefficients of some boron compounds and the trommel sieve waste in the energy range 15.746– 40.930 keV

    Microsoft Academic Search

    Orhan ?çelli; Salih Erzeneo?lu; Recep Boncukçuo?lu

    2003-01-01

    Mass attenuation coefficients of some boron compounds (H3BO3,Na2B4O7 and B3Al2O3) and the trommel sieve waste (TSW) have been measured by using an extremely narrow collimated-beam transmission method in the energy range 15.746–40.930keV. The characteristic K? and K? X-rays of Zr, Mo, Ag, In, Sb, Ba and Pr passed through H3BO3,Na2B4O7, B3Al2O3 and TSW were detected with a high-resolution Si(Li) detector.

  4. Quantitative measurement on optical attenuation coefficient of cell lines 5-8F and 6-10B using optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Li, Jianghua; Shen, Zhiyuan; He, Yonghong; Tu, Ziwei; Xia, Yunfei; Chen, Changshui; Liu, Songhao

    2012-10-01

    Oncogenesis and metastasis of tumor are difficult to detect during the clinic therapy. To explore the optical properties of tumorigenesis and metastasis in nasopharyngeal carcinoma (NPC), we assessed the NPC cell lines 5-8F and 6-10B by optical coherence tomography (OCT): first, the OCT images of the two different types of cell pellets were captured. Second, by fitting Beer's law to the averaged A-scans in these OCT datasets, the attenuation coefficients (?t) of the cells were extracted. The median attenuation coefficients (interquartile range (IQR)) of 5-8F and 6-10B were 6.79 mm-1 (IQR 6.52 to 7.23 mm-1) versus 8.06 mm-1 (IQR 7.65 to 8.40 mm-1), respectively (p < 0.01, df = 39). Subsequently, the results were compared with those obtained by polarization sensitive OCT, which further confirmed that the quantitative OCT analysis (by ?t) could differentiate the oncogenesis and metastasis NPC cell lines in real time non-invasively.

  5. Ex vivo determination of glucose permeability and optical attenuation coefficient in normal and adenomatous human colon tissues using spectral domain optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Zhao, Qingliang; Zhou, Chuanqing; Wei, Huajiang; He, Yonghong; Chai, Xinyu; Ren, Qiushi

    2012-10-01

    Recent reports have suggested that spectral domain optical coherence tomography (SD-OCT) is a useful tool for quantifying the permeability of hyperosmotic agents in various tissues. We report our preliminary results on quantification of glucose diffusion and assessment of the optical attenuation change due to the diffusion of glucose in normal and adenomatous human colon tissues in vitro by using a SD-OCT and then calculated the permeability coefficients (PC) and optical attenuation coefficients (AC). The PC of a 30% aqueous solution of glucose was 3.37±0.23×10-6 cm/s in normal tissue and 5.65±0.16×10-6 cm/s in cancerous colon tissue. Optical AC in a normal colon ranged from 3.48±0.37 to 2.68±0.82 mm-1 and was significantly lower than those seen in the cancerous tissue (8.48±0.95 to 3.16±0.69 mm-1, p<0.05). The results suggest that quantitative measurements of using PC and AC from OCT images could be a potentially powerful method for colon cancer detection.

  6. Chemical effects on K?/K? X-ray intensity ratios of Mo, Ag, Cd, Ba, La, Ce compounds and total mass attenuation coefficients of Fe and Cu

    NASA Astrophysics Data System (ADS)

    Sögüt, Ö.; Seven, S.; Baydas, E.; Büyükkasap, E.; Küçükönder, A.

    2001-08-01

    The K?/K? intensity ratios for pure Mo, Ag, Cd, Ba, La and Ce elements and for some of their compounds were investigated. The vacancies in the K shell were created by 59.5-keV ?-rays from a heavily filtered 241Am radioactive source. K X-rays were measured using a Si(Li) detector with a resolution of 155 eV at 5.9 keV. We observed chemical effects on K?/K? intensity ratios of Mo, Ag, Cd, Ba, La and Ce compounds. Detailed interpretation of data obtained from X-ray transmission measurements usually depends on the assumption that the contribution of each element is additive. This assumption yields the mixture rule for X-ray attenuation coefficients which is valid if molecular and chemical effects are negligible. We measured the total mass attenuation coefficients of Fe and Cu in various compounds. Self-absorption corrections were carried out on data for ligands in the different compounds. Our values were compared with the theoretical values for pure elements.

  7. Element analysis and calculation of the attenuation coefficients for gold, bronze and water matrixes using MCNP, WinXCom and experimental data

    NASA Astrophysics Data System (ADS)

    Esfandiari, M.; Shirmardi, S. P.; Medhat, M. E.

    2014-06-01

    In this study, element analysis and the mass attenuation coefficient for matrixes of gold, bronze and water with various impurities and the concentrations of heavy metals (Cu, Mn, Pb and Zn) are evaluated and calculated by the MCNP simulation code for photons emitted from Barium-133, Americium-241 and sources with energies between 1 and 100 keV. The MCNP data are compared with the experimental data and WinXCom code simulated results by Medhat. The results showed that the obtained results of bronze and gold matrix are in good agreement with the other methods for energies above 40 and 60 keV, respectively. However for water matrixes with various impurities, there is a good agreement between the three methods MCNP, WinXCom and the experimental one in low and high energies.

  8. Measurement of mass attenuation coefficients in some Cr, Co and Fe compounds around the absorption edge and the validity of the mixture rule

    Microsoft Academic Search

    U. Turgut; O. ?im?ek; E. Büyükkasap

    2007-01-01

    The total mass attenuation coefficients for elements Cr, Co and Fe and compounds CrCl2, CrCl3, Cr2(SO4)3K2SO4·24H2O, CoO, CoCl2, Co(CH3COO)2, FePO4, FeCl3·6H2O, Fe(SO4)2NH4·12H2O were measured at different energies between 4.508 and 14.142 keV using secondary excitation method. Ti, V, Cr, Mn, Fe, Co,\\u000a Ni, Cu, Zn, As, Se, Br, Rb, Sr were chosen as secondary exciters. 59.5 keV ?-rays emitted from

  9. X-Ray attenuation coefficients at different energies and the validity of the mixture rule for compounds around the absorption edge

    Microsoft Academic Search

    Ü. Turgut; Ö ?im?ek; E. Büyükkasap; M. Ertu?rul

    2002-01-01

    The total mass attenuation coefficients for the elements Co, Mn and Co2O3, compounds CoCl2.6H2O, CoSO4, CoSO4.7H2O, MnCO3, KMnO4, MnCl2.2H2O, and MnCl2.4H2O were measured at different energies between 4.508 and 11.210 keV using a secondary excitation method. Ti, Co, Ni, Cu, Zn, As, Se were chosen as secondary exciter. Gamma rays (59.5 keV) emitted from an 241Am annular source were used

  10. Absorption and Attenuation Coefficients Using the WET Labs ac-s in the Mid-Atlantic Bight: Field Measurements and Data Analysis

    NASA Technical Reports Server (NTRS)

    Ohi, Nobuaki; Makinen, Carla P.; Mitchell, Richard; Moisan, Tiffany A.

    2008-01-01

    Ocean color algorithms are based on the parameterization of apparent optical properties as a function of inherent optical properties. WET Labs underwater absorption and attenuation meters (ac-9 and ac-s) measure both the spectral beam attenuation [c (lambda)] and absorption coefficient [a (lambda)]. The ac-s reports in a continuous range of 390-750 nm with a band pass of 4 nm, totaling approximately 83 distinct wavelengths, while the ac-9 reports at 9 wavelengths. We performed the ac-s field measurements at nine stations in the Mid-Atlantic Bight from water calibrations to data analysis. Onboard the ship, the ac-s was calibrated daily using Milli Q-water. Corrections for the in situ temperature and salinity effects on optical properties of water were applied. Corrections for incomplete recovery of the scattered light in the ac-s absorption tube were performed. The fine scale of spectral and vertical distributions of c (lambda) and a (lambda) were described from the ac-s. The significant relationships between a (674) and that of spectrophotometric analysis and chlorophyll a concentration of discrete water samples were observed.

  11. LacR Is a Repressor of lacABCD and LacT Is an Activator of lacTFEG, Constituting the lac Gene Cluster in Streptococcus pneumoniae

    PubMed Central

    Afzal, Muhammad; Shafeeq, Sulman

    2014-01-01

    Comparison of the transcriptome of Streptococcus pneumoniae strain D39 grown in the presence of either lactose or galactose with that of the strain grown in the presence of glucose revealed the elevated expression of various genes and operons, including the lac gene cluster, which is organized into two operons, i.e., lac operon I (lacABCD) and lac operon II (lacTFEG). Deletion of the DeoR family transcriptional regulator lacR that is present downstream of the lac gene cluster revealed elevated expression of lac operon I even in the absence of lactose. This suggests a function of LacR as a transcriptional repressor of lac operon I, which encodes enzymes involved in the phosphorylated tagatose pathway in the absence of lactose or galactose. Deletion of lacR did not affect the expression of lac operon II, which encodes a lactose-specific phosphotransferase. This finding was further confirmed by ?-galactosidase assays with PlacA-lacZ and PlacT-lacZ in the presence of either lactose or glucose as the sole carbon source in the medium. This suggests the involvement of another transcriptional regulator in the regulation of lac operon II, which is the BglG-family transcriptional antiterminator LacT. We demonstrate the role of LacT as a transcriptional activator of lac operon II in the presence of lactose and CcpA-independent regulation of the lac gene cluster in S. pneumoniae. PMID:24951784

  12. Des Lacs River and Souris River

    USGS Multimedia Gallery

     The Des Lacs River coming in to the Souris River. Des Lacs River is the darker water, which is sediment and the Souris River is the lighter water. >Photo taken by USGS personnel on a Civil Air Patrol flight....

  13. Gamma-ray Emission from the gamma-ray-loud BL Lac Objects

    Microsoft Academic Search

    Guang-Zhong Xie; Ben-Zhong Dai; En-Wei Liang; Zhao-Hua Xie

    2001-01-01

    Using the HST observation data of BL Lac objects by Urry et al. and gamma-ray observation data, we find that there is a correlation between Fgamma and Fnuclei for gamma-ray-loud BL Lac objects (correlation coefficients: gamma=0.63, p=4.0 × 10-2), but no correlation between Fgamma and FOhost, where FOnuclei and FOhost are the fluxes of nuclei and host galaxy in V-band.

  14. X-ray attenuation coefficient measurements for photon energies 4.508–13.375 keV in Cu, Cr and their compounds and the validity of the mixture rule

    Microsoft Academic Search

    Ü Turgut; Ö ?im?ek; E Büyükkasap; M Ertu?rul

    2004-01-01

    To investigate the validity of the mixture rule which is used to compute the mass attenuation coefficients in compounds, the total mass attenuation coefficients for Cu, Cr elements and Cu2O, CuC2O4, CuCl2·2H2O, Cu(C2H3O2)2·H2O, Cr2O3, Cr(NO3)3, Cr2(SO4)3·H2O, Cr3(CH3CO7)(OH)2 compounds were measured at photon energies between 4.508 and 13.375keV by using the secondary excitation method. Ti, Mn, Fe, Ni, Zn, Ge, As,

  15. Measurement of the x-ray mass attenuation coefficient and determination of the imaginary component of the atomic form factor of tin over the energy range of 29-60 keV

    Microsoft Academic Search

    Martin D. de Jonge; Chanh Q. Tran; Christopher T. Chantler; Zwi Barnea; Bipin B. Dhal; David Paterson; Elliot P. Kanter; Stephen H. Southworth; Linda Young; Mark A. Beno; Jennifer A. Linton; Guy Jennings

    2007-01-01

    We use the x-ray extended-range technique (XERT) [C. T. Chantler et al., Phys. Rev. A 64, 062506 (2001)] to measure the mass attenuation coefficients of tin in the x-ray energy range of 29-60 keV to 0.04-3 % accuracy, and typically in the range 0.1-0.2 %. Measurements made over an extended range of the measurement parameter space are critically examined to

  16. Measurement of the x-ray mass attenuation coefficient and determination of the imaginary component of the atomic form factor of tin over the energy range of 29-60keV

    Microsoft Academic Search

    Martin D. de Jonge; Chanh Q. Tran; Christopher T. Chantler; Zwi Barnea; Bipin B. Dhal; David Paterson; Elliot P. Kanter; Stephen H. Southworth; Linda Young; Mark A. Beno; Jennifer A. Linton; Guy Jennings

    2007-01-01

    We use the x-ray extended-range technique (XERT) [C. T. Chantler , Phys. Rev. A 64, 062506 (2001)] to measure the mass attenuation coefficients of tin in the x-ray energy range of 29-60keV to 0.04-3% accuracy, and typically in the range 0.1-0.2% . Measurements made over an extended range of the measurement parameter space are critically examined to identify, quantify, and

  17. Measurement of the x-ray mass attenuation coefficient and determination of the imaginary component of the atomic form-factor of tin over the energy range of 29 keV-60 keV.

    SciTech Connect

    de Jonge, M. D.; Tran, C. Q.; Chantler, C. T.; Barnea, Z.; Dhal, B. P.; Paterson, D.; Kanter, E. P.; Southworth, S. H.; Young, L.; Beno, M. A.; Linton, J. A.; Jennings, G.; Univ. of Melbourne; Australian Synchrotron Project

    2007-01-01

    We use the x-ray extended-range technique (XERT) [C. T. Chantler et al., Phys. Rev. A 64, 062506 (2001)] to measure the mass attenuation coefficients of tin in the x-ray energy range of 29-60 keV to 0.04-3 % accuracy, and typically in the range 0.1-0.2 %. Measurements made over an extended range of the measurement parameter space are critically examined to identify, quantify, and correct a number of potential experimental systematic errors. These results represent the most extensive experimental data set for tin and include absolute mass attenuation coefficients in the regions of x-ray absorption fine structure, extended x-ray absorption fine structure, and x-ray absorption near-edge structure. The imaginary component of the atomic form factor f{sub 2} is derived from the photoelectric absorption after subtracting calculated Rayleigh and Compton scattering cross sections from the total attenuation. Comparison of the result with tabulations of calculated photoelectric absorption coefficients indicates that differences of 1-2 % persist between calculated and observed values.

  18. Measurement of the x-ray mass attenuation coefficient and determination of the imaginary component of the atomic form factor of tin over the energy range of 29-60 keV

    SciTech Connect

    Jonge, Martin D. de; Tran, Chanh Q.; Chantler, Christopher T.; Barnea, Zwi; Dhal, Bipin B.; Paterson, David; Kanter, Elliot P.; Southworth, Stephen H.; Young, Linda; Beno, Mark A.; Linton, Jennifer A.; Jennings, Guy [X-Ray Operations and Research, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439 (United States); School of Physics, University of Melbourne, Victoria 3010 (Australia); Australian Synchrotron Project, Major Projects Victoria, 800 Blackburn Road, Clayton, Victoria 3168 (Australia); Chemistry Division, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439 (United States); BESSRC-CAT, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439 (United States)

    2007-03-15

    We use the x-ray extended-range technique (XERT) [C. T. Chantler et al., Phys. Rev. A 64, 062506 (2001)] to measure the mass attenuation coefficients of tin in the x-ray energy range of 29-60 keV to 0.04-3 % accuracy, and typically in the range 0.1-0.2 %. Measurements made over an extended range of the measurement parameter space are critically examined to identify, quantify, and correct a number of potential experimental systematic errors. These results represent the most extensive experimental data set for tin and include absolute mass attenuation coefficients in the regions of x-ray absorption fine structure, extended x-ray absorption fine structure, and x-ray absorption near-edge structure. The imaginary component of the atomic form factor f{sub 2} is derived from the photoelectric absorption after subtracting calculated Rayleigh and Compton scattering cross sections from the total attenuation. Comparison of the result with tabulations of calculated photoelectric absorption coefficients indicates that differences of 1-2 % persist between calculated and observed values.

  19. Prospects for in vivo estimation of photon linear attenuation coefficients using postprocessing dual-energy CT imaging on a commercial scanner: Comparison of analytic and polyenergetic statistical reconstruction algorithms

    SciTech Connect

    Evans, Joshua D., E-mail: jevans2@mcvh-vcu.edu; Yu, Yaduo; Williamson, Jeffrey F. [Department of Radiation Oncology, Virginia Commonwealth University, Richmond, Virginia 23298 (United States)] [Department of Radiation Oncology, Virginia Commonwealth University, Richmond, Virginia 23298 (United States); Whiting, Bruce R. [Department of Radiology, University of Pittsburgh, Pittsburgh, Pennsylvania 15213 (United States)] [Department of Radiology, University of Pittsburgh, Pittsburgh, Pennsylvania 15213 (United States); O’Sullivan, Joseph A. [Department of Electrical and Systems Engineering, Washington University, St. Louis, Missouri 63130 (United States)] [Department of Electrical and Systems Engineering, Washington University, St. Louis, Missouri 63130 (United States); Politte, David G. [Mallinckrodt Institute of Radiology, Washington University, St. Louis, Missouri 63110 (United States)] [Mallinckrodt Institute of Radiology, Washington University, St. Louis, Missouri 63110 (United States); Klahr, Paul H. [Philips Healthcare, 595 Miner Rd., Highland Hts., Ohio 44143 (United States)] [Philips Healthcare, 595 Miner Rd., Highland Hts., Ohio 44143 (United States)

    2013-12-15

    Purpose: Accurate patient-specific photon cross-section information is needed to support more accurate model-based dose calculation for low energy photon-emitting modalities in medicine such as brachytherapy and kilovoltage x-ray imaging procedures. A postprocessing dual-energy CT (pDECT) technique for noninvasivein vivo estimation of photon linear attenuation coefficients has been experimentally implemented on a commercial CT scanner and its accuracy assessed in idealized phantom geometries. Methods: Eight test materials of known composition and density were used to compare pDECT-estimated linear attenuation coefficients to NIST reference values over an energy range from 10 keV to 1 MeV. As statistical image reconstruction (SIR) has been shown to reconstruct images with less random and systematic error than conventional filtered backprojection (FBP), the pDECT technique was implemented with both an in-house polyenergetic SIR algorithm, alternating minimization (AM), as well as a conventional FBP reconstruction algorithm. Improvement from increased spectral separation was also investigated by filtering the high-energy beam with an additional 0.5 mm of tin. The law of propagated uncertainty was employed to assess the sensitivity of the pDECT process to errors in reconstructed images. Results: Mean pDECT-estimated linear attenuation coefficients for the eight test materials agreed within 1% of NIST reference values for energies from 1 MeV down to 30 keV, with mean errors rising to between 3% and 6% at 10 keV, indicating that the method is unbiased when measurement and calibration phantom geometries are matched. Reconstruction with FBP and AM algorithms conferred similar mean pDECT accuracy. However, single-voxel pDECT estimates reconstructed on a 1 × 1 × 3 mm{sup 3} grid are shown to be highly sensitive to reconstructed image uncertainty; in some cases pDECT attenuation coefficient estimates exhibited standard deviations on the order of 20% around the mean. Reconstruction with the statistical AM algorithm led to standard deviations roughly 40% to 60% less than FBP reconstruction. Additional tin filtration of the high energy beam exhibits similar pDECT estimation accuracy as the unfiltered beam, even when scanning with only 25% of the dose. Using the law of propagated uncertainty, low Z materials are found to be more sensitive to image reconstruction errors than high Z materials. Furthermore, it is estimated that reconstructed CT image uncertainty must be limited to less than 0.25% to achieve a target linear-attenuation coefficient estimation uncertainty of 3% at 28 keV. Conclusions: That pDECT supports mean linear attenuation coefficient measurement accuracies of 1% of reference values for energies greater than 30 keV is encouraging. However, the sensitivity of the pDECT measurements to noise and systematic errors in reconstructed CT images warrants further investigation in more complex phantom geometries. The investigated statistical reconstruction algorithm, AM, reduced random measurement uncertainty relative to FBP owing to improved noise performance. These early results also support efforts to increase DE spectral separation, which can further reduce the pDECT sensitivity to measurement uncertainty.

  20. Prospects for in vivo estimation of photon linear attenuation coefficients using postprocessing dual-energy CT imaging on a commercial scanner: Comparison of analytic and polyenergetic statistical reconstruction algorithms

    PubMed Central

    Evans, Joshua D.; Whiting, Bruce R.; O’Sullivan, Joseph A.; Politte, David G.; Klahr, Paul H.; Yu, Yaduo; Williamson, Jeffrey F.

    2013-01-01

    Purpose: Accurate patient-specific photon cross-section information is needed to support more accurate model-based dose calculation for low energy photon-emitting modalities in medicine such as brachytherapy and kilovoltage x-ray imaging procedures. A postprocessing dual-energy CT (pDECT) technique for noninvasive in vivo estimation of photon linear attenuation coefficients has been experimentally implemented on a commercial CT scanner and its accuracy assessed in idealized phantom geometries. Methods: Eight test materials of known composition and density were used to compare pDECT-estimated linear attenuation coefficients to NIST reference values over an energy range from 10 keV to 1 MeV. As statistical image reconstruction (SIR) has been shown to reconstruct images with less random and systematic error than conventional filtered backprojection (FBP), the pDECT technique was implemented with both an in-house polyenergetic SIR algorithm, alternating minimization (AM), as well as a conventional FBP reconstruction algorithm. Improvement from increased spectral separation was also investigated by filtering the high-energy beam with an additional 0.5 mm of tin. The law of propagated uncertainty was employed to assess the sensitivity of the pDECT process to errors in reconstructed images. Results: Mean pDECT-estimated linear attenuation coefficients for the eight test materials agreed within 1% of NIST reference values for energies from 1 MeV down to 30 keV, with mean errors rising to between 3% and 6% at 10 keV, indicating that the method is unbiased when measurement and calibration phantom geometries are matched. Reconstruction with FBP and AM algorithms conferred similar mean pDECT accuracy. However, single-voxel pDECT estimates reconstructed on a 1 × 1 × 3 mm3 grid are shown to be highly sensitive to reconstructed image uncertainty; in some cases pDECT attenuation coefficient estimates exhibited standard deviations on the order of 20% around the mean. Reconstruction with the statistical AM algorithm led to standard deviations roughly 40% to 60% less than FBP reconstruction. Additional tin filtration of the high energy beam exhibits similar pDECT estimation accuracy as the unfiltered beam, even when scanning with only 25% of the dose. Using the law of propagated uncertainty, low Z materials are found to be more sensitive to image reconstruction errors than high Z materials. Furthermore, it is estimated that reconstructed CT image uncertainty must be limited to less than 0.25% to achieve a target linear-attenuation coefficient estimation uncertainty of 3% at 28 keV. Conclusions: That pDECT supports mean linear attenuation coefficient measurement accuracies of 1% of reference values for energies greater than 30 keV is encouraging. However, the sensitivity of the pDECT measurements to noise and systematic errors in reconstructed CT images warrants further investigation in more complex phantom geometries. The investigated statistical reconstruction algorithm, AM, reduced random measurement uncertainty relative to FBP owing to improved noise performance. These early results also support efforts to increase DE spectral separation, which can further reduce the pDECT sensitivity to measurement uncertainty. PMID:24320525

  1. Allostery and the lac Operon.

    PubMed

    Lewis, Mitchell

    2013-07-10

    The ability to regulate gene expression is essential for controlling metabolic events in a cell. Proteins that function like molecular switches respond to fluctuations in the environment to maintain homeostasis. The operon model, proposed by Jacob and Monod, provides a cogent depiction for how gene expression is regulated. A molecular mechanism for the regulation followed shortly with the theory for allosteric transition. Over the past half-century, the details of the lac operon and the allosteric model have been tested using genetic, biochemical, and structural techniques. Remarkably, the principles originally put forward 50 years ago remain essentially unchanged. Models for the operon and the theory of allosteric transitions are two of the most profound discoveries of molecular biology. PMID:23500493

  2. Transcriptional and functional analysis of galactooligosaccharide uptake by lacS in Lactobacillus acidophilus

    PubMed Central

    Andersen, Joakim M.; Barrangou, Rodolphe; Abou Hachem, Maher; Lahtinen, Sampo; Goh, Yong Jun; Svensson, Birte; Klaenhammer, Todd R.

    2011-01-01

    Probiotic microbes rely on their ability to survive in the gastrointestinal tract, adhere to mucosal surfaces, and metabolize available energy sources from dietary compounds, including prebiotics. Genome sequencing projects have proposed models for understanding prebiotic catabolism, but mechanisms remain to be elucidated for many prebiotic substrates. Although ?-galactooligosaccharides (GOS) are documented prebiotic compounds, little is known about their utilization by lactobacilli. This study aimed to identify genetic loci in Lactobacillus acidophilus NCFM responsible for the transport and catabolism of GOS. Whole-genome oligonucleotide microarrays were used to survey the differential global transcriptome during logarithmic growth of L. acidophilus NCFM using GOS or glucose as a sole source of carbohydrate. Within the 16.6-kbp gal-lac gene cluster, lacS, a galactoside-pentose-hexuronide permease-encoding gene, was up-regulated 5.1-fold in the presence of GOS. In addition, two ?-galactosidases, LacA and LacLM, and enzymes in the Leloir pathway were also encoded by genes within this locus and up-regulated by GOS stimulation. Generation of a lacS-deficient mutant enabled phenotypic confirmation of the functional LacS permease not only for the utilization of lactose and GOS but also lactitol, suggesting a prominent role of LacS in the metabolism of a broad range of prebiotic ?-galactosides, known to selectively modulate the beneficial gut microbiota. PMID:22006318

  3. Starspot proper motion in HK Lac

    NASA Astrophysics Data System (ADS)

    Olah, K.; Holl, A.; Gesztelyi, L.

    The spot proper motions in HK Lac observed by Olah et al. (1985) are discussed. It is shown that the two spotted areas on HK Lac move rapidly, similar to the motions of new spots in the sun. Possible explanations for the observed behavior of the spots are magnetic interconnection between the two areas or the simultaneous formation of new spots in both the old active region near phase 0.3 and the new active region near phase 0.6. The phases of active areas of HK Lac are illustrated for the period from 1978 to 1988.

  4. Mutagenesis in the lacI gene target of E. coli: improved analysis for lacI (d) and lacO mutants.

    PubMed

    Swerdlow, Sarah J; Schaaper, Roel M

    2014-12-01

    The lacI gene of E. coli has been a highly useful target for studies of mutagenesis, particularly for analysis of the specificity (spectrum) of mutations generated under a variety of conditions and in various genetic backgrounds. The gene encodes the repressor of the lac operon, and lacI-defective mutants displaying constitutive expression of the operon are readily selected. DNA sequencing of the lacI mutants has often been confined to the N-terminal region of the protein, as it presents a conveniently short target with a high density of detectably mutable sites. Mutants in this region are easily selected due to their dominance in a genetic complementation test (lacI (d) mutants). A potential complication in these studies is that constitutive expression of lac may also arise due to mutations in the lac operator (lacO mutants). Under some conditions, for example when analyzing spontaneous mutations, lacO mutants can comprise a very high fraction of the constitutive mutants due to a strong base-substitution hotspot in the lac operator. Such mutational hot spots diminish the return of the sequencing effort and do not yield significant new information. For this reason, a procedure to eliminate the lacO mutants prior to DNA sequencing is desirable. Here, we report a simple method that allows screening out of lacO mutants. This method is based on the lack of resistance of lacO mutants to kanamycin under conditions when the kan gene is expressed from a plasmid under control of the lac promoter-operator (lacPO). We show data validating the new approach with sets of known lacI (d) and lacO mutants, and further apply it to the generation of a new collection of spontaneous mutations, where lacO mutants have historically been a significant contributor. PMID:25379012

  5. BL Lac Objects in the Sloan Digital Sky Survey (SDSS)

    E-print Network

    A. C. Gupta; W. Yuan; X. Dong; T. Ji; H. -Y. Zhou; J. M. Bai; )

    2006-12-19

    We collected a sample of 661 confirmed and 361 possible BL Lac candidates from the recent catalog of BL Lac objects (Veron-Cetty & Veron 2006). We searched these sources in the recent data release DR5 of the Sloan Digital Sky Survey (SDSS) and found spectra were available for 169 and 109 confirmed and possible BL Lac candidates respectively. We found 32 candidates from confirmed and 19 candidates from possible BL Lac lists have non featureless spectra and are thus possibly not BL Lac candidates. We report here the preliminary results from our analysis of a sample of 278 BL Lac objects.

  6. Physiological regulation of a decontrolled lac operon.

    PubMed Central

    Wanner, B L; Kodaira, R; Neidhardt, F C

    1977-01-01

    The expression of the lac operon was studied under a variety of growth conditions in induced and in constitutive cells of Escherichia coli that carried different catabolite-insensitive lac promoters. Use of such "decontrolled" lac operons permitted a study of the expression of an operon that was presumably subject only to passive control. Since the use of toluenized cells was demonstrated not to be completely reliable, all enzyme assays were performed on sonic supernatant fluids. The cells contained different catabolite-insensitive promoters, which included the L1 and UV5 lac promoters, as well as others isolated in this study. There were three major observations. First, small but real carbon source effects were seen. Second, there was only a small change in beta-galactosidase specific activity with changes in the growth rate. This result implies a limited transcription and/or translation capacity within the cell. Third, at rapid growth rates, most promoters exhibited a decreased expression. The UV5 promoter, which was the "strongest" promoter, was an exception. A mechanism to explain this promoter-dependent control is discussed. PMID:323228

  7. Ultrasonic attenuation in pearlitic steel.

    PubMed

    Du, Hualong; Turner, Joseph A

    2014-03-01

    Expressions for the attenuation coefficients of longitudinal and transverse ultrasonic waves are developed for steel with pearlitic microstructure. This type of lamellar duplex microstructure influences attenuation because of the lamellar spacing. In addition, longitudinal attenuation measurements were conducted using an unfocused transducer with 10 MHz central frequency on the cross section of a quenched railroad wheel sample. The dependence of longitudinal attenuation on the pearlite microstructure is observed from the changes of longitudinal attenuation from the quenched tread surface to deeper locations. The results show that the attenuation value is lowest and relatively constant within the quench depth, then increases linearly. The experimental results demonstrate a reasonable agreement with results from the theoretical model. Ultrasonic attenuation provides an important non-destructive method to evaluate duplex microstructure within grains which can be implemented for quality control in conjunction with other manufacturing processes. PMID:24268679

  8. Midperiod Rayleigh wave attenuation model for Asia

    Microsoft Academic Search

    Anatoli L. Levshin; Xiaoning Yang; Mikhail P. Barmin; Michael H. Ritzwoller

    2010-01-01

    We present an attenuation model for midperiod Rayleigh waves in Central Asia and surrounding regions. This model is defined by maps of attenuation coefficient across the region of study in the period band 14–24 s. The model is constructed to characterize the regional variations in attenuation of seismic waves in the crust, which are related to the tectonic history of

  9. Dcembre 2011 Lac Tchad : les riverains

    E-print Network

    - rains : le Niger, le Nigeria, le Tchad et le Cameroun. Ce lac a connu d'importants changements ces- lier penchés sur les changements de systèmes de production dans la région de Bosso au Niger, petite, le niébé... Dans la vallée de la rivière Komadougou Yobe, au Niger, ils ont même entrepris la culture

  10. Experimental hypoxic-ischemic encephalopathy: comparison of apparent diffusion coefficients and proton magnetic resonance spectroscopy.

    PubMed

    Li, Yang-Kang; Liu, Guo-Rui; Zhou, Xiu-Guo; Cai, Ai-Qun

    2010-05-01

    This study aims to compare the apparent diffusion coefficients (ADCs) and proton magnetic resonance spectroscopy ((1)H-MRS) in the first 24 h of acute hypoxic-ischemic brain damage (HIBD) in piglets. Twenty-five 7-day-old piglets were subjected to transient bilateral common carotid artery occlusion followed by ventilation with 4% oxygen for 1 h. Diffusion-weighted imaging (DWI) and (1)H-MRS were performed on cessation of the insult or at 3, 6, 12 or 24 h after resuscitation (all n=5). ADCs, N-acetylaspartate/choline (NAA/Cho), NAA/creatine (NAA/Cr), lactate/NAA (Lac/NAA), Lac/Cho and Lac/Cr were calculated. Cerebral injury was evaluated by pathological study and Hsp70 immunohistochemical analysis. On cessation of the insult, ADCs, NAA/Cho and NAA/Cr reduced, Lac/NAA, Lac/Cho and Lac/Cr increased. From 3 to 12 h after resuscitation, ADCs, Lac/NAA, Lac/Cho and Lac/Cr recovered, NAA/Cho and NAA/Cr reduced. Twenty-four hours after resuscitation, ADCs reduced once more, Lac/NAA, Lac/Cho and Lac/Cr increased again, whereas NAA/Cho and NAA/Cr decreased continuously. Pathological study revealed mild cerebral edema on cessation of the insult and more and more severe cerebral injury after resuscitation. No Hsp70-positive cells were detected on cessation of the insult. From 3 to 12 hours after resuscitation, Hsp70-positive cells gradually increased. Twenty-four hours after resuscitation, Hsp70-positive cells decreased. Throughout the experiment, changes in NAA/Cho and pathology had the best correlation (R=-0.729). In conclusion, NAA/Cho is the most precise ratio to reflect the pathological changes of early HIBD. Transient ADCs and Lac ratios recovery do not predict the reversal of histological damage of early HIBD. Reducing astrocytic swelling is of great clinical significance. PMID:20071123

  11. VHE BL Lacs through the MAGIC glasses

    NASA Astrophysics Data System (ADS)

    Becerra González, Josefa; MAGIC Collaboration

    2015-03-01

    In this contribution an overview of the latest results on the study of BL Lac objects with the MAGIC telescopes at the very high energy (VHE, E>100 GeV) gamma-rays is presented. Three new VHE sources were detected during 2014, two BL Lac objects and the gravitational lensed blazar S3 0218+357. MAGIC detected very fast intra-night variability from IC 310. This detection points to smaller emitting regions than the event horizon, this is hard to be explained in the framework of the current theoretical models. The long term multi wavelength (MWL) study of the BL Lac PKS 1424+240 shows correlation between the radio and optical emission, pointing to a common origin. The MWL SED is not well fitted by a one-zone synchrotron-self Compton (SSC) model, but a two-zone SSC model can explain both, the MWL light curve and the SED. Spectral curvature has been found in the observed VHE spectrum from PG 1553+113. This is the first time that spectral curvature compatible with the EBL absorption is found in an individual object.

  12. Isolation and characterization of the lacA gene encoding beta-galactosidase in Bacillus subtilis and a regulator gene, lacR.

    PubMed Central

    Daniel, R A; Haiech, J; Denizot, F; Errington, J

    1997-01-01

    We have isolated transposon insertions in the lacA gene encoding an endogenous beta-galactosidase of Bacillus subtilis. Upstream of the putative operon containing lacA is a negative regulator, lacR, which encodes a product related to a family of regulators that includes the lactose repressor, lacI, of Escherichia coli. New strains with insertions in the lacA gene should be of use in studies using lacZ fusions in B. subtilis. PMID:9287030

  13. RNA polymerase structure and function at lac operon

    Microsoft Academic Search

    Sergei Borukhov; Jookyung Lee

    2005-01-01

    Transcription of E. coli lac operon by RNA polymerase (RNAP) is a classic example of how the basic functions of this enzyme, specifically the ability to recognize\\/bind promoters, melt the DNA and initiate RNA synthesis, is positively regulated by transcription activators, such as cyclic AMP-receptor protein, CRP, and negatively regulated by lac-repressor, LacI. In this review, we discuss the recent

  14. The Lac Cinquante Uranium Deposit, Nunavut, Canada

    NASA Astrophysics Data System (ADS)

    Bridge, N. J.; Banerjee, N. R.; Finnigan, C. S.; Carpenter, R.; Ward, J.

    2009-12-01

    The Lac Cinquante uranium deposit is located in the Kivalliq district of Nunavut approximately 350 km west of Rankin Inlet. The deposit is hosted in Archean greenstones that are unconformably overlain by the northeast trending Angikuni sub-basin in the Hearne Subprovince of the Western Churchill Province. Mineralization is found within the basement volcanics that have undergone hydrothermal alteration along fault zones. Three dominant styles of mineralization within the Archean greenstones has been documented by past studies including: disseminated pitchblende with base metals in tuffaceous metasediments, discrete pitchblende veins that cut across the metasediments, and quartz, carbonate, sulfides, and pitchblende in gash veins on 040 to 060 trending cross fractures. In this study we present newly acquired detailed outcrop-scale maps of the hydrothermally altered pitchblende gash veins that have been combined with an updated regional scale (1:5000) map to investigate the importance of the pitchblende gash veins in the formation of the ore zone. Combination of detailed outcrop maps with deposit scale geology provides valuable targets for drilling and help with understanding the relationship of gash veins to the main ore zones. Preliminary bulk-rock oxygen stable isotope analyses of drill core surrounding the main ore zone at the Lac Cinquante deposit are elevated above normal magmatic values. This is interpreted to represent an alteration envelope, possibly due to elevated fluid flow proximal to the ore zone. Additionally, newly acquired geochemical, mineralogical, and petrological data from drill core samples show evidence for late-stage alteration of the rocks surrounding the Lac Cinquante deposit. The combination of geochemical and mineralogical data will aid investigation of the extent and degree of hydrothermal alteration associated with formation of this ore deposit.

  15. Altered specificity in DNA binding by the lac repressor: a mutant lac headpiece that mimics the gal repressor.

    PubMed

    Kopke Salinas, Roberto; Folkers, Gert E; Bonvin, Alexandre M J J; Das, Devashish; Boelens, Rolf; Kaptein, Robert

    2005-09-01

    Recognition of the lac operator by the lac repressor involves specific interactions between residues in the repressor's recognition helix and bases in the DNA major groove. Tyr17 and Gln18, at positions 1 and 2 in the lac repressor recognition helix, can be exchanged for other amino acids to generate mutant repressors that display altered specificity. We have solved the solution structure of a protein-DNA complex of an altered-specificity mutant lac headpiece in which Tyr17 and Gln18 were exchanged for valine and alanine, respectively, as found in the recognition helix of the gal repressor. As previously described by Lehming et al. (EMBO J. 1987, 6, 3145-3153), this altered-specificity mutant of the lac repressor recognizes a variant lac operator that is similar to the gal operator Oe. The mutant lac headpiece showed the predicted specificity and is also able to mimic the gal repressor by recognizing and bending the natural gal operator Oe. These structural data show that, while most of the anchoring points that help the lac headpiece to assemble on the lac operator were preserved, a different network of protein-DNA interactions connecting Ala17 and Val18 to bases in the DNA major groove drives the specificity towards the altered operator. PMID:16094693

  16. X-Ray Form Factor, Attenuation and Scattering Tables

    National Institute of Standards and Technology Data Gateway

    SRD 66 X-Ray Form Factor, Attenuation and Scattering Tables (Web, free access)   This database collects tables and graphs of the form factors, the photoabsorption cross section, and the total attenuation coefficient for any element (Z <= 92).

  17. M87: A Misaligned BL LAC?

    E-print Network

    Zlatan I. Tsvetanov; George F. Hartig; Holland C. Ford; Michael A. Dopita; Gerard A. Kriss; Yichuan C. Pei; Linda L. Dressel; Richard J. Harms

    1997-11-20

    The nuclear region of M87 was observed with the Faint Object Spectrograph (FOS) on the Hubble Space Telescope (HST) at 6 epochs, spanning 18 months, after the HST image quality was improved with the deployment of the corrective optics (COSTAR) in December 1993. From the FOS target acquisition data, we have established that the flux from the optical nucleus of M87 varies by a factor ~2 on time scales of ~2.5 months and by as much as 25% over 3 weeks, and remains unchanged (<= 2.5%) on time scales of ~1 day. The changes occur in an unresolved central region <= 5 pc in diameter, with the physical size of the emitting region limited by the observed time scales to a few hundred gravitational radii. The featureless continuum spectrum becomes bluer as it brightens while emission lines remain unchanged. This variability combined with the observations of the continuum spectral shape, strong relativistic boosting and the detection of significant superluminal motions in the jet, strongly suggest that M87 belongs to the class of BL Lac objects but is viewed at an angle too large to reveal the classical BL Lac properties.

  18. Real-time conformational changes in LacY.

    PubMed

    Smirnova, Irina; Kasho, Vladimir; Kaback, H Ronald

    2014-06-10

    Galactoside/H(+) symport across the cytoplasmic membrane of Escherichia coli is catalyzed by lactose permease (LacY), which uses an alternating access mechanism with opening and closing of deep cavities on the periplasmic and cytoplasmic sides. In this study, conformational changes in LacY initiated by galactoside binding were monitored in real time by Trp quenching/unquenching of bimane, a small fluorophore covalently attached to the protein. Rates of change in bimane fluorescence on either side of LacY were measured by stopped flow with LacY in detergent or in proteoliposomes and were compared with rates of galactoside binding. With LacY in proteoliposomes, the periplasmic cavity is tightly sealed and the substrate-binding rate is limited by the rate of opening of this cavity. Rates of opening, measured as unquenching of bimane fluorescence, are 20-30 s(-1), independent of sugar concentration and essentially the same in detergent or in proteoliposomes. On the cytoplasmic side of LacY in proteoliposomes, slow bimane quenching (i.e., closing of the cavity) is observed at a rate that is also independent of sugar concentration and similar to the rate of sugar binding from the periplasmic side. Therefore, opening of the periplasmic cavity not only limits access of sugar to the binding site of LacY but also controls the rate of closing of the cytoplasmic cavity. PMID:24872451

  19. Real-time conformational changes in LacY

    PubMed Central

    Smirnova, Irina; Kasho, Vladimir; Kaback, H. Ronald

    2014-01-01

    Galactoside/H+ symport across the cytoplasmic membrane of Escherichia coli is catalyzed by lactose permease (LacY), which uses an alternating access mechanism with opening and closing of deep cavities on the periplasmic and cytoplasmic sides. In this study, conformational changes in LacY initiated by galactoside binding were monitored in real time by Trp quenching/unquenching of bimane, a small fluorophore covalently attached to the protein. Rates of change in bimane fluorescence on either side of LacY were measured by stopped flow with LacY in detergent or in proteoliposomes and were compared with rates of galactoside binding. With LacY in proteoliposomes, the periplasmic cavity is tightly sealed and the substrate-binding rate is limited by the rate of opening of this cavity. Rates of opening, measured as unquenching of bimane fluorescence, are 20–30 s?1, independent of sugar concentration and essentially the same in detergent or in proteoliposomes. On the cytoplasmic side of LacY in proteoliposomes, slow bimane quenching (i.e., closing of the cavity) is observed at a rate that is also independent of sugar concentration and similar to the rate of sugar binding from the periplasmic side. Therefore, opening of the periplasmic cavity not only limits access of sugar to the binding site of LacY but also controls the rate of closing of the cytoplasmic cavity. PMID:24872451

  20. Natural LacI from E. coli yields faster response and higher level of expression than the LVA-tagged LacI.

    PubMed

    Andreassen, Patrick Rosendahl; Fredberg, Sofie; Horan, Mattias; Knudsen, Maria Højberg; Jacobsen, Kirstine; Kjær, Andreas; Krogh, Thøger Jensen; Kronborg, Tina; Mattsson, Nicky Cordua; Schmidt, Sissel Ida; Wille, Heidi; Andersen, Ann

    2014-12-19

    The lac promoter is one of the most commonly used promoters for expression control of recombinant genes in E. coli. In the absence of galactosides, the lac promoter is repressed by its repressor protein LacI. Since the lac promoter is regulated by a repressor, overexpression of LacI is necessary for regulation when the promoter is introduced on a high-copy plasmid. For that purpose, a modified variant of LacI, a LVA-tagged LacI, was submitted to the Registry of Standard Biological Parts and has been used for more than 500 constructs since then. We have found, however, that natural LacI is superior to the LVA-tagged LacI as controller of expression. PMID:25524095

  1. Light attenuation on unicellular marine phytoplankton

    Microsoft Academic Search

    Tadeusz Krol; Maria Lotocka

    1994-01-01

    Sea phytoplankton plays a considerable role in the interactive processes between light and the sea. Its species composition and the physiological development phase influence the spectrum of the light attenuation coefficient in the sea. Laboratory measurements of light attenuation spectrum were carried out on three different phytoplankton monocultures of the unicellular green algae Chlorella vulgaris and the larger Chlorella kesleri

  2. Role of translation in the UTP-modulated attenuation at the pyrBI operon of Escherichia coli

    Microsoft Academic Search

    Kåre Clemmesen; Fons Bonekamp; Olle Karlström; Kaj Frank Jensen

    1985-01-01

    A 273 bp DNA fragment containing the attenuator of the pyrBI operon was inserted into a synthetic cloning site early in the lacZ gene on a plasmid. By this operation the first few codons of lacZ were joined through a linker to the last 39 codons of the open reading frame for the putative pyrB leader peptide. In addition a

  3. L'aération naturelle et artificielle des lacs

    Microsoft Academic Search

    P. Par Mercier

    1957-01-01

    Conclusion  Par ce qui prcde, on se rend compte que chaque lac constitue un cas particulier qui doit tre tudi pour lui-mme et que\\u000a l'aration artificielle d'un lac de grandes dimensions est susceptible d'tre ralise.\\u000a \\u000a A notre poque les lacs prennent de plus en plus d'importance comme rservoirs pouvant servir l'alimentation en eau potable.\\u000a Pour remplir ce rle il est indispensable

  4. Julius Smith LAC-2008 1 / 66 Virtual Electric Guitars and Effects Using Faust and Octave

    E-print Network

    Smith III, Julius Orion

    Julius Smith LAC-2008 ­ 1 / 66 Virtual Electric Guitars and Effects Using Faust and Octave Julius Smith CCRMA, Stanford University LAC-2008 March 1, 2008 #12;Outline Julius Smith LAC-2008 ­ 2 / 66 Smith LAC-2008 ­ 3 / 66 (Extended Karplus Strong, Sullivan extensions, early waveguide) · Some patents

  5. Chandra's First Decade Observing AR Lac

    NASA Astrophysics Data System (ADS)

    Ratzlaff, Peter; Drake, Jeremy J.; Durham, R. Nicholas; Kashyap, Vinay; Posson-Brown, Jennifer; Wargelin, Bradford J.

    2009-09-01

    X-ray observations of the eclipsing RS CVn-type binary AR Lacertae have been obtained every year from 1999 to 2008 with the Chandra High Resolution Camera imaging and spectroscopic detectors (HRC-I, HRC-S) as part of their gain and point spread function calibration. These represent the best quality data yet obtained on the long term variability of the X-ray emission of an RS CVn star, and are rendered especially valuable for the multi-epoch coverage of the AR Lac eclipses. The data are characterised by stochastic variability by factors of ˜2 on timescales of one to several ks, and by minor flaring events in which count rates are observed to be elevated by slightly larger factors. During primary eclipse, the X-ray count rate is generally observed at approximately 60% of its value outside of eclipse and during periods of relative quiescence. Little evidence for secondary eclipses is present in the data, reminiscent of earlier X-ray and EUV observations. The X-ray count rate modulation through the eclipses allow us to place an upper limit on the extent of a spherically symmetric coronae of about two stellar radii, the exact limit depending on the details of the coronal models and partition of emission between the component stars. We compare the observed Chandra count rates to earlier EUVE, EINSTEIN, EXOSAT and ROSAT observations and comment on the apparent lack of cyclic coronal activity on RS CVn-type binaries.

  6. A computational study of ?-lac mutants

    NASA Astrophysics Data System (ADS)

    Werner, Maria; Aurell, Erik

    2009-12-01

    We present a comprehensive, computational study of the properties of bacteriophage ? mutants designed by Atsumi and Little (2006 Proc. Natl. Acad. Sci. 103 4558-63). These phages underwent a genetic reconstruction where Cro was replaced by a dimeric form of the Lac repressor. To clarify the theoretical characteristics of these mutants, we built a detailed thermodynamic model. The mutants all have a different genetic wiring than the wild-type ?. One group lacks regulation of PRM by the lytic protein. These mutants only exhibit the lysogenic equilibrium, with no transiently active PR. The other group lacks the negative feedback from CI. In this group, we identify a handful of bi-stable mutants, although the majority only exhibit the lysogenic equilibrium. The experimental identification of functional phages differs from our predictions. From a theoretical perspective, there is no reason why only 4 out of 900 mutants should be functional. The differences between theory and experiment can be explained in two ways. Either, the view of the ? phage as a bi-stable system needs to be revised, or the mutants have in fact not undergone a modular replacement, as intended by Atsumi and Little, but constitute instead a wider systemic change.

  7. Tetramer opening in LacI-mediated DNA looping

    PubMed Central

    Rutkauskas, Danielis; Zhan, Hongli; Matthews, Kathleen S.; Pavone, Francesco S.; Vanzi, Francesco

    2009-01-01

    Lactose repressor protein (LacI) controls transcription of the genes involved in lactose metabolism in bacteria. Essential to optimal LacI-mediated regulation is its ability to bind simultaneously to two operators, forming a loop on the intervening DNA. Recently, several lines of evidence (both theoretical and experimental) have suggested various possible loop structures associated with different DNA binding topologies and LacI tetramer structural conformations (adopted by flexing about the C-terminal tetramerization domain). We address, specifically, the role of protein opening in loop formation by employing the single-molecule tethered particle motion method on LacI protein mutants chemically cross-linked at different positions along the cleft between the two dimers. Measurements on the wild-type and uncross-linked LacI mutants led to the observation of two distinct levels of short tether length, associated with two different DNA looping structures. Restricting conformational flexibility of the protein by chemical cross-linking induces pronounced effects. Crosslinking the dimers at the level of the N-terminal DNA binding head (E36C) completely suppresses looping, whereas cross-linking near the C-terminal tetramerization domain (Q231C) results in changes of looping geometry detected by the measured tether length distributions. These observations lead to the conclusion that tetramer opening plays a definite role in at least a subset of LacI/DNA loop conformations. PMID:19805348

  8. Lac Courte Oreilles Energy Analysis Project

    SciTech Connect

    Leslie Isham; Denise Johnson

    2009-04-01

    The Lac Courte Oreilles Tribe applied for first step funding in 2007 and was awarded in October of that year. We wanted to perform an audit to begin fulfilling two commitments we made to our membership and resolutions that we adopted. One was the Kyoto Protocol and reduce our carbon emissions by 25% and to produce 25% of our energy by sustainable means. To complete these goals we needed to begin with first assessing what our carbon emissions are and begin taking the steps to conserve on the energy we currently use. The First Step Grant gave us the opportunity to do this. Upon funding the Energy Project was formed under the umbrella of the LCO Public Works Department and Denise Johnson was hired as the coordinator. She quickly began fulfilling the objectives of the project. Denise began by contact the LCO College and hiring interns who were able to go to each Tribal entity and perform line logging to read and document the energy used for each electrical appliance. Data was also gathered for one full year from each entity for all their utility bills (gasoline, electric, natural gas, fuel oil, etc.). Relationships were formed with the Green Team and other Green Committees in the area that could assist us in this undertaking. The Energy Task Force was of great assistance as well recommending other committees and guidance to completing our project. The data was gathered, compiled and placed into spreadsheets that would be understandable for anyone who didn't have a background in Renewable Resources. While gathering the data Denise was also looking for ways to conserve energy usage, policies changes to implement and any possible viable renewable energy resources. Changes in the social behaviors of our members and employees will require further education by workshops, energy fairs, etc.. This will be looked into and done in coordination with our schools. The renewable resources seem most feasible are wind resources as well as Bio Mass both of which need further assessment and funding to do so will be sought. While we already are in ownership of a Hydro Dam it is currently not functioning to its full capacity we are seeking operation and maintenance firm proposals and funding sources. One of our biggest accomplishment this project gave us was our total Carbon Emissions 9989.45 tons, this will be the number that we will use to base our reductions from. It will help us achieve our goals we have set for ourselves in achieving the Kyoto Protocol and saving our Earth for our future generations. Another major accomplishment and lesson learned is we need to educate ourselves and our people on how to conserve energy to both impact the environment and our own budgets. The Lac Courte Oreilles (LCO) Energy Analysis Project will perform an energy audit to gather information on the Tribe's energy usage and determine the carbon emissions. By performing the audit we will be able to identify areas where conservation efforts are most viable and recommend policies that can be implemented. These steps will enable LCO to begin achieving the goals that have been set by the Tribal Governing Board and adopted through resolutions. The goals are to reduce emissions by 25% and to produce 25% of its energy using sustainable sources. The project objectives were very definitive to assist the Tribe in achieving its goals; reducing carbon emissions and obtaining a sustainable source of energy. The following were the outlined objectives: (1) Coordinate LCO's current and future conservation and renewable energy projects; (2) Establish working relationships with outside entities to share information and collaborate on future projects; (3) Complete energy audit and analyze LCO's energy load and carbon emissions; (4) Identify policy changes, education programs and conservation efforts which are appropriate for the LCO Reservation; and (5) Create a plan to identify the most cost effective renewable energy options for LCO.

  9. Probabilistic atlas-based segmentation of combined T1-weighted and DUTE MRI for calculation of head attenuation maps in integrated PET/MRI scanners.

    PubMed

    Poynton, Clare B; Chen, Kevin T; Chonde, Daniel B; Izquierdo-Garcia, David; Gollub, Randy L; Gerstner, Elizabeth R; Batchelor, Tracy T; Catana, Ciprian

    2014-01-01

    We present a new MRI-based attenuation correction (AC) approach for integrated PET/MRI systems that combines both segmentation- and atlas-based methods by incorporating dual-echo ultra-short echo-time (DUTE) and T1-weighted (T1w) MRI data and a probabilistic atlas. Segmented atlases were constructed from CT training data using a leave-one-out framework and combined with T1w, DUTE, and CT data to train a classifier that computes the probability of air/soft tissue/bone at each voxel. This classifier was applied to segment the MRI of the subject of interest and attenuation maps (?-maps) were generated by assigning specific linear attenuation coefficients (LACs) to each tissue class. The ?-maps generated with this "Atlas-T1w-DUTE" approach were compared to those obtained from DUTE data using a previously proposed method. For validation of the segmentation results, segmented CT ?-maps were considered to the "silver standard"; the segmentation accuracy was assessed qualitatively and quantitatively through calculation of the Dice similarity coefficient (DSC). Relative change (RC) maps between the CT and MRI-based attenuation corrected PET volumes were also calculated for a global voxel-wise assessment of the reconstruction results. The ?-maps obtained using the Atlas-T1w-DUTE classifier agreed well with those derived from CT; the mean DSCs for the Atlas-T1w-DUTE-based ?-maps across all subjects were higher than those for DUTE-based ?-maps; the atlas-based ?-maps also showed a lower percentage of misclassified voxels across all subjects. RC maps from the atlas-based technique also demonstrated improvement in the PET data compared to the DUTE method, both globally as well as regionally. PMID:24753982

  10. Experimental investigation of ?-ray attenuation in Jordanian building materials using HPGe-spectrometer

    Microsoft Academic Search

    Mohammad I. Awadallah; Mousa M. A. Imran

    2007-01-01

    The capabilities of some building materials used in Jordan to attenuate gamma radiation were tested. Measurements of the attenuation coefficients of limestone, bricks and concrete have been carried out using a HPGe-spectrometer. Narrow beam technique was used, with a multiple gamma radiation source of different energy lines. Results indicate that variations in the attenuation coefficient for all limestone samples, at

  11. Thrust-augmented vortex attenuation

    NASA Technical Reports Server (NTRS)

    Patterson, J. C., Jr.; Jordan, F. L., Jr.

    1977-01-01

    An experimental investigation was conducted to determine the vortex attenuating effect of engine thrust. Tests were made using a 0.03-scale model of the Boeing 747 transport aircraft as a vortex generating model. A Learjet-class probe model was used to measure the vortex induced rolling moment at a scale separation distance of 1.63 km. These tests were conducted at a lift coefficient of 1.4 at a model velocity of 30.48 m/s. The data presented indicate that engine thrust is effective as a vortex attenuating device when the engines are operated at high thrust levels and are positioned to direct the high energy engine wake into the core of the vortex. The greatest thrust vortex attenuation was obtained by operating the inboard engine thrust reversers at one-quarter thrust and the outboard engines at maximum forward thrust.

  12. Role of protons in sugar binding to LacY

    PubMed Central

    Smirnova, Irina; Kasho, Vladimir; Sugihara, Junichi; Vázquez-Ibar, José Luis; Kaback, H. Ronald

    2012-01-01

    WT lactose permease of Escherichia coli (LacY) reconstituted into proteoliposomes loaded with a pH-sensitive fluorophore exhibits robust uphill H+ translocation coupled with downhill lactose transport. However, galactoside binding by mutants defective in lactose-induced H+ translocation is not accompanied by release of an H+ on the interior of the proteoliposomes. Because the pKa value for galactoside binding is ?10.5, protonation of LacY likely precedes sugar binding at physiological pH. Consistently, purified WT LacY, as well as the mutants, binds substrate at pH 7.5–8.5 in detergent, but no change in ambient pH is observed, demonstrating directly that LacY already is protonated when sugar binds. However, a kinetic isotope effect (KIE) on the rate of binding is observed, indicating that deuterium substitution for protium affects an H+ transfer reaction within LacY that is associated with sugar binding. At neutral pH or pD, both the rate of sugar dissociation (koff) and the forward rate (kon) are slower in D2O than in H2O (KIE is ?2), and, as a result, no change in affinity (Kd) is observed. Alkaline conditions enhance the effect of D2O on koff, the KIE increases to 3.6–4.0, and affinity for sugar increases compared with H2O. In contrast, LacY mutants that exhibit pH-independent high-affinity binding up to pH 11.0 (e.g., Glu325 ? Gln) exhibit the same KIE (1.5–1.8) at neutral or alkaline pH (pD). Proton inventory studies exhibit a linear relationship between koff and D2O concentration at neutral and alkaline pH, indicating that internal transfer of a single H+ is involved in the KIE. PMID:23033496

  13. Integration and gene replacement in the Lactococcus lactis lac operon: induction of a cryptic phospho-beta-glucosidase in LacG-deficient strains.

    PubMed Central

    Simons, G; Nijhuis, M; de Vos, W M

    1993-01-01

    Insertions, replacement mutations, and deletions were introduced via single or double crossover recombination into the lacE (enzyme IIlac) and lacG (phospho-beta-galactosidase) genes of the Lactococcus lactis chromosomal lacABCDFEGX operon. LacG production was abolished in strains missing the lacG gene or carrying multicopy insertions in the lacE gene that affected expression of the lacG gene. However, these LacG-deficient strains could still ferment lactose slowly and were found to contain an enzymatic activity that hydrolyzed the chromogenic substrate o-nitrophenyl-beta-D-galactopyranoside phosphate. Induction of this phospho-beta-glycohydrolase activity coincided with the appearance of a new 55-kDa protein cross-reacting with anti-LacG antibodies that had a size similar to that of LacG but a higher isoelectric point (pI 5.2) and was not found in wild-type cells during growth on lactose. Since the phospho-beta-glycohydrolase activity and this protein with a pI of 5.2 were highly induced in both mutant and wild-type cells during growth on cellobiose that is likely to be transported via a phosphoenolpyruvate-dependent phosphotransferase system, we propose that this induced activity is a phospho-beta-glucosidase that also hydrolyzes lactose-6-phosphate. Images PMID:8349556

  14. Three New Eclipsing Binary Stars in Field of OP Lac

    NASA Astrophysics Data System (ADS)

    Lehký, Martin

    2009-03-01

    The new EW eclipsing binary HKV5 Lac = CzeV137 = USNO-B1.0 1454-0411281 (R.A. = 22h 34m 29.31s, Decl. = +55o 29' 03.6", J2000.0, R = 16.23 - 16.66 mag, Min. I = HJD 2454387.35273 + 0.387245 x E) and the new EA type eclipsing binary HKV6 Lac = CzeV138 = USNO-B1.0 1455-0409516 (R.A. = 22h 34m 16.26s, Decl. = +55o 34' 24.1", J2000.0, R = 14.10 - 14.23 mag, Min. I = HJD 2454387.58563 + 1.105815 x E) and the new EA type eclipsing binary HKV7 Lac = CzeV139 = USNO-B1.0 1455-0409575 (R.A. = 22h 34m 21.44s, Decl. = +55o 30' 13.8", J2000.0, R = 13.52 - 13.78 mag, Min. I = HJD 2454373.28108 + 1.324325 x E) have been found near the variable star OP Lac by 0.40-m f/5 reflector at Hradec Králové observatory.

  15. Photoacoustic imaging of lacZ gene expression

    E-print Network

    Wang, Lihong

    protein enables whole body imaging of small animals, although at low spatial resolution due to multiplePhotoacoustic imaging of lacZ gene expression in vivo Li Li,a, Roger J. Zemp,a, Gina Lungu,b George- aging as a promising candidate for imaging gene expression in vivo by exploiting a new contrast

  16. LUNSORT list of lunar orbiter data by LAC area

    NASA Technical Reports Server (NTRS)

    Hixon, S.

    1976-01-01

    Lunar orbiter (missions 1-5) photographic data are listed sequentially according to the number (1 to 147) LAC (Lunar Aeronautical Chart) areas by use of a computer program called LUNSORT. This listing, as well as a similar one from Apollo would simplify the task of identifying images of a given Lunar area. Instructions and sample case are included.

  17. SUPPORTING INFORMATION SEquence-Enabled Reassembly of -Lactamase (SEER-LAC)

    E-print Network

    Ghosh, Indraneel

    were similar with the construction of LacA-Zif268 except that LacB was cloned into C-terminal of p of the proteins is offered in Supplementary Figure 2. Supplementary Figure 1: Configuration and orientation of Lac

  18. Construction of Tn5 lac, a Transposon That Fuses lacZ Expression to Exogenous Promoters, and Its Introduction into Myxococcus xanthus

    Microsoft Academic Search

    Lee Kroos; Dale Kaiser

    1984-01-01

    A promoterless trp-lac fusion fragment was inserted near one end of the bacterial transposon Tn5 in the correct orientation to fuse lacZ gene expression to promoters outside Tn5. The resulting transposon, Tn5 lac, retains the kanamycin-resistance gene of Tn5 and transposes in Escherichia coli at 6% the frequency of Tn5 to many different sites in a bacteriophage lambda target. Expression

  19. Light attenuation characteristics of glacially-fed lakes

    NASA Astrophysics Data System (ADS)

    Rose, Kevin C.; Hamilton, David P.; Williamson, Craig E.; McBride, Chris G.; Fischer, Janet M.; Olson, Mark H.; Saros, Jasmine E.; Allan, Mathew G.; Cabrol, Nathalie

    2014-07-01

    Transparency is a fundamental characteristic of aquatic ecosystems and is highly responsive to changes in climate and land use. The transparency of glacially-fed lakes may be a particularly sensitive sentinel characteristic of these changes. However, little is known about the relative contributions of glacial flour versus other factors affecting light attenuation in these lakes. We sampled 18 glacially-fed lakes in Chile, New Zealand, and the U.S. and Canadian Rocky Mountains to characterize how dissolved absorption, algal biomass (approximated by chlorophyll a), water, and glacial flour contributed to attenuation of ultraviolet radiation (UVR) and photosynthetically active radiation (PAR, 400-700 nm). Variation in attenuation across lakes was related to turbidity, which we used as a proxy for the concentration of glacial flour. Turbidity-specific diffuse attenuation coefficients increased with decreasing wavelength and distance from glaciers. Regional differences in turbidity-specific diffuse attenuation coefficients were observed in short UVR wavelengths (305 and 320 nm) but not at longer UVR wavelengths (380 nm) or PAR. Dissolved absorption coefficients, which are closely correlated with diffuse attenuation coefficients in most non-glacially-fed lakes, represented only about one quarter of diffuse attenuation coefficients in study lakes here, whereas glacial flour contributed about two thirds across UVR and PAR. Understanding the optical characteristics of substances that regulate light attenuation in glacially-fed lakes will help elucidate the signals that these systems provide of broader environmental changes and forecast the effects of climate change on these aquatic ecosystems.

  20. DC attenuation meter

    DOEpatents

    Hargrove, Douglas L.

    2004-09-14

    A portable, hand-held meter used to measure direct current (DC) attenuation in low impedance electrical signal cables and signal attenuators. A DC voltage is applied to the signal input of the cable and feedback to the control circuit through the signal cable and attenuators. The control circuit adjusts the applied voltage to the cable until the feedback voltage equals the reference voltage. The "units" of applied voltage required at the cable input is the system attenuation value of the cable and attenuators, which makes this meter unique. The meter may be used to calibrate data signal cables, attenuators, and cable-attenuator assemblies.

  1. Role of protons in sugar binding to LacY.

    PubMed

    Smirnova, Irina; Kasho, Vladimir; Sugihara, Junichi; Vázquez-Ibar, José Luis; Kaback, H Ronald

    2012-10-16

    WT lactose permease of Escherichia coli (LacY) reconstituted into proteoliposomes loaded with a pH-sensitive fluorophore exhibits robust uphill H(+) translocation coupled with downhill lactose transport. However, galactoside binding by mutants defective in lactose-induced H(+) translocation is not accompanied by release of an H(+) on the interior of the proteoliposomes. Because the pK(a) value for galactoside binding is ?10.5, protonation of LacY likely precedes sugar binding at physiological pH. Consistently, purified WT LacY, as well as the mutants, binds substrate at pH 7.5-8.5 in detergent, but no change in ambient pH is observed, demonstrating directly that LacY already is protonated when sugar binds. However, a kinetic isotope effect (KIE) on the rate of binding is observed, indicating that deuterium substitution for protium affects an H(+) transfer reaction within LacY that is associated with sugar binding. At neutral pH or pD, both the rate of sugar dissociation (k(off)) and the forward rate (k(on)) are slower in D(2)O than in H(2)O (KIE is ?2), and, as a result, no change in affinity (K(d)) is observed. Alkaline conditions enhance the effect of D(2)O on k(off), the KIE increases to 3.6-4.0, and affinity for sugar increases compared with H(2)O. In contrast, LacY mutants that exhibit pH-independent high-affinity binding up to pH 11.0 (e.g., Glu325 ? Gln) exhibit the same KIE (1.5-1.8) at neutral or alkaline pH (pD). Proton inventory studies exhibit a linear relationship between k(off) and D(2)O concentration at neutral and alkaline pH, indicating that internal transfer of a single H(+) is involved in the KIE. PMID:23033496

  2. Expression of lacZ from the Promoter of the Escherichia coli spc Operon Cloned into Vectors Carrying the W205 trp-lac Fusion

    PubMed Central

    Liang, Sung-Tzu; Dennis, Patrick P.; Bremer, Hans

    1998-01-01

    The expression of lacZ has been analyzed and compared in a series of promoter cloning vectors by measuring the amount of lacZ mRNA by hybridization and the amount of ?-galactosidase by standard enzymatic assay. Expression was driven by the promoter, Pspc, of the spc ribosomal protein operon. The vectors contained either the standard W205 trp-lac fusion with the trp operon transcription terminator, trpt, located in the lacZ leader sequence, or a deletion derivative that functionally inactivates trpt. In the presence of trpt, lacZ expression was temperature dependent so that increasing the growth temperature reduced the accumulation of lacZ mRNA and ?-galactosidase activity. The frequency of transcript termination at trpt was estimated to be near zero at 20°C and at about 45% at 37°C. The amount of Pspc-derived lacZ mRNA and the amount of ?-galactosidase produced per lacZ mRNA varied, depending on the mRNA 5? leader sequence between Pspc and lacZ. These results demonstrate that the quantitative assessment of promoter activities with promoter cloning vectors requires careful analysis and interpretation. One particular construct without trpt did not seem to contain fortuitous transcription or translation signals generated at the fusion junction. In this strain, lacZ expression from Pspc was compared at the enzyme activity and mRNA levels with a previously constructed strain in which lacZ was linked to the tandem P1 and P2 promoters of the rrnB operon. At any given growth rate, the different activities of ?-galactosidase in these two strains were found to reflect the same differences in their amounts of lacZ mRNA. Assuming that the promoter-lacZ fusions in these strains reflect the properties of the promoters in their normal chromosomal setting, it was possible to estimate the absolute transcription activity of Pspc and the relative translation efficiency of Pspc-lacZ mRNA at different growth rates. Transcription from the spc promoter was found to increase from about 10 transcripts per min at a growth rate of 1.0 doublings/h to a maximum plateau of about 23 transcripts per min at growth rates above 1.5 doublings/h. The translation frequency of lacZ mRNA expressed from Pspc was unaffected by growth rates. PMID:9829916

  3. Expression of SofLAC, a new laccase in sugarcane, restores lignin content but not S:G ratio of Arabidopsis lac17 mutant.

    PubMed

    Cesarino, Igor; Araújo, Pedro; Sampaio Mayer, Juliana Lischka; Vicentini, Renato; Berthet, Serge; Demedts, Brecht; Vanholme, Bartel; Boerjan, Wout; Mazzafera, Paulo

    2013-04-01

    Lignin is a complex phenolic heteropolymer deposited in the secondarily thickened walls of specialized plant cells to provide strength for plants to stand upright and hydrophobicity to conducting cells for long-distance water transport. Although essential for plant growth and development, lignin is the major plant cell-wall component responsible for biomass recalcitrance to industrial processing. Peroxidases and laccases are generally thought to be responsible for lignin polymerization, but, given their broad substrate specificities and large gene families, specific isoforms involved in lignification are difficult to identify. This study used a combination of co-expression analysis, tissue/cell-type-specific expression analysis, and genetic complementation to correlate a sugarcane laccase gene, SofLAC, to the lignification process. A co-expression network constructed from 37 cDNA libraries showed that SofLAC was coordinately expressed with several phenylpropanoid biosynthesis genes. Tissue-specific expression analysis by quantitative RT-PCR showed that SofLAC was expressed preferentially in young internodes and that expression levels decrease with stem maturity. Cell-type-specific expression analysis by in situ hybridization demonstrated the localization of SofLAC mRNA in lignifying cell types, mainly in inner and outer portions of sclerenchymatic bundle sheaths. To investigate whether SofLAC is able to oxidize monolignols during lignification, the Arabidopsis lac17 mutant, which has reduced lignin levels, was complemented by expressing SofLAC under the control of the Arabidopsis AtLAC17 promoter. The expression of SofLAC restored the lignin content but not the lignin composition in complemented lac17 mutant lines. Taken together, these results suggest that SofLAC participates in lignification in sugarcane. PMID:23418623

  4. A Catalogue of XMM-Newton BL Lacs

    NASA Astrophysics Data System (ADS)

    de La Calle Pérez, I.; Loiseau, N.; Smith, M. J. S.

    2008-12-01

    An XMM-Newton catalogue of BL Lac X-ray properties is presented based on a cross-correlation with the 1122 BL Lac objects listed in the 12th edition of the Véron-Cetty and Véron (2006) catalogue. X-ray counterparts were searched for in the field of view of more than 5000 pointed observations available in the XMM-Newton Archive (XSA) that were public before February 2008. The cross-correlation yielded a total of 214 XMM-Newton observations, which after filtering, corresponds to 64 different sources. X-ray data from the three EPIC cameras were uniformly analyzed using the latest XMM-Newton Science Analysis System (SAS) version and correspondant calibration files. The results of the analysis are presented in terms of the spectral properties of the sample in the 0.2-10 keV energy band.

  5. Wind Resource Assessment Report: Mille Lacs Indian Reservation, Minnesota

    SciTech Connect

    Jimenez, A. C.

    2013-12-01

    The U.S. Environmental Protection Agency (EPA) launched the RE-Powering America's Land initiative to encourage development of renewable energy on potentially contaminated land and mine sites. EPA collaborated with the U.S. Department of Energy's (DOE's) National Renewable Energy Laboratory (NREL) and the Mille Lacs Band of Chippewa Indians to evaluate the wind resource and examine the feasibility of a wind project at a contaminated site located on the Mille Lacs Indian Reservation in Minnesota. The wind monitoring effort involved the installation of a 60-m met tower and the collection of 18 months of wind data at multiple heights above the ground. This report focuses on the wind resource assessment, the estimated energy production of wind turbines, and an assessment of the economic feasibility of a potential wind project sited this site.

  6. Imaging Redshift Estimates for Fermi BL Lac Objects

    NASA Astrophysics Data System (ADS)

    Stadnik, Matt; Romani, Roger W.

    2014-04-01

    We have obtained WIYN and SOAR i' images of BL Lacertae objects and used these to detect or constrain the flux of the host galaxy. Under common standard candle assumptions, these data provide estimates of, or lower bounds on, the redshift. Our targets are a set of flat-spectrum radio counterparts of high flux Fermi Large Area Telescope sources, with sensitive spectral observations showing them to be continuum-dominated BL Lac objects. In this sample, 5 of 11 BL Lac objects yielded significant host detections, with standard candle redshifts z = 0.13-0.58. Our estimates and lower bounds are generally in agreement with other redshifts estimates, although our z = 0.374 estimate for J0543-5532 implies a significantly sub-luminous host.

  7. The 2dF BL Lac Survey II

    E-print Network

    D. Londish; S. M. Croom; J. Heidt; B. J. Boyle; E. M. Sadler; M. Whiting; T. A. Rector; T. Pursimo; K. Chynoweth

    2006-10-05

    We report on our further analysis of the expanded and revised sample of potential BL Lac objects (the 2BL) optically identified from two catalogues of blue-selected (UV excess) point sources, the 2dF and 6dF QSO Redshift Surveys (2QZ and 6QZ). The 2BL comprises 52 objects with no apparent proper motion, over the magnitude range 16.0 < bj< 20.0. Follow-up high signal-to-noise spectra of 36 2BL objects and NIR imaging of 18 objects, together with data for 19 2BL objects found in the Sloan Digital Sky survey (SDSS), show 17 objects to be stellar, while a further 16 objects have evidence of weak, broad emission features, although for at least one of these the continuum level has clearly varied. Classification of three objects remains uncertain,with NIR results indicating a marked reduction in flux as compared to SDSS optical magnitudes. Seven objects have neither high signal-to-noise spectra nor NIR imaging. Deep radio observations of 26 2BL objects at the VLA resulted in only three further radio-detections, however none of the three is classed as a featureless continuum object. Seven 2BL objects with a radio detection are confirmed as candidate BL Lac objects while one extragalactic (z=0.494) continuum object is undetected at radio frequencies. One further radio-undetected object is also a potential BL Lac candidate. However it would appear that there is no significant population of radio-quiet BL Lac objects.

  8. Structure of sugar-bound LacY.

    PubMed

    Kumar, Hemant; Kasho, Vladimir; Smirnova, Irina; Finer-Moore, Janet S; Kaback, H Ronald; Stroud, Robert M

    2014-02-01

    Here we describe the X-ray crystal structure of a double-Trp mutant (Gly46?Trp/Gly262?Trp) of the lactose permease of Escherichia coli (LacY) with a bound, high-affinity lactose analog. Although thought to be arrested in an open-outward conformation, the structure is almost occluded and is partially open to the periplasmic side; the cytoplasmic side is tightly sealed. Surprisingly, the opening on the periplasmic side is sufficiently narrow that sugar cannot get in or out of the binding site. Clearly defined density for a bound sugar is observed at the apex of the almost occluded cavity in the middle of the protein, and the side chains shown to ligate the galactopyranoside strongly confirm more than two decades of biochemical and spectroscopic findings. Comparison of the current structure with a previous structure of LacY with a covalently bound inactivator suggests that the galactopyranoside must be fully ligated to induce an occluded conformation. We conclude that protonated LacY binds D-galactopyranosides specifically, inducing an occluded state that can open to either side of the membrane. PMID:24453216

  9. Structure of sugar-bound LacY

    PubMed Central

    Kumar, Hemant; Kasho, Vladimir; Smirnova, Irina; Finer-Moore, Janet S.; Kaback, H. Ronald; Stroud, Robert M.

    2014-01-01

    Here we describe the X-ray crystal structure of a double-Trp mutant (Gly46?Trp/Gly262?Trp) of the lactose permease of Escherichia coli (LacY) with a bound, high-affinity lactose analog. Although thought to be arrested in an open-outward conformation, the structure is almost occluded and is partially open to the periplasmic side; the cytoplasmic side is tightly sealed. Surprisingly, the opening on the periplasmic side is sufficiently narrow that sugar cannot get in or out of the binding site. Clearly defined density for a bound sugar is observed at the apex of the almost occluded cavity in the middle of the protein, and the side chains shown to ligate the galactopyranoside strongly confirm more than two decades of biochemical and spectroscopic findings. Comparison of the current structure with a previous structure of LacY with a covalently bound inactivator suggests that the galactopyranoside must be fully ligated to induce an occluded conformation. We conclude that protonated LacY binds d-galactopyranosides specifically, inducing an occluded state that can open to either side of the membrane. PMID:24453216

  10. Clustering of ?-Ray-selected 2LAC Fermi Blazars

    NASA Astrophysics Data System (ADS)

    Allevato, V.; Finoguenov, A.; Cappelluti, N.

    2014-12-01

    We present the first measurement of the projected correlation function of 485 ?-ray-selected blazars, divided into 175 BL Lacertae (BL Lacs) and 310 flat-spectrum radio quasars (FSRQs) detected in the 2 year all-sky survey by the Fermi-Large Area Telescope. We find that Fermi BL Lacs and FSRQs reside in massive dark matter halos (DMHs) with log Mh = 13.35+0.20-0.14 and log Mh = 13.40+0.15-0.19 h -1 M ?, respectively, at low (z ~ 0.4) and high (z ~ 1.2) redshift. In terms of clustering properties, these results suggest that BL Lacs and FSRQs are similar objects residing in the same dense environment typical of galaxy groups, despite their different spectral energy distributions, power, and accretion rates. We find no difference in the typical bias and hosting halo mass between Fermi blazars and radio-loud active galactic nuclei (AGNs), supporting the unification scheme simply equating radio-loud objects with misaligned blazar counterparts. This similarity in terms of the typical environment they preferentially live in, suggests that blazars tend to occupy the center of DMHs, as already pointed out for radio-loud AGNs. This implies, in light of several projects looking for the ?-ray emission from DM annihilation in galaxy clusters, a strong contamination from blazars to the expected signal from DM annihilation.

  11. Low energy gamma ray attenuation in multiphase water

    NASA Technical Reports Server (NTRS)

    Singh, Jag J.; Sprinkle, Danny R.; Eftekhari, Abe

    1990-01-01

    A gauging system is proposed to enable monitoring of slush density, solid-liquid interface, and slush level as well as its flow rate. It is based on the principle that the electromagnetic radiation mass attenuation coefficient of a multiphase chemical compound is constant for all relative phase concentrations. Results showing the essential constancy of mass attenuation coefficients for single-phase water vapor, liquid water, ice, and multiphase mixtures of water/ice are described.

  12. Attenuation estimation using spectral cross-correlation

    Microsoft Academic Search

    Hyungsuk Kim; Tomy Varghese

    2007-01-01

    Estimation of the local attenuation coefficient in soft tissue is important both for clinical diagnosis and for further analysis of ultrasound B-mode images. However, it is difficult to extract spectral properties in a small region of interest from noisy backscattered ultrasound radio frequency (RF) signals. Diffraction effects due to transducer beam focal properties also have to be corrected for accurate

  13. An adaptive controller based on disturbance attenuation

    Microsoft Academic Search

    David F. Chichka; Jason L. Speyer

    1995-01-01

    This paper discusses the control of linear systems with uncertain parameters in the control coefficient matrix, under the influence of both process and measurement noise. A disturbance attenuation approach is used, and from this a multiplayer game problem is generated. First, the minimax formulation is presented, which represents an upper bound on the game cost criterion. Second, a dynamic programming

  14. Light attenuation on unicellular marine phytoplankton

    NASA Astrophysics Data System (ADS)

    Krol, Tadeusz; Lotocka, Maria

    1994-10-01

    Sea phytoplankton plays a considerable role in the interactive processes between light and the sea. Its species composition and the physiological development phase influence the spectrum of the light attenuation coefficient in the sea. Laboratory measurements of light attenuation spectrum were carried out on three different phytoplankton monocultures of the unicellular green algae Chlorella vulgaris and the larger Chlorella kesleri and the blue-green alga Chroococcus minor. The cultures were subjected to chemical (NaOH and temperature) or physical (ultrasounds) factors which altered their internal cell structures. Distinct changes in the light attenuation spectrum were observed as a result of the modification of the internal cell structures. Light attenuation cross-sections of those phytoplankton cells were also determined.

  15. Pressure surge attenuator

    DOEpatents

    Christie, Alan M. (Swissvale, PA); Snyder, Kurt I. (Murrysville, PA)

    1985-01-01

    A pressure surge attenuation system for pipes having a fluted region opposite crushable metal foam. As adapted for nuclear reactor vessels and heads, crushable metal foam is disposed to attenuate pressure surges.

  16. Le campus numrique APe-LAC (animation pdagogique en e-learning et apprentissage collaboratif)

    E-print Network

    Paris-Sud XI, Université de

    Le campus numérique APe-LAC (animation pédagogique en e-learning et apprentissage collaboratif Distance, CNED. Gweidenfel@aol.com APe-LAC (Animation pédagogique en e-learning et apprentissage'explicitation de ces problèmes constitue le coeur de la formation APe-LAC qui se déroule évidemment de façon

  17. Estimation of Local Attenuation and Its Application to Rationalized Gain Control

    Microsoft Academic Search

    Xiaoying Li; Dong C. Liu

    2007-01-01

    The aim of this paper is to provide a local attenuation estimation algorithm from ultrasound images. Using the computed attenuation coefficients locally, we define a 2-D table for tissue attenuation compensation in the sense of a rationalized gain control. To handle the frequency shift in the broadband system, we use nonlinear least squares (NLS) data fitting directly to the local

  18. Signal Processing of Broadband Pulsed Ultrasound: Measurement of Attenuation of Soft Biological Tissues

    Microsoft Academic Search

    Avinash C. Kak; Kris A. Dines

    1978-01-01

    In this paper we will discuss the measurement of attenuation of soft tissues using broadband pulsed ultrasound. While all the methods presented here may be used for measuring the attenuation coefficient of single layers, some of the methods can also be used for measuring integrated attenuation of composite layers of soft tissue. These latter methods do not require knowledge of

  19. Three-dimensional attenuation map reconstruction using geometrical models and free-form deformations [SPECT application

    Microsoft Academic Search

    X. L. Battle; C. Le Rest; A. Turzo; Y. Bizais

    2000-01-01

    Addresses the issue of using deformable models to reconstruct an unknown attenuation map of the torso from a set of transmission scans. The authors assume the three-dimensional (3-D) distribution of attenuation coefficients to be piecewise uniform. They represent the unknown distribution by a set of closed surfaces defining regions having the same attenuating properties. The methods of reconstruction published so

  20. Inducible high-level expression vector for mammalian cells, pEF-LAC carrying human elongation factor 1alpha promoter and lac operator.

    PubMed

    Edamatsu, H; Kaziro, Y; Itoh, H

    1997-03-18

    We have constructed an inducible high-level expression vector, pEF-LAC. pEF-LAC has a modified human polypeptide chain elongation factor 1alpha (EF-1alpha) promoter containing three lactose operator sequences. Using the cat reporter gene, we characterized the transcriptional activity of pEF-LAC. In the transient transfection of NIH3T3 and BaF3 cells, the transcriptional activity of pEF-LAC was higher than that of the original human elongation factor 1alpha promoter, simian virus 40 (SV40) promoter, and Rous sarcoma virus (RSV) long terminal repeat (LTR). Cotransfection of the lactose repressor expression plasmid effectively suppressed the promoter activity of pEF-LAC, and the activity was fully recovered by addition of isopropyl beta-D-thiogalactopyranoside (IPTG). Even in the stable transfection of Rat-1 cells, the promoter activity of the integrated pEF-LAC was much higher than that of the RSV-LTR and regulated in an IPTG-dependent manner. These results suggest that pEF-LAC is a useful vector for the inducible high-level expression of the cloned gene in a variety of mammalian cells. PMID:9099894

  1. Does Black Hole Spin Play a Key Role in the Fsrq/bl Lac Dichotomy?

    NASA Astrophysics Data System (ADS)

    Mukhopadhyay, Banibrata

    2015-01-01

    It is believed that jets emerging from blazars (flat spectrum radio quasars (FSRQs) and BL Lacs) are almost aligned to the line-of-sight. BL Lacs usually exhibit lower luminosity and harder power law spectra at gamma-ray energies than FSRQs. It was argued previously that the difference in accretion rates is mainly responsible for the large observed luminosity mismatch between them. However, when intrinsic luminosities are derived by correcting for beaming effects, this mismatch is significantly reduced. We show that spin plays an important role to reveal the dichotomy of luminosity distributions between BL Lacs and FSRQs, suggesting BL Lacs to be low luminous and slow rotators compared to FSRQs.

  2. Tracer attenuation in groundwater

    NASA Astrophysics Data System (ADS)

    Cvetkovic, Vladimir

    2011-12-01

    The self-purifying capacity of aquifers strongly depends on the attenuation of waterborne contaminants, i.e., irreversible loss of contaminant mass on a given scale as a result of coupled transport and transformation processes. A general formulation of tracer attenuation in groundwater is presented. Basic sensitivities of attenuation to macrodispersion and retention are illustrated for a few typical retention mechanisms. Tracer recovery is suggested as an experimental proxy for attenuation. Unique experimental data of tracer recovery in crystalline rock compare favorably with the theoretical model that is based on diffusion-controlled retention. Non-Fickian hydrodynamic transport has potentially a large impact on field-scale attenuation of dissolved contaminants.

  3. Effect of collimator size and absorber thickness on gamma ray attenuation measurements for bakelite and perspex

    Microsoft Academic Search

    Gurdeep S. Sidhu; Karamjit Singh; Parjit S. Singh; Gurmel S. Mudahar

    1999-01-01

    The mass attenuation coefficient (m m ) of 662 keV gamma rays have been measured in the extended media of bakelite and perspex under different collimation conditions. The increase in attenuation coefficient is seen with increase in sample thickness as well as with collimator size due to the contribution of multiple scattered photons in the uncollided beam of 662 keV

  4. Yellowstone Attenuation Tomography from Ambient Seismic Noise

    NASA Astrophysics Data System (ADS)

    Doungkaew, N.; Seats, K.; Lawrence, J. F.

    2013-12-01

    The goal of this study is to create a tomographic attenuation image for the Yellowstone region by analyzing ambient seismic noise. An attenuation image generated from ambient noise should provide more information about the structure and properties beneath Yellowstone, especially the caldera, which is known to be active. I applied the method of Lawrence & Prieto [2011] to examine lateral variations in the attenuation structure of Yellowstone. Ambient noise data were collected from broadband seismic stations located around Yellowstone National Park from 1999-2013. Noise correlation functions derived from cross correlations of the ambient noise at two stations were used to calculate a distance dependent decay (an attenuation coefficient) at each period and distance. An inversion was then performed to isolate and localize the spatial attenuation coefficients within the study area. I observe high amplitude decay of the ambient noise at the Yellowstone caldera, most likely due to elevated temperature and crustal melts caused by volcanism, geothermal heat flow, and hydrothermal activity such as geysers.

  5. Chemical corrosion on gamma-ray attenuation properties of barite concrete

    Microsoft Academic Search

    I. Akkurt; H. Aky?ld?r?m; F. Karipçin; B. Mavi

    The variation of photon attenuation coefficient on the chemical media has been investigated. For this purposes the linear attenuations of barite concrete have been measured at 662, 1773 and 1332keV before leaving the chemical media and following a 6month period. The linear attenuation coefficients have been measured using gamma spectrometer that contains a NaI(Tl) detector and 16k channel MCA. It

  6. Comparative genomics and evolution of regulons of the LacI-family transcription factors

    PubMed Central

    Ravcheev, Dmitry A.; Khoroshkin, Matvei S.; Laikova, Olga N.; Tsoy, Olga V.; Sernova, Natalia V.; Petrova, Svetlana A.; Rakhmaninova, Aleksandra B.; Novichkov, Pavel S.; Gelfand, Mikhail S.; Rodionov, Dmitry A.

    2014-01-01

    DNA-binding transcription factors (TFs) are essential components of transcriptional regulatory networks in bacteria. LacI-family TFs (LacI-TFs) are broadly distributed among certain lineages of bacteria. The majority of characterized LacI-TFs sense sugar effectors and regulate carbohydrate utilization genes. The comparative genomics approaches enable in silico identification of TF-binding sites and regulon reconstruction. To study the function and evolution of LacI-TFs, we performed genomics-based reconstruction and comparative analysis of their regulons. For over 1300 LacI-TFs from over 270 bacterial genomes, we predicted their cognate DNA-binding motifs and identified target genes. Using the genome context and metabolic subsystem analyses of reconstructed regulons, we tentatively assigned functional roles and predicted candidate effectors for 78 and 67% of the analyzed LacI-TFs, respectively. Nearly 90% of the studied LacI-TFs are local regulators of sugar utilization pathways, whereas the remaining 125 global regulators control large and diverse sets of metabolic genes. The global LacI-TFs include the previously known regulators CcpA in Firmicutes, FruR in Enterobacteria, and PurR in Gammaproteobacteria, as well as the three novel regulators—GluR, GapR, and PckR—that are predicted to control the central carbohydrate metabolism in three lineages of Alphaproteobacteria. Phylogenetic analysis of regulators combined with the reconstructed regulons provides a model of evolutionary diversification of the LacI protein family. The obtained genomic collection of in silico reconstructed LacI-TF regulons in bacteria is available in the RegPrecise database (http://regprecise.lbl.gov). It provides a framework for future structural and functional classification of the LacI protein family and identification of molecular determinants of the DNA and ligand specificity. The inferred regulons can be also used for functional gene annotation and reconstruction of sugar catabolic networks in diverse bacterial lineages. PMID:24966856

  7. Galactoside-Binding Site in LacY

    PubMed Central

    2015-01-01

    Although an X-ray crystal structure of lactose permease (LacY) has been presented with bound galactopyranoside, neither the sugar nor the residues ligating the sugar can be identified with precision at ?3.5 Å. Therefore, additional evidence is important for identifying side chains likely to be involved in binding. On the basis of a clue from site-directed alkylation suggesting that Asn272, Gly268, and Val264 on one face of helix VIII might participate in galactoside binding, molecular dynamics simulations were conducted initially. The simulations indicate that Asn272 (helix VIII) is sufficiently close to the galactopyranosyl ring of a docked lactose analogue to play an important role in binding, the backbone at Gly268 may be involved, and Val264 does not interact with the bound sugar. When the three side chains are subjected to site-directed mutagenesis, with the sole exception of mutant Asn272 ? Gln, various other replacements for Asn272 either markedly decrease affinity for the substrate (i.e., high KD) or abolish binding altogether. However, mutant Gly268 ? Ala exhibits a moderate 8-fold decrease in affinity, and binding by mutant Val264 ? Ala is affected only minimally. Thus, Asn272 and possibly Gly268 may comprise additional components of the galactoside-binding site in LacY. PMID:24520888

  8. THERMAL CONDUCTIVITY AND ELEMENT FRACTIONATION IN EV Lac

    SciTech Connect

    Laming, J. Martin [Space Science Division, Naval Research Laboratory, Code 7674L, Washington, DC 20375 (United States); Hwang, Una, E-mail: Una.Hwang-1@nasa.go [NASA/GSFC Code 662, Greenbelt MD 20771, and Johns Hopkins University, Baltimore, MD 21218 (United States)

    2009-12-10

    We present a 100 ks Suzaku observation of the dMe flare star EV Lac, in which the star was captured undergoing a moderate 1500 s flare. During the flare, the count rate increased by about a factor of 50 and the spectrum showed overall enhanced element abundances relative to quiescence. While the quiescent element abundances confirm the inverse first ionization potential (FIP) effect previously documented for EV Lac, with relatively higher depletions for low FIP elements, abundances during the flare spectra show a composition closer to that of the stellar photosphere. We discuss these results in the context of models that explain abundance fractionation in the stellar chromosphere as a result of the ponderomotive force due to Alfven waves. Stars with FIP or inverse FIP effects arising from differently directed ponderomotive forces may have quite different abundance signatures in their evaporated chromospheric plasma during flares, if the same ponderomotive force also affects thermal conduction downward from the corona. The regulation of the thermal conductivity by the ponderomotive force requires a level of turbulence that is somewhat higher than is normally assumed, but plausible in filamentary conduction models.

  9. Design and analysis of LacI-repressed promoters and DNA-looping in a cyanobacterium

    PubMed Central

    2014-01-01

    Background Cyanobacteria are solar-powered prokaryotes useful for sustainable production of valuable molecules, but orthogonal and regulated promoters are lacking. The Lac repressor (LacI) from Escherichia coli is a well-studied transcription factor that is orthogonal to cyanobacteria and represses transcription by binding a primary lac operator (lacO), blocking RNA-polymerase. Repression can be enhanced through DNA-looping, when a LacI-tetramer binds two spatially separated lacO and loops the DNA. Ptrc is a commonly used LacI-repressed promoter that is inefficiently repressed in the cyanobacterium Synechocystis PCC 6803. Ptrc2O, a version of Ptrc with two lacO, is more efficiently repressed, indicating DNA-looping. To investigate the inefficient repression of Ptrc and cyanobacterial DNA-looping, we designed a Ptrc-derived promoter library consisting of single lacO promoters, including a version of Ptrc with a stronger lacO (Ptrc1O-proximal), and dual lacO promoters with varying inter-lacO distances (the Ptrc2O-library). Results We first characterized artificial constitutive promoters and used one for engineering a LacI-expressing strain of Synechocystis. Using this strain, we observed that Ptrc1O-proximal is similar to Ptrc in being inefficiently repressed. Further, the Ptrc2O-library displays a periodic repression pattern that remains for both non- and induced conditions and decreases with longer inter-lacO distances, in both E. coli and Synechocystis. Repression of Ptrc2O-library promoters with operators out of phase is less efficient in Synechocystis than in E. coli, whereas repression of promoters with lacO in phase is efficient even under induced conditions in Synechocystis. Two well-repressed Ptrc2O promoters were highly active when tested in absence of LacI in Synechocystis. Conclusions The artificial constitutive promoters herein characterized can be utilized for expression in cyanobacteria, as demonstrated for LacI. The inefficient repression of Ptrc and Ptrc1O-proximal in Synechocystis, as compared to E. coli, may be due to insufficient LacI expression, or differences in RNAP subunits. DNA-looping works as a transcriptional regulation mechanism similarly as in E. coli. DNA-looping contributes strongly to Ptrc2O-library repression in Synechocystis, even though they contain the weakly-repressed primary lacO of Ptrc1O-proximal and relatively low levels of LacI/cell. Hence, Synechocystis RNAP may be more sensitive to DNA-looping than E. coli RNAP, and/or the chromatin torsion resistance could be lower. Two strong and highly repressed Ptrc2O promoters could be used without induction, or together with an unstable LacI. PMID:24467947

  10. Utilization of lactose and presence of the phospho-?-galactosidase (lacG) gene in Lactococcus garvieae isolates from different sources.

    PubMed

    Aguado-Urda, Mónica; Cutuli, M Teresa; Blanco, M Mar; Aspiroz, Carmen; Tejedor, José L; Fernández-Garayzábal, José F; Gibello, Alicia

    2010-12-01

    This study evaluates the utilization of lactose (Lac) and the presence of the phospho-?-galactosidase (lacG) gene as markers for distinguishing between fish (Lac-/lacG-) and dairy isolates (Lac+/lacG+) of Lactococcus garvieae, using a panel of L. garvieae isolates from different sources. None of the fish isolates produced acid from lactose (Lac-), however Lac-/lacG- isolates were observed in pigs, cows, birds and humans. Most of the dairy isolates (77.8%) were Lac+/lacG+, but some dairy isolates did not produce acid from this sugar. Data in the present study show that the ability to metabolize lactose and the presence of the lacG gene are heterogeneously scattered among L. garvieae isolates of different sources. Therefore, the use of these criteria as markers to differentiate between L. garvieae isolates of dairy and fish origin should be considered with caution. PMID:21404213

  11. Structural and Enzymatic characterization of the lactonase SisLac from Sulfolobus islandicus

    PubMed Central

    Chabriere, Eric; Elias, Mikael

    2012-01-01

    Background A new member of the Phosphotriesterase-Like Lactonases (PLL) family from the hyperthermophilic archeon Sulfolobus islandicus (SisLac) has been characterized. SisLac is a native lactonase that exhibits a high promiscuous phosphotriesterase activity. SisLac thus represents a promising target for engineering studies, exhibiting both detoxification and bacterial quorum quenching abilities, including human pathogens such as Pseudomonas aeruginosa. Methodology/Principal Findings Here, we describe the substrate specificity of SisLac, providing extensive kinetic studies performed with various phosphotriesters, esters, N-acyl-homoserine lactones (AHLs) and other lactones as substrates. Moreover, we solved the X-ray structure of SisLac and structural comparisons with the closely related SsoPox structure highlighted differences in the surface salt bridge network and the dimerization interface. SisLac and SsoPox being close homologues (91% sequence identity), we undertook a mutational study to decipher these structural differences and their putative consequences on the stability and the catalytic properties of these proteins. Conclusions/Significance We show that SisLac is a very proficient lactonase against aroma lactones and AHLs as substrates. Hence, data herein emphasize the potential role of SisLac as quorum quenching agent in Sulfolobus. Moreover, despite the very high sequence homology with SsoPox, we highlight key epistatic substitutions that influence the enzyme stability and activity. PMID:23071703

  12. Radical coupling reaction of paramagnetic endohedral metallofullerene La@C82.

    PubMed

    Takano, Yuta; Yomogida, Akinori; Nikawa, Hidefumi; Yamada, Michio; Wakahara, Takatsugu; Tsuchiya, Takahiro; Ishitsuka, Midori O; Maeda, Yutaka; Akasaka, Takeshi; Kato, Tatsuhisa; Slanina, Zdenek; Mizorogi, Naomi; Nagase, Shigeru

    2008-12-01

    The thermal reaction of La@C(82)(C(2v)) with 3-triphenylmethyl-5-oxazolidinone (1) in toluene affords benzyl monoadducts La@C(82)(C(2v))(CH(2)C(6)H(5)) (2a-2d). The same monoadducts are also obtained by the photoirradiation of La@C(82)(C(2v)) in toluene without the existence of 1. These reactions are applicable to paramagnetic metallofullerenes, such as La@C(82)(C(s)) and Ce@C(82)(C(2v)). The photoirradiation of La@C(82)(C(2v)) in 1,2-dichlorobenzene in the presence of alpha,alpha,2,4-tetrachlorotoluene also affords the monoadducts La@C(82)(C(2v))(CHClC(6)H(3)Cl(2)) (3a-3d). The monoadducts are fully characterized by spectroscopic analyses. Single-crystal X-ray structure analysis for 3d reveals the unique structure. Theoretical calculations show that the cage carbons having high spin densities are selectively attacked by radical species to form the monoadducts linked by a carbon-carbon single bond. The thermal reaction of La@C(82)(C(2v)) with 1 in benzene affords metallofulleropyrrolidine La@C(82)(C(2v))(C(2)H(4)NCPh(3)) (5), unlike the reaction in toluene. PMID:18998645

  13. Variable laser attenuator

    DOEpatents

    Foltyn, S.R.

    1987-05-29

    The disclosure relates to low loss, high power variable attenuators comprising one or more transmissive and/or reflective multilayer dielectric filters. The attenuator is particularly suitable to use with unpolarized lasers such as excimer lasers. Beam attenuation is a function of beam polarization and the angle of incidence between the beam and the filter and is controlled by adjusting the angle of incidence the beam makes to the filter or filters. Filters are selected in accordance with beam wavelength. 9 figs.

  14. Variable laser attenuator

    DOEpatents

    Foltyn, Stephen R. (Los Alamos, NM)

    1988-01-01

    The disclosure relates to low loss, high power variable attenuators comprng one or more transmissive and/or reflective multilayer dielectric filters. The attenuator is particularly suitable to use with unpolarized lasers such as excimer lasers. Beam attenuation is a function of beam polarization and the angle of incidence between the beam and the filter and is controlled by adjusting the angle of incidence the beam makes to the filter or filters. Filters are selected in accordance with beam wavelength.

  15. Compensation for non-uniform attenuation in SPECT brain imaging

    SciTech Connect

    Glick, S.J.; King, M.A.; Pan, T.S. [Univ. of Massachusetts Medical Center, Worcester, MA (United States)] [and others

    1994-05-01

    Photon attenuation is a major limitation in performing quantitative SPECT brain imaging. A number of methods have been proposed for compensation of attenuation in regions of the body that can be modelled as a uniform attenuator. The magnitude of the errors introduced into reconstructed brain images by assuming the head to be a uniform attenuator are uncertain (the skull, sinus cavities and head holder all have different attenuation properties than brain tissue). Brain imaging is unique in that the radioisotope, for the most part, is taken up within a uniform attenuation medium (i.e., brain tissue) which is surrounded by bone (i.e., the skull) of a different density. Using this observation, Bellini`s method for attenuation compensation (which is an exact solution to the exponential Radon transform) has been modified to account for the different attenuation properties of the skull. To test this modified Bellini method, a simple mathematical phantom was designed to model the brain and a skull of varying thickness less than 7.5 mm. To model brain imaging with Tc-99m HMPAO, the attenuation coefficient of the brain tissue and skull were set to 0.15 cm{sup -1} and 0.22 cm{sup -1} respectively. A ray-driven projector which accounted for non-uniform attenuation was used to simulate projection data from 128 views. The detector response and scatter were not simulated. It was observed that reconstructions processed with uniform attenuation compensation (i.e., where it was assumed that the brain tissue and the skull had the same attenuation coefficient) provided errors of 6-20%, whereas those processed with the non-uniform Bellini algorithm were biased by only 0-5%.

  16. Comparison of Nitrate Attenuation Characterization Methods for Groundwater Remediation

    NASA Astrophysics Data System (ADS)

    Carroll, K. C.; Jordan, F. L.; Glenn, E. P.; Waugh, J.; Brusseau, M. L.

    2008-12-01

    Nitrate released from a former uranium mine tailings stockpile has contaminated groundwater near Monument Valley, Arizona. The results of previous studies suggest that nitrate attenuation is occurring at the site, but the feasibility of using natural attenuation as a remediation strategy remains uncertain. This investigation characterized the occurrence and rate of natural attenuation at the site using several methods. Spatial and temporal nitrate concentration data collected from a transect of monitoring wells located along the plume centerline were analyzed to evaluate overall rates of natural attenuation. The occurrence and rate of denitrification was evaluated through microcosm experiments, nitrogen isotopic fractionation analysis, and solute transport modeling. First-order rate coefficients calculated for each method were comparable. The composite natural attenuation rate coefficient was larger than the denitrification rate coefficient, which suggests that a combination of biological decay and dispersion/diffusion processes control nitrate attenuation at the site. Model simulations were conducted to estimate the time required for nitrate concentrations in the plume to decrease to 10 mg/L under existing conditions, which was approximately 150 years. Additional simulations were conducted to assess the potential reduction in cleanup time that would result from implementing enhanced denitrification via either methanol or ethanol injection. The results indicated that cleanup would be attained in approximately one-third the time estimated for natural attenuation.

  17. Factor Scores, Structure Coefficients, and Communality Coefficients

    ERIC Educational Resources Information Center

    Goodwyn, Fara

    2012-01-01

    This paper presents heuristic explanations of factor scores, structure coefficients, and communality coefficients. Common misconceptions regarding these topics are clarified. In addition, (a) the regression (b) Bartlett, (c) Anderson-Rubin, and (d) Thompson methods for calculating factor scores are reviewed. Syntax necessary to execute all four…

  18. Partial charge transfer in the shortest possible metallofullerene peapod, La@C82 ?[11]cycloparaphenylene.

    PubMed

    Iwamoto, Takahiro; Slanina, Zdenek; Mizorogi, Naomi; Guo, Jingdong; Akasaka, Takeshi; Nagase, Shigeru; Takaya, Hikaru; Yasuda, Nobuhiro; Kato, Tatsuhisa; Yamago, Shigeru

    2014-10-27

    [11]Cycloparaphenylene ([11]CPP) selectively encapsulates La@C82 to form the shortest possible metallofullerene-carbon nanotube (CNT) peapod, La@C82 ?[11]CPP, in solution and in the solid state. Complexation in solution was affected by the polarity of the solvent and was 16?times stronger in the polar solvent nitrobenzene than in the nonpolar solvent 1,2-dichlorobenzene. Electrochemical analysis revealed that the redox potentials of La@C82 were negatively shifted upon complexation from free La@C82 . Furthermore, the shifts in the redox potentials increased with polarity of the solvent. These results are consistent with formation of a polar complex, (La@C82 )(?-) ?[11]CPP(?+) , by partial electron transfer from [11]CPP to La@C82 . This is the first observation of such an electronic interaction between a fullerene pea and CPP pod. Theoretical calculations also supported partial charge transfer (0.07) from [11]CPP to La@C82 . The structure of the complex was unambiguously determined by X-ray crystallographic analysis, which showed the La atom inside the C82 near the periphery of the [11]CPP. The dipole moment of La@C82 was projected toward the CPP pea, nearly perpendicular to the CPP axis. The position of the La atom and the direction of the dipole moment in La@C82 ?[11]CPP were significantly different from those observed in La@C82 ?CNT, thus indicating a difference in orientation of the fullerene peas between fullerene-CPP and fullerene-CNT peapods. These results highlight the importance of pea-pea interactions in determining the orientation of the metallofullerene in metallofullerene-CNT peapods. PMID:25224281

  19. Adaptive Evolution of the Streptococcus pyogenes Regulatory Aldolase LacD.1

    PubMed Central

    Cusumano, Zachary

    2013-01-01

    In the human-pathogenic bacterium Streptococcus pyogenes, the tagatose bisphosphate aldolase LacD.1 likely originated through a gene duplication event and was adapted to a role as a metabolic sensor for regulation of virulence gene transcription. Although LacD.1 retains enzymatic activity, its ancestral metabolic function resides in the LacD.2 aldolase, which is required for the catabolism of galactose. In this study, we compared these paralogous proteins to identify characteristics correlated with divergence and novel function. Surprisingly, despite the fact that these proteins have identical active sites and 82% similarity in amino acid sequence, LacD.1 was less efficient at cleaving both fructose and tagatose bisphosphates. Analysis of kinetic properties revealed that LacD.1's adaptation was associated with a decrease in kcat and an increase in Km. Construction and analysis of enzyme chimeras indicated that non-active-site residues previously associated with the variable activities of human aldolase isoenzymes modulated LacD.1's affinity for substrate. Mutant LacD.1 proteins engineered to have LacD.2-like levels of enzymatic efficiency lost the ability to function as regulators, suggesting that an alteration in efficiency was required for adaptation. In competition under growth conditions that mimic a deep-tissue environment, LacD.1 conferred a significant gain in fitness that was associated with its regulatory activity. Taken together, these data suggest that LacD.1's adaptation represents a form of neofunctionalization in which duplication facilitated the gain of regulatory function important for growth in tissue and pathogenesis. PMID:23316044

  20. LacI-DNA-IPTG loops: equilibria among conformations by single-molecule FRET.

    PubMed

    Goodson, Kathy A; Wang, Zifan; Haeusler, Aaron R; Kahn, Jason D; English, Douglas S

    2013-04-25

    The E. coli Lac repressor (LacI) tetramer binds simultaneously to a promoter-proximal DNA binding site (operator) and an auxiliary operator, resulting in a DNA loop, which increases repression efficiency. Induction of the lac operon by allolactose reduces the affinity of LacI for DNA, but induction does not completely prevent looping in vivo. Our previous work on the conformations of LacI loops used a hyperstable model DNA construct, 9C14, that contains a sequence directed bend flanked by operators. Single-molecule fluorescence resonance energy transfer (SM-FRET) on a dual fluorophore-labeled LacI-9C14 loop showed that it adopts a single, stable, high-FRET V-shaped LacI conformation. Ligand-induced changes in loop geometry can affect loop stability, and the current work assesses loop population distributions for LacI-9C14 complexes containing the synthetic inducer IPTG. SM-FRET confirms that the high-FRET LacI-9C14 loop is only partially destabilized by saturating IPTG. LacI titration experiments and FRET fluctuation analysis suggest that the addition of IPTG induces loop conformational dynamics and re-equilibration between loop population distributions that include a mixture of looped states that do not exhibit high-efficiency FRET. The results show that repression by looping even at saturating IPTG should be considered in models for regulation of the operon. We propose that persistent DNA loops near the operator function biologically to accelerate rerepression upon exhaustion of inducer. PMID:23406418

  1. Mode-independent attenuation in evanescent-field sensors

    NASA Astrophysics Data System (ADS)

    Gnewuch, Harald; Renner, Hagen

    1995-03-01

    Generally, the total power attenuation in multimode evanescent-field sensor waveguides is nonproportional to the bulk absorbance because the modal attenuation constants differ. Hence a direct measurement is difficult and is additionally aggravated because the waveguide absorbance is highly sensitive to the specific launching conditions at the waveguide input. A general asymptotic formula for the modal power attenuation in strongly asymmetric inhomogeneous planar waveguides with arbitrarily distributed weak absorption in the low-index superstrate is derived. Explicit expressions for typical refractive-index profiles are given. Except when very close to the cutoff, the predicted asymptotic attenuation behavior agrees well with exact calculations. The ratio of TM versus TE absorption has been derived to be (2 - n0 2/nf2 ) for arbitrary profiles. Waveguides with a linear refractive-index profile show mode-independent attenuation coefficients within each polarization. Further, the asymptotic sensitivity is independent of the wavelength, so that it should be possible to directly measure the spectral variation of the bulk absorption. The mode independence of the attenuation has been verified experimentally for a second-order polynomial profile, which is close to a linear refractive-index distribution. In contrast, the attenuation in the step-profile waveguide has been found to depend strongly on the mode number, as predicted by theory. A strong spread of the modal attenuation coefficients is also predicted for the parabolic-profile waveguide sensor.

  2. Copyright 2002 by the Genetics Society of America Evidence That Selected Amplification of a Bacterial lac Frameshift

    E-print Network

    California at Davis, University of

    In the genetic system of Cairns and Foster, a nongrowing population of an E. coli lac frameshift mutant appears mutagenesis and behaves in every way like the original E. coli system. In both systems, lac revertants but favors only growth of cells that amplify their leaky mutant lac region (the amplification mutagenesis

  3. Electrical Breakdown in Lightning Arrestor Connector (LAC) Devices

    NASA Astrophysics Data System (ADS)

    Hjalmarson, Harold P.; Kambour, Kenneth; Pineda, Andrew C.

    2011-03-01

    Lightning arrestor connector (LAC) devices protect electronic devices by providing a conductive path to ground for electrical power surges caused by lightning. Such devices consist of an insulating material between electrodes. This insulation region is composed of an air gap and a high permittivity dielectric. In this presentation, the physics of the phenomena active in the early stages of the flow of transient electrical current will be described. The conditions that lead to thermal breakdown of the dielectric will also be discussed.--Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

  4. X-ray observations of BL Lac objects

    NASA Technical Reports Server (NTRS)

    Mushotzky, R. F.; Boldt, E. A.; Holt, S. A.; Pravdo, S. H.; Serlemitsos, P. J.; Swank, J. H.; Rothschild, R. H.

    1978-01-01

    The BL Lac objects MK501 and MK421 were observed with OSO-8 and HEAO-1 X-ray detectors in the 2-60 keV band. Their spectra are similar with best fitting power laws having energy index -.4 alpha 4. A soft X-ray excess is indicated in their spectra. There was no detectable X-ray absorption with implied column densities N sub H 1.5 x 10 to the 22d power at sq cm. MK421 was a factor 6 weaker in November 1977 than in May 1977. An identification of PKS0548-322 with a new source H0548,-32 is suggested.

  5. Seven Days in the Life of AR Lac

    NASA Astrophysics Data System (ADS)

    Ayres, T. R.; Brown, A.; Harper, G. M.; Korhonen, H.; Redfield, S.; Hawley, S. L.; Optical Support Team

    2005-12-01

    A week-long pointing on the short-period eclipsing RS CVn binary AR Lac (K0IV+G4IV; P=2d) by the Far-Ultraviolet Spectroscopic Explorer was coordinated with groundbased optical Doppler mapping, to provide an unprecedented view of structure, energetics, and dynamics of subcoronal activity, through time-resolved measurements of FUV diagnostics like C III ? 977, O VI ? 1031, and (coronal forbidden line) Fe XVIII ? 974. The observation was carried out over the period 29 November to 7 December 2004, with a total exposure of 225 ks, covering four revolutions of the binary. Three large flares were captured during this period, and numerous smaller ones, mainly on the K subgiant primary. We discuss the appearance of the FUV activity on the surfaces of the two hyperactive companions, with special emphasis on the eclipse intervals. This work was supported by a FUSE Guest Investigator grant.

  6. Fiber Attenuation To measure the attenuation coefficient of a multi-mode fiber, and to

    E-print Network

    Collins, Gary S.

    screw kit · ball-driver set · single-edged razor blade For the laser- · HeNe laser · laser mount · clamp clamp with two 4 1 -20 screws and clamp it to the short rod which you've mounted to the table. Put

  7. Estimation of interval anisotropic attenuation from reflection data

    Microsoft Academic Search

    Jyoti Behura; Ilya Tsvankin

    2008-01-01

    Knowledge of interval attenuation can be highly beneficial in reservoir char- acterization and lithology discrimination. Here, we combine the spectral-ratio method with velocity-independent layer-stripping to develop a technique for estimation of the interval phase attenuation coefficient from reflection seismic data. The algorithm is designed for arbitrarily anisotropic target layers, but the overburden is assumed to be laterally homogeneous with a

  8. Backscatter and attenuation properties of mammalian brain tissues

    NASA Astrophysics Data System (ADS)

    Wijekularatne, Pushpani Vihara

    Traumatic Brain Injury (TBI) is a common category of brain injuries, which contributes to a substantial number of deaths and permanent disability all over the world. Ultrasound technology plays a major role in tissue characterization due to its low cost and portability that could be used to bridge a wide gap in the TBI diagnostic process. This research addresses the ultrasonic properties of mammalian brain tissues focusing on backscatter and attenuation. Orientation dependence and spatial averaging of data were analyzed using the same method resulting from insertion of tissue sample between a transducer and a reference reflector. Apparent backscatter transfer function (ABTF) at 1 to 10 MHz, attenuation coefficient and backscatter coefficient (BSC) at 1 to 5 MHz frequency ranges were measured on ovine brain tissue samples. The resulting ABTF was a monotonically decreasing function of frequency and the attenuation coefficient and BSC generally were increasing functions of frequency, results consistent with other soft tissues such as liver, blood and heart.

  9. Landing gear noise attenuation

    NASA Technical Reports Server (NTRS)

    Moe, Jeffrey W. (Inventor); Whitmire, Julia (Inventor); Kwan, Hwa-Wan (Inventor); Abeysinghe, Amal (Inventor)

    2011-01-01

    A landing gear noise attenuator mitigates noise generated by airframe deployable landing gear. The noise attenuator can have a first position when the landing gear is in its deployed or down position, and a second position when the landing gear is in its up or stowed position. The noise attenuator may be an inflatable fairing that does not compromise limited space constraints associated with landing gear retraction and stowage. A truck fairing mounted under a truck beam can have a compliant edge to allow for non-destructive impingement of a deflected fire during certain conditions.

  10. lac Repressor Is an Antivirulence Factor of Salmonella enterica: Its Role in the Evolution of Virulence in Salmonella

    PubMed Central

    Eswarappa, Sandeepa M.; Karnam, Guruswamy; Nagarajan, Arvindhan G.; Chakraborty, Sangeeta; Chakravortty, Dipshikha

    2009-01-01

    The genus Salmonella includes many pathogens of great medical and veterinary importance. Bacteria belonging to this genus are very closely related to those belonging to the genus Escherichia. lacZYA operon and lacI are present in Escherichia coli, but not in Salmonella enterica. It has been proposed that Salmonella has lost lacZYA operon and lacI during evolution. In this study, we have investigated the physiological and evolutionary significance of the absence of lacI in Salmonella enterica. Using murine model of typhoid fever, we show that the expression of LacI causes a remarkable reduction in the virulence of Salmonella enterica. LacI also suppresses the ability of Salmonella enterica to proliferate inside murine macrophages. Microarray analysis revealed that LacI interferes with the expression of virulence genes of Salmonella pathogenicity island 2. This effect was confirmed by RT-PCR and Western blot analysis. Interestingly, we found that SBG0326 of Salmonella bongori is homologous to lacI of Escherichia coli. Salmonella bongori is the only other species of the genus Salmonella and it lacks the virulence genes of Salmonella pathogenicity island 2. Overall, our results demonstrate that LacI is an antivirulence factor of Salmonella enterica and suggest that absence of lacI has facilitated the acquisition of virulence genes of Salmonella pathogenicity island 2 in Salmonella enterica making it a successful systemic pathogen. PMID:19495420

  11. Specialized transduction with lambda plac5: dependence on recA and on configuration of lac and att lambda.

    PubMed Central

    Porter, R D; Lark, M W; Low, K B

    1981-01-01

    The construction of lambda plac5 transducing phages carrying various lacZ alleles is described. Genetically disabled (N- N- P-) lambda plac transducing the phages were used to study the dependence of specialized transduction on host RecA function and on the location of the lacZ gene in the recipient strain. In the absence of site-specific recombination at att lambda, transduction was completely dependent on host RecA function. Regardless of the configuration of att lambda, lambda plac transducing phages recombined at a 20- to 50-fold higher frequency with F42 lac than with a lac gene located in the cellular chromosome. Deletion mutants of lacZ in the recipient strain were used to show that the probability of lac recombination resulting from lambda plac infection is apparently proportional to the amount of homology between the parental lacZ genes. PMID:6454007

  12. A direct measurement of skull attenuation for quantitative SPECT

    SciTech Connect

    Turkington, T.G.; Gilland, D.R.; Jaszczak, R.J.; Greer, K.L.; Coleman, R.E. (Duke Univ. Medical Center, Durham, NC (United States). Dept. of Radiology); Smith, M.F. (Duke Univ., Durham, NC (United States). Dept. of Biomedical Engineering)

    1993-08-01

    The attenuation of 140 keV photons was measured in three empty skulls by placing a [sup 99m]Tc line source inside each one and acquiring projection data. These projections were compared to projections of the line source alone to determine the transmission through each point in the skull surrounding the line source. The effective skull thickness was calculated for each point using an assumed dense bone attenuation coefficient. The relative attenuation for this thickness of bone was compared to that of an equivalent amount of soft tissue to evaluate the increased attenuation of photons in brain SPECT relative to a uniform soft tissue approximation. For the skull regions surrounding most of the brain, the effective bone thickness varied considerably, but was generally less than 6 mm, resulting in a relative attenuation increases of less than 6%.

  13. Attenuator And Conditioner

    DOEpatents

    Anderson, Gene R. (Albuquerque, NM); Armendariz, Marcelino G. (Albuquerque, NM); Carson, Richard F. (Albuquerque, NM); Bryan, Robert P. (Albuquerque, NM); Duckett, III, Edwin B. (Albuquerque, NM); Kemme, Shanalyn Adair (Albuquerque, NM); McCormick, Frederick B. (Albuquerque, NM); Peterson, David W. (Sandia Park, NM)

    2006-04-04

    An apparatus and method of attenuating and/or conditioning optical energy for an optical transmitter, receiver or transceiver module is disclosed. An apparatus for attenuating the optical output of an optoelectronic connector including: a mounting surface; an array of optoelectronic devices having at least a first end; an array of optical elements having at least a first end; the first end of the array of optical elements optically aligned with the first end of the array of optoelectronic devices; an optical path extending from the first end of the array of optoelectronic devices and ending at a second end of the array of optical elements; and an attenuator in the optical path for attenuating the optical energy emitted from the array of optoelectronic devices. Alternatively, a conditioner may be adapted in the optical path for conditioning the optical energy emitted from the array of optoelectronic devices.

  14. The Physics Analysis of a Gas Attenuator with Argon as a Working Gas

    SciTech Connect

    Ryutov,, D.D.

    2010-12-07

    A gas attenuator is an important element of the LCLS facility. The attenuator must operate in a broad range of x-ray energies, provide attenuation coefficient between 1 and 10{sup 4} with the accuracy of 1% and, at the same time, be reliable and allow for many months of un-interrupted operation. S. Shen has recently carried out a detailed design study of the attenuator based on the use of nitrogen as a working gas. In this note we assess the features of the attenuator based on the use of argon. We concentrate on the physics issues, not the design features.

  15. Sustaining the natural and economical resources of the Lac Courte Oreilles, Leslie Isham; Jason Weaver

    SciTech Connect

    Isham, Leslie; Weaver, Jason

    2013-09-30

    The Lac Courte Oreilles Band of Lake Superior Chippewa Indians, located in northwest Wisconsin has developed a project, entitled Sustaining the Natural and Economic Resources of the LCO Ojibwe. This technical report is a summary of the project.

  16. 77 FR 27245 - Big Stone National Wildlife Refuge, Big Stone and Lac Qui Parle Counties, MN

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-05-09

    ...National Wildlife Refuge, Big Stone and Lac Qui Parle Counties, MN AGENCY: Fish and Wildlife Service, Interior. ACTION: Notice...Stone National Wildlife Refuge, 44843 County Road 19, Odessa, MN 56276. In-Person Drop Off: You may drop off...

  17. Mu-lac insertion-directed mutagenesis in a pectate lyase gene of Erwinia chrysanthemi.

    PubMed Central

    Diolez, A; Coleno, A

    1985-01-01

    The pelC gene, which encodes one of the five major pectate lyase (PL) isoenzymes in Erwinia chrysanthemi 3937, designated PLc, was subcloned from a hybrid lambda phage into a pBR322 derivative and mutagenized with a mini-Mu-lacZ transposable element able to form fusions to the lacZ gene. One plasmid (pAD1) which had an inactivated pelC gene and a Lac+ phenotype was selected in Escherichia coli. This plasmid was introduced into Erwinia chrysanthemi, and the pelC::mini-Mu insertion was substituted for the chromosomal allele by homologous recombination. This strain lacks the PLc isoenzyme. This Erwinia chrysanthemi strain has a Lac+ phenotype that is inducible by polygalacturonate, as are the wild-type PL activities. Images PMID:2993251

  18. Observations on the formation of clones containing araB-lacZ cistron fusions

    Microsoft Academic Search

    James A. Shapiro

    1984-01-01

    Casadaban (1976) developed a technique for isolating E. coli clones containing fusions of the amino terminal-encoding portion of any cistron with the carboxy terminal-encoding portion of lacZ. The technique utilizes prophage Mu homology to bring the two cistrons into proximity. I have followed the appearance over time of colonies containing araB-lacZ fusions from a strain where the begining of the

  19. Bistability of the lac Operon During Growth of Escherichia coli on Lactose and Lactose + Glucose

    Microsoft Academic Search

    Atul Narang; Sergei S. Pilyugin

    2008-01-01

    The lac operon of Escherichia coli can exhibit bistability. Early studies showed that bistability occurs during growth on TMG\\/succinate and lactose + glucose,\\u000a but not during growth on lactose. More recently, studies with lacGFP-transfected cells show bistability during growth on TMG\\/succinate,\\u000a but not during growth on lactose and lactose + glucose. In the literature, these results are invariably attributed to

  20. Bistability of the lac operon during growth of Escherichia coli on lactose and lactose + glucose

    Microsoft Academic Search

    A. Narang S. S. Pilyugin

    2007-01-01

    The lac operon of Escherichia coli exhibits bistability. Early studies showed that bistability occurs during growth on TMG\\/succinate and lactose + glucose, but not during growth on lactose. More recent studies with lacGFP-transfected cells show bistability with TMG\\/succinate, but not with lactose and lactose + glucose. In the literature, these results are attributed to variations of the positive feedback generated

  1. Seven Days in the Life of AR Lac

    NASA Astrophysics Data System (ADS)

    Ayres, T.

    A week-long FUSE stare at short-period eclipsing RS CVn binary AR Lac K0IV+G4IV; P2d), coordinated with groundbased radio imaging and optical Doppler mapping, will provide an unprecedented view of structure, energetics, and dynamics of hot-gas activity, through time-resolved measurements of FUV diagnostics like C III 977, O VI 1031, and (coronal forbidden line) Fe XVIII 974. As a class, RS CVns are notorious for extreme high-energy emissions even during quiescent periods, but are most spectacular during flare outbursts. Our project is the cool star equivalent of a Hubble Deep Field, in the time domain; a new window on magnetic activity in extreme environments ubiquitous in the Cosmos, but only now beginning to be characterized and understood. (Although the FUSE program is stand-alone, we plan to broaden and enhance the campaign by requesting Chandra HETGS and HST STIS time to be coordinated with the FUV spectroscopy.)

  2. Distinct element modeling of hydraulically fractured Lac du Bonnet granite

    NASA Astrophysics Data System (ADS)

    Al-Busaidi, A.; Hazzard, J. F.; Young, R. P.

    2005-06-01

    The aim of this study is to better understand the mechanics of fracture development and propagation during hydraulic fracturing. This paper presents some development and applications of discrete particle modeling of this problem. A discontinuum modeling approach idealizes the material as separate particles bonded together at their contact points and utilizes the breakage of individual structural units or bonds to represent damage. The numerical models are correlated with existing hydrofracture laboratory experiments, which are presented in other publications. A simulation of a laboratory-scale hydrofracture experiment and the acoustic emission (AE) data from the experiment is used to validate the synthetic AEs produced in the hydrofracture model. This technique has been used to examine the mechanics of fracture initiation and time and spatial distributions of AE. The modeling results demonstrate that the mechanism of hydraulically induced fracture in the Lac du Bonnet (LdB) granite core sample is predominantly tensile failure and that the shear cracks recorded in the hydrofracture experiment were due to slip on preexisting fractures. Numerical modeling of hydrofracture on homogeneous and heterogeneous synthetic samples seems to capture much of the behavior observed in the laboratory hydrofracture experiments.

  3. Population Dynamics of a Lac(-) Strain of Escherichia Coli during Selection for Lactose Utilization

    PubMed Central

    Foster, P. L.

    1994-01-01

    During selection for lactose utilization, Lac(+) revertants of FC40, a Lac(-) strain of Escherichia coli, appear at a high rate. Yet, no Lac(+) revertants appear in the absence of lactose, or in its presence if the cells have another, unfulfilled requirement for growth. This study investigates more fully the population dynamics of FC40 when incubated in the absence of a carbon source or when undergoing selection for lactose utilization. In the absence of a carbon source, the viable cell numbers do not change over 6 days. When incubated in liquid lactose medium, Lac(-) cells do not undergo any measurable increase in numbers or in turbidity for at least 2 days. When FC40 is plated on lactose minimum medium in the presence of scavenger cells, the upper limit to the amount of growth of Lac(-) cells during 5 days is one doubling, and there is no evidence for turnover (i.e., a balance between growth and death). The presence of a minority population that could form microcolonies was not detected. The implications of these results, plus the fact that the appearance of Lac(+) revertants during lactose selection is nearly constant with time, are discussed in reference to several models that have been postulated to account for adaptive mutations. PMID:7828809

  4. Multiple LacI-mediated loops revealed by Bayesian statistics and tethered particle motion

    PubMed Central

    Johnson, Stephanie; van de Meent, Jan-Willem; Phillips, Rob; Wiggins, Chris H.; Lindén, Martin

    2014-01-01

    The bacterial transcription factor LacI loops DNA by binding to two separate locations on the DNA simultaneously. Despite being one of the best-studied model systems for transcriptional regulation, the number and conformations of loop structures accessible to LacI remain unclear, though the importance of multiple coexisting loops has been implicated in interactions between LacI and other cellular regulators of gene expression. To probe this issue, we have developed a new analysis method for tethered particle motion, a versatile and commonly used in vitro single-molecule technique. Our method, vbTPM, performs variational Bayesian inference in hidden Markov models. It learns the number of distinct states (i.e. DNA–protein conformations) directly from tethered particle motion data with better resolution than existing methods, while easily correcting for common experimental artifacts. Studying short (roughly 100 bp) LacI-mediated loops, we provide evidence for three distinct loop structures, more than previously reported in single-molecule studies. Moreover, our results confirm that changes in LacI conformation and DNA-binding topology both contribute to the repertoire of LacI-mediated loops formed in vitro, and provide qualitatively new input for models of looping and transcriptional regulation. We expect vbTPM to be broadly useful for probing complex protein–nucleic acid interactions. PMID:25120267

  5. New Evidence for the Unified Scheme of BL Lac Objects and Fri Radio Galaxies

    E-print Network

    J. M. Bai; Myung Gyoon Lee

    2000-12-15

    In this paper, we collect radio and X-ray observations for most Fanaroff-Riley I (FRI) radio galaxies in the Zirbel-Baum radio galaxy sample, and investigate the distribution of the radio-to-X-ray effective spectral index, $\\alpha_{rx}$, to test the unified scheme of BL Lac objects and FRI radio galaxies. It is found that the range of $\\alpha_{rx}$ for FRI radio galaxies is almost the same as that for BL Lac objects, that the distribution of $\\alpha_{rx}$ probably peaks at the same position as BL Lac objects, and that the distribution of $\\alpha_{rx}$ for FRIs is similar to that for BL Lac objects. These suggest that there exist two subclasses of FRI radio galaxies: one is HBL-like, and the other is LBL-like, corresponding to high-energy-peaked (HBL) and low--energy-peaked (LBL) BL Lac objects, respectively. This result is consistent with previous VLA observations, and supports the unified scheme of BL Lac objects and FRI radio galaxies.

  6. Laser Measurement Of Convective-Heat-Transfer Coefficient

    NASA Technical Reports Server (NTRS)

    Porro, A. Robert; Hingst, Warren R.; Chriss, Randall M.; Seablom, Kirk D.; Keith, Theo G., Jr.

    1994-01-01

    Coefficient of convective transfer of heat at spot on surface of wind-tunnel model computed from measurements acquired by developmental laser-induced-heat-flux technique. Enables non-intrusive measurements of convective-heat-transfer coefficients at many points across surfaces of models in complicated, three-dimensional, high-speed flows. Measurement spot scanned across surface of model. Apparatus includes argon-ion laser, attenuator/beam splitter electronic shutter infrared camera, and subsystem.

  7. Planetary Ices Attenuation Properties

    NASA Astrophysics Data System (ADS)

    McCarthy, Christine; Castillo-Rogez, Julie C.

    In this chapter, we review the topic of energy dissipation in the context of icy satellites experiencing tidal forcing. We describe the physics of mechanical dissipation, also known as attenuation, in polycrystalline ice and discuss the history of laboratory methods used to measure and understand it. Because many factors - such as microstructure, composition and defect state - can influence rheological behavior, we review what is known about the mechanisms responsible for attenuation in ice and what can be inferred from the properties of rocks, metals and ceramics. Since attenuation measured in the laboratory must be carefully scaled to geologic time and to planetary conditions in order to provide realistic extrapolation, we discuss various mechanical models that have been used, with varying degrees of success, to describe attenuation as a function of forcing frequency and temperature. We review the literature in which these models have been used to describe dissipation in the moons of Jupiter and Saturn. Finally, we address gaps in our present knowledge of planetary ice attenuation and provide suggestions for future inquiry.

  8. RegR, a Global LacI/GalR Family Regulator, Modulates Virulence and Competence in Streptococcus pneumoniae

    PubMed Central

    Chapuy-Regaud, Sabine; Ogunniyi, A. David; Diallo, Nicole; Huet, Yvette; Desnottes, Jean-François; Paton, James C.; Escaich, Sonia; Trombe, Marie-Claude

    2003-01-01

    The homolactic and catalase-deficient pathogen Streptococcus pneumoniae is not only tolerant to oxygen but requires the activity of its NADH oxidase, Nox, to develop optimal virulence and competence for genetic transformation. In this work, we show that the global regulator RegR is also involved in these traits. Genetic dissection revealed that RegR regulates competence and the expression of virulence factors, including hyaluronidase. In bacteria grown in vitro, RegR represses hyaluronidase. At neutral pH, it increases adherence to A549 epithelial cells, and at alkaline pH, it acts upstream of the CiaRH two-component signaling system to activate competence. These phenotypes are not associated with changes in antibiotic resistance, central metabolism, and carbohydrate utilization. Although the RegR0 (where 0 indicates the loss of the protein) mutation is sufficient to attenuate experimental virulence of strain 23477 in mice, the introduction of an additional hyl0 (where 0 indicates the loss of function) mutation in the RegR0 strain 23302 dramatically reduces its virulence. This indicates that residual virulence of the RegR0 Hyl+ derivative is due to hyaluronidase and supports the dual role of RegR in virulence. This LacI/GalR regulator, not essential for in vitro growth in rich media, is indeed involved in the adaptive response of the pneumococcus via its control of competence, adherence, and virulence. PMID:12704136

  9. Effect of collimator size and absorber thickness on gamma ray attenuation measurements

    Microsoft Academic Search

    G. S. Sidhu; K. Singh; P. S. Singh; G. S. Mudahar

    1999-01-01

    Mass attenuation coefficients have been measured in extended media of soil and water for 662 keV gamma rays under different collimation conditions. A correlation effect due to absorber thickness and collimator size has been observed.

  10. X-ray Selected BL Lacs and Blazars

    E-print Network

    Eric S. Perlman

    1999-10-18

    With their rapid, violent variability and broad featureless continuum emission, blazars have puzzled astronomers for over two decades. Today blazars represent the only extragalactic objects detected in high-energy gamma-rays. Their spectral energy distributions (SEDs) are characteristically double-humped, with lower-energy emission originating as synchrotron radiation in a relativistically beamed jet, and higher-energy emission due to inverse-Compton processes. This has accentuated the biases inherent in any survey to favor objects which are bright in the survey band, and should serve as a cautionary note both to those designing new surveys as well as theorists attempting to model blazar properties. The location of the synchrotron peak determines which blazar population is dominant at GeV and TeV energies. At GeV energies, low-energy peaked, high luminosity objects, which have high $L_C/L_S$ ratios, dominate, while at TeV energies, high-energy peaked objects are all that is seen. I review the differences between low-energy peaked and high-energy peaked blazars, and models to explain those differences. I also look at efforts to bridge the gap between these classes with new surveys. Two new surveys have detected a large population of high-energy peaked emission line blazars (FSRQ), with properties somewhat different from previously known objects. This discovery has the potential to revolutionize blazar physics in a way comparable to the discovery of X-ray selected BL Lacs ten years ago by {\\it Einstein}. I cull from the new and existing surveys a list of $z<0.1$ high-energy peaked blazars which should be targets for new TeV telescopes. Among these are several high-energy peaked FSRQ.

  11. Radiofrequency attenuator and method

    DOEpatents

    Warner, Benjamin P. (Los Alamos, NM); McCleskey, T. Mark (Los Alamos, NM); Burrell, Anthony K. (Los Alamos, NM); Agrawal, Anoop (Tucson, AZ); Hall, Simon B. (Palmerston North, NZ)

    2009-01-20

    Radiofrequency attenuator and method. The attenuator includes a pair of transparent windows. A chamber between the windows is filled with molten salt. Preferred molten salts include quarternary ammonium cations and fluorine-containing anions such as tetrafluoroborate (BF.sub.4.sup.-), hexafluorophosphate (PF.sub.6.sup.-), hexafluoroarsenate (AsF.sub.6.sup.-), trifluoromethylsulfonate (CF.sub.3SO.sub.3.sup.-), bis(trifluoromethylsulfonyl)imide ((CF.sub.3SO.sub.2).sub.2N.sup.-), bis(perfluoroethylsulfonyl)imide ((CF.sub.3CF.sub.2SO.sub.2).sub.2N.sup.-) and tris(trifluoromethylsulfonyl)methide ((CF.sub.3SO.sub.2).sub.3C.sup.-). Radicals or radical cations may be added to or electrochemically generated in the molten salt to enhance the RF attenuation.

  12. Radiofrequency attenuator and method

    DOEpatents

    Warner, Benjamin P. (Los Alamos, NM); McCleskey, T. Mark (Los Alamos, NM); Burrell, Anthony K. (Los Alamos, NM); Agrawal, Anoop (Tucson, AZ); Hall, Simon B. (Palmerston North, NZ)

    2009-11-10

    Radiofrequency attenuator and method. The attenuator includes a pair of transparent windows. A chamber between the windows is filled with molten salt. Preferred molten salts include quarternary ammonium cations and fluorine-containing anions such as tetrafluoroborate (BF.sub.4.sup.-), hexafluorophosphate (PF.sub.6.sup.-), hexafluoroarsenate (AsF.sub.6.sup.-), trifluoromethylsulfonate (CF.sub.3SO.sub.3.sup.-), bis(trifluoromethylsulfonyl)imide ((CF.sub.3SO.sub.2).sub.2N.sup.-), bis(perfluoroethylsulfonyl)imide ((CF.sub.3CF.sub.2SO.sub.2).sub.2N.sup.-) and tris(trifluoromethylsulfonyl)methide ((CF.sub.3SO.sub.2).sub.3 C.sup.-). Radicals or radical cations may be added to or electrochemically generated in the molten salt to enhance the RF attenuation.

  13. Internal radiation attenuation system

    SciTech Connect

    Jacobson, E.B.

    1988-03-22

    This patent describes an internal radiation attenuation system for a radioactive environment having a substantially enclosed radioactive workspace having an internal configuration with at least one entrance portal. The workspace internal configuration has an upper wall or ceiling, side walls and a bottom wall, comprising: means for forming a frame for supporting radiation attenuation means to substantially conform to at least a portion of the inside of the workspace internal configuration. The frame means include interlocking segments, including means for assembling the segments into the frame means. The interlocking segments form a skeleton spaced around the periphery of the internal workspace, interlocked with one another. The frame means further include means for supporting the radiation attenuation means around at least a portion of the periphery of the internal workspace. The frame means skeleton form a free standing support structure standing and supported primarily by the bottom wall without vertical support from the ceiling.

  14. Local threshold for segmented attenuation correction of PET imaging of the thorax

    Microsoft Academic Search

    M. Xu; W. K. Luk; P. D. Cutler; W. M. Digby

    1994-01-01

    A local threshold for segmented attenuation correction technique has been developed for positron emission tomography using short (2-3 minutes) post-injection transmission scans. The technique implements an optimal threshold method on localized histograms to get pseudo-anatomic segmentation on transmission images. Theoretical values of attenuation coefficients are assigned to corresponding anatomic regions. Emission images are reconstructed using attenuation correction factors computed by

  15. A linear model approach for ultrasonic inverse problems with attenuation and dispersion

    E-print Network

    Boyer, Edmond

    . Absorption is caused by the excitation of the particles that converts sound energy into heat. Con- sequently precise estimation of the attenuation coefficient and of the sound velocity. A thickness estimation above. Attenuation is due to two basic causes, namely, scattering and absorption. Scattering results

  16. Attenuation of lateral propagating light in sea ice measured with an artificial lamp in winter Arctic

    Microsoft Academic Search

    J.-P. Zhao; T. Li; D. Barber; J.-P. Ren; M. Pucko; S.-J. Li; X. Li

    2010-01-01

    The attenuation property of a lateral propagating light (LPL) in sea ice was measured using an artificial lamp in the Canadian Arctic during the 2007\\/2008 winter. A measurement method is proposed and applied whereby a recording instrument is buried in the sea ice and an artificial lamp is moved across the instrument. The apparent attenuation coefficient ?(?) for the lateral

  17. Estimating Attenuation of Ultraviolet Radiation in Streams: Field and Laboratory Methods

    Microsoft Academic Search

    Patrick Belmont; Bruce R. Hargreaves; Donald P. Morris; Craig E. Williamson

    2007-01-01

    We adapted and tested a laboratory quantitative filter pad method and field-based microcosm method for estimating diffuse attenuation coefficients (Kd) of ultraviolet radiation (UVR) for a wide range of stream optical environments (Kd320 = 3-44 m )1 ). Logistical difficulties of direct measurements of UVR attenu- ation have inhibited widespread monitoring of this important parameter in streams. Suspended sediment concentrations

  18. Effect of finite absorber dimensions on gamma-ray attenuation measurements

    Microsoft Academic Search

    K. M. Varier; S. Nasiruddeen Kunju; K. Madhusudanan

    1986-01-01

    Using 137Cs gamma rays, the effect of finite absorber dimensions on attenuation measurements has been studied. Copper and mercury targets were used. Absorber dimensions up to five mean free paths were used. A correlated effect was observed in the measurements due to absorber thickness and its dimensions in the transverse directions. The values of the attenuation coefficients for copper and

  19. Shape effect of elongated grains on ultrasonic attenuation in polycrystalline materials

    Microsoft Academic Search

    L. Yang; O. I. Lobkis; S. I. Rokhlin

    2011-01-01

    Longitudinal and transverse wave attenuation coefficients are obtained in a simple integral form for ultrasonic waves in cubic polycrystalline materials with elongated grains. Dependences of attenuation on frequency and grain shape are described in detail. The explicit analytical solutions for ellipsoidal grains in the Rayleigh and stochastic frequency limits are given for a wave propagating in an arbitrary direction relative

  20. A theoretical comparison of attenuation measurement techniques from backscattered ultrasound echoes

    E-print Network

    Illinois at Urbana-Champaign, University of

    characterization of tissue pathologies using ultrasonic attenuation is strongly dependent on the accuracy, 43.20.Hq, 43.20.Fn, 43.20.Ei [CCC] Pages: 2316­2324 I. INTRODUCTION The ultrasonic attenuation coefficient is an important pa- rameter in the characterization of tissue pathologies. In liver disease

  1. Relationship Between Ultrasonic Attenuation, Size and Axial Strain Parameters for Ex Vivo Atherosclerotic Carotid Plaque

    Microsoft Academic Search

    Hairong Shi; Tomy Varghese; Robert J. Dempsey; Mohammed S. Salamat; James A. Zagzebski

    2008-01-01

    Many ultrasonic parameters, primarily related to attenuation and scatterer size, have been used to characterize the composition of atherosclerotic plaque tissue. In this study, we combine elastographic (axial strain ratio) and ultrasonic tissue characterization parameters, namely the attenuation coefficient and a scattering parameter associated with an “equivalent” scatterer size to delineate between fibrous, calcified, and lipidic plaque tissue. We present

  2. Effect of collimator size and absorber thickness on gamma ray attenuation measurements for bakelite and perspex

    Microsoft Academic Search

    Gurdeep S Sidhu; Karamjit Singh; Parjit S Singh; Gurmel S Mudahar

    1999-01-01

    The mass attenuation coefficient (?\\u000a m) of 662 keV gamma rays have been measured in the extended media of bakelite and perspex under different collimation conditions.\\u000a The increase in attenuation coefficient is seen with increase in sample thickness as well as with collimator size due to the\\u000a contribution of multiple scattered photons in the uncollided beam of 662 keV gamma

  3. X-Ray Attenuation and Absorption for Materials of Dosimetric Interest

    National Institute of Standards and Technology Data Gateway

    SRD 126 X-Ray Attenuation and Absorption for Materials of Dosimetric Interest (Web, free access)   Tables and graphs of the photon mass attenuation coefficient and the mass energy-absorption coefficient are presented for all of the elements Z = 1 to 92, and for 48 compounds and mixtures of radiological interest. The tables cover energies of the photon (x-ray, gamma ray, bremsstrahlung) from 1 keV to 20 MeV.

  4. Plane-wave attenuation anisotropy in orthorhombic media

    Microsoft Academic Search

    Yaping Zhu; Ilya Tsvankin

    2007-01-01

    Orthorhombic models are often used in the interpretation of azimuthally varying seismic signatures recorded over fractured reservoirs. Here, we develop an analytic framework for describ- ing the attenuation coefficients in orthorhombic media with orthorhombic attenuationi.e., the symmetry of both the real and imaginary parts of the stiffness tensor is identical under the as- sumption of homogeneous wave propagation. The analogous

  5. Simple rain attenuation prediction method for satellite radio links

    Microsoft Academic Search

    J. A. Garcia-Lopez; J. M. Hernando; J. M. Selga

    1988-01-01

    The desirable features of a rain attenuation prediction method to be used in satellite radio link engineering are established, and a method satisfying such features is proposed. The method is tested over 77 satellite links situated in Europe, the U.S., Japan, and Australia. Comparisons are made with the International Radio Consultative Committee (CCIR) method. Using the worldwide coefficients for the

  6. Modeling, evaluation, and asymptotic analysis of attenuation anisotropy

    NASA Astrophysics Data System (ADS)

    Shekar, Bharath Chandra

    Seismic attenuation is sensitive to the physical properties of the subsurface, which makes attenuation analysis a useful tool for reservoir characterization. In this thesis, I present algorithms for estimating directionally dependent attenuation coefficients and perform asymptotic and numerical analysis of wave propagation in attenuative anisotropic media. First, I introduce a methodology to estimate the S-wave interval attenuation coefficient by extending the layer-stripping method of Behura and Tsvankin (2009) to mode-converted (PS) waves. Kinematic reconstruction of pure shear (SS) events in the target layer and the overburden is performed by combining velocity-independent layer stripping with the PP+PS=SS method. Then, application of the spectral-ratio method and the dynamic version of velocity-independent layer stripping to the constructed SS reflections yields the S-wave interval attenuation coefficient in the target layer. The attenuation coefficient estimated for a range of source-receiver offsets can be inverted for the interval attenuation-anisotropy parameters. The method is tested on synthetic data generated with the anisotropic reflectivity method for layered VTI (transversely isotropic with a vertical symmetry axis) media and vertical symmetry planes of orthorhombic media. Then, I analyze a cross-hole data set generated by perforation shots set off in a horizontal borehole to induce hydraulic fracturing in a tight gas reservoir. The spectral-ratio method is applied to pairs of traces to set up a system of equations for directionally-dependent effective attenuation. Although the inversion provides clear evidence of attenuation anisotropy, the narrow range of propagation directions impairs the accuracy of anisotropy analysis. The observed variations of the attenuation coefficient between different perforation stages appear to be related to changes in the medium due to hydraulic fracturing and stimulation. Important insights into point-source radiation in attenuative anisotropic media can be gained by applying asymptotic methods. I derive the asymptotic Green's function in homogeneous, attenuative, arbitrarily anisotropic media using the steepest-descent method. The saddle-point condition helps describe the behavior of the far field slowness and group-velocity vectors and evaluate the inhomogeneity angle (the angle between the real and imaginary parts of the slowness vector). The results from the asymptotic analysis are compared with those from the ray-perturbation method for P-waves in TI media. Finally, I address the problem of efficient viscoelastic modeling in heterogeneous anisotropic media. The Kirchhoff scattering integral is employed to generate reflected P-waves, with the required Green's functions computed by summation of Gaussian beams. The influence of attenuation on the Gaussian beams is incorporated using ray-perturbation theory. The method is applied to generate synthetic data from a highly attenuative VTI medium above a horizontal reflector and a structurally complex acoustic model with a salt body.

  7. Tritium Attenuation by Distillation

    SciTech Connect

    Wittman, N.E.

    2001-07-31

    The objective of this study was to determine how a 100 Area distillation system could be used to reduce to a satisfactory low value the tritium content of the dilute moderator produced in the 100 Area stills, and whether such a tritium attenuator would have sufficient capacity to process all this material before it is sent to the 400 Area for reprocessing.

  8. Outward-facing conformers of LacY stabilized by nanobodies.

    PubMed

    Smirnova, Irina; Kasho, Vladimir; Jiang, Xiaoxu; Pardon, Els; Steyaert, Jan; Kaback, H Ronald

    2014-12-30

    The lactose permease of Escherichia coli (LacY), a highly dynamic polytopic membrane protein, catalyzes stoichiometric galactoside/H(+) symport by an alternating access mechanism and exhibits multiple conformations, the distribution of which is altered by sugar binding. We have developed single-domain camelid nanobodies (Nbs) against a LacY mutant in an outward (periplasmic)-open conformation to stabilize this state of the WT protein. Twelve purified Nbs inhibit lactose transport in right-side-out membrane vesicles, indicating that the Nbs recognize epitopes on the periplasmic side of LacY. Stopped-flow kinetics of sugar binding by WT LacY in detergent micelles or reconstituted into proteoliposomes reveals dramatic increases in galactoside-binding rates induced by interaction with the Nbs. Thus, WT LacY in complex with the great majority of the Nbs exhibits varied increases in access of sugar to the binding site with an increase in association rate constants (kon) of up to ? 50-fold (reaching 10(7) M(-1) ? s(-1)). In contrast, with the double-Trp mutant, which is already open on the periplasmic side, the Nbs have little effect. The findings are clearly consistent with stabilization of WT conformers with an open periplasmic cavity. Remarkably, some Nbs drastically decrease the rate of dissociation of bound sugar leading to increased affinity (greater than 200-fold for lactose). PMID:25512549

  9. Isolation of behavioral mutants of Azospirillum brasilense by using Tn5 lacZ.

    PubMed Central

    van Rhijn, P; Vanstockem, M; Vanderleyden, J; De Mot, R

    1990-01-01

    Tn5 lacZ mutants were generated with Azospirillum brasilense 7030 by mating that strain with Escherichia coli strains carrying suicide plasmid pCIB100 or pCIB110. Kanamycin-resistant Azospirillum colonies were obtained with a maximum frequency of 10(-6) per recipient cell. The potential of Tn5 lacZ for random transposon mutagenesis coupled to transcription analysis in A. brasilense 7030 was demonstrated. Sixty percent of all Kmr A. brasilense 7030 mutants expressed beta-galactosidase activity. Mutants affected in motility (Fla-) and general chemotaxis (Che-) were identified. Chromosomal insertions of Tn5 lacZ are involved, except for two Che- mutants. The latter che loci reside on a 90-megadalton plasmid. Expression of an acidic protein (Mr, 110,000) was abolished in these mutants. Images PMID:2160221

  10. A computational systems biology study of the lambda-lac mutants

    E-print Network

    Werner, Maria

    2007-01-01

    We present a comprehensive computational study of some 900 possible "lambda-lac" mutants of the lysogeny maintenance switch in phage lambda, of which up to date 19 have been studied experimentally (Atsumi & Little, PNAS 103: 4558-4563, (2006)). We clarify that these mutants realise regulatory schemes quite different from wild-type lambda, and can therefore be expected to behave differently, within the conventional mechanistic setting in which this problem has often been framed. We verify that indeed, within this framework, across this wide selection of mutants the lambda-lac mutants for the most part either have no stable lytic states, or should only be inducible with difficulty. In particular, the computational results contradicts the experimental finding that four lambda-lac mutants both show stable lysogeny and are inducible. This work hence suggests either that the four out of 900 mutants are special, or that lambda lysogeny and inducibility are holistic effects involving other molecular players or ot...

  11. A lacZ reporter gene expression atlas for 313 adult KOMP mutant mouse lines.

    PubMed

    West, David B; Pasumarthi, Ravi K; Baridon, Brian; Djan, Esi; Trainor, Amanda; Griffey, Stephen M; Engelhard, Eric K; Rapp, Jared; Li, Bowen; Jong, Pieter J de; Lloyd, K C Kent

    2015-04-01

    Expression of the bacterial beta-galactosidase reporter gene (lacZ) in the vector used for the Knockout Mouse Project (KOMP) is driven by the endogenous promoter of the target gene. In tissues from KOMP mice, histochemical staining for LacZ enzyme activity can be used to determine gene expression patterns. With this technique, we have produced a comprehensive resource of gene expression using both whole mount (WM) and frozen section (FS) LacZ staining in 313 unique KOMP mutant mouse lines. Of these, ?80% of mutants showed specific staining in one or more tissues, while ?20% showed no specific staining, ?13% had staining in only one tissue, and ?25% had staining in >6 tissues. The highest frequency of specific staining occurred in the brain (?50%), male gonads (42%), and kidney (39%). The WM method was useful for rapidly identifying whole organ and some substructure staining, while the FS method often revealed substructure and cellular staining specificity. Both staining methods had >90% repeatability in biological replicates. Nonspecific LacZ staining occurs in some tissues due to the presence of bacteria or endogenous enzyme activity. However, this can be effectively distinguished from reporter gene activity by the combination of the WM and FS methods. After careful annotation, LacZ staining patterns in a high percentage of mutants revealed a unique structure-function not previously reported for many of these genes. The validation of methods for LacZ staining, annotation, and expression analysis reported here provides unique insights into the function of genes for which little is currently known. PMID:25591789

  12. Photohadronic origin of ? -ray BL Lac emission: implications for IceCube neutrinos

    NASA Astrophysics Data System (ADS)

    Petropoulou, M.; Dimitrakoudis, S.; Padovani, P.; Mastichiadis, A.; Resconi, E.

    2015-04-01

    The recent IceCube discovery of 0.1-1 PeV neutrinos of astrophysical origin opens up a new era for high-energy astrophysics. Although there are various astrophysical candidate sources, a firm association of the detected neutrinos with one (or more) of them is still lacking. A recent analysis of plausible astrophysical counterparts within the error circles of IceCube events showed that likely counterparts for nine of the IceCube neutrinos include mostly BL Lacs, among which Mrk 421. Motivated by this result and a previous independent analysis on the neutrino emission from Mrk 421, we test the BL Lac-neutrino connection in the context of a specific theoretical model for BL Lac emission. We model the spectral energy distribution (SED) of the BL Lacs selected as counterparts of the IceCube neutrinos using a one-zone leptohadronic model and mostly nearly simultaneous data. The neutrino flux for each BL Lac is self-consistently calculated, using photon and proton distributions specifically derived for every individual source. We find that the SEDs of the sample, although different in shape and flux, are all well fitted by the model using reasonable parameter values. Moreover, the model-predicted neutrino flux and energy for these sources are of the same order of magnitude as those of the IceCube neutrinos. In two cases, namely Mrk 421 and 1H 1914-194, we find a suggestively good agreement between the model prediction and the detected neutrino flux. Our predictions for all the BL Lacs of the sample are in the range to be confirmed or disputed by IceCube in the next few years of data sampling.

  13. Attenuation of a Stoneley wave and higher Lamb modes due to the scattering by two-dimensional irregularities of the walls of a fluid-filled borehole

    Microsoft Academic Search

    G. A. Maximov; E. Ortega; E. V. Pod Yachev

    2007-01-01

    Attenuation of Stoneley waves and higher Lamb modes propagating along an irregular surface of a fluid-filled borehole is investigated. This problem generalizes the problem on the attenuation of Rayleigh waves by an irregular surface of an empty borehole [10]. The technique used to evaluate the attenuation coefficient is based on the perturbation method (surface irregularity heights are considered to be

  14. VizieR Online Data Catalog: CZ Lac multiperiodic Blazhko modulation (Sodor+, 2011)

    NASA Astrophysics Data System (ADS)

    Sodor, A.; Jurcsik, J.; Szeidl, B.; Varadi, M.; Henden, A.; Vida, K.; Hurta, Zs.; Posztobanyi, K.; Dekany, I.; Szing, A.

    2011-09-01

    CZ Lac was observed with a photometer attached to the 60-cm telescope of the Konkoly Observatory, Svabhegy, Budapest, through B and V filters on seven nights in 1967 (table A1), and 2 seasons between 2004 and 2005. We observed CZ Lac with the same, refurbished and automated 60-cm telescope equipped with a Wright Instruments 750x1100 CCD camera (field of view 17x24arcmin) in 2004 and 2005. About 29 000 frames were obtained in BV(RI)C bands. The data of the two seasons spanned 146 and 84d. (8 data files).

  15. Spectral energy distributions and high-energy emission of BL Lac type objects

    E-print Network

    Troitsky, Sergey

    2008-01-01

    Based on identifications from the Veron and Quasars.org catalogs, we determine the optical-to-X-ray spectral indices for a sample of 201 BL Lacs and search for trends in the distribution of these indices of the sources detected in high-energy bands. As is expected for the two-bump spectral energy distributions, TeV-detected objects are strong in X rays while EGRET-detected ones are low-energy peaked. Positional correlation with the arrival directions of ultra-high-energy cosmic rays from the previously studied AGASA, Yakutsk and High Resolution Fly's Eye samples is saturated by low-energy-peaked BL Lacs.

  16. Ultraviolet and X-ray observations of the BL Lac object PKS 05 8-322

    NASA Technical Reports Server (NTRS)

    Urry, C. M.; Mushotzky, R. F.; Hackney, K. R. H.; Hackney, R. L.

    1982-01-01

    Spectrophotometric observations of the BL Lac object PKS 0548-322 were made with ultraviolet and X-ray instruments on the IUE and HEAO-2 satellites. Two observations in each spectral region, one set of which was obtained simultaneously are presented. A power law of energy index approximately 1.0 gives a good description of the data from ultraviolet through X-ray frequencies. This source is reported to be variable on short timescales (Gilmore 1980); the implications of the spectral properties and apparent variability are discussed in light of a relativistic jet model. Findings support the jet picture of BL Lac objects.

  17. Simultaneous backscatter and attenuation estimation using a least squares method with constraints.

    PubMed

    Nam, Kibo; Zagzebski, James A; Hall, Timothy J

    2011-12-01

    Backscatter and attenuation variations are essential contrast mechanisms in ultrasound B-mode imaging. Emerging quantitative ultrasound methods extract and display absolute values of these tissue properties. However, in clinical applications, backscatter and attenuation parameters sometimes are not easily measured because of tissues inhomogeneities above the region-of-interest (ROI). We describe a least squares method (LSM) that fits the echo signal power spectra from a ROI to a three-parameter tissue model that simultaneously yields estimates of attenuation losses and backscatter coefficients. To test the method, tissue-mimicking phantoms with backscatter and attenuation contrast as well as uniform phantoms were scanned with linear array transducers on a Siemens S2000. Attenuation and backscatter coefficients estimated by the LSM were compared with those derived using a reference phantom method (Yao et al. 1990). Results show that the LSM yields effective attenuation coefficients for uniform phantoms comparable to values derived using the reference phantom method. For layered phantoms exhibiting nonuniform backscatter, the LSM resulted in smaller attenuation estimation errors than the reference phantom method. Backscatter coefficients derived using the LSM were in excellent agreement with values obtained from laboratory measurements on test samples and with theory. The LSM is more immune to depth-dependent backscatter changes than commonly used reference phantom methods. PMID:21963038

  18. Control algorithms for dynamic attenuators

    SciTech Connect

    Hsieh, Scott S., E-mail: sshsieh@stanford.edu [Department of Radiology, Stanford University, Stanford, California 94305 and Department of Electrical Engineering, Stanford University, Stanford, California 94305 (United States); Pelc, Norbert J. [Department of Radiology, Stanford University, Stanford California 94305 and Department of Bioengineering, Stanford University, Stanford, California 94305 (United States)] [Department of Radiology, Stanford University, Stanford California 94305 and Department of Bioengineering, Stanford University, Stanford, California 94305 (United States)

    2014-06-15

    Purpose: The authors describe algorithms to control dynamic attenuators in CT and compare their performance using simulated scans. Dynamic attenuators are prepatient beam shaping filters that modulate the distribution of x-ray fluence incident on the patient on a view-by-view basis. These attenuators can reduce dose while improving key image quality metrics such as peak or mean variance. In each view, the attenuator presents several degrees of freedom which may be individually adjusted. The total number of degrees of freedom across all views is very large, making many optimization techniques impractical. The authors develop a theory for optimally controlling these attenuators. Special attention is paid to a theoretically perfect attenuator which controls the fluence for each ray individually, but the authors also investigate and compare three other, practical attenuator designs which have been previously proposed: the piecewise-linear attenuator, the translating attenuator, and the double wedge attenuator. Methods: The authors pose and solve the optimization problems of minimizing the mean and peak variance subject to a fixed dose limit. For a perfect attenuator and mean variance minimization, this problem can be solved in simple, closed form. For other attenuator designs, the problem can be decomposed into separate problems for each view to greatly reduce the computational complexity. Peak variance minimization can be approximately solved using iterated, weighted mean variance (WMV) minimization. Also, the authors develop heuristics for the perfect and piecewise-linear attenuators which do not requirea priori knowledge of the patient anatomy. The authors compare these control algorithms on different types of dynamic attenuators using simulated raw data from forward projected DICOM files of a thorax and an abdomen. Results: The translating and double wedge attenuators reduce dose by an average of 30% relative to current techniques (bowtie filter with tube current modulation) without increasing peak variance. The 15-element piecewise-linear dynamic attenuator reduces dose by an average of 42%, and the perfect attenuator reduces dose by an average of 50%. Improvements in peak variance are several times larger than improvements in mean variance. Heuristic control eliminates the need for a prescan. For the piecewise-linear attenuator, the cost of heuristic control is an increase in dose of 9%. The proposed iterated WMV minimization produces results that are within a few percent of the true solution. Conclusions: Dynamic attenuators show potential for significant dose reduction. A wide class of dynamic attenuators can be accurately controlled using the described methods.

  19. Natural Attenuation Tool Kit

    NSDL National Science Digital Library

    Created by Julie Crosby, this site provides information and links to agencies and companies concerned with environmental remediation, in particular by natural attenuation. Although some sections are still under construction, Products provides interested parties with links to software and field applications. The Papers section contains four technical papers and six regulatory papers plus two publication metasites maintained by the Environmental Protection Agency (EPA). Other areas of interest at the site include links to government agencies and a list of conferences, updated regularly.

  20. In vivo localization of DNA sequences and visualization of large-scale chromatin organization using lac operator\\/repressor recognition

    Microsoft Academic Search

    Carmen C. Robinett; Aaron Straight; Gang Li; Carol Willhelm; Gail Sudlow; Andrew Murray; Andrew S. Belmont

    1996-01-01

    We report a new method for in situ localiza- tion of DNA sequences that allows excellent preserva- tion of nuclear and chromosomal ultrastructure and direct, in vivo observations. 256 direct repeats of the lac operator were added to vector constructs used for transfection and served as a tag for labeling by lac re- pressor. This system was first characterized by

  1. Comparison of apparent diffusion coefficients (ADC) and distributed diffusion coefficients (DDC) in high-grade gliomas

    PubMed Central

    Kwee, Thomas C.; Galbán, Craig J.; Tsien, Christina; Junck, Larry; Sundgren, Pia C.; Ivancevic, Marko K.; Johnson, Timothy D.; Meyer, Charles R.; Rehemtulla, Alnawaz; Ross, Brian D.; Chenevert, Thomas L.

    2010-01-01

    Purpose To compare apparent diffusion coefficients (ADCs) with distributed diffusion coefficients (DDCs) in high-grade gliomas. Materials and Methods Twenty patients with high-grade gliomas prospectively underwent diffusion-weighted magnetic resonance imaging. Traditional ADC maps were created using b-values of 0 and 1000 s/mm2. In addition, DDC maps were created by applying the stretched-exponential model using b-values of 0, 1000, 2000, and 4000 s/mm2. Whole-tumor ADCs and DDCs (in 10-3 mm2/s) were measured and analyzed with a paired t test, Pearson's correlation coefficient, and the Bland-Altman method. Results Tumor ADCs (1.14 ± 0.26) were significantly lower (P = 0.0001) than DDCs (1.64 ± 0.71). Tumor ADCs and DDCs were strongly correlated (R = 0.9716; P < 0.0001), but mean bias ± limits of agreement between tumor ADCs and DDCs was -0.50 ± 0.90. There was a clear trend toward greater discordance between ADC and DDC at high ADC values. Conclusion Under the assumption that the stretched-exponential model provides a more accurate estimate of the average diffusion rate than the mono-exponential model, our results suggest that for a little diffusion attenuation the mono-exponential fit works rather well for quantifying diffusion in high-grade gliomas, whereas it works less well for a greater degree of diffusion attenuation. PMID:20187193

  2. Prediction of slant path rain attenuation statistics at various locations

    NASA Technical Reports Server (NTRS)

    Goldhirsh, J.

    1977-01-01

    The paper describes a method for predicting slant path attenuation statistics at arbitrary locations for variable frequencies and path elevation angles. The method involves the use of median reflectivity factor-height profiles measured with radar as well as the use of long-term point rain rate data and assumed or measured drop size distributions. The attenuation coefficient due to cloud liquid water in the presence of rain is also considered. Absolute probability fade distributions are compared for eight cases: Maryland (15 GHz), Texas (30 GHz), Slough, England (19 and 37 GHz), Fayetteville, North Carolina (13 and 18 GHz), and Cambridge, Massachusetts (13 and 18 GHz).

  3. Pearson's Correlation Coefficient

    NSDL National Science Digital Library

    This tutorial on Pearson's Correlation Coefficient includes the definition, assumptions, and characteristics of r as well as related statistics and hypothesis test procedures. One section instructs users to find correlation in the WINKS software, but those without the software can still use the tutorial. An exercise is given at the end that can be done with any statistical software package.

  4. Point Biserial Correlation Coefficient

    NSDL National Science Digital Library

    Lowry, Richard, 1940-

    This page calculates the point biserial correlation coefficient for the case where one variable is dichotomous and the other is non-dichotomous. This page allows the user to input the data directly or copy and paste from a spreadsheet application and provides data summary.

  5. Bounding the Bogoliubov coefficients

    SciTech Connect

    Boonserm, Petarpa [School of Mathematics, Statistics, and Computer Science, Victoria University of Wellington, P.O. Box 600, Wellington (New Zealand); Visser, Matt [School of Mathematics, Statistics, and Computer Science, Victoria University of Wellington, P.O. Box 600, Wellington (New Zealand)], E-mail: matt.visser@mcs.vuw.ac.nz

    2008-11-15

    While over the last century or more considerable effort has been put into the problem of finding approximate solutions for wave equations in general, and quantum mechanical problems in particular, it appears that as yet relatively little work seems to have been put into the complementary problem of establishing rigourous bounds on the exact solutions. We have in mind either bounds on parametric amplification and the related quantum phenomenon of particle production (as encoded in the Bogoliubov coefficients), or bounds on transmission and reflection coefficients. Modifying and streamlining an approach developed by one of the present authors [M. Visser, Phys. Rev. A 59 (1999) 427-438, (arXiv:quant-ph/9901030)], we investigate this question by developing a formal but exact solution for the appropriate second-order linear ODE in terms of a time-ordered exponential of 2x2 matrices, then relating the Bogoliubov coefficients to certain invariants of this matrix. By bounding the matrix in an appropriate manner, we can thereby bound the Bogoliubov coefficients.

  6. Expression of the Escherichia coli lacZ Gene on a Plasmid Vector in a Cyanobacterium

    Microsoft Academic Search

    Jeffrey S. Buzby; Ronald D. Porter; S. Edward Stevens

    1985-01-01

    A biphasic plasmid vector was used to introduce the Escherichia coli K-12 lac operon into the unicellular cyanobacterium Agmenellum quadruplicatum PR-6. The PR-6 transformants expressed beta -galactosidase at nearly as high a level as did Escherichia coli transformants. In order to accomplish this, it was necessary to obtain PR-6 mutants that could be transformed by plasmids with unmodified recognition sites

  7. "Evaluating Popular Diets" Suzanne Tang, N.D., L.Ac.

    E-print Network

    Burke, Peter

    in the American J. of Medicine reported that 64 overweight, postmenopausal women on a low- fat, vegan diet lost"Evaluating Popular Diets" Suzanne Tang, N.D., L.Ac. Naturopathic Doctor and Licensed Acupuncturist scientific research is available to identify long-term safety and efficacy of most popular diets. #12;Popular

  8. Poteries anciennes décorées à la roulette dans la Région des Grands Lacs

    Microsoft Academic Search

    Christiane Desmedt

    1991-01-01

    Résumé L'article propose une classification générale de la poterie ancienne décorée à la roulette, dans la Région des Grands Lacs et en Afrique de l'Est. Un premier groupe de poterie, appelé ici W, caractérisé principalement par la roulette torsadée, est produit vraisemblablement dèsca 800 AD; cette poterie pourrait avoir été diffusée de la région Est vers la zone interlacustre par

  9. Progressive microcrack development in tests on Lac du Bonnet granite—II. Ultrasonic tomographic imaging

    Microsoft Academic Search

    T. M. Chow; I. L. Meglis; R. P. Young

    1995-01-01

    Thorough three-dimensional raypath coverage of transmitted ultrasonic waves was used to assess the development of microcrack damage in a cylinder of Lac du Bonnet grey granite subjected to uniaxial cyclic loading. The peak load for each cycle was increased gradually until volumetric strain reversal occurred during the 9th cycle. For the remaining 19 cycles, the peak load corresponded approximately to

  10. GEOSCIENCE AFRICA 2004 THE LAC DES ILES PALLADIUM DEPOSIT: MINERALIZATION DURING REPEATED

    E-print Network

    North Lac des Iles Intrusion, the gabbroic Mine Block Intrusion, and the Camp Lake hornblende gabbro [2 abutting an earlier solidi- fied, barren East Gabbro. The High Grade zone is characterized by abundant of secondary amphi- boles in the ore and moderate enrichment of Pd and alteration in adjacent East Gabbro

  11. X-RAY FLARES OF EV Lac: STATISTICS, SPECTRA, AND DIAGNOSTICS

    E-print Network

    Huenemoerder, David P.

    We study the spectral and temporal behavior of X-ray flares from the active M dwarf EV Lac in 200 ks of exposure with the Chandra/HETGS. We derive flare parameters by fitting an empirical function which characterizes the ...

  12. The environment of x ray selected BL Lacs: Host galaxies and galaxy clustering

    NASA Technical Reports Server (NTRS)

    Wurtz, Ron; Stocke, John T.; Ellingson, Erica; Yee, Howard K. C.

    1993-01-01

    Using the Canada-France-Hawaii Telescope, we have imaged a complete, flux-limited sample of Einstein Medium Sensitivity Survey BL Lacertae objects in order to study the properties of BL Lac host galaxies and to use quantitative methods to determine the richness of their galaxy cluster environments.

  13. SPECTROSCOPY OF THE LARGEST EVER {gamma}-RAY-SELECTED BL LAC SAMPLE

    SciTech Connect

    Shaw, Michael S.; Romani, Roger W.; Healey, Stephen E.; Michelson, Peter F. [Department of Physics/KIPAC, Stanford University, Stanford, CA 94305 (United States)] [Department of Physics/KIPAC, Stanford University, Stanford, CA 94305 (United States); Cotter, Garret; Potter, William J. [Department of Astrophysics, University of Oxford, Oxford OX1 3RH (United Kingdom)] [Department of Astrophysics, University of Oxford, Oxford OX1 3RH (United Kingdom); Readhead, Anthony C. S.; Richards, Joseph L.; Max-Moerbeck, Walter; King, Oliver G. [Department of Astronomy, California Institute of Technology, Pasadena, CA 91125 (United States)] [Department of Astronomy, California Institute of Technology, Pasadena, CA 91125 (United States)

    2013-02-20

    We report on spectroscopic observations covering most of the 475 BL Lacs in the second Fermi Large Area Telescope (LAT) catalog of active galactic nuclei (AGNs). Including archival measurements (correcting several erroneous literature values) we now have spectroscopic redshifts for 44% of the BL Lacs. We establish firm lower redshift limits via intervening absorption systems and statistical lower limits via searches for host galaxies for an additional 51% of the sample leaving only 5% of the BL Lacs unconstrained. The new redshifts raise the median spectroscopic z-tilde from 0.23 to 0.33 and include redshifts as large as z = 2.471. Spectroscopic redshift minima from intervening absorbers have z-tilde = 0.70, showing a substantial fraction at large z and arguing against strong negative evolution. We find that detected BL Lac hosts are bright ellipticals with black hole masses M {sub .} {approx} 10{sup 8.5} - 10{sup 9}, substantially larger than the mean of optical AGNs and LAT Flat Spectrum Radio Quasar samples. A slow increase in M {sub .} with z may be due to selection bias. We find that the power-law dominance of the optical spectrum extends to extreme values, but this does not strongly correlate with the {gamma}-ray properties, suggesting that strong beaming is the primary cause of the range in continuum dominance.

  14. Photometric study of the short-period eclipsing binary V441 Lac

    NASA Astrophysics Data System (ADS)

    Wang, Daimei; Zhang, Liyun; Han, Xianming L.; Agerer, Franz; Pi, Qingfeng; Wang, Shuai

    2015-04-01

    We present the first multi-color VRI CCD light curves of a short-period eclipsing binary star v441 Lac in this paper. We obtained our light curves on Oct. 4 and 8, 2013 at Xinglong station of National Astronomical Observatories, China. We updated the ephemeris of V441 Lac based on three new minima derived by our new observational data together with previously available light curve minima. By fitting the O-C (observed minus calculated) values of the minima, we found that the orbital period of V441 Lac exhibits an increasing trend of P ? = 5.67 (0.35) ×10-7 days/year, which might be explained by mass transfer from the secondary component to the primary one, or angular momentum exchange by magnetic activities. We also obtained the photometric orbital parameters with the Wilson & Devinney program. Our final result shows that the V441 Lac system is a semi-detached binary with the secondary component filling roche lobe.

  15. The cultural eutrophication of Lac la Biche, Alberta, Canada: a paleoecological study

    E-print Network

    Wolfe, Alexander P.

    The cultural eutrophication of Lac la Biche, Alberta, Canada: a paleoecological study D in northeastern Alberta, Canada, revealed that the lake was eutrophic before European settlement but has undergone additional cultural eutrophication in the past 30 to 50 years. Annual fluxes to sediments of phosphorus

  16. HOST PLANT RANGE OF LOBATE LAC SCALE, PARATACHARDINA LOBATA, IN FLORIDA.

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The lobate lac scale (Paratacharidina lobata) is a serious pest of woody native and ornamental plants in Florida and the Bahamas. This insect, which is native to India and Sri Lanka, was known to attack many plants the number of plants it attacked in Florida was unknown. Field observation and field ...

  17. The LAC Test: A New Look at Auditory Conceptualization and Literacy Development K-12.

    ERIC Educational Resources Information Center

    Lindamood, Charles; And Others

    The Lindamood Auditory Conceptualization (LAC) Test was constructed with the recognition that the process of decoding involves an integration of the auditory, visual, and motor senses. Requiring the manipulation of colored blocks to indicate conceptualization of test patterns spoken by the examiner, subtest 1 entails coding of identity, number,…

  18. Influence of attenuation on acoustic emission signals in carbon fiber reinforced polymer panels.

    PubMed

    Asamene, Kassahun; Hudson, Larry; Sundaresan, Mannur

    2015-05-01

    Influence of attenuation on acoustic emission (AE) signals in Carbon Fiber Reinforced Polymer (CFRP) crossply and quasi-isotropic panels is examined in this paper. Attenuation coefficients of the fundamental antisymmetric (A0) and symmetric (S0) wave modes were determined experimentally along different directions for the two types of CFRP panels. In the frequency range from 100kHz to 500kHz, the A0 mode undergoes significantly greater changes due to material related attenuation compared to the S0 mode. Moderate to strong changes in the attenuation levels were noted with propagation directions. Such mode and frequency dependent attenuation introduces major changes in the characteristics of AE signals depending on the position of the AE sensor relative to the source. Results from finite element simulations of a microscopic damage event in the composite laminates are used to illustrate attenuation related changes in modal and frequency components of AE signals. PMID:25682294

  19. Molecular phylogeny and biogeography of lac insects (Hemiptera: Kerriidae) inferred from nuclear and mitochondrial gene sequences.

    PubMed

    Chen, Hang; Chen, Xiaoming; Feng, Ying; Yang, Hui; He, Rui; Zhang, Wenfeng; Yang, Zixiang

    2013-10-01

    Lac insects are commercial scale insects with high economic value. The combined molecular phylogeny of 20 lac insect populations was generated using elongation factor 1 alpha, mitochondrial cytochrome c oxidase subunit I and the small subunit ribosomal RNA gene loci. The 20 populations of lac insects clustered into four distinct clades supported by high bootstrap values in maximum parsimony, maximum likelihood and Bayesian analyses. Clade A at the base of the dendrogram comprises Kerria ruralis and two populations of Kerria lacca and is the branch with most primitive species. Clade B includes K. lacca, Kerria sindica and the three populations P, V and Z from India. They clustered with high bootstrap support and have evolved later than those in Clade A. The three unidentified populations P, V and Z exhibited a close relationship with K. lacca and are the same species. In Clade C, three populations of Kerria yunnanensis (Ym, Yj and Yl), population Ys from Thailand and population H from India clustered as a group, in which population H clustered with Ym with 100 % bootstrap in all three analysis methods. In Clade D, Kerria chinensis, Kerria pusana and three populations of K. yunnanensis clustered together with strong support, and are located in the upper branches of the dendrogram and are recently evolved taxa. The majority of populations from the Indian subcontinent clade are more closely related to outgroup taxa from the primitive family Pseudococcidae, as compared to the Eurasian populations. Phylogenetic analysis reveals that the Indian subcontinent is the centre of original of lac insects which have translocated to the Eurasian Continent. Based on the theory of continental drift and existing fossil records, it is suggested that lac insect evolved from ancient scale insects during the late Cretaceous period when the Indian subcontinent drifted towards the Eurasian Continent. Changes in the global environment have impacted on the distribution and evolution of lac insects during the mid-Cretaceous and early Cenozoic. With increasing temperatures lac insects are likely to translocate to subtropical areas. PMID:24078090

  20. Substrate-induced changes in the structural properties of LacY

    PubMed Central

    Serdiuk, Tetiana; Madej, M. Gregor; Sugihara, Junichi; Kawamura, Shiho; Mari, Stefania A.; Kaback, H. Ronald; Müller, Daniel J.

    2014-01-01

    The lactose permease (LacY) of Escherichia coli, a paradigm for the major facilitator superfamily, catalyzes the coupled stoichiometric translocation of a galactopyranoside and an H+ across the cytoplasmic membrane. To catalyze transport, LacY undergoes large conformational changes that allow alternating access of sugar- and H+-binding sites to either side of the membrane. Despite strong evidence for an alternating access mechanism, it remains unclear how H+- and sugar-binding trigger the cascade of interactions leading to alternating conformational states. Here we used dynamic single-molecule force spectroscopy to investigate how substrate binding induces this phenomenon. Galactoside binding strongly modifies kinetic, energetic, and mechanical properties of the N-terminal 6-helix bundle of LacY, whereas the C-terminal 6-helix bundle remains largely unaffected. Within the N-terminal 6-helix bundle, the properties of helix V, which contains residues critical for sugar binding, change most radically. Particularly, secondary structures forming the N-terminal domain exhibit mechanically brittle properties in the unbound state, but highly flexible conformations in the substrate-bound state with significantly increased lifetimes and energetic stability. Thus, sugar binding tunes the properties of the N-terminal domain to initiate galactoside/H+ symport. In contrast to wild-type LacY, the properties of the conformationally restricted mutant Cys154?Gly do not change upon sugar binding. It is also observed that the single mutation of Cys154?Gly alters intramolecular interactions so that individual transmembrane helices manifest different properties. The results support a working model of LacY in which substrate binding induces alternating conformational states and provides insight into their specific kinetic, energetic, and mechanical properties. PMID:24711390

  1. The transition between BL Lac objects and flat spectrum radio quasars

    NASA Astrophysics Data System (ADS)

    Ghisellini, G.; Tavecchio, F.; Foschini, L.; Ghirlanda, G.

    2011-07-01

    We study the BL Lac objects detected in the 1-year all-sky survey of the Fermi satellite, with an energy spectral slope ?? in the 0.1-100 GeV band greater than 1.2. In the ?? versus ?-ray luminosity plane, these BL Lacs occupy the region populated by flat spectrum radio quasars (FSRQs). Studying the properties of their spectral energy distributions (SEDs) and of their emitting lines, we find that several of these BL Lacs have an SED similar to FSRQs and that they do have broad lines of large equivalent width (EW), and should be reclassified as FSRQs even adopting the current phenomenological definition (i.e. EW of the emitting line greater than 5 Å). In other cases, even if the EW is small, the emitting lines can be as luminous as in quasars, and again their SED is similar to the SED of FSRQs. Sources classified as BL Lacs with an SED appearing as intermediate between BL Lacs and FSRQs also have relatively weak broad emission lines and small EW, and can be considered as transition sources. These properties are confirmed also by model fitting that allows us to derive the relevant intrinsic jet parameters and the jet power. This study leads us to propose a physical distinction between the two classes of blazars, based on the luminosity of the broad-line region measured in Eddington units. The dividing line is of the order of LBLR/LEdd˜ 5 × 10-4, in good agreement with the idea that the presence of strong emitting lines is related to a transition in the accretion regime, becoming radiatively inefficient below a disc luminosity of the order of 1 per cent of the Eddington one.

  2. VizieR Online Data Catalog: The CLASS BL Lac sample (Marcha+, 2013)

    NASA Astrophysics Data System (ADS)

    Marcha, M. J. M.; Caccianiga, A.

    2014-04-01

    This paper presents a new sample of BL Lac objects selected from a deep (30mJy) radio survey of flat spectrum radio sources (the CLASS blazar survey). The sample is one of the largest well-defined samples in the low-power regime with a total of 130 sources of which 55 satisfy the 'classical' optical BL Lac selection criteria, and the rest have indistinguishable radio properties. The primary goal of this study is to establish the radio luminosity function (RLF) on firm statistical ground at low radio luminosities where previous samples have not been able to investigate. The gain of taking a peek at lower powers is the possibility to search for the flattening of the luminosity function which is a feature predicted by the beaming model but which has remained elusive to observational confirmation. In this study, we extend for the first time the BL Lac RLF down to very low radio powers ~1022W/Hz, i.e. two orders of magnitude below the RLF currently available in the literature. In the process, we confirm the importance of adopting a broader, and more physically meaningful set of classification criteria to avoid the systematic missing of low-luminosity BL Lacs. Thanks to the good statistics we confirm the existence of weak but significant positive cosmological evolution for the BL Lac population, and we detect, for the first time the flattening of the RLF at L~1025W/Hz in agreement with the predictions of the beaming model. (1 data file).

  3. The BL-Lac gamma-ray blazar PKS 0447-439 as a probable member of a group of galaxies at z = 0.343

    NASA Astrophysics Data System (ADS)

    Muriel, H.; Donzelli, C.; Rovero, A. C.; Pichel, A.

    2015-02-01

    Context. The BL-Lac blazar PKS 0447-439 is one of the brightest HE gamma-ray sources that were first detected by Fermi-LAT. It was also detected by H.E.S.S. at VHE gamma-rays, which allowed constraining the redshift of PKS 0447-439 by considering the attenuation caused by gamma-ray interactions with ambient photons in the extragalactic background light (EBL). This constraint agreed with color-magnitude and spectroscopic redshift constraints (0.179 1.2). This value was debated because if true, it would imply either that the relevant absorption processes of gamma-rays are not well understood or that the EBL is dramatically different from what is believed today. This high redshift was not confirmed by three independent new spectroscopic observations at high signal-to-noise ratios. The scenario is clear evidence of the difficulties in estimating the redshift of BL-Lac objects, whose optical spectra are typically featureless. Neither of the estimated redshifts for PKS 0447-439 are confirmed as yet. Aims: Given that BL-Lac are typically hosted by elliptical galaxies, which in turn are associated with groups, we aim to find the host group of galaxies of PKS 0447-439. The ultimate goal is to estimate a redshift for this blazar. Methods: Spectra of twenty-one objects in the field of view of PKS 0447-439 were obtained with the Gemini Multi-Object Spectrograph. Based on the redshifts and coordinates of these galaxies, we searched for groups of galaxies. Using a deep catalog of groups, we studied the probability of finding by chance a group of galaxies in the line of sight of PKS 0447-439. Results: We identified a group of galaxies that was not previously cataloged at z = 0.343 with seven members, a virial radius of 0.42 Mpc, and a velocity dispersion of 622 km s-1. We found that the probability of the host galaxy of PKS 0447-439 to be a member of the new group is ?97%. Therefore, we propose to adopt z = 0.343 ± 0.002 as the most likely redshift for PKS 0447-439.

  4. THE ATTENUATED RADON TRANSFORM: APPLICATION TO SINGLE-PHOTON EMISSION COMPUTED TOMOGRAPHY IN THE PRESENCE OF A VARIABLE ATTENUATING MEDIUM

    SciTech Connect

    Gullberg, Grant T.

    1980-03-01

    The properties of the attenuated Radon transform and its application to single-photon emission computed tomography (ECT) are analyzed in detail. In nuclear medicine and biological research, the objective of ECT is to describe quantitatively the position and strengths of internal sources of injected radiopharmaceuticals and radionuclides where the attenuation between the sources and detector is unknown. The problem is mathematically and practically quite different from well-known methods in transmission computed tomography (TCT) where only the attenuation is unknown. A mathematical structure using function theory and the theory of linear operators on Hilbert spaces is developed to better understand the spectral properties of the attenuated Radon transform. The continuous attenuated Radon transform is reduced to a matrix operator for discrete angular and lateral sampling, and the reconstruction problem reduces to a system of linear equations. For variable attenuation coefficients frequently found in imaging internal organs, the numerical methods developed in this paper involve iterative techniques of performing the generalized inverse. Its application to nuclear medicine is demonstrated by reconstructions of transverse sections of the brain, heart, and liver.

  5. Ultrasonic Attenuation in Zircaloy-4

    SciTech Connect

    Gomez, M.P. [Departamento de Ingenieria Electrica, Facultad Regional Buenos Aires, Universidad Tecnologica Nacional, Medrano 951 (C1179AAQ), Buenos Aires (Argentina); Banchik, A.D. [Grupo LMFAE, CAE, Comision Nacional de Energia Atomica, Presbitero Luis Gonzalez y Aragon 15 (B1802AYA), Ezeiza, Buenos Aires (Argentina); Lopez Pumarega, M.I. [Grupo de Ondas Elasticas, UA ENDE, CAC, Comision Nacional de Energia Atomica, Av. General Paz 1499 (1650) San Martin, Buenos Aires (Argentina); Ruzzante, J.E. [Departamento de Ingenieria Electrica, Facultad Regional Buenos Aires, Universidad Tecnologica Nacional, Medrano 951 (C1179AAQ), Buenos Aires (Argentina); Grupo de Ondas Elasticas, UA ENDE, CAC, Comision Nacional de Energia Atomica, Av. General Paz 1499 (1650) San Martin, Buenos Aires (Argentina)

    2005-04-09

    In this work the relationship between Zircaloy-4 grain size and ultrasonic attenuation behavior was studied for longitudinal waves in the frequency range of 10-90 MHz. The attenuation was analyzed as a function of frequency for samples with different mechanical and heat treatments having recrystallized and Widmanstatten structures with different grain size. The attenuation behavior was analyzed by different scattering models, depending on grain size, wavelength and frequency.

  6. Generalized Reflection Coefficients

    NASA Astrophysics Data System (ADS)

    Remling, Christian

    2015-02-01

    I consider general reflection coefficients for arbitrary one-dimensional whole line differential or difference operators of order 2. These reflection coefficients are semicontinuous functions of the operator: their absolute value can only go down when limits are taken. This implies a corresponding semicontinuity result for the absolutely continuous spectrum, which applies to a very large class of maps. In particular, we can consider shift maps (thus recovering and generalizing a result of Last-Simon) and flows of the Toda and KdV hierarchies (this is new). Finally, I evaluate an attempt at finding a similar general setup that gives the much stronger conclusion of reflectionless limit operators in more specialized situations.

  7. Tethered Particle Motion Reveals that LacI·DNA Loops Coexist with a Competitor-Resistant but Apparently Unlooped Conformation

    PubMed Central

    Revalee, Joel D.; Blab, Gerhard A.; Wilson, Henry D.; Kahn, Jason D.; Meiners, Jens-Christian

    2014-01-01

    The lac repressor protein (LacI) efficiently represses transcription of the lac operon in Escherichia coli by binding to two distant operator sites on the bacterial DNA and causing the intervening DNA to form a loop. We employed single-molecule tethered particle motion to observe LacI-mediated loop formation and breakdown in DNA constructs that incorporate optimized operator binding sites and intrinsic curvature favorable to loop formation. Previous bulk competition assays indirectly measured the loop lifetimes in these optimized DNA constructs as being on the order of days; however, we measured these same lifetimes to be on the order of minutes for both looped and unlooped states. In a range of single-molecule DNA competition experiments, we found that the resistance of the LacI-DNA complex to competitive binding is a function of both the operator strength and the interoperator sequence. To explain these findings, we present what we believe to be a new kinetic model of loop formation and DNA competition. In this proposed new model, we hypothesize a new unlooped state in which the unbound DNA-binding domain of the LacI protein interacts nonspecifically with nonoperator DNA adjacent to the operator site at which the second LacI DNA-binding domain is bound. PMID:24507611

  8. Measurement of Ligand-Induced Activation in Single Viable T Cells Using the lacZ Reporter Gene

    NASA Astrophysics Data System (ADS)

    Karttunen, Jaana; Shastri, Nilabh

    1991-05-01

    We have used the bacterial ?-galactosidase gene (lacZ) as a reporter gene for the rapid measurement of T-cell antigen receptor (TCR)-mediated activation of individual T cells. The reporter construct contained the lacZ gene under the control of the nuclear factor of activated T cells (NF-AT) element of the human interleukin 2 enhancer [Fiering, S., Northrop, J. P., Nolan, G. P., Matilla, P., Crabtree, G. R. & Herzenberg, L. A. (1990) Genes Dev. 4, 1823-1834]. The activity of the intracellular lacZ enzyme was analyzed by flow cytometric measurement of fluorescein accumulation in cells loaded with the fluorogenic ?-galactosidase substrate fluorescein di-?-D-galactopyranoside. As a model system, the T-cell hybridoma BO4H9.1, which is specific for the lysozyme peptide (amino acids 74-88)/A^b complex, was transfected with the NF-AT-lacZ construct. lacZ activity was induced in 50-100% of the transfectant cells following exposure to pharmacological agents, to the physiological peptide/major histocompatibility complex ligand, or to other TCR-specific stimuli. Interestingly, increasing concentrations of the stimulus increased the fraction of lacZ^+ cells, but not the level of lacZ activity per cell. Even under widely varying levels of stimulus, the level of lacZ activity in individual lacZ^+ cells remained within a remarkably narrow range. These results demonstrate that TCR-mediated activation can be readily measured in single T cells and strongly suggest that, once committed to activation, the level of NF-AT transcriptional activity in individual T cells is independent of the form or concentration of stimulus. This assay is likely to prove useful for the study of early activation events in individual T cells and of TCR ligands.

  9. Poly-LacNAc as an Age-Specific Ligand for Rotavirus P[11] in Neonates and Infants

    PubMed Central

    Liu, Yang; Huang, Pengwei; Jiang, Baoming; Tan, Ming; Morrow, Ardythe L.; Jiang, Xi

    2013-01-01

    Rotavirus (RV) P[11] is an unique genotype that infects neonates. The mechanism of such age-specific host restriction remains unknown. In this study, we explored host mucosal glycans as a potential age-specific factor for attachment of P[11] RVs. Using in vitro binding assays, we demonstrated that VP8* of a P[11] RV (N155) could bind saliva of infants (60.3%, N?=?151) but not of adults (0%, N?=?48), with a significantly negative correlation between binding of VP8* and ages of infants (P<0.01). Recognition to the infant saliva did not correlate with the ABO, secretor and Lewis histo-blood group antigens (HBGAs) but with the binding of the lectin Lycopersicon esculentum (LEA) that is known to recognize the oligomers of N-acetyllactosamine (LacNAc), a precursor of human HBGAs. Direct evidence of LacNAc involvement in P[11] binding was obtained from specific binding of VP8* with homopolymers of LacNAc in variable lengths through a glycan array analysis of 611 glycans. These results were confirmed by strong binding of VP8* to the Lec2 cell line that expresses LacNAc oligomers but not to the Lec8 cell line lacking the LacNAc. In addition, N155 VP8* and authentic P[11] RVs (human 116E and bovine B223) hemagglutinated human red blood cells that are known to express poly-LacNAc. The potential role of poly-LacNAc in host attachment and infection of RVs has been obtained by abrogation of 116E replication by the PAA-conjugated poly-LacNAc, human milk, and LEA positive infant saliva. Overall, our results suggested that the poly-LacNAc could serve as an age-specific receptor for P[11] RVs and well explained the epidemiology that P[11] RVs mainly infect neonates and young children. PMID:24244290

  10. Gamma-ray attenuation studies of PbO – BaO – B 2 O 3 glass system

    Microsoft Academic Search

    Narveer Singh; Kanwar Jit Singh; Kulwant Singh; Harvinder Singh

    2006-01-01

    PbO–BaO–B2O3 glass system has been investigated in terms of molar mass, mass attenuation coefficient and half value layer parameters by using gamma-ray at 511,662 and 1274keV photon energies. Gamma-ray attenuation coefficients of the prepared glass samples have been compared with tabulations based upon the results of XCOM. Good agreement has been observed between experimental and theoretical tabulations. Our results have

  11. A femtosecond laser study of the endohedral fullerenes Li@C60 and La@C82

    NASA Astrophysics Data System (ADS)

    Lassesson, A.; Hansen, K.; Jönsson, M.; Gromov, A.; Campbell, E. E. B.; Boyle, M.; Pop, D.; Schulz, C. P.; Hertel, I. V.; Taninaka, A.; Shinohara, H.

    2005-07-01

    The endohedral fullerenes La@C{82} and Li@C{60 } have been studied in the gas phase with femtosecond laser excitation. The two molecules show qualitatively the same behaviour with respect to ion yield vs. pulse energy, but markedly different fragmentation patterns, with La@C{82} fragmenting via the shrink-wrap mechanism and Li@C{60} predominantly losing the metal atom in the first fragmentation step. The ion yields and electron energy distributions of La@C{82} agree well with a recently developed model for fs laser ionisation of C{60}.

  12. Enhancing Tissue Attenuation Estimation from Backscattered Ultrasound Using Spatial Compounding and Synthetic Aperture Techniques

    NASA Astrophysics Data System (ADS)

    Klimonda, Ziemowit; Litniewski, Jerzy; Nowicki, Andrzej

    Ultrasonic diagnosis is a well-established technique in modern medicine. The ultrasonic scanners visualize the acoustical impedance variation within the tissue, allowing for the noninvasive insight into the body interior. However, imaging of other physical parameters of the tissue could provide additional diagnostic information. Here we consider the estimates of the attenuation coefficient calculated along the interrogating beam. It differs for various tissue types and the change of the attenuation often accompanies the pathological processes, such as tumors. We intend to develop the attenuation estimation and visualization technique that could be used in vivo and would expand the diagnostic ability of standard ultrasonic scanners. The tissue attenuation estimation technique based on backscattered ultrasonic signals spectral shift is presented. The commercial scanner with dedicated RF research module and the customized beam former were used to acquire the empirical data from the tissue mimicking phantoms. The instantaneous mean frequency (MF) of echo signals were collected using the mean frequency correlation estimator. The Singular Spectrum Analysis (SSA) technique was used for the MF trends extraction, and finally the MF trends were converted into the distribution of attenuation coefficient and the attenuation image was formed. The spatial compounding techniques were used to enhance the attenuation estimation precision. Also, the application of the synthetic aperture technique to RF data collection, combined with the attenuation estimation and imaging techniques will be presented.

  13. Nonlinear attenuation and dispersion in human calcaneus in vitro: Statistical validation and relationships to microarchitecture.

    PubMed

    Wear, Keith A

    2015-03-01

    Through-transmission measurements were performed on 30 human calcaneus samples in vitro. Nonlinear attenuation and dispersion measurements were investigated by estimating 95% confidence intervals of coefficients of polynomial expansions of log magnitude and phase of transmission coefficients. Bone mineral density (BMD) was measured with dual x-ray absorptiometry. Microarchitecture was measured with microcomputed tomography. Statistically significant nonlinear attenuation and nonzero dispersion were confirmed for a clinical bandwidth of 300-750?kHz in 40%-43% of bone samples. The mean linear coefficient for attenuation was 10.3?dB/cm MHz [95% confidence interval (CI): 9.0-11.6?dB/cm MHz]. The mean quadratic coefficient for attenuation was 1.6?dB/cm MHz(2) (95% CI: 0.4-2.8?dB/cm MHz(2)). Nonlinear attenuation provided little information regarding BMD or microarchitecture. The quadratic coefficient for phase (which is related to dispersion) showed moderate correlations with BMD (r?=?-0.65; 95% CI: -0.82 to -0.36), bone surface-to-volume ratio (r?=?0.47; 95% CI: 0.12-0.72) and trabecular thickness (r?=?-0.40; 95% CI: -0.67 to -0.03). Dispersion was proportional to bone volume fraction raised to an exponent of 2.1?±?0.2, which is similar to the value for parallel nylon-wire phantoms (2.4?±?0.2) and supports a multiple-scattering model for dispersion. PMID:25786928

  14. Fiber optic attenuator

    NASA Technical Reports Server (NTRS)

    Buzzetti, Mike F. (Inventor)

    1994-01-01

    A fiber optic attenuator of the invention is a mandrel structure through which a bundle of optical fibers is wrapped around in a complete circle. The mandrel structure includes a flexible cylindrical sheath through which the bundle passes. A set screw on the mandrel structure impacts one side of the sheath against two posts on the opposite side of the sheath. By rotating the screw, the sheath is deformed to extend partially between the two posts, bending the fiber optic bundle to a small radius controlled by rotating the set screw. Bending the fiber optic bundle to a small radius causes light in each optical fiber to be lost in the cladding, the amount depending upon the radius about which the bundle is bent.

  15. Pride attenuates nonconscious mimicry.

    PubMed

    Dickens, Leah; DeSteno, David

    2014-02-01

    Positive affect has been associated with increased nonconscious mimicry-an association that is quite logical given ties between positive mood and desires for social bonding. Yet positive emotions vary with respect to function, leading to the prediction that not all positive states might similarly increase mimicry. Pride, due to its association with higher status and self-focus, could be expected to attenuate affiliative behaviors such as mimicry. Participants in the present study were induced to experience one of three affective states (neutral, pride, general positivity), after which they interacted with a confederate who expressed a specific, neutral nonverbal behavior (i.e., foot shaking). Supporting past research, participants experiencing general positive affect evidenced greater mimicry as compared to participants in a neutral mood. In accord with predictions, participants experiencing pride mimicked the confederate's behavior significantly less than did those experiencing general positive affect or a neutral state. Regression analyses also confirmed that increasing intensities of pride predicted decreasing mimicry. PMID:24491248

  16. An attenuated philosophical gentleman.

    PubMed

    Christie, John R R

    2014-06-20

    Dr. Joseph Black had at one time, a house near us to the west. He was a striking and beautiful person; tall, very thin, and cadaverously pale; his hair carefully powdered, though there was little of it except what was collected in a long thin queue; his eyes dark, clear and large, like deep pools of pure water. He wore black speckless clothes, silk stockings, silver buckles, and either a slim green umbrella, or a genteel brown cane. The general frame and air were feeble and slender. The wildest boy respected Black. No lad could be irreverent toward a man so pale, so gentle, so elegant and so illustrious. So he glided, like a spirit, through our rather mischievous sportiveness, unharmed. He died seated, with a bowl of milk upon his knee, of which his ceasing to be did not spill a drop; a departure which it seemed, after the event, might have been foretold of this attenuated philosophical gentleman. PMID:24921110

  17. Prediction of Attenuation by Rain

    Microsoft Academic Search

    ROBERT K. CRANE

    1980-01-01

    A new model is presented for the prediction of attenuation by rain on either terrestrial or slant earth-to-space propagation paths. The model was developed using geophysical observations of the statistics of point rain rate, of the horizontal structure of rainfall, and of the vertical temperature structure of the atmosphere. The model was tested by comparison with attenuation distribution observations. The

  18. Inverse problems of ultrasound tomography in models with attenuation

    NASA Astrophysics Data System (ADS)

    Goncharsky, Alexander V.; Romanov, Sergey Y.

    2014-04-01

    We develop efficient methods for solving inverse problems of ultrasound tomography in models with attenuation. We treat the inverse problem as a coefficient inverse problem for unknown coordinate-dependent functions that characterize both the speed cross section and the coefficients of the wave equation describing attenuation in the diagnosed region. We derive exact formulas for the gradient of the residual functional in models with attenuation, and develop efficient algorithms for minimizing the gradient of the residual by solving the conjugate problem. These algorithms are easy to parallelize when implemented on supercomputers, allowing the computation time to be reduced by a factor of several hundred compared to a PC. The numerical analysis of model problems shows that it is possible to reconstruct not only the speed cross section, but also the properties of the attenuating medium. We investigate the choice of the initial approximation for iterative algorithms used to solve inverse problems. The algorithms considered are primarily meant for the development of ultrasound tomographs for differential diagnosis of breast cancer.

  19. Low-energy gamma ray attenuation characteristics of aviation fuels

    NASA Technical Reports Server (NTRS)

    Singh, Jag J.; Shen, Chih-Ping; Sprinkle, Danny R.

    1990-01-01

    Am241 (59.5 keV) gamma ray attenuation characteristics were investigated in 270 aviation fuel (Jet A and Jet A-1) samples from 76 airports around the world as a part of world wide study to measure the variability of aviation fuel properties as a function of season and geographical origin. All measurements were made at room temperature which varied from 20 to 27 C. Fuel densities (rho) were measured concurrently with their linear attenuation coefficients (mu), thus providing a measure of mass attenuation coefficient (mu/rho) for the test samples. In 43 fuel samples, rho and mu values were measured at more than one room temperature, thus providing mu/rho values for them at several temperatures. The results were found to be independent of the temperature at which mu and rho values were measured. It is noted that whereas the individual mu and rho values vary considerably from airport to airport as well as season to season, the mu/rho values for all samples are constant at 0.1843 + or - 0.0013 cu cm/gm. This constancy of mu/rho value for aviation fuels is significant since a nuclear fuel quantity gauging system based on low energy gamma ray attenuation will be viable throughout the world.

  20. Molar extinction coefficients of some fatty acids

    NASA Astrophysics Data System (ADS)

    Sandhu, G. K.; Singh, Kulwant; Lark, B. S.; Gerward, L.

    2002-10-01

    The attenuation of gamma rays in some fatty acids, viz. formic acid (CH 2O 2), acetic acid (C 2H 4O 2), propionic acid (C 3H 6O 2), butyric acid (C 4H 8O 2), n-hexanoic acid (C 6H 12O 2), n-caprylic acid (C 8H 16O 2), lauric acid (C 12H 24O 2), myristic acid (C 14H 28O 2), palmitic acid (C 16H 32O 2), oleic acid (C 18H 34O 2) and stearic acid (C 18H 36O 2), has been measured at the photon energies 81, 356, 511, 662, 1173 and 1332 keV. Experimental values for the molar extinction coefficient, the effective atomic number and the electron density have been derived and compared with theoretical calculations. There is good agreement between experiment and theory.

  1. Theoretical prediction of the source-detector separation distance suited to the application of the spatially resolved spectroscopy from the near-infrared attenuation data cube of tissues

    E-print Network

    Ri, Yong-Wu; Im, Song-Jin

    2014-01-01

    The modified Beer-Lambert law (MBL) and the spatially resolved spectroscopy are used to measure the tissue oxidation in muscles and brains by the continuous wave near-infrared spectroscopy. The spatially resolved spectroscopy predicts the change in the concentration of the absorber by measuring the slope of attenuation data according to the separation and calculating the absorption coefficients of tissue on the basis of the slop in attenuation at the separation distance satisfying the linearity of this slop. This study analyzed the appropriate source-detector separation distance by using the diffuse approximation resolution for photon migration when predicting the absorption coefficient by the spatially resolved spectroscopy on the basis of the reflective image of the tissue. We imagine the 3 dimensional attenuation image with the absorption coefficient, reduced scattering coefficient and separation distance as its axes and obtained the attenuation data cube by calculating the attenuation on a certain interva...

  2. Normal mode splitting function measurements of anelasticity and attenuation in the Earth's inner core

    NASA Astrophysics Data System (ADS)

    Mäkinen, Anna M.; Deuss, Arwen

    2013-07-01

    We have used the iterative spectral fitting method to measure both the elastic and anelastic splitting functions of 20 inner core sensitive normal modes. These modes show significant improvement in spectral fit when anelastic splitting function coefficients dst are introduced in addition to the elastic splitting function coefficients cst. We employ two separate anelastic treatments: (i) fully anelastic measurement, in which a complete set of anelastic splitting function coefficients is measured in addition to the elastic coefficients, and (ii) zonal anelastic measurement, in which anelasticity is only allowed in zonal splitting function coefficients. Together, these two approaches confirm that normal modes sensitive to the Earth's inner core resolve zonally dominant elastic and anelastic structures. The zonal dominance of anelasticity suggests that the inner core exhibit cylindrical attenuation anisotropy in addition to cylindrical velocity anisotropy. In particular, the zonally dominant anelasticity correlates with zonal elastic structure, that is, directions of higher velocity in the inner core also appear more attenuating.

  3. Continuously tunable fibre attenuator operating in the wavelength range near 1.5 {mu}m

    SciTech Connect

    Baum, Ol'ga I; Mishakov, Gennadii V; Sokolov, Viktor I [Institute of Laser and Information Technologies, Russian Academy of Sciences, Troitsk, Moscow Region (Russian Federation); Varlamova, Nina V; Zapadinskii, Boris I [N.N. Semenov Institute of Chemical Physics, Russian Academy of Sciences, Moscow (Russian Federation)

    2004-09-30

    A fibre attenuator is fabricated for the telecommunication wavelength range near 1.5 {mu}m in which a single-mode silica fibre with side polishing is used. The fibre surface is covered by a layer of fluorine-containing polymer with a large thermooptic coefficient. The principle of attenuator operation is based on a change in the conditions of total internal reflection for a guided mode in the polished region due to thermally induced variation in the refractive index of the fluoropolymer layer. The attenuator is insensitive to light polarisation, it has a continuously variable attenuation coefficient in the range 0.2-27 dB, and can be easily incorporated into fibreoptic links. (fibre optics)

  4. Gene expression and cell fusion analyzed by lacZ complementation in mammalian cells.

    PubMed Central

    Mohler, W A; Blau, H M

    1996-01-01

    Complementing reporter genes provide biological indicators of coincident expression of proteins in cells. We have adapted intracistronic complementation of the Escherichia coli lacZ gene for use in mammalian cells. Enzymatic activity detectable by quantitative biochemical assay, flow cytometry, or microscopy is produced upon convergent expression of two distinct mutant lacZ peptides within single cells, or upon fusion of cells expressing such mutants. A novel fluorescent substrate for beta-galactosidase (Fluor-X-Gal) increases detection and permits simultaneous microscopic visualization of other fluorescent markers. The enzymatic complementation described here should facilitate studies of cell fusion, cell lineage, and signal transduction, by producing activity only when two proteins are expressed at the same time and place in intact cells. Images Fig. 1 Fig. 2 PMID:8901597

  5. Quantitative approaches to the study of bistability in the lac operon of Escherichia coli

    PubMed Central

    Santillán, Moisés; Mackey, Michael C.

    2008-01-01

    In this paper, the history and importance of the lac operon in the development of molecular and systems biology are briefly reviewed. We start by presenting a description of the regulatory mechanisms in this operon, taking into account the most recent discoveries. Then we offer a survey of the history of the lac operon, including the discovery of its main elements and the subsequent influence on the development of molecular and systems biology. Next the bistable behaviour of the operon is discussed, both with respect to its discovery and its molecular origin. A review of the literature in which this bistable phenomenon has been studied from a mathematical modelling viewpoint is then given. We conclude with some brief remarks. PMID:18426771

  6. Multiwavelength Observations of Intermediate-Frequency-Peaked BL Lac Objects Detected by VERITAS

    NASA Astrophysics Data System (ADS)

    Furniss, A.; VERITAS Collaboration

    2010-10-01

    We report on the discovery of very high energy (VHE) emission (E > 200 GeV) from the intermediate-frequency-peaked BL Lac (IBL) objects PKS 1424+240, W Comae and 3C 66A by VERITAS. These IBL objects bridge the gap between low-energy-peaked and high-energy-peaked BL Lacs and are the first of their kind to be detected in this energy band. We present results on the energy spectra measured by VERITAS for W Comae and 3C 66A. Observation of these objects in flaring states prompted quasi-simultaneous observations in other wavebands. These MWL data allow the fitting of models to the double-peaked SED, in order to test how well the models describe the data and determine characteristics of the particle populations emitting these VHE photons. We also present the first detection of PKS 1424+240 in VHE gamma rays.

  7. 78 FR 3911 - Big Stone National Wildlife Refuge, Big Stone and Lac Qui Parle Counties, MN; Final Comprehensive...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-01-17

    ...National Wildlife Refuge, Big Stone and Lac Qui Parle Counties, MN; Final Comprehensive Conservation Plan and Finding of No Significant...U.S. Mail: Big Stone NWR, 44843 County Road 19, Odessa, MN 56276. FOR FURTHER INFORMATION CONTACT: Alice Hanley,...

  8. A 33 yr CONSTANCY OF THE X-RAY CORONAE OF AR Lac AND ECLIPSE DIAGNOSIS OF SCALE HEIGHT

    E-print Network

    Drake, Jeremy J.

    Extensive X-ray and EUV photometric observations of the eclipsing RS CVn system AR Lac were obtained over the years 1997-2013 with the Chandra X-Ray Observatory Extreme-Ultraviolet Explorer (EUVE). During primary eclipse, ...

  9. Model for the possible origin of anorthosite-syenite associations like the Laramie anorthosite complex (lac)

    SciTech Connect

    Lindsley, D.H.; Kolker, A.; Fuhrman, M.; Frost, B.R.

    1985-01-01

    Proterozoic massif anorthosites (ANT) have several unique attributes. Compared to typical tholeiitic layered mafic intrusions, they are distinctly evolved, with low mg numbers and high Ab/An ratios, and are also more potassic, with 1-2 wt% K/sub 2/O - 5-10% normative Or that occurs as antiperthite. They are closely associated in time and space with still more potassic rocks (MSY: monzonites, syenites, mangerites, etc.) considered by some to be comagmatic with the ANT and by others to be partial melts of the country rock. If the MSY are comagmatic, the parent magma is must be relatively potassic. Such a magma might pond and fractionate at the base of thin continental crust, with olivines and pyroxenes sinking and plagioclase floating, thereby depleting the magma in Mg and Eu. Crystal mushes of plagioclase would then intrude the crust diapirically to depths of 8-15 km, forming ANT. With continued fractionation the K- and Fe-enriched liquid would begin crystallizing ternary feldspars (as found at LAC); these too would float, forming crystal mushes (MSY) that would rise diapirically and intrude the ANT. The cumulate MSY would have no Eu anomaly (or a small positive one) as found at LAC; the liquid would have a strong negative Eu anomaly. Some contamination of the MSY suite by partial melts from the country rock is likely. This model can explain the virtual continuum in mineral compositions from ANT to MSY reported for LAC by Fuhrman and others (this volume). Parent magmas might be trachyandesitic; another candidate is the biotite gabbro found throughout the LAC.

  10. Fusion of Escherichia coli LacZ to the Cytochrome c Gene of Saccharomyces cerevisiae

    Microsoft Academic Search

    Leonard Guarente; Mark Ptashne

    1981-01-01

    Hybrid genes between the Escherichia coli lacZ gene and the iso-1-cytochrome c (CYC1) gene of Saccharomyces cerevisiae were constructed by recombination in vitro. Each of the hybrid genes encodes a chimeric protein with a cytochrome c moiety at the amino terminus and an active beta -galactosidase (beta -D-galactoside galactohydrolase, EC 3.2.1.23) moiety at the carboxy terminus. When these hybrids are

  11. Paleolimnological evidence of mining and demographic impacts on Lac Dauriat, Schefferville (subarctic Québec, Canada)

    Microsoft Academic Search

    Laurence Laperrière; Marie-Andrée Fallu; Sonja Hausmann; Reinhard Pienitz; Derek Muir

    2008-01-01

    Qualitative and quantitative analysis of fossil diatoms and geochemical signals preserved in the sediments of Lac Dauriat\\u000a (subarctic Quebec) were performed to evaluate the impacts of nearby mining activity and the expansion of the town of Schefferville\\u000a on the water quality of the lake, and to reconstruct the changes of its trophic status. The presence of taxa typical of nutrient-enriched

  12. Isolation and characterization of lac fusions to two nitrogen-regulated promoters

    Microsoft Academic Search

    Michael J. Stern; Christopher F. Higgins; Giovanna Ferro-Luzzi Ames

    1984-01-01

    Mud1 (Ap, lac, cts)-mediated fusions to argTr and dhuA, two transport operon promoters in Salmonella typhimurium, were isolated and characterized in order to investigate the regulation of these promoters. Using these fusions we showed that these promoters are under nitrogen regulation and that this effect, as well as the response to a promoter-up mutation in dhuA, is at the transcriptional

  13. Characterisation of Muta™Mouse ?gt10-lacZ transgene: evidence for in vivo rearrangements

    PubMed Central

    Shwed, Philip S.; Crosthwait, Jennifer; Douglas, George R.; Seligy, Vern L.

    2010-01-01

    The multicopy ?gt10-lacZ transgene shuttle vector of Muta™Mouse serves as an important tool for genotoxicity studies. Here, we describe a model for ?gt10-lacZ transgene molecular structure, based on characterisation of transgenes recovered from animals of our intramural breeding colony. Unique nucleotide sequences of the 47?513 bp monomer are reported with GenBank® assigned accession numbers. Besides defining ancestral mutations of the ?gt10 used to construct the transgene and the Muta™Mouse precursor (strain 40.6), we validated the sequence integrity of key ? genes needed for the Escherichia coli host-based mutation reporting assay. Using three polymerase chain reaction (PCR)-based chromosome scanning and cloning strategies, we found five distinct in vivo transgene rearrangements, which were common to both sexes, and involved copy fusions generating ?10 defective copies per haplotype. The transgene haplotype was estimated by Southern hybridisation and real-time–polymerase chain reaction, which yielded 29.0 ± 4.0 copies based on spleen DNA of Muta™Mouse, and a reconstructed CD2F1 genome with variable ?gt10-lacZ copies. Similar analysis of commercially prepared spleen DNA from Big Blue® mouse yielded a haplotype of 23.5 ± 3.1 copies. The latter DNA is used in calibrating a commercial in vitro packaging kit for E.coli host-based mutation assays of both transgenic systems. The model for ?gt10-lacZ transgene organisation, and the PCR-based methods for assessing copy number, integrity and rearrangements, potentially extends the use of Muta™Mouse construct for direct, genomic-type assays that detect the effects of clastogens and aneugens, without depending on an E.coli host, for reporting effects. PMID:20724577

  14. Energy absorption coefficients and photon kerma for LiF

    SciTech Connect

    Sharada, K.S.

    1982-01-01

    Accurate knowledge of energy absorption coefficients is needed to calculate the absorbed dose in any material. The photon kerma for LiF relative to air and soft tissue is computed using energy absorption coefficient values for Li, F, air, and tissue. Values of energy absorption coefficients for air are already available in J. H. Hubbell's (Photon Cross-Sections, Attenuation Coefficients and Energy Absorption Coefficients from 10 KeV to 100 GeV. National Standard Reference Data System-National Bureau of Standards Report No. 29, Washington, D. C., 1969) tables. Those for tissue are obtained by adding the weighted average of the energy absorption coefficients to the different elements constituting the tissue. For fluorine, they are computed from the values given by F. H. Attix and W. C. Roesche (Eds, Radiation Dosimetry, Vol. I, Fundamentals. Academic Press, New York/London, 1968) for CaF/sub 2/ and Ca. The values for lithium have been computed taking into consideration the photoelectric effect, Compton process, and pair production. Corrections for radiative energy losses, fluorescence yields, screening of electrons, etc., are appropriately applied. The energy absorption coefficients due to photoeffect, Compton scattering, and pair production are added to get the total. The energy absorption cross-section data for photon energies from 0.01 to 10 MeV are tabulated for each interaction.

  15. Use of ?-galactosidase (lacZ) gene ?-complementation as a novel approach for assessment of titanium oxide nanoparticles induced mutagenesis.

    PubMed

    Ahmad, Javed; Dwivedi, Sourabh; Alarifi, Saud; Al-Khedhairy, Abdulaziz A; Musarrat, Javed

    2012-09-18

    The mutagenic potential of titanium dioxide nanoparticles (TiO(2)-NPs) of an average size 30.6nm was investigated using ?-galactosidase (lacZ) gene complementation in plasmid pUC19/lacZ(-)Escherichia coli DH5? system. Plasmid pUC19 was treated with varying concentrations of TiO(2)-NPs and allowed to transfect the CaCl(2)-induced competent DH5? cells. The data revealed loss in transformation efficiency of TiO(2)-NPs treated plasmids as compared to untreated plasmid DNA in DH5? host cells. Induction of multiple mutations in ?-fragment of lacZ gene caused synthesis of non-functional ?-galactosidase enzyme, which resulted in a significant number of white (mutant) colonies of transformed E. coli cells. Screening of mutant transformants based on blue:white colony assay and DNA sequence analysis of lacZ gene fragment clearly demonstrated TiO(2)-NPs induced mutagenesis. Multiple alignment of selectable marker lacZ gene sequences from randomly selected mutants and control cells provided a gene specific map of TiO(2)-NPs induced mutations. Mutational analysis suggested that all nucleotide changes were point mutations, predominantly transversions (TVs) and transitions (TSs). A total of 32 TVs and 6 TSs mutations were mapped within 296 nucleotides (nt) long partial sequence of lacZ gene. The region between 102 and 147nt within lacZ gene sequence was found to be most susceptible to mutations with nine detectable point mutations (8 TVs and 1 TSs). Guanine base was determined to be more prone to TiO(2)-NPs induced mutations. This study suggested the pUC19/E. coli DH5?lacZ gene ?-complementation system, as a novel genetic approach for determining the mutagenic potential, and specificity of manufactured NPs and nanomaterials. PMID:22705419

  16. Application of gamma-ray attenuation technology in density measurement of a slurry reactor

    Microsoft Academic Search

    Jian Xu; Weisheng Wei; Kai Zhang

    2010-01-01

    Axial density profile of the gas-liquid-solid mixture in a slurry bubble column was measured by gamma-ray attenuation technology.\\u000a Several measures for improving measurement precision were presented based on the discussion on attenuation law. It was found\\u000a that the response frequency and the ray intensity should be as high as possible to improve the measurement precision. The\\u000a mass absorption coefficient depended

  17. Gamma-ray attenuation method as an efficient tool to investigate soil bulk density spatial variability

    Microsoft Academic Search

    L. F. Pires; J. A. Rosa; A. B. Pereira; R. C. J. Arthur; O. O. S. Bacchi

    2009-01-01

    The spatial variability of soil bulk density (?b) was measured by using the volumetric ring method (VRM) and the gamma-ray attenuation method (GAM). Collimated radiation from 3.7GBq of 241Am was used to evaluate the soil mass attenuation coefficient and its bulk density. Circular lead collimators were adjusted and aligned between source (D=1, 2 and 3mm) and detector (D=4.5mm). Results of

  18. Chemical corrosion and gamma-ray attenuation properties of Zr and Ti containing lead silicate glasses

    Microsoft Academic Search

    Rafi Ali Rahimi; Gholamreza Raisali; S.K. Sadrnezhaad; Anita Alipour

    2009-01-01

    Lead silicate glasses (LSGs) have high gamma-ray attenuation but low chemical durability properties. In this work, LSGs with (55.5–68.5wt%) PbO content containing ZrO2 and TiO2 additions were produced. The chemical corrosion of various produced LSGs in 0.5N HNO3 aqueous solution and determination of their gamma-ray attenuation coefficients for 60Co and 137Cs sources were investigated. The weight loss measurements, the SEM

  19. Torsional guided-wave attenuation in coal-tar-enamel-coated, buried piping

    Microsoft Academic Search

    H Kwun; S. Y Kim; M. S Choi; S. M Walker

    2004-01-01

    Attenuation of the fundamental torsional guided waves in a coal-tar-enamel-coated pipe was investigated experimentally over a 5–30-kHz frequency range and up to a 1.7-m soil cover. The attenuation coefficients in the coated pipe above the ground were an order of magnitude greater than in bare pipe and, over the frequency range studied, it increased approximately linearly with frequency. Soil cover

  20. TOWARD A RAYLEIGH WAVE ATTENUATION MODEL FOR ASIA AND SURROUNDING REGIONS

    Microsoft Academic Search

    Anatoli L. Levshin; Mikhail P. Barmin; Xiaoning Yang; Michael H. Ritzwoller

    We report on the progress toward the development of attenuation models for short-period (12-22 sec) Rayleigh waves in Asia and surrounding regions. This model is defined by maps of attenuation coefficients across the region of study in the specified period band. The model is designed to calibrate the regional surface-wave magnitude scale and to extend the teleseismic 'surface-wave magnitude -

  1. Discovering Associations in Biomedical Datasets by Link-based Associative Classifier (LAC)

    PubMed Central

    Yu, Pulan; Wild, David J.

    2012-01-01

    Associative classification mining (ACM) can be used to provide predictive models with high accuracy as well as interpretability. However, traditional ACM ignores the difference of significances among the features used for mining. Although weighted associative classification mining (WACM) addresses this issue by assigning different weights to features, most implementations can only be utilized when pre-assigned weights are available. In this paper, we propose a link-based approach to automatically derive weight information from a dataset using link-based models which treat the dataset as a bipartite model. By combining this link-based feature weighting method with a traditional ACM method–classification based on associations (CBA), a Link-based Associative Classifier (LAC) is developed. We then demonstrate the application of LAC to biomedical datasets for association discovery between chemical compounds and bioactivities or diseases. The results indicate that the novel link-based weighting method is comparable to support vector machine (SVM) and RELIEF method, and is capable of capturing significant features. Additionally, LAC is shown to produce models with high accuracies and discover interesting associations which may otherwise remain unrevealed by traditional ACM. PMID:23227228

  2. Radio-faint BL Lac objects and their impact on the radio/gamma-ray connection

    NASA Astrophysics Data System (ADS)

    Giroletti, Marcello; Pavlidou, V.; Reimer, A.; Taylor, G. B.; Tosti, G.; Giovannini, G.; Casadio, C.; Liuzzo, E.; Tamburri, S.

    2012-05-01

    Radio and gamma-ray emissions in Active Galactic Nuclei (AGNs) are both related to the presence of relativistic particles in jets. With the advent of the Fermi Large Area Telescope (LAT), and thanks to its large sensitivity up to several GeV, many observational results are changing our understanding of these phenomena. BL Lac objects, which made up only a fraction of the known extragalactic gamma-ray source population before Fermi, have now become the most abundant class. However, since they are relatively weak radio sources, most of them are poorly known as far as their parsec scale structure and multi-wavelength properties are concerned. For this reason, we have selected a complete sample of 42 low redshift BL Lacs (independently of their gamma-ray properties) to study with a multi-wavelength (radio, optical, X-ray, gamma-ray) approach. Here, we present results and images of sources in the sample (most of which have never been observed before), using new VLBA observations at 8 and 15 GHz. Beyond this sample of BL Lacs, the population of gamma-ray AGNs has also dramatically enlarged in the Fermi era, permitting us to discuss the presence of a correlation between radio and gamma-ray properties with improved statistical significance. We explore the radio-gamma relation with several hundreds sources and using both simultaneous and archival radio data, thus tackling the impact of time variability.

  3. X-Ray Spectral Variability Signatures of Flares in BL Lac Objects

    NASA Technical Reports Server (NTRS)

    Boettcher, Markus; Chiang, James; White, Nicholas E. (Technical Monitor)

    2002-01-01

    We are presenting a detailed parameter study of the time-dependent electron injection and kinematics and the self-consistent radiation transport in jets of intermediate and low-frequency peaked BL Lac objects. Using a time-dependent, combined synchrotron-self-Compton and external-Compton jet model, we study the influence of variations of several essential model parameters, such as the electron injection compactness, the relative contribution of synchrotron to external soft photons to the soft photon compactness, the electron- injection spectral index, and the details of the time profiles of the electron injection episodes giving rise to flaring activity. In the analysis of our results, we focus on the expected X-ray spectral variability signatures in a region of parameter space particularly well suited to reproduce the broadband spectral energy distributions of intermediate and low-frequency peaked BL Lac objects. We demonstrate that SSC- and external-Compton dominated models for the gamma-ray emission from blazars are producing significantly different signatures in the X-ray variability, in particular in the soft X-ray light curves and the spectral hysteresis at soft X-ray energies, which can be used as a powerful diagnostic to unveil the nature of the high-energy emission from BL Lac objects.

  4. The use of lacZ marker in enumeration of Azotobacter chroococcum in carrier based inoculants

    PubMed Central

    Solanki, Manu; Garg, Faquir C.

    2014-01-01

    A transconjugant of Azotobacter chroococcum Mac 27 tagged with lac Z(A. chroococcum Mac27 L) was found to possess high levels of ?-galactosidase activity constitutively. Further, the lac Z marker was found to be stably integrated into the chromosome of the A. chroococcum Mac 27 and did not have any adverse effect on growth, nitrogen fixation and excretion of ammonia. A quick method to determine the viable cell number in broth culture and carrier based inoculants has been developed on the basis of ?-galactosidase assay. It was found that there was a direct relationship between the number of cell as determined by standard plate count and intensity of colour that developed upon degradation of ONPG due to ?-galactosidase activity. The method was found to be sensitive enough to determine 1.7 × 106 CFU mL?1 in broth culture as well as carrier based Azotobacter inoculants. Further, it was observed that when A. chroococcum Mac27 L was inoculated on Brassica campestris, it could be detected in the presence of other bacteria capable of growing on Burks agar medium containing X-gal on the basis of lac Z genetic marker. PMID:25242946

  5. Structured Jets in BL Lac Objects: Efficient PeV Neutrino Factories?

    NASA Astrophysics Data System (ADS)

    Tavecchio, Fabrizio; Ghisellini, Gabriele; Guetta, Dafne

    2014-09-01

    The origin of high-energy neutrinos (0.1-1 PeV range) detected by IceCube remains a mystery. In this work, we explore the possibility that efficient neutrino production can occur in structured jets of BL Lac objects, characterized by a fast inner spine surrounded by a slower layer. This scenario has been widely discussed in the framework of the high-energy emission models for BL Lac objects and radio galaxies. One of the relevant consequences of a velocity structure is the enhancement of the inverse Compton emission caused by the radiative coupling of the two zones. We show that a similar boosting could occur for the neutrino output of the spine through the photo-meson reaction of high-energy protons scattering off the amplified soft target photon field of the layer. Assuming the local density and the cosmological evolution of ?-ray BL Lac object derived from Fermi Large Area Telescope data, we calculate the expected diffuse neutrino intensity, which can match the IceCube data for a reasonable choice of parameters.

  6. Are many radio-selected BL Lacs radio quasars in disguise?

    E-print Network

    D'Elia, V; Giommi, P; Turriziani, S

    2015-01-01

    We show that a blazar classification in BL Lacs and Flat Spectrum Radio Quasars may not be adequate when it relies solely on the equivalent widths (EWs) of optical lines. In fact, depending on redshift, some strong emission lines can fall in the infrared window and be missed. We selected a sample of BL Lacs with firm redshift identification and good visibility from Paranal. We targeted with the X-shooter spectrograph the five BL Lacs with z > 0.7, i.e., those for which the Halpha line, one of the strongest among blazars, falls outside the optical window and determined the EW of emission lines in both the infrared and optical bands. Two out of five sources show an observed Halpha EW > 5A (one has rest frame EW > 5A) and could be classified as FSRQs by one of the classification schemes used in the literature. A third object is border-line with an observed EW of 4.4 +/- 0.5A. In all these cases Halpha is the strongest emission line detected. The Halpha line of the other two blazars is not detected, but in one ca...

  7. Monzonites (MZ) and monzosyenites (MSY) associated with the Laramie anorthoside complex (LAC), Wyoming

    SciTech Connect

    Fuhrman, M.; Kolker, A.; Lindsley, D.H.; Frost, B.R.

    1985-01-01

    The relationship between Proterozoic massif anorthosites and the associated syenitic rocks remains controversial. Unlike most such complexes, the LAC is unmetamorphosed and hence is ideally suited to petrologic and geochemical tests of a possible comagmatic origin. The authors detailed mapping and petrologic studies of the MZ and MSY show that these rocks were nearly anhydrous and crystallized at 3-5 kbar, 950-1050/sup 0/C, and oxygen fugacities several log units below FMQ buffer. They intrude the anorthosite, although the radiometric ages are identical within error. They have found strong petrologic evidence for a close genetic relationship between the anorthositic rocks and the MZ and MSY: mineral-chemical trends - as expressed by feldspars; augites, and low-Ca pyroxenes - are virtually continuous from the anorthosite through MZ to MSY. In contrast, recent geochemical studies of the LAC indicate that the MSY cannot represent a liquid complementary to the anorthosite. Their studies suggest a possible explanation: the MSY, like the anorthosite, may be a cumulate rather than a liquid. Fine-grained MZ that forms a border facies of the MSY probably represents a liquid. The authors are also considering several other highly evolved units as possible liquids residual to the MSY; such liquids should show strong negative Eu anomalies. Rare-earth studies on the fine-grained MZ and on other rocks are under way. A model for the possible comagmatic formation of the LAC is given by Lindsley and others.

  8. Comparison of Deterministic and Stochastic Models of the lac Operon Genetic Network

    PubMed Central

    Stamatakis, Michail; Mantzaris, Nikos V.

    2009-01-01

    The lac operon has been a paradigm for genetic regulation with positive feedback, and several modeling studies have described its dynamics at various levels of detail. However, it has not yet been analyzed how stochasticity can enrich the system's behavior, creating effects that are not observed in the deterministic case. To address this problem we use a comparative approach. We develop a reaction network for the dynamics of the lac operon genetic switch and derive corresponding deterministic and stochastic models that incorporate biological details. We then analyze the effects of key biomolecular mechanisms, such as promoter strength and binding affinities, on the behavior of the models. No assumptions or approximations are made when building the models other than those utilized in the reaction network. Thus, we are able to carry out a meaningful comparison between the predictions of the two models to demonstrate genuine effects of stochasticity. Such a comparison reveals that in the presence of stochasticity, certain biomolecular mechanisms can profoundly influence the region where the system exhibits bistability, a key characteristic of the lac operon dynamics. For these cases, the temporal asymptotic behavior of the deterministic model remains unchanged, indicating a role of stochasticity in modulating the behavior of the system. PMID:19186128

  9. Comparison of deterministic and stochastic models of the lac operon genetic network.

    PubMed

    Stamatakis, Michail; Mantzaris, Nikos V

    2009-02-01

    The lac operon has been a paradigm for genetic regulation with positive feedback, and several modeling studies have described its dynamics at various levels of detail. However, it has not yet been analyzed how stochasticity can enrich the system's behavior, creating effects that are not observed in the deterministic case. To address this problem we use a comparative approach. We develop a reaction network for the dynamics of the lac operon genetic switch and derive corresponding deterministic and stochastic models that incorporate biological details. We then analyze the effects of key biomolecular mechanisms, such as promoter strength and binding affinities, on the behavior of the models. No assumptions or approximations are made when building the models other than those utilized in the reaction network. Thus, we are able to carry out a meaningful comparison between the predictions of the two models to demonstrate genuine effects of stochasticity. Such a comparison reveals that in the presence of stochasticity, certain biomolecular mechanisms can profoundly influence the region where the system exhibits bistability, a key characteristic of the lac operon dynamics. For these cases, the temporal asymptotic behavior of the deterministic model remains unchanged, indicating a role of stochasticity in modulating the behavior of the system. PMID:19186128

  10. Seismic attenuation in fractured media

    NASA Astrophysics Data System (ADS)

    Rao, Ying; Wang, Yanghua

    2015-02-01

    The prime objective of this paper is to quantitatively estimate seismic attenuation caused by fractures with different physical parameters. In seismic wave simulation, the fractured media are treated as the anisotropic media and fractures are represented by frequency-dependent elastic constants. Based on numerical experiments with three different parameters, namely viscosity, porosity and the Lamé parameters, this paper has the following observations. First, seismic attenuation is not affected by the viscosity within fractures, although it increases with the increase of porosity and decreases with the increase of the Lamé parameters within fractures. Among the latter two parameters, seismic attenuation is more sensitive to the Lamé parameters than to the porosity. Second, for the attenuation anisotropy, low frequencies have more anisotropic effect than high frequencies. For example, a 50?Hz wavefield has the strongest anisotropy effect if compared to 100 and 150?Hz wavefields. The attenuation anisotropy for low frequency (say 50?Hz) is more sensitive to the viscosity than the porosity and the Lamé parameters have the weakest effect among these three parameters. These observations suggest that low-frequency seismic attenuation, and especially the attenuation anisotropy in low frequency, would have great potential for fluid discrimination within fractured media.

  11. Coefficients of associated Legendre functions

    NASA Technical Reports Server (NTRS)

    Peasley, Q. D.

    1976-01-01

    The exact coefficients for the explicit forms of the associated Legendre functions Pm for integer values of m,n=0,1,2,...25 are presented in tabular form together with two cross-referenced listings of the zeroes for these functions rounded to five decimal places. The unfactored coefficients and the interger coefficients are presented in adjacent columns for each function. The greatest common factor and divisor have been removed and listed separately for the integer coefficients.

  12. Database and software for the analysis of mutations at the lacI gene in both transgenic rodents and bacteria.

    PubMed

    Cariello, N F; Gorelick, N J

    1996-01-01

    The use of transgenic rodents for the study of genetic toxicology has increased dramatically in the past several years. A great deal of the recent work has employed the lacI locus in transgenic mice. In addition to the transgenic data, a substantial amount of information exists regarding mutation of the lacI gene in bacteria. In an effort to centralize the information regarding mutations in the lacI gene in both rodents and bacteria, we have created a computerized database that contains information about DNA sequence alterations on about 500 mutations in transgenic rodents and 8,000 mutations in bacteria. We have also produced a software package for the analysis of the lacI database. Routines have been developed for the analysis of single base substitutions, including programs to (i) determine if two mutational spectra are different; (ii) determine if mutations show a DNA strand bias; (iii) determine the frequency of transitions and transversions; (iv) display the number and kind of mutations observed at each base in the coding region; (v) perform nearest neighbor analysis; and (vi) display mutable amino acids in the lacI protein. The software runs only on IBM-compatible machines running Microsoft Windows. The software and lacI database are freely available via the internet (http:/(/)sunsite.unc.edu/dnam/mainpage.++ +html). PMID:8991069

  13. SEISMIC ATTENUATION FOR RESERVOIR CHARACTERIZATION

    SciTech Connect

    Joel Walls; M.T. Taner; Gary Mavko; Jack Dvorkin

    2002-04-01

    Wave-induced variations of pore pressure in a partially-saturated reservoir result in oscillatory liquid flow. The viscous losses during this flow are responsible for wave attenuation. The same viscous effects determine the changes in the dynamic bulk modulus of the system versus frequency. These changes are necessarily linked to attenuation via the causality condition. We analytically quantify the frequency dependence of the bulk modulus of a partially saturated rock by assuming that saturation is patchy and then link these changes to the inverse quality factor. As a result, the P-wave attenuation is quantitatively linked to saturation and thus can serve as a saturation indicator.

  14. Frequency dispersion of ultrasonic velocity and attenuation of longitudinal waves propagating in 0.68Pb,,Mg1/3Nb2/3...O30.32PbTiO3 single crystals

    E-print Network

    Cao, Wenwu

    Frequency dispersion of ultrasonic velocity and attenuation of longitudinal waves propagating in 0 ultrasonic spectroscopy, the frequency dispersion of ultrasonic velocity and attenuation in the frequency coefficient and higher attenuation of ultrasonic waves in multiple-domain 1-x Pb Mg1/3Nb2/3 O3­xPbTiO3 single

  15. Dual energy CT for attenuation correction with PET/CT

    SciTech Connect

    Xia, Ting [Department of Bioengineering, University of Washington, Seattle, Washington 98105 (United States)] [Department of Bioengineering, University of Washington, Seattle, Washington 98105 (United States); Alessio, Adam M. [Department of Radiology, University of Washington, Seattle, Washington 98105 (United States)] [Department of Radiology, University of Washington, Seattle, Washington 98105 (United States); Kinahan, Paul E., E-mail: kinahan@uw.edu [Departments of Radiology and Bioengineering, University of Washington, Seattle, Washington 98105 (United States)

    2014-01-15

    Purpose: The authors evaluate the energy dependent noise and bias properties of monoenergetic images synthesized from dual-energy CT (DECT) acquisitions. These monoenergetic images can be used to estimate attenuation coefficients at energies suitable for positron emission tomography (PET) and single-photon emission computed tomography (SPECT) imaging. This is becoming more relevant with the increased use of quantitative imaging by PET/CT and SPECT/CT scanners. There are, however, potential variations in the noise and bias of synthesized monoenergetic images as a function of energy. Methods: The authors used analytic approximations and simulations to estimate the noise and bias of synthesized monoenergetic images of water-filled cylinders with different shapes and the NURBS-based cardiac-torso (NCAT) phantom from 40 to 520 keV, the range of SPECT and PET energies. The dual-kVp spectra were based on the GE Lightspeed VCT scanner at 80 and 140 kVp with added filtration of 0.5 mm Cu. The authors evaluated strategies of noise suppression with sinogram smoothing and dose minimization with reduction of tube currents at the two kVp settings. The authors compared the impact of DECT-based attenuation correction with single-kVp CT-based attenuation correction on PET quantitation for the NCAT phantom for soft tissue and high-Z materials of bone and iodine contrast enhancement. Results: Both analytic calculations and simulations displayed the expected minimum noise value for a synthesized monoenergetic image at an energy between the mean energies of the two spectra. In addition the authors found that the normalized coefficient of variation in the synthesized attenuation map increased with energy but reached a plateau near 160 keV, and then remained constant with increasing energy up to 511 keV and beyond. The bias was minimal, as the linear attenuation coefficients of the synthesized monoenergetic images were within 2.4% of the known true values across the entire energy range. Compared with no sinogram smoothing, sinogram smoothing can dramatically reduce noise in the DECT-derived attenuation map. Through appropriate selection of tube currents for high and low kVp scans, DECT can deliver roughly the same amount of radiation dose as that of a single kVp CT scan, but could be used for PET attenuation correction with reduced bias in contrast agent regions by a factor of ?2.6 and slightly reduced RMSE for the total image. Conclusions: When DECT is used for attenuation correction at higher energies, there is a noise amplification that is dependent on the energy of the synthesized monoenergetic image of linear attenuation coefficients. Sinogram smoothing reduces the noise amplification in DECT-derived attenuation maps without increasing bias. With an appropriate selection of CT techniques, a DECT scan with the same radiation dose as a single CT scan can result in a PET image with improved quantitative accuracy.

  16. Dual energy CT for attenuation correction with PET/CT

    PubMed Central

    Xia, Ting; Alessio, Adam M.; Kinahan, Paul E.

    2014-01-01

    Purpose: The authors evaluate the energy dependent noise and bias properties of monoenergetic images synthesized from dual-energy CT (DECT) acquisitions. These monoenergetic images can be used to estimate attenuation coefficients at energies suitable for positron emission tomography (PET) and single-photon emission computed tomography (SPECT) imaging. This is becoming more relevant with the increased use of quantitative imaging by PET/CT and SPECT/CT scanners. There are, however, potential variations in the noise and bias of synthesized monoenergetic images as a function of energy. Methods: The authors used analytic approximations and simulations to estimate the noise and bias of synthesized monoenergetic images of water-filled cylinders with different shapes and the NURBS-based cardiac-torso (NCAT) phantom from 40 to 520 keV, the range of SPECT and PET energies. The dual-kVp spectra were based on the GE Lightspeed VCT scanner at 80 and 140 kVp with added filtration of 0.5 mm Cu. The authors evaluated strategies of noise suppression with sinogram smoothing and dose minimization with reduction of tube currents at the two kVp settings. The authors compared the impact of DECT-based attenuation correction with single-kVp CT-based attenuation correction on PET quantitation for the NCAT phantom for soft tissue and high-Z materials of bone and iodine contrast enhancement. Results: Both analytic calculations and simulations displayed the expected minimum noise value for a synthesized monoenergetic image at an energy between the mean energies of the two spectra. In addition the authors found that the normalized coefficient of variation in the synthesized attenuation map increased with energy but reached a plateau near 160 keV, and then remained constant with increasing energy up to 511 keV and beyond. The bias was minimal, as the linear attenuation coefficients of the synthesized monoenergetic images were within 2.4% of the known true values across the entire energy range. Compared with no sinogram smoothing, sinogram smoothing can dramatically reduce noise in the DECT-derived attenuation map. Through appropriate selection of tube currents for high and low kVp scans, DECT can deliver roughly the same amount of radiation dose as that of a single kVp CT scan, but could be used for PET attenuation correction with reduced bias in contrast agent regions by a factor of ?2.6 and slightly reduced RMSE for the total image. Conclusions: When DECT is used for attenuation correction at higher energies, there is a noise amplification that is dependent on the energy of the synthesized monoenergetic image of linear attenuation coefficients. Sinogram smoothing reduces the noise amplification in DECT-derived attenuation maps without increasing bias. With an appropriate selection of CT techniques, a DECT scan with the same radiation dose as a single CT scan can result in a PET image with improved quantitative accuracy. PMID:24387525

  17. Tree attenuation at 869 MHz derived from remotely piloted aircraft measurements

    NASA Technical Reports Server (NTRS)

    Vogel, Wolfhard J.; Goldhirsh, Julius

    1986-01-01

    Attenuation due to single trees is experimentally investigated using UHF transmissions at 869 MHz between a remotely piloted aircraft and a ground receiver system located in a stationary vehicle. Single trees of each tree type in full foliage were found to attenuate from 10-20 dB, with an average median value of about 12 dB. Attenuation coefficients associated with path lengths through the foliage may on average be about 1 dB/m, with maximum values closer to 2 dB/m.

  18. Sound attenuation in a spin-1 Ising system near the critical temperature

    NASA Astrophysics Data System (ADS)

    Erdem, R.?za; Keskin, Mustafa

    2001-12-01

    Sound attenuation coefficient is calculated for a spin-1 Ising system on the basis of Onsager theory of irreversible processes and its behaviour near the second-order phase transition point or the critical point is analyzed according to various values of Onsager or phenomenological rate coefficients ( ?ij). For all ?S and ?Q values it is observed that the sound attenuation peaks occur below TC and depend on frequency ( ?) and on the value of the off-diagonal Onsager coefficient ( ?). On the other hand, in the hydrodynamic regime the attenuation converges to zero with a mean field exponent ( ?=1.0) just below the transition, while it vanishes above the critical temperature and then remains temperature-independent. Moreover, the behaviour of the sound attenuation as a function of frequency is also investigated and ?2 dependence is observed for the attenuation coefficient. These results are in a good agreement with ultrasonic investigations of some magnetic systems, such as MnF 2, FeF 2, and RbMnF 3.

  19. Attenuation correction for PET/MR: problems, novel approaches and practical solutions.

    PubMed

    Martinez-Möller, Axel; Nekolla, Stephan G

    2012-12-01

    Attenuation correction in PET is the primary prerequisite for quantification of the radiotracer's signal. Absolute quantification is the key to improve diagnostic performance, to enable comparisons between follow-up examinations and to perform pharmacokinetic modeling. A large fraction of the 511 keV annihilation photons from the positron emitters are scattered by the patient's body. Thus, they are discarded or do not even reach the PET detectors, while others are identified at the wrong location after being scattered. To account for these effects and thus generate quantitative PET images showing the actual activity distribution, it is necessary to determine an attenuation map with the appropriate attenuation coefficients for 511 keV photons at each voxel. In hybrid PET/CT systems, this is achieved using the information about the tissue electron density provided by the CT and adjusting it for the difference in photon energy. In PET/MR systems, there is no mechanism to directly measure the attenuation coefficients of the tissue. Determining the attenuation map in PET/MR is an important challenge involving two problems: the determination of the patient's attenuation map and the determination of the attenuation introduced by additional hardware components. We describe the approaches investigated to deal with these problems and, based on the experience with a fully integrated PET/MR system, we finally discuss potential solutions and limitations in a close to routine setting. PMID:22925653

  20. Optical absorption coefficient of magneto-optic garnet films

    SciTech Connect

    Liu Gong-qiang; Yu Zhi-qiang; Liu Xianglin

    1986-02-01

    This paper analyzes various factors contributing to optical attenuation in magneto-optic garnet films and derives expressions for the optical absorption and scattering coefficients ..cap alpha.. and ..gamma... The values of ..cap alpha.. and ..gamma.. for (BiTm)/sub 3/(FeGa)/sub 5/O/sub 12/ films were measured in a magneto-optic modulation device by comparing the magneto-optic rotations. Compared with other methods, this technique has two advantages: (1) absorption in the substrate is eliminated, and the measured values ..cap alpha.. are not affected by reflection at the film/substrate interface; (2) the optical scattering coefficient ..gamma.. can be separated from the optical absorption ..cap alpha.., so that the measured value ..cap alpha.. closely approximates the true optical absorption coefficient for magneto-optic garnet film materials.

  1. Prediction of attenuation by rain

    NASA Technical Reports Server (NTRS)

    Crane, R. K.

    1980-01-01

    A new model is presented for the prediction of attenuation by rain on either terrestrial or slant earth-to-space propagation paths. The model was developed using geophysical observations of the statistics of point rain rate, of the horizontal structure of rainfall, and of the vertical temperature structure of the atmosphere. The model was tested by comparison with attenuation distribution observations. The results show excellent agreement; the observations differ from model predictions by less than the rms deviations predicted by the model.

  2. Broadband time-domain reflectometry measurement of attenuation and phase velocity in highly attenuating suspensions with application to the ultrasound contrast medium Albunex.

    PubMed

    Hughes, M S; Klibanov, A L; Marsh, J N; Miller, J G; Brandenburger, G H

    2000-08-01

    We describe a technique for broadband measurements of the attenuation coefficient and phase velocity of highly attenuating liquid suspensions. To validate the technique we apply it to the ultrasound contrast agent Albunex at concentrations ranging from 0.69 x 10(6) particles/mL to 364 x 10(6) particles/mL. These longitudinal wave measurements were performed on Albunex suspensions maintained at 37 degrees C in a special time-domain reflectometer designed and constructed in our laboratory. The frequency-dependent attenuation coefficients and phase velocities obtained in the reflectometer are compared to broadband through-transmission measurements of these same quantities, which were also performed in our laboratory. Although comparison data between the two techniques are only available at lower concentrations, the agreement is quite good and serves to validate the methods described in this paper. PMID:10955648

  3. Trp replacements for tightly interacting Gly–Gly pairs in LacY stabilize an outward-facing conformation

    PubMed Central

    Smirnova, Irina; Kasho, Vladimir; Sugihara, Junichi; Kaback, H. Ronald

    2013-01-01

    Trp replacements for conserved Gly–Gly pairs between the N- and C-terminal six-helix bundles on the periplasmic side of lactose permease (LacY) cause complete loss of transport activity with little or no effect on sugar binding. Moreover, the detergent-solubilized mutants exhibit much greater thermal stability than WT LacY. A Cys replacement for Asn245, which is inaccessible/unreactive in WT LacY, alkylates readily in the Gly?Trp mutants, indicating that the periplasmic cavity is patent. Stopped-flow kinetic measurements of sugar binding with the Gly?Trp mutants in detergent reveal linear dependence of binding rates on sugar concentration, as observed with WT or the C154G mutant of LacY, and are compatible with free access to the sugar-binding site in the middle of the molecule. Remarkably, after reconstitution of the Gly?Trp mutants into proteoliposomes, the concentration dependence of sugar-binding rates increases sharply with even faster rates than measured in detergent. Such behavior is strikingly different from that observed for reconstituted WT LacY, in which sugar-binding rates are independent of sugar concentration because opening of the periplasmic cavity is limiting for sugar binding. The observations clearly indicate that Gly?Trp replacements, which introduce bulky residues into tight Gly–Gly interdomain interactions on the periplasmic side of LacY, prevent closure of the periplasmic cavity and, as a result, shift the distribution of LacY toward an outward-open conformation. PMID:23671103

  4. LacR Mutations Are Frequently Observed in Streptococcus intermedius and Are Responsible for Increased Intermedilysin Production and Virulence

    PubMed Central

    Tomoyasu, Toshifumi; Imaki, Hidenori; Masuda, Sachiko; Okamoto, Ayumi; Kim, Hyejin; Waite, Richard D.; Whiley, Robert A.; Kikuchi, Ken; Hiramatsu, Keiichi; Tabata, Atsushi

    2013-01-01

    Streptococcus intermedius secretes a human-specific cytolysin, intermedilysin (ILY), which is considered to be the major virulence factor of this pathogen. We screened for a repressor of ily expression by using random gene disruption in a low-ILY-producing strain (PC574). Three independent high-ILY-producing colonies that had plasmid insertions within a gene that has high homology to lacR were isolated. Validation of these observations was achieved through disruption of lacR in strain PC574 with an erythromycin cassette, which also led to higher hemolytic activity, increased transcription of ily, and higher cytotoxicity against HepG2 cells, compared to the parental strain. The direct binding of LacR within the ily promoter region was shown by a biotinylated DNA probe pulldown assay, and the amount of ILY secreted into the culture supernatant by PC574 cells was increased by adding lactose or galactose to the medium as a carbon source. Furthermore, we examined lacR nucleotide sequences and the hemolytic activity of 50 strains isolated from clinical infections and 7 strains isolated from dental plaque. Of the 50 strains isolated from infections, 13 showed high ILY production, 11 of these 13 strains had one or more point mutations and/or an insertion mutation in LacR, and almost all mutations were associated with a marked decline in LacR function. These results strongly suggest that mutation in lacR is required for the overproduction of ILY, which is associated with an increase in pathogenicity of S. intermedius. PMID:23798532

  5. Antibody biodistribution coefficients

    PubMed Central

    Shah, Dhaval K.; Betts, Alison M.

    2013-01-01

    Tissue vs. plasma concentration profiles have been generated from a physiologically-based pharmacokinetic model of monoclonal antibody (mAb). Based on the profiles, we hypothesized that a linear relationship between the plasma and tissue concentrations of non-binding mAbs could exist; and that the relationship may be generally constant irrespective of the absolute mAb concentration, time, and animal species being analyzed. The hypothesis was verified for various tissues in mice, rat, monkey, and human using mAb or antibody-drug conjugate tissue distribution data collected from diverse literature. The relationship between the plasma and various tissue concentrations was mathematically characterized using the antibody biodistribution coefficient (ABC). Estimated ABC values suggest that typically the concentration of mAb in lung is 14.9%, heart 10.2%, kidney 13.7%, muscle 3.97%, skin 15.7%, small intestine 5.22%, large intestine 5.03%, spleen 12.8%, liver 12.1%, bone 7.27%, stomach 4.98%, lymph node 8.46%, adipose 4.78%, brain 0.351%, pancreas 6.4%, testes 5.88%, thyroid 67.5% and thymus is 6.62% of the plasma concentration. The validity of using the ABC to predict mAb concentrations in different tissues of mouse, rat, monkey, and human species was evaluated by generating validation data sets, which demonstrated that predicted concentrations were within 2-fold of the observed concentrations. The use of ABC to infer tissue concentrations of mAbs and related molecules provides a valuable tool for investigating preclinical or clinical disposition of these molecules. It can also help eliminate or optimize biodistribution studies, and interpret efficacy or toxicity of the drug in a particular tissue. PMID:23406896

  6. Reference Material for Seebeck Coefficients

    NASA Astrophysics Data System (ADS)

    Edler, F.; Lenz, E.; Haupt, S.

    2015-03-01

    This paper describes a measurement method and a measuring system to determine absolute Seebeck coefficients of thermoelectric bulk materials with the aim of establishing reference materials for Seebeck coefficients. Reference materials with known thermoelectric properties are essential to allow a reliable benchmarking of different thermoelectric materials for application in thermoelectric generators to convert thermal into electrical energy or vice versa. A temperature gradient (1 to 8) K is induced across the sample, and the resulting voltage is measured by using two differential Au/Pt thermocouples. On the basis of the known absolute Seebeck coefficients of Au and Pt, the unknown Seebeck coefficient of the sample is calculated. The measurements are performed in inert atmospheres and at low pressure (30 to 60) mbar in the temperature range between 300 K and 860 K. The measurement results of the Seebeck coefficients of metallic and semiconducting samples are presented. Achievable relative measurement uncertainties of the Seebeck coefficient are on the order of a few percent.

  7. Prediction of spectral acceleration response ordinates based on PGA attenuation

    USGS Publications Warehouse

    Graizer, V.; Kalkan, E.

    2009-01-01

    Developed herein is a new peak ground acceleration (PGA)-based predictive model for 5% damped pseudospectral acceleration (SA) ordinates of free-field horizontal component of ground motion from shallow-crustal earthquakes. The predictive model of ground motion spectral shape (i.e., normalized spectrum) is generated as a continuous function of few parameters. The proposed model eliminates the classical exhausted matrix of estimator coefficients, and provides significant ease in its implementation. It is structured on the Next Generation Attenuation (NGA) database with a number of additions from recent Californian events including 2003 San Simeon and 2004 Parkfield earthquakes. A unique feature of the model is its new functional form explicitly integrating PGA as a scaling factor. The spectral shape model is parameterized within an approximation function using moment magnitude, closest distance to the fault (fault distance) and VS30 (average shear-wave velocity in the upper 30 m) as independent variables. Mean values of its estimator coefficients were computed by fitting an approximation function to spectral shape of each record using robust nonlinear optimization. Proposed spectral shape model is independent of the PGA attenuation, allowing utilization of various PGA attenuation relations to estimate the response spectrum of earthquake recordings.

  8. Anisotropy of Earth's inner core intrinsic attenuation from seismic normal mode models

    NASA Astrophysics Data System (ADS)

    Mäkinen, Anna M.; Deuss, Arwen; Redfern, Simon A. T.

    2014-10-01

    The Earth's inner core, the slowly growing sphere of solid iron alloy at the centre of our planet, is known to exhibit seismic anisotropy. Both normal mode and body wave studies have established that, when the global average is taken, compressional waves propagate faster in the North-South direction than in the equatorial plane. Recent body wave studies also indicate that this fast direction may be more attenuating, and interpret this anisotropic attenuation in terms of anisotropic scattering due to inner core texturing. Here we use the Earth's normal modes to study the attenuation anisotropy of both compressional and shear waves in the inner core. As normal modes have wavelengths several orders of magnitude longer than estimates of inner core grain size, any attenuation anisotropy quantified using normal modes must reflect the anisotropy of intrinsic (viscoelastic) attenuation of the crystalline inner core alloy. By inverting zonal anelastic and elastic normal mode splitting function coefficients of twenty inner core sensitive modes, we construct models of inner core intrinsic attenuation and velocity anisotropy. We find that, for compressional waves, the North-South direction is both fast and more strongly attenuating. The existence of intrinsic inner core attenuation anisotropy can be interpreted in terms of anisotropic Zener relaxation in the metallic alloy comprising the inner core. Such anisotropic Zener relaxation has only been observed in the presence of solute atoms, and is thus entirely consistent with the presence of a few atomic per cent of light elements in the Earth's inner core.

  9. The SOS-LUX-LAC-FLUORO-Toxicity-test on the International Space Station (ISS)

    NASA Astrophysics Data System (ADS)

    Rabbow, E.; Rettberg, P.; Baumstark-Khan, C.; Horneck, G.

    In the 21 st century, an increasing number of astronauts will visit the International Space Station (ISS) for prolonged times. Therefore it is of utmost importance to provide necessary basic knowledge concerning risks to their health and their ability to work on the station and during extravehicular activities (EVA) in free space. It is the aim of one experiment of the German project TRIPLE-LUX (to be flown on the ISS) to provide an estimation of health risk resulting from exposure of the astronauts to the radiation in space inside the station as well as during extravehicular activities on one hand, and of exposure of astronauts to unavoidable or as yet unknown ISS-environmental genotoxic substances on the other. The project will (i) provide increased knowledge of the biological action of space radiation and enzymatic repair of DNA damage, (ii) uncover cellular mechanisms of synergistic interaction of microgravity and space radiation and (iii) examine the space craft milieu with highly specific biosensors. For these investigations, the bacterial biosensor SOS-LUX-LAC-FLUORO-Toxicity-test will be used, combining the SOS-LUX-Test invented at DLR Germany (Patent) with the commercially available LAC-FLUORO-Test. The SOS-LUX-Test comprises genetically modified bacteria transformed with the pBR322-derived plasmid pPLS-1. This plasmid carries the promoterless lux operon of Photobacterium leiognathi as a reporter element under control of the DNA-damage dependent SOS promoter of ColD as sensor element. This system reacts to radiation and other agents that induce DNA damages with a dose dependent measurable emission of bioluminescence of the transformed bacteria. The analogous LAC-FLUORO-Test has been developed for the detection of cellular responses to cytotoxins. It is based on the constitutive expression of green fluorescent protein (GFP) mediated by the bacterial protein expression vector pGFPuv (Clontech, Palo Alto, USA). In response to cytotoxic agents, this system reacts with a dose-dependent reduction of GFP-fluorescence. Currently, a fully automated miniaturized hardware system for the bacterial set up, which includes measurements of luminescence and fluorescence or absorption and the image analysis based evaluation is under development. During the first mission of the SOS-LUX-LAC-FLUORO-Toxicity-Test on the ISS, a standardized, DNA-damaging radiation source still to be determined will be used as a genotoxic inducer. A panel of recombinant Salmonella typhimurium strains carrying either the SOS-LUX plasmid or the fluorescence-mediating lac-GFPuv plasmid will be used to determine in parallel on one microplate the genotoxic and the cytotoxic action of the applied radiation in combination with microgravity. Either in addition to or in place of the fluorometric measurements of the cytotoxic agents, photometric measurements will simultaneously monitor cell growth, giving additional data on survival of the cells. The obtained data will be available on line during the TRIPLE-LUX mission time. Though it is the main goal during the TRIPLE-LUX mission to measure the radiation effect in microgravity, the SOS-LUX-LAC-FLUORO-Toxicity-test in principle is also applicable as a biomonitor for the detection and measurement of genotoxic substances in air or in the (recycled) water system on the ISS or on earth in general.

  10. Coefficient Alpha: A Reliability Coefficient for the 21st Century?

    ERIC Educational Resources Information Center

    Yang, Yanyun; Green, Samuel B.

    2011-01-01

    Coefficient alpha is almost universally applied to assess reliability of scales in psychology. We argue that researchers should consider alternatives to coefficient alpha. Our preference is for structural equation modeling (SEM) estimates of reliability because they are informative and allow for an empirical evaluation of the assumptions…

  11. The Connection among Gamma-ray Burst Host-Galaxies, BL Lacs and Quasars

    E-print Network

    A. Rej

    1999-01-19

    A possible connection among host-galaxies of gamma-ray bursts, BL Lacs and quasars is analysed. It is believed that the gamma-ray bursts, which do not show radio or infrared emission, occur in faint blue dwarf galaxies, that are seen around radio-quiet quasars, which lie in clusters. The GRB counterparts, which show radio emission, may be associated with more evolved starbursting environments, and arise from red galaxies, that are observed around some radio-loud quasars lying in richer clusters. The absorption lines are believed to arise from gases, that move in the intergalactic medium, due to tidal interactions occuring among the compact galaxies in the cluster environment. The connections between intra-day variable BL Lac-blazars and radio emitting gamma-ray hosts are also studied. The hosts of gamma-ray bursts, BL Lacs and quasars are believed to represent different evolutionary phases of a particular type of galaxy with a "twisted" morphology. They mostly occur in star formation environments and evolve from a galaxy possessing no AGN, but consisting of very massive young stellar sytems, to galaxies possessing developed AGNs, like in quasars, whose gas content have been exhausted in giving birth to the stars at the AGN core. In between these two phases, these galaxies may pass through the state of the red objects, which contain a new born quasar hidden under dust.This evolutionary history of the morphologies and the environment, where GRBs may occur is believed to be related to the process of formation of galaxies and large scale structures. Moreover, the starbursting peaks at different redshifts may indicate a universe that is different from the standard cosmolgy.

  12. Flexible Gates Generate Occluded Intermediates in the Transport Cycle of LacY?

    PubMed Central

    Stelzl, Lukas S.; Fowler, Philip W.; Sansom, Mark S.P.; Beckstein, Oliver

    2014-01-01

    The major facilitator superfamily (MFS) transporter lactose permease (LacY) alternates between cytoplasmic and periplasmic open conformations to co-transport a sugar molecule together with a proton across the plasma membrane. Indirect experimental evidence suggested the existence of an occluded transition intermediate of LacY, which would prevent leaking of the proton gradient. As no experimental structure is known, the conformational transition is not fully understood in atomic detail. We simulated transition events from a cytoplasmic open conformation to a periplasmic open conformation with the dynamic importance sampling molecular dynamics method and observed occluded intermediates. Analysis of water permeation pathways and the electrostatic free-energy landscape of a solvated proton indicated that the occluded state contains a solvated central cavity inaccessible from either side of the membrane. We propose a pair of geometric order parameters that capture the state of the pathway through the MFS transporters as shown by a survey of available crystal structures and models. We present a model for the occluded state of apo-LacY, which is similar to the occluded crystal structures of the MFS transporters EmrD, PepTSo, NarU, PiPT and XylE. Our simulations are consistent with experimental double electron spin–spin distance measurements that have been interpreted to show occluded conformations. During the simulations, a salt bridge that has been postulated to be involved in driving the conformational transition formed. Our results argue against a simple rigid-body domain motion as implied by a strict “rocker-switch mechanism” and instead hint at an intricate coupling between two flexible gates. PMID:24513108

  13. Lac Télé structure, Republic of Congo: Geological setting of a cryptozoological and biodiversity hotspot, and evidence against an impact origin

    NASA Astrophysics Data System (ADS)

    Master, Sharad

    2010-11-01

    Lac Télé is a large lake, ˜5.6 km in diameter, with an ovoid shape, situated at 17°10'E, 1°20'N, in the great tropical rain forest region of the Republic of Congo. This lake has attracted widespread attention, mainly because of the legends among the local people that it harbours a strange animal known as the Mokele-Mbembe, but also because it is situated in a region that is a hotbed of biodiversity and conservation efforts with respect to various endangered mammalian species, including gorillas and chimpanzees. Because of its appearance, Lac Télé has been regarded as a possible meteorite impact structure. Various expeditions, studying cryptozoology, conservation ecology, biodiversity, and the impact hypothesis, have visited Lac Télé in the past several decades. The Lac Télé structure is located in the NW part of the intracratonic Congo Basin, in a region dominated by Holocene alluvium, dense tropical rain forest, and swamps which form part of the basin of the Likouala aux Herbes, a multi-branched meandering river flowing over very low gradients into the Sangha river, a major tributary of the Congo river. Previous bathymetric studies have shown that the average depth of Lac Télé is only 4 m, including organic-rich silty sediments. The structure is that of a flat-bottomed dish. Modelling of the Lac Télé as an impact structure indicates a number of features which ought to be present. The absence of any of these features, coupled with the irregular ovoid shape, the palynological record, and the location of the structure at the intersection of major regional lineaments, is regarded as evidence against the impact hypothesis. Lac Télé as an isolated lake ecosystem is not unique in the Congo Basin, and there are several other similar small shallow isolated lakes surrounded by rain forest and marshes, some of which formed by damming of drainage systems by neotectonic faults. It is suggested that the formation of Lac Télé may be related to its location over neotectonically reactivated regional lineaments, which are also seismically active. Lac Télé and other similar hydrologic systems may be biodiversity hotspots because they acted as refugia following neotectonic hydrological re-organization of the Congo Basin.

  14. A Maximum Likelihood Approach to Determine Sensor Radiometric Response Coefficients for NPP VIIRS Reflective Solar Bands

    NASA Technical Reports Server (NTRS)

    Lei, Ning; Chiang, Kwo-Fu; Oudrari, Hassan; Xiong, Xiaoxiong

    2011-01-01

    Optical sensors aboard Earth orbiting satellites such as the next generation Visible/Infrared Imager/Radiometer Suite (VIIRS) assume that the sensors radiometric response in the Reflective Solar Bands (RSB) is described by a quadratic polynomial, in relating the aperture spectral radiance to the sensor Digital Number (DN) readout. For VIIRS Flight Unit 1, the coefficients are to be determined before launch by an attenuation method, although the linear coefficient will be further determined on-orbit through observing the Solar Diffuser. In determining the quadratic polynomial coefficients by the attenuation method, a Maximum Likelihood approach is applied in carrying out the least-squares procedure. Crucial to the Maximum Likelihood least-squares procedure is the computation of the weight. The weight not only has a contribution from the noise of the sensor s digital count, with an important contribution from digitization error, but also is affected heavily by the mathematical expression used to predict the value of the dependent variable, because both the independent and the dependent variables contain random noise. In addition, model errors have a major impact on the uncertainties of the coefficients. The Maximum Likelihood approach demonstrates the inadequacy of the attenuation method model with a quadratic polynomial for the retrieved spectral radiance. We show that using the inadequate model dramatically increases the uncertainties of the coefficients. We compute the coefficient values and their uncertainties, considering both measurement and model errors.

  15. What makes the lac-pathway switch: identifying the fluctuations that trigger phenotype switching in gene regulatory systems

    PubMed Central

    Bhogale, Prasanna M.; Sorg, Robin A.; Veening, Jan-Willem; Berg, Johannes

    2014-01-01

    Multistable gene regulatory systems sustain different levels of gene expression under identical external conditions. Such multistability is used to encode phenotypic states in processes including nutrient uptake and persistence in bacteria, fate selection in viral infection, cell-cycle control and development. Stochastic switching between different phenotypes can occur as the result of random fluctuations in molecular copy numbers of mRNA and proteins arising in transcription, translation, transport and binding. However, which component of a pathway triggers such a transition is generally not known. By linking single-cell experiments on the lactose-uptake pathway in E. coli to molecular simulations, we devise a general method to pinpoint the particular fluctuation driving phenotype switching and apply this method to the transition between the uninduced and induced states of the lac-genes. We find that the transition to the induced state is not caused only by the single event of lac-repressor unbinding, but depends crucially on the time period over which the repressor remains unbound from the lac-operon. We confirm this notion in strains with a high expression level of the lac-repressor (leading to shorter periods over which the lac-operon remains unbound), which show a reduced switching rate. Our techniques apply to multistable gene regulatory systems in general and allow to identify the molecular mechanisms behind stochastic transitions in gene regulatory circuits. PMID:25245949

  16. Spectral energy distributions and high-energy emission of BL Lac type objects

    E-print Network

    Sergey Troitsky

    2008-07-11

    Based on identifications from the Veron and Quasars.org catalogs, we determine the optical-to-X-ray spectral indices for a sample of 201 BL Lac type objects (BLLs) and search for trends in the distribution of these indices of the sources detected in high-energy bands. We find that EGRET-detected sources are low-energy peaked and that the positional correlation with the arrival directions of ultra-high-energy cosmic rays from the previously studied AGASA, Yakutsk and High Resolution Fly's Eye samples is dominated by low-energy-peaked BLLs.

  17. Analysis of LAC Observations of Clusters of Galaxies and Supernova Remnants

    NASA Technical Reports Server (NTRS)

    Hughes, J.

    1996-01-01

    The following publications are included and serve as the final report: The X-ray Spectrum of Abell 665; Clusters of Galaxies; Ginga Observation of an Oxygen-rich Supernova Remnant; Ginga Observations of the Coma Cluster and Studies of the Spatial Distribution of Iron; A Measurement of the Hubble Constant from the X-ray Properties and the Sunyaev-Zel'dovich Effect of Abell 2218; Non-polytropic Model for the Coma Cluster; and Abundance Gradients in Cooling Flow Clusters: Ginga LAC (Large Area Counter) and Einstein SSS (Solid State Spectrometer) Spectra of A496, A1795, A2142, and A2199.

  18. New statistical results on the optical IDV data of BL Lac S5 0716+714

    NASA Astrophysics Data System (ADS)

    Bogdan, D?nil?; Alexandru, Marcu; Raluca, Mocanu Gabriela

    2015-03-01

    This paper reports on the statistical behavior of the optical Intraday Variability of BL Lac S5 0716+714. Available Intraday Variability data in the optical are tested to see whether or not the magnitude is lognormally distributed. Our results consistently indicate that this is not the case. This is in agreement with a previous discussion about data for the same object but in a different observational period. Simultaneously, the spectral slope of the light curves is calculated. The implications of these findings on models that describe both the location and source of Intraday Variability are presented.

  19. Lac du Flambeau Band of Lake Superior Chippewa Indians Strategic Energy Plan

    SciTech Connect

    Bryan Hoover

    2009-11-16

    This plan discusses the current energy use on the Lac du Flambeau Reservation, the current status of the Tribe's energy program, as well as the issues and concerns with energy on the reservation. This plan also identifies and outlines energy opportunities, goals, and objectives for the Tribe to accomplish. The overall goal of this plan is to address the energy situation of the reservation in a holistic manner for the maximum benefit to the Tribe. This plan is an evolving document that will be re-evaluated as the Tribe's energy situation changes.

  20. Evaluation of critical indicators in the process of acquiring supplies and services LAC-UFPE

    NASA Astrophysics Data System (ADS)

    Caetano, V. F.; Ferreira, C. V.; dos Santos, M. J.; Honorato, F. A.

    2015-01-01

    In laboratories linked to public universities and accredited by the NBR ISO/IEC 17025, to meet efficiently item 4.6 (procurement of supplies and services) is a challenge that can be accomplished by programming based on historical purchases and services. In this study, we evaluated the critical procurement items to meet the quality management system of the LAC-UFPE: reagents, certified reference material, of equipment parts, maintenance and calibration of equipment and instruments. It was found that the most critical item is the certified reference material, the purchase or repair of which must be expedited within 125 days prior to the receipt to occur within the desired period.

  1. Observations of the high-frequency-peaked BL Lac object 1ES 1218 +304 with VERITAS

    NASA Astrophysics Data System (ADS)

    Fortin, Pascal

    The VERITAS collaboration has observed the high-frequency-peaked BL Lac object 1ES 1218 +30.4 using an array of several imaging Cherenkov telescopes located at the Fred Laurence Whipple Observatory in Southern Arizona. A gamma-ray signal was detected with high significance for the observations taken during several months in the 2006-2007 observing season. Here we present the detection of 1ES 1218 +30.4 in very high energy gamma-rays and a study of its time variability.

  2. Attenuation of a Stoneley wave and higher Lamb modes due to the scattering by two-dimensional irregularities of the walls of a fluid-filled borehole

    Microsoft Academic Search

    G. A. Maximov; E. Ortega; E. V. Pod”yachev

    2007-01-01

    Attenuation of Stoneley waves and higher Lamb modes propagating along an irregular surface of a fluid-filled borehole is investigated.\\u000a This problem generalizes the problem on the attenuation of Rayleigh waves by an irregular surface of an empty borehole [10].\\u000a The technique used to evaluate the attenuation coefficient is based on the perturbation method (surface irregularity heights\\u000a are considered to be

  3. Experimental investigation of gamma-ray attenuation in Jordanian building materials using HPGe-spectrometer.

    PubMed

    Awadallah, Mohammad I; Imran, Mousa M A

    2007-01-01

    The capabilities of some building materials used in Jordan to attenuate gamma radiation were tested. Measurements of the attenuation coefficients of limestone, bricks and concrete have been carried out using a HPGe-spectrometer. Narrow beam technique was used, with a multiple gamma radiation source of different energy lines. Results indicate that variations in the attenuation coefficient for all limestone samples, at the same energy line, are within the experimental uncertainties. On the basis of the results achieved, an empirical formula mu(m)=AE(-0.44) was proposed to calculate attenuation at various incident energies. Limestone of average thickness 7cm was found to stop 75% of a gamma beam of energy 662keV. Meanwhile a brick of effective thickness 7cm was found to stop 60% of the same beam. The total attenuation coefficient of concrete calculated at 1333keV was 11.2m(-1), which is less than that of limestone and bricks. PMID:17368884

  4. Study of DCT coefficient distributions

    Microsoft Academic Search

    Stephen Smoot

    1996-01-01

    Many image and video compression schemes perform the discrete cosine transform (DCT) to represent image data in frequency space. An analysis of a broad suite of images confirms previous finding that a Laplacian distribution can be used to model the luminance AC coefficients. This model is expanded and applied to color space (Cr\\/Cb) coefficients. In MPEG, the DCT is used

  5. Modelling radiative mean absorption coefficients

    Microsoft Academic Search

    J.-F. Ripoll; B. Dubroca; G. Duffa

    2001-01-01

    We define and compute mean absorption coefficients for the macroscopic models of radiative transfer. These coefficients take into account the anisotropic form of the photon emission and lead to a better computation of a photonic flow far from the radiative equilibrium. They are deduced by averaging a specific radiative intensity on the space of frequency and are generalized versions of

  6. Ultrasonic Attenuation and Speed of Sound of Cornstarch Suspensions

    E-print Network

    Johnson, Benjamin L; Miller, James G; Katz, Jonathan I; 10.1121/1.4789926

    2013-01-01

    The goal of this study is to contribute to the physics underlying the material properties of suspensions that exhibit shear thickening through the ultrasonic characterization of suspensions of cornstarch in a density-matched solution. Ultrasonic measurements at frequencies in the range of 4 to 8 MHz of the speed of sound and the frequency-dependent attenuation properties are reported for concentrations of cornstarch in a density-matched aqueous (cesium chloride brine) suspension, ranging up to 40% cornstarch. The speed of sound is found to range from 1483 +/- 10 m/s in pure brine to 1765 +/- 9 m/s in the 40% cornstarch suspension. The bulk modulus of a granule of cornstarch is inferred to be (1.2 +/- 0.1) X 10^{10} Pa. The attenuation coefficient at 5 MHz increases from essentially zero in brine to 12.0 +/- 1.2 dB/cm at 40% cornstarch.

  7. Ultrasonic Attenuation and Speed of Sound of Cornstarch Suspensions

    E-print Network

    Benjamin L. Johnson; Mark R. Holland; James G. Miller; Jonathan I. Katz

    2013-03-20

    The goal of this study is to contribute to the physics underlying the material properties of suspensions that exhibit shear thickening through the ultrasonic characterization of suspensions of cornstarch in a density-matched solution. Ultrasonic measurements at frequencies in the range of 4 to 8 MHz of the speed of sound and the frequency-dependent attenuation properties are reported for concentrations of cornstarch in a density-matched aqueous (cesium chloride brine) suspension, ranging up to 40% cornstarch. The speed of sound is found to range from 1483 +/- 10 m/s in pure brine to 1765 +/- 9 m/s in the 40% cornstarch suspension. The bulk modulus of a granule of cornstarch is inferred to be (1.2 +/- 0.1) X 10^{10} Pa. The attenuation coefficient at 5 MHz increases from essentially zero in brine to 12.0 +/- 1.2 dB/cm at 40% cornstarch.

  8. Estimating contaminant attenuation half-lives in alluvial groundwater systems

    SciTech Connect

    Tardiff, Mark F.; Katzman, Danny

    2007-03-13

    One aspect of describing contamination in an alluvial aquifer is estimating changes in concentrations over time. A variety of statistical methods are available for assessing trends in contaminant concentrations. We present a method that extends trend analysis to include estimating the coefficients for the exponential decay equation and calculating contaminant attenuation half-lives. The conceptual model for this approach assumes that the rate of decline is proportional to the contaminant concentration in an aquifer. Consequently, the amount of time to remove a unit quantity of the contaminant inventory from an aquifer lengthens as the concentration decreases. Support for this conceptual model is demonstrated empirically with log-transformed time series of contaminant data. Equations are provided for calculating system attenuation half-lives for non-radioactive contaminants.

  9. SEISMIC ATTENUATION FOR RESERVOIR CHARACTERIZATION

    SciTech Connect

    Joel Walls; M.T. Taner; Naum Derzhi; Gary Mavko; Jack Dvorkin

    2003-04-01

    In this report we will show results of seismic and well log derived attenuation attributes from a deep water Gulf of Mexico data set. This data was contributed by Burlington Resources and Seitel Inc. The data consists of ten square kilometers of 3D seismic data and three well penetrations. We have computed anomalous seismic absorption attributes on the seismic data and have computed Q from the well log curves. The results show a good correlation between the anomalous absorption (attenuation) attributes and the presence of gas as indicated by well logs.

  10. Dicistronic LacZ and alkaline phosphatase reporter constructs permit simultaneous histological analysis of expression from multiple transgenes.

    PubMed

    Li, X; Wang, W; Lufkin, T

    1997-11-01

    We report here the development of convenient dicistronic transgenic markers for the rapid and efficient simultaneous analysis of transgene activity in transgenic mice. Two sensitive histological markers, the beta-galactosidase (beta-gal)-encoding lacZ gene and the human placental alkaline phosphatase (hpAP) gene, have been fused to the internal ribosome entry sequence (IRES) from the encephalomyocarditis virus, which directs efficient mRNA cap-independent entry of the translation apparatus in mammalian cells. The IRES permits efficient translation of either lacZ or hpAP when placed anywhere within transgene exonic sequences, including both 5' and 3' untranslated regions. In addition, the production of constructs for transgenic analysis of DNA regulatory elements is greatly facilitated with IRES-lacZ or IRES-hpAP, since the IRES relieves the need for complicated in frame transgene protein fusions to produce a functional beta-gal or hpAP protein. PMID:9383553

  11. Position of the lacZX90 mutation and hybridization between complete and incomplete beta-galactosidase.

    PubMed Central

    Mandecki, W; Fowler, A V; Zabin, I

    1981-01-01

    The position of the termination codon in lacZX90 was determined by isolation of a lac+ revertant. Lysine was found to replace tyrosine at position 1,012 of beta-galactosidase, indicating that X90 protein lacked the carboxyl-terminal 10 residues. A heat- and urea-sensitive hybrid enzyme was formed in vivo when supC, which supplies tyrosine to the position in the polypeptide corresponding to the nonsense codon, was used to suppress lacZX90. This result shows that suppression that adds back the original amino acid may not lead to the production of the wild-type enzyme if the latter is multimeric, because incomplete chains can be incorporated into the oligomer. PMID:6790520

  12. Intelligent Local Avoided Collision (iLAC) MAC Protocol for Very High Speed Wireless Network

    NASA Astrophysics Data System (ADS)

    Hieu, Dinh Chi; Masuda, Akeo; Rabarijaona, Verotiana Hanitriniala; Shimamoto, Shigeru

    Future wireless communication systems aim at very high data rates. As the medium access control (MAC) protocol plays the central role in determining the overall performance of the wireless system, designing a suitable MAC protocol is critical to fully exploit the benefit of high speed transmission that the physical layer (PHY) offers. In the latest 802.11n standard [2], the problem of long overhead has been addressed adequately but the issue of excessive colliding transmissions, especially in congested situation, remains untouched. The procedure of setting the backoff value is the heart of the 802.11 distributed coordination function (DCF) to avoid collision in which each station makes its own decision on how to avoid collision in the next transmission. However, collision avoidance is a problem that can not be solved by a single station. In this paper, we introduce a new MAC protocol called Intelligent Local Avoided Collision (iLAC) that redefines individual rationality in choosing the backoff counter value to avoid a colliding transmission. The distinguishing feature of iLAC is that it fundamentally changes this decision making process from collision avoidance to collaborative collision prevention. As a result, stations can avoid colliding transmissions with much greater precision. Analytical solution confirms the validity of this proposal and simulation results show that the proposed algorithm outperforms the conventional algorithms by a large margin.

  13. Singlet oxygen-induced mutations in M13 lacZ phage DNA.

    PubMed Central

    Decuyper-Debergh, D; Piette, J; Van de Vorst, A

    1987-01-01

    The mutagenic consequences of damages to M13 mp19 RF DNA produced by singlet oxygen have been determined in a forward mutational system capable of detecting all classes of mutagenic events. When the damaged M13 mp19 RF DNA is used to transfect competent E. coli JM105 cells, a 16.6-fold increase in mutation frequency is observed at 5% survivors when measured as a loss of alpha-complementation. The enhanced mutagenicity is largely due to single-nucleotide substitutions, frameshift events and double-mutations. The single-nucleotide substitutions occur in the regulatory and in the structural part of the lacZ gene under the predominant form of a G:C to T:A transversion. The spectrum of mutations detected among the M13 lacZ phages surviving the singlet oxygen treatment is totally different from those appearing spontaneously. SOS induction mediated through u.v.-irradiation of bacteria leads to an increase of the mutation frequency in the M13 surviving to the singlet oxygen treatment. The mutation spectrum in this case is a mixture between those observed with the spontaneous mutants and the mutants induced by singlet oxygen. Lesions introduced in the M13 mp19 RF DNA can be partly repaired by the enzymatic machinery of the bacteria. It turns out that excision-repair and SOS repair are probably involved in the removal of these lesions by singlet oxygen. PMID:3121306

  14. In vitro transcription accurately predicts lac repressor phenotype in vivo in Escherichia coli

    PubMed Central

    2014-01-01

    A multitude of studies have looked at the in vivo and in vitro behavior of the lac repressor binding to DNA and effector molecules in order to study transcriptional repression, however these studies are not always reconcilable. Here we use in vitro transcription to directly mimic the in vivo system in order to build a self consistent set of experiments to directly compare in vivo and in vitro genetic repression. A thermodynamic model of the lac repressor binding to operator DNA and effector is used to link DNA occupancy to either normalized in vitro mRNA product or normalized in vivo fluorescence of a regulated gene, YFP. An accurate measurement of repressor, DNA and effector concentrations were made both in vivo and in vitro allowing for direct modeling of the entire thermodynamic equilibrium. In vivo repression profiles are accurately predicted from the given in vitro parameters when molecular crowding is considered. Interestingly, our measured repressor–operator DNA affinity differs significantly from previous in vitro measurements. The literature values are unable to replicate in vivo binding data. We therefore conclude that the repressor-DNA affinity is much weaker than previously thought. This finding would suggest that in vitro techniques that are specifically designed to mimic the in vivo process may be necessary to replicate the native system. PMID:25097824

  15. Veritas Observations of Relativistic Outflows in - and Intermediate-Frequency BL Lac Objects

    NASA Astrophysics Data System (ADS)

    Prokoph, Heike

    2014-03-01

    The majority of blazars detected at very high energies (VHE; E > 100 GeV) are high-frequency-peaked BL Lac objects (HBLs). Low- and intermediate-frequency-peaked BL Lacs (LBLs/IBLs with synchrotron-peak frequencies in the infrared and optical regime) are generally more powerful, more luminous, and have a richer jet environment than HBLs. However, only a handful of these IBL and LBLs have been detected by ground-based gamma-ray telescopes, typically during high-flux states. The VERITAS array has been monitoring five known VHE LBLs/IBLs since 2009: 3C 66A, W Comae, PKS 1424+240, S5 0716+714 and BL Lacertae, with typical exposures of 5-10 hours per year. The results of these long-term observations are presented, including a bright, subhour-scale VHE flare of BL Lacertae in June 2011, the first low-state detections of 3C 66A and W Comae, and the detection and characterization of the IBL B2 1215+30.

  16. Systemic RNAi Delivery to the Muscles of ROSA26 Mice Reduces lacZ Expression

    PubMed Central

    Wei, Jessica; Chamberlain, Joel R.

    2014-01-01

    RNAi has potential for therapeutically downregulating the expression of dominantly inherited genes in a variety of human genetic disorders. Here we used the ROSA26 mouse, which constitutively expresses the bacterial lacZ gene in tissues body wide, as a model to test the ability to downregulate gene expression in striated muscles. Recombinant adeno-associated viral vectors (rAAVs) were generated that express short hairpin RNAs (shRNAs) able to target the lacZ mRNA. Systemic delivery of these rAAV6 vectors led to a decrease of ?-galactosidase expression of 30–50-fold in the striated muscles of ROSA26 mice. However, high doses of vectors expressing 21 nucleotide shRNA sequences were associated with significant toxicity in both liver and cardiac muscle. This toxicity was reduced in cardiac muscle using lower vector doses. Furthermore, improved knockdown in the absence of toxicity was obtained by using a shorter (19 nucleotide) shRNA guide sequence. These results support the possibility of using rAAV vectors to deliver RNAi sequences systemically to treat dominantly inherited disorders of striated muscle. PMID:25127128

  17. ISO observations of the BL Lac object PKS 2155-304

    E-print Network

    E. Bertone; G. Tagliaferri; G. Ghisellini; A. Treves; L. Chiappetti; L. Maraschi

    1999-08-06

    The Infrared Space Observatory (ISO) observed the BL Lac object PKS 2155-304 16 times from 1996, May 7 to June 8, with both the ISOCAM camera and the ISOPHOT photometer, as part of a more general multiwavelength campaign. Two additional observations were performed on 1996, November 23 and 1997, May 15. This is the first time that there are simultaneous mid and far infrared data in a multiwavelength monitoring of a BL Lac object. We obtained four light curves at 4.0, 14.3, 60 and 90 microns, and a broad-band filter spectrum from 2.8 to 170 micron. No variability was detected in the infrared, although the source was varying at shorter wavelengths. The IR spectrum can be fitted by a single power law with an energy spectral index alfa = 0.40 +/- 0.06 and it can be explained as due to synchrotron emission only, with no noticeable contributions from thermal sources. Using the simultaneous data, we constructed the SED of PKS 2155-304.

  18. Arabinose-induction of lac-derived promoter systems for penicillin acylase production in Escherichia coli.

    PubMed

    Narayanan, Niju; Hsieh, Ming-Yi; Xu, Yali; Chou, C Perry

    2006-01-01

    Arabinose was shown to serve as an effective inducer for induction of the lac-derived promoters in Escherichia coli using penicillin acylase (PAC) as a model protein. Upon the induction with a conventional inducer, isopropyl-beta-d-thiogalactopyranoside (IPTG), for pac overexpression, which is regulated by the trc or (DE3)/T7 promoter, the production of PAC was limited by the accumulation of PAC precursors (proPAC) as inclusion bodies. Negative cellular responses, such as growth inhibition and cell lysis, were frequently observed, resulting in a low pac expression level and poor culture performance. Interestingly, these technical hurdles can be overcome simply through the use of arabinose as an inducer. The results indicate that arabinose not only induced the lac-derived promoter systems (i.e., trc and (DE3)/T7) for pac (or LL pac) overexpression but also facilitated the posttranslational processing of proPAC for maturation. However, the arabinose-inducibility appears to be host-dependent and becomes less observable in the strains with a mutation in the ara operon. The arabinose-inducibility was also investigated in the expression system with the coexistence of the trc promoter system regulating pac expression and another arabinose-inducible promoter system of araB regulating degP coexpression. PMID:16739941

  19. Stability of RNA Virus Attenuation Approaches

    PubMed Central

    Kenney, Joan L.; Volk, Sara M.; Pandya, Jyotsna; Wang, Eryu; Liang, Xiaodong; Weaver, Scott C.

    2011-01-01

    The greatest risk from live-attenuated vaccines is reversion to virulence. Particular concerns arise for RNA viruses, which exhibit high mutation frequencies. We examined the stability of 3 attenuation strategies for the alphavirus, Venezuelan equine encephalitis virus (VEEV): a traditional, point mutation-dependent attenuation approach exemplified by TC-83; a rationally designed, targeted-mutation approach represented by V3526; and a chimeric vaccine, SIN/TC/ZPC. Our findings suggest that the chimeric strain combines the initial attenuation of TC-83 with the greater phenotypic stability of V3526, highlighting the importance of the both initial attenuation and stability for live-attenuated vaccines. PMID:21288800

  20. Laboratory investigations of low frequency sound attenuation over combustion flat perforated wall sheet

    E-print Network

    Boyer, Edmond

    layer MPPs have also been developed [5, 6, 7, 10] to broaden the sound absorption band. AlthoughLaboratory investigations of low frequency sound attenuation over combustion flat perforated wall geometric parameters. The results from the measured absorption coefficient and impedance show that the steel

  1. Effects of shock-induced cracks on the ultrasonic velocity and attenuation in granite

    Microsoft Academic Search

    Huirong A. Ai; Thomas J. Ahrens

    2007-01-01

    (1) Measurements of the compressional wave velocity and the attenuation coefficients of 1-cm cubes were conducted. Samples were taken at various radii and depths beneath a 20 ? 20 ? 15 cm San Marcos granite block, impacted by a lead bullet at a velocity of 1200 m\\/s. The damage parameters of the cubes are calculated from the measured preimpact and

  2. Investigating Attenuation, Scattering Phase Center, and Total Height Using Simulated Interferometric SAR Images of Forested Areas

    Microsoft Academic Search

    Laetitia Thirion-Lefevre; Elise Colin-Koeniguer

    2007-01-01

    The objective of this paper is to examine the link between the attenuation coefficients and the interferometric phase center heights, for several frequencies from P- to L-band, and to study the extent to which it depends on the canopy architecture and description. This paper relies on the use of a coherent and full polarimetric scattering model, which simulates the fields

  3. Effects of shock-induced cracks on the ultrasonic velocity and attenuation in granite

    Microsoft Academic Search

    Huirong A. Ai; Thomas J. Ahrens

    2007-01-01

    Measurements of the compressional wave velocity and the attenuation coefficients of 1-cm cubes were conducted. Samples were taken at various radii and depths beneath a 20 × 20 × 15 cm San Marcos granite block, impacted by a lead bullet at a velocity of 1200 m\\/s. The damage parameters of the cubes are calculated from the measured preimpact and postimpact

  4. Evaluation of Water Amount in Hydrated Ethanol Fuel by Gamma-ray Attenuation Technique

    Microsoft Academic Search

    José M. de Oliveira Jr; I´talo C. O. Silva; Bruno R. Malaquias; Antonio C. G. Martins

    2011-01-01

    In this work, is presented an alternative and non conventional technique for evaluate the water amount present in the hydrated ethanol used as automotive fuel. The standard technique used in this kind of measure is the use of densimeter. The proposal of this work is based on the measure of the linear attenuation coefficient of hydrated ethanol, using the gamma-ray

  5. The feasibility of ranking material fracture toughness by ultrasonic attenuation measurements

    NASA Technical Reports Server (NTRS)

    Vary, A.

    1975-01-01

    A preliminary study was conducted to assess the feasibility of ultrasonically ranking material fracture toughness. Specimens of two grades of maraging steel for which fracture toughness values were measured were subjected to ultrasonic probing. The slope of the attenuation coefficient vs frequency curve was empirically correlated with the plane strain fracture toughness value for each grade of steel.

  6. A New Approach for Detecting Attenuation Changes During High-Intensity Focused

    E-print Network

    Illinois at Urbana-Champaign, University of

    resulting from heating. To date, parametric images of attenuation coefficient from backscattered ultrasound to thermal damage [2]. Furthermore, knowledge of acoustic absorption is required to accurately predict heat have been associated with acoustic cavitation [3], which can make controlling HIFU difficult. Current

  7. The feasibility of ranking material fracture toughness by ultrasonic attenuation measurements

    NASA Technical Reports Server (NTRS)

    Vary, A.

    1975-01-01

    A preliminary study was conducted to assess the feasibility of ultrasonically ranking material fracture toughness. Specimens of two grades of maraging steel for which fracture toughness values were measured were subjected to ultrasonic probing. The slope of the attenuation coefficient versus frequency curve was empirically correlated with the plane strain fracture toughness value for each grade of steel.

  8. Database and software for the analysis of mutations at the lacZ locus in transgenic rodents.

    PubMed

    Cariello, N F; Douglas, G R

    1996-01-01

    The use of transgenic rodents is becoming increasingly widespread in genetic toxicology. In an effort to centralize and standardize the information regarding mutations in rodents bearing the lacZ transgene, we have created a computerized database that contains published information about DNA sequence alterations on over 100 mutants. Information on the literature citation, mutagenic conditions, organs from specific animals, mutation frequency in each organ, specific mutation, amino acid change, and other data are provided for each mutant. We have also produced a software package for the analysis of the lacZ database. Routines have been developed for the analysis of single base substitutions, including programs to 1) determine whether two mutational spectra are statistically different, 2) determine whether mutations show a DNA strand bias, 3) determine the frequency of transitions and transversions, 4) display the number and kind of mutations observed at each base in the coding region, 5) perform nearest-neighbor analysis, and 6) display mutable amino acids in the lacZ protein. The software runs only on IBM-compatible machines running Microsoft Windows. The software and lacZ database are freely available via the Internet (http:@sunsite.unc.edu/dnam/mainpage.ht ml). These programs simplify the analysis of the rapidly increasing information about lacZ mutation. The programs permit the facile comparison between different lacZ data sets as well as the identification of mutational patterns that may be of importance to experimenters studying the mechanisms of mutation and mutational spectra in transgenic animals. PMID:8844996

  9. GB6 J1058+5628: A NEW QUASI-PERIODIC BL LAC OBJECT FROM THE ASIAGO PLATE ARCHIVE

    SciTech Connect

    Nesci, R., E-mail: roberto.nesci@uniroma1.i [Physics Department, University of Roma La Sapienza, Piazzale A. Moro 2, I-00185 Roma (Italy)

    2010-06-15

    We present the historic photographic light curves of three little known blazars (two BL Lac objects and one FSRQ), GB6 J1058+5628, GB6 J1148+5254, and GB6 J1209+4119, spanning a time interval of about 50 years, mostly built using the Asiago plate archive. All objects show evident long-term variability, over which short-term variations are superposed. One source, GB6 J1058+5628, showed a marked quasi-periodic variability of 1 mag on timescale of about 6.3 years, making it one of the few BL Lac objects with a quasi-periodic behavior.

  10. A KPC-scale X-ray jet in the BL LAC Source S5 2007+777

    NASA Technical Reports Server (NTRS)

    Sambruna, Rita; Maraschi, Laura; Tavecchio, Fabrizio

    2008-01-01

    The BL Lac S3 2007++777, a classical radio-selected BL Lac from the sample of Stirkel et al. exhibiting an extended (19") radio jet. was observed with Chandra revealing an X-ray jet with simi1ar morphology. The hard X-ray spectrum and broad band SED is consistent with an IC/CMB origin for the X-ray emission, implying a highly relativistic flow at small angle to the line of sight with an unusually large deprojected length, 300 kpc. A structured jet consisting of a fast spine and slow wall is consistent with the observations.

  11. MASTER serendipitous observations of the gamma-ray flaring BL Lac CGRaBS J0211+1051

    NASA Astrophysics Data System (ADS)

    Kudelina, I.; Gorbovskoy, E.; Balanutsa, P.; Lipunov, V.; Kornilov, V.; Belinski, A.; Shatskiy, N.; Tyurina, N.; Kuvshinov, D.; Chazov, V.; Kuznetsov, A.; Zimnukhov, D.; Kornilov, M.; Tlatov, A.; Parhomenko, A. V.; Dormidontov, D.; Yurkov, V.; Sergienko, Yu.; Varda, D.; Krushinski, V.; Zalozhnih, I.; Popov, A.; Ivanov, K.; Yazev, S.; Budnev, N.; Konstantinov, E.; Chuvalaev, O.; Poleschuk, V.; Gres, O.; Shumkov, V.; Shurpakov, S.

    2011-01-01

    Following the gamma-ray flare of the BL Lac object CGRaBS J0211+1051 (also known as MG1 J021114+1051, and 1FGL J0211.2+1049, Abdo et al. 2010, ApJS, 188, 405) detected by Fermi LAT on 2011 January 23 (ATel #3120), we try to find images of the BL Lac in our DATA BASE. We find 16 serendipitous optical unfiltered observations by MASTER-Net sites from 03 feb 2004 to 26 Jan 2011. In all cases we use the same Apogee CCD on the wide field telescopes.

  12. SEISMIC ATTENUATION FOR RESERVOIR CHARACTERIZATION

    SciTech Connect

    Joel Walls; M.T. Taner; Gary Mavko; Jack Dvorkin

    2002-07-01

    In fully-saturated rock and at ultrasonic frequencies, the microscopic squirt flow induced between the stiff and soft parts of the pore space by an elastic wave is responsible for velocity-frequency dispersion and attenuation. In the seismic frequency range, it is the macroscopic cross-flow between the stiffer and softer parts of the rock. We use the latter hypothesis to introduce simple approximate equations for velocity-frequency dispersion and attenuation in a fully water saturated reservoir. The equations are based on the assumption that in heterogeneous rock and at a very low frequency, the effective elastic modulus of the fully-saturated rock can be estimated by applying a fluid substitution procedure to the averaged (upscaled) dry frame whose effective porosity is the mean porosity and the effective elastic modulus is the Backus-average (geometric mean) of the individual dry-frame elastic moduli of parts of the rock. At a higher frequency, the effective elastic modulus of the saturated rock is the Backus-average of the individual fully-saturated-rock elastic moduli of parts of the rock. The difference between the effective elastic modulus calculated separately by these two methods determines the velocity-frequency dispersion. The corresponding attenuation is calculated from this dispersion by using (e.g.) the standard linear solid attenuation model.

  13. Fused fiber optic variable attenuator

    Microsoft Academic Search

    Val Morozov; Haining Fan; Louay Eldada; Long Yang; Yuan Shi

    2000-01-01

    We demonstrate a fused fiber optic variable attenuator with a polymer sub-cladding layer. It exhibits a wide dynamic range of 1.5-45 dB, relatively flat wavelength response, and high thermal sensitivity of up to 3 dB\\/°C

  14. Multidimensional Hadron Attenuation Gevorg Karyan

    E-print Network

    Multidimensional Hadron Attenuation Gevorg Karyan A. I. Alikhanyan National Science Laboratory, Yerevan, Armenia E-mail: gevkar@mail.desy.de Hadron multiplicity ratios in semi-inclusive deep-) and protons(p, ¯p) as a function of the virtual photon energy , its virtuality Q2, the fractional hadron

  15. ML radio frequency attenuating connector

    Microsoft Academic Search

    M. G. Prewett

    1982-01-01

    In the increasingly harsh radio frequency environment associated with modern aerospace and missile systems, it is essential that safety standards are maintained or improved where electrically initiated explosive devices are involved. The Radio Frequency Attenuating Connector (RFAC) effectively protects igniters from electromagnetic interference both in hand held and installed modes. The RFAC provides a highly reliable pinless connector interface utilizing

  16. Modification of atmospheric extinction coefficient of non-line-of-sight ultraviolet communication under weak turbulence

    NASA Astrophysics Data System (ADS)

    Li, Bifeng; Wang, Hongxing; Wu, Xiaojun; Song, Bo; Hu, Hao

    2015-03-01

    A calculation method of scintillation attenuation (SA) for non-line-of-sight (NLOS) ultraviolet (UV) communication is proposed on the basis of weak turbulence theory. To improve the channel model under turbulent environment, the atmospheric extinction coefficient in combination with UV single-scatter approximation model is modified based on SA. The in-depth analysis and interesting conclusion of atmospheric extinction coefficient named the turbulence coefficient versus different factors, including refractive-index structure parameter at the ground with measurement data, transceiver range and transceiver apex angles, are conducted.

  17. Colloque ECLIPSE II, 15 et 16 octobre 2007, CNRS Paris 1 Culture du millet et rosion des sols depuis l'Age du Bronze autour du Lac

    E-print Network

    Paris-Sud XI, Université de

    depuis l'Age du Bronze autour du Lac du Bourget : Apport des lipides sédimentaires au projet APHRODYTE Néolithique au Moyen Age. L'analyse des lipides préservés dans les sédiments du Lac du Bourget révèle la'Âge du Bronze est caractérisé par de fortes concentrations en miliacine, traduisant la culture intensive

  18. Anisotropy of magnetic susceptibility versus lattice-and shape-preferred orientation in the Lac Tio hemo-ilmenite ore body

    E-print Network

    Bascou, Jérôme

    Keywords: Magnetic fabric EBSD Image analysis Iron­titanium ore Anorthosite The Lac Tio hemo-ilmenite ore body crops out in the outer portion of the 1.06 Ga Lac Allard anorthosite, a member of the Havre-Saint-Pierre anorthosite suite from the Grenville province of North America. It is made up of ilmenitite (commonly

  19. LacZ transgenic mice and immunoelectron microscopy: an ultrastructural method for dual localization of beta-galactosidase and horseradish peroxidase.

    PubMed

    St John, Patricia L; Abrahamson, Dale R

    2007-12-01

    Transgenic animals bearing the reporter gene, LacZ, encoding the histochemical enzyme, beta-galactosidase, are increasingly becoming available. Similarly, antibody conjugates consisting of specific IgGs coupled to horseradish peroxidase (HRP) are widely used for Western blotting, ELISA, and immunohistochemistry. Here we provide a detailed fixation and histochemical protocol for the simultaneous electron microscopic visualization and discrimination of beta-galactosidase and peroxidase reaction products within mouse kidney. After incubation of transgenic LacZ tissues with IgG-HRP conjugates, samples were lightly fixed with 2% paraformaldehyde and 0.4% glutaraldehyde and processed for peroxidase histochemistry. Tissues underwent beta-galactosidase histochemistry, were refixed with glutaraldehyde, osmicated, and embedded. In Flk1/LacZ mice, we immunolocalized anti-laminin beta1 chain IgG-HRP specifically to developing glomerular basement membranes, whereas Flk1/LacZ was expressed only by glomerular endothelial cells. In Epas1/LacZ mice, we immunolocalized anti-platelet endothelial cell adhesion molecule-1 specifically to glomerular endothelial plasma membranes, whereas Epas1/LacZ was expressed by both glomerular endothelial and mesangial cells. This dual ultrastructural localization technique should be broadly applicable for immunoelectron microscopic studies in LacZ transgenic animals, particularly those where LacZ expression and antibody-HRP binding are both relatively abundant. PMID:17827164

  20. Study on laser and infrared attenuation performance of carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Liu, Xiang-cui; Liu, Qing-hai; Dai, Meng-yan; Cheng, Xiang; Fang, Guo-feng; Zhang, Tong; Liu, Haifeng

    2014-11-01

    In recent years, the weapon systems of laser and infrared (IR) imaging guidance have been widely used in modern warfare because of their high precision and strong anti-interference. However, military smoke, a rapid and effective passive jamming method, can effectively counteract the attack of precision-guided weapons by their scattering and absorbing effects. The traditional smoke has good visible light (0.4-0.76?m) obscurant performance, but hardly any effects to other electromagnetic wave bands while the weapon systems of laser and IR imaging guidance usually work in broad band, including the near-infrared (1-3?m), middle-infrared (3-5?m), far-infrared (8-14?m), and so on. Accordingly, exploiting new effective obscurant materials has attracted tremendous interest worldwide nowadays. As is known, the nano-structured materials have lots of unique properties comparing with the traditional materials suggesting that they might be the perfect alternatives to solve the problems above. Carbon nanotubes (CNTs) are well-ordered, all-carbon hollow graphitic nano-structured materials with a high aspect ratio, lengths from several hundred nanometers to several millimeters. CNTs possess many unique intrinsic physical-chemical properties and are investigated in many areas reported by the previous studies. However, no application research about CNTs in smoke technology field is reported yet. In this paper, the attenuation performances of CNTs smoke to laser and IR were assessed in 20m3 smoke chamber. The testing wavebands employed in experiments are 1.06?m and 10.6?m laser, 3-5?m and 8-14?m IR radiation. The main parameters were obtained included the attenuation rate, transmission rate, mass extinction coefficient, etc. The experimental results suggest that CNTs smoke exhibits excellent attenuation ability to the broadband IR radiation. Their mass extinction coefficients are all above 1m2·g-1. Nevertheless, the mass extinction coefficients vary with the sampling time and smoke particles concentrations, even in the same testing waveband. With the time going the mass extinction coefficients will increase gradually. Based on the above results, theoretical calculations are also carried out for further exploitations. In general, CNTs smoke behaves excellent attenuation ability toward laser and IR under the experimental conditions. Therefore, they have great potentials to develop new smoke obscurant materials which could effectively interfere with broadband IR radiation including 1.06?m, 10.6?m, 3-5?m and 8-12?m IR waveband.

  1. Generation of attenuation map for MR-based attenuation correction of PET data in the head area employing 3D short echo time MR imaging

    NASA Astrophysics Data System (ADS)

    Khateri, Parisa; Salighe Rad, Hamidreza; Fathi, Anahita; Ay, Mohammad Reza

    2013-02-01

    Attenuation correction is a crucial step to get accurate quantification of Positron Emission Tomography (PET) data. An attenuation map to provide attenuation coefficients at 511 keV can be generated using Magnetic Resonance Images (MRI). One of the main steps involved in MR-based attenuation correction (MRAC) of PET data is to separate bone from air. Low signal intensity of bone in conventional MRI makes it difficult to separate bone from air in the head area, while their attenuation coefficients are very different. In literature, several groups proposed ultrashort echo-time (UTE) sequences to differentiate bone from air [4,5,7], because these sequences are capable of imaging tissues with short T2* relaxation time, such as cortical bone; however, they are difficult to use, expensive and time-consuming. Employing short echo-time (STE) MRI in combination with long echo-time (LTE) MRI, and along with high performance image processing algorithms is a good substitute for UTE-based PET attenuation correction; they are widely available, easy to use, inexpensive and much faster than UTE pulse sequences. In this work, we propose the use of STE sequences along with LTE ones, as well as a dedicated image processing method to differentiate bone from air cavities in the head area by creating contrast between the tissues. Attenuation coefficients at 511 kev, relying on literature [5], will then be assigned to the voxels. Acquisition was performed on a clinical 3T Tim Trio scanner (Siemens Medical Solution, Erlangen, Germany), employing a dual echo sequence. To achieve an optimized protocol with the best result for discrimination of bone and air, two types of acquisitions were performed, with and without fat suppression; the acquisition parameters were as follows: TE=1.21/5 ms, TR=5/17, FA=30, and TE=1.12/3.16 ms, TR=5/5, FA=12 for non-fat-suppressed and fat-suppressed protocol, respectively. Contrast enhancement and tissue segmentation were applied as processing steps, to successfully classify voxels into bone, air and soft tissue classes, yielding accuracy, sensitivity and specificity of 88%, 77% and 94%, for non-fat suppressed acquisition, respectively. This method could potentially be as an efficient method for generation of attenuation map in 511 keV for MR-based attenuation correction of PET data in clinical PET/MR applications with mixed air and bone signals.

  2. Neutron attenuation characteristics of polyethylene, polyvinyl chloride, and heavy aggregate concrete and mortars.

    PubMed

    Abdul-Majid, S; Othman, F

    1994-03-01

    Polyethylene and polyvinyl chloride pellets were introduced into concrete to improve its neutron attenuation characteristics while several types of heavy coarse aggregates were used to improve its gamma ray attenuation properties. Neutron and gamma ray attenuation were studied in concrete samples containing coarse aggregates of barite, pyrite, basalt, hematite, and marble as well as polyethylene and polyvinyl chloride pellets in narrow-beam geometry. The highest neutron attenuation was shown by polyethylene mortar, followed by polyvinyl chloride mortar; barite and pyrite concrete showed higher gamma ray attenuation than ordinary concrete. Broad-beam and continuous (infinite) medium geometries were used to study the neutron attenuation of samples containing polymers at different concentrations with and without heavy aggregates, the fitting equations were established, and from these the neutron removal coefficients were deduced. In a radiation field of neutrons and gamma rays, the appropriate concentration of polymer and heavy aggregate can be selected to give the optimum total dose attenuation depending on the relative intensities of each type of radiation. This would give much better design flexibility over ordinary concrete. The compressive strength tests performed on mortar and concrete samples showed that their value, in general, decreases as polymer concentration increases and that the polyvinyl chloride mortar showed higher values than the polyethylene mortar. For general construction purposes, the compression strength was considered acceptable in these samples. PMID:8106253

  3. Neutron attenuation characteristics of polyethylene, polyvinyl chloride, and heavy aggregate concrete and mortars

    SciTech Connect

    Abdul-Majid, S.; Othman, F. [King Abdulaziz Univ., Jeddah (Saudi Arabia)

    1994-03-01

    Polyethylene and polyvinyl chloride pellets were introduced into concrete to improve its neutron attenuation characteristics while several types of heavy coarse aggregates were used to improve its gamma ray attenuation properties. Neutron and gamma ray attenuation were studied in concrete samples containing coarse aggregates of barite, pyrite, basalt, hematite, and marble as well as polyethylene and polyvinyl chloride pellets in narrow-beam geometry. The highest neutron attenuation was shown by polyethylene mortar, followed by polyvinyl chloride mortar; barite and pyrite concrete showed higher gamma ray attenuation than ordinary concrete. Broad-beam and continuous (infinite) medium geometries were used to study the neutron attenuation of samples containing polymers at different concentrations with and without heavy aggregates, the fitting equations were established, and from these the neutron removal coefficients were deduced. In a radiation field of neutrons and gamma rays, the appropriate concentration of polymer and heavy aggregate can be selected to give the optimum total dose attenuation depending on the relative intensities of each type of radiation. This would give much better design flexibility over ordinary concrete. The compressive strength tests performed on mortar and concrete samples showed that their value, in general, decreases as polymer concentration increases and that the polyvinyl chloride mortar showed higher values than the polyethylene mortar. For general construction purposes, the compression strength was considered acceptable in these samples. 34 refs., 16 figs., 4 tabs.

  4. Calculations of radar backscattering coefficient of vegetation-covered soils

    NASA Technical Reports Server (NTRS)

    Mo, T.; Schmugge, T. J.; Jackson, T. J. (principal investigators)

    1983-01-01

    A model for simulating the measured backscattering coefficient of vegetation-covered soil surfaces includes both coherent and incoherent components of the backscattered radar pulses from a rough sil surface. The effect of vegetation canopy scattering is also incorporated into the model by making the radar pulse subject to two-way attenuation and volume scattering when it passes through the vegetation layer. Model results agree well with the measured angular distributions of the radar backscattering coefficient for HH polarization at the 1.6 GHz and 4.75 GHz frequencies over grass-covered fields. It was found that the coherent scattering component is very important at angles near nadir, while the vegetation volume scattering is dominant at incident angles 30 degrees.

  5. A set of lacZ mutations in Escherichia coli that allow rapid detection of each of the six base substitutions

    SciTech Connect

    Cupples, C.G.; Miller, J.H.

    1989-07-01

    We describe the construction of six strains of Escherichia coli with different mutations at the same coding position in the lacZ gene, which specifies the active site glutamic acid residue at position 461 in beta'-galactosidase. Each strain is Lac- and reverts to Lac+ only by restoring the glutamic acid codon. The strains have been designed so that each reverts via one of the six base substitutions. The set of strains allows detection of each transition and transversion simply by monitoring the Lac- to Lac+ frequency, as demonstrated here with characterized mutagens and mutator alleles. These strains are useful for rapidly determining the mutagenic specificity of mutagens at a single site, for detecting low levels of stimulation of certain base substitutions, for monitoring specific base changes in response to various experimental conditions or strain backgrounds, and for isolating new mutator strains.

  6. The Seebeck coefficient of iodine

    E-print Network

    Perez-Fernandez, Domingo Miguel

    1968-01-01

    THE SEEBECK COEFFICIENT OF IODINE A Thesis By DOMINGO M. PEREZ-F~EZ Submitted to the Graduate College of the Texas A&M University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE January 1968 Major Subject...; Physics THE SEEBECK COEFFICIENT OF IODINE A Thesis By DOMINGO M. PEREZ-FERNANDEZ Approved as to style and content by: ( airman of Co ittee) (Member) (Head of Depa ment) (Member) ( ember) (Member) (Member) January 1968 ACKNONLEDGEMENTS...

  7. Recombination coefficients for iron ions

    NASA Technical Reports Server (NTRS)

    Woods, D. T.; Shull, J. M.; Sarazin, C. L.

    1981-01-01

    Radiative recombination coefficients for all Fe ions are calculated by use of the Milne relation of detailed balance. Analytic fits are made to the dielectronic recombination rates computed by Jacobs (1977) and the Burgess general formula (1965). Higher level rates are treated hydrogenically by a quantum defect method based on the energies of the levels. Recombination coefficients for Fe I to Fe 26 are listed.

  8. ENHANCEMENTS TO NATURAL ATTENUATION: SELECTED CASE STUDIES

    SciTech Connect

    Vangelas, K; W. H. Albright, W; E. S. Becvar, E; C. H. Benson, C; T. O. Early, T; E. Hood, E; P. M. Jardine, P; M. Lorah, M; E. Majche, E; D. Major, D; W. J. Waugh, W; G. Wein, G; O. R. West, O

    2007-05-15

    In 2003 the US Department of Energy (DOE) embarked on a project to explore an innovative approach to remediation of subsurface contaminant plumes that focused on introducing mechanisms for augmenting natural attenuation to achieve site closure. Termed enhanced attenuation (EA), this approach has drawn its inspiration from the concept of monitored natural attenuation (MNA).

  9. Gamma-ray attenuation in the vicinity of the K edge in molybdenum, tin, lanthanum, gadolinium, tungsten, lead, and uranium

    Microsoft Academic Search

    Y. Harima; D. K. Trubey; Y. Sakomoto; S. Tanaka

    1991-01-01

    This paper reports on the values of gamma-ray buildup factors and attenuation coefficients that rise steeply as the source energy decreases near the K edge in heavy materials and discontinuously fall at the K edge. However, the exposure rate attenuation factor, A(E,r) = D(E)B(E,μr), given as a function of the penetration depth in centimeters, is relatively constant in the vicinity

  10. Converting Sabine absorption coefficients to random incidence absorption coefficients.

    PubMed

    Jeong, Cheol-Ho

    2013-06-01

    Absorption coefficients measured by the chamber method are referred to as Sabine absorption coefficients, which sometimes exceed unity due to the finite size of a sample and non-uniform intensity in the reverberation chambers under test. In this study, conversion methods from Sabine absorption coefficients to random incidence absorption coefficients are proposed. The overestimations of the Sabine absorption coefficient are investigated theoretically based on Miki's model for porous absorbers backed by a rigid wall or an air cavity, resulting in conversion factors. Additionally, three optimizations are suggested: An optimization method for the surface impedances for locally reacting absorbers, the flow resistivity for extendedly reacting absorbers, and the flow resistance for fabrics. With four porous type absorbers, the conversion methods are validated. For absorbers backed by a rigid wall, the surface impedance optimization produces the best results, while the flow resistivity optimization also yields reasonable results. The flow resistivity and flow resistance optimization for extendedly reacting absorbers are also found to be successful. However, the theoretical conversion factors based on Miki's model do not guarantee reliable estimations, particularly at frequencies below 250 Hz and beyond 2500?Hz. PMID:23742349

  11. A method for estimating radiation interaction coefficients for tissues from single energy CT

    NASA Astrophysics Data System (ADS)

    Midgley, S. M.

    2014-12-01

    A parametric model for the x-ray linear attenuation coefficient is used to describe the compositional dependence of Hounsfield numbers measured by medical CT scanners. Measurements with materials of known density and composition, that span and evenly sample the compositional range of tissues, are written as linear simultaneous equations and solved for model coefficients. An algorithm is identified for this purpose. Results are expressed as atomic cross-sections in units of barn per electron divided by the attenuation coefficient for water. With the CT scanner characterised, a virtual CT scan can be simulated to predict HN for tissues based upon their known density and composition. Similar calculations using the tabulations and mixture rule deliver attenuation coefficients and mass energy absorption coefficients for mono-energetic radiation 10 keV to 20 MeV. Results are presented for measurements with a radiotherapy CT simulator, the RMI-467 phantom with tissue substitute materials, plus common polymer materials and silicon. Published measurements with earlier generations of the phantom and tissue substitutes using different CT scanners are also considered. Measured atomic cross-sections differ from expectations for mono-energetic radiation due to the use of a filtered spectrum and energy integrating detection system. The cross-sections for different CT scanners are similar, without large variations with kVp. Results are presented showing the relationship between predicted HN for tissues, electron density and photon interaction coefficients for healthy tissues and mono-energetic radiation. A strategy is suggested for accommodating strongly attenuating materials such as calculi and metallic implants.

  12. A method for estimating radiation interaction coefficients for tissues from single energy CT.

    PubMed

    Midgley, S M

    2014-12-01

    A parametric model for the x-ray linear attenuation coefficient is used to describe the compositional dependence of Hounsfield numbers measured by medical CT scanners. Measurements with materials of known density and composition, that span and evenly sample the compositional range of tissues, are written as linear simultaneous equations and solved for model coefficients. An algorithm is identified for this purpose. Results are expressed as atomic cross-sections in units of barn per electron divided by the attenuation coefficient for water. With the CT scanner characterised, a virtual CT scan can be simulated to predict HN for tissues based upon their known density and composition. Similar calculations using the tabulations and mixture rule deliver attenuation coefficients and mass energy absorption coefficients for mono-energetic radiation 10 keV to 20 MeV. Results are presented for measurements with a radiotherapy CT simulator, the RMI-467 phantom with tissue substitute materials, plus common polymer materials and silicon. Published measurements with earlier generations of the phantom and tissue substitutes using different CT scanners are also considered. Measured atomic cross-sections differ from expectations for mono-energetic radiation due to the use of a filtered spectrum and energy integrating detection system. The cross-sections for different CT scanners are similar, without large variations with kVp. Results are presented showing the relationship between predicted HN for tissues, electron density and photon interaction coefficients for healthy tissues and mono-energetic radiation. A strategy is suggested for accommodating strongly attenuating materials such as calculi and metallic implants. PMID:25393760

  13. Terahertz atmospheric attenuation and continuum effects

    NASA Astrophysics Data System (ADS)

    Slocum, David M.; Goyette, Thomas M.; Slingerland, Elizabeth J.; Giles, Robert H.; Nixon, William E.

    2013-05-01

    Remote sensing over long path lengths has become of greater interest in the terahertz frequency region. Applications such as pollution monitoring and detection of energetic chemicals are of particular interest. Although there has been much attention to atmospheric effects over narrow frequency windows, accurate measurements across a wide spectrum is lacking. The water vapor continuum absorption spectrum was investigated using Fourier Transform Spectroscopy. The continuum effect gives rise to an excess absorption that is unaccounted for in just a resonant line spectrum simulation. The transmission of broadband terahertz radiation from 0.300THz - 1.5THz through air with varying relative humidity levels was recorded for multiple path lengths. From these data, the absorption coefficient as a function of frequency was determined and compared with model calculations. The intensity and location of the strong absorption lines were in good agreement with spectral databases such as the 2008 HITRAN database and the JPL database. However, a noticeable continuum effect was observed particularly in the atmospheric transmission windows. A small discrepancy still remained even after accounting for continuum absorption using the best available data from the literature. This discrepancy, when projected over a one kilometer path length, typical of distances used in remote sensing, can cause a 30dB difference between calculated and observed attenuation. From the experimental and resonant line simulation spectra the air-broadening continuum parameter was calculated and compared with values available in the literature.

  14. Accuracy of CT-based attenuation correction in PET/CT bone imaging

    NASA Astrophysics Data System (ADS)

    Abella, Monica; Alessio, Adam M.; Mankoff, David A.; MacDonald, Lawrence R.; Vaquero, Juan Jose; Desco, Manuel; Kinahan, Paul E.

    2012-05-01

    We evaluate the accuracy of scaling CT images for attenuation correction of PET data measured for bone. While the standard tri-linear approach has been well tested for soft tissues, the impact of CT-based attenuation correction on the accuracy of tracer uptake in bone has not been reported in detail. We measured the accuracy of attenuation coefficients of bovine femur segments and patient data using a tri-linear method applied to CT images obtained at different kVp settings. Attenuation values at 511 keV obtained with a 68Ga/68Ge transmission scan were used as a reference standard. The impact of inaccurate attenuation images on PET standardized uptake values (SUVs) was then evaluated using simulated emission images and emission images from five patients with elevated levels of FDG uptake in bone at disease sites. The CT-based linear attenuation images of the bovine femur segments underestimated the true values by 2.9 ± 0.3% for cancellous bone regardless of kVp. For compact bone the underestimation ranged from 1.3% at 140 kVp to 14.1% at 80 kVp. In the patient scans at 140 kVp the underestimation was approximately 2% averaged over all bony regions. The sensitivity analysis indicated that errors in PET SUVs in bone are approximately proportional to errors in the estimated attenuation coefficients for the same regions. The variability in SUV bias also increased approximately linearly with the error in linear attenuation coefficients. These results suggest that bias in bone uptake SUVs of PET tracers ranges from 2.4% to 5.9% when using CT scans at 140 and 120 kVp for attenuation correction. Lower kVp scans have the potential for considerably more error in dense bone. This bias is present in any PET tracer with bone uptake but may be clinically insignificant for many imaging tasks. However, errors from CT-based attenuation correction methods should be carefully evaluated if quantitation of tracer uptake in bone is important.

  15. AUTOMATIC CREATION OF A GENETIC NETWORK FOR THE lac OPERON FROM OBSERVED DATA BY MEANS OF GENETIC PROGRAMMING

    E-print Network

    Fernandez, Thomas

    to automatically create (reverse engineer) a computer program representing the logic underlying the genetic network "reverse engineer" the logic underlying a genetic network. This reverse engineering entails creating bothAUTOMATIC CREATION OF A GENETIC NETWORK FOR THE lac OPERON FROM OBSERVED DATA BY MEANS OF GENETIC

  16. Phylogenetic, structural and functional analyses of the LacI-GalR family of bacterial transcription factors

    Microsoft Academic Search

    Chuck Chuong Nguyen; Milton H. Saier

    1995-01-01

    Phylogenetic tree construction for 25 sequenced members of the LacI-GalR family (LGF) of transcription factors revealed that almost all branches are similar in length, radiating essentially from a single point. This observation suggests that most of these proteins arose by duplication events which occurred at a specific time in evolutionary history, and that further duplication events were rare. Analyses of

  17. In vivo localization of DNA sequences and visualization of large-scale chromatin organization using lac operator/repressor recognition

    PubMed Central

    1996-01-01

    We report a new method for in situ localization of DNA sequences that allows excellent preservation of nuclear and chromosomal ultrastructure and direct, in vivo observations. 256 direct repeats of the lac operator were added to vector constructs used for transfection and served as a tag for labeling by lac repressor. This system was first characterized by visualization of chromosome homogeneously staining regions (HSRs) produced by gene amplification using a dihydrofolate reductase (DHFR) expression vector with methotrexate selection. Using electron microscopy, most HSRs showed approximately 100-nm fibers, as described previously for the bulk, large-scale chromatin organization in these cells, and by light microscopy, distinct, large-scale chromatin fibers could be traced in vivo up to 5 microns in length. Subsequent experiments demonstrated the potential for more general applications of this labeling technology. Single and multiple copies of the integrated vector could be detected in living CHO cells before gene amplification, and detection of a single 256 lac operator repeat and its stability during mitosis was demonstrated by its targeted insertion into budding yeast cells by homologous recombination. In both CHO cells and yeast, use of the green fluorescent protein-lac repressor protein allowed extended, in vivo observations of the operator-tagged chromosomal DNA. Future applications of this technology should facilitate structural, functional, and genetic analysis of chromatin organization, chromosome dynamics, and nuclear architecture. PMID:8991083

  18. Sliding and target location of DNA-binding proteins: an NMR view of the lac repressor system.

    PubMed

    Loth, Karine; Gnida, Manuel; Romanuka, Julija; Kaptein, Robert; Boelens, Rolf

    2013-05-01

    In non-specific lac headpiece-DNA complexes selective NMR line broadening is observed that strongly depends on length and composition of the DNA fragments. This broadening involves amide protons found in the non-specific lac-DNA structure to be interacting with the DNA phosphate backbone, and can be ascribed to DNA sliding of the protein along the DNA. This NMR exchange broadening has been used to estimate the 1D diffusion constant for sliding along non-specific DNA. The observed 1D diffusion constant of 4×10(-12) cm(2)/s is two orders of magnitude smaller than derived from previous kinetic experiments, but falls in the range of values determined more recently using single molecule methods. This strongly supports the notion that sliding could play at most a minor role in the association kinetics of binding of lac repressor to lac operator and that other processes such as hopping and intersegment transfer contribute to facilitate the DNA recognition process. PMID:23568265

  19. Host acceptance tests of parasitoids from Indian Paratachardina lobata on the invasive lobate lac scale in Florida

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The invasive lobate lac scale identified as Paratachardina lobata (Hemiptera: Keriidae), native to southern India and Sri Lanka, is a severe threat to native and economic plants in southern Florida. Four parasitoid species, from southern India associated with Paratachardina lobata, were tested in qu...

  20. Structure-Based Rational Design to Enhance the Solubility and Thermostability of a Bacterial Laccase Lac15

    PubMed Central

    Fang, Zemin; Zhou, Peng; Chang, Fei; Yin, Qiang; Fang, Wei; Yuan, Jing; Zhang, Xuecheng; Xiao, Yazhong

    2014-01-01

    Bacterial laccases are ideal alternatives of fungal laccases for specific industrial applications due to specific characteristics such as alkalescence dependence and high chloride tolerance. However, some bacterial laccases presented as inclusion bodies when expressing in Escherichia coli and showed thermal instability. In this study, rational design was employed to enhance the solubility and the thermostablity of the bacterial laccase Lac15-His6 based on the crystal structure obtained previously. After deletion of His-tag and residues323–332, the obtained Lac15D was completely expressed in soluble form even at a higher temperature of 28°C, compared to only 50% of Lac15-His6 expressed solubly at 16°C. It showed a two-time higher activity at temperatures lower than 35°C and a half-life increasing from 72 min to 150 min at 45°C. When used in chromogenic reactions, Lac15D showed constant activity toward dye precursors and their combinations under alkaline conditions, demonstrating its application potential in hair coloring biotechnology. PMID:25036001

  1. Fibronectin-binding proteins are required for biofilm formation by community-associated methicillin-resistant Staphylococcus aureus strain LAC.

    PubMed

    McCourt, Jennifer; O'Halloran, Dara P; McCarthy, Hannah; O'Gara, James P; Geoghegan, Joan A

    2014-04-01

    Community-associated methicillin-resistant Staphylococcus aureus of the USA300 lineage is emerging as an important cause of medical device-related infection. However, few factors required for biofilm accumulation by USA300 strains have been identified, and the processes involved are poorly understood. Here, we identify S. aureus proteins required for the USA300 isolate LAC to form biofilm. A mutant with a deletion of the fnbA and fnbB genes did not express the fibronectin-binding proteins FnBPA and FnBPB and lacked the ability to adhere to fibronectin or to form biofilm. Biofilm formation by the mutant LAC?fnbAfnbB could be restored by expression of FnBPA or FnBPB from a plasmid demonstrating that both of these proteins can mediate biofilm formation when expressed by LAC. Expression of FnBPA and FnBPB increased bacterial aggregation suggesting that fibronectin-binding proteins can promote the accumulation phase of biofilm. Loss of fibronectin-binding proteins reduced the initial adherence of bacteria, indicating that these proteins are also involved in primary attachment. In summary, these findings improve our understanding of biofilm formation by the USA300 strain LAC by demonstrating that the fibronectin-binding proteins are required. PMID:24628034

  2. 78 FR 45556 - Notice of Intent to Prepare an Environmental Impact Statement for the Proposed Lac du Flambeau...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-07-29

    ...Acquisition and Casino Project in Shullsburg, Wisconsin AGENCY: Bureau of Indian Affairs, Interior...casino project in the City of Shullsburg, Wisconsin, proposed by the Lac du Flambeau Band...444 N. Judgement Street, Shullsburg, Wisconsin. You may mail, hand deliver, or...

  3. Institutions and Incentives for R&D: Implications for L.A.C. Economies Walter G. Park,

    E-print Network

    Lansky, Joshua

    in LAC. Strong conclusions are hard to draw given the limitations with the theory and empirical evidence an efficiency point of view. A greater balanceis needed between public and private R&D. Thus, an R&D matching is the issue of what influences R&D activities. Is it market structure, market size, resources, institutions

  4. The variability and periods in the BL Lac AO 0235+164

    NASA Astrophysics Data System (ADS)

    Fan, J. H.; Kurtanidze, O.; Liu, X.; Liu, Y.; Wang, H. T.; Yuan, Y. H.; Hao, J. M.; Wu, D. X.; Cai, W.; Xiao, H. B.; Pei, Z. Y.

    2015-03-01

    Variability is one of the extreme observational properties of BL Lacertae objects. AO 0235+164 is a well studied BL Lac through the whole electro-magnetic wavebands, it is violently variable in the optical bands. In the present work, we show its optical R band photometric observations carried out during the period of Nov. 2006 to Dec. 2012 using the Ap6E CCD camera attached to the primary focus of the 70 cm meniscus telescope at Abastumani Observatory, Georgia. It shows a large variation of ?R = 4.88 mag (14.20 - 19.08 mag) during our monitoring period. When periodicity analysis methods are adopted to its R observations from our Abastumani monitoring programme and those in the literature, the signs of some periods, P 1 = 8.26 yr, P 2 = 0.55 yr, P 3 = 0.85 yr, P 4 = 1.99 yr are found.

  5. Spatial Diagnostics of Potential X-ray Remnants in Old Novae T Aur and DK Lac

    NASA Astrophysics Data System (ADS)

    Drake, Jeremy

    2013-09-01

    We propose 5 and 3 ks ACIS-S snapshots of potentially extended X-ray remnants of two old classical novae, T Aur and DK Lac. They are the likely counterparts of X-ray sources discovered in our Swift survey of old classical novae, and each target has a spatially-resolved optical remnant with a size of order arcseconds. The additional short Chandra snapshots will confirm or reject the tentative Swift identifications through pinpoint astrometry, and will distinguish between extended remnant emission or rejuvenated accretion. Both are important for understanding binary evolution and also potential post-outburst hibernation, while detection of extended emission will represent extremely rare additions to the exclusive club of X-ray emitting classical nova remnants.

  6. Gene fusions with lacZ by duplication insertion in the radioresistant bacterium Deinococcus radiodurans

    SciTech Connect

    Lennon, E.; Minton, K.W. (Uniformed Services Univ. of the Health Sciences, Bethesda, MD (USA))

    1990-06-01

    Deinococcus radiodurans is the most-studied species of a eubacterial family characterized by extreme resistance to DNA damage. We have focused on developing molecular biological techniques to investigate the genetics of this organism. We report construction of lacZ gene fusions by a method involving both in vitro splicing and the natural transformation of D. radiodurans. Numerous fusion strains were identified by expression of beta-galactosidase. Among these fusion strains, several were inducible by exposure to the DNA-damaging agent mitomycin C, and four of the inducible fusion constructs were cloned in Escherichia coli. Hybridization studies indicate that one of the damage-inducible genes contains a sequence reiterated throughout the D. radiodurans chromosome. Survival measurements show that two of the fusion strains have increased sensitivity to mitomycin C, suggesting that the fusions within these strains inactivate repair functions.

  7. Multiwavelength Observations of 6 BL Lac Objects in 2008-2012

    NASA Astrophysics Data System (ADS)

    Morozova, D. A.; Jorstad, S. G.; Marscher, A. P.; Larionov, V. M.; Troitskiy, I. S.; Blinov, D. A.; Agudo, I.; Smith, P. S.

    2013-12-01

    We present results of 4 years of VLBA monitoring along with ?-ray and optical R-band photometric observations of 6 BL Lac objects (3C 66A, S5 0716+71, PKS 0735+17, S4 0954+68, W Com, and OT 081). We have analyzed total intensity images obtained with the VLBA at 43 GHz and investigated the kinematic evolution of the parsec scale jets of the sources. For all sources we compare flux variations in the VLBI core and bright superluminal knots with ?-ray and optical light curves. The majority of ?-ray flares have optical counterparts. 67% of the ?-ray events are coincident with the appearance of new superluminal knots and/or flares in the millimeter-wave core. These results support the conclusion that for many flares in blazars the region of the ?-ray and optical emission is located in the vicinity or downstream of the mm-wave VLBI core.

  8. Local elastic constants of LacI and implications for allostery.

    PubMed

    Ribeiro, Andre A S T; Ortiz, Vanessa

    2015-04-01

    Allostery connects subtle changes in a protein's potential energy surface, induced by perturbations like ligand-binding, to significant changes in its function. Understanding this phenomenon and predicting its occurrence are major goals of current research in biophysics and molecular biology. In this paper we introduce a novel approach for studying complex structural transformations such as those typical for allostery. We show that the calculation and analysis of atomic elastic constants of a known allosterically regulated protein, lac repressor, highlights regions that are particularly prone to suffer structural deformation and are experimentally linked to allosteric function. The calculations are based on a high resolution, all-atom description of the protein. We also show that, for the present system, modifying the description of the system from an all-atom forcefield to an elastic network model yields qualitatively different results, indicating the importance of adequately describing the local environment surrounding the different parts of the protein. PMID:25700189

  9. Analysis of Optical Variations of BL Lac Object AO 0235+164

    NASA Astrophysics Data System (ADS)

    Hong-tao, Wang

    2014-03-01

    Historical optical BVRI band data are combined on the BL Lac object AO 0235 + 164. In order to examine the possible existence of lags and correlations between variations in different optical bands from this source, a statistical analysis is performed through the Discrete Correlation Function (DCF) method. Monte Carlo simulations called Flux Redistribution/Random Subset Selection (FR/RSS) are performed to obtain statistically meaningful values for the cross-correlation time lags and their related uncertainties. The analysis confirms that the variations in different optical light curves are strongly correlated, with no or very weak lag within the errors. Long term variability of color indices are also analysed. No color variabilities are found.

  10. Targeting of lacZ reporter gene expression with radioiodine-labelled phenylethyl-beta- d-thiogalactopyranoside.

    PubMed

    Lee, Kyung-Han; Byun, Sang Sung; Choi, Joon Hun; Paik, Jin-Young; Choe, Yearn Seong; Kim, Byung-Tae

    2004-03-01

    There has recently been increasing interest in the development of radioprobes that specifically target proteins transcribed from expression of reporter genes of interest. The purpose of this study was to develop a radioprobe that targets one of the most widely used reporter genes, the bacterial lacZ gene. We synthesised and purified radioiodine-labelled phenylethyl-beta- d-thiogalactopyranoside (PETG), a competitive inhibitor specific against Escherichia coli beta-galactosidase. We showed that [(125)I]iodo-PETG specifically binds to beta-galactosidase as verified by column chromatography and polyacrylamide gel electrophoresis after incubation of radiotracer with the protein. We also showed through enzyme kinetic studies that iodo-PETG retains inhibitory action against beta-galactosidase activity. COS-7 cells infected with a recombinant adenovirus expressing the lacZ gene had viral titre-dependent enhancements in [(125)I]iodo-PETG uptake ( r(2)=0.897; P=0.001), which reached up to 642.5%+/-16.7% of control levels ( P<0.00001). Moreover, the level of uptake was highly correlated to luminescent measurements of beta-galactosidase activity ( r(2)=0.878; P<0.0001). These results confirm that radioiodine-labelled PETG specifically targets beta-galactosidase and that its uptake rates faithfully reflect levels of expression of the lacZ reporter gene. Further investigations were performed in nude mice bearing human neuroblastoma tumours transferred with the lacZ gene. Compared with control tumours, lacZ-expressing tumours were slightly better visualised on [(123)I]iodo-PETG images and had a modest increase in tumour to muscle count ratio (2.6+/-0.2 vs 1.9+/-0.1, P<0.05). The present results provide proof-of-principle for the potential of radiolabelled inhibitors as promising radiotracers to monitor lacZ gene expression levels. Future modifications to improve cell permeability should enhance in vivo contrast levels and may allow the use of radiolabelled beta-galactosidase inhibitors for non-invasive monitoring of lacZ gene expression. PMID:14745516

  11. SEISMIC ATTENUATION FOR RESERVOIR CHARACTERIZATION

    SciTech Connect

    Joel Walls; M.T. Taner; Gary Mavko; Jack Dvorkin

    2002-01-01

    In Section 1 of this first report we will describe the work we are doing to collect and analyze rock physics data for the purpose of modeling seismic attenuation from other measurable quantities such as porosity, water saturation, clay content and net stress. This work and other empirical methods to be presented later, will form the basis for ''Q pseudo-well modeling'' that is a key part of this project. In Section 2 of this report, we will show the fundamentals of a new method to extract Q, dispersion, and attenuation from field seismic data. The method is called Gabor-Morlet time-frequency decomposition. This technique has a number of advantages including greater stability and better time resolution than spectral ratio methods.

  12. Ultrasound fields in attenuating media.

    PubMed

    Lerch, R; Friedrich, W

    1986-10-01

    For medical ultrasonic imaging and for nondestructive testing, the attenuation of pressure waves and the resulting shift in wave velocity are important features in commonly used transmission media such as biological tissue. An algorithm for the numerical evaluation of pressure field distributions generated by ultrasonic transducers is presented. The attenuation and dispersion of the sound transmission medium are taken into consideration. The sound fields are computed numerically for continuous wave as well as pulse excitation. The transducer has plane or gently curved geometry and is embedded in a plane rigid baffle. The numerically determined pressure fields are presented as 3D plots, as gray-scale images for a fixed time stamp (like a snapshot), or as isobars regarding the maximum values over time for each local point in the area under investigation. The algorithm described here can be utilized as a tool for design of ultrasound transducers, especially array antennas. PMID:3771930

  13. Resonant ultrasonic attenuation in emulsions

    NASA Astrophysics Data System (ADS)

    Brunet, Thomas; Mascaro, Benoit; Poncelet, Olivier; Aristégui, Christophe; Raffy, Simon; Mondain-Monval, Olivier; Leng, Jacques

    2013-08-01

    We report the achievement of scattering resonant emulsions devoted to the frequency-control of acoustic attenuation in the megahertz range. By means of robotics, we produced highly monodisperse, in both size and shape, fluorinated-oil droplet suspensions, providing experimental evidence of several Mie scattering resonances. Ultrasonic experiments performed in such complex media are compared, with an excellent quantitative agreement, to theoretical predictions derived within the framework of the independent scattering approximation.

  14. Optical observations of BL Lac object ON 231 (W Comae) during 2010 March-April

    NASA Astrophysics Data System (ADS)

    Cheng, Xin-Lun; Zhang, You-Hong; Xu, Lei

    2013-03-01

    This paper presents optical BVRI photometry of the intermediate-energy-peaked BL Lac object ON 231 (W Comae). It was observed for five nights during 2010 March-April with the 80-cm Tsinghua-NAOC Telescope (TNT). Although no extremely large variations were seen on either intra- or internight time-scales, a flare-like event was recorded on March 17. On a time-scale of ˜5 h, the source exhibited a change of ˜0.15 mag in the B band and variations of ˜0.1 mag in V, R and I bands. On either intra- or internight time-scales, the variability amplitudes appear to be larger for shorter wavelengths. Cross-correlation analysis suggests that the R-band variations lagged the B-band ones by ˜1200 s on March 17. To our best knowledge, this is the first time that a time lag has been claimed for the optical variability of ON 231. Bluer-when-brighter trends were present for all intranight variations. On the plot of B - R colour indices against B magnitudes, however, the correlations between the two parameters shifted vertically relative to each other on different nights, indicating that the source slightly changed its optical spectral slope from night to night. The averaged spectral energy distributions of each night are similar, perhaps the consequence of low-amplitude variability during our observational season. The intranight optical variations of ON 231, along with those of other similar sources, e.g. BL Lacertae and S5 0716+714, are quite similar to those of high-energy-peaked BL Lac objects. Both can be ascribed to synchrotron emission produced by the most energetic relativistic electrons residing in the magnetized relativistic jet roughly aligned with our line of sight.

  15. A hadronic origin for ultra-high-frequency-peaked BL Lac objects

    NASA Astrophysics Data System (ADS)

    Cerruti, M.; Zech, A.; Boisson, C.; Inoue, S.

    2015-03-01

    Current Cherenkov telescopes have identified a population of ultra-high-frequency peaked BL Lac objects (UHBLs), also known as extreme blazars, that exhibit exceptionally hard TeV spectra, including 1ES 0229+200, 1ES 0347-121, RGB J0710+591, 1ES 1101-232, and 1ES 1218+304. Although one-zone synchrotron-self-Compton (SSC) models have been generally successful in interpreting the high-energy emission observed in other BL Lac objects, they are problematic for UHBLs, necessitating very large Doppler factors and/or extremely high minimum Lorentz factors of the emitting leptonic population. In this context, we have investigated alternative scenarios where hadronic emission processes are important, using a newly developed (lepto-)hadronic numerical code to systematically explore the physical parameters of the emission region that reproduces the observed spectra while avoiding the extreme values encountered in pure SSC models. Assuming a fixed Doppler factor ? = 30, two principal parameter regimes are identified, where the high-energy emission is due to: (1) proton-synchrotron radiation, with magnetic fields B ˜ 1-100 G and maximum proton energies Ep; max ? 1019 eV; and (2) synchrotron emission from p-?-induced cascades as well as SSC emission from primary leptons, with B ˜ 0.1-1 G and Ep; max ? 1017 eV. This can be realized with plausible, sub-Eddington values for the total (kinetic plus magnetic) power of the emitting plasma, in contrast to hadronic interpretations for other blazar classes that often warrant highly super-Eddington values.

  16. LacZ ?-galactosidase: Structure and function of an enzyme of historical and molecular biological importance

    PubMed Central

    Juers, Douglas H; Matthews, Brian W; Huber, Reuben E

    2012-01-01

    This review provides an overview of the structure, function, and catalytic mechanism of lacZ ?-galactosidase. The protein played a central role in Jacob and Monod's development of the operon model for the regulation of gene expression. Determination of the crystal structure made it possible to understand why deletion of certain residues toward the amino-terminus not only caused the full enzyme tetramer to dissociate into dimers but also abolished activity. It was also possible to rationalize ?-complementation, in which addition to the inactive dimers of peptides containing the “missing” N-terminal residues restored catalytic activity. The enzyme is well known to signal its presence by hydrolyzing X-gal to produce a blue product. That this reaction takes place in crystals of the protein confirms that the X-ray structure represents an active conformation. Individual tetramers of ?-galactosidase have been measured to catalyze 38,500 ± 900 reactions per minute. Extensive kinetic, biochemical, mutagenic, and crystallographic analyses have made it possible to develop a presumed mechanism of action. Substrate initially binds near the top of the active site but then moves deeper for reaction. The first catalytic step (called galactosylation) is a nucleophilic displacement by Glu537 to form a covalent bond with galactose. This is initiated by proton donation by Glu461. The second displacement (degalactosylation) by water or an acceptor is initiated by proton abstraction by Glu461. Both of these displacements occur via planar oxocarbenium ion-like transition states. The acceptor reaction with glucose is important for the formation of allolactose, the natural inducer of the lac operon. PMID:23011886

  17. Questions about using of atmospheric attenuation calculating the nominal ocular hazard distance

    NASA Astrophysics Data System (ADS)

    Gustafsson, K. Ove S.

    2013-10-01

    The distance where risk for injuries or damage of an eye, when laser irradiance level exceeded the Maximum Permissible Exposure (MPE), is equal to the Nominal Ocular Hazard Distance (NOHD). The common way calculating the NOHD abandons the use of atmospheric attenuation as a lowering the laser safety ranges in the civil society. The NOHD for a typical designator laser (using e.g. Nd:YAG laser) with small divergence can be several tens of kilometers. One way handling those risk distances, which might be too long for ordinary firing ranges or embargoed areas, are probabilistic calculations of danger and including the atmospheric attenuation. For such long laser beam path the atmospheric transmission attenuation will be significant. The suppression of the risk distance can be substantial even for moderate extinctions coefficient if the atmospheric attenuation is included within the calculations of Ocular Hazard Distance (OHD). NOHD is compared to the OHD in a attempt to get an impression of the reduction of the distance as function of visibility or the extinction coefficient. A simple simulation shows that OHD might be reduced by 60% - 70% compared to NOHD at a visibility of 50 km. The contribution also discusses the use of Lambert W function compared to other methods accounting for atmospheric attenuation in laser safety range calculations.

  18. GPR data noise attenuation on the curvelet transform

    NASA Astrophysics Data System (ADS)

    Bao, Qian-Zong; Li, Qing-Chun; Chen, Wen-Chao

    2014-09-01

    Signal extraction is critical in GRP data processing and noise attenuation. When the target depth is shallow, its reflection echo signal will overlap with the background noise, affecting the detection of arrival time and localization of the target. Thus, we propose a noise attenuation method based on the curvelet transform. First, the original signal is transformed into the curvelet domain, and then the curvelet coefficients of the background noise are extracted according to the distribution features that differ from the effective signal. In the curvelet domain, the coarse-scale curvelet atom is isotropic. Hence, a two-dimensional directional filter is designed to estimate the high-energy background noise in the coarsescale domain, and then, attenuate the background noise and highlight the effective signal. In this process, we also use a subscale threshold value of the curvelet domain to filter out random noise. Finally, we compare the proposed method with the average elimination and 2D continuous wavelet transform methods. The results show that the proposed method not only removes the background noise but also eliminates the coherent interference and random noise. The numerical simulation and the real data application suggest and verify the feasibility and effectiveness of the proposed method.

  19. Underwater optical wireless communications: depth dependent variations in attenuation.

    PubMed

    Johnson, Laura J; Green, Roger J; Leeson, Mark S

    2013-11-20

    Depth variations in the attenuation coefficient for light in the ocean were calculated using a one-parameter model based on the chlorophyll-a concentration C(c) and experimentally-determined Gaussian chlorophyll-depth profiles. The depth profiles were related to surface chlorophyll levels for the range 0-4??mg/m², representing clear, open ocean. The depth where C(c) became negligible was calculated to be shallower for places of high surface chlorophyll; 111.5 m for surface chlorophyll 0.8attenuation for underwater ocean communication links, calculated to be 0.0092??m?¹ at a wavelength of 430 nm. By combining this with satellite surface-chlorophyll data, it is possible to quantify the attenuation between any two locations in the ocean, with applications for low-noise or secure underwater communications and vertical links from the ocean surface. PMID:24513735

  20. Methods of Attenuation Correction for Dual-Wavelength and Dual-Polarization Weather Radar Data

    NASA Technical Reports Server (NTRS)

    Meneghini, R.; Liao, L.

    2007-01-01

    In writing the integral equations for the median mass diameter and number concentration, or comparable parameters of the raindrop size distribution, it is apparent that the forms of the equations for dual-polarization and dual-wavelength radar data are identical when attenuation effects are included. The differential backscattering and extinction coefficients appear in both sets of equations: for the dual-polarization equations, the differences are taken with respect to polarization at a fixed frequency while for the dual-wavelength equations, the differences are taken with respect to frequency at a fixed polarization. An alternative to the integral equation formulation is that based on the k-Z (attenuation coefficient-radar reflectivity factor) parameterization. This-technique was originally developed for attenuating single-wavelength radars, a variation of which has been applied to the TRMM Precipitation Radar data (PR). Extensions of this method have also been applied to dual-polarization data. In fact, it is not difficult to show that nearly identical equations are applicable as well to dualwavelength radar data. In this case, the equations for median mass diameter and number concentration take the form of coupled, but non-integral equations. Differences between this and the integral equation formulation are a consequence of the different ways in which attenuation correction is performed under the two formulations. For both techniques, the equations can be solved either forward from the radar outward or backward from the final range gate toward the radar. Although the forward-going solutions tend to be unstable as the attenuation out to the range of interest becomes large in some sense, an independent estimate of path attenuation is not required. This is analogous to the case of an attenuating single-wavelength radar where the forward solution to the Hitschfeld-Bordan equation becomes unstable as the attenuation increases. To circumvent this problem, the equations can be expressed in the form of a final-value problem so that the recursion begins at the far range gate and proceeds inward towards the radar. Solving the problem in this way traditionally requires estimates of path attenuation to the final gate: in the case of orthogonal linear polarizations, the attenuations at horizontal and vertical polarizations (same frequency) are required while in the dual-wavelength case, attenuations at the two frequencies (same polarization) are required.

  1. Relationship between Ultrasonic Attenuation, Size and Axial Strain Parameters for ex-vivo Atherosclerotic Carotid Plaque

    PubMed Central

    Shi, Hairong; Varghese, T.; Dempsey, R.J.; Salamat, M.S.; Zagzebski, J.A.

    2008-01-01

    Many ultrasonic parameters, primarily related to attenuation and scatterer size, have been used to characterize the composition of atherosclerotic plaque tissue. In this study we combine elastographic (axial strain ratio) and ultrasonic tissue characterization parameters, namely the attenuation coefficient and a scattering parameter associated with an “equivalent” scatterer size to delineate between fibrous, calcified, and lipidic plaque tissue. We present results obtained from 44 ex-vivo atherosclerotic plaque specimens obtained after carotid endarterectomy on human patients. Our results in the frequency range 2.5~7.5MHz indicate that softer plaques (with higher values of the strain ratio) are usually associated with larger equivalent scatterer size estimates (200 ~500 µm) and lower values of the attenuation coefficient slope (<1 dB/cm/MHz). On the other hand, stiffer plaques (with lower strain ratio values) are associated with smaller equivalent scatterer size estimates (100 ~200 µm) and higher values of the attenuation coefficient slope (1~3 dB/cm/MHz). These results indicate that ultrasonic tissue characterization and strain parameters have the potential to differentiate between different plaque types. These parameters can also be estimated from radiofrequency data acquired under in-vivo conditions and may help the clinician decide on appropriate interventional techniques. PMID:18490099

  2. Relationship between ultrasonic attenuation, size and axial strain parameters for ex vivo atherosclerotic carotid plaque.

    PubMed

    Shi, Hairong; Varghese, Tomy; Dempsey, Robert J; Salamat, Mohammed S; Zagzebski, James A

    2008-10-01

    Many ultrasonic parameters, primarily related to attenuation and scatterer size, have been used to characterize the composition of atherosclerotic plaque tissue. In this study, we combine elastographic (axial strain ratio) and ultrasonic tissue characterization parameters, namely the attenuation coefficient and a scattering parameter associated with an "equivalent" scatterer size to delineate between fibrous, calcified, and lipidic plaque tissue. We present results obtained from 44 ex vivo atherosclerotic plaque specimens obtained after carotid endarterectomy on human patients. Our results in the frequency range 2.5 - 7.5 MHz indicate that softer plaques (with higher values of the strain ratio) are usually associated with larger equivalent scatterer size estimates (200 - 500 microm) and lower values of the attenuation coefficient slope (<1 dB/cm/MHz). On the other hand, stiffer plaques (with lower strain ratio values) are associated with smaller equivalent scatterer size estimates (100 - 200 microm) and higher values of the attenuation coefficient slope (1 - 3 dB/cm/MHz). These results indicate that ultrasonic tissue characterization and strain parameters have the potential to differentiate between different plaque types. These parameters can be estimated from radio-frequency data acquired under in vivo conditions and may help the clinician decide on appropriate interventional techniques. PMID:18490099

  3. Assessment of natural radioactivity and mass attenuation coefficients of brick and roofing tile used in Turkey

    Microsoft Academic Search

    N. Damla; U. Cevik; A. I. Kobya; A. Celik; N. Celik; I. Y?ld?r?m

    2011-01-01

    In this study the distribution of natural radionuclides (226Ra, 232Th, 40K) in brick and roofing tile samples commonly used as building materials in Turkey was measured by using gamma spectrometry. The activity concentrations, radium equivalent activities (Raeq), representative level index, indoor absorbed dose rate in air values and annual effective dose due to the intake of the above-mentioned radionuclides in

  4. Radiation dose estimation and mass attenuation coefficients of cement samples used in Turkey

    Microsoft Academic Search

    N. Damla; U. Cevik; A. I. Kobya; A. Celik; N. Celik; R. Van Grieken

    2010-01-01

    Different cement samples commonly used in building construction in Turkey have been analyzed for natural radioactivity using gamma-ray spectrometry. The mean activity concentrations observed in the cement samples were 52, 40 and 324Bqkg?1 for 226Ra, 232Th and 40K, respectively. The measured activity concentrations for these radionuclides were compared with the reported data of other countries and world average limits. The

  5. Determination of power-law attenuation coefficient and dispersion spectra in multi-wall carbon nanotube

    E-print Network

    Gladden, Josh

    for a set of multi-wall carbon nanotube MWCNT -nylon composites from pure nylon to 20% MWCNT by weight the mechanical strength and stiffness or other physical properties e.g., electrical and thermal conductance have about 50 times the tensile strength of stainless steel 100 GPa vs 2 GPa and five times the thermal

  6. Assessment of satellite derived diffuse attenuation coefficients and euphotic depths in south Florida coastal waters

    EPA Science Inventory

    Optical data collected in coastal waters off South Florida and in the Caribbean Sea between January 2009 and December 2010 were used to evaluate products derived with three bio-optical inversion algorithms applied to MOIDS/Aqua, MODIS/Terra, and SeaWiFS satellite observations. Th...

  7. Characterizing the vertical diffuse attenuation coefficient for downwelling irradiance in coastal waters: Implications for water

    E-print Network

    Rundquist, Donald C.

    waters: Implications for water penetration by high resolution satellite data Deepak R. Mishra a,, Sunil body comes from a surface layer of water of depth 1/Kd, the results showed that a typical satellite sensor (such as IKONOS) can penetrate up to 8 m in the blue band, 6 m in green, and 2 m in the red region

  8. Seebeck coefficient of one electron

    SciTech Connect

    Durrani, Zahid A. K., E-mail: z.durrani@imperial.ac.uk [Department of Electrical and Electronic Engineering, Imperial College London, South Kensington Campus, London SW7 2AZ (United Kingdom)

    2014-03-07

    The Seebeck coefficient of one electron, driven thermally into a semiconductor single-electron box, is investigated theoretically. With a finite temperature difference ?T between the source and charging island, a single electron can charge the island in equilibrium, directly generating a Seebeck effect. Seebeck coefficients for small and finite ?T are calculated and a thermally driven Coulomb staircase is predicted. Single-electron Seebeck oscillations occur with increasing ?T, as one electron at a time charges the box. A method is proposed for experimental verification of these effects.

  9. Lactosylated Gramicidin-based lipid nanoparticles (Lac-GLN) for targeted delivery of anti-miR-155 to hepatocellular carcinoma

    PubMed Central

    Zhang, Mengzi; Zhou, Xiaoju; Wang, Bo; Yung, Bryant C.; Lee, Ly J.; Ghoshal, Kalpana; Lee, Robert J.

    2013-01-01

    Lactosylated gramicidin-containing lipid nanoparticles (Lac-GLN) were developed for delivery of anti-microRNA-155 (anti-miR-155) to hepatocellular carcinoma (HCC) cells. MiR-155 is an oncomiR frequently elevated in HCC. The Lac-GLN formulation contained N-lactobionyl-dioleoyl phosphatidylethanolamine (Lac-DOPE), a ligand for the asialoglycoprotein receptor (ASGR), and an antibiotic peptide gramicidin A. The nanoparticles exhibited a mean particle diameter of 73 nm, zeta potential of +3.5 mV, anti-miR encapsulation efficiency of 88%, and excellent colloidal stability at 4°C. Lac-GLN effectively delivered anti-miR-155 to HCC cells with a 16.1- and 4.1-fold up-regulation of miR-155 targets C/EBP? and FOXP3 genes, respectively, and exhibited significant greater efficiency over Lipofectamine 2000. In mice, intravenous injection of Lac-GLN containing Cy3-anti-miR-155 led to preferential accumulation of the anti-miR-155 in hepatocytes. Intravenous administration of 1.5 mg/kg anti-miR-155 loaded Lac-GLN resulted in up-regulation of C/EBP? and FOXP3 by 6.9- and 2.2- fold, respectively. These results suggest potential application of Lac-GLN as a liver-specific delivery vehicle for anti-miR therapy. PMID:23567045

  10. Hybrid approach for attenuation correction in PET/MR scanners

    NASA Astrophysics Data System (ADS)

    Santos Ribeiro, A.; Rota Kops, E.; Herzog, H.; Almeida, P.

    2014-01-01

    Aim: Attenuation correction (AC) of PET images is still one of the major limitations of hybrid PET/MR scanners. Different methods have been proposed to obtain the AC map from morphological MR images. Although, segmentation methods normally fail to differentiate air and bone regions, while template or atlas methods usually cannot accurately represent regions anatomically different from the template image. In this study a feed forward neural network (FFNN) algorithm is presented which directly outputs the attenuation coefficients by non-linear regression of the images acquired with an ultrashort echo time (UTE) sequence guided by the template-based AC map (TAC-map). Materials and methods: MR as well as CT data were acquired in four subjects. The UTE images and the TAC-map were the inputs of the presented FFNN algorithm for training as well as classification. The resulting attenuation maps were compared with CT-based, PNN-based and TAC maps. All the AC maps were used to reconstruct the PET emission data which were then compared for the different methods. Results: For each subject dice coefficients D were calculated between each method and the respective CT-based AC maps. The resulting Ds show higher values for all FFNN-based tissues comparatively to both TAC-based and PNN-based methods, particularly for bone tissue (D=0.77, D=0.51 and D=0.71, respectively). The AC-corrected PET images with the FFNN-based map show an overall lower relative difference (RD=3.90%) than those AC-corrected with the PNN-based (RD=4.44%) or template-based (RD=4.43%) methods. Conclusion: Our results show that an enhancement of current methods can be performed by combining both information of new MR image sequence techniques and general information provided from template techniques. Nevertheless, the number of tested subjects is statistically low and current analysis for a larger dataset is being carried out.

  11. The relationship between phytoplankton concentration and light attenuation in ocean waters

    NASA Technical Reports Server (NTRS)

    Phinney, David A.; Yentsch, Charles S.

    1986-01-01

    The accuracy of chlorophyll estimates by ocean color algorithms is affected by the variability of particulate attenuation; the presence of dissolved organic matter; and the nonlinear inverse relationship between the attenuation coefficient, K, and chlorophyll. Data collected during the Warm Core Rings Program were used to model the downwelling light field and determine the impact of these errors. A possible mechanism for the nonlinearity of K and chlorophyll is suggested; namely, that changing substrate from nitrate-nitrogen to ammonium causes enhanced blue absorption by photosynthetic phytoplankton in oligotrophic surface waters.

  12. Hydrocarbon detection using adaptively selected spectrum attenuation

    NASA Astrophysics Data System (ADS)

    Wang, Lingling; Gao, Jinghuai; Xu, Zongben; Weng, Bing; Jiang, Xiudi

    2014-06-01

    Hydrocarbon reservoir usually shows the characteristics of low frequency amplifying and high frequency attenuating, which has been used as hydrocarbon indicator. However, reflection interference may also cause these phenomenons. In this paper, we propose an adaptively selected spectrum attenuation method to reduce the impact of the reflection interference in hydrocarbon detection. We first evaluate spectrum attenuation of seismic data by calculating the ratio of high frequency to low frequency components for each trace in the time-frequency domain. Notice that high frequency components are not really attenuated by interference as they appear, they can be recovered later, so we use an edge-preserving smoothing (EPS) method to smooth the equivalent local peak frequencies (ELPFs) located at the local peaks of seismic envelope to measure the attenuation trend of a seismic trace, and choose the spectrum attenuation whose high frequency components are really attenuated to locate the hydrocarbon. A real seismic data example demonstrates that the spectrum attenuation calculated by the ratio can avoid the impact of strong reflection, and the selected spectrum attenuation can reduce the effect of interference, which makes it more reliable in locating hydrocarbons than use the spectrum attenuation directly.

  13. Estimating the polyserial correlation coefficient

    Microsoft Academic Search

    Edward J. Bedrick; Frederick C. Breslin

    1996-01-01

    We develop simple noniterative estimators of the polyserial correlation coefficient. A general relationship between the polyserial correlation and the point polyserial correlation is exploited to give extensions of Pearson's, Brogden's, and Lord's biserial estimators to the multicategory setting. The small sample and asmptotic properties of these estimators are studied in some detail. A comparison with maximum likelihood estimates shows that

  14. A linear model approach for ultrasonic inverse problems with attenuation and dispersion.

    PubMed

    Carcreff, Ewen; Bourguignon, Sébastien; Idier, Jérôme; Simon, Laurent

    2014-07-01

    Ultrasonic inverse problems such as spike train deconvolution, synthetic aperture focusing, or tomography attempt to reconstruct spatial properties of an object (discontinuities, delaminations, flaws, etc.) from noisy and incomplete measurements. They require an accurate description of the data acquisition process. Dealing with frequency-dependent attenuation and dispersion is therefore crucial because both phenomena modify the wave shape as the travel distance increases. In an inversion context, this paper proposes to exploit a linear model of ultrasonic data taking into account attenuation and dispersion. The propagation distance is discretized to build a finite set of radiation impulse responses. Attenuation is modeled with a frequency power law and then dispersion is computed to yield physically consistent responses. Using experimental data acquired from attenuative materials, this model outperforms the standard attenuation-free model and other models of the literature. Because of model linearity, robust estimation methods can be implemented. When matched filtering is employed for single echo detection, the model that we propose yields precise estimation of the attenuation coefficient and of the sound velocity. A thickness estimation problem is also addressed through spike deconvolution, for which the proposed model also achieves accurate results. PMID:24960708

  15. The HC-LAC: a Platform for Modeling Hydrology and Climate Change in Latin America and the Caribbean

    NASA Astrophysics Data System (ADS)

    Moreda, F.; Wyatt, A.; Bruhn, M.; Wheaton, W.; Miralles-Wilhelm, F.; Muñoz-Castillo, R.; Rineer, J.

    2013-05-01

    This platform, called the Hydrology and Climate Change in Latin America and The Caribbean, or "HC-LAC", is an integrated quantitative simulation of hydrology and climate change. The HC-LAC is composed of two principal components: the Analytical Hydrography Dataset (AHD) and an enhanced version of the Generalized Watershed Loading Function (GWLF). The AHD is a spatially explicit surface water data layer of Central and South America derived from digital elevation data from the Shuttle Radar Topography Mission (SRTM) and modified by the USGS to provide more accurate flow between cells in the raster data. For the LAC area, AHD consists 230, 000 catchments and stream segments with an average area of 100 km2 and length of 10 km, respectively. The AHD data structure is patterned after the US National Hydrography Dataset Plus (NHDPlus), thus providing a proven structure for flexible data integration and analyses necessary for spatial models like the HC-LAC. The structure of the AHD enables the implementation of water balance modeling and general routing of flows through the stream network thus supporting a range of environmental models. GWLF is applied on each AHD catchment which is characterized by multiple land use and soil type. The response of each land use in a given catchment is modeled separately in generating stream flow as well as recharge to soil storage. The stream flows generated from each catchment are routed through stream networks, providing total flow at any point in the stream network. A pilot implementation of the HC-LAC was established for the Rio Grande basin in North West Argentina (drainage area 6,700 km2). The model was parameterized and calibrated using readily available data. Three stream flow time series were generated using a reference climate case and two climate change projections. The reference case was based on historical records and assumes no climate change. The two climate change projections were generated using the IPCC "A2" high emissions scenario with two general circulation models: the UKMO Hadley CM3 (used frequently in Argentina) and the CSIRO Mk3 (the "dry" scenario used by World Bank) for the period 2012-2060. The three stream flow time series were used to calculate unmet water demand for urban water supply and irrigation, taking into account various measures to adopt to climate change. The HC-LAC was also used to generate a complete surface flow database for the Rio Grande basin, which is proving useful for analysis of a variety of current and future water resource management issues by the local governmental agencies.

  16. SEISMIC ATTENUATION FOR RESERVOIR CHARACTERIZATION

    SciTech Connect

    Joel Walls; M.T. Taner; Naum Derzhi; Gary Mavko; Jack Dvorkin

    2003-04-01

    In this report we will show some new Q related seismic attributes on the Burlington-Seitel data set. One example will be called Energy Absorption Attribute (EAA) and is based on a spectral analysis. The EAA algorithm is designed to detect a sudden increase in the rate of exponential decay in the relatively higher frequency portion of the spectrum. In addition we will show results from a hybrid attribute that combines attenuation with relative acoustic impedance to give a better indication of commercial gas saturation.

  17. ML radio frequency attenuating connector

    NASA Astrophysics Data System (ADS)

    Prewett, M. G.

    In the increasingly harsh radio frequency environment associated with modern aerospace and missile systems, it is essential that safety standards are maintained or improved where electrically initiated explosive devices are involved. The Radio Frequency Attenuating Connector (RFAC) effectively protects igniters from electromagnetic interference both in hand held and installed modes. The RFAC provides a highly reliable pinless connector interface utilizing inductive coupling techniques and eliminates the need to use high-power bridgewires typically driven from a 28V dc aircraft or missile power bus. The conventional triggering circuits and data bussing can be replaced in the RFAC by fiber optics.

  18. Attenuation map reconstruction from TOF PET data

    E-print Network

    Yang, Qingsong; Wang, Ge

    2013-01-01

    To reconstruct a radioactive tracer distribution with positron emission tomography (PET), the background attenuation correction is needed to eliminate image artifacts. Recent research shows that time-of-flight (TOF) PET data determine the attenuation sinogram up to a constant, and its gradient can be computed using an analytic algorithm. In this paper, we study a direct estimation of the sinogram only from TOF PET data. First, the gradient of the attenuation sinogram is estimated using the aforementioned algorithm. Then, a relationship is established to link the differential attenuation sinogram and the underlying attenuation background. Finally, an iterative algorithm is designed to determine the attenuation sinogram accurately and stably. A 2D numerical simulation study is conducted to verify the correctness of our proposed approach.

  19. Turbidity coefficients from normal direct solar irradiance in Central Spain

    NASA Astrophysics Data System (ADS)

    Bilbao, J.; Román, R.; Miguel, A.

    2014-06-01

    Atmospheric turbidity causes attenuation of solar radiation reaching the earth's surface under a cloudless sky. The Ångström turbidity coefficient and the aerosol optical thickness, AOD550, were obtained from 10-minute direct normal solar irradiance measurements recorded in a rural area of Castilla y León region, Spain, from July 2010 to December 2012. During the study period, the diurnal variation of the mean monthly 10-minute turbidity coefficient increased in early morning, remained with fluctuations around noon, and increased or diminished in the evening, near sunset. The monthly turbidity coefficient shows an annual cycle with minimum values in winter and maximum values in summer, varying between 0.04 in winter and 0.16 in summer. The frequency distribution of 10-min Ångström turbidity coefficient on cloudless days shows that 0.65% of values are below 0.02, 84.50% between 0.02 and 0.15, and 14.85% above 0.15. Comparing at solar noon AOD550nm retrieved from MODIS (MODerate resolution Imaging Spectroradiometer on-board the Terra satellite) with those estimated from direct normal solar radiation measurements shows a good correlation coefficient of 0.78, although MODIS values are lower than estimated ones. High turbidity situations were investigated depending on the season and air-mass origin; the results show that they might be attributed to aerosol dust from the Sahara desert.The most significant high turbidity situations were investigated on base of wind at 700 mb and air-mass origin; the result shows that this might be attributed to aerosol dust from the Sahara desert.

  20. General relationships between ultrasonic attenuation and dispersion

    NASA Technical Reports Server (NTRS)

    Odonnell, M.; Jaynes, E. T.; Miller, J. G.

    1978-01-01

    General relationships between the ultrasonic attenuation and dispersion are presented. The validity of these nonlocal relationships hinges only on the properties of causality and linearity, and does not depend upon details of the mechanism responsible for the attenuation and dispersion. Approximate, nearly local relationships are presented and are demonstrated to predict accurately the ultrasonic dispersion in solutions of hemoglobin from the results of attenuation measurements.

  1. SEISMIC ATTENUATION FOR RESERVOIR CHARACTERIZATION

    SciTech Connect

    Joel Walls; M.T. Taner; Naum Derzhi; Gary Mavko; Jack Dvorkin

    2003-12-01

    We have developed and tested technology for a new type of direct hydrocarbon detection. The method uses inelastic rock properties to greatly enhance the sensitivity of surface seismic methods to the presence of oil and gas saturation. These methods include use of energy absorption, dispersion, and attenuation (Q) along with traditional seismic attributes like velocity, impedance, and AVO. Our approach is to combine three elements: (1) a synthesis of the latest rock physics understanding of how rock inelasticity is related to rock type, pore fluid types, and pore microstructure, (2) synthetic seismic modeling that will help identify the relative contributions of scattering and intrinsic inelasticity to apparent Q attributes, and (3) robust algorithms that extract relative wave attenuation attributes from seismic data. This project provides: (1) Additional petrophysical insight from acquired data; (2) Increased understanding of rock and fluid properties; (3) New techniques to measure reservoir properties that are not currently available; and (4) Provide tools to more accurately describe the reservoir and predict oil location and volumes. These methodologies will improve the industry's ability to predict and quantify oil and gas saturation distribution, and to apply this information through geologic models to enhance reservoir simulation. We have applied for two separate patents relating to work that was completed as part of this project.

  2. Dust Attenuation at High Redshift

    NASA Astrophysics Data System (ADS)

    Skinner, Danielle; Anderson, Lauren M.; Quinn, Thomas R.; Governato, Fabio; Tremmel, Michael J.

    2015-01-01

    In this work we study the dust distribution of the 100 most massive systems in the Vulcan simulation, a new state of the art cosmological simulation of a 25 Mpc per side volume, with unprecedented spatial resolution. The galaxies in our sample have typical stellar masses of 10**8.5-10.5 solar masses and star formation rates in the range 1-100 solar masses per year, typical of galaxies observed in the CANDELS survey. Interstellar dust remarkably affects how we observe galaxies - it comprises only ~ 0.1% of the total mass in a galaxy yet absorbs nearly 50% of it's starlight and reradiates it as far infrared continuum emission. Here we use a complete set of resolved systems to study how this attenuation varies with halo mass and metallicity, as well as star formation history, and orientation at high redshift. To measure the effects of dust we use Sunrise, a 3D radiative transfer code, which processes stellar light through dust in arbitrary geometries, and calculates the SED of every resolution element, from the far-UV to far-infrared. Using Sunrise, we can realistically calculate the attenuation of each resolved galaxy to quantify its variation with physical quantities. In addition, with these 'simulated observations', we compare our sample to the high redshift IRX-beta relationship observed in Lyman break galaxies, and investigate the cause of its intrinsic scatter.

  3. Attenuation in Superconducting Rectangular Waveguides

    NASA Astrophysics Data System (ADS)

    Yeap, Kim Ho; Mei Teh, Joyce Shu; Nisar, Humaira; Yeong, Kee Choon; Hirasawa, Kazuhiro

    2015-03-01

    We present an accurate analysis on the attenuation of waves, propagating in rectangular waveguides with superconducting walls. The wavenumbers kx and ky in the x and y directions, respectively, are first obtained as roots of a set of transcendental equations developed by matching the tangential fields at the surface of the wall with the electrical properties of the wall material. The complex conductivity of the superconducting waveguide is obtained from the extended Mattis-Bardeen theory. The propagation constant kz is found by substituting the values of kx and ky into the dispersion relation. We have computed and compared the loss in the waveguides below and above the critical temperature. At frequencies above the cutoff frequency fc but below the gap frequency fg, the loss in the superconducting waveguide is significantly lower than that in a normal conducting waveguide. Above the gap frequency, however, the result indicates that the attenuation in the waveguide below the critical temperature is higher than that at room temperature. We attribute the higher loss as due to the higher surface resistance and field penetration for superconducting waveguides operating above the gap frequency.

  4. Functional homology between the yeast regulatory proteins GAL4 and LAC9: LAC9-mediated transcriptional activation in Kluyveromyces lactis involves protein binding to a regulatory sequence homologous to the GAL4 protein-binding site.

    PubMed Central

    Breunig, K D; Kuger, P

    1987-01-01

    As shown previously, the beta-galactosidase gene of Kluyveromyces lactis is transcriptionally regulated via an upstream activation site (UASL) which contains a sequence homologous to the GAL4 protein-binding site in Saccharomyces cerevisiae (M. Ruzzi, K.D. Breunig, A.G. Ficca, and C.P. Hollenberg, Mol. Cell. Biol. 7:991-997, 1987). Here we demonstrate that the region of homology specifically binds a K. lactis regulatory protein. The binding activity was detectable in protein extracts from wild-type cells enriched for DNA-binding proteins by heparin affinity chromatography. These extracts could be used directly for DNase I and exonuclease III protection experiments. A lac9 deletion strain, which fails to induce the beta-galactosidase gene, did not contain the binding factor. The homology of LAC9 protein with GAL4 (J.M. Salmeron and S. A. Johnston, Nucleic Acids Res. 14:7767-7781, 1986) strongly suggests that LAC9 protein binds directly to UASL and plays a role similar to that of GAL4 in regulating transcription. Images PMID:2830492

  5. The Physics of the Gas Attenuator for the Linac Coherent Light Source (LCLS)

    SciTech Connect

    Ryutov, D.D.; Bionta, R.M.; Hau-Riege, S.P.; Kishiyama, K.I.; McMahon, D.; Roeben, M.D.; Shen, S.; /LLNL, Livermore; Stefan, P.M.; /SLAC; ,

    2011-02-07

    A systematic assessment of a variety of physics issues affecting the performance of the LCLS X-ray beam attenuator is presented. Detailed analysis of the gas flow in the gas attenuator and in the apertures is performed. A lot of attention is directed towards the gas ionization and heating by intense X-ray pulses. The role of these phenomena in possible deviations of the attenuation coefficient from its 'dialed in' value is evaluated and found small in most cases. Other sources of systematic and statistical errors are also discussed. The regimes where the errors may reach a few percent correspond to the lower X-ray energies (less than 2 keV) and highest beam intensities. Other effects discussed include chemical interaction of the gas with apertures, shock formation in the transonic flow in the apertures of the attenuator, generation of electromagnetic wakes in the gas, and head-to-tail variation of the attenuation caused by the ionization of gas or solid. Possible experimental tests of the consistency of the physics assumptions used in the concept of the gas attenuator are discussed. Interaction of X-rays with the solid attenuator (that will be used at higher X-ray energies, from 2.5 to 8 keV) is considered and thermo-mechanical effects caused by the beam heating are evaluated. Wave-front distortions induced by non-uniform heating of both the solid and the gas are found to be small. An overall conclusion drawn from the analysis presented is that the attenuator will be a reliable and highly versatile device, provided that some caution is exercised in its use for highest beam intensities at lowest X-ray energies.

  6. An MRI-based Attenuation Correction Method for Combined PET/MRI Applications.

    PubMed

    Fei, Baowei; Yang, Xiaofeng; Wang, Hesheng

    2009-02-27

    We are developing MRI-based attenuation correction methods for PET images. PET has high sensitivity but relatively low resolution and little anatomic details. MRI can provide excellent anatomical structures with high resolution and high soft tissue contrast. MRI can be used to delineate tumor boundaries and to provide an anatomic reference for PET, thereby improving quantitation of PET data. Combined PET/MRI can offer metabolic, functional and anatomic information and thus can provide a powerful tool to study the mechanism of a variety of diseases. Accurate attenuation correction represents an essential component for the reconstruction of artifact-free, quantitative PET images. Unfortunately, the present design of hybrid PET/MRI does not offer measured attenuation correction using a transmission scan. This problem may be solved by deriving attenuation maps from corresponding anatomic MR images. Our approach combines image registration, classification, and attenuation correction in a single scheme. MR images and the preliminary reconstruction of PET data are first registered using our automatic registration method. MRI images are then classified into different tissue types using our multiscale fuzzy C-mean classification method. The voxels of classified tissue types are assigned theoretical tissue-dependent attenuation coefficients to generate attenuation correction factors. Corrected PET emission data are then reconstructed using a three-dimensional filtered back projection method and an order subset expectation maximization method. Results from simulated images and phantom data demonstrated that our attenuation correction method can improve PET data quantitation and it can be particularly useful for combined PET/MRI applications. PMID:23682307

  7. Transport coefficients of quantum plasmas

    SciTech Connect

    Bennaceur, D.; Khalfaoui, A.H. (Centre de Developpement des Technologies Avancees/Secretariat d'Etat a la Recherche Scientifique et l'Environment, Laboratoire de Fusion Thermonucleaire, 2 boulevard Frantz Fanon, Boite Postale 1017 Alger-gare (Algeria))

    1993-09-01

    Transport coefficients of fully ionized plasmas with a weakly coupled, completely degenerate electron gas and classical ions with a wide range of coupling strength are expressed within the Bloch transport equation. Using the Kohler variational principle the collision integral of the quantum Boltzmann equation is derived, which accounts for quantum effects through collective plasma oscillations. The physical implications of the results are investigated through comparisons with other theories. For practical applications, electrical and thermal conductivities are derived in simple analytical formulas. The relation between these two transport coefficients is expressed in an explicit form, giving a generalized Wiedemann-Franz law, where the Lorentz ratio is a dependent function of the coupling parameter and the degree of degeneracy of the plasma.

  8. Portable vapor diffusion coefficient meter

    DOEpatents

    Ho, Clifford K. (Albuquerque, NM)

    2007-06-12

    An apparatus for measuring the effective vapor diffusion coefficient of a test vapor diffusing through a sample of porous media contained within a test chamber. A chemical sensor measures the time-varying concentration of vapor that has diffused a known distance through the porous media. A data processor contained within the apparatus compares the measured sensor data with analytical predictions of the response curve based on the transient diffusion equation using Fick's Law, iterating on the choice of an effective vapor diffusion coefficient until the difference between the predicted and measured curves is minimized. Optionally, a purge fluid can forced through the porous media, permitting the apparatus to also measure a gas-phase permeability. The apparatus can be made lightweight, self-powered, and portable for use in the field.

  9. Consistent transport coefficients in astrophysics

    NASA Technical Reports Server (NTRS)

    Fontenla, Juan M.; Rovira, M.; Ferrofontan, C.

    1986-01-01

    A consistent theory for dealing with transport phenomena in stellar atmospheres starting with the kinetic equations and introducing three cases (LTE, partial LTE, and non-LTE) was developed. The consistent hydrodynamical equations were presented for partial-LTE, the transport coefficients defined, and a method shown to calculate them. The method is based on the numerical solution of kinetic equations considering Landau, Boltzmann, and Focker-Planck collision terms. Finally a set of results for the transport coefficients derived for a partially ionized hydrogen gas with radiation was shown, considering ionization and recombination as well as elastic collisions. The results obtained imply major changes is some types of theoretical model calculations and can resolve some important current problems concerning energy and mass balance in the solar atmosphere. It is shown that energy balance in the lower solar transition region can be fully explained by means of radiation losses and conductive flux.

  10. High temperature Seebeck coefficient metrology

    SciTech Connect

    Martin, J. [Materials Science and Engineering Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (United States); Tritt, T. [Department of Physics and Astronomy, Clemson University, Clemson, South Carolina 29634 (United States); Uher, C. [Department of Physics, University of Michigan, Ann Arbor, Michigan 48109 (United States)

    2010-12-15

    We present an overview of the challenges and practices of thermoelectric metrology on bulk materials at high temperature (300 to 1300 K). The Seebeck coefficient, when combined with thermal and electrical conductivity, is an essential property measurement for evaluating the potential performance of novel thermoelectric materials. However, there is some question as to which measurement technique(s) provides the most accurate determination of the Seebeck coefficient at high temperature. This has led to the implementation of nonideal practices that have further complicated the confirmation of reported high ZT materials. To ensure meaningful interlaboratory comparison of data, thermoelectric measurements must be reliable, accurate, and consistent. This article will summarize and compare the relevant measurement techniques and apparatus designs required to effectively manage uncertainty, while also providing a reference resource of previous advances in high temperature thermoelectric metrology.

  11. Circumstantial evidence for cytochrome b1 involvement in the functioning of lac-permease in respiring Escherichia coli.

    PubMed

    Yariv, J

    1996-10-21

    The structure of the haem-binding site of cytochrome b1 and particularly the fact that the two protein ligands of the haem are methionines could explain a correlation found between loss of lac-permease activity and replacement of methionine by norleucine in the protein of aerobically respiring E. coli. If cytochrome b1 is essential for lac-permease mediated transport in whole bacteria as this correlation suggests, translocation of substrate by this permease must be coupled to electron transport. Such a dependence would invalidate the chemiosmotic interpretation of lactose transport in E. coli in its present form and would be in variance with the coupling-by-energy theories of lactose transport that exempted translocation from dependence on energy yielding processes. PMID:8944892

  12. A novel method to assay herpes simplex virus neutralizing antibodies using BHKICP6LacZ-5 (ELVIS) cells.

    PubMed

    Ashley, R L; Dalessio, J; Sekulovich, R E

    1997-01-01

    A novel method for determining neutralizing serum antibody titers to herpes simplex virus type 2 (HSV-2) was developed based on reduction of infectivity in BHKICP6LacZ-5 (ELVIS) cells; baby hamster kidney (BHK) cells that have been genetically engineered to contain the Escherichia coli LacZ gene under the control of an inducible herpes simplex virus type 1 (HSV-1) promoter. The test has a semiautomated, colorimetric readout resulting in rapid, objective readings of infectivity reduction. Extent of neutralization is calculated against a calibration curve of virus infectivity generated in each run. HSV-2 neutralizing activity can be detected with serum dilutions in excess of 1:5120. PMID:9473152

  13. Escherichia coli-mycobacteria shuttle vectors for operon and gene fusions to lacZ: the pJEM series.

    PubMed Central

    Timm, J; Lim, E M; Gicquel, B

    1994-01-01

    A series of Escherichia coli-mycobacteria shuttle plasmids for the isolation and study of gene regulatory sequences was constructed. These pJEM vectors contain an efficient transcription terminator and multiple cloning sites and allow either operon or gene fusions to lacZ. By constructing operon fusions with pJEM15, we assessed various previously characterized mycobacterial promoters in the fast-growing species Mycobacterium smegmatis and the slow-growing species M. bovis BCG. Our results suggest that M. smegmatis and M. bovis BCG RNA polymerases do not share the same specificity. To isolate new mycobacterial promoters, an M. tuberculosis DNA library was generated, using pJEM13, and screened in M. smegmatis. Several Lac+ clones were isolated, and the beta-galactosidase activity was measured. Images PMID:7961429

  14. Semi-metallic single-component crystal of soluble La@C82 derivative with high electron mobility.

    PubMed

    Sato, Satoru; Seki, Shu; Honsho, Yoshihito; Wang, Lu; Nikawa, Hidefumi; Luo, Guangfu; Lu, Jing; Haranaka, Masayuki; Tsuchiya, Takahiro; Nagase, Shigeru; Akasaka, Takeshi

    2011-03-01

    We prepared an organic conductor crystal having extremely high electron mobility, in which the adamantylidene (Ad) derivative of La@C(82) (an endohedral metallofullerene known as a n-type semiconductor) is aligned in an orderly fashion. The single-component crystal exhibits high electron mobility of ? > 10 cm(2) V(-1) s(-1) along the c axis under normal temperatures and pressures in the atmosphere, as shown by flash-photolysis time-resolved microwave conductivity (TRMC) measurements, which are the highest of reported organic conductors measured by TRMC. According to density functional calculations, the single crystal of La@C(82)Ad is semi-metallic, with a small band gap of 0.005 eV. PMID:21294573

  15. Identification of the merR gene of R100 by using mer-lac gene and operon fusions.

    PubMed Central

    Foster, T J; Brown, N L

    1985-01-01

    Transcriptional (operon) and translational (gene) fusions between the R100 merR gene and lacZ were constructed in vitro in a pBR322 plasmid carrying the mer genes derived from plasmid R100. The translational fusions were oriented in the opposite direction to and divergently from the merTCAD genes. This shows that the reading frame previously thought to be merR was incorrect. Expression of the gene fusion was repressed in trans by a compatible plasmid carrying the R100 merR+ gene, as was a similarly oriented transcriptional fusion. In contrast, expression of beta-galactosidase by the lac fragment located at the same site but in the opposite orientation was at a lower level and was not repressed by merR+. Images PMID:2993235

  16. A highly sensitive and specific electrochemical sensing method for robust detection of Escherichia coli lac Z gene sequence.

    PubMed

    Li, Fengqin; Yu, Zhigang; Qu, Haichao; Zhang, Guiling; Yan, Hong; Liu, Xin; He, Xunjun

    2015-06-15

    Based on the interaction mode of capture probe-target-signal probe (CP-T-SP), a simple but efficient electrochemical sensing method is developed for robust detection of Escherichia coli (E. coli) lac Z gene sequence. The sensing system is simply composed of two probes with CP attached to the surface of gold electrode and methylene blue (MB)-labeled SP free in the detecting solution. Two duplexes are formed with the target DNA, an E. coli lac Z gene sequence, hybridizing with two ends of CP and SP separately. This structure can position the MB labels near to the electrode surface, thereby resulting in the change of detecting current. The proposed sensor exhibits a high sensitivity with a detection limit of ?30fM for target DNA and good mismatch discrimination ability (MDA). This method can also be applied to the construction of other sensors for the analysis of similar designated pathogenic bacteria gene sequence (PBGS). PMID:25562734

  17. Factoring polynomials with rational coefficients

    Microsoft Academic Search

    A. K. Lenstra; H. W. Lenstra; L. Lovfiasz

    1982-01-01

    In this paper we present a polynomial-time algorithm to solve the following problem: given a non-zero polynomial fe Q(X) in one variable with rational coefficients, find the decomposition of f into irreducible factors in Q(X). It is well known that this is equivalent to factoring primitive polynomials feZ(X) into irreducible factors in Z(X). Here we call f~ Z(X) primitive if

  18. Optimal Bounds on Texture Coefficients

    Microsoft Academic Search

    Roberto Paroni

    2000-01-01

    Let w be the orientation distribution function of a polycrystalline aggregate of crystallites with symmetry G\\u000a cr and with group of texture symmetry G\\u000a tex. In this paper we obtain a “recipe” on how to derive optimal bounds on the texture coefficients W\\u000a \\u000a lmn\\u000a associated with w. In particular, we find explicit bounds in the case in which G\\u000a tex

  19. Nature of optical remote sensing coefficient

    Microsoft Academic Search

    Vladimir I. Haltrin

    2004-01-01

    The remote sensing coefficient or radiance reflection coefficient is a principal product of atmospheric correction algorithms applied to the remotely measured optical images of the ocean. This coefficient contains information about angular structure of light radiance, roughness of the ocean surface, and optical properties of the water. This presentation analyses remote sensing coefficient and presents it as a product of

  20. Swell and the drag coefficient

    NASA Astrophysics Data System (ADS)

    Potter, Henry

    2015-02-01

    Simultaneous measurements of waves and turbulent fluxes were collected from a moored surface buoy in the Philippine Sea. Waves were partitioned into their wind sea and swell components, and the ratio of swell to wind sea energy was used to assign a swell index. The 10-m neutral drag coefficient was calculated using the eddy correlation method. Four hundred hours of data were processed in 30 minute runs for wind speeds 8.5 to 16.5 m s-1 when the peak wave direction was within 90° of the wind direction and included observations during mixed seas, swell dominant, and wind sea dominant conditions. The data were analyzed to explore the influence of swell on the drag coefficient. It was found that when compared to periods of equal wind speed, the drag coefficient was reduced up to 37 % when swell energy was twice that of the wind sea energy. It is believed that this reduction was due to a decrease in the turbulent flux around the swell frequency, suggesting that the swell diminishes the surface aerodynamic roughness.