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1

Out-of-field activity in the estimation of mean lung attenuation coefficient in PET/MR  

NASA Astrophysics Data System (ADS)

In clinical PET/MR, photon attenuation is a source of potentially severe image artifacts. Correction approaches include those based on MR image segmentation, in which image voxels are classified and assigned predefined attenuation coefficients to obtain an attenuation map. In whole-body imaging, however, mean lung attenuation coefficients (LAC) can vary by a factor of 2, and the choice of inappropriate mean LAC can have significant impact on PET quantification. Previously, we proposed a method combining MR image segmentation, tissue classification and Maximum Likelihood reconstruction of Attenuation and Activity (MLAA) to estimate mean LAC values. In this work, we quantify the influence of out-of-field (OOF) accidental coincidences when acquiring data in a single bed position. We therefore carried out GATE simulations of realistic, whole-body activity and attenuation distributions derived from data of three patients. A bias of 15% was found and significantly reduced by removing OOF accidentals from our data, suggesting that OOF accidentals are the major contributor to the bias. We found approximately equal contributions from OOF scatter and OOF randoms, and present results after correction of the bias by rescaling of results. Results using temporal subsets suggest that 30-second acquisitions may be sufficient for estimation mean LAC with less than 5% uncertainty if mean bias can be corrected for.

Berker, Yannick; Salomon, André; Kiessling, Fabian; Schulz, Volkmar

2014-01-01

2

Measurements of spectral attenuation coefficients in the lower Chesapeake Bay  

NASA Technical Reports Server (NTRS)

The spectral transmission was measured for water samples taken in the lower Chesapeake Bay to allow characterization of several optical properties. The coefficients of total attenuation, particle attenuation, and absorption by dissolved organic matter were determined over a wavelength range from 3500 A to 8000 A. The data were taken over a 3 year period and at a number of sites so that an indication of spatial and temporal variations could be obtained. The attenuations determined in this work are, on the average, 10 times greater than those obtained by Hulburt in 1944, which are commonly accepted in the literature for Chesapeake Bay attenuation.

Houghton, W. M.

1983-01-01

3

Calculation of beta-ray attenuation coefficients through thin foils  

Microsoft Academic Search

Through the use of the P1 approximation to the linear transport equation and assuming that electrons only undergo elastic interactions with atoms, the fraction of transmitted beta-rays through foils is calculated arriving at the well-known exponential dependence with foil thickness. The resulting attenuation coefficients are in good agreement with experimental values.

F. Legarda; R. Idoeta

1995-01-01

4

Attenuation coefficient estimates of mouse and rat chest wall  

Microsoft Academic Search

Attenuation coefficients of intercostal tissues were estimated from chest walls removed postmortem (pm) from 41 6-to-7-week-old female ICR mice and 27 10-to-11-week-old female Sprague-Dawley rats. These values were determined from measurements through the intercostal tissues, from the surface of the skin to the parietal pleura. Mouse chest walls were sealed in plastic wrap and stored at 4\\\\°C until evaluated, and

Geraldine A. Teotico; Rita J. Miller; Leon A. Frizzell; James F. Zachary; William D. O'Brien

2001-01-01

5

Temporal Variations of Seismic Coda: Attenuation-Coefficient View  

NASA Astrophysics Data System (ADS)

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.

Morozov, I. B.

2010-12-01

6

Apparent Linear Attenuation Coefficients in Phase Contrast X-Ray Tomography  

PubMed Central

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

Yan, Aimin; Wu, Xizeng

2011-01-01

7

Representative Elementary Length to Measure Soil Mass Attenuation Coefficient  

PubMed Central

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

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

2014-01-01

8

Representative elementary length to measure soil mass attenuation coefficient.  

PubMed

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

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

2014-01-01

9

Determination of the attenuation coefficients by visible and ultraviolet radiation in heavy water  

Microsoft Academic Search

A long-path-length transmission cell has been used to measure the attenuation coefficients of purified HâO and DâO at various wavelengths between 250 and 580 nm. The principles governing the procedures and corrections for various sources of light attenuation in the transmission cell components are discussed. Detailed chemical histories of the HâO and DâO samples are given. The measured attenuation coefficients

L. P. Boivin; W. F. Davidson; R. S. Storey; D. Sinclair; E. D. Earle

1986-01-01

10

Determination of attenuation coefficients of single mode optical fiber standards to be used in OTDR calibrations  

NASA Astrophysics Data System (ADS)

The subject of this paper is the determination of attenuation coefficients of single mode optical fiber standards used in both loss and distance scales calibrations of OTDR instruments by applying "cut-back" method, and "loop transit time" measurements. In cut-back measurements a modified radiometer with InGaAs having 5 mm diameter active area, cooled to 77 K, was constructed and used. To derive attenuation coefficients after the completion of cut-back measurements, the loop transit time measurements were performed for standard fibers. Total expanded uncertainty was calculated as 3.30×10-3 for determination of attenuation coefficients.

Çelikel, Oguz; Küçüko?lu, Mehmet; Durak, Murat; Samadov, Farhad

2005-07-01

11

Effective density and mass attenuation coefficient for building material in Brazil  

Microsoft Academic Search

This paper presents values for density and mass attenuation coefficient of building materials commonly used in Brazil. Transmission measurements were performed to provide input information for simulations with MCNP4B code. The structure for the clay bricks was simulated as a mix of all material layers and an effective density determined. The mass attenuation coefficients were determined for the 50–3000keV gamma-ray

I. C. P. Salinas; C. C. Conti; R. T. Lopes

2006-01-01

12

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

NASA Astrophysics Data System (ADS)

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.

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

2013-03-01

13

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

Microsoft Academic Search

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.

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

1990-01-01

14

The role of the reflection coefficient in precision measurement of ultrasonic attenuation  

NASA Technical Reports Server (NTRS)

Ultrasonic attenuation measurements using contact, pulse-echo techniques are sensitive to surface roughness and couplant thickness variations. This can reduce considerable inaccuracies in the measurement of the attenuation coefficient for broadband pulses. Inaccuracies arise from variations in the reflection coefficient at the buffer-couplant-sample interface. The reflection coefficient is examined as a function of the surface roughness and corresponding couplant thickness variations. Interrelations with ultrasonic frequency are illustrated. Reliable attenuation measurements are obtained only when the frequency dependence of the reflection coefficient is incorporated in signal analysis. Data are given for nickel 200 samples and a silicon nitride ceramic bar having surface roughness variations in the 0.3 to 3.0 microns range for signal bandwidths in the 50 to 100 MHz range.

Generazio, E. R.

1984-01-01

15

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

PubMed

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. PMID:20702925

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

16

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

NASA Astrophysics Data System (ADS)

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.

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

17

Robust determination of mass attenuation coefficients of materials with unknown thickness and density  

NASA Astrophysics Data System (ADS)

An alternative approach is used to measure normalized mass attenuation coefficients (µ/?) of materials with unknown thickness and density. The adopted procedure is based on the use of simultaneous emission of K? and K? X-ray lines as well as gamma peaks from radioactive sources in transmission geometry. 109Cd and 60Co radioactive sources were used for the purpose of the investigation. It has been observed that using the simultaneous X- and/or gamma rays of different energy allows accurate determination of relative mass attenuation coefficients by eliminating the dependence of µ/? on thickness and density of the material.

Kurudirek, M.; Medhat, M. E.

2014-07-01

18

Effective density and mass attenuation coefficient for building material in Brazil.  

PubMed

This paper presents values for density and mass attenuation coefficient of building materials commonly used in Brazil. Transmission measurements were performed to provide input information for simulations with MCNP4B code. The structure for the clay bricks was simulated as a mix of all material layers and an effective density determined. The mass attenuation coefficients were determined for the 50-3,000 keV gamma-ray energy range. A comparison with results for similar materials found in the literature showed good agreement. PMID:16257357

Salinas, I C P; Conti, C C; Lopes, R T

2006-01-01

19

Author's personal copy Assessment of satellite-derived diffuse attenuation coefficients and euphotic depths  

E-print Network

form 16 October 2012 Accepted 4 December 2012 Available online xxxx Keywords: Ocean color Remote sensing MODIS SeaWiFS Bio-optical algorithm Diffuse attenuation coefficient Euphotic depth Optical data 2010 were used to evaluate products derived with three bio-optical inversion algorithms applied

Meyers, Steven D.

20

Determination of power-law attenuation coefficient and dispersion spectra in multi-wall carbon nanotube  

E-print Network

for a set of multi-wall carbon nanotube MWCNT -nylon composites from pure nylon to 20% MWCNT by weight conductivity of copper. Incorporating nano-scale particles into a matrix to construct a macro-scale compositeDetermination of power-law attenuation coefficient and dispersion spectra in multi-wall carbon

Gladden, Josh

21

Quantitative RNFL attenuation coefficient measurements by RPE-normalized OCT data  

NASA Astrophysics Data System (ADS)

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).

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

2012-03-01

22

Total attenuation coefficients and scattering phase functions of tissues and phantom materials at 633 nm  

SciTech Connect

Measurements have been made of the total attenuation coefficient sigma t and the scattering phase function, S(theta), of 632.8 nm of light for a number of animal model tissues, blood, and inert scattering and absorbing media. Polystyrene microspheres of known size and refractive index, for which sigma t and S(theta) can be calculated by Mie theory, were used to test the experimental methods. The purpose of the study was to define typical ranges for these optical properties of tissues, as a contribution to the development of experimental and theoretical methods of light dosimetry in tissue, particularly related to photodynamic therapy of solid tumors. The results demonstrate that, for the representative tissues studied, the total attenuation coefficients are of the order of 10-100 mm-1, and that the scattering is highly forward peaked, with average cosine of scatter in the range 0.6-0.97.

Flock, S.T.; Wilson, B.C.; Patterson, M.S.

1987-09-01

23

Effective atomic numbers and mass attenuation coefficients of some thermoluminescent dosimetric compounds for total photon interaction  

Microsoft Academic Search

Effective atomic numbers for total gamma-ray interaction with some selected thermoluminescent dosimetric compounds such as barium acetate, barium sulfate, calcium carbonate, calcium sulfate, calcium sulfate dihydrate, cadmium sulfate (anhydrous), cadmium sulfate, strontium sulfate, and lithium fluoride have been calculated in the 1-keV to 20-MeV energy region. Experimental mass attenuation coefficients and effective atomic numbers for these compounds at selected photon

Shivaramu; R. Amutha; V. Ramprasath

1999-01-01

24

Results of a monte carlo investigation of the diffuse attenuation coefficient.  

PubMed

There has been a large effort to relate the apparent optical properties of ocean water to the inherent optical properties, which are the absorption coefficient a, the scattering coefficient b, and the scattering phase function rho(theta). The diffuse attenuation coefficient kdiff' has most often been considered an apparent optical property. However, kdiff' can be considered a quasi-inherent property kdiff' when defined as a steady-state light distribution attenuation coefficient. The Honey-Wilson research empirically relates kdiff' to a and b. The Honey-Wilson relation most likely applies to a limited range of water types because it does not include dependence on rho(theta). A series of Monte Carlo simulations were initiated to calculate kdiff' in an unstratified water column. The calculations, which reflected open ocean water types, used ranges of the single-scattering albedo omega(0) and the mean forward-scattering angle theta(m) for two analytic phase functions with different shapes. It was found that kdiff' is nearly independent of the shape of rho(theta) and can be easily parameterized in terms of a, b, and theta(m) for 0.11

Concannon, B M; Davis, J P

1999-08-20

25

Nondestructive scheme for measuring the attenuation coefficient of polymer optical fiber.  

PubMed

Based on the fiber macrobending and the refractive index matching technologies, a measurement scheme is proposed to gauge the attenuation coefficient of polymer optical fibers in this Letter. It is noteworthy that, by realizing both the light injecting into and the light extracting out the fiber core via the fiber cladding, this scheme will not induce any destruction during the whole measurement. Some related experiments and the theoretical verifications are given together with the nondestructive measurement principle. The comparison between the experimental results of this scheme and that of the cut-back scheme indicates a good feasibility of our scheme. As a result, it is promised to have a potential application for achieving the on-line attenuation monitoring that has never been introduced. PMID:23455125

Lin, Xiao; Ren, Liyong; Liang, Jian

2013-02-15

26

Measurement of mass attenuation coefficients around the K absorption edge by parametric X-rays  

NASA Astrophysics Data System (ADS)

When electrons at relativistic velocities pass through a crystal plate, such as silicon, photons are emitted around the Bragg angle for X-ray diffraction. This phenomenon is called parametric X-ray radiation (PXR). The monochromaticity and directivity of PXR are adequate and the energy can be changed continuously by rotating the crystal. This study measured the mass attenuation coefficient around the K-shell absorption edge of Nb, Zr and Mo as a PXR application of monochromatic hard X-ray radiation sources.

Tamura, Masaya; Akimoto, Tadashi; Aoki, Yohei; Ikeda, Jiro; Sato, Koichi; Fujita, Fumiyuki; Homma, Akira; Sawamura, Teruko; Narita, Masakuni

2002-05-01

27

Measurements of mass attenuation coefficient, effective atomic number and electron density of some amino acids  

NASA Astrophysics Data System (ADS)

The mass attenuation coefficients of some amino acids, such as DL-aspartic acid-LR(C4H7NO4), L-glutamine (C4H10N2O3), creatine monohydrate LR(C4H9N3O2H2O), creatinine hydrochloride (C4H7N3O·HCl) L-asparagine monohydrate(C4H9N3O2H2O), L-methionine LR(C5H11NO2S), were measured at 122, 356, 511, 662, 1170, 1275 and 1330 keV photon energies using a well-collimated narrow beam good geometry set-up. The gamma-rays were detected using NaI (Tl) scintillation detection system with a resolution of 0.101785 at 662 keV. The attenuation coefficient data were then used to obtain the effective atomic numbers (Zeff), and effective electron densities (Neff) of amino acids. It was observed that the effective atomic number (Zeff) and effective electron densities (Neff) initially decrease and tend to be almost constant as a function of gamma-ray energy. Zeff and Neff experimental values showed good agreement with the theoretical values with less than 1% error for amino acids.

Kore, Prashant S.; Pawar, Pravina P.

2014-05-01

28

Remote sensing of the diffuse attenuation coefficient of ocean water. [coastal zone color scanner  

NASA Technical Reports Server (NTRS)

A technique was devised which uses remotely sensed spectral radiances from the sea to assess the optical diffuse attenuation coefficient, K (lambda) of near-surface ocean water. With spectral image data from a sensor such as the coastal zone color scanner (CZCS) carried on NIMBUS-7, it is possible to rapidly compute the K (lambda) fields for large ocean areas and obtain K "images" which show synoptic, spatial distribution of this attenuation coefficient. The technique utilizes a relationship that has been determined between the value of K and the ratio of the upwelling radiances leaving the sea surface at two wavelengths. The relationship was developed to provide an algorithm for inferring K from the radiance images obtained by the CZCS, thus the wavelengths were selected from those used by this sensor, viz., 443, 520, 550 and 670 nm. The majority of the radiance arriving at the spacecraft is the result of scattering in the atmospheric and is unrelated to the radiance signal generated by the water. A necessary step in the processing of the data received by the sensor is, therefore, the effective removal of these atmospheric path radiance signals before the K algorithm is applied. Examples of the efficacy of these removal techniques are given together with examples of the spatial distributions of K in several ocean areas.

Austin, R. W.

1981-01-01

29

Mass attenuation coefficients of soil and sediment samples using gamma energies from 46.5 to 1332 keV.  

PubMed

Mass attenuation coefficients of various soil and sediment samples (density range between 1.0 and 1.7 g cm(-3)) collected from 60 sites distributed in Syrian land have been determined for gamma lines of 46.5, 59.5, 88, 122, 165, 392, 661, 1173, and 1332 keV using gamma spectrometry and simulation software program X-com. The average mass attenuation coefficients for the studied samples were found to be 0.513, 0.316, 0.195, 0.155, 0.134, 0.096, 0.077, 0.058, and 0.055 cm(2) g(-1) at previous energies, respectively. The results have shown that Ca and Fe contents of the samples have strong effect on the mass attenuation coefficient at lower energies. In addition, self-attenuation correction factors determined using mass attenuation coefficient was in good agreement with addition spiked reference material method provided that the sample thickness is 2.7 cm. However, mass attenuation coefficients determined in this study can be used for determination of gamma emitters at energy ranges from 46.5 to 1332 keV in any soil and sediment samples having density of 1.0-1.7 g cm(-3). PMID:23103572

Al-Masri, M S; Hasan, M; Al-Hamwi, A; Amin, Y; Doubal, A W

2013-02-01

30

Effective atomic numbers and mass attenuation coefficients of some thermoluminescent dosimetric compounds for total photon interaction  

SciTech Connect

Effective atomic numbers for total gamma-ray interaction with some selected thermoluminescent dosimetric compounds such as barium acetate, barium sulfate, calcium carbonate, calcium sulfate, calcium sulfate dihydrate, cadmium sulfate (anhydrous), cadmium sulfate, strontium sulfate, and lithium fluoride have been calculated in the 1-keV to 20-MeV energy region. Experimental mass attenuation coefficients and effective atomic numbers for these compounds at selected photon energies of 26.3, 33.2, 59.54, and 661.6 keV have been obtained from good geometry transmission measurements and compared with theoretical values. The effect of absorption edge on effective atomic numbers and its variation with energy, and nonvalidity of the Bragg`s mixture rule at incident photon energies closer to the absorption edges of constituent elements of compounds are discussed.

Shivaramu; Amutha, R.; Ramprasath, V. [Indira Gandhi Centre for Atomic Research, Kalpakkam (India). Safety Research and Health Physics Group

1999-05-01

31

Diel variability of the beam attenuation and backscattering coefficients in the northwestern Mediterranean Sea (BOUSSOLE site)  

NASA Astrophysics Data System (ADS)

diel variability of the particulate beam attenuation coefficient, cp, and of the particulate backscattering coefficient, bbp, were investigated during five seasonal cycles at an oceanic site in the northwestern Mediterranean Sea, covering contrasting physical and trophic situations. We observed a diel cycle in cp and bbp, related to changes in phytoplankton properties (i.e., size and refractive index) induced by the accumulation of carbon within phytoplankton cells associated with photosynthetic processes, during the winter mixing of the water column, the development of the spring phytoplankton bloom, its decline, and during the summer oligotrophy. The relative amplitude of the cp diel variability was much larger during the spring bloom (20-50%) than during other seasons (10-20%), whereas that of bbp is steadily around 20% and does not show significant seasonal variability. The minimal cp and bbp occurred at sunrise and are synchronized, whereas maximum bbp values are often reached 3-6 h before those for cp (except during bloom conditions), which occur near sunset. These different amplitudes and timing are tentatively explained using Mie computations, which allow discerning the respective roles of changes in the particle size distribution and refractive index. The differences observed here in the diel cycles of cp and bbp show that they cannot be used interchangeably to determine the daily increase of the particle pool. This result has implications on the feasibility to determine net community production from the bbp diel changes, when only bbp is measured in situ or available from ocean color observations.

Kheireddine, Malika; Antoine, David

2014-08-01

32

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

NASA Astrophysics Data System (ADS)

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.

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

2014-09-01

33

Evaluation of Moisture-Related Attenuation Coefficient and Water Diffusion Velocity in Human Skin Using Optical Coherence Tomography  

PubMed Central

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

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

2013-01-01

34

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

Microsoft Academic Search

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

Samuel Pichardo; Vivian W. Sin; Kullervo Hynynen

2011-01-01

35

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

NASA Astrophysics Data System (ADS)

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.

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

2014-07-01

36

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

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

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

2000-01-01

37

Measurements of attenuation coefficient for evaluating the hardness of a cataract lens by a high-frequency ultrasonic needle transducer  

NASA Astrophysics Data System (ADS)

A cataract is a clouding of the lens in the eye that affects vision. Phacoemulsification is the mostly common surgical method for treating cataracts, and determining that the optimal phacoemulsification energy is dependent on measuring the hardness of the lens. This study explored the use of an ultrasound needle transducer for invasive measurements of ultrasound attenuation coefficient to evaluate the hardness of the cataract lens. A 47 MHz high-frequency needle transducer with a diameter of 0.9 mm was fabricated by a polarized PMN-33%PT single crystal in the present study. The attenuation coefficients at different stages of an artificial porcine cataract lens were measured using the spectral shift approach. The hardness of the cataract lens was also evaluated by mechanical measurement of its elastic properties. The results demonstrated that the ultrasonic attenuation coefficient was increased from 0.048 ± 0.02 to 0.520 ± 0.06 dB mm-1 MHz-1 corresponding to an increase in Young's modulus from 6 ± 0.4 to 96 ± 6.2 kPa as the cataract further developed. In order to evaluate the feasibility of combining needle transducer and phacoemulsification probe for real-time measurement during cataract surgery, the needle transducer was mounted on the phacoemulsification probe for a vibration test. The results indicated that there was no apparent damage to the tip of the needle transducer and the pulse-echo test showed that a good performance in sensitivity was maintained after the vibration test.

Huang, Chih-Chung; Chen, Ruimin; Tsui, Po-Hsiang; Zhou, Qifa; Humayun, Mark S.; Shung, K. Kirk

2009-10-01

38

Determination of absorption coefficients in highly scattering media from changes in attenuation and phase  

Microsoft Academic Search

The accurate, quantitative analysis of absorption and scattering properties in tissue is a central problem in biochemical optics, in particular for the determination of hemoglobin and oxyhemoglobin concentrations. Because of light scattering, the absolute concentrations of these chromophores (i.e., the absorption coefficient) cannot easily be inferred. A new method for the estimation of the absorption coefficients in scattering media, based

Matthias Kohl; Russell Watson; Mark Cope

1996-01-01

39

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

PubMed Central

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

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

2011-01-01

40

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

NASA Astrophysics Data System (ADS)

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.

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

2011-01-01

41

Quantitative measurement of optical attenuation coefficients of cell lines CNE1, CNE2, and NP69 using optical coherence tomography.  

PubMed

The radiotherapy-related types of nasopharyngeal carcinoma (NPC) have been established, which give the most effective treatment for NPC patients using the individual therapy. To diagnose the types of NPC, we assess the general NPC cell lines CNE1, CNE2 and normal nasopharyngeal cell line NP69 using optical coherence tomography (OCT) in two steps: firstly, the OCT images of the three different types of cell pellets are captured. Secondly, by fitting Beer's law to the averaged A-scans in these OCT datasets, the attenuation coefficients (? t ) of the cells can be extracted. The median attenuation coefficients (interquartile range) of CNE1, CNE2, and NP69 are 5.58 mm(-1) (IQR 5.55 to 5.65 mm(-1)), 5.91 mm(-1) (IQR 5.82 to 5.88 mm(-1)), and 8.96 mm(-1) (IQR 8.80 to 9.47 mm(-1)), respectively. The distinguishable quantitative OCT analysis (by ? t ) shows that the types of NPC could potentially be differentiated in real time and noninvasive. PMID:22618158

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

2013-02-01

42

Ultrasonic Attenuation and Backscatter Coefficient Estimates of Rodent-Tumor-Mimicking Structures: Comparison of Results among Clinical Scanners  

PubMed Central

In vivo estimations of the frequency-dependent acoustic attenuation (?) and backscatter (?) coefficients using radio frequency (RF) echoes acquired with clinical ultrasound systems must be independent of the data acquisition setup and the estimation procedures. In a recent in vivo assessment of these parameters in rodent mammary tumors, overall agreement was observed among ? and ? estimates using data from four clinical imaging systems. In some cases, particularly in highly attenuating heterogeneous tumors, multi-system variability was observed. This paper compares ? and ? estimates of a well-characterized rodent-tumor-mimicking homogeneous phantom scanned using 7 transducers with the same four clinical imaging systems: a Siemens Acuson S2000, an Ultrasonix RP, a Zonare Z.one, and a VisualSonics Vevo2100. ? and ? estimates of lesion-mimicking spheres in the phantom were independently assessed by three research groups, who analyzed their system’s RF echo signals. Imaging-system-based estimates of ? and ? of both lesion-mimicking spheres were comparable to through-transmission laboratory estimates and to predictions using Faran’s theory, respectively. A few notable variations in results among the clinical systems were observed, but the average and maximum percent difference between ? estimates and laboratory-assessed values was 11% and 29%, respectively. Excluding a single outlier dataset, the average and maximum average difference between ? estimates for the clinical systems and values predicted from scattering theory was 16% and 33%, respectively. These results were an improvement over previous inter-laboratory comparisons of attenuation and backscatter estimates. Although the standardization of our estimation methodologies can be further improved, this study validates our results from previous rodent breast-tumor model studies. PMID:22518954

Nam, Kibo; Rosado-Mendez, Ivan M.; Wirtzfeld, Lauren A.; Pawlicki, Alexander D.; Kumar, Viksit; Madsen, Ernest L.; Ghoshal, Goutam; Lavarello, Roberto J.; Oelze, Michael L.; Bigelow, Timothy A.; Zagzebski, James A.; O'Brien, William D.; Hall, Timothy J.

2012-01-01

43

Dual-energy attenuation coefficient decomposition with differential filtration and application to a microCT scanner  

PubMed Central

Dual-energy x-ray computed tomography (DECT) has the capability to decompose attenuation coefficients using two basis functions and has proved its potential in reducing beam-hardening artifacts from reconstructed images. The method typically involves two successive scans with different x-ray tube voltage settings. This work proposes an approach to dual-energy imaging through x-ray beam filtration that requires only one scan and a single tube voltage setting. It has been implemented in a preclinical microCT tomograph with minor modifications. Retrofitting of the microCT scanner involved the addition of an automated filter wheel and modifications to the acquisition and reconstruction software. Results show that beam-hardening artifacts are reduced to noise level. Acquisition of a ?-Compton image is well suited for attenuation-correction of PET images while dynamic energy selection (4D viewing) offers flexibility in image viewing by adjusting contrast and noise levels to suit the task at hand. All dual-energy and single energy reference scans were acquired at the same soft tissue dose level of 50 mGy. PMID:20107245

Taschereau, R; Silverman, R W; Chatziioannou, A F

2010-01-01

44

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

SciTech Connect

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.

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

2012-09-25

45

Deriving effective atomic numbers from DECT based on a parameterization of the ratio of high and low linear attenuation coefficients  

NASA Astrophysics Data System (ADS)

Dual energy computed tomography (DECT) can provide simultaneous estimation of relative electron density ?e and effective atomic number Zeff. The ability to obtain these quantities (?e, Zeff) has been shown to benefit selected radiotherapy applications where tissue characterization is required. The conventional analysis method (spectral method) relies on knowledge of the CT scanner photon spectra which may be difficult to obtain accurately. Furthermore an approximate empirical attenuation correction of the photon spectrum through the patient is necessary. We present an alternative approach based on a parameterization of the measured ratio of low and high kVp linear attenuation coefficients for deriving Zeff which does not require the estimation of the CT scanner spectra. In a first approach, the tissue substitute method (TSM), the Rutherford parameterization of the linear attenuation coefficients was employed to derive a relation between Zeff and the ratio of the linear attenuation coefficients measured at the low and high kVp of the CT scanner. A phantom containing 16 tissue mimicking inserts was scanned with a dual source DECT scanner at 80 and 140 kVp. The data from the 16 inserts phantom was used to obtain model parameters for the relation between Zeff and \\mu \\big|_{140kVp}^{80kVp}. The accuracy of the method was evaluated with a second phantom containing 4 tissue mimicking inserts. The TSM was compared to a more complex approach, the reference tissue method (RTM), which requires the derivation of stoichiometric fit parameters. These were derived from the 16 inserts phantom scans and used to calculate CT numbers at 80 and 140 kVp for a set of tabulated reference human tissues. Model parameters for the parameterization of \\mu \\big|_{140\\;kVp}^{80\\;kVp} were estimated for this reference tissue dataset and compared to the results of the TSM. Residuals on Zeff for the reference tissue dataset for both TSM and RTM were compared to those obtained from the spectral method. The tissue substitutes were well fitted by the TSM with R2 = 0.9930. Residuals on Zeff for the phantoms were similar between the TSM and spectral methods for Zeff < 8 while they were improved by the TSM for higher Zeff. The RTM fitted the reference tissue dataset well with R2 = 0.9999. Comparing the Zeff extracted from TSM and the more complex RTM to the known values from the reference tissue dataset yielded errors of up to 0.3 and 0.15 units of Zeff respectively. The parameterization approach yielded standard deviations which were up to 0.3 units of Zeff higher than those observed with the spectral method for Zeff around 7.5. Procedures for the DECT estimation of Zeff removing the need for estimates of the CT scanner spectra have been presented. Both the TSM and the more complex RTM performed better than the spectral method. The RTM yielded the best results for the reference human tissue dataset reducing errors from up to 0.3 to 0.15 units of Zeff compared to the simpler TSM. Both TSM and RTM are simpler to implement than the spectral method which requires estimates of the CT scanner spectra.

Landry, Guillaume; Seco, Joao; Gaudreault, Mathieu; Verhaegen, Frank

2013-10-01

46

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

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

J. H. Hubbell; Stephen M Seltzer

1995-01-01

47

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

SciTech Connect

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.

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

48

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

SciTech Connect

The compounds, Na{sub 2}B{sub 4}O{sub 7}, H{sub 3}BO{sub 3}, CdCl{sub 2} 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 and agree very well with the results obtained by Xcom code. Experiment and computation show that, H{sub 3}BO{sub 3} has the highest gamma ray attenuation coefficient among the aforementioned compounds. (author)

Jalali, Majid [Esfahan Nuclear Technology Center - ENTC (Iran, Islamic Republic of)

2006-07-01

49

Measurement of mass attenuation coefficients of Eremurus-Rhizophora spp. particleboards for X-ray in the 16.63-25.30 keV energy range  

NASA Astrophysics Data System (ADS)

The roots of Eremurus spp. were used as a bio-adhesive in the fabrication of Rhizophora spp. particleboards. The mass attenuation coefficients of Eremurus-Rhizophora spp. particleboard of six samples with two different weight percentages of the Eremurus spp. root (6% and 12%) and three various Rhizophora spp. particle sizes (?149 ?m, 149-500 ?m and 500-1000 ?m) were determined by using X-ray fluorescence (XRF) photons in 16.63 keV and 25.30 keV of the photon energy range. The results were compared with theoretically calculated mass attenuations using the XCOM computer program for younger-age (breast 1: 75% muscle+25% fat), middle-age (breast 2: 50% muscle+50% fat), and old-age (breast 3: 25% muscle+75% fat) breasts. The results indicated that Eremurus-Rhizophora spp. particleboard is the appropriate suitable phantom in the diagnostic energy region. The mass attenuation coefficient in the low weight percentage of the bio-adhesive and the large Rhizophora spp. particle size were found very close to breast 1. Moreover the mass attenuation coefficient of the sample with high weight percentage of the bio-adhesive and small Rhizophora spp. particle size was found very close to water as a standard material phantom. In addition, the viscosity of dissolved Eremurus spp. root in water could be considerably higher than that of formaldehyde-based adhesives, which affects on some properties such as high strength and high binding.

Tousi, E. T.; Bauk, S.; Hashim, R.; Jaafar, M. S.; Abuarra, A.; Aldroobi, K. S. A.; Al-Jarrah, A. M.

2014-10-01

50

Quantitative measurement of attenuation coefficients of bladder biopsies using optical coherence tomography for grading urothelial carcinoma of the bladder  

NASA Astrophysics Data System (ADS)

Real-time grading of bladder urothelial carcinoma (UC) is clinically important, but the current standard for grading (histopathology) cannot provide this information. Based on optical coherence tomography (OCT)-measured optical attenuation (?t), the grade of bladder UC could potentially be assessed in real time. We evaluate ex vivo whether ?t differs between different grades of UC and benign bladder tissue. Human bladder tissue specimens are examined ex vivo by 850-nm OCT using dynamic focusing. Three observers independently determine the ?t from the OCT images, and three pathologists independently review the corresponding histology slides. For both methods, a consensus diagnosis is made. We include 76 OCT scans from 54 bladder samples obtained in 20 procedures on 18 patients. The median (interquartile range) ?t of benign tissue is 5.75 mm-1 (4.77 to 6.14) versus 5.52 mm-1 (3.47 to 5.90), 4.85 mm-1 (4.25 to 6.50), and 5.62 mm-1 (5.01 to 6.29) for grade 1, 2, and 3 UC, respectively (p = 0.732). Interobserver agreement of histopathology is ``substantial'' [Kappa 0.62, 95% confidence interval (IC) 0.54 to 0.70] compared to ``almost perfect'' [interclass correlation coefficient (ICC) 0.87, 95% CI 0.80 to 0.92] for OCT. Quantitative OCT analysis (by ?t) does not detect morphological UC changes. This may be due to factors typical for an ex-vivo experimental setting.

Cauberg, Evelyne C. C.; de Bruin, Daniël M.; Faber, Dirk J.; de Reijke, Theo M.; Visser, Mike; de La Rosette, Jean J. M. C. H.; van Leeuwen, Ton G.

2010-11-01

51

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

Microsoft Academic Search

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

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

2005-01-01

52

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

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.

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

2003-01-01

53

Inter-comparison of thermal and optical methods for determination of atmospheric black carbon and attenuation coefficient from an urban location in northern India  

NASA Astrophysics Data System (ADS)

The simultaneous measurements of black carbon (BC, based on Aethalometer) and elemental carbon (EC, using thermo-optical EC-OC analyzer) in airborne particles collected from an urban location (Kanpur) in northern India are reported here. The strategy for site-selection is most relevant in order to assess the relative dominance of emissions from coal-fired industries, fossil-fuel combustion and biomass burning on the seasonal variability of EC (BC) concentrations. An inter-comparison of the analytical data ( n = 32) suggests that BC mass concentration is ˜ 20% higher than that of EC. However, attenuation coefficient ( bATN) measured by the two analytical instruments shows good agreement (slope = 0.97, n = 27), establishing the validity of bATN derived from thermo-optical EC-OC analyzer. Furthermore, slope (20.7 m 2 g - 1 ) of a linear-fit to the data ( n = 48, R2 = 0.86) for surface EC concentration (EC s ? 8 ?g C cm - 2 ) and optical-attenuation (ATN ? 180) measured at 678 nm on thermo-optical analyzer provides an independent and novel way of determining the "site-specific" attenuation cross-section ( ?ATN).

Ram, Kirpa; Sarin, M. M.; Tripathi, S. N.

2010-08-01

54

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

NASA Astrophysics Data System (ADS)

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.

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

2012-10-01

55

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)

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.

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

2012-10-01

56

Release and attenuation of PCB (polychlorinated biphenyl) congeners: Measurement of desorption kinetics and equilibrium sorption partition coefficients  

SciTech Connect

Polychlorinated biphenyls (PCBs) have been used widely in electrical equipment such as capacitors and transformers because of their coolant-insulation properties. However, their use has been discontinued because of their perceived toxicity to humans and other organisms in conjunction with their environmental persistence. This report provides information on the desorption or release rates of individual PCB congeners from four utility substation soils contaminated with Aroclor mixtures when these soils are in contact with water and the distribution of these congeners between the rapidly and the slowly released fractions of the total congeners bound to the soils. In addition to this kinetic information, experimental equilibrium sorption (partition) coefficients for individual PCB congeners have been measured for a series of eight soils differing in their organic carbon and clay mineral contents, from various locations throughout the United States. From these coefficients, a predictive relationship was derived for estimating partitioning coefficients for soils and congeners for which no sorption data are available. 49 refs., 9 figs., 13 tabs.

Girvin, D.C.; Sklarew, D.S.; Scott, A.J.; Zipperer, J.P. (Pacific Northwest Lab., Richland, WA (USA))

1990-06-01

57

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)

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.

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

2008-01-01

58

A new model for the vertical spectral diffuse attenuation coefficient of downwelling irradiance in turbid coastal waters: validation with in situ measurements.  

PubMed

The vertical spectral diffuse attenuation coefficient of Kd is an important optical property related to the penetration and availability of light underwater, which is of fundamental interest in studies of ocean physics and biology. Models developed in the recent decades were mainly based on theoretical analyses and numerical (radiative transfer) simulations to estimate this property in optically deep waters, thus leaving inadequate knowledge of its variability at multiple depths and wavelengths, covering a wide range of solar incident geometry, in turbid coastal waters. In the present study, a new model is developed to quantify the vertical, spatial and temporal variability of K(d) at multiple wavelengths and to quantify its dependence with respect to solar incident geometry under differing sky conditions. Thus, the new model is derived as a function of inherent optical properties (IOPs - absorption a and backscattering b(b)), solar zenith angle and depth parameters. The model results are rigorously evaluated using time-series and discrete in situ data from clear and turbid coastal waters. The K(d) values derived from the new model are found to agree with measured data within the mean relative error 0.02~6.24% and R² 0.94~0.99. By contrast, the existing models have large errors when applied to the same data sets. Statistical results of the new model for the vertical spectral distribution of K(d) in clear oceanic waters (for different solar zenith and in-water conditions) are also good when compared to those of the existing models. These results suggest that the new model can provide an improved interpretation about the variation of the vertical spectral diffuse attenuation coefficient of downwelling irradiance, which will have important implications for ocean physics, biogeochemical cycles and underwater applications in both relatively clear and turbid coastal waters. PMID:24514558

Simon, Arthi; Shanmugam, Palanisamy

2013-12-01

59

LacR is a repressor of lacABCD and LacT is an activator of lacTFEG, constituting the lac gene cluster in Streptococcus pneumoniae.  

PubMed

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

Afzal, Muhammad; Shafeeq, Sulman; Kuipers, Oscar P

2014-09-01

60

X-ray mass attenuation coefficients and imaginary components of the atomic form factor of zinc over the energy range of 7.2-15.2 keV  

SciTech Connect

The x-ray mass attenuation coefficients of zinc are measured in a high-accuracy experiment between 7.2 and 15.2 keV with an absolute accuracy of 0.044% and 0.197%. This is the most accurate determination of any attenuation coefficient on a bending-magnet beamline and reduces the absolute uncertainty by a factor of 3 compared to earlier work by advances in integrated column density determination and the full-foil mapping technique described herein. We define a relative accuracy of 0.006%, which is not the same as either the precision or the absolute accuracy. Relative accuracy is the appropriate parameter for standard implementation of analysis of near-edge spectra. Values of the imaginary components f'' of the x-ray form factor of zinc are derived. Observed differences between the measured mass attenuation coefficients and various theoretical calculations reach a maximum of about 5% at the absorption edge and up to 2% further than 1 keV away from the edge. The measurements invite improvements in the theoretical calculations of mass attenuation coefficients of zinc.

Rae, Nicholas A.; Chantler, Christopher T.; Barnea, Zwi; Jonge, Martin D. de; Tran, Chanh Q.; Hester, James R. [School of Physics, University of Melbourne, Victoria 3010 (Australia); Australian Synchrotron, Victoria 3168 (Australia); La Trobe University, Victoria 3086 (Australia); Australian Nuclear Science and Technology Organisation, New South Wales 2234 (Australia)

2010-02-15

61

Evolution and Biophysics of the Escherichia coli lac Operon  

NASA Astrophysics Data System (ADS)

To understand, predict, and control the evolution of living organisms, we consider biophysical effects and molecular network architectures. The lactose utilization system of E. coli is among the most well-studied molecular networks in biology, making it an ideal candidate for such studies. Simulations show how the genetic architecture of the wild-type operon attenuates large metabolic intermediate fluctuations that are predicted to occur in an equivalent system with the component genes on separate operons. Quantification of gene expression in the lac operon evolved in growth conditions containing constant lactose, alternating with glucose, or constant glucose, shows characteristic gene expression patterns depending on conditions. We are simulating these conditions to show context-dependent biophysical sources and costs of different lac operon architectures.

Ray, J. Christian; Igoshin, Oleg; Quan, Selwyn; Monds, Russell; Cooper, Tim; Balázsi, Gábor

2011-03-01

62

Influence of compensator thickness, field size, and off-axis distance on the effective attenuation coefficient of a cerrobend compensator for intensity-modulated radiation therapy  

SciTech Connect

Intensity-modulated radiation therapy (IMRT) can be performed by using compensators. To make a compensator for an IMRT practice, it is required to calculate the effective attenuation coefficient (?{sub eff}) of its material, which is affected by various factors. We studied the effect of the variation of the most important factors on the calculation of the ?{sub eff} of the cerrobend compensator for 6-MV photon beams, including the field size, compensator thickness, and off-axis distance. Experimental measurements were carried out at 100 cm source-to-surface distance and 10 cm depth for the 6-MV photon beams of an Elekta linac using various field size, compensator thickness, and off-axis settings. The field sizes investigated ranged from 4 × 4 to 25 × 25 cm{sup 2} and the cerrobend compensator thicknesses from 0.5–6 cm. For a fixed compensator thickness, variation of the ?{sub eff} with the field size ranged from 3.7–6.8%, with the highest value attributed to the largest compensator thickness. At the reference field size of 10 × 10 cm{sup 2}, the ?{sub eff} varied by 16.5% when the compensator thickness was increased from 0.5–6 cm. However, the variation of the ?{sub eff} with the off-axis distance was only 0.99% at this field size, whereas for the largest field size, it was more significant. Our results indicated that the compensator thickness and field size have the most significant effect on the calculation of the compensator ?{sub eff} for the 6-MV photon beam. Therefore, it is recommended to consider these parameters when calculating the compensator thickness for an IMRT practice designed for these beams. The off-axis distance had a significant effect on the calculation of the ?{sub eff} only for the largest field size. Hence, it is recommended to consider the effect of this parameter only for field sizes larger than 25 × 25 cm{sup 2}.

Haghparast, Abbas [Department of Medical Physics, Faculty of Medical Sciences, Tarbiat Modares University, Tehran, Islamic Republic of Iran (Iran, Islamic Republic of); Hashemi, Bijan, E-mail: bhashemi@modares.ac.ir [Department of Medical Physics, Faculty of Medical Sciences, Tarbiat Modares University, Tehran, Islamic Republic of Iran (Iran, Islamic Republic of); Eivazi, Mohammad Taghi [Department of Medical Physics, Faculty of Medicine, Kermanshah University of Medical Sciences, Kermanshah, Islamic Republic of Iran (Iran, Islamic Republic of)

2013-04-01

63

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

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,

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

2004-01-01

64

Allostery and the lac Operon.  

PubMed

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

Lewis, Mitchell

2013-07-10

65

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

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.

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

66

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

PubMed Central

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

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

2011-01-01

67

Imaging Redshift Estimates for Fermi BL Lacs  

NASA Astrophysics Data System (ADS)

We have measured i’’ images of BL Lacertae objects (BL Lacs) 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 (LAT) sources, with deep spectral observations showing them to be continuum-dominated BL Lacs. Host galaxies were detected by fitting the imaging data from each object to a variable model of a BL Lac consisting of a point source AGN and a galaxy profile. In this sample 6 of 11 BL Lacs yielded significant host detections, with standard candle redshifts z=0.10-0.66. These, and the remaining lower bounds are in good agreement with other redshifts estimates for these sources.

Stadnik, Matthew; Romani, R. W.

2014-01-01

68

Impact of Scientific Lac Cultivation Training on Lac Economy – A Study in Jharkhand  

Microsoft Academic Search

The study has reported the impact of training on lac growers in terms of host utilization, livelihood conditions and income and employment generation. The study is based on the data collected from randomly selected 500 lac growers (trained and untrained) in the Ranchi and West Singhbhum districts of Jharkhand in the years 2003-04 and 2004-05. The host utilization has been

Govind Pal

2009-01-01

69

Imaging Redshift Estimates for Fermi BL Lacs  

E-print Network

We have obtained WIYN and SOAR i' images of BL Lacertae objects (BL Lacs) 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 (LAT) sources, with sensitive spectral observations showing them to be continuum-dominated BL Lacs. In this sample 5 of 11 BL Lacs 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.

Stadnik, Matt

2014-01-01

70

BL Lac Objects and Relativistic Beaming Model  

E-print Network

In this paper: 1. The assumption of the dependence of Doppler factor on the emission frequency (Fan et al. 1993) is used to explain the observational differences between the radio-selected BL Lac objects(RBLs) and the X-Ray-Selected BL Lac objects (XBLs): a) Hubble relation; b) different multiwavelength correlations; c) different regions in the effective spectral index diagram; d) different polarization. The results suggest that RBLs and XBLs are the same. 2. From the analysis of the relation between infrared magnitude and redshift, it is proposed that the parent population of BL Lac objects should be FRI radio galaxies and FRII(G) radio galaxies showing the optical spectra of a galaxy. 3. From the superluminal motion, the assumption (Fan et al. 1993) is confirmed. 4. Based on the relation between polarization and Doppler factor (Fan et al. 1997, A&A, 327, 947), it is proposed that the ratio of the beamed luminosity to the unbeamed luminosity in the source frame of OVVs/HPQs is smaller than that of BL Lac objects.

J. H. Fan

1998-09-02

71

Optical and NIR photometry of BL Lac  

NASA Astrophysics Data System (ADS)

We report optical and NIR data for the blazar BL Lac, associated with the Gamma ray source 2FGLJ2202.8+4216 (z = 0.0686). NIR data were obtained during early commissioning of the new IO:I imaging camera installed on the 2.0 metre Liverpool Telescope (LT), La Palma.

Jermak, H. E.; Barnsley, R. M.; Steele, I. A.

2014-10-01

72

Insertional mutant analysis reveals that long-chain acyl-CoA synthetase 1 (LACS1), but not LACS8, functionally overlaps with LACS9 in Arabidopsis seed oil biosynthesis.  

PubMed

Triacylglycerols (TAGs) are major storage materials that accumulate in developing seeds and serve as carbon and energy reserves for germination and growth of the seedling. One of the critical reactions in TAG biosynthesis is activation of fatty acyl chains to fatty acyl CoAs, catalyzed by long-chain acyl CoA synthetases (LACSs). Of the nine LACSs identified in Arabidopsis, only LACS9 is known to reside in the plastid, the site of de novo fatty acid synthesis, and is considered the major LACS isoform involved in plastidial fatty acid export for TAG formation. Because the lacs9 null mutant did not show any detectable phenotype, it was hypothesized that at least one additional LACS enzyme must be active in the plastid. Expression analyses to identify potential plastid-localized LACSs involved in TAG biosynthesis revealed that, in addition to LACS9, isoforms LACS1, LACS2, LACS4 and LACS8 are transcribed in the seed. LACS8 showed the highest expression level in the embryo and a high sequence similarity with LACS9, and was therefore characterized further and shown to be associated with the ER, not the plastid. Furthermore, disruption of LACS8 in the lacs8 mutant and lacs8 lacs9 double mutant, and over-expression of LACS8, did not affect the seed fatty acid content. In contrast, 11 and 12% decreases in fatty acid content were detected in lacs1 lacs9 and lacs1 lacs8 lacs9 seeds, respectively, indicating that LACS1 and LACS9 have overlapping functions in TAG biosynthesis. This result is surprising because, unlike LACS9, LACS1 is localized in the ER and has been shown to be involved in cuticular lipid synthesis. PMID:21143684

Zhao, Lifang; Katavic, Vesna; Li, Fengling; Haughn, George W; Kunst, Ljerka

2010-12-01

73

A recent NIR Flare of BL Lac  

NASA Astrophysics Data System (ADS)

We report on a recent NIR flare of BL Lac, associated with the Gamma ray source 2FGLJ2202.8+4216 (z = 0.0686). On October 2nd,2014 (JD, 2456932.786) we obtained NIR photometry for this object and found it with enhanced fluxes, corresponding to: J = 11.334 +/- 0.04, H = 10.473 +/- 0.03 and Ks = 9.657 +/- 0.04.

Carrasco, L.; Porras, A.; Recillas, E.; Mayya, D. Y.; Carraminana, A.

2014-10-01

74

Ultrasonic attenuation in pearlitic steel.  

PubMed

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

Du, Hualong; Turner, Joseph A

2014-03-01

75

M87: A Misaligned BL LAC?  

E-print Network

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.

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

76

The Energy Landscape of Hyperstable LacI-DNA Loops  

NASA Astrophysics Data System (ADS)

The Escherichia coli LacI protein represses transcription of the lac operon by blocking access to the promoter through binding at a promoter-proximal DNA operator. The affinity of tetrameric LacI (and therefore the repression efficiency) is enhanced by simultaneous binding to an auxiliary operator, forming a DNA loop. Hyperstable LacI-DNA loops were previously shown to be formed on DNA constructs that include a sequence-directed bend flanked by operators. Biochemical experiments showed that two such constructs (9C14 and 11C12) with different helical phasing between the operators and the DNA bend form different DNA loop shapes. The geometry and topology of the loops and the relevance of alternative conformations suggested by probable flexible linkers in LacI remain unclear. Bulk and single molecule fluorescence resonance energy transfer (SM-FRET, with D. English) experiments on a dual fluorophore-labeled 9C14-LacI loop demonstrate that it adopts a single, stable, rigid closed-form loop conformation. Here, we characterize the LacI-9C14 loop by SM-FRET as a function of inducer isopropyl-?,D-thiogalactoside (IPTG) concentration. Energy transfer measurements reveal partial but incomplete destabilization of loop formation by IPTG. Surprisingly, there is no change in the energy transfer efficiency of the remaining looped population. Models for the regulation of the lac operon often assume complete disruption of LacI-operator complexes upon inducer binding to LacI. Our work shows that even at saturating IPTG there is still a significant population of LacI-DNA complexes in a looped state, in accord with previous in vivo experiments that show incomplete induction (with J. Maher). Finally, we will report progress on characterizing the ``energy landscape'' for DNA looping upon systematic variation of the DNA linkers between the operators and the bending locus. Rod mechanics simulations (with N. Perkins) provide testable predictions on loop stability, topology, and FRET.

Kahn, Jason

2009-03-01

77

Comprehensive biophysical model of the lac operon Kate Patterson  

E-print Network

Comprehensive biophysical model of the lac operon Kate Patterson Department of Mathematics;Abstract We introduce and analyze a detailed biophysical model of the control of the lac operon. The model connects two spatial scales: the biophysical parameters of molecular interactions at a molecular scale

Mischaikow, Konstantin

78

Multifrequency spectra of BL Lac objects  

NASA Technical Reports Server (NTRS)

A program to obtain simultaneous multifrequency spectra of BL Lacertae objects that are known X-ray sources is discussed. The IUE spectra are generally featureless and well-fitted by power law models. For the faintest exposures, Gaussian extraction of the spectrum can greatly impove the signal-to-noise. Most program objects vary in the ultraviolet, although the time scales are not known because of limited observing time. The broadband spectra of BL Lacs exhibit a range of characteristics but the curvature is always downward and the shape is generally smooth. This can be interpreted as synchrotron emission from a relativistic jet; different jet models are possible, and each allows a range of values for the bulk velocity, magnetic field strength, and electron density. Synchrotron models are not required, however an accretion disk model also gives a good fit to the ultraviolet-through-X-ray continuum.

Urry, C. M.; Kondo, Y.; Mufson, S. L.; Wandel, A.

1988-01-01

79

Modeling BL Lac Emission Lines: A Preview  

NASA Astrophysics Data System (ADS)

We present preliminary results based on a model of the emission from active galactic nuclei (AGN) combining special relativistic magnetohydrodynamics (RMHD), radiative transfer effects, and the spin rate of the super-massive black hole (SMBH). The RMHD code, PLUTO, can compute radiative cooling losses at each user definable time step and we use these capabilities to generate spectra. Additionally, the code will be used to model temporal variability of total broad band flux and line emission. We will use these model results to compare with observed spectra of AGN, focusing on blazars with the goal of predicting line strengths in BL Lac objects. We present methods for estimating line strengths from our simulated results.

Fernandes, Sunil; Schlegel, Eric M.; Packham, Chris

2012-12-01

80

The physical properties of Fermi BL Lac objects jets  

NASA Astrophysics Data System (ADS)

We investigate the physical properties of BL Lac objects (BL Lacs) jets by modelling the quasi-simultaneous spectral energy distributions (SEDs) of 22 Fermi BL Lacs in the frame of a simple one-zone synchrotron self-Compton (SSC) model. We obtained the best-fitting model parameters and their uncertainties for each BL Lac through the ?2-minimization procedure and discussed their implications on the physical processes. The modelling results show that the one-zone SSC model can successfully fit the SEDs of high-synchrotron-peaked BL Lacs (HBLs) and intermediate-synchrotron-peaked BL Lacs (IBLs), but fails to explain the SEDs of low-synchrotron-peaked BL Lacs. The statistical analysis results for model parameters are summarized as follows. (1) No correlation is found between magnetic field (B) and the broken energy of relativistic electrons distribution (? ^' }_b) for HBLs and IBLs, but there are inverse correlations between ? ^' }_b and the radius of emitting blob (R^' }_b) as well as the electrons number K^' }_e for HBLs and IBLs. It is therefore concluded that the variation of ? ^' }_b is mainly caused by that of R^' }_b rather than B for HBLs and IBLs. (2) The Poynting flux in jets cannot account for the observed radiations since the power in Poynting flux is smaller than the radiative power, and the cold protons could be the primary energy carrier in the jets.

Yan, Dahai; Zeng, Houdun; Zhang, Li

2014-04-01

81

The physical properties of Fermi BL Lac objects jets  

E-print Network

We investigate the physical properties of BL Lac objects (BL Lacs) jets by modeling the quasi-simultaneous spectral energy distributions (SEDs) of 22 {\\it Fermi} BL Lac objects in the frame of a simple one-zone synchrotron self-Compton (SSC) model. We obtained the best-fit model parameters and their uncertainties for each BL Lac object through the $\\chi^2$-minimization procedure and discussed their implications on the physical processes. The modeling results show that the one-zone SSC model can successfully fit the SEDs of high-synchrotron-peaked BL Lacs (HBLs) and intermediate-synchrotron-peaked BL Lacs (IBLs), but fails to explain the SEDs of low-synchrotron-peaked BL Lacs (LBLs). The statistical analysis results for model parameters are summarized as follows. (1) No correlation is found between magnetic field ($B$) and the broken energy of relativistic electrons distribution ($\\gamma^{\\prime}_{\\rm b}$) for HBLs and IBLs, but there are inverse correlations between $\\gamma^{\\prime}_{\\rm b}$ and the radius of...

Yan, Dahai; Zhang, Li

2014-01-01

82

Improved management of Butea monosperma (Lam.) Taub for lac production in India  

Microsoft Academic Search

Lac, a natural resin produced by the lac insect Kerria lacca, is an important income-generating non-timber forest product in India. It is expected that the potential for lac production could increase with India's recent changes in forest policy which encourage the natural regeneration of degraded lands. A review is presented on improved management systems of lac production on Butea monosperma

Vanessa Sequeira; Peter G. Bezkorowajnyj

1998-01-01

83

Optical imaging and spectroscopy of BL Lac objects  

E-print Network

We present optical images and spectroscopy for a dozen of BL Lac objects. Most of these objects were not previously studied and we give for the first time the properties of their host galaxies. The properties of the new host galaxies are generally consistent with those derived in previous optical studies. We found a case (1101-23) where the external isophotes of the galaxy are clearly boxy. In addition we gathered spectroscopy for several BL Lac objects with unknown redshift and for companion galaxies. This allowed us to derive a tentative redshift for two new BL Lacs and to investigate the environment around PKS 0829+04. These data complement existing data available in the literature on host galaxies of BL Lacs and their (close) environments.

Renato Falomo; Marie-Helene Ulrich

2000-04-04

84

BL Lac candidates for TeV observations (Massaro+, 2013)  

NASA Astrophysics Data System (ADS)

BL Lac objects are the most numerous class of extragalactic TeV-detected sources. One of the biggest difficulties in investigating their TeV emission is due to their limited number, since only 47 BL Lac objects are known to be TeV emitters. In this paper, we propose new criteria to select TeV BL Lac candidates based on infrared and X-ray observations. We apply our selection criteria to the BL Lac objects listed in the ROMA-BZCAT catalog (Cat. J/A+A/495/691), thereby identifying 41 potential TeV emitters. We then perform a search over a more extended sample combining the ROSAT bright source catalog (Cat. IX/10) and the WISE all-sky survey (Cat. II/311), revealing 54 additional candidates for TeV observations. Our investigation also led to a tentative classification of 16 unidentified X-ray sources as BL Lac candidates. This analysis provides new interesting BL Lac targets for future observations with ground-based Cherenkov telescopes. (3 data files).

Massaro, F.; Paggi, A.; Errando, M.; D'Abrusco, R.; Masetti, N.; Tosti, G.; Funk, S.

2013-09-01

85

Elimination of bandwidth effect in attenuation measurement with picosecond ultrasonics  

NASA Astrophysics Data System (ADS)

We study the broadening effect of probing pulse light on the apparent attenuation of the Brillouin oscillation measured with picosecond ultrasonics. We observe experimentally that the attenuation of the Brillouin oscillation is sensitive to the bandwidth, and the apparent attenuation coefficient increases as the bandwidth increases, being far from the intrinsic attenuation coefficient. Theoretical calculation is performed to reconstruct the observed oscillations, and it is confirmed that there are several factors affecting the apparent attenuation in addition to the bandwidth. We finally propose equations that deduce the contribution of the broadening to the apparent attenuation of the Brillouin oscillation.

Maehara, Atsushi; Nakamura, Nobutomo; Ogi, Hirotsugu; Hirao, Masahiko

2014-08-01

86

Attenuation of \\  

Microsoft Academic Search

Tested and confirmed the hypothesis that scopolamine attenuates habituation occurring within a training session as well as that occurring between training sessions. Subcutaneous scopolamine injections (.5 mg\\/kg) reduced spontaneous wheel running in 8 female prairie dogs. The same dosage did not affect the threshold for wheel running induced by electrical brain stimulation (EBS) in 6 Ss in Exp II. Exp

R. H. Carlson; M. G. Sanders; A. Tal; W. G. Wood

1975-01-01

87

Sugar recognition by CscB and LacY  

PubMed Central

The sucrose permease (CscB) and lactose permease (LacY) of Escherichia coli belong to the oligosaccharide/H+ symporter sub-family of the Major Facilitator Superfamily, and both catalyze sugar/H+ symport across the cytoplasmic membrane. Thus far, there is no common substrate for the two permeases; CscB transports sucrose and LacY is highly specific for galactopyranosides. Determinants for CscB sugar specificity are unclear, but the structural organization of key residues involved in sugar binding appears to be similar in CscB and LacY. In this study, several sugars containing galactopyranosyl, glucopyranosyl, or fructofuranosyl moieties were tested for transport with cells overexpressing either CscB or LacY. CscB recognizes not only sucrose but also fructose and lactulose, but glucopyranosides are not transported and do not inhibit sucrose transport. The findings indicate that CscB exhibits practically no specificity with respect to the glucopyranosyl moiety of sucrose. Inhibition of sucrose transport by CscB tested with various fructofuranosides suggests that the C3-OH of the fructofuranosyl ring may be important for recognition by CscB. Lactulose is readily transported by LacY, where specificity is directed toward the galactopyranosyl ring, and the affinity of LacY for lactulose is similar to that observed for lactose. The studies demonstrate that the substrate specificity of the CscB is directed towards the fructofuranosyl moiety of substrate, while the specificity of LacY is directed towards the galactopyranosyl moiety. PMID:22106930

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

2011-01-01

88

Coefficient scaling.  

PubMed

We prove a remarkably simple but powerful recursion relation for the coefficients of iterated polynomials. We also prove that the recursion relation holds for the coefficients of certain functions of the iterated polynomial. Using the recursion relations, we obtain a closed-form expression for the average number of closed-loop self-avoiding walks per site on a family of fractal lattices. We describe numerical results, which exhibit log-periodic oscillations, and find good agreement between these results and the theory developed here, which predicts the existence of the log-periodic oscillations and their amplitudes. Finally, we discuss insights gained into the mathematical origins of critical phenomena. PMID:11969435

Paul, G

1999-05-01

89

Dynamic model of gene regulation for the lac operon  

NASA Astrophysics Data System (ADS)

Gene regulatory network is a collection of DNA which interact with each other and with other matter in the cell. The lac operon is an example of a relatively simple genetic network and is one of the best-studied structures in the Escherichia coli bacteria. In this work we consider a deterministic model of the lac operon with a noise term, representing the stochastic nature of the regulation. The model is written in terms of a system of simultaneous first order differential equations with delays. We investigate an analytical and numerical solution and analyse the range of values for the parameters corresponding to a stable solution.

Angelova, Maia; Ben-Halim, Asma

2011-03-01

90

Experimental study of attenuation properties of normoxic polymer gel dosimeters  

Microsoft Academic Search

The change in linear attenuation coefficient with absorbed dose has been investigated for aqueous polyacrylamide, gelatine and tetrakis (PAGAT) and aqueous methacrylic acid, gelatine and tetrakis (MAGAT) normoxic polymer gel dosimeters using tetrakis (hydroxy methyl) phosphonium chloride as the antioxidant. The measured linear attenuation coefficient increased linearly with absorbed dose up to 15 Gy for PAGAT gels and 10 Gy

S Brindha; A J Venning; B Hill; C Baldock

2004-01-01

91

Structural explanation for allolactose (lac operon inducer) synthesis by lacZ ?-galactosidase and the evolutionary relationship between allolactose synthesis and the lac repressor.  

PubMed

?-Galactosidase (lacZ) has bifunctional activity. It hydrolyzes lactose to galactose and glucose and catalyzes the intramolecular isomerization of lactose to allolactose, the lac operon inducer. ?-Galactosidase promotes the isomerization by means of an acceptor site that binds glucose after its cleavage from lactose and thus delays its exit from the site. However, because of its relatively low affinity for glucose, details of this site have remained elusive. We present structural data mapping the glucose site based on a substituted enzyme (G794A-?-galactosidase) that traps allolactose. Various lines of evidence indicate that the glucose of the trapped allolactose is in the acceptor position. The evidence includes structures with Bis-Tris (2,2-bis(hydroxymethyl)-2,2',2?-nitrilotriethanol) and L-ribose in the site and kinetic binding studies with substituted ?-galactosidases. The site is composed of Asn-102, His-418, Lys-517, Ser-796, Glu-797, and Trp-999. Ser-796 and Glu-797 are part of a loop (residues 795-803) that closes over the active site. This loop appears essential for the bifunctional nature of the enzyme because it helps form the glucose binding site. In addition, because the loop is mobile, glucose binding is transient, allowing the release of some glucose. Bioinformatics studies showed that the residues important for interacting with glucose are only conserved in a subset of related enzymes. Thus, intramolecular isomerization is not a universal feature of ?-galactosidases. Genomic analyses indicated that lac repressors were co-selected only within the conserved subset. This shows that the glucose binding site of ?-galactosidase played an important role in lac operon evolution. PMID:23486479

Wheatley, Robert W; Lo, Summie; Jancewicz, Larisa J; Dugdale, Megan L; Huber, Reuben E

2013-05-01

92

Structural Explanation for Allolactose (lac Operon Inducer) Synthesis by lacZ ?-Galactosidase and the Evolutionary Relationship between Allolactose Synthesis and the lac Repressor  

PubMed Central

?-Galactosidase (lacZ) has bifunctional activity. It hydrolyzes lactose to galactose and glucose and catalyzes the intramolecular isomerization of lactose to allolactose, the lac operon inducer. ?-Galactosidase promotes the isomerization by means of an acceptor site that binds glucose after its cleavage from lactose and thus delays its exit from the site. However, because of its relatively low affinity for glucose, details of this site have remained elusive. We present structural data mapping the glucose site based on a substituted enzyme (G794A-?-galactosidase) that traps allolactose. Various lines of evidence indicate that the glucose of the trapped allolactose is in the acceptor position. The evidence includes structures with Bis-Tris (2,2-bis(hydroxymethyl)-2,2?,2?-nitrilotriethanol) and l-ribose in the site and kinetic binding studies with substituted ?-galactosidases. The site is composed of Asn-102, His-418, Lys-517, Ser-796, Glu-797, and Trp-999. Ser-796 and Glu-797 are part of a loop (residues 795–803) that closes over the active site. This loop appears essential for the bifunctional nature of the enzyme because it helps form the glucose binding site. In addition, because the loop is mobile, glucose binding is transient, allowing the release of some glucose. Bioinformatics studies showed that the residues important for interacting with glucose are only conserved in a subset of related enzymes. Thus, intramolecular isomerization is not a universal feature of ?-galactosidases. Genomic analyses indicated that lac repressors were co-selected only within the conserved subset. This shows that the glucose binding site of ?-galactosidase played an important role in lac operon evolution. PMID:23486479

Wheatley, Robert W.; Lo, Summie; Jancewicz, Larisa J.; Dugdale, Megan L.; Huber, Reuben E.

2013-01-01

93

Photoacoustic imaging of lacZ gene expression  

E-print Network

for molecular imaging research. © 2007 Society of Photo-Optical Instrumentation Engineers. DOI: 10 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

Wang, Lihong

94

Spectroscopy of BL Lac objects of extraordinary luminosity  

E-print Network

Aims. We aim to determine the redshift (or stringent lower limits) of a number of bright BL Lacs objects. Methods. We secured medium resolution optical and near-infrared spectra of 4 bright BL Lac objects of unknown redshift using the spectrograph X-Shooter at the ESO-VLT. Results. In spite of the high quality of the spectra and the extended spectral range of the observations we have not detected intrisic spectral features for these sources. However we are able to provide strigent lower limits to their redshift. In particular, for the two TeV sources PG 1553+113 and H 1722+119 we infer z > 0.30 and z > 0.35 respectively. We also detect an intervening Ca II absorption doublet in the spectrum of MH 2136-428 that is ascribed to the the halo of a nearby giant elliptical galaxy at \\sim 100 kpc of projected distance. Conclusions. Under the hypothesis that all BL Lacs are hosted by luminous bulge dominated galaxies, the present state of art spectroscopic observations of bright BL Lacs indicate that these objects are...

Landoni, Marco; Treves, Aldo; Sbarufatti, Boris

2014-01-01

95

LUNSORT list of lunar orbiter data by LAC area  

NASA Technical Reports Server (NTRS)

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.

Hixon, S.

1976-01-01

96

An Experimental and Theoretical Study of the Inhibition of Escherichia coli lac  

E-print Network

An Experimental and Theoretical Study of the Inhibition of Escherichia coli lac Operon Gene the inhibition of Escherichia coli lac operon gene expression by anti- gene oligos. Our model predicted 74: 220­229, 2001. Keywords: Escherichia coli lac operon; antigene oligo- nucleotide; triplex

Relue, Patricia

97

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

E-print Network

SUPPORTING INFORMATION FOR SEquence-Enabled Reassembly of -Lactamase (SEER-LAC): a Sensitive Method Tucson, AZ 85721 520-621-6331 office ghosh@email.arizona.edu #12;Ooi et al., SEER-LAC Supporting Information 2 SEER peptide design. LacA portion of -lactamase was constructed by PCR using 5'-GAGGAGGAGGGATC

Ghosh, Indraneel

98

Les mandres du dveloppement agricole au Lac Alaotra, Madagascar Entre inconstance politique et innovation technique  

E-print Network

shaped an agricultural history which built itself more or less between East bank and West bank and integration to markets. Key words : agriculture, development, policy, innovation, Lac Alaotra, Madagascar / BV Lac Alaotra Résumé L'histoire mouvementée de l'évolution de l'agriculture au Lac Alaotra

Paris-Sud XI, Université de

99

Thrust-augmented vortex attenuation  

NASA Technical Reports Server (NTRS)

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.

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

1977-01-01

100

Attenuated Influenza A Virus.  

National Technical Information Service (NTIS)

An attenuated influenza virus of a first strain is described together with a method for preparing the attenuated influenza virus. The attenuated influenza virus of the first strain comprises a sufficient number of single strand RNA segments of negative po...

P. Palese, T. Muster, B. R. Murphy, M. Enami, M. Bergmann

1992-01-01

101

Wind Resource Assessment Report: Mille Lacs Indian Reservation, Minnesota  

SciTech Connect

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.

Jimenez, A. C.

2013-12-01

102

Positive and Negative Control of the Lac Operon  

NASA Astrophysics Data System (ADS)

We present a mathematical model for the positive and negative control of lac operon. We investigate a steady state solution for the coupled nonlinear differential equations representing the dynamic behaviors of the repressor-inducer components of negative control as well as the cyclic AMP receptor components of the positive control. A dimensionless derivation of the lac operon system is employed to produce singularly perturbed models. The first model represents the dynamical behavior of the operator while the slow model represents the dynamical behaviors of the inducer and the repressor. We use the singular perturbation theory to show that the behavior of the system can be described as a rapid on-off switch of structural gene transformation.

Qaddour, Jihad S.; Werman, Steven D.; Misra, Prasanta K.

1997-03-01

103

Imaging Redshift Estimates for Fermi BL Lac Objects  

NASA Astrophysics Data System (ADS)

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.

Stadnik, Matt; Romani, Roger W.

2014-04-01

104

A Catalogue of XMM-Newton BL Lacs  

NASA Astrophysics Data System (ADS)

A catalogue of XMM-Newton BL Lac is presented based on a cross-correlation with the 1374 BL Lac objects listed in the 13th edition of the Veron-Cetty and Veron (2010) catalogue. X-ray counterparts were searched for in the field of view of more than 10000 pointed observations available in the XMM-Newton Archive (XSA) that were public before June 2012. The cross-correlation yielded around 250 XMM-Newton observations, which correspond to 162 different sources. X-ray data from the three EPIC cameras and Optical Monitor data were uniformly analyzed using the latest XMMNewton Science Analysis System (SAS) version. The catalogue collects X-ray spectral properties, including flux variability, of the sample in the 0.2 - 10 keV energy band.

Rouco, A.; de la Calle, I.; Held, J.; Racero, E.

2014-07-01

105

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

PubMed

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

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

2013-04-01

106

Radio Properties of REX BL Lacs and Galaxies  

E-print Network

Detailed VLA observations have been gathered for a number of sources classified as either BL Lacs or galaxies, derived from the REX survey. We focus in particular on the sources identified by us, for which we have in hand homogeneous optical data, to study in more detail than allowed by the NVSS the radio properties of these sources in the framework of AGN unified models.

Anna Wolter; A. Caccianiga; T. Maccacaro; R. Della Ceca; I. M. Gioia; F. Cavallotti; M. Minoia

2000-10-04

107

Radio and Gamma-ray emission in nearby BL Lacs  

NASA Astrophysics Data System (ADS)

The advent of Fermi is changing our understanding on the radio and ?-ray emission in active galactic nuclei. Unlike pre-Fermi ideas, BL Lac objects are found to be the most abundant emitters in the ?-ray band. However, since they are relatively weak radio sources, most of their parsec-scale structure and their multifrequency properties are poorly understood and/or have not been investigated in a systematic fashion. Here we are analyzing the radio and ?-ray emission properties of a sample of 42 BL Lacs selected with no constraint on their radio and ?-ray emission. Thanks to new Very Long Baseline Array observations at 8 and 15 GHz for the whole sample, we discuss their parsec-scale structure. Parsec-scale radio emission is observed in the majority of the sources at both frequencies. The comparison between our results in radio and gamma-ray bands points out the presence of a large number of faint BL Lacs showing ``non-classical'' properties such as low source compactness, low core dominance, no gamma-ray emission.

Giovannini, G.; Liuzzo, E.; Boccardi, B.; Giroletti, M.

2014-07-01

108

Structure of sugar-bound LacY  

PubMed Central

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

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

2014-01-01

109

Clustering of gamma-ray selected 2LAC Fermi Blazars  

E-print Network

We present the first measurement of the projected correlation function of 485 gamma-ray selected Blazars, divided in 175 BLLacertae (BL Lacs) and 310 Flat Spectrum Radio Quasars (FSRQs) detected in the 2-year all-sky survey by Fermi-Large Area Telescope. We find that Fermi BL Lacs and FSRQs reside in massive dark matter halos (DMHs) with logMh=13.35+0.20/-0.14 and logMh = 13.40+0.15/-0.19 Msun/h, 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 distribution, power and accretion rate. We find no difference in the typical bias and hosting halo mass between Fermi Blazars and radio-loud AGN, supporting the unifcation scheme simply equating radio-loud objects with misaligned Blazar counterparts. This similarity in terms of typical environment they preferentially live in, suggests that Blazars preferential...

Allevato, Viola; Cappelluti, Nico

2014-01-01

110

ENREGISTREMENT DE L'HISTOIRE DE LA VÉGÉTATION TARDIGLACIAIRE ET HOLOCÈNE DANS UN GRAND LAC : LE LAC D'ANNECY (FRANCE)  

Microsoft Academic Search

noncée. ABSTRACT Lateglacial and Holocene veg- etation history as recorded in a large lake: Lac d'Annecy, France. The pollen, palynofacies and phytoplankton study of a 44 m long core from in Lac d'Annecy reveals the major vege- tation changes and related organic sedimen- tation recorded in a large lake of the french northern alpine foreland since the last glacia- tion.

Fernand DAVID; Geneviève FARJANEL; URA CNRS

2000-01-01

111

Attenuation Relationship of Arias Intensity for Taiwan  

NASA Astrophysics Data System (ADS)

Arias intensity (AI) reflects the complete acceleration time history duration of ground vibrations. It correlates well with several commonly used demand measure of structural performance, liquefaction, and seismic slope stability. A good attenuation equation can reflect the characteristics of the ground-motion attenuation for a region, and can be used to predict the ground-motion value of a specific site for seismic resistance design. This study analyzed two local empirical attenuation relationships, one for the crustal earthquakes and the other for the subduction zone earthquakes, based on the strong ground-motion data from TSMIP and SMART1 array in Taiwan. Maximum likelihood method and mixed-effect model were used with non-linear regression analyses to determine coefficients. The result shows that adding terms of Vs30 and focal mechanism can effectively reduce the standard deviation in the attenuation models. To compare with other AI attenuation equations, the AI value predicted by our crustal earthquake attenuation equation is higher in the near field and is lower in the far field than the researches in other regions. The subduction zone earthquake attenuation equation predicts higher AI value than the crustal earthquake attenuation equation does.

Sung, C.; Hsieh, P.; Lin, P.; Lee, C.

2008-12-01

112

OTDR calibration for attenuation measurement  

NASA Astrophysics Data System (ADS)

The cut-back method is the standard test method to check the attenuation of optical fibers. The advantages of this method are low uncertainty, good reproducibility, and an applicability in a broad spectral range. But for some applications, especially in the field service, the optical time domain reflectometry seems to be more useful because (1) this method is non-destructive, (2) measurements can be made from one end of the fiber, and (3) the back-scattered signal contains information about the longitudinal homogeneity of the fiber or the fiber system. For an approval of this technique as a second standard test method, an uncertainty of 0.01 dB/km of the attenuation coefficient measurement is required. This small uncertainty demands a calibration of the loss scale of the optical time domain reflectometer (OTDR) used. Therefore, a calibration procedure is proposed using a standard fiber as a scale unit. The specification of this fiber, the preparation as a standard and its calibration in an accredited calibration laboratory, are discussed. An uncertainty of about 0.005 dB should be achievable in attenuation measurement of the standard. The calibration of the power scale of the OTDR with the aid of transfer standard, lead-in fiber and/or attenuator, and a proposal for linearizing the scale of power response are presented.

Moeller, Werner; Heitmann, Walter; Reich, Manfred

1991-09-01

113

What powers the most relativistic jets? - I. BL Lacs  

NASA Astrophysics Data System (ADS)

The dramatic relativistic jets pointing directly at us in BL Lacertae (BL Lac) objects can be well modelled by bulk motion beaming of synchrotron self-Compton emission powered by a low Eddington fraction accretion flow. Nearly 500 of these active galactic nuclei (AGN) are seen in the second Fermi Large Area Telescope catalogue of AGN. We combine the jet models which describe individual spectra with the expected jet parameter scalings with mass and mass accretion rate to predict the expected number of Fermi detected sources given the number densities of AGN from cosmological simulations. We select only sources with Eddington scaled mass accretion rate <0.01 (i.e. radiatively inefficient flows), and include cooling, orientation effects and the effects of absorption from pair production on the extragalactic infrared background. These models overpredict the number of Fermi detected BL Lacs by a factor of 1000! This clearly shows that one of the underlying assumptions is incorrect, almost certainly that jets do not scale simply with mass and accretion rate. The most plausible additional parameter which can affect the region producing the Fermi emission is black hole spin. We can reproduce the observed numbers of BL Lacs if such relativistic jets are only produced by the highest spin (a* > 0.8) black holes, in agreement with the longstanding spin-jet paradigm. This also requires that high spins are intrinsically rare, as predicted by the cosmological simulations for growing black hole mass via chaotic (randomly aligned) accretion episodes, where only the most massive black holes have high spin due to black hole-black hole mergers.

Gardner, Emma; Done, Chris

2014-02-01

114

Sensitivity of benzene natural attenuation to variations in kinetic and transport parameters in Liwa Aquifer, UAE.  

PubMed

Dissolved benzene was detected in the shallow unconfined Liwa aquifer (UAE). This aquifer represents the main freshwater source for a nearby residence camp area. A finite element model is used to simulate the fate, transport, and attenuation of the dissolved benzene plume to help decision makers assess natural attenuation as a viable remediation option. Sensitivity of benzene attenuation to uncertainties in the estimation of some of the kinetic and transport parameters is studied. It was found that natural attenuation is more sensitive to microbial growth rate and half saturation coefficients of both benzene and oxygen than initial biomass concentration and dispersivity coefficients. Increasing microbial growth rate by fourfold increased natural attenuation effectiveness after 40 years by 10%; while decreasing it by fourfold decreased natural attenuation effectiveness by 77%. On the other hand, increasing half saturation coefficient by fourfold decreased natural attenuation effectiveness by 46% in 40 years. Decreasing the same parameter fourfold caused natural attenuation effectiveness to increase by 9%. PMID:20237911

Mohamed, Mohamed M; Saleh, Nawal E; Sherif, Mohsen M

2010-04-01

115

THERMAL CONDUCTIVITY AND ELEMENT FRACTIONATION IN EV Lac  

SciTech Connect

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.

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

116

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

PubMed Central

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

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

117

Light attenuation on unicellular marine phytoplankton  

NASA Astrophysics Data System (ADS)

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.

Krol, Tadeusz; Lotocka, Maria

1994-10-01

118

The sedentary survey of extreme high energy peaked BL Lacs  

NASA Astrophysics Data System (ADS)

The multi-frequency "Sedentary Survey" is a deep, statistically complete, radio flux limited sample comprising 150 BL Lacertae objects distinguished by their extremely high X-ray to radio flux ratio (f_x/f_r), ranging from five hundred to over five thousand times that of typical BL Lacs discovered in radio surveys. This large excess of high energy photons compared to radio emission is thought to be due to synchrotron radiation that in these sources reaches the UV or the X-ray band. The name "Sedentary Survey" originates from the multi-frequency technique used to select the sample that was expected to be so efficient as to allow the conduction of some preliminary statistical studies even without the need to identify the candidates through optical spectroscopy. The details of the selection criteria and the preliminary results have been published in Giommi et al. (1999, MNRAS, 310, 465). In this paper we present the final, 100% identified, catalog together with the optical, X-ray and broad-band Spectral Energy Distributions (SED) constructed combining literature multi-frequency data with non-simultaneous optical observations and BeppoSAX~X-ray data, when available. The SEDs confirm that the peak of the synchrotron power in these objects is located at very high energies. BeppoSAX~wide band X-ray observations show that, in most cases, the X-ray spectra are convex and well described by a logarithmic parabola model peaking (in a ? f(?)~vs.~? representation) between 0.02 to several keV. Although detailed X-ray spectral data are available for only about one fifth of the sources the observed peaks never reach energies well above 10 keV (as in Mkn 501 during the large X-ray flare of April 1997 and in 1ES 2344+514 in December 1996) implying that hard X-ray synchrotron peak energies are rare and probably associated with strong flaring events. Owing to the high synchrotron energies involved most of the sources in the catalog are likely to be TeV emitters, with the closest and brightest ones probably detectable by the present generation of Cherenkov telescopes. However, only 50% (3 out of 6) of the presently established TeV BL Lacs are actually included in the survey suggesting that the hardest peaks may be associated with secondary synchrotron components that can be detected only above the soft X-ray band. The existence of secondary emission regions is suggested by the strong X-ray spectral curvature that in some objects predicts an optical flux much below the observed emission. The optical spectrum of about one fourth of the sources is totally featureless hampering any redshift or luminosity determination. Because this implies that the non-thermal nuclear emission must be well above that of the host galaxy, these objects are likely to be the most powerful sources in the survey and therefore be examples of the yet unreported high radio luminosity high energy peaked BL Lacs. The existence of such objects would be at odds with the claimed inverse proportionality between radio power and synchrotron peak energy known as the "blazar sequence". At the low-power end of the luminosity dynamical range, where the non-thermal optical continuum falls below the emission from the host galaxy, recognition issues start becoming important since BL Lacs in this luminosity regime can hardly be recognized as such, but rather as radio galaxies or simply as elliptical galaxies. We have found a small sample of bright nearby elliptical galaxies that are candidate low radio power high energy peaked BL Lacs.

Giommi, P.; Piranomonte, S.; Perri, M.; Padovani, P.

2005-04-01

119

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

PubMed Central

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

2014-01-01

120

Tracer attenuation in groundwater  

NASA Astrophysics Data System (ADS)

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.

Cvetkovic, Vladimir

2011-12-01

121

A comprehensive toolbox for the rapid construction of lacZ fusion reporters.  

PubMed

?-Galactosidase encoded by lacZ remains a popular reporter enzyme. Here, we present three fast and convenient tools that facilitate rapid construction of reporter lacZ fusions. The first enables the simple generation of lacZ (slacZ)-based chromosomally encoded reporter fusions within the lac operon in Escherichia coli using Red®/ET® recombination. The slacZ tool is based on rpsL counter-selection in combination with homologous recombination catalyzed by the ? Red recombinase, and blue/white screening. This permits construction of transcriptional and translational reporter lacZ fusions within a day. The second tool allows the introduction of lacZ reporter fusions into the chromosome by a single-crossover method. The strategy relies on the ?-origin-based suicide vector pNPTS138-R6KT, which can only replicate in ?pir E. coli strains. The third tool comprises four pBBR1-based broad-host-range vectors for transcriptional and translational lacZ fusions. The functionality of our toolbox was confirmed by the K(+)-dependent activation of kdp promoter-lacZ fusions in vivo. PMID:23022912

Fried, Luitpold; Lassak, Jürgen; Jung, Kirsten

2012-12-01

122

The lac operon, 2D animationSite: DNA Interactive (www.dnai.org)  

NSDL National Science Digital Library

Francois Jacob and Jacques Monod figured out how bacteria controlled the production of an enzyme called beta-galactosidase. This system of feedback and negative regulation became the lac operon and was the first model for the control of protein production. Walter Gilbert and his group later isolated the lac operon repressor.

2008-10-06

123

Limits of Acceptable Change and Natural Resources Planning: When is LAC Useful, When is it Not?  

Microsoft Academic Search

Abstract Abstract Abstract Abstract—Limits of Acceptable Change (LAC) was originally for- mulated to deal with the issue of recreation carrying capacity in wilderness. Enthusiasm for the process has led to questions about its applicability to a broad range of natural resource issues—both within and outside of protected areas. This paper uses a generic version of the LAC process to identify

David N. Cole; Stephen F. McCool

124

Les mandres du dveloppement agricole au Lac Alaotra, Madagascar Entre inconstance politique et innovation technique  

E-print Network

. This conflict of temporalities shaped an agricultural history which built itself more or less between East bank and integration to markets. Key words : agriculture, development, policy, innovation, Lac Alaotra, Madagascar L'histoire mouvementée de l'évolution de l'agriculture au Lac Alaotra, principal grenier à riz de

Paris-Sud XI, Université de

125

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

PubMed

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

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

2013-04-25

126

Partial charge transfer in the shortest possible metallofullerene peapod, la@c82 ?[11]cycloparaphenylene.  

PubMed

[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

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

2014-10-27

127

Electrical Breakdown in Lightning Arrestor Connector (LAC) Devices  

NASA Astrophysics Data System (ADS)

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.

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

2011-03-01

128

Photometric and polarimetric study of two BL LAC objects  

SciTech Connect

The results are given of polarimetric and photometric observations of the BL Lac objects OI 090.4 over the period 1979-1982 and B2 1418 + 54 over the period 1980-1982. For both objects it was noted that there was variability on a time scale of from several years to several days. The comparison of the polarimetric parameters indicates the existence of a preferred direction of polarization both for B2 1418 + 54 (theta /sub O/ = 120/sup 0/), and for OI 090.4 (theta /sub O/ = 50/sup 0/), which points to a stable magnetic field. For OI 090.4 it was observed that there was a certain dependence of the polarization parameters on the wavelength.

Marchenko, S.G.

1985-07-01

129

BL LAC X-Ray Spectra: Simpler Than we Thought  

SciTech Connect

We report results from XMM-Newton observations of thirteen X-ray bright BL Lacertae objects, selected from the Einstein Slew Survey sample. The spectra are generally well fit by power-law models, with four objects having hard ({alpha} < 1; F{sub v} {proportional_to} {nu}{sup -{alpha}}) spectra that indicates synchrotron peaks at > 5 keV. None of our spectra show line features, indicating that soft X-ray absorption ''notches'' must be rare amongst BL Lacs, rather than common or ubiquitous as had previously been asserted. We find significant curvature in most of the spectra. This curvature is almost certainly intrinsic, as it appears nearly constant from 0.5 to 6 keV, an observation which is inconsistent with the small columns seen in these sources.

Perlman, E.

2004-04-09

130

Starspots and stellar flares on EV Lac and YZ CMi  

NASA Astrophysics Data System (ADS)

For the purpose of investigating the relation between the occurrence of spots on red dwarf stars and the incidence of stellar flares, the stars EV Lac and YZ CMi were contemporaneously monitored for flare and spot activity in 1979-1981. Direct comparisons and statistical tests are not able to reveal positive relationships between flare frequency or flare energy and the position of the spotted region. Both stars have rotational axis inclinations and spot positions such that the dominating spot region is (partly) visible to the observer at all times. The existence of smaller flare producing active regions elsewhere on the stars cannot be ruled out either. A nonuniqueness problem prevents us from drawing firm conclusions, but suggests that spot/flare relations should be searched for on stars with a flat topped starspot light curve, indicating a certain interval of time during which the spot region rotates completely out of view.

Pettersen, B. R.; Kern, G. A.; Evans, D. S.

1983-07-01

131

SPECTROSCOPY OF BROAD-LINE BLAZARS FROM 1LAC  

SciTech Connect

We report on optical spectroscopy of 165 flat spectrum radio quasars (FSRQs) in the Fermi 1LAC sample, which have helped allow a nearly complete study of this population. Fermi FSRQs show significant evidence for non-thermal emission even in the optical; the degree depends on the {gamma}-ray hardness. They also have smaller virial estimates of hole mass than the optical quasar sample. This appears to be largely due to a preferred (axial) view of the {gamma}-ray FSRQ and non-isotropic (H/R {approx} 0.4) distribution of broad-line velocities. Even after correction for this bias, the Fermi FSRQs show higher mean Eddington ratios than the optical population. A comparison of optical spectral properties with Owens Valley Radio Observatory radio flare activity shows no strong correlation.

Shaw, Michael S.; Romani, Roger W.; Healey, Stephen E.; Michelson, Peter F. [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); 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)

2012-03-20

132

Magmatic mineralization and hydrothermal enrichment of the High Grade Zone at the Lac des Iles palladium mine, northern Ontario, Canada  

Microsoft Academic Search

The economic mineralization of Pd at the Lac des Iles mine occurs in the gabbroic rocks of the Mine Block Intrusion in the 2.69 Ga Lac des Iles Intrusive Complex. The complex intruded the tonalitic rocks of the Lac des Iles greenstone belt in the Wabigoon Subprovince of the Superior Province of Canada. We conducted a detailed study on the Pd

John G. Hinchey; Kéiko H. Hattori

2005-01-01

133

Factor Scores, Structure Coefficients, and Communality Coefficients  

ERIC Educational Resources Information Center

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…

Goodwyn, Fara

2012-01-01

134

Absorption Ångström exponents of aerosols and light absorbing carbon (LAC) obtained from in situ data in Covilhã, central Portugal.  

PubMed

A field campaign was conducted from October 2009 to July 2010 at Covilhã, a small town located in the region of Beira Interior (Portugal) in the interior of the Iberian Peninsula. The ambient light-absorption coefficient, ?(a) (522 nm), obtained from a Particle Soot Absorption Photometer (PSAP), presented a daily mean value of 12.1 Mm?¹ (StD = 7.3 Mm?¹). The wavelength dependence of aerosol light absorption is investigated through the Ångström parameter, ?(a). The ?(a) values for the pair of wavelengths 470-660 nm ranged from 0.86 to 1.47 during the period of measurements. The PSAP data were used to infer the mass of light absorbing carbon (LAC) and the daily mean varied from 0.1 to 6.8 ?g m?³. A detailed study of special events with different aerosol characteristics is carried out and, to support data interpretation, air masses trajectory analysis is performed. PMID:23138695

Mogo, S; Cachorro, V E; de Frutos, A; Rodrigues, A

2012-12-01

135

Variable laser attenuator  

DOEpatents

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.

Foltyn, S.R.

1987-05-29

136

Structural dynamics of the lac repressor-DNA complex revealed by a multiscale simulation  

PubMed Central

A multiscale simulation of a complex between the lac repressor protein (LacI) and a 107-bp-long DNA segment is reported. The complex between the repressor and two operator DNA segments is described by all-atom molecular dynamics; the size of the simulated system comprises either 226,000 or 314,000 atoms. The DNA loop connecting the operators is modeled as a continuous elastic ribbon, described mathematically by the nonlinear Kirchhoff differential equations with boundary conditions obtained from the coordinates of the terminal base pairs of each operator. The forces stemming from the looped DNA are included in the molecular dynamics simulations; the loop structure and the forces are continuously recomputed because the protein motions during the simulations shift the operators and the presumed termini of the loop. The simulations reveal the structural dynamics of the LacI–DNA complex in unprecedented detail. The multiple domains of LacI exhibit remarkable structural stability during the simulation, moving much like rigid bodies. LacI is shown to absorb the strain from the looped DNA mainly through its mobile DNA-binding head groups. Even with large fluctuating forces applied, the head groups tilt strongly and keep their grip on the operator DNA, while the remainder of the protein retains its V-shaped structure. A simulated opening of the cleft of LacI by 500-pN forces revealed the interactions responsible for locking LacI in the V-conformation. PMID:15863616

Villa, Elizabeth; Balaeff, Alexander; Schulten, Klaus

2005-01-01

137

High-energy cosmic neutrinos from spine-sheath BL Lac jets  

E-print Network

We recently proposed that structured (spine-sheath) jets associated to BL Lac objects offer a suitable environment for the production of the extragalactic high-energy ($E>100$ TeV) neutrino recently revealed by IceCube. Our previous analysis was limited to low-power BL Lac objects. We extend our preliminary study to the entire BL Lac population. We assume that the power of cosmic rays as well as the radiative luminosity of the sheath depend linearly on the the jet power. In turn, we assume that the latter is well traced by the $\\gamma$-ray luminosity. We exploit the BL Lac $\\gamma$-ray luminosity function and its cosmic evolution as recently inferred from Fermi-LAT data to derive the expected neutrino cumulative intensity from the entire BL Lac population. When considering only the low-power BL Lacs, a large cosmic ray power for each source is required to account for the neutrino flux. Instead, if BL Lacs of all powers produce neutrinos, the power demand decreases, and the required cosmic ray power becomes of...

Tavecchio, F

2014-01-01

138

The cosmological evolution of BL Lacs: The REX point of view  

E-print Network

We present the results on the cosmological evolution of BL Lac objects as derived from a statistically complete sample of 44 BL Lacs selected from the X-ray bright tail of the REX survey. With this sample, we have investigated the cosmological properties of BL Lacs taking into account the radio, optical and X-ray limits. We infer that no evolution is clearly visible down to the flux limits reached by our sample. On the other hand, deeper samples are probably needed in order to detect the negative evolution found in the EMSS sample. The identification of such deeper sample, extracted from the REX survey, is in progress.

A. Caccianiga; T. Maccacaro; A. Wolter; R. Della Ceca; I. M. Gioia

2000-09-25

139

Nucleotide and deduced amino acid sequences of the lacR, lacABCD, and lacFE genes encoding the repressor, tagatose 6-phosphate gene cluster, and sugar-specific phosphotransferase system components of the lactose operon of Streptococcus mutans.  

PubMed Central

The complete nucleotide sequences of lacRABCDF and partial nucleotide sequence of lacE from the lactose operon of Streptococcus mutans are presented. Comparison of the streptococcal lac determinants with those of Staphylococcus aureus and Lactococcus lactis indicate exceptional protein and nucleotide identity. The deduced polypeptides also demonstrate significant, but lower, sequence similarity with the corresponding lactose proteins of Lactobacillus casei. Additionally, LacR has sequence homology with the repressor (DeoR) of the Escherichia coli deoxyribonucleotide operon, while LacC is similar to phosphokinases (FruK and PfkB) from E. coli. The primary translation products of the lacRABCDFE genes are polypeptides of 251 (M(r) 28,713), 142 (M(r) 15,610), 171 (M(r) 18,950), 310 (M(r) 33,368), 325 (M(r) 36,495), 104 (M(r) 11,401), and 123 (NH2-terminal) amino acids, respectively. As inferred from their direct homology to the staphylococcal lac genes, these determinants would encode the repressor of the streptococcal lactose operon (LacR), galactose-6-phosphate isomerase (LacA and LacB), tagatose-6-phosphate kinase (LacC), tagatose-1,6-bisphosphate aldolase (LacD), and the sugar-specific components enzyme III-lactose (LacF) and enzyme II-lactose (LacE) of the S. mutans phosphoenolpyruvate-dependent phosphotransferase system. The nucleotide sequence encompassing the S. mutans lac promoter appears to contain repeat elements analogous to those of S. aureus, suggesting that repression and catabolite repression of the lactose operons may be similar in these organisms. Images PMID:1400164

Rosey, E L; Stewart, G C

1992-01-01

140

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

E-print Network

" method. This amounts to coupling the laser beam into the fiber at one end, approximating the "stable mode the laser in the laser mount and align the beam along a row of threaded holes in the table. Fiber Coupler and Output Positioner- Attach the fiber coupler to the table so that its axis is aligned with the laser beam

Collins, Gary S.

141

Seismic wave characteristics in anisotropic attenuating media  

NASA Astrophysics Data System (ADS)

A synthetic seismogram is a tool to investigate seismic wave characteristics in anisotropic attenuating media. A numerical technique for the computation of synthetic seismograms in a homogeneous, as well as in a multilayered anisotropic medium was developed. Full waveform theory is used to compute the synthetic seismograms. The medium can be elastic or viscoelastic. In the latter case, attenuation is introduced by giving materials complex elastic constants. To ensure that there are no false arrivals in the synthetic seismogram, it is important to carefully control the integration kernel singularity points, especially those due to repeated roots of the associated Green-Christoffel equation. A novel approach is developed to safely track the continuity of the integration kernel and, hence, the polarization vectors in critical and supercritical zones. The reflectivity approach is followed to consider wave propagation in a multilayered medium. A simple and concise implementation of this method is developed. This approach also enables one to investigate frequency dependent reflection coefficients varying with incidence angle and azimuth. The modeling of reflection coefficients in fractured media suggests that amplitude versus offset and azimuth (AVOAz) can be helpful in detecting fractured reservoirs. In a new development, the effect of attenuation on P- and S-wave radiation patterns in viscoelastic anisotropic media is investigated. The understanding of radiation patterns in homogeneous media is applied to interpret various wave types in attenuating multilayered media. Both the amplitude and the frequency content of the synthetic seismograms are affected by attenuation properties of the media. The spectral decomposition technique is found to be useful in our understanding of the attenuation effects. Seismic anisotropy in shales is a complex phenomenon. A number of theoretical shale models are investigated to study the effects of clay orientation, aspect ratio of cracks, porosity and fluid types on the synthetic seismograms.

Sinha, Satish

142

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

Federal Register 2010, 2011, 2012, 2013

...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...

2012-05-09

143

[Diversity of grasshopper community in lac plantation-farmland ecosystem].  

PubMed

The grasshopper communities in the paddy field, dry land, natural forest, and plantation forest of lac plantation-farmland ecosystem in Lvchun County, Yunnan were investigated by sweep netting. A total of 1426 grasshoppers belonging to 33 species, 22 genena, and 5 families were captured. In the paddy field, dry land, natural forest, and plantation forest of the ecosystem, the species richness S were 16.333, 13.000, 11.000, and 12.000, Margalef index was 2.873, 2.266, 2.335, and 2. 137, Shannon-Wiener index was 2.034, 1.976, 1.982, and 1.488, Simpson index was 0.196, 0.189, 0.174, and 0.323, and Pielou index was 0.728, 0.787, 0.829, 0.599, respectively. This ecosystem had a lower diversity of grasshopper communities, and different land use habitats in the ecosystem had different species component and diversity. In paddy field, grasshopper had a higher diversity than in dry land, but its evenness and stability were moderate; in natural forest, the diversity was high and the stability was strong; while in plantation forest, the diversity was low and the stability was weak. There existed species exchange in different land use habitats in the ecosystem. PMID:19637617

Li, Qiao; Chen, You-qing; Chen, Yan-lin; Chen, Zhen

2009-03-01

144

LacCore: Support for the terrestrial sediment core research community  

Microsoft Academic Search

LacCore, the National Lacustrine Core Facility, has been funded by the US National Science Foundation and the University of Minnesota for the past decade as a public facility to support the terrestrial sediment core research community. LacCore provides free or low-cost access to an array of expensive equipment and instrumentation in the field and lab, training for a variety of

K. L. Brady; A. J. Noren; A. Myrbo; E. Ito

2009-01-01

145

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

PubMed

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

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

2014-12-01

146

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

PubMed Central

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

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

2014-01-01

147

Regulation of Endothelial-Specific Transgene Expression by the LacI Repressor Protein In Vivo  

PubMed Central

Genetically modified mice have played an important part in elucidating gene function in vivo. However, conclusions from transgenic studies may be compromised by complications arising from the site of transgene integration into the genome and, in inducible systems, the non-innocuous nature of inducer molecules. The aim of the present study was to use the vascular system to validate a technique based on the bacterial lac operon system, in which transgene expression can be repressed and de-repressed by an innocuous lactose analogue, IPTG. We have modified an endothelium specific promoter (TIE2) with synthetic LacO sequences and made transgenic mouse lines with this modified promoter driving expression of mutant forms of connexin40 and an independently translated reporter, EGFP. We show that tissue specificity of this modified promoter is retained in the vasculature of transgenic mice in spite of the presence of LacO sequences, and that transgene expression is uniform throughout the endothelium of a range of adult systemic and cerebral arteries and arterioles. Moreover, transgene expression can be consistently down-regulated by crossing the transgenic mice with mice expressing an inhibitor protein LacIR, and in one transgenic line, transgene expression could be de-repressed rapidly by the innocuous inducer, IPTG. We conclude that the modified bacterial lac operon system can be used successfully to validate transgenic phenotypes through a simple breeding schedule with mice homozygous for the LacIR protein. PMID:24755679

Baillie, Brett K.; Hill, Caryl E.; Matthaei, Klaus I.

2014-01-01

148

Regulation of endothelial-specific transgene expression by the LacI repressor protein in vivo.  

PubMed

Genetically modified mice have played an important part in elucidating gene function in vivo. However, conclusions from transgenic studies may be compromised by complications arising from the site of transgene integration into the genome and, in inducible systems, the non-innocuous nature of inducer molecules. The aim of the present study was to use the vascular system to validate a technique based on the bacterial lac operon system, in which transgene expression can be repressed and de-repressed by an innocuous lactose analogue, IPTG. We have modified an endothelium specific promoter (TIE2) with synthetic LacO sequences and made transgenic mouse lines with this modified promoter driving expression of mutant forms of connexin40 and an independently translated reporter, EGFP. We show that tissue specificity of this modified promoter is retained in the vasculature of transgenic mice in spite of the presence of LacO sequences, and that transgene expression is uniform throughout the endothelium of a range of adult systemic and cerebral arteries and arterioles. Moreover, transgene expression can be consistently down-regulated by crossing the transgenic mice with mice expressing an inhibitor protein LacI(R), and in one transgenic line, transgene expression could be de-repressed rapidly by the innocuous inducer, IPTG. We conclude that the modified bacterial lac operon system can be used successfully to validate transgenic phenotypes through a simple breeding schedule with mice homozygous for the LacI(R) protein. PMID:24755679

Morton, Susan K; Chaston, Daniel J; Baillie, Brett K; Hill, Caryl E; Matthaei, Klaus I

2014-01-01

149

Landing gear noise attenuation  

NASA Technical Reports Server (NTRS)

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.

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

2011-01-01

150

A numeric evaluation of attenuation from ambient noise correlation functions  

NASA Astrophysics Data System (ADS)

The ambient noise correlation function (NCF) calculated between seismic stations contains, under appropriate conditions, accurate travel time information. However, NCF amplitudes are highly debated due to noise source intensity and distribution, seismic intrinsic attenuation, scattering, and elastic path effects such as focusing and defocusing. We prove with various numerical simulations that the NCFs calculated for a uniformly dispersive medium using the coherency method preserve accurate geometrical spreading and attenuation decay. We show that for a wide range of noise source distributions, the coherency of the noise correlation functions matches a Bessel function decaying exponentially with a specific attenuation coefficient. Conditions needed to obtain these results include averaging over long enough time intervals, a uniformly distributed seismic network, and a good distribution of far-field noise sources. We also show that the estimated attenuation coefficient corresponds to the interstation and not the noise-source-to-receiver structure.

Lawrence, Jesse F.; Denolle, Marine; Seats, Kevin J.; Prieto, Germán. A.

2013-12-01

151

Attenuator And Conditioner  

DOEpatents

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.

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

152

Time domain attenuation estimation method from ultrasonic backscattered signals  

PubMed Central

Ultrasonic attenuation is important not only as a parameter for characterizing tissue but also for compensating other parameters that are used to classify tissues. Several techniques have been explored for estimating ultrasonic attenuation from backscattered signals. In the present study, a technique is developed to estimate the local ultrasonic attenuation coefficient by analyzing the time domain backscattered signal. The proposed method incorporates an objective function that combines the diffraction pattern of the source/receiver with the attenuation slope in an integral equation. The technique was assessed through simulations and validated through experiments with a tissue mimicking phantom and fresh rabbit liver samples. The attenuation values estimated using the proposed technique were compared with the attenuation estimated using insertion loss measurements. For a data block size of 15 pulse lengths axially and 15 beamwidths laterally, the mean attenuation estimates from the tissue mimicking phantoms were within 10% of the estimates using insertion loss measurements. With a data block size of 20 pulse lengths axially and 20 beamwidths laterally, the error in the attenuation values estimated from the liver samples were within 10% of the attenuation values estimated from the insertion loss measurements. PMID:22779499

Ghoshal, Goutam; Oelze, Michael L.

2012-01-01

153

Backscatter and attenuation properties of mammalian brain tissues  

NASA Astrophysics Data System (ADS)

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.

Wijekularatne, Pushpani Vihara

154

Spectral characterization of 4 MV Bremsstrahlung by attenuation analysis.  

PubMed

The "quality of radiation" for a high energy x-ray beam can be specified by its attenuation curve in a selected material. The inverse Laplace transform of the attenuation curve can be used as an approximate indication of the energy spectrum of the beam. Existing mathematical procedures for this purpose have been evaluated and were found to poorly represent measured transmission data for 4 MV x-rays from a linear accelerator. The transmission data between 1 and 0.002 could be fitted within the experimental uncertainty by expressing the logarithmic transmission as a second order polynomial of attenuator thickness. The inverse Laplace transform them becomes a Gaussian function of the attenuation coefficient. This new version of "attenuation analysis" provides a practical method for specification of the quality of the radiation in this energy range. PMID:6798393

Huang, P H; Kase, K R; Bjärngard, B E

1981-01-01

155

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

PubMed Central

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

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

2003-01-01

156

RegR, a global LacI/GalR family regulator, modulates virulence and competence in Streptococcus pneumoniae.  

PubMed

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 RegR(0) (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 hyl(0) (where 0 indicates the loss of function) mutation in the RegR(0) strain 23302 dramatically reduces its virulence. This indicates that residual virulence of the RegR(0) 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

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

2003-05-01

157

Escherichia coli lacZ gene as a biochemical and histochemical marker in plant cells.  

PubMed

Several lacZ chimeric genes were constructed by fusing the truncated lacZ sequence of Escherichia coli to N-terminal sequences of few other genes. Promoters used to direct expression of the chimeric genes were the promoter for 35S RNA of cauliflower mosaic virus (P35S) as well as those of the small subunit gene of ribulose bisphosphate carboxylase and the octopine synthase gene. These constructs were introduced into tobacco cells using a Ti plasmid of Agrobacterium tumefaciens, and beta-galactosidase activity in uncloned and cloned calli derived from the crown galls were examined. The results showed that the P35S-linked lacZ chimeric gene is expressed very efficiently. When slices of the crown gall carrying this chimeric gene were placed on plates containing indicator XGal, localized areas of the outgrowth turned deep blue, whereas no such areas were found in the crown gall having promoter-less lacZ. Calli from galls containing this construct expressed beta-galactosidase activity at an eight-fold higher level (approx. 7000 units/mg protein) than the endogenous activity (approx. 900 units/mg protein). Some of the calli displayed over 20-fold higher activity. Actively growing mini calli expressing activity higher than 4000 units/mg protein dyed deep blue on XGal agar medium such that they were distinguishable from calli having no lacZ. Half of the uncloned P35S-lacZ transformant calli showed activity higher than this level. These results indicate that the lacZ gene linked to a strong promoter such as P35S is useful as a biochemical and histochemical marker gene in plant cells. PMID:3138164

Matsumoto, S; Takebe, I; Machida, Y

1988-06-15

158

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

SciTech Connect

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.

Ryutov,, D.D.

2010-12-07

159

Exploiting level anti-crossings (LACs) in the rotating frame for transferring spin hyperpolarization.  

PubMed

A method of transferring hyperpolarization among scalar-coupled nuclear spins is proposed, which is based on spin mixing at energy Level Anti-Crossing (LAC) regions. To fulfill LAC conditions a resonant RF-field was applied with properly set frequency and amplitude. In this situation LACs occur between the nuclear spin levels in the rotating doubly tilted reference frame. The validity of the approach is demonstrated by taking as an example the transfer of para-hydrogen induced polarization in a symmetric molecule, whose coupled spin network can be modeled as a four-spin AA'MM'-system with two pairs of 'isochronous' spins. For this spin system LAC positions have been identified; rules for the sign of spin polarization have been established. The dependence of the polarization transfer efficiency on the RF-field parameters and on the time profile of switching off the RF-field has been studied in detail; experimental results are in excellent agreement with the theory developed. In general, exploiting LACs in the rotating doubly tilted frame is a powerful tool for manipulating hyperpolarization in multispin systems. PMID:24870026

Pravdivtsev, Andrey N; Yurkovskaya, Alexandra V; Lukzen, Nikita N; Vieth, Hans-Martin; Ivanov, Konstantin L

2014-09-21

160

High-Resolution Radio Imaging of Gravitational Lensing Candidates in the 1 Jansky BL Lac Sample  

E-print Network

While BL Lacertae objects are widely believed to be highly beamed, low-luminosity radio galaxies, many radio-selected BL Lacs have extended radio power levels and optical emission lines that are too luminous to be low-luminosity radio galaxies. Also, Stocke & Rector discovered an excess of MgII absorption systems along BL Lac sightlines compared to quasars, suggesting that gravitational lensing may be another means of creating the BL Lac phenomenon in some cases. We present a search for gravitationally-lensed BL Lacs with deep, high-resolution, two-frequency VLA radio maps of seven lensing candidates from the 1 Jansky BL Lac sample. We find that none of these objects are resolved into an Einstein ring like B 0218+357, nor do any show multiple images of the core. All of the lensing candidates that were resolved show a flat-spectrum core and very unusual, steep-spectrum extended morphology that is incompatible with a multiply lensed system. Thus, while these observations do not rule out microlensing, no macrolensing is observed.

T. A. Rector; J. T. Stocke

2003-02-19

161

The Sedentary Multi-Frequency Survey of HBL BL Lacs: an Update  

NASA Astrophysics Data System (ADS)

New results from the Sedentary Multi-Frequency Survey of HBL BL Lacs (Giommi, Menna and Padovani 1999) are presented. The survey, which is based on a highly efficient (>80%) multi-frequency statistical selection method and includes 155 objects, is currently spectroscopically identified at the 83% level and is the largest flux limited and complete sample of BL Lacs existing today. Here we report on updated results on the radio LogN-LogS and the Ve / Va test together with a preliminary version of the radio luminosity function. Our results ( = 0.41 ± 0.02) confirm the negative cosmological evolution of HBL BL Lacs at low radio fluxes (fr about 3.5-20 mJy) and set important constraints to emission models and Blazar unification schemes. We also present BeppoSAX observations of 4 BL Lacs of the Sedentary Survey which confirm that the Spectral Energy Distributions (SEDs) of these sources are typical of extreme HBL BL Lacs.

Perri, M.; Giommi, P.; Piranomonte, S.; Padovani, P.

162

Spatial and seasonal variation in wave attenuation over Zostera noltii  

NASA Astrophysics Data System (ADS)

Wave attenuation is a recognized function of sea grass ecosystems which is believed to depend on plant characteristics. This paper presents field data on wave attenuance collected over a 13 month period in a Zostera noltii meadow. The meadow showed a strong seasonality with high shoot densities in summer (approximately 4,600 shoots/m2) and low densities in winter (approximately 600 shoots/m2). Wave heights and flow velocities were measured along a transect at regular intervals during which the site was exposed to wind waves and boat wakes that differ in wave period and steepness. This difference was used to investigate whether wave attenuation by sea grass changes with hydrodynamic conditions. A seasonal change in wave attenuation was observed from the data. Results suggest that a minimum shoot density is necessary to initiate wave attenuation by sea grass. Additionally, a dependence of wave attenuation on hydrodynamics was found. Results suggest that the threshold shoot density varies with wave period and a change in energy dissipation toward the shore was observed once this threshold was exceeded. An attempt was made to quantify the bed roughness of the meadow; the applicability of this roughness value in swaying vegetation is discussed. Finally, the drag coefficient for the meadow was computed: A relationship between wave attenuance and vegetation Reynolds number was found which allows comparing the wave attenuating effect of Zostera noltii to other plant species.

Paul, M.; Amos, C. L.

2011-08-01

163

[Analysis of main pigments and other ingredients in lac color product].  

PubMed

The contents of the main pigments and other ingredients in commercial lac color products were determined by HPLC using an RP-18 column with 0.1 mol/L citric acid buffer solution-methanol (16:5) as the mobile phase, and a photodiode array (PDA) detector set at 280 nm and 490 nm. The main pigments were confirmed by PDA and electrospray ionization mass spectrometry. Laccaic acids A, B, C and E were detected in all lac color products, and the ratio of content of laccaic acid A in all products was over 50%. The total contents of laccaic acids A, B and C in lac color food additive products and reagent products were 775-858, 797 and 779 g/kg, respectively. As for the contents of ingredients except pigments in commercial food additive products, the maximum moisture content was about 10%, and ether-soluble substances amounted to 0.5-3.6%. PMID:11486376

Hirata, K; Uematsu, Y; Suzuki, K; Iida, K; Yasuda, K; Saito, K

2001-04-01

164

The sedentary survey of extreme high-energy peaked BL Lacs. III. Results from optical spectroscopy  

NASA Astrophysics Data System (ADS)

Aims:The multi-frequency sedentary survey is a flux-limited, statistically well-defined sample of highly X-ray dominated (i.e., with a very high X-ray to radio flux ratio) BL Lacertae objects, which includes 150 sources. In this paper, the third of the series, we report the results of a dedicated optical spectroscopy campaign that, together with results from other independent optical follow-up programs, led to the spectroscopic identification of all sources in the sample. Methods: We carried out a systematic spectroscopic campaign for the observation of all unidentified objects of the sample using the ESO 3.6 m, the KPNO 4 m, and the TNG optical telescopes. Results: We present new identifications and optical spectra for 76 sources, 50 of which are new BL Lac objects, 18 are sources previously referred as BL Lacs but for which no redshift information was available, and 8 are broad emission-line AGNs. We find that the multi-frequency selection technique used to build the survey is highly efficient (~90%) in selecting BL Lacs objects. We present positional and spectroscopic information for all confirmed BL Lac objects. Our data allowed us to determine 36 redshifts out of the 50 new BL Lacs and 5 new redshifts for the previously known objects. The redshift distribution of the complete sample is presented and compared with that of other BL Lacs samples. For 26 sources without recognizable absorption features, we calculated lower limits to the redshift using a method based on simulated optical spectra with different ratios between jet and galaxy emission. For a subsample of 38 object with high-quality spectra, we find a correlation between the optical spectral slope, the 1.4 GHz radio luminosity, and the Ca H&K break value, indicating that for powerful/beamed sources the optical light is dominated by the non-thermal emission from the jet.

Piranomonte, S.; Perri, M.; Giommi, P.; Landt, H.; Padovani, P.

2007-08-01

165

The Sedentary Multi-Frequency Survey. I. Statistical Identification and Cosmological Properties of HBL BL Lacs  

E-print Network

We have assembled a multi-frequency database by cross-correlating the NVSS catalog of radio sources with the RASSBSC list of soft X-ray sources, obtaining optical magnitude estimates from the Palomar and UK Schmidt surveys as provided by the APM and COSMOS on-line services. By exploiting the nearly unique broad-band properties of High-Energy Peaked (HBL) BL Lacs we have statistically identified a sample of 218 objects that is expected to include about 85% of BL Lacs and that is therefore several times larger than all other published samples of HBLs. Using a subset (155 objects) that is radio flux limited and statistically well-defined we have derived the \\vovm distribution and the LogN-LogS of extreme HBLs (fx/fr >= 3E-10 erg/cm2/s/Jansky) down to 3.5 mJy. We find that the LogN-LogS flattens around 20 mJy and that = 0.42 +/- 0.02. This extends to the radio band earlier results, based on much smaller X-ray selected samples, about the anomalous cosmological observational properties of HBL BL Lacs. A comparison with the expected radio LogN-LogS of all BL Lacs (based on a beaming model) shows that extreme HBLs make up roughly 2% of the BL Lac population, independently of radio flux. This result, together with the flatness of the radio logN-logS at low fluxes, is in contrast with the predictions of a recent model which assumes an anti-correlation between peak frequency and bolometric luminosity. The extreme fx/fr flux ratios and high X-ray fluxes of these BL Lacs makes them good candidate TeV sources, some of the brighter (and closer) ones possibly detectable with the current generation of Cerenkov telescopes.

P. Giommi; M. T. Menna; P. Padovani

1999-07-01

166

The Sedentary Survey of Extreme High Energy Peaked BL Lacs III. Results from Optical Spectroscopy  

E-print Network

The multi-frequency Sedentary Survey is a flux limited, statistically well-defined sample of highly X-ray dominated BL Lacertae objects (HBLs) which includes 150 sources. In this paper, the third of the series, we report the results of a dedicated optical spectroscopy campaign that, together with results from other independent optical follow up programs, led to the spectroscopic identification of all sources in the sample. We carried out a systematic spectroscopic campaign for the observation of all unidentified objects of the sample using the ESO 3.6m, the KPNO 4m, and the TNG optical telescopes. We present new identifications and optical spectra for 76 sources, 50 of which are new BL Lac objects, 18 are sources previously referred as BL Lacs but for which no redshift information was available, and 8 are broad emission lines AGNs. We find that the multi-frequency selection technique used to build the survey is highly efficient (about 90%) in selecting BL Lacs objects. We present positional and spectroscopic information for all confirmed BL Lac objects. Our data allowed us to determined 36 redshifts out of the 50 new BL Lacs and 5 new redshifts for the previously known objects. The redshift distribution of the complete sample is presented and compared with that of other BL Lacs samples. For 26 sources without recognizable absorption features, we calculated lower limits to the redshift using a method based on simulated optical spectra with different ratios between jet and galaxy emission. For a subsample of 38 object with high-quality spectra, we find a correlation between the optical spectral slope, the 1.4 GHz radio luminosity, and the Ca H&K break value, indicating that for powerful/beamed sources the optical light is dominated by the non-thermal emission from the jet.

S. Piranomonte; M. Perri; P. Giommi; H. Landt; P. Padovani

2007-04-13

167

A single mutation in the core domain of the lac repressor reduces leakiness  

E-print Network

repress expression, are listed in the right column (in bold or italics to indicate whether they confer the I+ or Is phenotype, respectively). Figure 3 GFP production kinetics for LacI and LacIWF. Cells transformed with either pLIGFP (blue/cyan) or p... ,48], was fused to maltose-binding protein (MBP) and cloned in place of GFP to give plasmids pLIHP and pLIHP_W220F. In the absence of the inducer, cells transformed with the pLIHP_W220F plasmid showed growth curves that are indistinguishable from those of cells...

Gatti-Lafranconi, Pietro; Dijkman, Willem P; Devenish, Sean RA; Hollfelder, Florian

2013-07-08

168

?-Galactosidase staining of lacZ fusion proteins in whole tissue preparations.  

PubMed

The lacZ gene product, ?-galactosidase, has classically been used as a reporter of gene expression. ?-Galactosidase activity can be detected using a chromogenic substrate, X-gal, which leaves an intense blue precipitate when cleaved by the enzyme. Insertion of the lacZ coding DNA targeted into a specific gene creates a ?-galactosidase-tagged fusion protein that is expressed under the endogenous promoter. Analysis of the hybrid protein takes advantage of the chromogenic detection system, as the distribution and relative abundance of the expressed protein can be efficiently visualized. PMID:23681629

Cooper, Margaret A; Zhou, Renping

2013-01-01

169

Expression of the transposable lac operon Tn951 in Rhodopseudomonas sphaeroides.  

PubMed Central

The transposon Tn951 (lac) was introduced into the photosynthetic bacterium Rhodopseudomonas sphaeroides 2.4.1, which is normally Lac-, via the P-group plasmid RP1. beta-Galactosidase was produced constitutively in both chemotrophically and phototrophically grown cells, and the levels were found to be the same but low. Mutants were isolated, however, that were able to grow on lactose minimal medium and which expressed different levels of beta-galactosidase when grown chemotrophically or phototrophically. The beta-galactosidase levels found in all R. sphaeroides strains were much less than those found in Escherichia coli. PMID:6290458

Nano, F E; Kaplan, S

1982-01-01

170

Mutant lac repressors with new specificities hint at rules for protein--DNA recognition.  

PubMed Central

Proteins which recognize specific sequences of DNA play a fundamental role in the regulation of protein synthesis in all organisms. A particular helix of the bacterial protein lac repressor recognizes the bases in the major groove of the lac operator. We show that the first two residues of this recognition helix interact independently with two base pairs. This allows us in many cases to predict repression as an indicator of strength of the repressor-operator complex. Rules of recognition can be derived for 16 symmetric operators. They also apply to the gal repressor and possibly to other bacterial repressors. Images Fig. 2. PMID:2178920

Lehming, N; Sartorius, J; Kisters-Woike, B; von Wilcken-Bergmann, B; Muller-Hill, B

1990-01-01

171

Tritium Attenuation by Distillation  

SciTech Connect

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.

Wittman, N.E.

2001-07-31

172

Effective x-ray attenuation measurements with full field digital mammography  

SciTech Connect

This work shows that effective x-ray attenuation coefficients may be estimated by applying Beer's Law to phantom image data acquired with the General Electric Senographe 2000D full field digital mammography system. Theoretical developments are provided indicating that an approximate form of the Beer's relation holds for polychromatic x-ray beams. The theoretical values were compared with experimentally determined measured values, which were estimated at various detector locations. The measured effective attenuation coefficients are in agreement with those estimated with theoretical developments and numerical integration. The work shows that the measured quantities show little spatial variation. The main ideas are demonstrated with polymethylmethacrylate and breast tissue equivalent phantom imaging experiments. The work suggests that the effective attenuation coefficients may be used as known values for radiometric standardization applications that compensate for the image acquisition influences. The work indicates that it is possible to make quantitative attenuation coefficient measurements from a system designed for clinical purposes.

Heine, John J.; Behera, Madhusmita [The H. Lee Moffitt Cancer Center and Research Institute, 12902 Magnolia Drive, Tampa, Florida 33612-4799 (United States)

2006-11-15

173

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

Microsoft Academic Search

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

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

1994-01-01

174

Program Evaluation: Outcomes of Participation in Lac Du Bois, the French Language Village of Concordia Language Villages  

ERIC Educational Resources Information Center

The purpose of this study was to describe perceptions of stakeholders (leadership of Concordia Language Villages, staff members and villagers of "Lac du Bois", the French Language Village of Concordia Language Villages), related to achievement of the mission statement. The research question was: How do stakeholders in "Lac du…

Clementi, Donna L.

2012-01-01

175

Attenuation of Radiation by Dr. James E. Parks  

E-print Network

in the material. The range of charged particles at a given energy is defined as the average distance they travel charged particles interact with materials, (3) to study the 3 primary ways that gamma rays interact attenuation coefficients for beta particles and gamma rays. Theory There are two primary types of radiation

Dai, Pengcheng

176

Modeling, evaluation, and asymptotic analysis of attenuation anisotropy  

NASA Astrophysics Data System (ADS)

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.

Shekar, Bharath Chandra

177

BL Lac contribution to the Extragalactic Gamma-Ray Background  

E-print Network

Very high energy gamma-rays(E>20GeV) from blazars traversing cosmological distances through the metagalactic radiation field can convert to electron-positron pairs in photon-photon collisions. The converted gamma-rays initiate electromagnetic cascades driven by inverse-Compton scattering off the microwave background photons. The cascades shift the injected gamma ray spectrum to MeV-GeV energies. Randomly oriented magnetic fields rapidly isotropize the secondary electron-positron beams resulting from the beamed blazar gamma ray emission, leading o faint gamma-ray halo. Using a model for the time-dependent metagalactic radiation field consistent with all currently available far-infrared-to-optical data, we compute (i) the expected gamma-ray attenuation in blazar spectra, and (ii) the cascade contribution from faint, unresolved blazars to the extragalactic gamma-ray background as measured by EGRET, assuming a generic emitted spectrum extending to an energy of 10 TeV. The latter cascade contribution to the EGRET background is fed by the assumed >20 GeV emission from the hitherto undiscovered sources, and we estimate their dN-dz distribution taking into account that the nearby (z<0.2) fraction of these sources must be consistent with the known (low) numbers of sources above 300 GeV.

Tanja Kneiske; Karl Mannheim

2004-11-05

178

Cloud attenuation at millimeter wavelengths  

Microsoft Academic Search

Total atmospheric attenuation under conditions of complete and cloud cover was measured at frequencies of 15 and 35 GHz in the Boston area. The attenuations were actually inferred from extinction measurements using the sun as a source. Measurements were made at 29 elevation angles from 1 to 20 deg, and the angular dependence of the attenuation was examined. For most

Edward E. Altshuler; Richard A. Marr

1989-01-01

179

Multiple Lac-mediated loops revealed by Bayesian statistics and tethered particle motion  

E-print Network

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 co-existing 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 (TPM), a versatile and commonly-used in vitro single-molecule technique. Our method, vbTPM, is based on a variational Bayes treatment of hidden Markov models. It learns the number of distinct states (i.e., DNA-protein conformations) directly from TPM data with better resolution than existing methods, while easily correcting for common experimental artifacts. Studying short (roughly 100 bp) LacI-mediated loops, we are able to resolve three distinct loop structures, more than previously reported at ...

Johnson, Stephanie; Phillips, Rob; Wiggins, Chris H; Lindén, Martin

2014-01-01

180

Ecological Characteristics of Streams in the Barrenlands near Lac de Gras, N.W.T., Canada  

Microsoft Academic Search

We examined spatiotemporal variation in the physical, chemical, and biological characteristics of pristine streams that represent a range of conditions near Lac de Gras in the Barrenlands region of the Northwest Territories, Canada. Principal component analysis organized streams into four groups on the basis of seven physical characteristics. Despite broad differences among groups in physical characteristics, variation in chemical and

NICHOLAS E. JONES; WILLIAM M. TONN; GARRY J. SCRIMGEOUR; CHRIS KATOPODIS

2003-01-01

181

Spectroscopy of the Largest Ever ?-Ray-selected BL Lac Sample  

NASA Astrophysics Data System (ADS)

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 \\tilde{z} from 0.23 to 0.33 and include redshifts as large as z = 2.471. Spectroscopic redshift minima from intervening absorbers have \\tilde{z}= 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 • ~ 108.5 - 109, substantially larger than the mean of optical AGNs and LAT Flat Spectrum Radio Quasar samples. A slow increase in M • 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 ?-ray properties, suggesting that strong beaming is the primary cause of the range in continuum dominance.

Shaw, Michael S.; Romani, Roger W.; Cotter, Garret; Healey, Stephen E.; Michelson, Peter F.; Readhead, Anthony C. S.; Richards, Joseph L.; Max-Moerbeck, Walter; King, Oliver G.; Potter, William J.

2013-02-01

182

STRUCTURAL ASPECTS REGARDING TO THE IMAGE OF ICE HOTEL BALEA LAC BREND  

Microsoft Academic Search

Applying a poll-based survey provides important information regarding the tourist offer particulars in Bâlea Lac area. On the day the survey is performed its main advantage is also outlined: the fact that this information display a good accuracy, are obtained in a short time span and involving relatively low expenses. Data collection and centralization of the answers provided by interviewed

Marian ZAHARIA; Cristian Valentin HAPENCIUC; Ioana ZAHEU

2008-01-01

183

Chronology and depositional processes of the laminated sediment record from Lac d'Annecy, French Alps  

Microsoft Academic Search

A high resolution sediment record spanning the entire time since the ice retreat after the Last Glacial Maximum has been recovered from Lac d'Annecy. The main focus of this study is to develop a reliable chronology of the record and to evaluate the environmental variability during the period of Late Würmian ice retreat. Most of the record is laminated. These

Achim Brauer; Joël Casanova

2001-01-01

184

Palyno- and chronostratigraphy of a long sequence from Lac d'Annecy (northern outer Alps, France)  

Microsoft Academic Search

Pollen analysis (absolute and relative frequencies) of a 44 m sedimentary sequence from Lac d'Annecy provides a record of vegetation history since deglaciation in the northern part of the French alpine foreland. Sixteen pollen zones are described and compared with those obtained from sites in adjacent areas, and 17 AMS radiocarbon dates provide a chronology which enables a minimum age

F. David; G. Farjanel; M. P. Jolly

2001-01-01

185

Elastic Rod Model of a DNA Loop in the Lac Operon  

NASA Astrophysics Data System (ADS)

We use the theory of elasticity to compute the shape of the DNA loop bridging the gap in the crystal structure of the lac repressor-DNA complex. The Kirchhoff system of equations with boundary conditions derived from the crystal structure is solved using a continuation method. This approach can be applied effectively to find coarse-grained conformational minima of DNA loops.

Balaeff, Alexander; Mahadevan, L.; Schulten, Klaus

1999-12-01

186

Weak operator binding enhances simulated lac repressor-mediated DNA looping.  

PubMed

The 50th anniversary of Biopolymers coincides closely with the like celebration of the discovery of the Escherichia coli (lac) lactose operon, a classic genetic system long used to illustrate the influence of biomolecular structure on function. The looping of DNA induced by the binding of the Lac repressor protein to sequentially distant operator sites on DNA continues to serve as a paradigm for understanding long-range genomic communication. Advances in analyses of DNA structures and in incorporation of proteins in computer simulations of DNA looping allow us to address long-standing questions about the role of protein-mediated DNA loop formation in transcriptional control. Here we report insights gained from studies of the sequence-dependent contributions of the natural lac operators to Lac repressor-mediated DNA looping. Novel superposition of the ensembles of protein-bound operator structures derived from NMR measurements reveals variations in DNA folding missed in conventional structural alignments. The changes in folding affect the predicted ease with which the repressor induces loop formation and the ways that DNA closes between the protein headpieces. The peeling of the auxiliary operators away from the repressor enhances the formation of loops with the 92-bp wildtype spacing and hints of a structural reason behind their weak binding. © 2013 Wiley Periodicals, Inc. Biopolymers 99: 1070-1081, 2013. PMID:23818216

Colasanti, Andrew V; Grosner, Michael A; Perez, Pamela J; Clauvelin, Nicolas; Lu, Xiang-Jun; Olson, Wilma K

2013-12-01

187

Gamma-Ray Bright BL Lac Object RX J1211+2242.  

National Technical Information Service (NTIS)

RX J1211+2242 is an optically faint (B approximately equal to 19.2mag) but X-ray bright (f2-10kev = 5 x l0(exp -12)erg per square centimeter per second) AGN, which has been shown to be a BL Lac object at redshift z = 0.455. The ROSAT X-ray, Calar Alto opt...

V. Beckmann, P. Favre, F. Tavecchio, T. Bussien, J. Fliri, A. Wolter

2004-01-01

188

Lac operon problem, 2D animationSite: DNA Interactive (www.dnai.org)  

NSDL National Science Digital Library

The first model for the control of protein production was the lac operon. This system of feedback and negative regulation is used by bacteria, however, the general principles also apply to higher organisms. Another method of protein regulation involves the unwrapping of DNA.

2008-10-06

189

RATAN-600 multi-frequency data for the BL Lac objects  

E-print Network

We present a new catalogue of the RATAN-600 multi-frequency measurements for BL Lac objects. The purpose of this catalogue is to compile the BL Lac multi-frequency data that is acquired with the RATAN-600 simultaneously at several frequencies. The BL Lac objects emit a strongly variable and polarized non-thermal radiation across the entire electromagnetic spectrum from radio to gamma-rays and represent about one percent of known AGNs. They belong to the blazar population and differ from other blazars featureless optical spectrum, which sometimes have absorption lines, or have weak and narrow emission lines. One of the most effective ways of studying the physics of BL Lacs is the use of simultaneous multi-frequency data. The multi-frequency broadband radio spectrum was obtained simultaneously with an accuracy of up to 1-2 minutes for four to six frequencies: 1.1, 2.3, 4.8, 7.7, 11.2, and 21.7 GHz. The catalogue is based on the RATAN-600 observations and on the data from: equatorial coordinate and redshift, R-b...

Mingaliev, M G; Udovitskiy, R Yu; Mufakharov, T V; Nieppola, E; Erkenov, A K

2014-01-01

190

The ultraviolet spectrum of the high red shift BL Lac object 0215+015  

Microsoft Academic Search

The hydrogen Lyman lines of the red shift systems in BL Lac 0215 + 015 were studied by combining three low dispersion IUE spectra. Lyman alpha lines are identified from four of the red shift systems. In the Za = 1.649 system, Lyman beta, gamma and delta lines are noted. Features attributed to zero red shift, galactic MgII and FeII

J. C. Blades; M. Pettini; R. W. Hunstead; H. S. Murdoch

1982-01-01

191

Ultrasonic assisted dyeing. IV. Dyeing of cationised cotton with lac natural dye  

Microsoft Academic Search

The dyeing of cationised cotton fabrics with lac natural dye has been studied using both conventional and ultrasonic techniques. The effects of dye bath pH, salt concentration, ultrasonic power, dyeing time and temperature were studied and the resulting shades obtained by dyeing with ultrasonic and conventional techniques were compared. Colour strength values obtained were found to be higher with ultrasonic

M. M. Kamel; Reda M. El-Shishtawy; B. M. Youssef; H. Mashaly

2007-01-01

192

Factors Influencing the Hooking Mortality of Walleyes Caught by Recreational Anglers on Mille Lacs, Minnesota  

Microsoft Academic Search

Recent implementation of size-based regulations in recreational fisheries for walleye Sander vitreus have led to more released walleyes and presumably to more losses of released fish. We conducted this study to estimate hooking mortality in Mille Lacs, Minnesota, and to determine factors that influence the survival of released walleyes. Volunteers and Minnesota Department of Natural Resources employees sampled walleyes with

Keith A. Reeves; Richard E. Bruesewitz

2007-01-01

193

VizieR Online Data Catalog: High energy peaked BL Lacs optical spectros. (Piranomonte+, 2007)  

NASA Astrophysics Data System (ADS)

Spectroscopic observations of the Sedentary sources still unidentified and of BL Lacs without redshift were carried out during the period 1999-2003 at the KPNO 4m, at the ESO 3.6m and at the TNG telescopes. (3 data files).

Piranomonte, S.; Perri, M.; Giommi, P.; Landt, H.; Padovani, P.

2007-10-01

194

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

PubMed

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

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

2013-10-01

195

Adaptive mutation: General mutagenesis is not a programmed response to stress but results from rare coamplification of dinB with lac  

Microsoft Academic Search

In a particular genetic system, selection stimulates reversion of a lac mutation and causes genome-wide mutagenesis (adaptive mutation). Selection allows rare plated cells with a duplication of the leaky lac allele to initiate clones within which further lac amplification improves growth rate. Growth and amplification add mutational targets to each clone and thereby increase the likelihood of reversion. We suggest

E. Susan Slechta; Kim L. Bunny; Elisabeth Kugelberg; Eric Kofoid; Dan I. Andersson; John R. Roth

2003-01-01

196

Substrate-induced changes in the structural properties of LacY  

PubMed Central

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

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

2014-01-01

197

Experimental and theoretical studies on visible light attenuation in water  

E-print Network

In this study we describe lab experiments on determining the above water reflectance Rrs coefficient, and the water attenuation coefficient Kd for fresh water. Different types of screens (totally absorbent, gray, etc.) were submerged in water (0-0.6 m) and illuminated from outside. The spectral density of the water leaving radiance was measured for different depths. The results were ran by a code which took into account the geometry of the incident irradiation, the geometry of the screen under water, and boundary conditions at the water surface provided by the radiation transfer theory. From the experimental data and our model we obtain the spectral distribution of the attenuation coefficient for fresh water and compared it with other data in literature. These experiments, performed in the Nonlinear Wave Lab at ERAU# represent just a preliminary calibration of the experimental protocol. More tests with water of different degrees of turbidity, and possibly wave filed at the water surface are in progress and wi...

Simpson, A; Cho, H J; Liu, H

2014-01-01

198

Multiwavelength Observations of the BL Lac PKS 2155-304 with the H.E.S.S. Cherenkov Telescopes  

NASA Astrophysics Data System (ADS)

The High Energy Stereoscopic System (H.E.S.S.) has observed the X-ray selected BL Lac object PKS 2155—304 in 2003 between October 19 and November 26 in Very High Energy (VHE) ?-rays (E ? 160 GeV here). Observations were carried out simultaneously for the first time with the PCA on board the RXTE satellite, the Robotic Optical Transient Search Experiment (ROTSE) and the Nançay decimetric radiotelescope (NRT). Intranight variability of the order of 80% is reported in the VHE band, the source being detected with a high significance on each night it was observed. More significant variability is found in the X-ray and optical bands on kilosecond timescales along with flux-dependent spectral changes in the X-rays. No correlation can be established between the X-ray and the ?-ray fluxes, or any of the other wavebands, over the small range of observed variability. The average H.E.S.S. spectrum is a very soft power law with a photon index of 3.37±0.07. The energy output in the 2-10 keV and in the VHE ?-ray range are found to be similar, with the X-rays and the optical fluxes at a level comparable to some of the lowest historical measurements indicating that PKS 2155—304 was in a low or quiescent state during the observations. Both a leptonic and a hadronic model are used to find the underlying physical parameters that can be found with these observations. These parameters are found to be sensitive to the model of Extragalactic Background Light (EBL) that attenuates the VHE signal at the redshift considered here.

Giebels, Berrie; H.E.S.S. Collaboration

199

Tethered particle motion reveals that LacI·DNA loops coexist with a competitor-resistant but apparently unlooped conformation.  

PubMed

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

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

2014-02-01

200

OCT skin image enhancement through attenuation compensation.  

PubMed

The enhancement of optical coherence tomography (OCT) skin images can help dermatologists investigate the morphologic information of the images more effectively. In this paper, we propose an enhancement algorithm with the stages that includes speckle reduction, skin layer detection, and attenuation compensation. A weighted median filter is designed to reduce the level of speckle while preserving the contrast. A novel skin layer detection technique is then applied to outline the main skin layers: stratum corneum, epidermis, and dermis. The skin layer detection algorithm does not make any assumption about the structure of the skin. A model of the light attenuation is then used to estimate the attenuation coefficient of the stratum corneum, epidermis, and dermis layers. The performance of the algorithm has been evaluated qualitatively based on visual evaluation and quantitatively using two no-reference quality metrics: signal-to-noise ratio and contrast-to-noise ratio. The enhancement algorithm is tested on 35 different skin OCT images, which show significant improvements in the quality of the images, especially in the structures at deeper levels. PMID:22858930

Hojjatoleslami, Ali; Avanaki, Mohammad R N

2012-07-20

201

Poly-LacNAc as an age-specific ligand for rotavirus P[11] in neonates and infants.  

PubMed

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

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

2013-01-01

202

First attenuation study at Usu volcano (Hokkaido, Japan)  

NASA Astrophysics Data System (ADS)

2D and 3D attenuation structures of Usu volcano has been obtained with measurements of diffusion model and coda-normalization method, respectively, with the same data-set used to develop the 3D velocity tomography by Onizawa et al., (2007). We have obtained intrinsic and scattering 2D maps applying the diffusion model which is an approximation of the general energy transport theory developed by Wegler and Lühr (2001) and Wegler (2003). As a result of the theoretical curves with the energy envelopes of the seismograms, we have obtained intrinsic attenuation coefficient and diffusivity coefficient values in the frequency range of 4-16 Hz. Then, We have quantified the contribution of intrinsic and scattering attenuation by inverse quality factor because is more representative. Finally, with a new representation method based in the Gaussian probability function distribution, we have represented the inverse quality factors obtained into 2D contour maps. To obtain 3D attenuation tomography of Deception Island, we have used more than 2000 waveforms recorded at over 288 on land seismic stations. The rays were traced in a 3D velocity model. We have inverted the spectral ratios obtained with the coda normalization method to obtain total-Q values. We resolve 1 km cubic cells. Both results, 2D maps and 3D attenuation structure, have shown that there is likewise agreement with the velocity tomography: the low velocity zones being consistent with regions featuring high attenuation effects and the high velocity zones with regions featuring low attenuation effects. This new models will be a complement to the better understanding of velocity anomalies and will allow remove some grades of uncertainty of the other studies.

Prudencio, Janire; Taira, Taka'aki; De Siena, Luca; Onizawa, Shin'ya; Ibañez, Jesús; Hellweg, Margaret; Del Pezzo, Edoardo; Aoyama, Hiroshi; García-Yeguas, Araceli; Oshima, Hiromitsu; Díaz-Moreno, Alejandro

2014-05-01

203

Ultrasonic attenuation in superconducting molybdenum-rhenium alloys.  

NASA Technical Reports Server (NTRS)

Investigation of longitudinal sound attenuation in superconducting Mo-Re alloys as a function of temperature, magnetic field, and frequency. Evaporated thin film CdS transducers were used for the measurements at frequencies up to 3 GHz. The normal state attenuation coefficient was found to be proportional to the square of frequency over this frequency range. Measurements in zero magnetic field yielded a value of the energy gap parameter close to the threshold value of 3.56 kTc, appropriate to a weakly coupled dirty limit superconductor.

Ashkin, M.; Deis, D. W.; Gottlieb, M.; Jones, C. K.

1971-01-01

204

Ultrasonic Attenuation in Zircaloy-4  

SciTech Connect

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.

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

205

Vertebrate caudal gene expression gradients investigated by use of chick cdx-A\\/ lacZ and mouse cdx-1\\/ lacZ reporters in transgenic mouse embryos: evidence for an intron enhancer  

Microsoft Academic Search

The vertebrate caudal proteins, being upstream regulators of the Hox genes, play a role in establishment of the body plan. We describe analysis of two orthologous caudal genes (chick cdx-A and mouse cdx-1) by use of lacZ reporters expressed in transgenic mouse embryos. The expression patterns show many similarities to the expression of endogenous mouse cdx-1. At 8.7 days, cdx\\/lacZ

Stephen J. Gaunt; Deborah Drage; Adam Cockley

2003-01-01

206

Enhancing lysosome biogenesis attenuates BNIP3-induced cardiomyocyte death  

PubMed Central

Hypoxia-inducible pro-death protein BNIP3 (BCL-2/adenovirus E1B 19-kDa interacting protein 3), provokes mitochondrial permeabilization causing cardiomyocyte death in ischemia-reperfusion injury. Inhibition of autophagy accelerates BNIP3-induced cell death, by preventing removal of damaged mitochondria. We tested the hypothesis that stimulating autophagy will attenuate BNIP3-induced cardiomyocyte death. Neonatal rat cardiac myocytes (NRCMs) were adenovirally transduced with BNIP3 (or LacZ as control; at multiplicity of infection = 100); and autophagy was stimulated with rapamycin (100 nM). Cell death was assessed at 48 h. BNIP3 expression increased autophagosome abundance 8-fold and caused a 3.6-fold increase in cardiomyocyte death as compared with control. Rapamycin treatment of BNIP3-expressing cells led to further increase in autophagosome number without affecting cell death. BNIP3 expression led to accumulation of autophagosome-bound LC3-II and p62, and an increase in autophagosomes, but not autolysosomes (assessed with dual fluorescent mCherry-GFP-LC3 expression). BNIP3, but not the transmembrane deletion variant, interacted with LC3 and colocalized with mitochondria and lysosomes. However, BNIP3 did not target to lysosomes by subcellular fractionation, provoke lysosome permeabilization or alter lysosome pH. Rather, BNIP3-induced autophagy caused a decline in lysosome numbers with decreased expression of the lysosomal protein LAMP-1, indicating lysosome consumption and consequent autophagosome accumulation. Forced expression of transcription factor EB (TFEB) in BNIP3-expressing cells increased lysosome numbers, decreased autophagosomes and increased autolysosomes, prevented p62 accumulation, removed depolarized mitochondria and attenuated BNIP3-induced death. We conclude that BNIP3 expression induced autophagosome accumulation with lysosome consumption in cardiomyocytes. Forced expression of TFEB, a lysosomal biogenesis factor, restored autophagosome processing and attenuated BNIP3-induced cell death. PMID:22302006

Ma, Xiucui; Godar, Rebecca J.; Liu, Haiyan; Diwan, Abhinav

2012-01-01

207

Dynamics and bistability in a reduced model of the lac operon  

NASA Astrophysics Data System (ADS)

It is known that the lac operon regulatory pathway is capable of showing bistable behavior. This is an important complex feature, arising from the nonlinearity of the involved mechanisms, which is essential to understand the dynamic behavior of this molecular regulatory system. To find which of the mechanisms involved in the regulation of the lac operon is the origin of bistability, we take a previously published model which accounts for the dynamics of mRNA, lactose, allolactose, permease and ?-galactosidase involvement and simplify it by ignoring permease dynamics (assuming a constant permease concentration). To test the behavior of the reduced model, three existing sets of data on ?-galactosidase levels as a function of time are simulated and we obtain a reasonable agreement between the data and the model predictions. The steady states of the reduced model were numerically and analytically analyzed and it was shown that it may indeed display bistability, depending on the extracellular lactose concentration and growth rate.

Yildirim, Necmettin; Santillán, Moisés; Horike, Daisuke; Mackey, Michael C.

2004-06-01

208

[9] GENE FUSIONS IN YEAST 167 [9] Construction and Use of Gene Fusions to lacZ  

E-print Network

Z) constructed by Casada- ban and Cohen, r to investigate the expression of the sequences around the yeast URA3 in Escherichia coli. 5 These facts have led several workers to construct mutations of the lacZ gene (which

Botstein, David

209

Toward an Integrated Model of Protein-DNA Recognition as Inferred from NMR Studies on the Lac Repressor System  

E-print Network

-DNA Affinity 3570 3. Plasticity in Protein-DNA Recognition 3571 3.1. Lac Protein Binding to Its Natural Propagation and the Interaction Pathway in Protein-DNA Recognition 3580 5.1. Redistribution of the Native

Kalodimos, Charalampos "Babis"

210

Intra-night Optical Variability of BL Lacs, Radio-Quiet Quasars and Radio-Loud Quasars  

E-print Network

We report optical monitoring observations of 20 high-luminosity AGN, 12 of which are radio-quiet quasars (RQQs). Intra-night optical variability (INOV) was detected for 13 of the 20 objects, including 5 RQQs. The variations are distinctly stronger and more frequent for blazars than for the other AGN classes. By combining these data with results obtained earlier in our program, we have formed an enlarged sample consisting of 9 BL Lacs, 19 RQQs and 11 lobe-dominated radio-loud quasars. The moderate level of rapid optical variability found for both RQQs and radio lobe-dominated quasars argues against a direct link between INOV and radio-loudness. We supplemented the present observations of 3 BL Lacs with additional data from the literature. In this extended sample of 12 well observed BL Lacs, stronger INOV is found for the EGRET detected BL Lacs.

C. S. Stalin; A. C. Gupta; Gopal-Krishna; P. J. Wiita; R. Sagar

2004-10-06

211

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

Federal Register 2010, 2011, 2012, 2013

...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,...

2013-01-17

212

Lightning Detection by LAC Onboard the Japanese Venus Climate Orbiter, Planet-C  

Microsoft Academic Search

Lightning activity in Venus has been a mystery for a long period, although many studies based on observations both by spacecraft\\u000a and by ground-based telescope have been carried out. This situation may be attributed to the ambiguity of these evidential\\u000a measurements. In order to conclude this controversial subject, we are developing a new type of lightning detector, LAC (Lightning\\u000a and

Y. Takahashi; J. Yoshida; Y. Yair; T. Imamura; M. Nakamura

2008-01-01

213

Chlorinated hydrocarbons in eggs of grey heron ( Ardea cinerea L.) in France (Lac de Grandlieu)  

Microsoft Academic Search

Nineteen eggs of grey heron (Ardea cinera L.) were collected from nests in France (Lac de Grandlieu) for OCP and PCB residue analysis. ?-HCH, ?-HCH, dieldrine, p,p?-DDD and p,p?-DDT were never detected in any of the eggs. In contrast, significant amounts of HCB, ?-HCH, ?-HCH, HE, p,p?-DDE and PCBs were quantified by GC\\/ECD and identified by GC\\/MS in most of

Isabelle de Cruz; Christian Mougin; Gérard Grolleau

1997-01-01

214

Tracking Micrometastasis to Multiple Organs with lacZ -tagged CWR22R Prostate Carcinoma Cells  

Microsoft Academic Search

SUMMARY Metastasis to organs other than lung is rarely observed in animal model sys- tems of human prostate carcinoma (PCA), with the exception of already metastatic isolates of human PCA cultured for long periods of time. To analyze more directly the evolution of metastatic variants from primary PCA tumor isolates, the lacZ histochemical marker gene was transfected into the CWR22Rv1

Julianne L. Holleran; Carson J. Miller; Lloyd A. Culp

215

Photoelectric monitoring of flare stars AD Leo, EV Lac and YZ CMi from 1980 to 1984  

NASA Astrophysics Data System (ADS)

Simultaneous UBV observations of UV Ceti-type flare stars were performed at Tokyo Astronomical Observatory's Okayama Station during 1980-1984. The stars observed were AD Leo, EV Lac, and YZ CMi. A three-color simultaneous photometer with an unrefrigerated EMI 6256 photomultiplier was used. The integrated intensity for each flare computed by integrated U, B, and V light curves in the relative intensity scale is given.

Ichimura, Kihachiro; Shimizu, Yasuhiro

1986-07-01

216

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

NASA Astrophysics Data System (ADS)

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.

Tavecchio, Fabrizio; Ghisellini, Gabriele; Guetta, Dafne

2014-09-01

217

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

PubMed

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 × 10(6) 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

Solanki, Manu; Garg, Faquir C

2014-01-01

218

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

NASA Technical Reports Server (NTRS)

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.

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

2002-01-01

219

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

E-print Network

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.

M. Boettcher; J. Chiang

2002-08-12

220

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

PubMed Central

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.

Solanki, Manu; Garg, Faquir C.

2014-01-01

221

The Sedentary Survey of Extreme High Energy Peaked BL Lacs III. Results from Optical Spectroscopy  

E-print Network

The multi-frequency Sedentary Survey is a flux limited, statistically well-defined sample of highly X-ray dominated BL Lacertae objects (HBLs) which includes 150 sources. In this paper, the third of the series, we report the results of a dedicated optical spectroscopy campaign that, together with results from other independent optical follow up programs, led to the spectroscopic identification of all sources in the sample. We carried out a systematic spectroscopic campaign for the observation of all unidentified objects of the sample using the ESO 3.6m, the KPNO 4m, and the TNG optical telescopes. We present new identifications and optical spectra for 76 sources, 50 of which are new BL Lac objects, 18 are sources previously referred as BL Lacs but for which no redshift information was available, and 8 are broad emission lines AGNs. We find that the multi-frequency selection technique used to build the survey is highly efficient (about 90%) in selecting BL Lacs objects. We present positional and spectroscopic ...

Piranomonte, S; Giommi, P; Landt, H; Padovani, P

2007-01-01

222

The Sedentary Multi-Frequency Survey; 1, Statistical Identification and Cosmological Properties of HBL BL Lacs  

E-print Network

We have assembled a multi-frequency database by cross-correlating the NVSS catalog of radio sources with the RASSBSC list of soft X-ray sources, obtaining optical magnitude estimates from the Palomar and UK Schmidt surveys as provided by the APM and COSMOS on-line services. By exploiting the nearly unique broad-band properties of High-Energy Peaked (HBL) BL Lacs we have statistically identified a sample of 218 objects that is expected to include about 85% of BL Lacs and that is therefore several times larger than all other published samples of HBLs. Using a subset (155 objects) that is radio flux limited and statistically well-defined we have derived the \\vovm distribution and the LogN-LogS of extreme HBLs (fx/fr >= 3E-10 erg/cm2/s/Jansky) down to 3.5 mJy. We find that the LogN-LogS flattens around 20 mJy and that = 0.42 +/- 0.02. This extends to the radio band earlier results, based on much smaller X-ray selected samples, about the anomalous cosmological observational properties of HBL BL Lacs. A comparison...

Giommi, P; Padovani, P

1999-01-01

223

A new photometric and spectroscopic study of the eclipsing binaries CC Her and CM Lac: Physical parameters and evolutionary status  

E-print Network

New complete light and radial velocities curves were obtained for the eclipsing binaries CC Her and CM Lac. The data are analysed with modern techniques in order to derive the physical parameters of the systems and study their present evolutionary status. We found that CC Her is a classical Algol type binary, while CM Lac is a detached system with two Main Sequence stars in asynchronous orbit.

Liakos, Alexios

2014-01-01

224

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

PubMed

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

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

2012-09-18

225

Cloud attenuation at millimeter wavelengths  

NASA Astrophysics Data System (ADS)

Total atmospheric attenuation under conditions of complete and cloud cover was measured at frequencies of 15 and 35 GHz in the Boston area. The attenuations were actually inferred from extinction measurements using the sun as a source. Measurements were made at 29 elevation angles from 1 to 20 deg, and the angular dependence of the attenuation was examined. For most cloud conditions the attenuation was found to be proportional to the slant path distance through the absorbing atmosphere. For elevation angles above about 8 deg, a flat earth approximation is valid and the slant path distance is proportional to the cosecant of the elevation angle. For low elevation angles the slant path distance is a function of the effective earth radius and the effective height of the attenuating atmosphere, in addition to the elevation angle. A statistical technique for determining the radius and height is described. A zenith attenuation was extrapolated from each set of data. The humidity and frequency dependence of the attenuation was examined. An algorithm for estimating total atmospheric attenuation as a function of elevation angle, frequency, and surface absolute humidity was derived.

Altshuler, Edward E.; Marr, Richard A.

1989-11-01

226

Prediction of Attenuation by Rain  

Microsoft Academic Search

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

ROBERT K. CRANE

1980-01-01

227

Seismic viscoelastic attenuation Submitted to  

E-print Network

the resultant elastic deformation (strain) in the material lags in time the applied stress induced by the wave T of a seismic body wave given by the expression exp(- f T/Q). The apparent Q combines the energy lost to heat attenuate? The attenuation of seismic waves is due to three effects: geometric spreading, intrinsic

Cormier, Vernon F.

228

Suicide Risk: Amplifiers and Attenuators.  

ERIC Educational Resources Information Center

Attempts to integrate findings on correlates of suicide and violent risk in terms of a theory called a two-stage model of countervailing forces, which assumes that the strength of aggressive impulses is modified by amplifiers and attenuators. The vectorial interaction of amplifiers and attenuators creates an unstable equilibrium making prediction…

Plutchik, Robert; Van Praag, Herman M.

1994-01-01

229

Low-energy gamma ray attenuation characteristics of aviation fuels  

NASA Technical Reports Server (NTRS)

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.

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

1990-01-01

230

Inverse problems of ultrasound tomography in models with attenuation  

NASA Astrophysics Data System (ADS)

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.

Goncharsky, Alexander V.; Romanov, Sergey Y.

2014-04-01

231

Attenuation of an air shock wave by perforated baffles  

SciTech Connect

One of the ways of attenuating an air shock wave (ASW) is to use a perforated shield; the parameters of the ASW behind a perforated baffle in the form of a steel sheet with holes are determined by the amplitude of the incident ASW and the sheet perforation coefficient. The authors examine the effects of the perforated shield structure on the ASW behind it and examples are given where the results can be used in the design of test chambers.

Klapovskii, V.E.; Grigor'ev, G.S.; Logvenov, A.Y.; Mineev, V.N.; Vershinin, V.Y.

1984-03-01

232

Low-Frequency Sound Absorption and Attenuation in Marine Medium  

Microsoft Academic Search

Original experimental data are analyzed on the low-frequency sound attenuation in the Mediterranean, Black, and Baltic Seas, Sea of Japan, and the north-western region of the Pacific Ocean. In these regions, waters significantly differ in their temperatures and salinities. The analysis is aimed at obtaining an expression for calculating the low-frequency absorption coefficient in sea water. The analysis uses the

R. A. Vadov

2000-01-01

233

Low-frequency sound absorption and attenuation in marine medium  

Microsoft Academic Search

Original experimental data are analyzed on the low-frequency sound attenuation in the Mediterranean, Black, and Baltic Seas,\\u000a Sea of Japan, and the north-western region of the Pacific Ocean. In these regions, waters significantly differ in their temperatures\\u000a and salinities. The analysis is aimed at obtaining an expression for calculating the low-frequency absorption coefficient\\u000a in sea water. The analysis uses the

R. A. Vadov

2000-01-01

234

Mouse Leydig Cells with Different Androgen Production Potential Are Resistant to Estrogenic Stimuli but Responsive to Bisphenol A Which Attenuates Testosterone Metabolism  

PubMed Central

It is well known that estrogens and estrogen-like endocrine disruptors can suppress steroidogenic gene expression, attenuate androgen production and decrease differentiation of adult Leydig cell lineage. However, there is no information about the possible link between the potency of Leydig cells to produce androgens and their sensitivity to estrogenic stimuli. Thus, the present study explored the relationship between androgen production potential of Leydig cells and their responsiveness to estrogenic compounds. To investigate this relationship we selected mouse genotypes contrasting in sex hormone levels and differing in testosterone/estradiol (T/E2) ratio. We found that two mouse genotypes, CBA/Lac and C57BL/6j have the highest and the lowest serum T/E2 ratio associated with increased serum LH level in C57BL/6j compared to CBA/Lac. Analysis of steroidogenic gene expression demonstrated significant upregulation of Cyp19 gene expression but coordinated suppression of LHR, StAR, 3?HSDI and Cyp17a1 in Leydig cells from C57BL/6j that was associated with attenuated androgen production in basal and hCG-stimulated conditions compared to CBA/Lac mice. These genotype-dependent differences in steroidogenesis were not linked to changes in the expression of estrogen receptors ER? and Gpr30, while ER? expression was attenuated in Leydig cells from C57BL/6j compared to CBA/Lac. No effects of estrogenic agonists on steroidogenesis in Leydig cells from both genotypes were found. In contrast, xenoestrogen bisphenol A significantly potentiated hCG-activated androgen production by Leydig cells from C57BL/6j and CBA/Lac mice by suppressing conversion of testosterone into corresponding metabolite 5?-androstane-3?,17?-diol. All together our data indicate that developing mouse Leydig cells with different androgen production potential are resistant to estrogenic stimuli, while xenoestrogen BPA facilitates hCG-induced steroidogenesis in mouse Leydig cells via attenuation of testosterone metabolism. This cellular event can cause premature maturation of Leydig cells that may create abnormal intratesticular paracrine milieu and disturb proper development of germ cells. PMID:23967237

Savchuk, Iuliia; Soder, Olle; Svechnikov, Konstantin

2013-01-01

235

LacR Mutations Are Frequently Observed in Streptococcus intermedius and Are Responsible for Increased Intermedilysin Production and Virulence  

PubMed Central

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

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

236

SEISMIC ATTENUATION FOR RESERVOIR CHARACTERIZATION  

SciTech Connect

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.

Joel Walls; M.T. Taner; Gary Mavko; Jack Dvorkin

2002-04-01

237

The SOS-LUX-LAC-FLUORO-Toxicity-test on the International Space Station (ISS).  

PubMed

In the 21st 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. PMID:12971406

Rabbow, E; Rettberg, P; Baumstark-Khan, C; Horneck, G

2003-01-01

238

The SOS-LUX-LAC-FLUORO-Toxicity-test on the International Space Station (ISS)  

NASA Astrophysics Data System (ADS)

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.

Rabbow, E.; Rettberg, P.; Baumstark-Khan, C.; Horneck, G.

239

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

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...

Ri, Yong-Wu; Im, Song-Jin

2014-01-01

240

The Connection among Gamma-ray Burst Host-Galaxies, BL Lacs and Quasars  

E-print Network

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.

A. Rej

1999-01-19

241

Flexible Gates Generate Occluded Intermediates in the Transport Cycle of LacY?  

PubMed Central

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

Stelzl, Lukas S.; Fowler, Philip W.; Sansom, Mark S.P.; Beckstein, Oliver

2014-01-01

242

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)

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.

Master, Sharad

2010-11-01

243

High-Level Expression of Bacillus naganoensis Pullulanase from Recombinant Escherichia coli with Auto-Induction: Effect of lac Operator  

PubMed Central

Pullulanase plays an important role in specific hydrolysis of branch points in amylopectin and is generally employed as an important enzyme in starch-processing industry. So far, however, the production level of pullulanase is still somewhat low from wide-type strains and even heterologous expression systems. Here the gene encoding Bacillus naganoensis pullulanase was amplified and cloned. For expression of the protein, two recombinant systems, Escherichia coli BL21(DE3)/pET-20b(+)-pul and E. coli BL21(DE3)/pET-22b(+)-pul, were constructed, both bearing T7 promoter and signal peptide sequence, but different in the existance of lac operator and lacI gene encoding lac repressor. Recombinant pullulanase was initially expressed with the activity of up to 14 U/mL by E. coli BL21(DE3)/pET-20b(+)-pul with IPTG induction in LB medium, but its expression level reduced continually with the extension of cryopreservation time and basal expression was observed. However, E. coli BL21(DE3)/pET-22b(+)-pul , involving lac operator downstream of T7 promoter to regulate foreign gene transcription, exhibited pullulanase activity consistently without detected basal expression. By investigating the effect of lac operator, basal expression of foreign protein was found to cause expression instability and negative effect on production of target protein. Thus double-repression strategy was proposed that lac operators in both chromosome and plasmid were bound with lac repressor to repress T7 RNA polymerase synthesis and target protein expression before induction. Consequently, the total activity of pullulanase was remarkably increased to 580 U/mL with auto-induction by lac operator-involved E. coli BL21(DE3)/pET-22b(+)-pul. When adding 0.6% glycine in culture, the extracellular production of pullulanase was significantly improved with the extracellular activity of 502 U/mL, which is a relatively higher level achieved to date for extracellular production of pullulanase. The successful expression of pullulanase with lac operator regulation provides an efficient way for enhancement of expression stability and hence high-level production of target protein in recombinant E. coli. PMID:24194930

Xu, Yan; Chen, Wen Bo; Mu, Xiao Qing; Wang, Xinye; Xiao, Rong

2013-01-01

244

Analysis of LAC Observations of Clusters of Galaxies and Supernova Remnants  

NASA Technical Reports Server (NTRS)

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.

Hughes, J.

1996-01-01

245

Parameters of Flares on Star EV Lac in 2010-2011  

NASA Astrophysics Data System (ADS)

We present low-resolution spectroscopic observations of star EV Lac. Data were obtained during May, June, August 2010 and May 2011 using the 60-cm Cassegrain telescope at Terskol Peak (North Caucasus, 3100 m a.s.l.). Algorithms and special software were developed for comfortable and quickly processing a large array data because of the lack of suitable software. We processed and analyzed 14800 images with spectra in range from 330 nm to 900 nm with resolution R = 50-100. The temperature and the size of the flare were estimated.

Rieznik, K.; Rechetnyk, M.

2013-11-01

246

The Long-term Light Variation of BL Lac Object 1ES 1959+650  

NASA Astrophysics Data System (ADS)

According to the data of optical observations of the Tuorla Observatory in Finland, using the power spectrum method, DCF (Discrete Correlation Function) method, and Jurkevich method, respectively, we analyzed the periodicity of the long-term light variation of the BL Lac object 1ES 1959+650, and obtained its light period to be P =1.4±0.3 yr. Assuming that the origin of the periodicity is concerned with the accretion disk, we obtained the region where the instability of this source occurs being R =9.65 Rg, here Rg represents the Schwarzschild radius.

Yu-hai, YUAN; Fu-qing, LIU

2014-07-01

247

The Luminosity Function of the Host Galaxies of QSOs and BL Lac Objects  

NASA Astrophysics Data System (ADS)

A clear insight of the galaxies hosting active galactic nuclei is of fundamental importance for understanding the processes of galaxies and nuclei formation and their cosmic evolution. A good characterization of the host galaxies properties requires images of excellent quality in order to disentangle the light of the galaxy from that of the bright nucleus. To this aim HST has provided a major improvement of data on QSOs (Disney et al. 1995; Bahcall et al. 1996,1997; Boyce et al. 1998; McLure et al. 1999; Hamilton et al. 2000; Kukula et al. 2001) and BL Lacs (Scarpa et al. 2000, Urry et al. 2000).

Carangelo, Nicoletta; Falomo, Renato; Treves, Aldo

248

Lac du Flambeau Band of Lake Superior Chippewa Indians Strategic Energy Plan  

SciTech Connect

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.

Bryan Hoover

2009-11-16

249

Low consumption power variable optical attenuator with sol-gel derived organic/inorganic hybrid materials.  

PubMed

An integrated optical waveguide variable optical attenuator (VOA) made of organic/inorganic hybrid materials was fabricated. At 1550 nm, the VOA showed a very low activation power of about 13 mW, due to the large thermo-optic coefficients of the hybrid materials. The optical power attenuations achieved were more than 25 dB for both TE and TM polarization. The response time of the device was less than 4.7 ms. PMID:19516774

Li, Dongxiao; Zhang, Yanwu; Liu, Liying; Xu, Lei

2006-06-26

250

Low consumption power variable optical attenuator with sol-gel derived organic/inorganic hybrid materials  

NASA Astrophysics Data System (ADS)

An integrated optical waveguide variable optical attenuator (VOA) made of organic/inorganic hybrid materials was fabricated. At 1550 nm, the VOA showed a very low activation power of about 13 mW, due to the large thermo-optic coefficients of the hybrid materials. The optical power attenuations achieved were more than 25 dB for both TE and TM polarization. The response time of the device was less than 4.7 ms.

Li, Dongxiao; Zhang, Yanwu; Liu, Liying; Xu, Lei

2006-06-01

251

Ocean response to attenuation of visible light by phytoplankton in the Gulf of St. Lawrence  

Microsoft Academic Search

The presence of phytoplankton affects the attenuation of the visible range of solar radiation in the upper ocean. An optically-coupled circulation model is used to examine the impact of phytoplankton on sea-surface temperature, stratification, circulation and air–sea non-solar heat fluxes in the Gulf of St. Lawrence. The attenuation coefficients are calculated by a spectral model of irradiance in the visible

Li Zhai; Charles Tang; Trevor Platt; Shubha Sathyendranath

2011-01-01

252

What makes the lac-pathway switch: identifying the fluctuations that trigger phenotype switching in gene regulatory systems.  

PubMed

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

Bhogale, Prasanna M; Sorg, Robin A; Veening, Jan-Willem; Berg, Johannes

2015-02-01

253

The effect of LacI autoregulation on the performance of the lactose utilization system in Escherichia coli.  

PubMed

The lactose operon of Escherichia coli is a paradigm system for quantitative understanding of gene regulation in prokaryotes. Yet, none of the many mathematical models built so far to study the dynamics of this system considered the fact that the Lac repressor regulates its own transcription by forming a transcriptional roadblock at the O3 operator site. Here we study the effect of autoregulation on intracellular LacI levels and also show that cAMP-CRP binding does not affect the efficiency of autoregulation. We built a mathematical model to study the role of LacI autoregulation in the lactose utilization system. Previously, it has been argued that negative autoregulation can significantly reduce noise as well as increase the speed of response. We show that the particular molecular mechanism, a transcriptional roadblock, used to achieve self-repression in the lac system does neither. Instead, LacI autoregulation balances two opposing states, one that allows quicker response to smaller pulses of external lactose, and the other that minimizes production costs in the absence of lactose. PMID:23658223

Semsey, Szabolcs; Jauffred, Liselotte; Csiszovszki, Zsolt; Erdossy, János; Stéger, Viktor; Hansen, Sabine; Krishna, Sandeep

2013-07-01

254

Instrumentation to Measure the Backscattering Coefficient bb for Arbitrary Phase Functions  

E-print Network

as ?diffuse reflectance?. Another frequently encountered pair of AOP?s are the diffuse attenuation coefficients of updwelling and downdwelling light in the water, Ku and Kd, respectively: Ku = ? 1Eu dEu dz (2.23) Kd = ? 1Ed dEd dz (2.24) 11 In order... as ?diffuse reflectance?. Another frequently encountered pair of AOP?s are the diffuse attenuation coefficients of updwelling and downdwelling light in the water, Ku and Kd, respectively: Ku = ? 1Eu dEu dz (2.23) Kd = ? 1Ed dEd dz (2.24) 11 In order...

Haubrich, David

2011-10-21

255

Another Approach to Model Attenuation  

NASA Astrophysics Data System (ADS)

Attenuation in the upper crust is a complex problem and a full understanding of where intrinsic attenuation remains problematic. This is particularly true in earth materials saturated with highly viscous liquids such as magma or bitumens. In fluid saturated materials, attenuation mechanisms have focused primarily on global and local type of fluid displacements. That is, the mechanisms have assumed that attenuation was produced only by fluid motions relative to the solids. Less emphasis has been placed on the potential mechanism for absorption within the fluids themselves. Here, we examine the mechanism of attenuation within the fluids themselves via rheological relaxation theory approach. In particular, the role of viscosity is generally examined with results on the frequency dependence on wave speed dispersion and attenuation. The evolution of elastic waveforms through such absorbing materials are also studied to evaluate the potential effects on seismic wave propagation. This work may also have implications towards the use of ultrasonic laboratory measurements in the interpretation of seismic frequency measurements.

Schmitt, D. R.; Qi, X.

2006-12-01

256

Coefficient Alpha: A Reliability Coefficient for the 21st Century?  

ERIC Educational Resources Information Center

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…

Yang, Yanyun; Green, Samuel B.

2011-01-01

257

Numerical analysis of a novel straight polymer channel waveguide based variable optical attenuator  

NASA Astrophysics Data System (ADS)

Depending on their chemical structures, polymer materials show large variation of thermo-optical coefficient. Utilizing this property a novel straight polymer channel waveguide based variable optical attenuator (VOA) was proposed. This article presents some numerical analysis results of this type of VOA devices. The results show that the proposed design can offer an attenuation level of more than 30 dB with less than 25 mW electrical power consumption, and achieve less than 0.3 dB polarization dependent loss at the attenuation level of 20 dB.

Xiao, Gao Zhi; Zhang, Zhiyi; Grover, Chander P.

2004-11-01

258

Induction of lacZ Mutations in Muta(TM)Mouse Primary Hepatocytes  

PubMed Central

We have developed an in vitro mutation assay using primary hepatocytes from the transgenic Muta™Mouse. Primary hepatocytes were isolated using a two-step perfusion method with purification by Percoll, cultured, and treated with benzo[a]pyrene (BaP), 2-amino-1-methyl-6-phenyl- imidazo[4,5-b]pyridine (PhIP), 3-nitrobenzoanthrone (3-NBA), and cigarette smoke condensate (CSC). The mean lacZ mutant frequency (MF) for the solvent control was approximately twofold greater than the spontaneous MF observed in liver tissue. A concentration-dependent increase in MF (up to 3.7-fold above control) was observed following exposure to BaP. Fourfold and twofold increases in mutant frequency were observed for 3-NBA and PhIP exposures, respectively, without the addition of any exogenous metabolic activation. A slight but statistically significant increase in lacZ MF was observed for CSC, but only at the lowest concentration. This is the first report demonstrating that mutations can be detected in cultured primary hepatocytes from Muta™Mouse. The preliminary results presented suggest that the Muta™Mouse primary hepatocyte mutagenicity assay can be used as a cost-effective tool for screening of environmental mutagens and therapeutic products. Environ. Mol. Mutagen. 51:330–337, 2010. © 2009 Wiley-Liss, Inc. PMID:19953605

Chen, Guosheng; Gingerich, John; Soper, Lynda; Douglas, George R; White, Paul A

2010-01-01

259

In vitro transcription accurately predicts lac repressor phenotype in vivo in Escherichia coli  

PubMed Central

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

2014-01-01

260

An Analysis of Periodic Components in BL Lac Object S5 0716 +714 with MUSIC Method  

NASA Astrophysics Data System (ADS)

Multiple signal classification (MUSIC) algorithms are introduced to the estimation of the period of variation of BL Lac objects.The principle of MUSIC spectral analysis method and theoretical analysis of the resolution of frequency spectrum using analog signals are included. From a lot of literatures, we have collected a lot of effective observation data of BL Lac object S5 0716 + 714 in V, R, I bands from 1994 to 2008. The light variation periods of S5 0716 +714 are obtained by means of the MUSIC spectral analysis method and periodogram spectral analysis method. There exist two major periods: (3.33±0.08) years and (1.24±0.01) years for all bands. The estimation of the period of variation of the algorithm based on the MUSIC spectral analysis method is compared with that of the algorithm based on the periodogram spectral analysis method. It is a super-resolution algorithm with small data length, and could be used to detect the period of variation of weak signals.

Tang, J.

2012-01-01

261

Semiparametric Estimation of Index Coefficients  

Microsoft Academic Search

This paper gives a solution to the problem of estimating coefficients of index models, through the estimation of the density-weighted average derivative of a general regression function. A normalized version of the density-weighted average derivative can be estimated by certain linear instrumental variables coefficients. The estimators, based on sample analogies of the product moment representation of the average derivative, are

James L. Powell; James H. Stock; Thomas M. Stoker

1989-01-01

262

MASTER serendipitous observations of the gamma-ray flaring BL Lac CGRaBS J0211+1051  

NASA Astrophysics Data System (ADS)

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.

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

263

Multi-Wave Luminosity of High-Synchrotron-Peaked TeV BL Lacs Detected by Fermi LAT  

NASA Astrophysics Data System (ADS)

We have studied the correlations between luminosities (L R, L IR, L ?) in the radio, near-infrared and ?-ray wave bands for HSP TeV BL Lacs. The results show that there are significant intrinsic correlations between L R and L ? and between L IR and L ? in all states (high/average/low), and suggest that for HSP TeV BL Lacs, the Synchrotron Self-Compton radiation (SSC) is the main mechanism of high energy ?-ray emission, and the inverse Compton scattering of circum-nuclear dust is likely to be an important complementary mechanism.

Xiong, Dingrong; Zhang, Xiong; Zheng, Yonggang

2014-11-01

264

A KPC-scale X-ray jet in the BL LAC Source S5 2007+777  

NASA Technical Reports Server (NTRS)

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.

Sambruna, Rita; Maraschi, Laura; Tavecchio, Fabrizio

2008-01-01

265

Three hundred years of human-induced change in an urban lake: paleolimnological analysis of Lac Saint-Augustin, Québec City, Canada  

Microsoft Academic Search

Lac Saint-Augustin provides a unique record of anthropogenic change during the settlement and evolution of Quebec City, one of North America's oldest cities. Lac Saint-Augustin is an urban lake that has been subject to three cen- turies of direct human impacts, with the most pronounced changes in trophic status and chemistry occurring within the last few decades. This accelerated eutrophication

Reinhard Pienitz; Karine Roberge; Warwick F. Vincent

2006-01-01

266

Shock attenuating apparatus and method  

SciTech Connect

This patent describes an apparatus for attenuating a shock in a tool string within a well, comprising a body in extensible under tension loading. It comprises means for connecting the body into the tool string; and undergoing plastic deformation in response to an explosive impact load for serially dissipating energy of a shock wave propagated in the body in response to the explosion impact load wherein the means for undergoing deformation and dissipating energy includes a wall of the body wherein a plurality of indentations are defined. This patent also describes a method of attenuating shock from an explosion in a well. It comprises lowering into the well an explosive connected to a shock attenuating member; detonating the explosive whereby an impact load with a shock wave is generated; and collapsing without severing the member in response to the impact load and dissipating energy of the shock wave from a plurality of surfaces of the member.

Navarette, M.; Walker, J.L.

1992-06-02

267

Sound attenuation in magnetorheological fluids  

NASA Astrophysics Data System (ADS)

In this work, the attenuation of ultrasonic elastic waves propagating through magnetorheological (MR) fluids is analysed as a function of the particle volume fraction and the magnetic field intensity. Non-commercial MR fluids made with iron ferromagnetic particles and two different solvents (an olive oil based solution and an Araldite-epoxy) were used. Particle volume fractions of up to 0.25 were analysed. It is shown that the attenuation of sound depends strongly on the solvent used and the volume fraction. The influence of a magnetic field up to 212 mT was studied and it was found that the sound attenuation increases with the magnetic intensity until saturation is reached. A hysteretic effect is evident once the magnetic field is removed.

Rodríguez-López, J.; Elvira, L.; Resa, P.; Montero de Espinosa, F.

2013-02-01

268

Anisotropy of Earth's inner core intrinsic attenuation from seismic normal mode models  

NASA Astrophysics Data System (ADS)

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.

Mäkinen, Anna M.; Deuss, Arwen; Redfern, Simon A. T.

2014-10-01

269

On the apparent attenuation in the spatial coherence estimated from seismic arrays  

NASA Astrophysics Data System (ADS)

Several recent studies have used the coherence of seismic noise between stations to retrieve the phase slowness and attenuation. However, there is considerable debate on the feasibility of attenuation retrieval, its interpretation, and its dependence on the noise directionality and has been the subject of several analytical and numerical studies. In this article, we perform a detailed analysis of the various factors that play a role in the estimation of spatial coherence and attenuation from seismic arrays using data from the Southern California Seismic Network. For instance, certain common preprocessing steps such as averaging neighboring frequencies to improve the estimate are sufficient to introduce attenuation-like effects. The presence of first-mode surface Rayleigh wave and P waves in addition to the fundamental mode in Southern California (at frequencies 0.05-0.2 Hz) suggests that the underlying spatial coherence is better modeled as a linear combination of the above wave types. Although this describes the observed coherence better than a simple zeroth-order Bessel function, the resulting phase cancelations due to the multiple seismic waves can be misconstrued as attenuation if not taken into consideration. Using simulations, we show that due to the slowness inhomogeneity, azimuthally averaging the coherence is not equivalent to homogenizing the medium and instead introduces apparent attenuation in the coherence due to interference. Trying to fit an exponential decay model to this apparent attenuation results in an attenuation coefficient which is similar to previously published results.

Menon, Ravishankar; Gerstoft, Peter; Hodgkiss, William S.

2014-04-01

270

SINGLE-PHOTON EMISSION COMPUTED TOMOGRAPHY: COMPENSATION FOR CONSTANT ATTENUATION  

SciTech Connect

A back-projection of filtered projection (BKFIL) reconstruction algorithm is presented that is applicable to single-photon emission computed tomography (ECT) in the presence of a constant attenuating medium such as the brain. The filters used in transmission computed tomography (TCT) - comprised of a ramp multiplied by window functions - are modified so that the single-photon ECT filter is a function of the constant attenuation coefficient. The filters give good reconstruction results with sufficient angular and lateral sampling. With continuous samples the BKFIL algorithm has a point spread function that is the Hankel transform of the window function. The resolution and s tistical properties of the filters are demonstrated by various simulations. Statistical formulas for the reconstructed image show that the square of the percent-root-mean square uncertainty (%RMS) of the reconstruction is inversely proportional to the total measured counts. The results indicate that constant attenuation can be compensated for in single-photon ECT by using an attenuation-dependent filter that reconstructs the transverse section reliably. Computer time requirements are two times that of conventional TCT or positron ECT and there is no increase in memory requirements.

Gullberg, Grant T.; Budinger, Thomas F.

1980-06-01

271

Compact plasmonic variable optical attenuator.  

PubMed

We demonstrate plasmonic nanowire-based thermo-optic variable optical attenuators operating in the 1525-1625 nm wavelength range. The devices have a footprint as low as 1 mm, extinction ratio exceeding 40 dB, driving voltage below 3 V, and full modulation bandwidth of 1 kHz. The polarization dependent loss is shown to be critically dependent on the nanowire geometry but devices with polarization-dependent loss as low as +/-2.5 dB PDL over most of the attenuation range have been fabricated. We propose an even more compact device design to reduce insertion loss to approximately 1 dB. PMID:18825193

Leosson, Kristjan; Rosenzveig, Tiberiu; Hermannsson, Petur G; Boltasseva, Alexandra

2008-09-29

272

Time-reverse modelling of acoustic wave propagation in attenuating media  

NASA Astrophysics Data System (ADS)

Time-reverse modelling (TRM) of acoustic wave propagation has been widely implemented in seismic migration and time-reversal source imaging. The basic assumption of this modelling is that the wave equation is time-invariant in non-attenuating media. In the Earth, attenuation often invalidates this assumption of time-invariance. To overcome this problem, I propose a TRM approach that compensates for attenuation and dispersion effects during the wave propagation in attenuating media. This approach is based on a viscoacoustic wave equation which explicitly separates attenuation and dispersion following a constant-Q model. Compensating for attenuation and dispersion during TRM is achieved by reversing the sign of the attenuation operator coefficient while leaving the counterpart dispersion parameter unchanged in this viscoacoustic wave equation. A low-pass filter is included to avoid amplifying high-frequency noise during TRM. I demonstrate the effects of the filter on the attenuation and the phase velocity by comparing with theoretical solutions in a 1-D Pierre shale homogeneous medium. Three synthetic examples are used to demonstrate the feasibility of attenuation compensation during TRM. The first example uses a 1-D homogeneous model to demonstrate the accuracy of the numerical implementation of the methodology. The second example shows the applicability of source location using a 2-D layering model. The last example uses a 2-D cross-well synthetic experiment to show that the methodology can also be implemented in conjunction with reverse-time migration to image subsurface reflectors. When attenuation compensation is included, I find improved estimation of the source location, the excitation timing of the point source, the magnitude of the focused source wavelet and the reflectivity image of reflectors, particularly for deep structures underneath strongly attenuating zones.

Zhu, Tieyuan

2014-04-01

273

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  

NASA Astrophysics Data System (ADS)

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 small in comparison with the wavelength) and the mean field method. As a result, an expression is obtained for the partial coefficients of the eigenmode attenuation due to the scattering of eigenmodes by the irregularities of the borehole walls into the same or other eigenmodes, as well as into the bulk longitudinal and transverse waves. The frequency-dependent behavior of the partial attenuation coefficients of both Stoneley waves and higher modes is analyzed against the ratio between the irregularity correlation length and the borehole radius for different correlation functions of irregularities.

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

2007-02-01

274

Dark optical solitons in power law media with time-dependent coefficients  

Microsoft Academic Search

This Letter talks about the dynamics of dark optical solitons that are governed by the nonlinear Schrödinger's equation with power law nonlinearity. The solitons are considered in presence of linear attenuation, third order dispersion and self-steepening terms, all with time-dependent coefficients. The solitary wave ansatz is used to carry out the integration and an exact soliton solution is obtained. It

Manirupa Saha; Amarendra K. Sarma; Anjan Biswas

2009-01-01

275

Superfund record of decision (EPA Region 5): Ripon City Landfill, Fond du Lac County, Ripon, WI, March 27, 1996  

SciTech Connect

The Ripon FF/LN landfill Superfund site is located at the intersection of Highways FF and NN in the Town of Ripon, Fond du Lac County, Wisconsin. The selected source control remedy is Alternative O, Composite Landfill Cap and Passive Gas Venting in conjunction with a groundwater monitoring plan.

NONE

1996-06-01

276

AUTOMATIC CREATION OF A GENETIC NETWORK FOR THE lac OPERON FROM OBSERVED DATA BY MEANS OF GENETIC PROGRAMMING  

E-print Network

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

Fernandez, Thomas

277

Multiple Co-Evolutionary Networks Are Supported by the Common Tertiary Scaffold of the LacI/GalR Proteins  

E-print Network

Seq Release 47 (May 07, 2011) [82]. E. coli does not contain an ortholog of CcpA, so the homolog from Bacillus subtilis subsp. subtilis str. 168 was designated as the reference sequence. In order to map amino acid positions to the LacI reference numbering...

Parente, Daniel J.; Swint-Kruse, Liskin

2013-12-31

278

Variations in the Microcystin Production of Planktothrix rubescens (Cyanobacteria) Assessed from a Four-Year Survey of Lac du  

E-print Network

November 2005 Abstract Between 1999 and 2002, a routine survey of water quality in the Lac du Bourget chromatography coupled to diode array detection and mass spectrometry, we found that two main variants ([D-Asp3, but act indirectly by affecting growth rate. Introduction In recent years, an increasing number of papers

Jacquet, Stéphan

279

The diffusive influx and carrier efflux have a strong effect on the bistability of the lac operon in Escherichia coli  

E-print Network

in Escherichia coli Jason T. Noel a , Sergei S. Pilyugin b , Atul Narang c,Ã? a Department of Chemical Engineering of Escherichia coli exhibits bistability. Most models in the literature assume that the inducer enters the cell of lac bistability during growth of Escherichia coli K12 MG1655 on TMG and succinate/glucose. To this end

Pilyugin, Sergei S.

280

Sliding and target location of DNA-binding proteins: an NMR view of the lac repressor system.  

PubMed

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

Loth, Karine; Gnida, Manuel; Romanuka, Julija; Kaptein, Robert; Boelens, Rolf

2013-05-01

281

Sequence-Enabled Reassembly of -Lactamase (SEER-LAC): A Sensitive Method for the Detection of Double-Stranded DNA  

E-print Network

Sequence-Enabled Reassembly of -Lactamase (SEER-LAC): A Sensitive Method for the Detection of a predefined DNA sequence. This system, designated sequence-enabled reassembly (SEER), was demonstrated in vitro to produce a DNA-concentration-dependent signal. Here we endow the SEER system with catalytic

Ghosh, Indraneel

282

Spatial–temporal patterns of gene expression in mouse skeletal muscle after injection of lacZ plasmid DNA  

Microsoft Academic Search

Gene therapy for muscular diseases requires the efficient transfection of a large proportion of myofiber cells within a given muscle. In the present experiments, patterns of ?-galactosidase expression were examined in mouse rectus femoris muscles at various time-points after a single injection of lacZ encoded plasmid DNA. ?-Galactosidase expression was detected 3 h after injection and rose to peak levels

SG Doh; HL Vahlsing; J Hartikka; X Liang; M Manthorpe

1997-01-01

283

Optical Spectroscopy of BL Lac Objects:new redshifts and mis-identified sources  

E-print Network

We are carrying out a multi-purpose program of high signal to noise optical spectroscopy at medium resolution of 30 BL Lac objects. Here we report the detection of three new redshifts, and the discovery of three misclassified sources. The new redshifts refer to PKS0754+100 (z=0.266), H-1914-194 (z=0.137) and 1ES0715-259, for which we derive a redshift of z=0.465 and also a ``new'' classification a Steep Spectrum Radio Quasar. In two cases (UM493 and 1620+103) stellar spectra indicate a wrong classification. The three sources with new redshift measurement show strong [OIII] emission in their spectra and their host galaxy properties are known. The central black hole masses derived using the M_{BH}-L_{bulge} and the M_{BH}-\\sigma([OIII]) relations are compared.

N. Carangelo; R. Falomo; J. Kotilainen; A. Treves; M. -H. Ulrich

2003-06-30

284

TeV gamma-ray observations of three X-ray selected BL Lacs  

E-print Network

Despite extensive surveys of extragalactic TeV gamma-ray candidates only 3 sources have so far been detected. All three are northern hemisphere objects and all three are low-redshift X-ray selected BL Lacs (XBLs). In this paper we present the results of observations of the three nearest southern hemisphere XBLs (PKS0548-322, PKS2005-489 and PKS2155-304) with the CANGAROO 3.8m imaging telescope. During the period of observation we estimate that the threshold of the 3.8m telescope was around 1.5TeV. Searches for both steady and short timescale emission have been performed for each source. Additionally, we are able to monitor the X-ray state of each source on a daily basis and we have made contemporaneous measurements of optical activity for PKS0548-322 and PKS2155-304.

M. D. Roberts; P. McGee; S. A. Dazeley; P. G. Edwards; T. Hara; J. Holder; A. Kawachi; T. Kifune; Y. Matsubara; Y. Mizumoto; M. Mori; H. Muraishi; Y. Muraki; T. Naito; K. Nishijima; S. Ogio; T. Osaki; J. R. Patterson; G. P. Rowell; T. Sako; K. Sakurazawa; R. Susukita; T. Tamura; T. Tanimori; G. J. Thornton; S. Yanagita; T. Yoshida; T. Yoshikoshi

1999-02-01

285

A method for monitoring nuclear absorption coefficients of aviation fuels  

NASA Technical Reports Server (NTRS)

A technique for monitoring variability in the nuclear absorption characteristics of aviation fuels has been developed. It is based on a highly collimated low energy gamma radiation source and a sodium iodide counter. The source and the counter assembly are separated by a geometrically well-defined test fuel cell. A computer program for determining the mass attenuation coefficient of the test fuel sample, based on the data acquired for a preset counting period, has been developed and tested on several types of aviation fuel.

Sprinkle, Danny R.; Shen, Chih-Ping

1989-01-01

286

Random seismic noise attenuation using the Wavelet Transform  

NASA Astrophysics Data System (ADS)

In this paper we propose a technique of random noises attenuation from seismic data using the discrete and continuous wavelet transforms. Firstly the discrete wavelet transform (DWT) is applied to denoise seismic data. This last is based on the threshold method applied at the modulus of the DWT. After we calculate the continuous wavelet transform of the denoised seismic seismogram, the final denoised seismic seismogram is the continuous wavelet transform coefficients at the low scale. Application at a synthetic seismic seismogram shows the robustness of the proposed tool for random noises attenuation. We have applied this idea at a real seismic data of a vertical seismic profile realized in Algeria. Keywords: Seismic data, denoising, DWT, CWT, random noise.

Aliouane, L.; Ouadfeul, S.; Boudella, A.; Eladj, S.

2012-04-01

287

Estimating contaminant attenuation half-lives in alluvial groundwater systems  

SciTech Connect

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.

Tardiff, Mark F.; Katzman, Danny

2007-03-13

288

Ultrasonic Attenuation and Speed of Sound of Cornstarch Suspensions  

E-print Network

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.

Johnson, Benjamin L; Miller, James G; Katz, Jonathan I; 10.1121/1.4789926

2013-01-01

289

Ultrasonic Attenuation and Speed of Sound of Cornstarch Suspensions  

E-print Network

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.

Benjamin L. Johnson; Mark R. Holland; James G. Miller; Jonathan I. Katz

2013-03-20

290

Ultrasonic attenuation and speed of sound of cornstarch suspensions.  

PubMed

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) × 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. PMID:23464011

Johnson, Benjamin L; Holland, Mark R; Miller, James G; Katz, Jonathan I

2013-03-01

291

LacZ ?-galactosidase: Structure and function of an enzyme of historical and molecular biological importance  

PubMed Central

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

Juers, Douglas H; Matthews, Brian W; Huber, Reuben E

2012-01-01

292

Activation of Silent gal Genes in the lac-gal Regulon of Streptococcus thermophilus  

PubMed Central

Streptococcus thermophilus strain CNRZ 302 is unable to ferment galactose, neither that generated intracellularly by lactose hydrolysis nor the free sugar. Nevertheless, sequence analysis and complementation studies with Escherichia coli demonstrated that strain CNRZ 302 contained structurally intact genes for the Leloir pathway enzymes. These were organized into an operon in the order galKTE, which was preceded by a divergently transcribed regulator gene, galR, and followed by a galM gene and the lactose operon lacSZ. Results of Northern blot analysis showed that the structural gal genes were transcribed weakly, and only in medium containing lactose, by strain CNRZ 302. However, in a spontaneous galactose-fermenting mutant, designated NZ302G, the galKTE genes were well expressed in cells grown on lactose or galactose. In both CNRZ 302 and the Gal+ mutant NZ302G, the transcription of the galR gene was induced by growth on lactose. Disruption of galR indicated that it functioned as a transcriptional activator of both the gal and lac operons while negatively regulating its own expression. Sequence analysis of the gal promoter regions of NZ302G and nine other independently isolated Gal+ mutants of CNRZ 302 revealed mutations at three positions in the galK promoter region, which included substitutions at positions ?9 and ?15 as well as a single-base-pair insertion at position ?37 with respect to the main transcription initiation point. Galactokinase activity measurements and analysis of gusA reporter gene fusions in strains containing the mutated promoters suggested that they were gal promoter-up mutations. We propose that poor expression of the gal genes in the galactose-negative S. thermophilus CNRZ 302 is caused by naturally occurring mutations in the galK promoter. PMID:11157930

Vaughan, Elaine E.; van den Bogaard, Patrick T. C.; Catzeddu, Pasquale; Kuipers, Oscar P.; de Vos, Willem M.

2001-01-01

293

Optical observations of BL Lac object ON 231 (W Comae) during 2010 March-April  

NASA Astrophysics Data System (ADS)

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.

Cheng, Xin-Lun; Zhang, You-Hong; Xu, Lei

2013-03-01

294

Multiple Ant Species Tending Lac Insect Kerria yunnanensis (Hemiptera: Kerriidae) Provide Asymmetric Protection against Parasitoids  

PubMed Central

This study investigated the effects of ant attendance on the parasitoid community and parasitism of lac insect Kerria yunnanensis aggregations in Yunnan province, China. We manipulated ant attendance to establish three treatments: (1) ant exclusion; (2) low ant attendance by several ant species; and (3) high ant attendance by Crematogaster macaoensis. Five parasitoid species were collected, with two species contributing 82.7 and 13.2% of total abundance respectively. Total parasitoid abundance was lowest in the February sample when K. yunnanensis was in its younger life stage, being significantly lower in the ant exclusion treatment. In April, all three treatments had significantly different parasitoid abundances, being highest in the ant exclusion treatment and the lowest in the high ant attendance treatment. When ants were present, there were strong negative relationships between total parasitoid abundance and ant abundance, with the relationships being dependent upon the ant species composition and abundance. The patterns of total parasitoid abundance were driven by the two most abundant parasitoid species. Parasitoid species richness did not differ among treatments or between sample times, however, multivariate analysis confirmed that overall parasitoid community structure differed significantly among treatments and between sample times, with the high ant attendance treatment differing most from the other two treatments. Interestingly the absence of ants did not result in increased parasitism from four of the five parasitoids. Ants in lac insect farming systems have a clear role for agricultural pest management. A full understanding of the asymmetric abilities of ants to influence parasitoid communities, and affect parasitism of hosts will require further experimental manipulation to assess the relative roles of 1) the abundance of each individual ant species on parasitoid access to hosts, 2) competition among parasitoids, and 3) the interaction between the first two factors. PMID:24887398

Li, Qiao; Hoffmann, Benjamin D.; Zhang, Wei

2014-01-01

295

The Sedentary Survey of Extreme High Energy Peaked BL Lacs. II. The Catalog and Spectral Properties  

E-print Network

The multi-frequency `Sedentary Survey' is a deep, statistically complete, radio flux limited sample comprising 150 BL Lacertae objects distinguished by their extremely high X-ray to radio flux ratio, ranging from five hundred to over five thousand times that of typical BL Lacs discovered in radio surveys. This paper presents the final, 100% identified, catalog together with the optical, X-ray and broad-band SEDs constructed combining literature multi-frequency data with non-simultaneous optical observations and BeppoSAX X-ray data, when available. The SEDs confirm that the peak of the synchrotron power in these objects is located at very high energies. BeppoSAX wide band X-ray observations show that, in most cases, the X-ray spectra are convex and well described by a logarithmic parabola model peaking (in a E f(E) vs E representation) between 0.02 to several keV. Owing to the high synchrotron energies involved most of the sources in the catalog are likely to be TeV emitters, with the closest and brightest ones probably detectable by the present generation of Cherenkov telescopes. The optical spectrum of about one fourth of the sources is totally featureless. Because this implies that the non-thermal emission must be well above that of the host galaxy, these objects are likely to be the most powerful sources in the survey and therefore be examples of the yet unreported high radio luminosity-high energy peaked BL Lacs.

P. Giommi; S. Piranomonte; M. Perri; P. Padovani

2004-11-03

296

Transient attenuation in optical fibers  

SciTech Connect

Low and high energy pulsed electron beams were used to generate radiation-induced transient attenuation in high-OH, Suprasil core, PCS fibers, demonstrating the energy dependence of the radiation damage and recovery mechanisms. A radiation resistant low-OH fiber was studied and its performance contrasted to that of high-OH materials. Several fibers with differing core compositions were also studied.

Hopkins, A.A.; Kelly, R.E.; Looney, L.D.; Lyons, P.B.

1984-01-01

297

NATURAL ATTENUATION OF CHLORINATED SOLVENTS  

EPA Science Inventory

The protocol will simply describe in detail, with references and illustrations, the approach currently used by staff of the SPRD to evaluate natural attenuation of chlorinated solvents in ground water. Staff of SPRD, and staff of the Air Force Center for environmental excellence...

298

Pure path attenuation measurements of long-period Rayleigh waves across the Tibet Plateau  

Microsoft Academic Search

A method is presented to derive pure path attenuation coefficients of Rayleigh waves, in the period range 30-90 s, across the Tibet Plateau, using events located within Tibet and observed at teleseismic distances. This method uses data from 2 events and 2 stations simultaneously, these being aligned along a great circle path, and, for relatively small events, is practically free

Barbara Romanowicz

1984-01-01

299

Measurement and calculation of shock wave attenuation in a rough duct  

NASA Astrophysics Data System (ADS)

Shock wave attenuation a duct with rough walls was calculated using an approximate method and measured experimentally in a systematic manner, which made it possible to determine impulse losses in shock waves by comparing the analytical and experimental data. Expressions relating the loss coefficient to the regular surface roughness were then used for calculating the rate of gas detonation in ducts with rough walls.

Gel'Fand, B. E.; Frolov, S. M.; Medvedev, S. P.

1990-06-01

300

Optical properties of highly scattering media determined from changes in attenuation, phase, and modulation depth  

Microsoft Academic Search

The optical properties of scattering media determine the attenuation (A) and the transit time () of light diffusely reflected from the medium as well as the phase ((Phi) ) and modulation depth (M) of an intensity modulated light wave. Here it is described how the absorption coefficient can be derived from the ratio of changes in A, (Phi) and M.

Matthias Kohl; Russell W. Watson; Mark Cope

1997-01-01

301

Sound attenuation, shear viscosity, and mutual diffusivity behavior in the nitroethane-cyclohexane critical mixture  

Microsoft Academic Search

The shear viscosity ?s, mutual diffusion coefficient D, and ultrasonic attenuation spectra of the nitroethane-cyclohexane mixture of critical composition have been measured at various temperatures near the critical temperature Tc. The relaxation rate of order parameter fluctuations resulting from a combined evaluation of the ?s and D data follows power law behavior with the theoretical exponent and with the large

R. Behrends; I. Iwanowski; M. Kosmowska; A. Szala; U. Kaatze

2004-01-01

302

The attenuation of solar UV radiation in lakes and the role of dissolved organic carbon  

Microsoft Academic Search

Diffuse attenuation coefficients (&) for solar UV radiation (UVR) (305, 320, 340, 380 nm, and PAR) were measured in the mixed layer of 65 lake sites in Alaska, Colorado, and Pennsylvania and the Bariloche region of Argentina. Integrated mixed layer samples of lake water were concurrently collected, and a multivariate approach was used to model Kd with a number of

DONALD P. MORRIS; HORACIO ZAGARESE; CRAIG E. WILLIAMSON; ESTEBAN G. BALSEIRO; BRUCE R. HARGREAVES; BEATRIZ MODENUTTI; ROBERT MOELLER; CLAUDIA QUEIMALINOS

1995-01-01

303

Acoustic attenuation in ferroelectric Sn2P2S6 crystals  

NASA Astrophysics Data System (ADS)

The temperature and frequency dependencies of sound attenuation for the proper uniaxial ferroelectric Sn2P2S6, which has a strong nonlinear interaction of the polar soft optic and fully symmetrical optic modes that is related to the triple well potential, were studied by Brillouin spectroscopy. It was found that the sound velocity anomaly is described in the Landau-Khalatnikov approximation with one relaxation time. For explanation of the observed temperature and frequency dependencies of the sound attenuation in the ferroelectrric phase, the accounting of several relaxation times is needed and, for quantitative calculations, the mode Gruneisen coefficients are more appropriate as interacting parameters than are the electrostrictive coefficients. Relaxational sound attenuation by domain walls also appears in the ferroelectric phase of Sn2P2S6 crystals.

Kohutych, Anton A.; Yevych, Ruslan M.; Perechinskii, Sergij I.; Vysochanskii, Yulian M.

2010-12-01

304

Photon mass energy transfer coefficients for elements z=1 to 92 and 48 additional substances of dosimetric interest.  

PubMed

Photon mass energy transfer coefficient is an essential factor when converting photon energy fluence into kinetic energy released per unit mass (kerma). Although mass attenuation coefficient and mass energy absorption coefficients can be looked up in databases, the mass energy transfer coefficient values are still controversial. In this paper, the photon mass energy transfer coefficients for elements Z=1-92 were calculated based on cross-sectional data for each photon interaction type. Mass energy transfer coefficients for 48 compounds and/or mixtures of dosimetric interest were calculated from coefficient data for elements using Bragg's additivity rule. We additionally developed software that can search these coefficient data for any element or substance of dosimetric interest. The database and software created in this paper should prove useful for radiation measurements and/or dose calculations. PMID:25055949

Kato, Hideki

2014-07-01

305

Lactosylated Gramicidin-based lipid nanoparticles (Lac-GLN) for targeted delivery of anti-miR-155 to hepatocellular carcinoma  

PubMed Central

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

Zhang, Mengzi; Zhou, Xiaoju; Wang, Bo; Yung, Bryant C.; Lee, Ly J.; Ghoshal, Kalpana; Lee, Robert J.

2013-01-01

306

Lag1p and Lac1p are essential for the Acyl-CoA-dependent ceramide synthase reaction in Saccharomyces cerevisae.  

PubMed

Lag1p and Lac1p are two homologous transmembrane proteins of the endoplasmic reticulum in Saccharomyces cerevisiae. Homologous genes have been found in a wide variety of eukaryotes. In yeast, both genes, LAC1 and LAG1, are required for efficient endoplasmic reticulum-to-Golgi transport of glycosylphosphatidylinositol-anchored proteins. In this study, we show that lag1 Delta lac1 Delta cells have reduced sphingolipid levels due to a block of the fumonisin B1-sensitive and acyl-CoA-dependent ceramide synthase reaction. The sphingolipid synthesis defect in lag1 Delta lac1 Delta cells can be partially corrected by overexpression of YPC1 or YDC1, encoding ceramidases that have been reported to have acyl-CoA-independent ceramide synthesis activity. Quadruple mutant cells (lag1 Delta lac1 Delta ypc1 Delta ydc1 Delta) do not make any sphingolipids, but are still viable probably because they produce novel lipids. Moreover, lag1 Delta lac1 Delta cells are resistant to aureobasidin A, an inhibitor of the inositolphosphorylceramide synthase, suggesting that aureobasidin A may be toxic because it leads to increased ceramide levels. Based on these data, LAG1 and LAC1 are the first genes to be identified that are required for the fumonisin B1-sensitive and acyl-CoA-dependent ceramide synthase reaction. PMID:11694577

Schorling, S; Vallée, B; Barz, W P; Riezman, H; Oesterhelt, D

2001-11-01

307

Nonlinear Acoustics FDTD method including Frequency Power Law Attenuation for Soft Tissue Modeling  

E-print Network

This paper describes a model for nonlinear acoustic wave propagation through absorbing and weakly dispersive media, and its numerical solution by means of finite differences in time domain method (FDTD). The attenuation is based on multiple relaxation processes, and provides frequency dependent absorption and dispersion without using computational expensive convolutional operators. In this way, by using an optimization algorithm the coefficients for the relaxation processes can be obtained in order to fit a frequency power law that agrees the experimentally measured attenuation data for heterogeneous media over the typical frequency range for ultrasound medical applications. Our results show that two relaxation processes are enough to fit attenuation data for most soft tissues in this frequency range including the fundamental and the first ten harmonics. Furthermore, this model can fit experimental attenuation data that do not follow exactly a frequency power law over the frequency range of interest. The main...

Jiménez, Noé; Sánchez-Morcillo, Víctor; Camarena, Francisco; Hou, Yi; Konofagou, Elisa E

2014-01-01

308

Determination of acoustic attenuation in the Hudson River Estuary by means of ship noise observations.  

PubMed

Analysis of sound propagation in a complex urban estuary has application to underwater threat detection systems, underwater communication, and acoustic tomography. One of the most important acoustic parameters, sound attenuation, was analyzed in the Hudson River near Manhattan using measurements of acoustic noise generated by passing ships and recorded by a fixed hydrophone. Analysis of the ship noise level for varying distances allowed estimation of the sound attenuation in the frequency band of 10-80 kHz. The effective attenuation coefficient representing the attenuation loss above cylindrical spreading loss had only slight frequency dependence and can be estimated by the frequency independent value of 0.058 dBm. PMID:18537300

Roh, Heui-Seol; Sutin, Alexander; Bunin, Barry

2008-06-01

309

Precision digitally-controlled variable attenuation circuit  

Microsoft Academic Search

A precise digitally-controlled variable attenuation circuit for adjusting the attenuation of a signal in an external circuit includes a signal magnitude detector, a resistance adjustment control, and a resistance divider network. The signal magnitude detector has lower and upper threshold limits representing a desired range of attenuation and is operable to receive and compare a control signal with the lower

Kenneth L. Atwood; Hyun S. Kim; Kang M. Lee

1993-01-01

310

Conversion coefficients for superheavy elements  

E-print Network

In this paper we report on internal conversion coefficients for Z = 111 to Z = 126 superheavy elements obtained from relativistic Dirac-Fock (DF) calculations. The effect of the atomic vacancy created during the conversion process has been taken into account using the so called "Frozen Orbital" approximation. The selection of this atomic model is supported by our recent comparison of experimental and theoretical conversion coefficients across a wide range of nuclei. The atomic masses, valence shell electron configurations, and theoretical atomic binding energies required for the calculations were adopted from a critical evaluation of the published data. The new conversion coefficient data tables presented here cover all atomic shells, transition energies from 1 keV up to 6000 keV, and multipole orders of 1 to 5. A similar approach was used in our previous calculations [1] for Z = 5 - 110.

T. Kibédi; M. B. Trzhaskovskaya; M. Gupta; A. E. Stuchbery

2011-03-03

311

Conversion coefficients for superheavy elements  

E-print Network

In this paper we report on internal conversion coefficients for Z = 111 to Z = 126 superheavy elements obtained from relativistic Dirac-Fock (DF) calculations. The effect of the atomic vacancy created during the conversion process has been taken into account using the so called "Frozen Orbital" approximation. The selection of this atomic model is supported by our recent comparison of experimental and theoretical conversion coefficients across a wide range of nuclei. The atomic masses, valence shell electron configurations, and theoretical atomic binding energies required for the calculations were adopted from a critical evaluation of the published data. The new conversion coefficient data tables presented here cover all atomic shells, transition energies from 1 keV up to 6000 keV, and multipole orders of 1 to 5. A similar approach was used in our previous calculations [1] for Z = 5 - 110.

Kibédi, T; Gupta, M; Stuchbery, A E

2011-01-01

312

Ultrasonic Attenuation and Backscatter Coefficient Estimates of Rodent-Tumor-Mimicking Structures: Comparison of  

E-print Network

ALEXANDER D. PAWLICKI, 2 VIKSIT KUMAR, 3 ERNEST L. MADSEN, 1 GOUTAM GHOSHAL, 2 ROBERTO J. LAVARELLO,2-mimicking spheres in the phantom were independ- ently assessed by three research groups, who analyzed their system- timates. Although the standardization of our estimation methodologies can be further improved, this study

Illinois at Urbana-Champaign, University of

313

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...

314

Method for determining damping coefficients  

NASA Astrophysics Data System (ADS)

There is disclosed a method for determining damping coefficients, the method including the steps of providing a damper assembly including a bar of known parameters, and a viscous damper, wherein a first end of the bar is disposed in the viscous damper while the second end of the bar is free, applying a known force to the second end of the bar in a direction toward the first end of the bar, measuring the response function of the assembly, comprising the ratio of the bar acceleration to the applied force, determining the eigenvalues of the response function, and from the eigenvalues computing the damping coefficient of the damper assembly.

Austin, Stephen A.; Hull, Andrew J.; Hurdis, David A.; Kasper, Kent D.

1995-05-01

315

Seebeck coefficient of one electron  

NASA Astrophysics Data System (ADS)

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.

Durrani, Zahid A. K.

2014-03-01

316

A method for estimating radiation interaction coefficients for tissues from single energy CT.  

PubMed

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

Midgley, S M

2014-12-01

317

Acoustic attenuation of hybrid silencers  

Microsoft Academic Search

The acoustic attenuation of a single-pass, perforated concentric silencer filled with continuous strand fibers is investigated first theoretically and experimentally. The study is then extended to a specific type of hybrid silencer that consists of two single-pass perforated filling chambers combined with a Helmholtz resonator. One-dimensional analytical and three-dimensional boundary element methods (BEM) are employed for the predictions of the

A. Selamet; I. J. Lee; N. T. Huff

2003-01-01

318

The HC-LAC: a Platform for Modeling Hydrology and Climate Change in Latin America and the Caribbean  

NASA Astrophysics Data System (ADS)

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.

Moreda, F.; Wyatt, A.; Bruhn, M.; Wheaton, W.; Miralles-Wilhelm, F.; Muñoz-Castillo, R.; Rineer, J.

2013-05-01

319

NOMENCLATURE CD fuselage drag coefficient  

E-print Network

coefficient F vector of overall forces and moments l fuselage half-length Nb number of blades R rotor radius vi induced velocity advance ratio blade azimuth rotor rotational speed Subscripts/superscripts c coaxial helicopter with a stiff main rotor system and a tail-mounted propulsor are investigated using

Alonso, Juan J.

320

Geometrical content of Leslie coefficients  

NASA Astrophysics Data System (ADS)

In this work, we will study how the effective geometry acquired by nematic molecules under thermal vibration contribute to the determination of the Leslie coefficients. To do this, we will divide this work in two sections. In the first section, we present the geometrical fundamentals of the so-called Hess-Baalss (HB) approach [D. Baalss and S. Hess, Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.57.86 57, 86 (1986)] where we show that its basic assumptions can be understood as a geometrical interpretation of de Gennes’ passage from the microscopic to the macroscopic order parameter. In the second section, we use an extended version of the HB approach [M. Simões, K. Yamaguti, and A. J. Palangana, Phys. Rev. EPHRVAO1539-375510.1103/PhysRevE.80.061701 80, 061701 (2009)] to obtain the geometrical contribution to each Leslie coefficient. Our results will be compared with experimental data, and we will show that the Miesowicz’s coefficients are connected as long as the ratio ?3/?4 between these Leslie coefficients can be considered small.

Simões, M.; da Silva, J. L. Correia

2011-05-01

321

Coefficient of Meteor Plasma Radiation  

Microsoft Academic Search

We present a historical review of the problem of obtaining the meteor plasma radiation coefficient. Meteor spectrophotometry endures to fail in determining spectral line profiles, because an existing spectrograph has to give a monochrome image of the meteors instead of a spectral line. Therefore, it is rather difficult to take the self-absorption magnitude as affecting the decrease of radiation intensity

V. A. Smirnov

2000-01-01

322

Effective Viscosity Coefficient of Nanosuspensions  

NASA Astrophysics Data System (ADS)

Systematic calculations of the effective viscosity coefficient of nanosuspensions have been performed using the molecular dynamics method. It is established that the viscosity of a nanosuspension depends not only on the volume concentration of the nanoparticles but also on their mass and diameter. Differences from Einstein's relation are found even for nanosuspensions with a low particle concentration.

Rudyak, V. Ya.; Belkin, A. A.; Egorov, V. V.

2008-12-01

323

Conversion coefficients for superheavy elements  

Microsoft Academic Search

In this paper we report on internal conversion coefficients for Z = 111 to Z = 126 superheavy elements obtained from relativistic Dirac-Fock (DF) calculations. The effect of the atomic vacancy created during the conversion process has been taken into account using the so called \\

T. Kibédi; M. B. Trzhaskovskaya; M. Gupta; A. E. Stuchbery

2011-01-01

324

Logistic Regression with Random Coefficients.  

ERIC Educational Resources Information Center

An approximation to the likelihood for the generalized linear models with random coefficients is derived and is the basis for an approximate Fisher scoring algorithm. The method is illustrated on the logistic regression model for one-way classification, but it has an extension to the class of generalized linear models and to more complex data…

Longford, Nicholas T.

325

Identities for generalized hypergeometric coefficients  

SciTech Connect

Generalizations of hypergeometric functions to arbitrarily many symmetric variables are discussed, along with their associated hypergeometric coefficients, and the setting within which these generalizations arose. Identities generalizing the Euler identity for {sub 2}F{sub 1}, the Saalschuetz identity, and two generalizations of the {sub 4}F{sub 3} Bailey identity, among others, are given. 16 refs.

Biedenharn, L.C.; Louck, J.D.

1991-01-01

326

Regulation of enterobactin iron transport in Escherichia coli: characterization of ent::Mu d(Apr lac) operon fusions.  

PubMed

The vector Mu d(Apr lac) was utilized to construct operon fusions in the Escherichia coli enterobactin (ent) biosynthetic and transport genes. Enzyme assays indicated a 5- to 15-fold increase in the expression of beta-galactosidase when the fusion strains were grown under iron-deficient conditions. The polarity effects seen by Mu d insertions into entA, entC, and entE were consistent with a single operon, entA(CGB)E. The direction of transcription from iron-regulated promoters was determined by directional transfer of selected genetic markers after the insertion of F'ts114 lac+. Regulatory mutants were isolated in the fusion strains by the selection for constitutive expression of beta-galactosidase and the iron-regulated outer membrane proteins. PMID:6227609

Fleming, T P; Nahlik, M S; McIntosh, M A

1983-12-01

327

Novel insights from hybrid LacI/GalR proteins: family-wide functional attributes and biologically significant variation in transcription repression  

E-print Network

LacI/GalR transcription regulators have extensive, non-conserved interfaces between their regulatory domains and the 18 amino acids that serve as ‘linkers’ to their DNA-binding domains. These non-conserved interfaces might ...

Meinhardt, Sarah; Manley Jr., Michael W.; Becker, Nicole A.; Hessman, Jacob A.; Maher III, L. James; Swint-Kruse, Liskin

2012-09-08

328

P-lacW Insertional Mutagenesis on the Second Chromosome of Drosophila melanogaster: Isolation of Lethals With Different Overgrowth Phenotypes  

Microsoft Academic Search

A single P-element insertional mutagenesis experiment was carried out for the second chromosome of Drosophila melanogaster using the P-lacW transposon. Out of 15,475 insertions on the second chromosome, 2,308 lethal and 403 semilethal mutants (altogether 2,711) were recovered. After eliminating clusters, 72% of the mutants represent independent insertions. Some of the mutants with larval, prepupal or pupal lethal phases have

Tibor Torok; Gabriella Tick; Martha Alvarado; Istvan Kiss

1993-01-01

329

Biochemical characteristics and genetic diversity of Vibrio spp. and Aeromonas hydrophila strains isolated from the Lac of Bizerte (Tunisia)  

Microsoft Academic Search

This study characterized the phenotypic and genetic properties of Vibrio spp. and Aeromonas\\u000a hydrophila strains isolated from seawater and mussels (Mytilus\\u000a edulis and Crassostrea\\u000a gigas) cultured in mollusc farm localized in the lac of Bizerte. The 37 strains (31 strains of V.\\u000a alginolyticus, one strain of V. fluvialis, one strain of V. parahaemolyticus and four strains of A.\\u000a hydrophila) typed

Snoussi Mejdi; Noumi Emira; Messaoud Ali; Hajlaoui Hafedh; Bakhrouf Amina

2010-01-01

330

Structure of the DNA-Binding Region of lac Repressor Inferred from Its Homology with cro Repressor  

Microsoft Academic Search

It is shown that the amino acid sequence and the DNA gene sequence of the 25 amino-terminal residues of the lac repressor protein of Escherichia coli are homologous with the sequences of five DNA-binding proteins: the cro repressor proteins from phage lambda and phage 434, the cI and cII proteins from phage lambda , and the repressor protein from Salmonella

B. W. Matthews; D. H. Ohlendorf; W. F. Anderson; Y. Takeda

1982-01-01

331

Petit-Lac (western Lake Geneva) environment and climate history from deglaciation to the present: a synthesis  

Microsoft Academic Search

During the past decade, the presentation of seismic and sedimentological data has allowed reconstruction of the environment and climate history of the Petit-Lac (western Lake Geneva). Methods such as high-resolution seismics, sediment core analysis (macroscopic description, grain-size analysis, mineralogy) and palynology have been used to infer the changes in the lake's environment from deglaciation to the present. However, no final

Stephanie Girardclos; Julien Fiore; Anne-Marie Rachoud-Schneider; Ira Baster; Walter Wildi

2005-01-01

332

Indicateurs liés à la qualité de l'eau et comportements. Application aux lacs d'Annecy et du Bourget  

Microsoft Academic Search

[fre] La recherche d'indicateurs d'environnement correspond à une approche certes descriptive, mais qui a le mérite de déboucher assez rapidement sur le plan pratique. Nous présentons les résultats d'une application au cas de deux lacs alpins : Annecy et le Bourget. Elle repose sur une mise en relation de paramètres de nature hydrobiologique et de données socio-économiques. . L'étude comparée

François Bonnieux; Gérard Miclet; Pierre Rainelli

1978-01-01

333

Probing BL Lac and Cluster Evolution via a Wide-angle, Deep X-ray Selected Sample  

Microsoft Academic Search

The WARPS survey (Wide-Angle ROSAT Pointed Survey) has been constructed from the archive of all public ROSAT PSPC observations, and is a subset of the WGACAT catalog. WARPS will include a complete sample of >= 100 BL Lacs at F_x >= 10(-13) erg s(-1) cm(-2) . A second selection technique will identify ~ 100 clusters at 0.15

E. Perlman; L. Jones; N. White; L. Angelini; P. Giommi; I. McHardy; G. Wegner

1994-01-01

334

A LacI-Family Regulator Activates Maltodextrin Metabolism of Enterococcus faecium  

PubMed Central

Enterococcus faecium is a gut commensal of humans and animals. In the intestinal tract, E. faecium will have access to a wide variety of carbohydrates, including maltodextrins and maltose, which are the sugars that result from the enzymatic digestion of starch by host-derived and microbial amylases. In this study, we identified the genetic determinants for maltodextrin utilization of E. faecium E1162. We generated a deletion mutant of the mdxABCD-pulA gene cluster that is homologous to maltodextrin uptake genes in other Gram-positive bacteria, and a deletion mutant of the mdxR gene, which is predicted to encode a LacI family regulator of mdxABCD-pulA. Both mutations impaired growth on maltodextrins but had no effect on the growth on maltose and glucose. Comparative transcriptome analysis showed that eight genes (including mdxABCD-pulA) were expressed at significantly lower levels in the isogenic ?mdxR mutant strain compared to the parental strain when grown on maltose. Quantitative real-time RT-PCR confirmed the results of transcriptome analysis and showed that the transcription of a putative maltose utilization gene cluster is induced in a semi-defined medium supplemented with maltose but is not regulated by MdxR. Understanding the maltodextrin metabolism of E. faecium could yield novel insights into the underlying mechanisms that contribute to the gut commensal lifestyle of E. faecium. PMID:23951303

Zhang, Xinglin; Rogers, Malbert; Bierschenk, Damien; Bonten, Marc J. M.; Willems, Rob J. L.; van Schaik, Willem

2013-01-01

335

Regulation of d-Xylose Metabolism in Caulobacter crescentus by a LacI-Type Repressor?  

PubMed Central

In the oligotrophic freshwater bacterium Caulobacter crescentus, d-xylose induces expression of over 50 genes, including the xyl operon, which encodes key enzymes for xylose metabolism. The promoter (PxylX) controlling expression of the xyl operon is widely used as a tool for inducible heterologous gene expression in C. crescentus. We show here that PxylX and at least one other promoter in the xylose regulon (PxylE) are controlled by the CC3065 (xylR) gene product, a LacI-type repressor. Electrophoretic gel mobility shift assays showed that operator binding by XylR is greatly reduced in the presence of d-xylose. The data support the hypothesis that there is a simple regulatory mechanism in which XylR obstructs xylose-inducible promoters in the absence of the sugar; the repressor is induced to release DNA upon binding d-xylose, thereby freeing the promoter for productive interaction with RNA polymerase. XylR also has an effect on glucose metabolism, as xylR mutants exhibit reduced expression of the Entner-Doudoroff operon and their ability to utilize glucose as a sole carbon and energy source is compromised. PMID:17933895

Stephens, Craig; Christen, Beat; Watanabe, Kelly; Fuchs, Thomas; Jenal, Urs

2007-01-01

336

Genotype to Phenotype Mapping and the Fitness Landscape of the E. coli lac Promoter  

PubMed Central

Genotype-to-phenotype maps and the related fitness landscapes that include epistatic interactions are difficult to measure because of their high dimensional structure. Here we construct such a map using the recently collected corpora of high-throughput sequence data from the 75 base pairs long mutagenized E. coli lac promoter region, where each sequence is associated with its phenotype, the induced transcriptional activity measured by a fluorescent reporter. We find that the additive (non-epistatic) contributions of individual mutations account for about two-thirds of the explainable phenotype variance, while pairwise epistasis explains about 7% of the variance for the full mutagenized sequence and about 15% for the subsequence associated with protein binding sites. Surprisingly, there is no evidence for third order epistatic contributions, and our inferred fitness landscape is essentially single peaked, with a small amount of antagonistic epistasis. There is a significant selective pressure on the wild type, which we deduce to be multi-objective optimal for gene expression in environments with different nutrient sources. We identify transcription factor (CRP) and RNA polymerase binding sites in the promotor region and their interactions without difficult optimization steps. In particular, we observe evidence for previously unexplored genetic regulatory mechanisms, possibly kinetic in nature. We conclude with a cautionary note that inferred properties of fitness landscapes may be severely influenced by biases in the sequence data. PMID:23650500

Otwinowski, Jakub; Nemenman, Ilya

2013-01-01

337

The Lac Des Iles Palladium Deposit, Ontario, Canada. Part II. Halogen variations in apatite  

NASA Astrophysics Data System (ADS)

Analysis of apatite from the Mine Block Intrusion (MBI) of the Lac des Iles Igneous Complex shows two pronounced trends in the halogens. Apatite from relatively fresh norite and melanorites from the Pd-sulfide zone contain up to 57 mol% chlorapatite endmember with significant hydroxyapatite component. In contrast, in altered rock (amphibolite and greenschist assemblages) the chlorapatite component is typically less than 10 mol% with wide variation in the F- and OH-endmember components. The latter trend is attributed to Cl loss to degassing and alteration, whereas the former is attributed to Cl enrichment in the ore-bearing rocks. It is suggested that the relatively H2O-rich and intermediate Cl content of the early igneous fluids degassed from the deeper levels of the MBI can explain the high Pd/Pt and Pd/Ir ratios of the deposit. A model is presented in which disseminated Pd-rich sulfides are initially introduced by a high-temperature magmatic fluid that also influenced crystallization to produce the gross modal variations of the igneous host rock. This high-temperature mineralization event was subsequently modified by the influx of late igneous and country fluids at amphibolite to greenschist conditions.

Schisa, Paul; Boudreau, Alan; Djon, Lionnel; Tchalikian, Arnaud; Corkery, John

2014-08-01

338

BL LAC OBJECT PKS B1144-379: AN EXTREME SCINTILLATOR  

SciTech Connect

Rapid variability in the radio flux density of the BL Lac object PKS B1144-379 has been observed at four frequencies, ranging from 1.5 to 15 GHz, with the Very Large Array and the University of Tasmania's Ceduna antenna. Intrinsic and line-of-sight effects were examined as possible causes of this variability, with interstellar scintillation best explaining the frequency dependence of the variability timescales and modulation indices. This scintillation is consistent with a compact source 20-40 {mu}as or 0.15-0.3 pc in size. The inferred brightness temperature for PKS B1144-379 (assuming that the observed variations are due to scintillation) is 6.2 Multiplication-Sign 10{sup 12} K at 4.9 GHz, with approximately 10% of the total flux in the scintillating component. We show that scintillation surveys aimed at identifying variability timescales of days to weeks are an effective way to identify the active galactic nuclei with the highest brightness temperatures.

Turner, R. J.; Ellingsen, S. P.; Shabala, S. S.; Blanchard, J.; Lovell, J. E. J.; McCallum, J. N. [School of Mathematics and Physics, Private Bag 37, University of Tasmania, Hobart, TAS 7001 (Australia); Cimo, G. [Joint Institute for VLBI in Europe, Postbus 2, 7990 AA Dwingeloo (Netherlands)

2012-08-01

339

Genotype to phenotype mapping and the fitness landscape of the E. coli lac promoter.  

PubMed

Genotype-to-phenotype maps and the related fitness landscapes that include epistatic interactions are difficult to measure because of their high dimensional structure. Here we construct such a map using the recently collected corpora of high-throughput sequence data from the 75 base pairs long mutagenized E. coli lac promoter region, where each sequence is associated with its phenotype, the induced transcriptional activity measured by a fluorescent reporter. We find that the additive (non-epistatic) contributions of individual mutations account for about two-thirds of the explainable phenotype variance, while pairwise epistasis explains about 7% of the variance for the full mutagenized sequence and about 15% for the subsequence associated with protein binding sites. Surprisingly, there is no evidence for third order epistatic contributions, and our inferred fitness landscape is essentially single peaked, with a small amount of antagonistic epistasis. There is a significant selective pressure on the wild type, which we deduce to be multi-objective optimal for gene expression in environments with different nutrient sources. We identify transcription factor (CRP) and RNA polymerase binding sites in the promotor region and their interactions without difficult optimization steps. In particular, we observe evidence for previously unexplored genetic regulatory mechanisms, possibly kinetic in nature. We conclude with a cautionary note that inferred properties of fitness landscapes may be severely influenced by biases in the sequence data. PMID:23650500

Otwinowski, Jakub; Nemenman, Ilya

2013-01-01

340

The Gamma-Ray Bright BL Lac Object RX J1211+2242  

NASA Technical Reports Server (NTRS)

RX J1211+2242 is an optically faint (B approximately equal to 19.2mag) but X-ray bright (f2-10kev = 5 x l0(exp -12)erg per square centimeter per second) AGN, which has been shown to be a BL Lac object at redshift z = 0.455. The ROSAT X-ray, Calar Alto optical, and NVSS radio data suggest that the peak of the synchrotron emission of this object is at energies as high as several keV. BeppoSAX observations have been carried out simultaneously with optical observations in order to extend the coverage to higher energies. The new data indeed indicate a turn-over in the 2 - 10keV energy region. We propose that RX J1211+2242 is the counterpart of the unidentified EGRET source 3EG J1212+2304, making it a gamma-ray emitter with properties similar to, for example, Markarian 501 in its bright state, though being at a much larger distance.

Beckmann, V.; Favre, P.; Tavecchio, F.; Bussien, T.; Fliri, J.; Wolter, A.

2004-01-01

341

Coordinative interactions between porphyrins and C60, La@C82, and La2@C80.  

PubMed

For the first time, a C(60) derivative (1) and two different lanthanum metallofullerene derivatives, La@C(82)Py(2) and La(2)@C(80)Py (3), that feature a pyridyl group as a coordination site for transition-metal ions have been synthesized and integrated as electron acceptors into coordinative electron-donor/electron-acceptor hybrids. Zinc tetraphenylporphyrin (ZnP) served as an excited-state electron donor in this respect. Our investigations, by means of steady-state and time-resolved photophysical techniques found that electron transfer governs the excited-state deactivation in all of these systems, namely 1/ZnP, 2/ZnP, and 3/ZnP, whereas, in the ground state, notable electronic interactions are lacking. Variation of the electron-accepting fullerene or metallofullerene moieties provides the incentive for fine-tuning the binding constants, the charge-separation kinetics, and the charge-recombination kinetics. To this end, the binding constants, which ranged from log K(assoc) =3.94-4.38, are dominated by axial coordination, with minor contributions from the orbital overlap of the curved and planar ? systems. The charge-separation and charge-recombination kinetics, which are in the order of 10(10) and 10(8) s(-1) , relate to the reduction potential of the fullerene and metallofullerenes, respectively. PMID:23180466

Tsuchiya, Takahiro; Rudolf, Marc; Wolfrum, Silke; Radhakrishnan, Shankara Gayathri; Aoyama, Ryo; Yokosawa, Yuya; Oshima, Azusa; Akasaka, Takeshi; Nagase, Shigeru; Guldi, Dirk M

2013-01-01

342

Accumulation and therapeutic modulation of 6-sulfo LacNAc+ dendritic cells in multiple sclerosis  

PubMed Central

Objective: To examine the potential role of 6-sulfo LacNAc+ (slan) dendritic cells (DCs) displaying pronounced proinflammatory properties in the pathogenesis of multiple sclerosis (MS). Methods: We determined the presence of slanDCs in demyelinated brain lesions and CSF samples of patients with MS. In addition, we explored the impact of methylprednisolone, interferon-?, glatiramer acetate, or natalizumab on the frequency of blood-circulating slanDCs in patients with MS. We also evaluated whether interferon-? modulates important proinflammatory capabilities of slanDCs. Results: SlanDCs accumulate in highly inflammatory brain lesions and are present in the majority of CSF samples of patients with MS. Short-term methylprednisolone administration reduces the percentage of slanDCs in blood of patients with MS and the proportion of tumor necrosis factor-?– or CD150-expressing slanDCs. Long-term interferon-? treatment decreases the percentage of blood-circulating slanDCs in contrast to glatiramer acetate or natalizumab. Furthermore, interferon-? inhibits the secretion of proinflammatory cytokines by slanDCs and their capacity to promote proliferation and differentiation of T cells. Conclusion: Accumulation of slanDCs in highly inflammatory brain lesions and their presence in CSF indicate that slanDCs may play an important role in the immunopathogenesis of MS. The reduction of blood-circulating slanDCs and the inhibition of their proinflammatory properties by methylprednisolone and interferon-? may contribute to the therapeutic efficiency of these drugs in patients with MS. PMID:25340085

Thomas, Katja; Dietze, Kristin; Wehner, Rebekka; Metz, Imke; Tumani, Hayrettin; Schultheiss, Thorsten; Gunther, Claudia; Schakel, Knut; Reichmann, Heinz; Bruck, Wolfgang; Schmitz, Marc

2014-01-01

343

The Sedentary Survey of Extreme High Energy Peaked BL Lacs. II. The Catalog and Spectral Properties  

E-print Network

The multi-frequency `Sedentary Survey' is a deep, statistically complete, radio flux limited sample comprising 150 BL Lacertae objects distinguished by their extremely high X-ray to radio flux ratio, ranging from five hundred to over five thousand times that of typical BL Lacs discovered in radio surveys. This paper presents the final, 100% identified, catalog together with the optical, X-ray and broad-band SEDs constructed combining literature multi-frequency data with non-simultaneous optical observations and BeppoSAX X-ray data, when available. The SEDs confirm that the peak of the synchrotron power in these objects is located at very high energies. BeppoSAX wide band X-ray observations show that, in most cases, the X-ray spectra are convex and well described by a logarithmic parabola model peaking (in a E f(E) vs E representation) between 0.02 to several keV. Owing to the high synchrotron energies involved most of the sources in the catalog are likely to be TeV emitters, with the closest and brightest one...

Giommi, P; Perri, M; Padovani, P

2004-01-01

344

The depolarization-attenuated backscatter relationship for dust plumes.  

PubMed

This study identified the relationship between the layer-integrated attenuated backscatter coefficient and layer-integrated depolarization ratio of dust plumes and compared it with that of cloud, using CALIPSO LIDAR measurements. The histogram distribution of the integrated color ratio for dust and cloud was also examined. On the basis of the layer-integrated attenuated backscatter coefficient and layer-integrated depolarization ratio relation, a simple method of detecting dust plumes was developed. A case study of dust identification over the Taklimakan Desert was conducted and compared with the current CALIPSO products. The result shows that the proposed method can significantly improve the classification of cloud and dust plumes and can supplement the current space-borne LIDAR discrimination approach, especially over dust source regions. In addition, The zonal and meridional mean occurrence derived by the proposed method and the CALIPSO's method were compared for Asian dust over East Asia region (30°N -45°N, 80°E -180°E) using the night measurements of CALIPSO from March to May, 2007. The comparison showed that the dust occurrence obtained from the proposed method is larger than that of CALIPSO's method. The dust could be found up to around 6-8 km (Above Sea Level, ASL) near the Taklimakan desert region, and maximum occurrence is over 80%. The transport altitude remained at 3 km-7 km (ASL) as the dust was transported across the Pacific Ocean. PMID:23842305

Zhou, Tian; Huang, Jianping; Huang, Zhongwei; Liu, Jingjing; Wang, Wencai; Lin, Lei

2013-07-01

345

An investigation on gamma attenuation behaviour of titanium diboride reinforced boron carbide-silicon carbide composites  

NASA Astrophysics Data System (ADS)

In this study, titanium diboride (TiB2) reinforced boron carbide-silicon carbide composites were investigated against Cs-137 and Co-60 gamma radioisotope sources. The composite materials include 70% boron carbide (B4C) and 30% silicon carbide (SiC) by volume. Titanium diboride was reinforced to boron carbide-silicon carbide composites as additive 2% and 4% by volume. Average particle sizes were 3.851 µm and 170 nm for titanium diboride which were reinforced to the boron carbide silicon carbide composites. In the experiments the gamma transmission technique was used to investigate the gamma attenuation properties of the composite materials. Linear and mass attenuation coefficients of the samples were determined. Theoretical mass attenuation coefficients were calculated from XCOM computer code. The experimental results and theoretical results were compared and evaluated with each other. It could be said that increasing the titanium diboride ratio causes higher linear attenuation values against Cs-137 and Co-60 gamma radioisotope sources. In addition decreasing the titanium diboride particle size also increases the linear and mass attenuation properties of the titanium diboride reinforced boron carbide-silicon carbide composites.

Buyuk, Bulent; Beril Tugrul, A.

2014-04-01

346

Determining attenuation properties of interfering fast and slow ultrasonic waves in cancellous bone  

PubMed Central

Previous studies have shown that interference between fast waves and slow waves can lead to observed negative dispersion in cancellous bone. In this study, the effects of overlapping fast and slow waves on measurements of the apparent attenuation as a function of propagation distance are investigated along with methods of analysis used to determine the attenuation properties. Two methods are applied to simulated data that were generated based on experimentally acquired signals taken from a bovine specimen. The first method uses a time-domain approach that was dictated by constraints imposed by the partial overlap of fast and slow waves. The second method uses a frequency-domain log-spectral subtraction technique on the separated fast and slow waves. Applying the time-domain analysis to the broadband data yields apparent attenuation behavior that is larger in the early stages of propagation and decreases as the wave travels deeper. In contrast, performing frequency-domain analysis on the separated fast waves and slow waves results in attenuation coefficients that are independent of propagation distance. Results suggest that features arising from the analysis of overlapping two-mode data may represent an alternate explanation for the previously reported apparent dependence on propagation distance of the attenuation coefficient of cancellous bone. PMID:21973378

Nelson, Amber M.; Hoffman, Joseph J.; Anderson, Christian C.; Holland, Mark R.; Nagatani, Yoshiki; Mizuno, Katsunori; Matsukawa, Mami; Miller, James G.

2011-01-01

347

Light-responsive control of bacterial gene expression: precise triggering of the lac promoter activity using photocaged IPTG.  

PubMed

Light can be used to control numerous cellular processes including protein function and interaction as well as gene expression in a non-invasive fashion and with unprecedented spatiotemporal resolution. However, for chemical phototriggers tight, gradual, and homogeneous light response has never been attained in living cells. Here, we report on a light-responsive bacterial T7 RNA polymerase expression system based on a photocaged derivative of the inducer molecule isopropyl-?-d-thiogalactopyranoside (IPTG). We have comparatively analyzed different Escherichia coli lac promoter-regulated expression systems in batch and microfluidic single-cell cultivation. The lacY-deficient E. coli strain Tuner(DE3) harboring additional plasmid-born copies of the lacI gene exhibited a sensitive and defined response to increasing IPTG concentrations. Photocaged IPTG served as a synthetic photo-switch to convert the E. coli system into an optogenetic expression module allowing for precise and gradual light-triggering of gene expression as demonstrated at the single cell level. PMID:24894989

Binder, Dennis; Grünberger, Alexander; Loeschcke, Anita; Probst, Christopher; Bier, Claus; Pietruszka, Jörg; Wiechert, Wolfgang; Kohlheyer, Dietrich; Jaeger, Karl-Erich; Drepper, Thomas

2014-08-01

348

Characterisation and discrimination of various types of lac resin using gas chromatography mass spectrometry techniques with quaternary ammonium reagents.  

PubMed

A variety of lac resin samples obtained from artists' suppliers, industrial manufacturers, and museum collections were analysed using gas chromatography mass spectrometry (GCMS) and reactive pyrolysis GCMS with quaternary ammonium reagents. These techniques allowed a detailed chemical characterisation of microgram-sized samples, based on the detection and identification of derivatives of the hydroxy aliphatic and cyclic (sesquiterpene) acids that compose the resin. Differences in composition could be related to the nature of the resin, e.g. wax-containing (unrefined), bleached, or aged samples. Furthermore, differences in the relative abundances of aliphatic hydroxyacids appear to be associated with the biological source of the resin. The diagnostic value of newly characterised lac components, including 8-hydroxyacids, is discussed here for the first time. Identification of derivatised components was aided by AMDIS deconvolution software, and discrimination of samples was enhanced by statistical evaluation of data using principal component analysis. The robustness of the analyses, together with the minimal sample size required, make these very powerful approaches for the characterisation of lac resin in museum objects. The value of such analyses for enhancing the understanding of museum collections is illustrated by two case studies of objects in the collection of the Philadelphia Museum of Art: a restorer's varnish on a painting by Luca Signorelli, and a pictorial inlay in an early nineteenth-century High Chest by George Dyer. PMID:24642395

Sutherland, K; del Río, J C

2014-04-18

349

Detection of QTLs to reduce cadmium content in rice grains using LAC23/Koshihikari chromosome segment substitution lines  

PubMed Central

To advance the identification of quantitative trait loci (QTLs) to reduce Cd content in rice (Oryza sativa L.) grains and breed low-Cd cultivars, we developed a novel population consisting of 46 chromosome segment substitution lines (CSSLs) in which donor segments of LAC23, a cultivar reported to have a low grain Cd content, were substituted into the Koshihikari genetic background. The parental cultivars and 32 CSSLs (the minimum set required for whole-genome coverage) were grown in two fields with different natural levels of soil Cd. QTL mapping by single-marker analysis using ANOVA indicated that eight chromosomal regions were associated with grain Cd content and detected a major QTL (qlGCd3) with a high F-test value in both fields (F = 9.19 and 5.60) on the long arm of chromosome 3. The LAC23 allele at qlGCd3 was associated with reduced grain Cd levels and appeared to reduce Cd transport from the shoots to the grains. Fine substitution mapping delimited qlGCd3 to a 3.5-Mbp region. Our results suggest that the low-Cd trait of LAC23 is controlled by multiple QTLs, and qlGCd3 is a promising candidate QTL to reduce the Cd level of rice grain. PMID:24273423

Abe, Tadashi; Nonoue, Yasunori; Ono, Nozomi; Omoteno, Motoyasu; Kuramata, Masato; Fukuoka, Shuichi; Yamamoto, Toshio; Yano, Masahiro; Ishikawa, Satoru

2013-01-01

350

Frameshift mutagenicity of aromatic amines related to aminofluorene in a lacZ reversion assay in E. coli  

SciTech Connect

We studied in the mutagenicity of three aromatic amines in a lacZ reversion assay in E. coli: 2-nitrofluorene (NF), N-2-acetylaminofluorene (AAF), and N-hydroxy-N-2-acetylaminofluorene (NHA). Mutations that confer the Lac{sup +} phenotype were measured using an F{prime} factor from strain CC109 of Cupples et al. The F{prime} contains a lacZ mutation that reverts by a -2 frameshift at a site of repetitive dinucleotides (CG{sub 5} to CG{sub 4}). The F{prime} was transferred into strains carrying an LPS{sup d} mutation that increases permeability to aromatic amines and a plasmid (pYG219) that contains the Salmonella nat gene, which confers N- and O-acetyltransferase (NAT/OAT) activity. Mutagenesis was measured by papillation assays and quantitative reversion assays. The results show that the LPS{sup d} mutation, conferring enhanced permeability, facilitates measuring the mutagenicity of aromatic amines but is not absolutely required, in that a lower level of mutagenicity is detected in LPS{sup +} strains. The NAT/OAT activity conferred by pYG219 strongly potentiates the mutagenicity of NF and NHA. The mutagenicity of NF is undoubtedly ascribable to aminofluorene (AF) adducts: The mutagenicity of NHA may be due either to AAF adducts or to AF adducts produced by deacetylation. Surprisingly, AAF was weakly mutagenic in a NAT/OAT LPS{sup d} strain even without metabolic activation by a mammalian cytochrome P450.

Hoffmann, G.R. [Holy Cross College, Worcester, MA (United States); Janel-Bintz, R.; Fuchs, R.P.P. [CNRS, Strasbourg (France)

1997-10-01

351

The linear optical and magneto-optical susceptibilities and geometric effects of nine La@C82 (C82) crystal isomers  

NASA Astrophysics Data System (ADS)

Using the extended Su-Schrieffer-Heeger model in conjunction with the local field method and Ewald method, we have calculated the linear susceptibility ? for nine different La@C82 (C82) crystal isomers. Our numerical calculation results indicate that the spectral shapes of the susceptibilities tensor of the La@C82 (C82) crystal turn out to be determined mainly by the geometrical distributions of the pentagons in the fullerene and endohedral structures.

Rostampour, E.

2014-10-01

352

Copyright0 1987 by the GeneticsSocietyof America A Tn10-lacZ-kanR-URA3Gene Fusion Transposon for Insertion  

E-print Network

Copyright0 1987 by the GeneticsSocietyof America A Tn10-lacZ-kanR-URA3Gene Fusion Transposon or translation start signals,an intact URA3 gene, and a RanR determinant. The lacZ gene can be activated be substituted for URA3 in the availableconstructs. The mini-Tn 10-LUKsystem has several important advantages. (1

Botstein, David

353

Vectors that facilitate the replacement of transcriptional lacZ fusions in Streptococcus mutans and Bacillus subtilis with fusions to gfp or gusA  

Microsoft Academic Search

Plasmid vectors have been constructed for Streptococcus mutans and Bacillus subtilis that make possible rapid replacement of the widely used reporter gene lacZ (encoding ?-galactosidase) with either gfp (encoding green fluorescent protein) or gusA (encoding ?-glucuronidase). The lacZ?gfp replacement vectors greatly facilitate the analysis of the spatial location of gene expression in biofilms of S. mutans and in sporulating B.

Vasant K. Chary; Monica Busuioc; John A. Renye; Patrick J. Piggot

2005-01-01

354

Isolation of a novel insertion sequence from Mycobacterium fortuitum using a trap vector based on inactivation of a lacZ reporter gene  

Microsoft Academic Search

An insertion sequence of Mycobacterium fortuitum has been isolated using a trap vector following insertion in and inactivation of the lacZ reporter gene. The trap vector is a temperature-sensitive (ts) Escherichia coli-mycobacterium shuttle plasmid, pCD4, which contains ts oriM, the kanamycin-resistance gene as a selection marker and a lacZ expression cassette. The ts mutation present in pCD4 functions in mycobacteria

Morris Waskar; Deepak Kumar; Ajai Kumar; Ranjana Srivastava

355

Filamentous Coliphage M13 as a Cloning Vehicle: Insertion of a HindII Fragment of the lac Regulatory Region in M13 Replicative Form in vitro  

Microsoft Academic Search

A HindII restriction fragment comprising the Escherichia coli lac regulatory region and the genetic information for the alpha peptide of beta -galactosidase (beta -D-galactoside galactohydrolase, EC 3.2.1.23) has been inserted into 1 of the 10 Bsu I cleavage sites of M13 by blunt end ligation. A stable hybrid phage was isolated and identified by its ability to complement the lac

Joachim Messing; Bruno Gronenborn; Benno Muller-Hill; Peter Hans Hofschneider

1977-01-01

356

Isolation and Characterization of Three Streptococcus pneumoniae Transformation-Specific Loci by Use of a lacZ Reporter Insertion Vector  

Microsoft Academic Search

Although more than a dozen new proteins are produced when Streptococcus pneumoniae cells become com- petent for genetic transformation, only a few of the corresponding genes have been identified to date. To find genes responsible for the production of competence-specific proteins, a random lacZ transcriptional fusion library was constructed in S. pneumoniae by using the insertional lacZ reporter vector pEVP3.

EKATERINA V. PESTOVA; DONALD A. MORRISON

1998-01-01

357

Relationship between Ultrasonic Attenuation, Size and Axial Strain Parameters for ex-vivo Atherosclerotic Carotid Plaque  

PubMed Central

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

Shi, Hairong; Varghese, T.; Dempsey, R.J.; Salamat, M.S.; Zagzebski, J.A.

2008-01-01

358

High temperature Seebeck coefficient metrology  

SciTech Connect

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.

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

359

Portable vapor diffusion coefficient meter  

DOEpatents

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.

Ho, Clifford K. (Albuquerque, NM)

2007-06-12

360

Hybrid approach for attenuation correction in PET/MR scanners  

NASA Astrophysics Data System (ADS)

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.

Santos Ribeiro, A.; Rota Kops, E.; Herzog, H.; Almeida, P.

2014-01-01

361

Lac-regulated system for generating adenovirus 5 vaccine vectors expressing cytolytic human immunodeficiency virus 1 genes  

PubMed Central

Adenovirus (Ad) vectors have been developed as human immunodeficiency-1 (HIV-1) vaccine vectors because they consistently induce immune responses in preclinical animal models and human trials. Strong promoters and codon-optimization are often used to enhance vaccine-induced HIV-1 gene expression and immunogenicity. However, if the transgene is inherently cytotoxic in the cell line used to produce the vector, and is expressed at high levels, it is difficult to rescue a stable Ad HIV-1 vaccine vector. Therefore we hypothesized that generation of Ad vaccine vectors expressing cytotoxic genes, such as HIV-1 env, would be more efficient if expression of the transgene was down regulated during Ad rescue. To test this hypothesis, a Lac repressor-operator system was applied to regulate expression of reporter luciferase and HIV-1 env transgenes during Ad rescue. The results demonstrate that during Ad rescue, constitutive expression of the Lac repressor in 293 cells reduced transgene expression levels to approximately 5% of that observed in the absence of regulation. Furthermore, Lag-regulation translated into more efficient Ad rescue compared to traditional 293 cells. Importantly, Ad vectors rescued with this system showed high levels of transgene expression when transduced into cells that lack the Lac repressor protein. The Lac-regulated system also facilitated the rescue of modified Ad vectors that have non-native receptor tropism. These tropism-modified Ad vectors infect a broader range of cell types than the unmodified Ad, which could increase their effectiveness as a vaccine vector. Overall, the Lac-regulated system described here (i) is backwards compatible with Ad vector methods that employ bacterial-mediated homologous recombination (ii) is adaptable for the engineering of tropism-modified Ad vectors and (iii) does not require co-expression of regulatory genes from the vector or the addition of exogenous chemicals to induce or repress transgene expression. This system therefore could facilitate the development of Ad-based vaccine candidates that otherwise would not be feasible to generate. PMID:19409930

Zhao, Chunxia; Crews, Charles Jefferson; Derdeyn, Cynthia A.; Blackwell, Jerry L.

2009-01-01

362

Planar waveguide-based silica-polymer hybrid variable optical attenuator and its associated polymers.  

PubMed

We have proposed a silica-polymer hybrid variable optical attenuator that we made by creating two trenches along the core of a straight silica planar waveguide and filling the trenches with a polymer. The polymer, which had a superhigh thermo-optic coefficient, was specially designed and developed in this study to lower the power consumption of the device. We achieved a maximum attenuation of -29 dB for the device by changing the polymer's temperature by only 7 degrees C. The device has a very low power consumption at 2-3 mW/channel, making it a good candidate for integration with arrayed waveguide gratings. PMID:15861849

Zhang, Zhiyi; Xiao, Gao Zhi; Zhao, Ping; Grover, Chander P

2005-04-20

363

Planar waveguide-based silica-polymer hybrid variable optical attenuator and its associated polymers  

NASA Astrophysics Data System (ADS)

We have proposed a silica-polymer hybrid variable optical attenuator that we made by creating two trenches along the core of a straight silica planar waveguide and filling the trenches with a polymer. The polymer, which had a superhigh thermo-optic coefficient, was specially designed and developed in this study to lower the power consumption of the device. We achieved a maximum attenuation of -29 dB for the device by changing the polymer's temperature by only 7 °C. The device has a very low power consumption at 2-3 mW/channel, making it a good candidate for integration with arrayed waveguide gratings.

Zhang, Zhiyi; Zhi Xiao, Gao; Zhao, Ping; Grover, Chander P.

2005-04-01

364

The relationship between phytoplankton concentration and light attenuation in ocean waters  

NASA Technical Reports Server (NTRS)

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.

Phinney, David A.; Yentsch, Charles S.

1986-01-01

365

Understanding BL Lacertae objects. Structural and kinematic mode changes in the BL Lac object PKS 0735+178  

NASA Astrophysics Data System (ADS)

Context. We present evidence that parsec-scale jets in BL Lac objects may be significantly distinct in kinematics from their counterparts in quasars. We argued this previously for the BL lac sources 1803+784 and 0716+714 and report here a similar pattern for another well-known BL Lac object, PKS 0735+178, whose nuclear jet is found to exhibit kinematics atypical of quasars. Aims: By analyzing the pc-scale jet morphology and its changes in 0735+178 we seek to understand the emission processes in BL Lac objects and to decipher their differences from quasars. A detailed study of the jet components' motion reveals that the standard AGN paradigm of apparent superluminal motion does not always describe the kinematics in BL Lac objects. We study 0735+178 here to augment and improve the understanding of the peculiar motions in the jets of BL Lac objects as a class. Methods: We analyzed 15 GHz VLBA (Very Long Baseline Array) observations (2 cm/MOJAVE survey) performed at 23 epochs between 1995.27 and 2008.91. Multiple Gaussians were fitted to the derived VLBA data, to trace the kinematical and flux density evolution of the individual VLBI (Very Long Baseline Interferometry) components in the nuclear jet. We then compared the jet kinematics with the optical and radio light curves available for this BL Lac object and point out some striking correlations between the properties of the radio knots and the features in the light curves. Results: We found a drastic structural mode change in the VLBI jet of 0735+178, between 2000.4 and 2001.8 when its twice sharply bent trajectory turned into a linear shape. We further found that this jet had undergone a similar transition sometime between December 1981 and June 1983. A mode change, occurring in the reverse direction (between mid-1992 and mid-1995) has already been reported in the literature. These structural mode changes are found to be reflected in changed kinematical behavior of the nuclear jet, manifested as an apparent superluminal motion and stationarity of the radio knots. In addition, we found the individual mode changes to correlate in time with the maxima in the optical light curve. The last two transitions occurred before a (modest) radio flare. The behavior of this pc-scale jet appears to favor a scenario involving non-ballistic motions of the radio knots, produced by the precession of a continuous jet within the ambient medium. Conclusions: This is the third BL Lac object (after 1803+784 and 0716+714) analyzed by us, which reveals kinematic properties in the parsec-scale radio jet, which are atypical of quasars. For several years, the components in the jet are not found to be separating from the core but instead to be moving perpendicularly to the ridge line of the jet. In 0735+178 this unusual behavior has been particularly conspicuous. Curiously, however, fast apparent superluminal motion characteristic of quasars were present in this jet between the epochs ~1995 and ~2000. Thus we found for this BL Lac object a drastic change in the kinematics of the nuclear jet, i.e, transition from “typical superluminal” to an unusual “stationary” state. Interestingly, we found that this change is accompanied with a mode change in the nuclear jet's morphology. The long sequences of VLBA images reported here for this BL Lac object do not support the commonly assumed connection between radio flux-density outbursts and the ejection of new VLBI components. In contrast, the two mode changes seem correlated with the radio flares and are more likely an outcome of a changing viewing angle of the same knots. We propose therefore that all these observed features of the nuclear jet of 0735+178 and their correlation with the optical and radio flares might hold significant promise to better understand the basic difference between BL Lac objects and quasars.

Britzen, S.; Witzel, A.; Gong, B. P.; Zhang, J. W.; Gopal-Krishna; Goyal, A.; Aller, M. F.; Aller, H. D.; Zensus, J. A.

2010-06-01

366

Calculation Of Pneumatic Attenuation In Pressure Sensors  

NASA Technical Reports Server (NTRS)

Errors caused by attenuation of air-pressure waves in narrow tubes calculated by method based on fundamental equations of flow. Changes in ambient pressure transmitted along narrow tube to sensor. Attenuation of high-frequency components of pressure wave calculated from wave equation derived from Navier-Stokes equations of viscous flow in tube. Developed to understand and compensate for frictional attenuation in narrow tubes used to connect aircraft pressure sensors with pressure taps on affected surfaces.

Whitmore, Stephen A.

1991-01-01

367

Estimating Rain Attenuation In Satellite Communication Links  

NASA Technical Reports Server (NTRS)

Attenuation computed with help of statistical model and meteorological data. NASA Lewis Research Center Satellite Link Attenuation Model (SLAM) program QuickBASIC computer program evaluating static and dynamic statistical assessment of impact of rain attenuation on communication link established between Earth terminal and geosynchronous satellite. Application in specification, design, and assessment of satellite communication links for any terminal location in continental United States. Written in Microsoft QuickBASIC.

Manning, R. M.

1991-01-01

368

The first direct measurements of upper oceanic crustal compressional wave attenuation  

NASA Astrophysics Data System (ADS)

The first direct measurement of compressional wave attenuation of the uppermost 650 m of oceanic crust was performed using data recorded by seafloor hydrophones and large (56-116 kg), deep, explosive sources. The site was 13 km east of the southernmost Juan de Fuca Ridge on crust 0.4 m.y. old Spectral ratios were performed between bottom refracting waves and direct water waves, adjusted for spreading losses and transmission coefficient losses. Several tests of the data were performed, demonstrating that attenuation is linearly related to frequency between 15 and 140 Hz, but frequency-independent components of attenuation are also evident. Values of compressional wave Q cluster between 20 and 50 and do not show any systematic variation with depth over 650 m. The attenuation results also indicate the presence of heterogeneities within the crust, as the solutions for each receiver's data set are significantly different. No evidence for azimuthal variations of attenuation are supported by the data, although the data do not optimally sample a wide variation of azimuths. Our attenuation values are judged to be normal to higher than expected for the whole oceanic crust, based upon comparisons to results from synthetic seismogram modeling by others and by modeling signal to noise ratios of typical seismic refraction profiles. The results are consistent with recent laboratory measurements at ultrasonic frequencies for dry and saturated basalts at seafloor pressures and temperatures.

Jacobson, R. S.; Lewis, B. T. R.

1990-10-01

369

Operation of the breeze tunnel to determine mass extinction coefficients  

SciTech Connect

The breeze tunnel at the Edgewood Research, Development and Engineering Center (ERDEC) at Aberdeen Proving Ground, Maryland, is a unique facility for determining the efficacy of released smoke/obscurants in flowing air as a function of controlling variables. Optimum material feed characteristics and generator operating conditions can be determined. The facility allows investigation of the effects of different generator operating variables, airborne concentrations, and airborne particle sizes on mass extinction coefficients. The breeze tunnel is now available for Department of Defense (DoD) trials. During trials in the breeze tunnel, obscurants have been released from the compact-disc-generator, the IR-Log generator, and the XM56 generator. Obscurant release rates have ranged from an instantaneous puff to a continuous release of 10 lb/min. Extinction can be measured in the visual, infrared, and millimeter ranges of the electromagnetic spectrum. Experimental conditions allow calculation of mass extinction coefficients as a function of generator variables, including material release rates. Average mass extinction coefficients address attenuation from obscurants, both single primary particles and aggregates.

Sehmel, G.A. [Pacific Northwest Lab., Richland, WA (United States); Bonfante, R.; Catalano, E.; Rouse, W.G.; Banks, D.R. [Edgewood Research, Development and Engineering Center, Aberdeen Proving Ground, MD (United States)

1993-06-01

370

Hypomaturation Enamel Defects in Klk4 Knockout/LacZ Knockin Mice*  

PubMed Central

Kallikrein 4 (Klk4) is believed to play an essential role in enamel biomineralization, because defects in KLK4 cause hypomaturation amelogenesis imperfecta. We used gene targeting to generate a knockin mouse that replaces the Klk4 gene sequence, starting at the translation initiation site, with a lacZ reporter gene. Correct targeting of the transgene was confirmed by Southern blot and PCR analyses. Histochemical X-gal (5-bromo-4-chloro-3-indolyl-?-d-galactopyranoside) staining demonstrated expression of ?-galactosidase in maturation stage ameloblasts. No X-gal staining was observed in secretory stage ameloblasts or in odontoblasts. Retained enamel proteins were observed in the maturation stage enamel of the Klk4 null mouse, but not in the Klk4 heterozygous or wild-type mice. The enamel layer in the Klk4 null mouse was normal in thickness and contained decussating enamel rods but was rapidly abraded following weaning, despite the mice being maintained on soft chow. In function the enamel readily fractured within the initial rod and interrod enamel above the parallel enamel covering the dentino-enamel junction. Despite the lack of Klk4 and the retention of enamel proteins, significant levels of crystal maturation occurred (although delayed), and the enamel achieved a mineral density in some places greater than that detected in bone and dentin. An important finding was that individual enamel crystallites of erupted teeth failed to grow together, interlock, and function as a unit. Instead, individual crystallites seemed to spill out of the enamel when fractured. These results demonstrate that Klk4 is essential for the removal of enamel proteins and the proper maturation of enamel crystals. PMID:19578120

Simmer, James P.; Hu, Yuanyuan; Lertlam, Rangsiyakorn; Yamakoshi, Yasuo; Hu, Jan C.-C.

2009-01-01

371

Predictions of the High-Energy Emission from BL Lac objects: The Case of W Comae  

E-print Network

Spectral fitting of the radio through hard X-ray emission of BL Lac objects has previously been used to predict their level of high-energy (GeV - TeV) emission. In this paper, we point out that such spectral fitting can have very large uncertainties with respect to predictions of the VHE emission. This is demonstrated with the example of W Comae. We show that the best currently available contemporaneous optical - X-ray spectrum of W Comae still allows for a large range of possible parameters, resulting in drastically different > 40 GeV fluxes. We find that all acceptable leptonic-model fits to the optical - X-ray emission of W Comae predict a cut-off of the high-energy emission around ~ 100 GeV. We suggest that detailed measurements and analysis of the soft X-ray variability of W Comae may be used to break the degeneracy in the choice of possible fit parameters, and thus allow a more reliable prediction of the VHE emission from this object. Using the available soft X-ray variability measured by BeppoSAX, we predict a > 40 GeV flux from W Comae of ~ (0.4 - 1) * 10^{-10} photons/(cm^2 s) with no significant emission at E > 100 GeV for a leptonic jet model. We compare our results concerning leptonic jet models with detailed predictions of the hadronic Synchrotron-Proton Blazar model. This hadronic model predicts > 40 GeV fluxes very similar to those found for the leptonic models, but results in > 100 GeV emission which should be clearly detectable with future high-sensitivity instruments like VERITAS. Thus, we suggest this object as a promising target for VHE gamma-ray and co-ordinated broadband observations to distinguish between leptonic and hadronic jet models for blazars.

M. Boettcher; R. Mukherjee; A. Reimer

2002-08-07

372

The Production Coefficients of Feeds  

E-print Network

.. deduct 0.14. The following is an example of the method of calculating the fat value of a roughage : JOHNSON GRASS HAY, 100 POUNDS. Digestible protein ............. 3.3 XO.235= 0.78 Digestible fat ................. O.YX0.474= 0... of the Johnson grass hay added *to a ration already sufficient to maintain the animal should produce 8.21 pounds fat. The fat value is the productive value for fattening, when the feed is used for fat and for no other purpose. THE PRODUCTION COEFFICIENT...

Fraps, G. S. (George Stronach)

1916-01-01

373

Fracture-Induced Anisotropic Attenuation  

NASA Astrophysics Data System (ADS)

The triaxial nature of the tectonic stress in the earth's crust favors the appearance of vertical fractures. The resulting rheology is usually effective anisotropy with orthorhombic and monoclinic symmetries. In addition, the presence of fluids leads to azimuthally varying attenuation of seismic waves. A dense set of fractures embedded in a background medium enhances anisotropy and rock compliance. Fractures are modeled as boundary discontinuities in the displacement u and particle velocity v as [{\\varvec{ kappa}}\\cdot {u} + {\\varvec{?}} \\cdot {v} ], where the brackets denote discontinuities across the fracture surface, {\\varvec{kappa}} is a fracture stiffness, and {\\varvec{?}} is a viscosity related to the energy loss. We consider a transversely isotropic background medium (e.g., thin horizontal plane layers), with sets of long vertical fractures. Schoenberg and Muir's theory combines the background medium and sets of vertical fractures to provide the 13 complex stiffnesses of the long-wavelength equivalent monoclinic and viscoelastic medium. Long-wavelength equivalent means that the dominant wavelength of the signal is much longer than the fracture spacing. The symmetry plane is the horizontal plane. The equations for orthorhombic and transversely isotropic media follow as particular cases. We compute the complex velocities of the medium as a function of frequency and propagation direction, which provide the phase velocities, energy velocities (wavefronts), and quality factors. The effective medium ranges from monoclinic symmetry to hexagonal (transversely isotropic) symmetry from the low- to the high-frequency limits in the case of a particle-velocity discontinuity (lossy case) and the attenuation shows typical Zener relaxation peaks as a function of frequency. The attenuation of the coupled waves may show important differences when computed versus the ray or phase angles, with triplication appearing in the Q factor of the qS wave. We have performed a full-wave simulation to compute the field corresponding to the coupled qP-qS waves in the symmetry plane of an effective monoclinic medium. The simulations agree with the predictions of the plane-wave analysis.

Carcione, José M.; Santos, Juan E.; Picotti, Stefano

2012-09-01

374

Osmotic coefficients of electrolyte solutions.  

PubMed

In this paper, the osmotic coefficient, phi, of electrolyte solutions is considered. According to the Gibbs-Duhem equation, the calculation of phi follows from that of the mean activity coefficient, gamma, based on a pseudolattice approach recently proposed. For any given electrolyte, the whole range of concentrations providing gamma

Moggia, Elsa

2008-01-31

375

Virial coefficients of model alkanes  

NASA Astrophysics Data System (ADS)

We report the results from Mayer-sampling Monte Carlo calculations of the virial coefficients of the united-atom TraPPE-UA model of normal alkanes. For alkane chain lengths from n =2 to 20 (where n is the number of carbon atoms), results are given for the virial coefficients B2, B3, and B4; results for B5 are given for chains up to length n =12; and results for B6 are given for chains of length n =2, 3, and 4. In all cases, values are given for temperatures ranging from 200 K to 2000 K in 20-50 K increments. The values are used to calculate the equation of state for butane and the pressure-density behavior is compared to experimental data at 350 and 550 K. Critical points are calculated for all systems and compared to simulation data previously taken for the same molecular model, and to experiment. The comparison with temperature is very good (within 1.5% for all chain lengths up to n =12), while the critical density is underestimated by about 5%-15% and the critical pressure is given within about 10%. The convergence behavior of the virial equation of state as applied across the n-alkane series is well characterized by corresponding states, meaning that the accuracy at a given density relative to the critical density does not deteriorate with increasing chain length.

Schultz, Andrew J.; Kofke, David A.

2010-09-01

376

The Physics of the Gas Attenuator for the Linac Coherent Light Source (LCLS)  

SciTech Connect

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.

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

377

Expression of optical diffusion coefficient in high-absorption turbid media  

NASA Astrophysics Data System (ADS)

The optical diffusion coefficient in a homogeneous turbid medium with high absorption was determined by steady-state measurements of the light transmission under the infinite-boundary condition. The intensity of the transmission was well described by the solution of the optical diffusion equation. Moreover, the optical diffusion coefficient D was given by a constant, , where is the reduced scattering coefficient, up to the absorption coefficient of about . These results mean that attenuation by absorption only contributes to exponential attenuation along the optical path defined by the scattering coefficient and geometry of the system even in high-absorption turbid media such as the pathological living tissues of bleeding or haematoma.

Nakai, T.; Nishimura, G.; Yamamoto, K.; Tamura, M.

1997-12-01

378

Black Carbon Concentrations and Diesel Vehicle Emission Factors Derived from Coefficient of Haze Measurements in California: 1967-2003  

Microsoft Academic Search

We have derived ambient black carbon (BC) concentrations and estimated emission factors for on-road diesel vehicles from archived Coefficient of Haze (COH) data that was routinely collected beginning in 1967 at 11 locations in the San Francisco Bay Area. COH values are a measure of the attenuation of light by particles collected on a white filter, and available data indicate

CynthiaL Tast; Thomas W. Kirchstetter; Jeffery Aguiar; Shaheen Tonse; T. Novakov; David Fairley

2007-01-01

379

Site attenuation with log-periodic antennas  

Microsoft Academic Search

Site attenuation measurements made with biconical antennas below 200 MHz are found to agree rather well with calculations based on point dipole antennas. The log-periodic dipole antennas used above 200 MHz differ more drastically than the biconical from an ideal point dipole. Discrepancies arising from the use of log-periodic antennas are examined, and a simple modification of the site attenuation

J. D. Gavenda

1993-01-01

380

LONG TERM MONITORING FOR NATURAL ATTENUATION  

EPA Science Inventory

We have good statistical methods to: (1) determine whether concentrations of a contaminant are attenuating over time, (2) determine the rate of attenuation and confidence interval on the rate, and (3) determine whether concentrations have met a particular clean up goal. We do no...

381

Seismic wave characteristics in anisotropic attenuating media  

Microsoft Academic Search

A synthetic seismogram is a tool to investigate seismic wave characteristics in anisotropic attenuating media. A numerical technique for the computation of synthetic seismograms in a homogeneous, as well as in a multilayered anisotropic medium was developed. Full waveform theory is used to compute the synthetic seismograms. The medium can be elastic or viscoelastic. In the latter case, attenuation is

Satish Sinha

2006-01-01

382

Light attenuation on Chlorella vulgaris cells  

NASA Astrophysics Data System (ADS)

The laboratory measurements of spectrum of light attenuation on phytoplankton particles i.e. monoculture of unicellural green algae Chlorella vulgaris are presented. The measurements were carried out for alive culture and the cultures subjected to chemical (NaOH) or physical (ultrasounds) modification. The distinct changes in the light attenuation spectrum were a result of modification of the internal cell structures.

Krol, Tadeusz; Lotocka, Maria

1993-12-01

383

Isolation of fusions between the lac genes and several genes of the exu regulon: Analysis of their regulation, determination of the transcription direction of the uxaC-uxaA operon, in Escherichia coli K-12  

Microsoft Academic Search

Gene fusions between the lac structural genes and different genes of the hexuronate system were isolated by the two methods described by Casadaban (1976, 1979). Mud (Aprlac) mutants which have the lac genes fused to te regulatory region of exuT, uxaC, uxaA and uxaB genes were constructed. Separately, the lac genes carried by a ?plac-Mu hybrid phage were placed into

Nicole Hugouvieux-Cotte-Pattat; Janine Robert-Baudouy

1981-01-01

384

Signal attenuation and box-counting fractal analysis of optical coherence tomography images of arterial tissue  

PubMed Central

The sensitivity of optical coherence tomography images to sample morphology is tested by two methods. The first method estimates the attenuation of the OCT signal from various regions of the probed tissue. The second method uses a box-counting algorithm to calculate the fractal dimensions in the regions of interest identified in the images. Although both the attenuation coefficient as well as the fractal dimension correlate very well with the anatomical features of the probed samples; the attenuation method provides a better sensitivity. Two types of samples are used in this study: segments of arteries collected from atherosclerosis–prone Watanabe rabbits (WHHL-MI) and healthy segments of porcine coronary arteries. PMID:21258464

Popescu, Dan P.; Flueraru, Costel; Mao, Youxin; Chang, Shoude; Sowa, Michael G.

2010-01-01

385

Signal attenuation and box-counting fractal analysis of optical coherence tomography images of arterial tissue.  

PubMed

The sensitivity of optical coherence tomography images to sample morphology is tested by two methods. The first method estimates the attenuation of the OCT signal from various regions of the probed tissue. The second method uses a box-counting algorithm to calculate the fractal dimensions in the regions of interest identified in the images. Although both the attenuation coefficient as well as the fractal dimension correlate very well with the anatomical features of the probed samples; the attenuation method provides a better sensitivity. Two types of samples are used in this study: segments of arteries collected from atherosclerosis-prone Watanabe rabbits (WHHL-MI) and healthy segments of porcine coronary arteries. PMID:21258464

Popescu, Dan P; Flueraru, Costel; Mao, Youxin; Chang, Shoude; Sowa, Michael G

2010-01-01

386

Lac Repressor Mediated DNA Looping: Monte Carlo Simulation of Constrained DNA Molecules Complemented with Current Experimental Results  

PubMed Central

Tethered particle motion (TPM) experiments can be used to detect time-resolved loop formation in a single DNA molecule by measuring changes in the length of a DNA tether. Interpretation of such experiments is greatly aided by computer simulations of DNA looping which allow one to analyze the structure of the looped DNA and estimate DNA-protein binding constants specific for the loop formation process. We here present a new Monte Carlo scheme for accurate simulation of DNA configurations subject to geometric constraints and apply this method to Lac repressor mediated DNA looping, comparing the simulation results with new experimental data obtained by the TPM technique. Our simulations, taking into account the details of attachment of DNA ends and fluctuations of the looped subsegment of the DNA, reveal the origin of the double-peaked distribution of RMS values observed by TPM experiments by showing that the average RMS value for anti-parallel loop types is smaller than that of parallel loop types. The simulations also reveal that the looping probabilities for the anti-parallel loop types are significantly higher than those of the parallel loop types, even for loops of length 600 and 900 base pairs, and that the correct proportion between the heights of the peaks in the distribution can only be attained when loops with flexible Lac repressor conformation are taken into account. Comparison of the in silico and in vitro results yields estimates for the dissociation constants characterizing the binding affinity between O1 and Oid DNA operators and the dimeric arms of the Lac repressor. PMID:24800809

Biton, Yoav Y.; Kumar, Sandip; Dunlap, David; Swigon, David

2014-01-01

387

Topological analysis of a haloacid permease of a Burkholderia sp. bacterium with a PhoA-LacZ reporter  

PubMed Central

Background 2-Haloacids can be found in the natural environment as degradative products of natural and synthetic halogenated compounds. They can also be generated by disinfection of water and have been shown to be mutagenic and to inhibit glyceraldehyde-3-phosphate dehydrogenase activity. We have recently identified a novel haloacid permease Deh4p from a bromoacetate-degrading bacterium Burkholderia sp. MBA4. Comparative analyses suggested that Deh4p is a member of the Major Facilitator Superfamily (MFS), which includes thousands of membrane transporter proteins. Members of the MFS usually possess twelve putative transmembrane segments (TMS). Deh4p was predicted to have twelve TMS. In this study we characterized the topology of Deh4p with a PhoA-LacZ dual reporters system. Results Thirty-six Deh4p-reporter recombinants were constructed and expressed in E. coli. Both PhoA and LacZ activities were determined in these cells. Strength indices were calculated to determine the locations of the reporters. The results mainly agree with the predicted model. However, two of the TMS were not verified. This lack of confirmation of the TMS, using a reporter, has been reported previously. Further comparative analysis of Deh4p has assigned it to the Metabolite:H+ Symporter (MHS) 2.A.1.6 family with twelve TMS. Deh4p exhibits many common features of the MHS family proteins. Deh4p is apparently a member of the MFS but with some atypical features. Conclusion The PhoA-LacZ reporter system is convenient for analysis of the topology of membrane proteins. However, due to the limitation of the biological system, verification of some of the TMS of the protein was not successful. The present study also makes use of bioinformatic analysis to verify that the haloacid permease Deh4p of Burkholderia sp. MBA4 is a MFS protein but with atypical features. PMID:19878597

2009-01-01

388

Negative Regulation ofAdenylate Cyclase Gene(cya) Expression by Cyclic AMP-Cyclic AMP Receptor Protein inEscherichia coli: Studies withcya-lac Protein andOperonFusion Plasmids  

Microsoft Academic Search

Weconstructed cya-lac protein andoperonfusion plasmids invitro. Theeffect ofcyclic AMP (cAMP) on cya expression was examined bymeasuring thesynthesis of 3-galactosidase inEscherichia colicells containing fused plasmids. Inthecya-lacZ fused protein system, cya expression wasstrongly repressed byexogenous cAMP.Functional cAMPreceptor protein (CRP) was necessaryforthis effect. Ontheother hand, inatet-lacZ fused protein asacontrol system, tetexpression wasnotaffected bycAMP.Theinhibition ofcyaexpression by cAMPwas lsoobserved inthecya-lac fused operonsystem, although itwas necessarytoincrease

MAKOTO KAWAMUKAI; RYUTARO UTSUMI; TOHRU KOMANO

1985-01-01

389

Dependence of light attenuation and backscattering on collagen concentration and chondrocyte density in agarose scaffolds  

NASA Astrophysics Data System (ADS)

Optical coherence tomography (OCT) has been applied for high resolution imaging of articular cartilage. However, the contribution of individual structural elements of cartilage on OCT signal has not been thoroughly studied. We hypothesize that both collagen and chondrocytes, essential structural components of cartilage, act as important light scatterers and that variation in their concentrations can be detected by OCT through changes in backscattering and attenuation. To evaluate this hypothesis, we established a controlled model system using agarose scaffolds embedded with variable collagen concentrations and chondrocyte densities. Using OCT, we measured the backscattering coefficient (µb) and total attenuation coefficient (µt) in these scaffolds. Along our hypothesis, light backscattering and attenuation in agarose were dependent on collagen concentration and chondrocyte density. Significant correlations were found between µt and chondrocyte density (? = 0.853, p < 0.001) and between µt and collagen concentration (? = 0.694, p < 0.001). µb correlated significantly with chondrocyte density (? = 0.504, p < 0.001) but not with collagen concentration (? = 0.103, p = 0.422) of the scaffold. Thus, quantitation of light backscattering and, especially, attenuation could be valuable when evaluating the integrity of soft tissues, such as articular cartilage with OCT.

Puhakka, P. H.; Ylärinne, J. H.; Lammi, M. J.; Saarakkala, S.; Tiitu, V.; Kröger, H.; Virén, T.; Jurvelin, J. S.; Töyräs, J.

2014-11-01

390

Dependence of light attenuation and backscattering on collagen concentration and chondrocyte density in agarose scaffolds.  

PubMed

Optical coherence tomography (OCT) has been applied for high resolution imaging of articular cartilage. However, the contribution of individual structural elements of cartilage on OCT signal has not been thoroughly studied. We hypothesize that both collagen and chondrocytes, essential structural components of cartilage, act as important light scatterers and that variation in their concentrations can be detected by OCT through changes in backscattering and attenuation. To evaluate this hypothesis, we established a controlled model system using agarose scaffolds embedded with variable collagen concentrations and chondrocyte densities. Using OCT, we measured the backscattering coefficient (µb) and total attenuation coefficient (µt) in these scaffolds. Along our hypothesis, light backscattering and attenuation in agarose were dependent on collagen concentration and chondrocyte density. Significant correlations were found between µt and chondrocyte density (? = 0.853, p < 0.001) and between µt and collagen concentration (? = 0.694, p < 0.001). µb correlated significantly with chondrocyte density (? = 0.504, p < 0.001) but not with collagen concentration (? = 0.103, p = 0.422) of the scaffold. Thus, quantitation of light backscattering and, especially, attenuation could be valuable when evaluating the integrity of soft tissues, such as articular cartilage with OCT. PMID:25310088

Puhakka, P H; Ylärinne, J H; Lammi, M J; Saarakkala, S; Tiitu, V; Kröger, H; Virén, T; Jurvelin, J S; Töyräs, J

2014-11-01

391

Errors in MR-based attenuation correction for brain imaging with PET/MR scanners  

NASA Astrophysics Data System (ADS)

AimAttenuation correction of PET data acquired by hybrid MR/PET scanners remains a challenge, even if several methods for brain and whole-body measurements have been developed recently. A template-based attenuation correction for brain imaging proposed by our group is easy to handle and delivers reliable attenuation maps in a short time. However, some potential error sources are analyzed in this study. We investigated the choice of template reference head among all the available data (error A), and possible skull anomalies of the specific patient, such as discontinuities due to surgery (error B). Materials and methodsAn anatomical MR measurement and a 2-bed-position transmission scan covering the whole head and neck region were performed in eight normal subjects (4 females, 4 males). Error A: Taking alternatively one of the eight heads as reference, eight different templates were created by nonlinearly registering the images to the reference and calculating the average. Eight patients (4 females, 4 males; 4 with brain lesions, 4 w/o brain lesions) were measured in the Siemens BrainPET/MR scanner. The eight templates were used to generate the patients' attenuation maps required for reconstruction. ROI and VOI atlas-based comparisons were performed employing all the reconstructed images. Error B: CT-based attenuation maps of two volunteers were manipulated by manually inserting several skull lesions and filling a nasal cavity. The corresponding attenuation coefficients were substituted with the water's coefficient (0.096/cm). ResultsError A: The mean SUVs over the eight templates pairs for all eight patients and all VOIs did not differ significantly one from each other. Standard deviations up to 1.24% were found. Error B: After reconstruction of the volunteers' BrainPET data with the CT-based attenuation maps without and with skull anomalies, a VOI-atlas analysis was performed revealing very little influence of the skull lesions (less than 3%), while the filled nasal cavity yielded an overestimation in cerebellum up to 5%. ConclusionsThe present error analysis confirms that our template-based attenuation method provides reliable attenuation corrections of PET brain imaging measured in PET/MR scanners.

Rota Kops, Elena; Herzog, Hans

2013-02-01

392

M-Bonomial Coefficients and Their Identities  

ERIC Educational Resources Information Center

In this note, we introduce M-bonomial coefficients or (M-bonacci binomial coefficients). These are similar to the binomial and the Fibonomial (or Fibonacci-binomial) coefficients and can be displayed in a triangle similar to Pascal's triangle from which some identities become obvious.

Asiru, Muniru A.

2010-01-01

393

Third Order Elastic Coefficients of Rocks  

Microsoft Academic Search

We present a methodology to determine third order elastic (TOE) coefficients of rock from velocity measurements at different hydrostatic stress level. TOE coefficients help us to obtain a quantitative measure of the variation of velocity with stress. It is one of the most general ways to parameterize the stress sensitivity of rocks. We usually determine the isotropic TOE coefficients from

K. Bandyopadhyay

2006-01-01

394

Soccer Ball Lift Coefficients via Trajectory Analysis  

ERIC Educational Resources Information Center

We performed experiments in which a soccer ball was launched from a machine while two high-speed cameras recorded portions of the trajectory. Using the trajectory data and published drag coefficients, we extracted lift coefficients for a soccer ball. We determined lift coefficients for a wide range of spin parameters, including several spin…

Goff, John Eric; Carre, Matt J.

2010-01-01

395

FREQUENCY DEPENDENT ATTENUATION ANALYSIS OF GROUND-PENETRATING RADAR DATA  

E-print Network

FREQUENCY DEPENDENT ATTENUATION ANALYSIS OF GROUND- PENETRATING RADAR DATA John H. Bradford, CGISS, Boise State University, Boise, ID Abstract I investigate the frequency dependence of attenuation materials attenuation is approximately linear with frequency over the bandwidth of the GPR signal

Barrash, Warren

396

Attenuation of diacylglycerol second messengers  

SciTech Connect

Diacylglycerol(DAG) derived from phosphatidylinositol activates protein kinase C in agonist-stimulated cells. At least two pathways may contribute to the attenuation of the DAG signal: (1) phosphorylation to phosphatidic acid(PA) by DAG kinase(DGK), and (2) deacylation by DAG and monoacylglycerol lipases. A number of DAG analogs were tested as substrates and inhibitors of partially purified pig brain DGK. Two analogs were potent inhibitors in vitro, 1-monooleoylglycerol(MOG,K/sub I/ = 91 ..mu..M) and diotanoylethyleneglycol (diC/sub 8/EG, K/sub I/ = 58 ..mu..M). These compounds were tested in human platelets. DiC/sub 8/EG inhibited (70 - 100%) (/sup 32/P/sub i/) incorporation into PA in thrombin-stimulated platelets. Under these conditions the DAG signal was somewhat long-lived but was still metabolized, presumably by the lipase pathway. MOG treatment elevated DAG levels up to 4-fold in unstimulated platelets. The DAG formed was in a pool where it did not activate protein kinase C. Thrombin-stimulation of MOG-treated platelets resulted in DAG levels 10-fold higher than control platelets. This appears to be due to the inability of these platelets to metabolize agonist-linked DAG via the lipase pathway. The development of specific inhibitors of DAG kinase and DAG lipase, in conjunction with mass quantification of DAG levels as used here, will provide further insights into the regulation of DAG second messengers.

Bishop, W.R.; Ganong, B.R.; Bell, R.M.

1986-05-01

397

Universal Sound Attenuation in Amorphous Solids at Low-Temperatures  

E-print Network

Disordered solids are known to exhibit quantitative universalities at low temperatures, the most striking of which is the ultrasonic attenuation coefficient Q. The established theory of tunneling two state systems (TTLS) in its original form (i.e. without extra fitting functions and parameters), is unable to explain this universality. While the TTLS model can be modified, particularly by including long range phonon induced interactions to explain the universal value of Q, (a) it is not clear that the essential features of the original model that has been successful in explaining the experimental data is preserved, and (b) even if it is, it is not clear that the postulates of the original model remain necessary. The purpose of this study is to derive the universal acoustic absorption and related quantities observed in disordered solids by starting from a many-body quantum theory of unspecified amorphous blocks that mutually interact through the strain field. Based on very generic assumptions and having no adjustable fitting parameters, the frequency and initial state averaged macroscopic attenuation of a group of interacting disordered blocks is calculated in the low temperature regime by a novel "trace method", which then is iterated up-to experimental length scales through a real space renormalization group approach. Then using a heuristic second-order perturbation argument, the frequency dependence of Q is found, and combined with the previous result to yield the observed universal values in the MHz-Ghz range of frequencies. It is concluded that strong microscopic postulates are not necessary in order to explain the thermal conductivity, velocity shift and sound attenuation of disordered media in the low temperature regime.

Dervis Can Vural

2012-03-06

398

Radon emanation coefficients for phosphogypsum.  

PubMed

Phosphogypsum is a by-product of the phosphate fertilizer industry which is stockpiled in large quantities world-wide. Phosphogypsum consists mainly of dihydrate gypsum (CaSO42H2O) but also contains elevated concentrations of 226Ra and other inorganic species which originate from the processing of phosphate rock. 222Rn gas is the first decay product of 226Ra and has been identified as one of the major environmental concerns associated with phosphogypsum. This study was conducted to determine effects of particle size, weathering, and moisture content on the 222Rn emanation coefficient (epsilon) for phosphogypsum. Average epsilon for air-dry, unfractionated phosphogypsums derived from Togo, Florida, or Idaho rock was approximately 12%. Average epsilon for fine fraction phosphogypsum (< 20 microns diameter) was greater than for unfractionated phosphogypsum by a factor of 4.6, 1.4, and 4.4 for samples derived from Idaho rock, Togo rock, and Florida rock, respectively. Phosphogypsum samples subjected to an artificial weathering procedure lost 40% mass, with no change in epsilon. Increasing water content was found to first slightly decrease, then to increase epsilon compared to air-dry samples; epsilon for 100% saturated phosphogypsum was 1.9-fold greater than in air-dry phosphogypsum. Particle size sorting could account for variability of 222Rn exhalation at repositories. Very high moisture contents could slightly increase 222Rn emanation, but exhalation would likely be reduced due to slow diffusion through porosity of saturated phosphogypsum. PMID:7558842

Rutherford, P M; Dudas, M J; Arocena, J M

1995-10-01

399

Hybrid nature of 0846+51W1: a BL Lac object with a narrow line Seyfert 1 nucleus  

E-print Network

We have found a NLS1 nucleus in the extensively studied eruptive BL Lac, 0846+51W1, out of a large sample of NLS1 compiled from the spectroscopic dataset of SDSS DR1. Its optical spectrum can be well decomposed into three components, a power law component from the relativistic jet, a stellar component from the host galaxy, and a component from a typical NLS1 nucleus. The emission line properties of 0846+51W1, FWHM(Hbeta) ~ 1710 km s^-1 and [OIII]5007/Hbeta ~ 0.32 when it was in faint state, fulfil the conventional definition of NLS1. Strong FeII emission is detected in the SDSS spectrum, which is also typical of NLS1s. We try to estimate its central black hole mass using various techniques and find that 0846+51W1 is very likely emitting at a few times 10% L_Edd. We speculate that Seyfert-like nuclei, including NLS1s, might be concealed in a significant fraction of BL Lacs but have not been sufficiently explored due to the fact that, by definition, the optical-UV continuum of such kind of objects are often overwhelmed by the synchrotron emission.

Hong-Yan Zhou; Ting-Gui Wang; Xiao-Bo Dong; Cheng Li; Xue-Guang Zhang

2004-11-10

400

Plasmid-based lacZalpha assay for DNA polymerase fidelity: application to archaeal family-B DNA polymerase.  

PubMed

The preparation of a gapped pUC18 derivative, containing the lacZalpha reporter gene in the single-stranded region, is described. Gapping is achieved by flanking the lacZalpha gene with sites for two related nicking endonucleases, enabling the excision of either the coding or non-coding strand. However, the excised strand remains annealed to the plasmid through non-covalent Watson-Crick base-pairing; its removal, therefore, requires a heat-cool cycle in the presence of an exactly complementary competitor DNA. The gapped plasmids can be used to assess DNA polymerase fidelity using in vitro replication, followed by transformation into Escherichia coli and scoring the blue/white colony ratio. Results found with plasmids are similar to the well established method based on gapped M13, in terms of background ( approximately 0.08% in both cases) and the mutation frequencies observed with a number of DNA polymerases, providing validation for this straightforward and technically uncomplicated approach. Several error prone variants of the archaeal family-B DNA polymerase from Pyrococcus furiosus have been investigated, illuminating the potential of the method. PMID:19515939

Jozwiakowski, Stanislaw K; Connolly, Bernard A

2009-08-01

401

An Analysis of Light Periods of BL Lac Object S5 0716+714 with the MUSIC Algorithm  

NASA Astrophysics Data System (ADS)

The multiple signal classi?cation (MUSIC) algorithm is introduced to the estimation of light periods of BL Lac objects. The principle of the MUSIC algorithm is given, together with a testing on its spectral resolution by using a simulative signal. From a lot of literature, we have collected a large number of effective observational data of the BL Lac object S5 0716+714 in the three optical wavebands V, R, and I from 1994 to 2008. The light periods of S5 0716+714 are obtained by means of the MUSIC algorithm and average periodogram algorithm, respectively. It is found that there exist two major periodic components, one is the period of (3.33±0.08) yr, another is the period of (1.24±0.01) yr. The comparison of the performances of periodicity analysis of two algorithms indicates that the MUSIC algorithm has a smaller requirement on the sample length, as well as a good spectral resolution and anti-noise ability, to improve the accuracy of periodicity analysis in the case of short sample length.

Tang, Jie

2012-07-01

402

Reliable prediction of complex phenotypes from a modular design in free energy space: an extensive exploration of the lac operon.  

PubMed

The basic methodology for designing, altering, and constructing biological systems is increasingly relying on well-established engineering principles to move forward from trial and error approaches to reliably predicting the system behavior from the properties of the components and their interactions. The inherent complexity of even the simplest biological systems, however, often precludes achieving such predictive power. A prototypical example is the lac operon, one of the best-characterized genetic systems, which still poses serious challenges for understanding the results of combining its parts into novel setups. The reason is the pervasive complex hierarchy of events involved in gene regulation that extend from specific protein-DNA interactions to the combinatorial assembly of nucleoprotein complexes. Here, we integrate such complexity into a few-parameter model to accurately predict gene expression from a few simple rules to connect the parts. The model accurately reproduces the observed transcriptional activity of the lac operon over a 10,000-fold range for 21 different operator setups, different repressor concentrations, and tetrameric and dimeric forms of the repressor. Incorporation of the calibrated model into more complex scenarios accurately captures the induction curves for key operator configurations and the temporal evolution of the ?-galactosidase activity of cell populations. PMID:23654358

Vilar, Jose M G; Saiz, Leonor

2013-10-18

403

Multiple Co-Evolutionary Networks Are Supported by the Common Tertiary Scaffold of the LacI/GalR Proteins  

PubMed Central

Protein families might evolve paralogous functions on their common tertiary scaffold in two ways. First, the locations of functionally-important sites might be “hard-wired” into the structure, with novel functions evolved by altering the amino acid (e.g. Ala vs Ser) at these positions. Alternatively, the tertiary scaffold might be adaptable, accommodating a unique set of functionally important sites for each paralogous function. To discriminate between these possibilities, we compared the set of functionally important sites in the six largest paralogous subfamilies of the LacI/GalR transcription repressor family. LacI/GalR paralogs share a common tertiary structure, but have low sequence identity (?30%), and regulate a variety of metabolic processes. Functionally important positions were identified by conservation and co-evolutionary sequence analyses. Results showed that conserved positions use a mixture of the “hard-wired” and “accommodating” scaffold frameworks, but that the co-evolution networks were highly dissimilar between any pair of subfamilies. Therefore, the tertiary structure can accommodate multiple networks of functionally important positions. This possibility should be included when designing and interpreting sequence analyses of other protein families. Software implementing conservation and co-evolution analyses is available at https://sourceforge.net/projects/coevolutils/. PMID:24391951

Parente, Daniel J.; Swint-Kruse, Liskin

2013-01-01

404

VizieR Online Data Catalog: X-ray/radio data of high energy peaked BL Lacs (Giommi+, 2005)  

NASA Astrophysics Data System (ADS)

The fully identified complete sample including 150 extreme HBL BL Lacs is presented in Table 1 where we give the source name built with the catalog identification code SHBL (where S stands for "Sedentary" survey and HBL for High energy peaked BL Lacs) and the arcsecond precision optical coordinates of the source taken from the APM and COSMOS on-line services; we give also the RASS name, the X-ray flux (0.1-2.4keV), the radio flux (20cm, from the NVSS survey), and the optical apparent V magnitude (from APM and COSMOS) respectively; we give the redshift when available and the reference for the optical identification. In Table 2 we report properties for five bright elliptical galaxies/low luminosity HBLs in the original sample of high fX/fr sources of Paper I (Giommi et al., 1999MNRAS.310..465G). In Table 3 the 19 rejected emission line AGNs together with their properties are presented. (4 data files).

Giommi, P.; Piranomonte, S.; Perri, M.; Padovani, P.

2005-01-01

405

Index-free heat kernel coefficients  

NASA Astrophysics Data System (ADS)

Using index-free notation, we present the diagonal values 0264-9381/15/8/014/img1 of the first five heat kernel coefficients 0264-9381/15/8/014/img2 associated with a general Laplace-type operator on a compact Riemannian space without boundary. The fifth coefficient 0264-9381/15/8/014/img3 appears here for the first time. For the special case of a flat space, but with a gauge connection, the sixth coefficient is given too. Also provided are the leading terms for any coefficient, both in ascending and descending powers of the Yang-Mills and Riemann curvatures, to the same order as required for the fourth coefficient. These results are obtained by directly solving the relevant recursion relations, working in the Fock-Schwinger gauge and Riemann normal coordinates. Our procedure is thus non-covariant, but we show that for any coefficient the `gauged', respectively `curved', version is found from the corresponding `non-gauged', respectively `flat', coefficient by making some simple covariant substitutions. These substitutions being understood, the coefficients retain their `flat' form and size. In this sense the fifth and sixth coefficient have only 26 and 75 terms, respectively, allowing us to write them down. Using index-free notation also clarifies the general structure of the heat kernel coefficients. In particular, in flat space we find that from the fifth coefficient onward, certain scalars are absent. This may be relevant for the anomalies of quantum field theories in ten or more dimensions.

van de Ven, Anton E. M.

1998-08-01

406

Spatial distribution of intrinsic and scattering seismic attenuation in active volcanic islands - II: Deception Island images  

NASA Astrophysics Data System (ADS)

In this work, we present regional maps of the inverse intrinsic quality factor (Qi-1), the inverse scattering quality factor (Qs-1) and total inverse quality factor (Qt-1) for the volcanic environment of Deception Island (Antarctica). Our attenuation study is based on diffusion approximation, which permits us to obtain the attenuation coefficients for every single couple source-receiver separately. The data set used in this research is derived from an active seismic experiment using more than 5200 offshore shots (air guns) recorded at 32 onshore seismic stations and four ocean bottom seismometers. To arrive at a regional distribution of these values, we used a new mapping technique based on a Gaussian space probability function. This approach led us to create `2-D probabilistic maps' of values of intrinsic and scattering seismic attenuation. The 2-D tomographic images confirm the existence of a high attenuation body below an inner bay of Deception Island. This structure, previously observed in 2-D and 3-D velocity tomography of the region, is associated with a massive magma reservoir. Magnetotelluric studies reach a similar interpretation of this strong anomaly. Additionally, we observed areas with lower attenuation effects that bear correlation with consolidated structures described in other studies and associated with the crystalline basement of the area. Our calculations of the transport mean-free path and absorption length for intrinsic attenuation gave respective values of ? 950 m and 5 km, which are lower than the values obtained in tectonic regions or volcanic areas such as Tenerife Island. However, as observed in other volcanic regions, our results indicate that scattering effects dominate strongly over the intrinsic attenuation.

Prudencio, Janire; Ibáñez, Jesús M.; García-Yeguas, Araceli; Del Pezzo, Edoardo; Posadas, Antonio M.

2013-12-01

407

Improved efficiency Si-photonic attenuator.  

PubMed

A forward-biased p-i-n diode integrated with a ridge waveguide forms a basic Si attenuator building block. Disruptive power improvement was achieved through a recessed contact configuration by limiting the amount of Si volume for carrier recombination. A device model was established by using realistic surface recombination velocities instead of effective carrier lifetime concept to understand the device physics of the afore-mentioned Si attenuator. PMID:18852785

Zheng, D W; Smith, B T; Asghari, M

2008-10-13

408

The attenuation of strong shock waves  

E-print Network

THE ATTENUATION OF STRONG SHOCK WAVES A Thesis By Ronald Crecelius Kirkpatrick Submitted to the Graduate School of the Agricultural and Mechanical College of Texas in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE... May 1963 Major Subject: Physics. THE ATTENUATION OF STRONG SHOCK WAVES A Thesis By Ronald Crecelius Kirkpatrick Approved as to style and content by: (Chairman of Committee (He of Departme ) May 1963 TABLE OF CONTENTS INT R ODU C TI ON ~Pe e...

Kirkpatrick, Ronald Crecelius

2012-06-07

409

Live Attenuated Cholera Vaccines: Flagella and Reactogenicity  

Microsoft Academic Search

\\u000a The rational design of attenuated Vibrio cholerae strains has been an attractive method for live cholera vaccine development because the major mechanisms of V. cholerae virulence are well defined and convalescence from cholera, the disease it causes, is a strongly immunizing process. After\\u000a decades of effort to develop safe live attenuated cholera vaccines, however, the appearance of reactogenicity, defined as

D. Ewen Cameron; John J. Mekalanos

410

Variable attenuation of amphetamine effects by lithium.  

PubMed

In an open study of 8 subjects, approximately half showed some attenuation of CNS stimulant effects of amphetamine after pretreatment with lithium. Two showed specific blockade of euphoria, with persistence of some CNS stimulant effects. In 3 subjects lithium did not appear to affect the response to amphetamine. Lithium caused significant attenuation of the amphetamine-induced increase in systolic blood pressure for the group as a whole. PMID:443465

Angrist, B; Gershon, S

1979-06-01

411

Lactobacillus acidophilus attenuates downregulation of DRA function and expression in inflammatory models.  

PubMed

Probiotics, including Lactobacilli, are commensal bacteria that have been used in clinical trials and experimental models for the prevention and treatment of diarrheal disorders. Our previous studies have shown that Lactobacillus acidophilus (LA) and its culture supernatant (CS) stimulated Cl(-)/HCO3 (-) exchange activity, acutely via an increase in the surface levels of downregulated in adenoma (DRA, SLC26A3) and in long-term treatments via increasing its expression involving transcriptional mechanisms. However, the role of LA in modulating DRA activity under inflammatory conditions is not known. Current in vitro studies using human intestinal epithelial Caco-2 cells examined the efficacy of LA or its CS in counteracting the inhibitory effects of interferon-? (IFN-?) on Cl(-)/HCO3 (-) exchange activity. Pretreatment of cells with LA or LA-CS for 1 h followed by coincubation with IFN-? significantly alleviated the inhibitory effects of IFN-? on Cl(-)/HCO3 (-) exchange activity. In the in vivo model of dextran sulfate sodium-induced experimental colitis (3% in drinking water for 7 days) in C57BL/6J mice, administration of live LA (3 × 10(9) colony-forming units) via oral gavage attenuated colonic inflammation. LA administration also counteracted the colitis-induced decrease in DRA mRNA and protein levels. Efficacy of LA or its secreted soluble factors in alleviating inflammation and inflammation-associated dysregulation of DRA activity could justify their therapeutic potential in inflammatory diarrheal diseases. PMID:25059823

Singh, Varsha; Kumar, Anoop; Raheja, Geetu; Anbazhagan, Arivarasu N; Priyamvada, Shubha; Saksena, Seema; Jhandier, Muhammad Nauman; Gill, Ravinder K; Alrefai, Waddah A; Borthakur, Alip; Dudeja, Pradeep K

2014-09-15

412

Attenuation of noise by motorcycle safety helmets.  

PubMed

For workers such as police motorcyclists or couriers, traffic and engine noise reaching the ears is an important factor contributing to the overall condition of their work. This noise can be reduced with motorcycle helmets. In this study, insertion loss of motorcycle helmets was measured with the microphone-in-real-ear technique and sound attenuation with the real-ear-at-threshold method. Results for 3 Nolan helmets show essentially no protection against external noise in the frequency range <250 Hz. In the frequency range >500 Hz, attenuation increases linearly at a rate of 8-9 dB per octave, to ~30 dB at 8 kHz. Lack of attenuation in the low-frequency range may cause annoying effects. In addition, high attenuation in the high-frequency range may decrease intelligibility of speech signals for a rider in a helmet. Attenuation measured in this study does not take into account noise generated by turbulent wind around the helmet. Thus, the measured values of attenuation represent a motorcycle rider's best conditions of hearing. PMID:19744370

M?y?ski, Rafa?; Koz?owski, Emil; Zera, Jan

2009-01-01

413

An Empirical Assessment of Exposure Measurement Error and Effect Attenuation in Bipollutant Epidemiologic Models  

PubMed Central

Background: Using multipollutant models to understand combined health effects of exposure to multiple pollutants is becoming more common. However, complex relationships between pollutants and differing degrees of exposure error across pollutants can make health effect estimates from multipollutant models difficult to interpret. Objectives: We aimed to quantify relationships between multiple pollutants and their associated exposure errors across metrics of exposure and to use empirical values to evaluate potential attenuation of coefficients in epidemiologic models. Methods: We used three daily exposure metrics (central-site measurements, air quality model estimates, and population exposure model estimates) for 193 ZIP codes in the Atlanta, Georgia, metropolitan area from 1999 through 2002 for PM2.5 and its components (EC and SO4), as well as O3, CO, and NOx, to construct three types of exposure error: ?spatial (comparing air quality model estimates to central-site measurements), ?population (comparing population exposure model estimates to air quality model estimates), and ?total (comparing population exposure model estimates to central-site measurements). We compared exposure metrics and exposure errors within and across pollutants and derived attenuation factors (ratio of observed to true coefficient for pollutant of interest) for single- and bipollutant model coefficients. Results: Pollutant concentrations and their exposure errors were moderately to highly correlated (typically, > 0.5), especially for CO, NOx, and EC (i.e., “local” pollutants); correlations differed across exposure metrics and types of exposure error. Spatial variability was evident, with variance of exposure error for local pollutants ranging from 0.25 to 0.83 for ?spatial and ?total. The attenuation of model coefficients in single- and bipollutant epidemiologic models relative to the true value differed across types of exposure error, pollutants, and space. Conclusions: Under a classical exposure-error framework, attenuation may be substantial for local pollutants as a result of ?spatial and ?total with true coefficients reduced by a factor typically < 0.6 (results varied for ?population and regional pollutants). Citation: Dionisio KL, Baxter LK, Chang HH. 2014. An empirical assessment of exposure measurement error and effect attenuation in bipollutant epidemiologic models. Environ Health Perspect 122:1216–1224;?http://dx.doi.org/10.1289/ehp.1307772 PMID:25003573

Baxter, Lisa K.; Chang, Howard H.

2014-01-01

414

Stress-associated scattering attenuation and intrinsic attenuation of laboratory ultrasonic waves  

NASA Astrophysics Data System (ADS)

In comparison with seismic velocity and static moduli connected with the large-scale heterogeneous structure, seismic coda attenuation, in response to the small-scale random heterogeneities, has proved to be more sensitive to stress changes. Thus, it has a better chance to become one of the critical values for examining the state of stress changes in rocks. We perform an experiment on ultrasonic scattering using a cylindrical rock sample associated with intra-grain pores and fractures to study the effect of pore-pressure induced stress changes on coda attenuation as a combination of intrinsic attenuation and scattering attenuation. The main problem is to handle multiple side-reflected waves from the rock sample boundaries that may contaminate the ultrasonic coda waves. We analyze the ultrasonic coda data by employing a strongly scattering cylindrical model with two types of extreme boundary conditions. The study confirms that the induced heterogeneous cracks in cylindrical rock make a great impact on estimate of scattering parameters and lead to different stress or frequency dependence of coda attenuation. Comparisons of scattering attenuation and intrinsic attenuation indicate the ultrasonic coda attenuation is mainly contributed by scattering attenuation especially at high frequencies or high stresses.

Wei, W.; Fu, L.

2012-12-01

415

Temporal Variability of Pesticide Concentrations in Homes and Implications for Attenuation Bias in Epidemiologic Studies  

PubMed Central

Background: Residential pesticide exposure has been linked to adverse health outcomes in adults and children. High-quality exposure estimates are critical for confirming these associations. Past epidemiologic studies have used one measurement of pesticide concentrations in carpet dust to characterize an individual’s average long-term exposure. If concentrations vary over time, this approach could substantially misclassify exposure and attenuate risk estimates. Objectives: We assessed the repeatability of pesticide concentrations in carpet dust samples and the potential attenuation bias in epidemiologic studies relying on one sample. Methods: We collected repeated carpet dust samples (median = 3; range, 1–7) from 21 homes in Fresno County, California, during 2003–2005. Dust was analyzed for 13 pesticides using gas chromatography–mass spectrometry. We used mixed-effects models to estimate between- and within-home variance. For each pesticide, we computed intraclass correlation coefficients (ICCs) and the estimated attenuation of regression coefficients in a hypothetical case–control study collecting a single dust sample. Results: The median ICC was 0.73 (range, 0.37–0.95), demonstrating higher between-home than within-home variability for most pesticides. The expected magnitude of attenuation bias associated with using a single dust sample was estimated to be ? 30% for 7 of the 13 compounds evaluated. Conclusions: For several pesticides studied, use of one dust sample to represent an exposure period of approximately 2 years would not be expected to substantially attenuate odds ratios. Further study is needed to determine if our findings hold for longer exposure periods and for other pesticides. PMID:23462689

Ward, Mary H.; Bell, Erin M.; Whitehead, Todd P.; Gunier, Robert B.; Friesen, Melissa C.; Nuckols, John R.

2013-01-01

416

The maraging-steel blades of the Virgo super attenuator  

NASA Astrophysics Data System (ADS)

The blades are crucial components of the Virgo super attenuators. The material used for their construction is maraging steel, a low-carbon-content alloy with high ultimate tensile strength and low creep under stress. Young's modulus, the shear modulus, the Poisson ratio and the corresponding elastic energy-loss coefficients have been measured. The measurements have been performed on specimens subjected to the same thermal treatments as those of elements for the Virgo interferometer realized with maraging steel. In addition, anelastic properties of the material subjected to different thermal treatments have been measured. It has been found that, for a maraging-steel structure (one free of plastic deformation), which undergoes an excitation with flexural vibrations, the elastic energy-loss coefficient can vary over a wide range as a function of the thermal treatment of the material and it is dominated by the thermo-elastic effect. The main reason for such a great alteration is supposed to be the dependence of the thermal conductivity on the average sizes of the precipitate particles and their relative separations.

Braccini, S.; Casciano, C.; Cordero, F.; Corvace, F.; DeSanctis, M.; Franco, R.; Frasconi, F.; Majorana, E.; Paparo, G.; Passaquieti, R.; Rapagnani, P.; Ricci, F.; Righetti, D.; Solina, A.; Valentini, R.

2000-05-01

417

Measurement of Attenuation with Airborne and Ground-Based Radar in Convective Storms Over Land and Its Microphysical Implications  

NASA Technical Reports Server (NTRS)

Observations by the airborne X-band Doppler radar (EDOP) and the NCAR S-band polarimetric (S-POL) radar from two field experiments are used to evaluate the Surface ref'ercnce technique (SRT) for measuring the path integrated attenuation (PIA) and to study attenuation in deep convective storms. The EDOP, flying at an altitude of 20 km, uses a nadir beam and a forward pointing beam. It is found that over land, the surface scattering cross-section is highly variable at nadir incidence but relatively stable at forward incidence. It is concluded that measurement by the forward beam provides a viable technique for measuring PIA using the SRT. Vertical profiles of peak attenuation coefficient are derived in vxo deep convective storms by the dual-wavelength method. Using the measured Doppler velocity, the reflectivities at. the two wavelengths, the differential reflectivity and the estimated attenuation coefficients, it is shown that: supercooled drops and dry ice particles probably co-existed above the melting level in regions of updraft, that water-coated partially melted ice particles probably contributed to high attenuation below the melting level, and that the data are not readil explained in terms of a gamma function raindrop size distribution.

Tian, Lin; Heymsfield, G. M.; Srivastava, R. C.; Starr, D. OC. (Technical Monitor)

2001-01-01

418

Measurement of Attenuation with Airborne and Ground-Based Radar in Convective Storms Over Land Its Microphysical Implications  

NASA Technical Reports Server (NTRS)

Observations by the airborne X-band Doppler radar (EDOP) and the NCAR S-band polarimetric (S-Pol) radar from two field experiments are used to evaluate the surface reference technique (SRT) for measuring the path integrated attenuation (PIA) and to study attenuation in deep convective storms. The EDOP, flying at an altitude of 20 km, uses a nadir beam and a forward pointing beam. It is found that over land, the surface scattering cross-section is highly variable at nadir incidence but relatively stable at forward incidence. It is concluded that measurement by the forward beam provides a viable technique for measuring PIA using the SRT. Vertical profiles of peak attenuation coefficient are derived in two deep convective storms by the dual-wavelength method. Using the measured Doppler velocity, the reflectivities at the two wavelengths, the differential reflectivity and the estimated attenuation coefficients, it is shown that: supercooled drops and (dry) ice particles probably co-existed above the melting level in regions of updraft, that water-coated partially melted ice particles probably contributed to high attenuation below the melting level.

Tian, Lin; Heymsfield, G. M.; Srivastava, R. C.; O'C.Starr, D. (Technical Monitor)

2001-01-01

419

Separation of intrinsic and scattering attenuation in southern California using TERRAscope data  

SciTech Connect

A multiple lapse time window analysis was applied to three-component broadband seismograms recorded at five TERRAscope stations in southern California to separate scattering and intrinsic attenuation. Seismic energies were integrated over three consecutive lapse time intervals: 0-15, 15-30, and 30-45 s (measured from the S arrival for approximately 30 earthquakes with hypocentral distances of less than 70 km from each station). Using the fundamental separability of source, site, and path effects for coda waves, the integrated energies for different magnitude earthquakes were normalized to a common source size at each station, and the effect of near-site amplification is removed. Subsequently, the authors constructed a group of geometric spreading-corrected normalized energy-distance curves for each station region over frequency bands 0.5-1, 1-2, 2-4, and 4-8 Hz for all five stations. Two more frequency bands, 8-16 and 16-32 Hz, were added at stations PAS and SVD, for which higher sample rate data were available. A theoretical model of body wave energy propagation in a randomly heterogeneous elastic medium was employed to interpret the observation. Two parameters describe the medium in this model. These are the scattering attenuation coefficients {eta}{sub s} and the intrinsic attenuation coefficient {eta}{sub i}. By assuming that scattering is isotropic and including all orders of multiple scattering, this model predicts the spatial and temporal distribution of seismic energy. A two-step least squares fitting procedure was used to find the best fitting model parameters. The results show the following: (1) the seismic albedo, B{sub 0} = {eta}{sub s}/({eta}{sub i} + {eta}{sub s}), increases with decreasing frequency for all station regions. (2) Significant differences exist for the scattering attenuation coefficient {eta}{sub s} and seismic albedo B{sub 0} among stations at lower frequencies. 21 refs., 12 figs., 1 tab.

Jin, Anshu; Adams, D.; Aki, Keiiti [Univ. of Southern California, Los Angeles, CA (United States)] [Univ. of Southern California, Los Angeles, CA (United States); Mayeda, K. [Lawrence Livermore National Lab., CA (United States)] [Lawrence Livermore National Lab., CA (United States)

1994-09-10

420

Relationship between direct and converse flexoelectric coefficients  

NASA Astrophysics Data System (ADS)

Flexoelectric effect, as a universal electromechanical coupling, has drawn lots of interests in dielectric materials. However, due to the restrictions of present measurement techniques, only part of coefficients has been experimentally examined. In this study, we derived the coordinate-dependent Gibbs free energy density function in the inhomogeneous spatial field to investigate the relationship between the direct and converse flexoelectric coefficients. In crystalline mediums and systems, the direct and converse flexoelectric coefficients are proved to equivalent according to the Maxwell relation. These results will broaden the application of the Maxwell relation into non-linear spatial field, and provide the guideline for experimental measurement and prediction of flexoelectric coefficients.

Shu, Longlong; Li, Fei; Huang, Wenbin; Wei, Xiaoyong; Yao, Xi; Jiang, Xiaoning

2014-10-01