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1

Attenuation coefficients for water quality trading.  

PubMed

Water quality trading has been proposed as a cost-effective approach for reducing nutrient loads through credit generation from agricultural or point source reductions sold to buyers facing costly options. We present a systematic approach to determine attenuation coefficients and their uncertainty. Using a process-based model, we determine attenuation with safety margins at many watersheds for total nitrogen (TN) and total phosphorus (TP) loads as they transport from point of load reduction to the credit buyer. TN and TP in-stream attenuation generally increases with decreasing mean river flow; smaller rivers in the modeled region of the Ohio River Basin had TN attenuation factors per km, including safety margins, of 0.19-1.6%, medium rivers of 0.14-1.2%, large rivers of 0.13-1.1%, and very large rivers of 0.04-0.42%. Attenuation in ditches transporting nutrients from farms to receiving rivers is 0.4%/km for TN, while for TP attenuation in ditches can be up to 2%/km. A 95 percentile safety margin of 30-40% for TN and 6-10% for TP, applied to the attenuation per km factors, was determined from the in-stream sensitivity of load reductions to watershed model parameters. For perspective, over 50 km a 1% per km factor would result in 50% attenuation = 2:1 trading ratio. PMID:24866482

Keller, Arturo A; Chen, Xiaoli; Fox, Jessica; Fulda, Matt; Dorsey, Rebecca; Seapy, Briana; Glenday, Julia; Bray, Erin

2014-06-17

2

The photon attenuation coefficients of barite, marble and limra  

Microsoft Academic Search

The linear attenuation coefficients ? (cm?1) and total mass attenuation coefficients ?? (cm2 g?1) of ?-rays for barite, marble and limra have been calculated using the XCOM program (Version 3.1) at energies from 1 keV to 300 MeV. The calculated results were compared with the estimation coefficients ?? based on the measured total linear attenuation coefficients (?).

I. Akkurt; S. Kilincarslan; C. Basyigit

2004-01-01

3

Evolution of Inbreeding Coefficients and Effective Size in the Population of Saguenay Lac-St.Jean (Québec)  

Microsoft Academic Search

We computed mean inbreeding coefficients (FIT, FIS, and FST) based on approximately 2,700 ascending pedigrees of contemporary people from Saguenay Lac-St-Jean (Quebec, Canada). This allowed us to appreciate the accumulated inbreeding and to follow the evolution of these coefficients since the founding of Quebec. One of the results was the expected increase in FST. Relying on this parameter, we computed

Soufia Mourali-Chebil; Evelyne Heyer

2006-01-01

4

Evolution of Inbreeding Coefficients and Effective Size in the Population of Saguenay Lac-St.Jean (Que´bec)  

Microsoft Academic Search

We computed mean inbreeding coefficients (FIT, FIS, and FST) based on approximately 2,700 ascending pedigrees of contemporary people from Saguenay Lac-St-Jean (Que´bec, Canada). This allowed us to appreciate the accumulated inbreeding and to follow the evolution of these coefficients since the founding of Que´bec. One of the results was the expected increase in FST. Relying on this parameter, we computed

Soufia Mourali-Chebil; Evelyne Heyer

2006-01-01

5

Attenuation coefficients of body tissues using principal-components analysis  

Microsoft Academic Search

Principal-components analysis is used to obtain a set of parameters for dual-energy radiography that completely describes the attenuation coefficient of any tissue over a given energy range. These parameters are the weighted averages of the densities of the elements present in a substance. Principal-components (PC) parameters are calculated for several soft tissues from measured attenuation coefficients published by Phelps et

J. B. Weaver; A. L. Huddleston

2009-01-01

6

Determination of Dimensionless Attenuation Coefficient in Shaped Resonators  

NASA Technical Reports Server (NTRS)

The value of dimensionless attenuation coefficient is an important factor when numerically predicting high-amplitude acoustic waves in shaped resonators. Both the magnitude of the pressure waveform and the quality factor rely heavily on this dimensionless parameter. Previous authors have stated the values used, but have not completely explained their methods. This work fully describes the methodology used to determine this important parameter. Over a range of frequencies encompassing the fundamental resonance, the pressure waves were experimentally measured at each end of the shaped resonators. At the corresponding dimensionless acceleration, the numerical code modeled the acoustic waveforms generated in the resonator using various dimensionless attenuation coefficients. The dimensionless attenuation coefficient that most closely matched the pressure amplitudes and quality factors of the experimental and numerical results was determined to be the value to be used in subsequent studies.

Daniels, C.; Steinetz, B.; Finkbeiner, J.; Raman, G.; Li, X.

2003-01-01

7

Measurement of Acoustic Attenuation and Absorption Coefficients using Thermometry  

Microsoft Academic Search

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

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

2007-01-01

8

Uranium Soft X-Ray Total Attenuation Coefficients.  

National Technical Information Service (NTIS)

Uranium total attenuation coefficients were measured continuously from 0.84 to 6.0 keV and at selected higher energies using a vacuum single crystal diffractometer and flow-proportional counter. Statistical fluctuations ranged from 0.5% to 2%. The overall...

N. K. Del Grande A. J. Oliver

1981-01-01

9

Inferential Procedures for Correlation Coefficients Corrected for Attenuation.  

ERIC Educational Resources Information Center

A model and computation procedure based on classical test score theory are presented for determination of a correlation coefficient corrected for attenuation due to unreliability. Delta and Monte Carlo method applications are discussed. A power analysis revealed no serious loss in efficiency resulting from correction for attentuation. (TJH)

Hakstian, A. Ralph; And Others

1988-01-01

10

Gamma-ray attenuation coefficients in bismuth borate glasses  

Microsoft Academic Search

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

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

2002-01-01

11

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

12

Apparent linear attenuation coefficients in phase contrast X-ray tomography  

NASA Astrophysics Data System (ADS)

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.

Yan, Aimin; Wu, Xizeng

2011-08-01

13

A parameterization scheme for the x-ray linear attenuation coefficient and energy absorption coefficient.  

PubMed

A novel parameterization of x-ray interaction cross-sections is developed, and employed to describe the x-ray linear attenuation coefficient and mass energy absorption coefficient for both elements and mixtures. The new parameterization scheme addresses the Z-dependence of elemental cross-sections (per electron) using a simple function of atomic number, Z. This obviates the need for a complicated mathematical formalism. Energy dependent coefficients describe the Z-direction curvature of the cross-sections. The composition dependent quantities are the electron density and statistical moments describing the elemental distribution. We show that it is possible to describe elemental cross-sections for the entire periodic table and at energies above the K-edge (from 6 keV to 125 MeV), with an accuracy of better than 2% using a parameterization containing not more than five coefficients. For the biologically important elements 1 < or = Z < or = 20, and the energy range 30-150 keV, the parameterization utilizes four coefficients. At higher energies, the parameterization uses fewer coefficients with only two coefficients needed at megavoltage energies. PMID:15083673

Midgley, S M

2004-01-21

14

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

Microsoft Academic Search

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

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

2002-01-01

15

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.

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

2014-01-01

16

Can the Lambert-Beer law be applied to the diffuse attenuation coefficient of ocean water?  

Microsoft Academic Search

Radiative transfer theory is combined with a bio-optical model of Case 1 waters and an optical model of the atmosphere to simulate the transport of radiation in the ocean-atmosphere system. The results are treated as experimental data to study the downwelling irradiance attenuation coefficient. It is shown that the downwelling irradiance attenuation coefficient just beneath the surface and the mean

HOWARD R. GORDON

1989-01-01

17

The attenuation coefficient of an acoustic wave propagating in a turbulent flow in a long pipeline  

NASA Astrophysics Data System (ADS)

Results of experiments on measuring the attenuation coefficient for acoustic waves propagating in long oil and petroleum product pipelines are presented. A comparison of experimental results with theory is performed. An approximate dependence of the attenuation coefficient on the dimensionless parameter of the flow is proposed.

Barabanov, S. A.; Glikman, B. F.

2009-03-01

18

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

19

Factors That Attenuate the Correlation Coefficient and Its Analogs.  

ERIC Educational Resources Information Center

The correlation coefficient is an integral part of many other statistical techniques (analysis of variance, t-tests, etc.), since all analytic methods are actually correlational (G. V. Glass and K. D. Hopkins, 1984). The correlation coefficient is a statistical summary that represents the degree and direction of relationship between two variables.…

Dolenz, Beverly

20

Two means method for the attenuation coefficient determination of archaeological ceramics from the North of Parana.  

National Technical Information Service (NTIS)

This work reports an alternative methodology for the linear attenuation coefficient determination ((mu) (rho)) of irregular form samples, in such a way that is not necessary to consider the sample thickness. With this methodology, indigenous archaeologica...

R. M. C. Silva

1997-01-01

21

Ultrasonic attenuation and kinetic coefficients in pure and random uniaxial ferromagnets with dipolar interactions  

Microsoft Academic Search

The ultrasonic attenuation and kinetic coefficients in pure and random uniaxial ferromagnets with both short range exchange and long range dipolar interactions are calculated near the critical point using renormalization group theory. The dispersion and temperature dependences found differ logarithmically from classical theory and suggest new experiments. In the pure system a recent phenomenological calculation of the ultrasonic attenuation in

B. Schaub; H. G. Schuster

1978-01-01

22

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

23

Calculation and validation of the use of effective attenuation coefficient for attenuation correction in In-111 SPECT  

SciTech Connect

Nuclear medicine tracers using {sup 111}In as a radiolabel are increasing in their use, especially in the domain of oncologic imaging. In these applications, it often is critical to have the capability of quantifying radionuclide uptake and being able to relate it to the biological properties of the tumor. However, images from single photon emission computed tomography (SPECT) can be degraded by photon attenuation, photon scattering, and collimator blurring; without compensation for these effects, image quality can be degraded, and accurate and precise quantification is impossible. Although attenuation correction for SPECT is becoming more common, most implementations can only model single energy radionuclides such as {sup 99m}Tc and {sup 123}I. Thus, attenuation correction for {sup 111}In is challenging because it emits two photons (171 and 245 keV) at nearly equal rates (90.2% and 94% emission probabilities). In this paper, we present a method of calculating a single 'effective' attenuation coefficient for the dual-energy emissions of {sup 111}In, and that can be used to correct for photon attenuation in radionuclide images acquired with this radionuclide. Using this methodology, we can derive an effective linear attenuation coefficient {mu}{sub eff} and an effective photon energy E{sub eff} based on the emission probabilities and linear attenuation coefficients of the {sup 111}In photons. This approach allows us to treat the emissions from {sup 111}In as a single photon with an effective energy of 210 keV. We obtained emission projection data from a tank filled with a uniform solution of {sup 111}In. The projection data were reconstructed using an iterative maximum-likelihood algorithm with no attenuation correction, and with attenuation correction assuming photon energies of 171, 245, and 210 keV (the derived E{sub eff}). The reconstructed tomographic images demonstrate that the use of no attenuation correction, or correction assuming photon energies of 171 or 245 keV introduces inaccuracies into the reconstructed radioactivity distribution when compared against the effective energy method. In summary, this work provides both a theoretical framework and experimental methodology of attenuation correction for the dual-energy emissions from {sup 111}In. Although these results are specific to {sup 111}In, the foundation could easily be extended to other multiple-energy isotopes.

Seo, Youngho; Wong, Kenneth H.; Hasegawa, Bruce H. [Physics Research Laboratory, Department of Radiology, University of California, San Francisco, California 94143 (United States); Physics Research Laboratory, Department of Radiology, University of California, San Francisco, California 94143 and Joint Graduate Group in Bioengineering, University of California, San Francisco and Berkeley, California 94143 (United States); Physics Research Laboratory, Department of Radiology, University of California, San Francisco, California 94143, Department of Nuclear Engineering, University of California, Berkeley, California 94720 (United States) and Joint Graduate Group in Bioengineering, University of California, San Francisco and Berkeley, California 94143 (United States)

2005-12-15

24

FXG mass attenuation coefficient evaluation for radiotherapy routine  

Microsoft Academic Search

The knowledge of a radioactive beam energy or quality is important in radiotherapy once it is correlated with the type, size, and localization of the tumor. One indicative of the radiation quality is the half-value-layer (HVL), the material thickness which reduces the beam intensity to half. The analysis of a treatment beam spectrum can be inferred through its homogeneity coefficient

M. V. Moreira; A. de Almeida; R. T. Costa; L. A. Perles

2004-01-01

25

Comparison between different spectral models of the diffuse attenuation and absorption coefficients of seawater  

NASA Astrophysics Data System (ADS)

The goal of this work is to verify different spectral models of the diffuse attenuation and absorption coefficients of sea water and to work out a recommendation for their use. It is shown that the spectral models of the diffuse attenuation coefficient Kd((lambda) ) developed by Austin, Petzold, 1984 and by Volynsky, Sud'bin, 1992 correspond with each other, as well the models of Ivanov, Shemshura, 1973 and of Kopelevich, Shemshura, 1988 for calculation of the spectral absorption coefficient a((lambda) ) on the values of Kd((lambda) ). Theoretical foundation of the relation between a((lambda) ) and Kd((lambda) ) is given. The up-to-date physical model of the sea water light absorption is considered and checked by means of comparison with measured values of the attenuation coefficient at the ultraviolet and visible spectral ranges.

Kopelevich, Oleg V.; Filippov, Yuri V.

1994-10-01

26

FXG mass attenuation coefficient evaluation for radiotherapy routine  

NASA Astrophysics Data System (ADS)

The knowledge of a radioactive beam energy or quality is important in radiotherapy once it is correlated with the type, size, and localization of the tumor. One indicative of the radiation quality is the half-value-layer (HVL), the material thickness which reduces the beam intensity to half. The analysis of a treatment beam spectrum can be inferred through its homogeneity coefficient (HC, ratio between the first and the second HVL) that for values >= 0.7 has the indication to be adequate for treatments. Another important indicator of radiation quality is the mass absorption coefficient (cm2/g), related to the photons energies absorbed in a particular exposed material. Once that several materials can be used as radiation detectors for X and ? dosimetry, this work has the purpose to verify the ferrous Xylenol gelatin (FXG) material performance, through its ?/? behavior and compare it with the ?/? behavior for soft tissue. The X and ? energies where selected, in the energies normally used in radiotherapy and their spectra were evaluated using the HC coefficient. The ?/?, for the FXG material, were obtained experimentally and from simulation with X-COM and a developed routine using the GEANT4 Library. From the results from all ?/? values obtained for the FXG material, when compared to those from water, one can see similar behaviors, when one considers measurements for energies greater than 78.0 keV. These results indicate that, once the human body is composed with +/-80 % of water, the FXG for the energies used, could also be used as soft tissue simulator.

Moreira, M. V.; de Almeida, A.; Costa, R. T.; Perles, L. A.

2004-01-01

27

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

SciTech Connect

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

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

2007-07-15

28

Synoptic water clarity assessment in the Florida Keys using diffuse attenuation coefficient estimated from Landsat imagery  

Microsoft Academic Search

The diffuse attenuation coefficient, K (m–1), is a measure of the effective attenuation of light in the water column. It characterizes water clarity and is used as a\\u000a proxy for water quality. Mapping of shallow water benthic habitats using optical means, including daytime visible satellite\\u000a imagery, requires knowledge of K to correct for water column effects such as light absorption

D. Palandro; C. Hu; S. Andréfouët; F. E. Muller-Karger

29

Synoptic water clarity assessment in the Florida Keys using diffuse attenuation coefficient estimated from Landsat imagery  

Microsoft Academic Search

The diffuse attenuation coefficient, K (m? 1), is a measure of the effective attenuation of light in the water column. It characterizes water clarity and is used as a\\u000a proxy for water quality. Mapping of shallow water benthic habitats using optical means, including daytime visible satellite\\u000a imagery, requires knowledge of K to correct for water column effects such as light

D. Palandro; C. Hu; S. Andréfouët; F. E. Muller-Karger

2004-01-01

30

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

31

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

32

Left ventricular volume: physical basis for attenuation corrections in radionuclide determinations  

SciTech Connect

Absolute left ventricular volume has been calculated from gated blood pool studies by estimating an attenuation correction for left ventricular counts. The physical basis of these corrections was studied by evaluating x-ray photon attenuation from CT scans of the thorax. CT numbers were converted to linear attenuation coefficients (LACs) at 140 keV, and LACs from the center of the left ventricle or esophagus to the chest wall were determined in 12 patients of various body habitus. The mean LACs were virtually identical but were less than the LAC of water. These results suggest that conventional methods overestimate attenuation and show that LAC variability between individuals can be large. Better methods of attenuation correction may improve count-based estimates of left ventricular volume.

Nickoloff, E.L.; Perman, W.H.; Esser, P.D.; Bashist, B.; Alderson, P.O.

1984-08-01

33

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

NASA Astrophysics Data System (ADS)

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

Hopkins, Deidre; Maqbool, Muhammad; Islam, Mohammed

2009-10-01

34

Calculation of radiation attenuation coefficients, effective atomic numbers and electron densities for some building materials.  

PubMed

Some building materials, regularly used in Turkey, such as sand, cement, gas concrete (lightweight, aerated concrete), tile and brick, have been investigated in terms of mass attenuation coefficient (?/?), effective atomic, numbers (Z(eff)), effective electron densities (N(e)) and photon interaction cross section (?(a)) at 14 different energies from 81- to 1332-keV gamma-ray energies. The gamma rays were detected by using gamma-ray spectroscopy, a High Purity Germanium (HPGe) detector. The elemental compositions of samples were analysed using an energy dispersive X-ray fluorescence spectrometer. Mass attenuation coefficients of these samples have been compared with tabulations based upon the results of WinXcom. The theoretical mass attenuation coefficients were estimated using the mixture rule and the experimental values of investigated parameters were compared with the calculated values. The agreement of measured values of mass attenuation coefficient, effective atomic numbers, effective electron densities and photon interaction cross section with the theory has been found to be quite satisfactory. PMID:22128356

Damla, N; Baltas, H; Celik, A; Kiris, E; Cevik, U

2012-07-01

35

Comparison of attenuation coefficients for VVER-440 and VVER-1000 pressure vessels  

SciTech Connect

The paper summarizes the attenuation coefficient of the neutron fluence with E > 0.5 MeV through a reactor pressure vessel for vodo-vodyanoi energetichesky reactor (VVER) reactor types measured and/or calculated for mock-up experiments, as well as for operated nuclear power plant (NPP) units. The attenuation coefficient is possible to evaluate directly only by using the retro-dosimetry, based on a combination of the measured activities from the weld sample and concurrent ex-vessel measurement. The available neutron fluence attenuation coefficients (E > 0.5 MeV), calculated and measured at a mock-up experiment simulating the VVER-440-unit conditions, vary from 3.5 to 6.15. A similar situation is used for the calculations and mock-up experiment measurements for the VVER-1000 RPV, where the attenuation coefficient of the neutron fluence varies from 5.99 to 8.85. Because of the difference in calculations for the real units and the mock-up experiments, the necessity to design and perform calculation benchmarks both for VVER-440 and VVER-1000 would be meaningful if the calculation model is designed adequately to a given unit. (authors)

Marek, M.; Rataj, J.; Vandlik, S. [Reactor Physics Dept., Research Centre Rez, Husinec 130, 25068 (Czech Republic)

2011-07-01

36

Accurate measurement of total attenuation coefficient of thin tissue with optical coherence tomography  

Microsoft Academic Search

Noninvasive accurate measurements of tissue optical properties are needed for many diagnostic and therapeutic applications. Optical coherence tomography (OCT) recently proposed for high-resolution imaging in tissue can potentially be applied for accurate, noninvasive, and high-resolution measurement of tissue total attenuation coefficient. However, confocal function (dependence of OCT sensitivity on the distance of probed site from the focal plane of the

Alexander I. Kholodnykh; Irina Y. Petrova; Massoud Motamedi; Rinat O. Esenaliev

2003-01-01

37

Reduction of TGS image reconstruction times using separable attenuation coefficient models  

SciTech Connect

The tomographic gamma scanner (TGS) method for assaying transuranic and low-level waste produces low-resolution {open_quotes}density{close_quotes} images of 208-l waste drums at two or more transmission gamma-ray energies and uses these to make detailed attenuation corrections at neighboring emission gamma-ray energies. For example, we have used the 136-, 285-, and 401-keV lines from a {sup 75}Se transmission source to correct for attenuation of the 129-, 203-, 345-, and 414-keV lines in {sup 239}Pu assays. The list can expand to 20 or more emission energies when performing multiple-isotope assays. Methods for projecting attenuation images from transmission to emission energies were recently discussed with emphasis on the problems encountered when the opacity of a sample leads to poor counting statistics. This report focuses on increases in computational speed that can be attained by using separable attenuation coefficient models.

Estep, R.J.; Prettyman, T.H.; Sheppard, G.A. [Los Alamos National Lab., Livermore, CA (United States)

1995-12-31

38

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.

2012-02-01

39

Parametric imaging of the local attenuation coefficient in human axillary lymph nodes assessed using optical coherence tomography  

PubMed Central

We report the use of optical coherence tomography (OCT) to determine spatially localized optical attenuation coefficients of human axillary lymph nodes and their use to generate parametric images of lymphoid tissue. 3D-OCT images were obtained from excised lymph nodes and optical attenuation coefficients were extracted assuming a single scattering model of OCT. We present the measured attenuation coefficients for several tissue regions in benign and reactive lymph nodes, as identified by histopathology. We show parametric images of the measured attenuation coefficients as well as segmented images of tissue type based on thresholding of the attenuation coefficient values. Comparison to histology demonstrates the enhancement of contrast in parametric images relative to OCT images. This enhancement is a step towards the use of OCT for in situ assessment of lymph nodes.

Scolaro, Loretta; McLaughlin, Robert A.; Klyen, Blake R.; Wood, Benjamin A.; Robbins, Peter D.; Saunders, Christobel M.; Jacques, Steven L.; Sampson, David D.

2012-01-01

40

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

Microsoft Academic Search

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

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

1996-01-01

41

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

PubMed

The simultaneous PET data reconstruction of emission activity and attenuation coefficient distribution is presented, where the attenuation image is constrained by exploiting an external transmission source. Data are acquired in time-of-flight (TOF) mode, allowing in principle for separation of emission and transmission data. Nevertheless, here all data are reconstructed at once, eliminating the need to trace the position of the transmission source in sinogram space. Contamination of emission data by the transmission source and vice versa is naturally modeled. Attenuated emission activity data also provide additional information about object attenuation coefficient values. The algorithm alternates between attenuation and emission activity image updates. We also proposed a method of estimation of spatial scatter distribution from the transmission source by incorporating knowledge about the expected range of attenuation map values. The reconstruction of experimental data from the Siemens mCT scanner suggests that simultaneous reconstruction improves attenuation map image quality, as compared to when data are separated. In the presented example, the attenuation map image noise was reduced and non-uniformity artifacts that occurred due to scatter estimation were suppressed. On the other hand, the use of transmission data stabilizes attenuation coefficient distribution reconstruction from TOF emission data alone. The example of improving emission images by refining a CT-based patient attenuation map is presented, revealing potential benefits of simultaneous CT and PET data reconstruction. PMID:23648397

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

2013-06-01

42

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

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

43

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

44

Studies on mass attenuation coefficient, effective atomic number and electron density of some thermoluminescent dosimetric compounds  

NASA Astrophysics Data System (ADS)

Mass attenuation coefficient, ?m , effective atomic number, Zeff, and effective electron density, Nel, were determined experimentally and theoretically for some thermoluminescent dosimetric (TLD) compounds such as MgSO4, CdSO4, Al2O3, Mg2SiO4, ZnSO4, CaSO4, CaF2, NaSO4, Na4P2O7, Ca5F(PO4)3, SiO2, CaCO3 and BaSO4 at 8.04, 8.91, 13.37, 14.97, 17.44, 19.63, 22.10, 24.90, 30.82, 32.06, 35.40, 36.39, 37.26, 43.74, 44.48, 50.38, 51.70, 53.16, 80.99, 276.40, 302.85, 356.01, 383.85 and 661.66 keV photon energies by using an HPGe detector with a resolution of 182 eV at 5.9 keV. The theoretical mass attenuation coefficients were estimated using mixture rule. The calculated values were compared with the experimental values for all compounds. Good agreement has been observed between experimental and theoretical values within experimental uncertainties.

Önder, P.; Tur?ucu, A.; Demir, D.; Gürol, A.

2012-12-01

45

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

46

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

47

Determination of mass attenuation coefficients, effective atomic and electron numbers for some natural minerals  

NASA Astrophysics Data System (ADS)

The total mass attenuation coefficients ( ? m) for SiO 2 {Quartz (1 1 0 1), Quartz (1 1 0 0) and Quartz (0 0 0 1)}, KAlSi 3O 8 {Orthoclase (0 1 0), Orthoclase (1 0 0)}, CaSO 4·2H 2O (gypsum), FeS 2 (pyrite) and Mg 2Si 2O 6 (pyroxene) natural minerals were measured at 22.1, 25.0, 59.5 and 88.0 keV photon energies. The ?- and X-rays were counted by a Si(Li) detector with a resolution of 160 eV at 5.9 keV. Atomic and electronic cross sections ( ? t and ? e), the effective atomic and electron numbers or electron densities ( Z eff and N eff) were determined using the obtained ? m values for investigated samples.

Han, I.; Demir, L.; ?ahin, M.

2009-09-01

48

Calculation of solar attenuation coefficient using ACCOS V along a critical scattering path  

NASA Technical Reports Server (NTRS)

An appraisal of the optical properties of the AVHRR is made for a proposed orbital trajectory which results in an unexpected solar stray-light path; i.e., bypassing the external scan mirror and Cassegrain telescope and proceeding directly to the inner conical baffle. This stray-light path is directed onto an internal beamsplitter which, in turn, is directly observed by the detectors. Stray-light analysis, as a goal, seeks to remove or minimize the influence of such critical scattering paths. The AVHRR path is evaluated using a standard optical ray-tracing program, ACCOS V. To determine the expected sensor degradation, a calculation of the expected attenuation coefficient of scattered sunlight in the AVHRR sensor is estimated based on this important critical scattering path.

Ames, Alan J.

1989-01-01

49

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

NASA Technical Reports Server (NTRS)

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

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

2005-01-01

50

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

PubMed

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

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

2012-07-01

51

An improvement to the full-foil mapping technique for high accuracy measurement of X-ray mass attenuation coefficients  

Microsoft Academic Search

The limiting uncertainty in recent high accuracy measurements of the mass attenuation coefficient is the measurement of the integrated column density. An improvement in the design of the absorption foil holder is described which reduces the integrated column density uncertainty. The new design allows the edges of the foil to be more accurately mapped by the X-ray beam by reducing

Nicholas A. Rae; Jack L. Glover; Christopher T. Chantler

2010-01-01

52

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

PubMed

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

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

2010-04-15

53

Quantification of optical attenuation coefficient based on continuous wavelet transform of photoacoustic signals measured by a focused broadband acoustic sensor  

NASA Astrophysics Data System (ADS)

We proposed a method of quantifying the effective attenuation coefficients of optical absorbers which uses the continuous wavelet transform to calculate the time-resolved frequency spectra of photoacoustic (PA) signals. In order to apply the method to blood oxygenation monitoring of blood vessels, this study discusses how to reduce the effects of blood vessel diameters, which influences on the time resolved frequency spectra of PA signals. Numerical simulations which calculate the PA signals produced from blood vessel phantoms with various diameters were performed. The simulations revealed that the frequency of PA signal became independent from the vessel diameters by measuring the PA signal from small area. The frequencies of simulated PA signals were proportional to the effective attenuation coefficients with a correlation coefficient of 0.99, and a slope of 0.035 MHz/cm-1 under condition that the measurement area was 4.0 mm at a frequency of 1.5 MHz. Thus we used the focused acoustic sensor of which focusing the foregoing measurement area. It consisted of a P(VDF-TrFE) film, which was characterized by broad frequency band. As results of experiments using the focused acoustic sensor, the frequencies of PA signals produced from blood vessel phantoms were proportional to the effective attenuation coefficients with correlation coefficient of 0.96 although the frequencies were suffered from deviations of 0.135 MHz, which corresponded to the effective attenuation coefficient of 3.46 cm-1. Since the large deviations were caused by experimental factors such as sensor alignment, it is required to improve robustness to the experimental factors.

Hirasawa, T.; Okawa, S.; Fujita, M.; Kushibiki, T.; Ishihara, M.

2014-03-01

54

X-ray attenuation coefficients and photoelectric cross sections of Cu, Fe and Sn for the energy range 3-29 KeV.  

National Technical Information Service (NTIS)

The document contains the following two papers: X-ray attenuation coefficient and photoelectric cross sections of Sn for the Energy Range 3.3 KeV to 29.1 KeV - by Wang Dachun, Yang Hua and Luo Pingan. X-ray attenuation coefficients and photoelectric cross...

Wang Dachun Yang Hua Luo Pingan Ding Xunliang Wang Xinfu

1991-01-01

55

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

NASA Astrophysics Data System (ADS)

The half-value thicknesses, linear and mass attenuation coefficients of biological samples such as bone, muscle, fat and water have been measured at 140, 364 and 662 keV ?-ray energies by using the ATOMLABTM-930 medical spectrometer. The ?-rays were obtained from 99mTc, 131I and 137Cs ?-ray point sources. Also theoretical calculations have been performed in order to obtain the half-value thicknesses and, mass and linear attenuation coefficients at photon energies 0.001 keV 20 MeV for bone, muscle and water samples. The calculated value and the experimental results of this work and the other results in literature are found to be in good agreement.

Akar, A.; Balta?, H.; Çevik, U.; Korkmaz, F.; Okumu?o?lu, N. T.

2006-11-01

56

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

NASA Technical Reports Server (NTRS)

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

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

1981-01-01

57

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

PubMed

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

Demir, Faruk

2010-01-01

58

Bibliography of Photon Total Cross Section (Attenuation Coefficient) Measurements 10 eV to 13.5 GeV, 1907-1993.  

National Technical Information Service (NTIS)

A bibliography is presented of papers reporting absolute measurements of photon (XUV, x-ray, gamma-ray, bremsstrahlung) total interaction cross sections or attenuation coefficients for the elements and some compounds. The energy range covered is from 10 e...

J. H. Hubbell

1994-01-01

59

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

PubMed Central

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.

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

2010-01-01

60

Determination of radiation attenuation coefficients of heavyweight and normal-weight concretes containing colemanite and barite for 0.663 MeV ?-rays  

Microsoft Academic Search

Accurate measurements have been made to determine radiation transmission of concretes produced with barite, colemanite and normal aggregate by using beam transmission method for 0.663MeV ?-rays energy of 137Cs radioactive isotopes by using NaI(Tl) scintillation detector. Linear and mass attenuation coefficients of thirteen heavy- and four normal-weight concretes were calculated. It was determined that the linear attenuation coefficient (?, cm?1)

F. Demir; G. Budak; R. Sahin; A. Karabulut; M. Oltulu; A. Un

2011-01-01

61

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.

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

2011-01-01

62

An Empirical Expression to Estimate Specific Attenuation Coefficient due to fog at Frequencies from 100 to 300GHz  

NASA Astrophysics Data System (ADS)

A simple expression is presented to quickly estimate specific attenuation coefficient due to fog within the ranges of 100~300GHz and -8~20°C based on the Rayleigh approximation which is not very convenient. To evaluate the expression's estimation performance, the Pearson correlation coefficient (PCC) and maximal absolute value of the relative errors (MAVRE) are calculated. The maximum value of PCC is 1 and it reflects the fitting performance of an empirical expression. MAVRE denotes the largest deviation between a set of estimated values and corresponding theoretical values. Calculations show the PCC and MAVRE of the proposed expression are 0.99985 and 4.162%, respectively. Furthermore, a comparison analysis shows that the new expression has much better estimation performance than other two empirical expressions: the modified Mao expression and the Zhao expression.

Liu, Yun-Long; Hu, Meng-Hao

2013-08-01

63

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

64

Assessment of natural radiation exposure levels and mass attenuation coefficients of lime and gypsum samples used in Turkey.  

PubMed

The activity concentrations of 226Ra, 232Th, and 40K in lime and gypsum samples used as building materials in Turkey were measured using gamma spectrometry. The mean activity concentrations of 226Ra, 232Th, and 40K were found to be 38±16, 20±9, and 156±54 Bq kg(-1) for lime and found to be 17±6, 13±5, and 429±24 Bq kg(-1) for gypsum, respectively. The radiological hazards due to the natural radioactivity in the samples were inferred from calculations of radium equivalent activities (Raeq), indoor absorbed dose rate in the air, the annual effective dose, and gamma and alpha indices. These radiological parameters were evaluated and compared with the internationally recommended limits. The experimental mass attenuation coefficients (?/?) of the samples were determined in the energy range 81-1,332 keV. The experimental mass attenuation coefficients were compared with theoretical values obtained using XCOM. It is found that the calculated values and the experimental results are in good agreement. PMID:19921450

Damla, Nevzat; Cevik, U?ur; Kobya, Ali Ihsan; Celik, Ahmet; Celik, Necati

2010-11-01

65

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.

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

2010-01-01

66

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

67

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

NASA Astrophysics Data System (ADS)

Creep damage in SUS304 steel samples fabricated by a hot isostatic press (HIP) at 1050°C was evaluated using the electromagnetic acoustic resonance (EMAR), noise energy and ultrasonic spectroscopy (first moment) methods. The coefficients of attenuation of 1.1 to 5.4 MHz electromagnetically excited acoustic waves in the samples were investigated. By reducing diffraction loss and the loss to the electromagnetic acoustic transducer due to transmission of the ultrasonic waves via mechanical contacts, it was possible to detect shear wave attenuation coefficients as low as 2.5×10-4/microsecond at 1.1 MHz. With specimens fabricated at pressure of 170MPa, the attenuation coefficient increased in proportion to frequency up to 5.4 MHz, whereas with specimens fabricated at pressure lower than 80 MPa the attenuation coefficient increased rapidly above 4 MHz. The void fraction was found to be greater in specimens fabricated under lower pressure, which may be responsible for the markedly higher ultrasonic attenuation in the specimens fabricated at pressure lower than 80MPa. It was apparent from the experiments that the EMAR method detects creep voids with greater sensitivity than the other methods. Accordingly we hope it will be possible for the EMAR method to be used on real facilities in the future.

Nishida, Hidetaka; Yamaguchi, Hiroshi; Yoshida, Masashi

68

Determination of mass attenuation coefficients, effective atomic and electron numbers, mean free paths and kermas for PbO, barite and some boron ores  

NASA Astrophysics Data System (ADS)

The total mass attenuation coefficients, ? m, for PbO, barite, colemanite, tincal and ulexite were determined at 80.1, 302.9, 356.0, 661.7 and 1250.0 keV photon energies by using NaI (Tl) scintillation detector. Effective atomic number, Z eff, effective electron number, N eff, total atomic cross-section, ? t, total electronic cross-section, ? e, mean free path, mfp, and kerma relative to air were determined experimentally and theoretically. The theoretical mass attenuation coefficients were estimated using mixture rule. The calculated values were compared with the experimental values for all samples.

Un, A.; Sahin, Y.

2011-07-01

69

Calculating concentration of inhaled radiolabeled particles from external gamma counting: External counting efficiency and attenuation coefficient of thorax  

SciTech Connect

We determined the overall external counting efficiency of radiolabeled particles deposited in the sheep lung. This efficiency permits the noninvasive calculation of the number of particles and microcuries from gamma-scintillation lung images of the live sheep. Additionally, we have calculated the attenuation of gamma radiation (120 keV) by the posterior chest wall and the gamma-scintillation camera collection efficiency of radiation emitted from the lung. Four methods were employed in our experiments: (1) by light microscopic counting of discrete carbonized polystyrene particles with a count median diameter (CMD) of 2.85 microns and tagged with cobalt-57, we delineated a linear relationship between the number of particles and the emitted counts per minute (cpm) detected by well scintillation counting; (2) from this conversion relationship we determined the number of particles inhaled and deposited in the lungs by scintillation counting fragments of dissected lung at autopsy; (3) we defined a linear association between the number of particles or microcuries contained in the lung and the emitted radiation as cpm detected by a gamma scintillation camera in the live sheep prior to autopsy; and (4) we compared the emitted radiation from the lungs of the live sheep to that of whole excised lungs in order to calculate the attenuation coefficient (ac) of the chest wall. The mean external counting efficiency was 4.00 X 10(4) particles/cpm (5.1 X 10(-3) microCi/cpm), the camera collection efficiency was 1 cpm/10(4) disintegrations per minute (dpm), and the ac had a mean of 0.178/cm. The external counting efficiency remained relatively constant over a range of particles and microcuries, permitting a more general use of this ratio to estimate number of particles or microcuries depositing after inhalation in a large mammalian lung if a similarly collimated gamma camera system is used.

Langenback, E.G.; Foster, W.M.; Bergofsky, E.H.

1989-01-01

70

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

71

Measurement of the x-ray mass attenuation coefficient and the imaginary part of the form factor of silicon using synchrotron radiation  

SciTech Connect

We used the x-ray extended-range technique to measure the x-ray mass attenuation coefficients of silicon with an accuracy between 0.27% and 0.5% in the 5 keV-20 keV energy range. Subtraction of the x-ray scattering contribution enabled us to derive the corresponding x-ray photoelectric absorption coefficients and determine the absolute value of the imaginary part of the atomic form factor of silicon. Discrepancies between the experimental values of the mass attenuation coefficients and theoretically calculated values are discussed. New approaches to the theoretical calculation will be required to match the precision and accuracy of the experimental results.

Tran, C.Q.; Chantler, C.T.; Barnea, Z.; Paterson, D.; Cookson, D.J. [School of Physics, University of Melbourne, Victoria 3010 (Australia); SRI-CAT, APS, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439 (United States); ANSTO, Private Mail Bag 1, Menai, New South Wales 2234 (Australia); Chem-Mat-CARS-CAT (Sector 15, Building 434D), Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 6043 (United States)

2003-04-01

72

SS Lac Revisited  

Microsoft Academic Search

We have evidence confirming changes in light curve amplitude of the former eclipsing and current SB2 system SS Lac in the open cluster NGC 7209. Remeasured Harvard plate data and published and compiled data sets reveal that the depth of the primary minimum increased between the 1890s and early 1900s and decreased in the 1920s and 1930s. Peak fittings of

E. F. Milone; S. J. Schiller; U. Munari; J. Kallrath

1999-01-01

73

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

74

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

75

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

PubMed

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. PMID:21198187

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

2010-01-01

76

Retrieval of the spectral diffuse attenuation coefficient Kd(?) in open and coastal ocean waters using a neural network inversion  

NASA Astrophysics Data System (ADS)

The diffuse attenuation coefficient, Kd(?) is a fundamental radiometric parameter that is used to assess the light availability in the water column. A neural network approach is developed to assess Kd(?) at any visible wavelengths from the remote sensing reflectances as measured by the SeaWiFS satellite sensor. The neural network (NN) inversion is trained using a combination of simulated and in-situ data sets covering a broad range ofKd(?), between 0.0073 m-1 at 412 nm and 12.41 m-1at 510 nm. The performance of the retrieval is evaluated against two data sets, one consisting of mainly synthetic data while the other one contains in-situ data only and is compared to those obtained with previous published empirical (NASA, Morel and Maritorena (2001) and Zhang and Fell (2007)) and semi-analytical (Lee et al., 2005b) algorithms. On the in-situ data set from the COASTLOOC campaign, the retrieval accuracy of the present algorithm is quite similar to published algorithms for oligotrophic and mesotrophic ocean waters. But for Kd(490) > 0.25 m-1, the NN approach allows to retrieve Kd(490) with a much better accuracy than the four other methods. The results are consistent when compared with other SeaWiFS wavelengths. This new inversion is as suitable in the open ocean waters as in the turbid waters. The work here is straightforwardly applicable to the MERIS sensor and with few changes to the MODIS-AQUA sensor. The algorithm in matlab and C code is provided as auxiliary material.

Jamet, C.; Loisel, H.; Dessailly, D.

2012-10-01

77

SS Lac Revisited  

NASA Astrophysics Data System (ADS)

We have evidence confirming changes in light curve amplitude of the former eclipsing and current SB2 system SS Lac in the open cluster NGC 7209. Remeasured Harvard plate data and published and compiled data sets reveal that the depth of the primary minimum increased between the 1890s and early 1900s and decreased in the 1920s and 1930s. Peak fittings of the amplitude with phase suggests a peak amplitude centered ca. 1911.5, with eclipse onset at about 1885 and effective eclipse cessation late in 1937. We thus concur with the findings of Lehmann (IBVS 3610, 1991), that the apparent inclination varies with time and that a central eclipse occurred about 1911, and of Mossakovskaya (Astron. Lett., 19, 35, 1993), that eclipses ceased prior to 1940. Estimates of SS Lac from plates taken at Tashkent between 1937 and 1940 serve to confirm these results. We have completed now an exhaustive study of the radial velocity curves of Tomasella & Munari (1998, A&A, 335, 561) and all three potentially useful archival light curves available to us, and will discuss the implications of the solutions for models of the system and the cluster to which it belongs. This work was supported in part by grants to Milone from NSERC of Canada, and the URGC of the University of Calgary.

Milone, E. F.; Schiller, S. J.; Munari, U.; Kallrath, J.

1999-05-01

78

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

PubMed

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. PMID:22338654

Chantler, C T; Islam, M T; Rae, N A; Tran, C Q; Glover, J L; Barnea, Z

2012-03-01

79

Studies on mass attenuation coefficient, effective atomic number and electron density of some amino acids in the energy range 0.122-1.330 MeV  

NASA Astrophysics Data System (ADS)

The total mass attenuation coefficients of some amino acids, such as Glycine (C2H5NO2), DL-Alanine (C3H7NO2), Proline (C5H9NO2), L-Leucine (C6H13NO2 ), L-Arginine (C6H14N4O2) and L-Arginine Monohydrochloride (C6H15ClN4O2), 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 10.2% 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) tend to be almost constant as a function of gamma-ray energy. The results show that, the experimental values of mass attenuation coefficients, effective atomic numbers and effective electron densities are in good agreement with the theoretical values with less than 1% error.

Pawar, Pravina P.; Bichile, Govind K.

2013-11-01

80

Mass attenuation coefficients and effective atomic numbers in phosphate glass containing Bi 2O 3, PbO and BaO at 662 keV  

NASA Astrophysics Data System (ADS)

In this work, the mass attenuation coefficients, partial interactions and the effective atomic numbers ( Zeff) of Bi 2O 3, PbO and BaO in xR mO n:(100- x)P 2O 5 (where x=30? x?70 (% by weight)) glass system have been investigated on the basis of the mixture rule at 662 keV. The total and partial interactions were calculated by WinXCom software. It has been found that the total mass attenuation coefficients of glasses increase with increasing Bi 2O 3 and PbO concentrations, due to the increasing photoelectric absorption in glass samples. However, Compton scattering gives dominant contribution to the total mass attenuation coefficients for the studied glass samples. The Zeff increases with increase in Bi 2O 3, PbO and BaO concentrations. For comparison, the Zeff of PbO glasses are comparable to that of Bi 2O 3 glasses and Zeff of both glasses are greater than BaO glasses. These results are very useful for designing radiation shielding glass and reflecting the influence of bismuth, barium, and lead content in radiation shielding phosphate glass. Besides the mentioned usefulness of the new materials, development of lead-free radiation protecting glass also leaves non-toxic impact on our environment.

Kaewkhao, J.; Limsuwan, P.

2010-07-01

81

Parameters and computer software for the evaluation of mass attenuation and mass energy-absorption coefficients for body tissues and substitutes  

PubMed Central

The mass attenuation and energy-absorption coefficients (radiation interaction data), which are widely used in the shielding and dosimetry of X-rays used for medical diagnostic and orthovoltage therapeutic procedures, are strongly dependent on the energy of photons, elements and percentage by weight of elements in body tissues and substitutes. Significant disparities exist in the values of percentage by weight of elements reported in literature for body tissues and substitutes for individuals of different ages, genders and states of health. Often, interested parties are in need of these radiation interaction data for body tissues or substitutes with percentage by weight of elements and intermediate energies that are not tabulated in literature. To provide for the use of more precise values of these radiation interaction data, parameters and computer programs, MUA_T and MUEN_T are presented for the computation of mass attenuation and energy-absorption coefficients for body tissues and substitutes of arbitrary percentage-by-weight elemental composition and photon energy ranging between 1 keV (or k-edge) and 400 keV. Results are presented, which show that the values of mass attenuation and energy-absorption coefficients obtained from computer programs are in good agreement with those reported in literature.

Okunade, Akintunde A.

2007-01-01

82

Parameters and computer software for the evaluation of mass attenuation and mass energy-absorption coefficients for body tissues and substitutes.  

PubMed

The mass attenuation and energy-absorption coefficients (radiation interaction data), which are widely used in the shielding and dosimetry of X-rays used for medical diagnostic and orthovoltage therapeutic procedures, are strongly dependent on the energy of photons, elements and percentage by weight of elements in body tissues and substitutes. Significant disparities exist in the values of percentage by weight of elements reported in literature for body tissues and substitutes for individuals of different ages, genders and states of health. Often, interested parties are in need of these radiation interaction data for body tissues or substitutes with percentage by weight of elements and intermediate energies that are not tabulated in literature. To provide for the use of more precise values of these radiation interaction data, parameters and computer programs, MUA_T and MUEN_T are presented for the computation of mass attenuation and energy-absorption coefficients for body tissues and substitutes of arbitrary percentage-by-weight elemental composition and photon energy ranging between 1 keV (or k-edge) and 400 keV. Results are presented, which show that the values of mass attenuation and energy-absorption coefficients obtained from computer programs are in good agreement with those reported in literature. PMID:21157532

Okunade, Akintunde A

2007-07-01

83

Diffuse attenuation coefficients Kd(PAR) at the estuarine North Sea-Baltic Sea transition: time-series, partitioning, absorption, and scattering  

NASA Astrophysics Data System (ADS)

The study is based on a 1 year record ( n=46) of the diffuse attenuation coefficient— Kd(PAR) (m -1)—in combination with CTD-casts at one position in Århus Bay, Kattegat, the North Sea-Baltic Sea estuarine transition. Water samples were collected occasionally for determination of suspended particulate matter (SPM) and chromomorphic dissolved organic matter (CDOM). The Kd(PAR) varied between 0.152 and 0.557 (m -1) with an average of 0.293 (m -1). The depth of the photic zone (1% light level) varied between 8.3 and 15.7 m at maximum and average Kd(PAR). Maximum Kd(PAR) values occurred in periods of high chl-a concentrations. The average CDOM absorption coefficient was 0.232 (m -1) whereas the average chl-a and inorganic SPM concentrations equalled 3.3 (mg m -3) and 4.5 (g m -3). Light attenuation partitioning in percent was: water (9), CDOM (17), SPM (42), and phytoplankton (32) at average conditions. Attenuation by phytoplankton reached up to 74% at high chl-a concentrations whereas SPM light attenuation reached 45% at high SPM concentrations. Results show that light attenuation in the bay is governed by phytoplankton and SPM concentrations whereas CDOM is of less significance. Light absorption in the PAR range— a(PAR)—ranged between 0.262 (m -1) at average conditions and 0.49 (m -1) at maximum phytoplankton concentrations. Scattering was governed by SPM at average conditions whereas phytoplankton scattering was higher than SPM scattering at chl-a concentrations >4.5 (mg m -3).

Lund-Hansen, Lars Chresten

2004-10-01

84

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

85

Attenuation of Bearing Transmitted Noise. Volume I. Spring and Damping Coefficients for the Tilting-Pad Journal Bearing.  

National Technical Information Service (NTIS)

A method for calculating spring and damping coefficients for the tilting pad journal bearing is presented. The analysis includes the effect of pad inertia. Numerical results are given in form of design curves for the centrally pivoted 4 shoe, 5 shoe, 6 sh...

J. Lund

1964-01-01

86

Nucleotide sequence of Klebsiella pneumoniae lac genes.  

PubMed Central

The nucleotide sequences of the Klebsiella pneumoniae lacI and lacZ genes and part of the lacY gene were determined, and these genes were located and oriented relative to one another. The K. pneumoniae lac operon is divergent in that the lacI and lacZ genes are oriented head to head, and complementary strands are transcribed. Besides base substitutions, the lacZ genes of K. pneumoniae and Escherichia coli have suffered short distance shifts of reading frame caused by additions or deletions or both during evolutionary divergence from a common ancestral gene. Relative to corresponding E. coli sequences, the nucleotide sequences of the lacZ and lacY genes are 61 and 67% conserved, and the lacI genes are 49% conserved. A comparison of both nucleotide and amino acid sequences revealed that the K. pneumoniae and E. coli lacI genes and lac repressor proteins each are related to the galR gene and gal repressor of E. coli to about the same extent. In terms of evolutionary relationships, the divergence of the forerunner of the galR gene from an ancestral lac repressor gene preceded separation and differentiation of the K. pneumoniae and E. coli lac repressor genes.

Buvinger, W E; Riley, M

1985-01-01

87

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

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

88

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

89

Observations of OM/OC and specific attenuation coefficients (SAC) in ambient fine PM at a rural site in central Ontario, Canada  

NASA Astrophysics Data System (ADS)

Ambient particulate matter (PM) samples were collected on quartz filters at a rural site in central Ontario during an intensive study in 2007. The concentrations of organic carbon (OC), pyrolysis organic carbon (POC), and elemental carbon (EC) were determined by thermal analysis. The concentrations are compared to the organic aerosol mass concentration (OM) measured with an Aerodyne C-ToF Aerosol Mass Spectrometer (AMS) and to the particle absorption coefficient (basp) obtained from a Radiance Research Particle Soot Absorption Photometer (PSAP). The total organic mass to organic carbon ratios (OM/OC) and specific attenuation coefficients (SAC=basp/EC) are derived. Proportionality of the POC mass with the oxygen mass in the aerosols estimated from the AMS offers a potential means to estimate OM/OC from thermal measurements only. The mean SAC for the study is 3.8±0.3 m2 g-1. It is found that the SAC is independent of or decrease with increasing particle mass loading, depending on whether or not the data are separated between aerosols dominated by more recent anthropogenic input and aerosols dominated by longer residence time or biogenic components. There is no evidence to support an enhancement of light absorption by the condensation of secondary material to particles, suggesting that present model simulations built on such an assumption may overestimate atmospheric warming by BC.

Chan, T. W.; Huang, L.; Leaitch, W. R.; Sharma, S.; Brook, J. R.; Slowik, J. G.; Abbatt, J. P. D.; Brickell, P. C.; Liggio, J.; Li, S.-M.; Moosmüller, H.

2010-03-01

90

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

91

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

92

OM/OC Ratio and Specific Attenuation Coefficient in Ambient Particulate Matter at a Rural Site in Southern Ontario: Implications for Aerosol Aging and Emission Sources  

NASA Astrophysics Data System (ADS)

Carbonaceous species (organic carbon (OC) and elemental carbon (EC)) contribute a large portion of atmospheric fine particle mass and influence air quality, human health, and climate forcing. However, their emission sources and atmospheric aging processes are not well understood. The OM/OC ratio, defined as the organic mass per unit OC mass, is useful to understand the degree of oxidation of aerosol particles in atmospheric processes. We define the modified BC/EC (mod BC/EC) ratio as the ratio of the non-scattering corrected absorption coefficient per unit mass of EC. The mod BC/EC ratio has a similar meaning as the site specific attenuation coefficient, which is an important parameter used to convert light absorption measurements to black carbon mass. The mod BC/EC ratio can vary due to light scattering effect on absorption measurements, in which the oxygenated organics may play a role. The pyrolysis organic carbon (POC) is defined as the carbon mass fraction obtained at T= 870°C under a pure helium environment using the thermal separation method [Huang et al., 2006]. Since POC mass is generally proportional to the amount of oxygenated OC, studying the relationships among OC, EC, POC, as well as OM/OC and mod BC/EC ratios may help us understand the mechanisms of aerosol aging from different emission sources. Two 1-month field studies were conducted at a rural site in southern Ontario (NW of Toronto) during fall 2005 and spring 2007. Quartz filter samples were collected and analyzed for OC, POC, and EC concentrations using a thermal/optical method [Huang et al., 2006]. Together with the total organic matter measured by an Aerodyne Aerosol Mass Spectrometer (AMS) and the absorption coefficient obtained from a Particle Soot Absorption Photometer (PSAP), the OM/OC and mod BC/EC ratios for ambient aerosols were obtained. Our results show that when air mass was mainly from south, OC, POC, and EC were relatively high, with average ratios of OC/EC, OM/OC, and POC/EC as 1.94, 1.41, and 0.52, respectively; this indicates significant anthropogenic impacts and relatively large portion of oxygenated OC, which might be due to either primary emissions or photo-chemical reactions occurred in a short period of time. When air mass was mainly from north, OC, POC, and EC were much lower, with average ratios of OC/EC, OM/OC, and POC/EC as 3.10, 1.20, and 0.79, respectively; this suggests less influence from anthropogenic emissions and relatively aged air mass from biogenic-source dominated clean air. Using POC, we estimate the specific attenuation at the site to be 5.8 m2 g-1 independent of the air mass origin. The relationships among OM/OC, mod BC/EC, and POC will be further discussed. References: Huang, L., Brook, J.R., Zhang, W., Li, S.M., Graham, L., Ernst, D., Chivulescu, A., and Lu, G. (2006) Stable isotope measurements of carbon fractions (OC/EC) in airborne particulate: a new dimension for source characterization and apportionment, Atmospheric Environment, 40, 2690-2705.

Chan, T. W.; Huang, L.; Leaitch, R.; Sharma, S.; Brook, J.; Slowik, J.; Abbatt, J.

2008-05-01

93

NIR brightening of BL LAC  

NASA Astrophysics Data System (ADS)

We report on the recent observation that revealed a NIR brightening of the prototype blazar, BL LAC itself. On October 30th,2013 (JD 2456595.735567), its flux in the H band corresponded to the magnitude H = 10.124 +/- 0.03. It is brightest since the time we started monitoring his object in the NIR (JD2454358.657246). Our observations were carried out with the 2.1m telescope of the Guillermo Haro Observatory operated by the National Institute for Astrophysics, Optics and Electronics (Mexico), equipped with the instrument CANICA a NIR camera.

Carrasco, L.; Recillas, E.; Porras, A.; Chavushyan, V.; Carraminana, A.

2013-11-01

94

Insights into the sliding movement of the lac repressor nonspecifically bound to DNA.  

PubMed

The Lac repressor finds its DNA binding sequences with an association rate 2 orders of magnitude higher than what is expected for a random diffusive process. This experimental data stimulated numerous theoretical and experimental studies, which led to the facilitated diffusion model. In facilitated diffusion, the Lac repressor binds nonspecifically to DNA. This nonspecific binding is followed by an exploration of the DNA molecule in a reduced space. Single-molecule imaging confirmed that the Lac repressor may move along the DNA molecule; however, it is still under debate whether the LacI movement proceeds through sliding, with a continuous close contact between the protein and DNA, or through hopping between adjacent binding sites. We have investigated the one-dimensional sliding movement of the Lac repressor along nonspecific DNA by full-atomistic molecular dynamics simulations and free-energy calculations based on the umbrella sampling technique. The computed free-energy profile along a helical trajectory was periodic, with periodicity equal to the distance between successive nucleotides and an energy barrier between successive minima of 8.7 +/- 0.7 kcal/mol. The results from the molecular simulations were subsequently used in a Langevin dynamics framework to estimate the diffusion coefficient of the Lac repressor sliding along nonspecific DNA. The computed diffusion coefficient is close to the lower limit of the experimental range. PMID:20095570

Furini, Simone; Domene, Carmen; Cavalcanti, Silvio

2010-02-18

95

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

PubMed

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 (?(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 ?(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 cm² and the cerrobend compensator thicknesses from 0.5-6 cm. For a fixed compensator thickness, variation of the ?(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 cm², the ?(eff) varied by 16.5% when the compensator thickness was increased from 0.5-6 cm. However, the variation of the ?(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 ?(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 ?(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 cm². PMID:22835650

Haghparast, Abbas; Hashemi, Bijan; Eivazi, Mohammad Taghi

2013-01-01

96

SS Lac in Open Cluster NGC 7209  

Microsoft Academic Search

We present IUE observations in far ultraviolet region for SS Lac in open cluster NGC 7209. The IUE short wavelength spectrum and long wavelength spectrum were merged to produce an energy distribution curve between 1200A and 3200A. The curve has been unreddened to take out reddening effect. Then the surface temperature, gravity and abundance of SS Lac were determined based

Young Woon Kang

1997-01-01

97

SS Lac - the Effect of Cluster Environment  

Microsoft Academic Search

We attempt to model in some detail the interesting triple system SS Lac located in the galactic cluster NGC 7209 which stopped eclipsing in about 1950. We find that our model of SS Lac is quite constrained by the relatively good observational data of this system and leads to a specific inclination (29°) of the outer orbit relative to the

Ludmila Kiseleva-Eggleton; Peter Eggleton

2003-01-01

98

NIR brightening of BL LAC  

NASA Astrophysics Data System (ADS)

We report that BL LAC cross identified with the Fermi LAT Gamma Ray source 2FGLJ2202.8+4216 is undergoing a significant NIR brigthening, on October 16th,2013 JD2456581.771019 we determined the flux in the H band to corresponde to H = 10.396 +/- 0.05. That is to be compared with the flux determined for this object on JD 2456282.665081 when the flux was H = 11.979 +/- 0.07. Observations were carried out with the 2.1m telescope of the Guillermo Haro Observatory operated by the National Institute for Astrophysics, Optics and Electronics (Mexico), equipped with the instrument CANICA a NIR camera.

Carrasco, L.; Recillas, E.; Porras, A.; Carraminana, A.

2013-10-01

99

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

SciTech Connect

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

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

2007-03-15

100

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

SciTech Connect

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

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

2007-01-01

101

Measurement of the x-ray mass attenuation coefficient and determination of the imaginary component of the atomic form factor of molybdenum over the 13.5-41.5-keV energy range  

SciTech Connect

We use the x-ray extended-range technique (XERT) [Chantler et al., Phys. Rev. A 64, 062506 (2001)] to measure the mass attenuation coefficients of molybdenum in the x-ray energy range of 13.5-41.5 keV to 0.02-0.15 % accuracy. Measurements made over an extended range of the measurement parameter space are critically examined to identify, quantify, and correct where necessary a number of experimental systematic errors. These results represent the most extensive experimental data set for molybdenum and include absolute mass attenuation coefficients in the regions of the x-ray absorption fine structure (XAFS) and x-ray-absorption near-edge structure (XANES). The imaginary component of the atomic form-factor f{sub 2} is derived from the photoelectric absorption after subtracting calculated Rayleigh and Compton scattering cross sections from the total attenuation. Comparison of the result with tabulations of calculated photoelectric absorption coefficients indicates that differences of 1-15 % persist between the calculated and observed values.

Jonge, Martin D. de; Tran, Chanh Q.; Chantler, Christopher T.; Barnea, Zwi; Dhal, Bipin B.; Cookson, David J.; Lee, Wah-Keat; Mashayekhi, Ali [School of Physics, University of Melbourne, Melbourne, Victoria 3010 (Australia); Chem-Mat-CARS, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439 (United States); XOR 1-ID, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439 (United States)

2005-03-01

102

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.

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

2011-01-01

103

Measurement of mass attenuation coefficients of Rhizophora spp. binderless particleboards in the 16.59-25.26 keV photon energy range and their density profile using x-ray computed tomography.  

PubMed

The mass attenuation coefficients of Rhizophora spp. binderless particleboard with four different particle sizes (samples A, B, C and D) and natural raw Rhizophora spp. wood (sample E) were determined using single-beam photon transmission in the energy range between 16.59 and 25.26 keV. This was done by determining the attenuation of K(?1) X-ray fluorescent (XRF) photons from niobium, molybdenum, palladium, silver and tin targets. The results were compared with theoretical values of young-age breast (Breast 1) and water calculated using a XCOM computer program. It was found that the mass attenuation coefficient of Rhizophora spp. binderless particleboards to be close to the calculated XCOM values in water than natural Rhizophora spp. wood. Computed tomography (CT) scans were then used to determine the density profile of the samples. The CT scan results showed that the Rhizophora spp. binderless particleboard has uniform density compared to natural Rhizophora spp. wood. In general, the differences in the variability of the profile density decrease as the particle size of the pellet samples decreases. PMID:22304963

Marashdeh, M W; Bauk, S; Tajuddin, A A; Hashim, R

2012-04-01

104

Determination of self attenuation coefficient and relative TL efficiency of CaSO 4 :Dy, LiF:Mg,Cu,P and LiF:Mg,Ti TLDs - An alternate approach  

NASA Astrophysics Data System (ADS)

Self attenuation of TL and relative TL efficiency of polytetra fluoro ethylene (PTFE) embedded CaSO 4:Dy disc, LiF:Mg,Ti (MTS) disc and LiF:Mg,Cu,P (MCP-N) chip were determined in the present study for photons of energy 10-34 keV. The relative TL efficiency was determined using an alternative approach in which ratio of experimental response and corrected theoretical response was used instead of measuring the absolute TL emission in photon counting mode. For CaSO 4:Dy disc, it was found that with increasing the proportion of CaSO 4:Dy phosphor in the disc, the light attenuation coefficient increases. The light attenuation coefficient of MTS disc and MCP-N chip was found to be 23.4 and 45.5 cm -1, respectively. The relative TL efficiency in the photon energy range of 10-34 keV for MTS discs and MCP-N chips, evaluated in the present study matches well with the reported values in the literature.

Bakshi, A. K.; Chatterjee, S.; Palani Selvam, T.; Joshi, V. J.; Chougaonkar, M. P.

2011-10-01

105

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

106

Effect of stretching DNA on lac Repressor 1D-diffusion revealed by the combination of single-molecule localization and manipulation  

NASA Astrophysics Data System (ADS)

Here we report the effect of DNA tension on lac repressor 1D-diffusion through a combination of single-molecule localization and optical trapping. The diffusion coefficient shows a parabolic dependence on DNA tension.

Belcastro, G.; Mónico, C.; Capitanio, M.; Vanzi, F.; Pavone, F. S.

2013-06-01

107

Towards improved hardware component attenuation correction in PET/MR hybrid imaging  

NASA Astrophysics Data System (ADS)

In positron emission tomography/computed tomography (PET/CT) hybrid imaging attenuation correction (AC) of the patient tissue and patient table is performed by converting the CT-based Hounsfield units (HU) to linear attenuation coefficients (LAC) of PET. When applied to the new field of hardware component AC in PET/magnetic resonance (MR) hybrid imaging, this conversion method may result in local overcorrection of PET activity values. The aim of this study thus was to optimize the conversion parameters for CT-based AC of hardware components in PET/MR. Systematic evaluation and optimization of the HU to LAC conversion parameters has been performed for the hardware component attenuation map (µ-map) of a flexible radiofrequency (RF) coil used in PET/MR imaging. Furthermore, spatial misregistration of this RF coil to its µ-map was simulated by shifting the µ-map in different directions and the effect on PET quantification was evaluated. Measurements of a PET NEMA standard emission phantom were performed on an integrated hybrid PET/MR system. Various CT parameters were used to calculate different µ-maps for the flexible RF coil and to evaluate the impact on the PET activity concentration. A 511 keV transmission scan of the local RF coil was used as standard of reference to adapt the slope of the conversion from HUs to LACs at 511 keV. The average underestimation of the PET activity concentration due to the non-attenuation corrected RF coil in place was calculated to be 5.0% in the overall phantom. When considering attenuation only in the upper volume of the phantom, the average difference to the reference scan without RF coil is 11.0%. When the PET/CT conversion is applied, an average overestimation of 3.1% (without extended CT scale) and 4.2% (with extended CT scale) is observed in the top volume of the NEMA phantom. Using the adapted conversion resulting from this study, the deviation in the top volume of the phantom is reduced to -0.5% and shows the lowest standard deviation inside the phantom in comparison to all other conversions. Simulation of a µ-map misregistration shows acceptable results for shifts below 5 mm for the flexible surface RF coil. The adapted conversion from HUs to LAC at 511 keV within this study can improve hardware component AC in PET/MR hybrid imaging as shown for a flexible RF surface coil. Furthermore, these results have a direct impact on the improvement of the hardware component AC of the examined flexible RF coil in conjunction with position determination.

Paulus, D. H.; Tellmann, L.; Quick, H. H.

2013-11-01

108

Contacts between the lac repressor and the thymines in the lac operator.  

PubMed Central

We have identified important points of contact between the lac repressor and the lac operator by crosslinking the repressor to bromouracil-substituted operator. We substituted bromouracils for thymines in a 55-base-long restriction fragment containing the lac operator and labeled one or the other 5' end with 32P. Ultraviolet irradiation of this fragment produced single-strand breakds at the bromouracils. We examined breakage at each bromouracil in the sequence by denaturing the DNA and displaying the UV-generated fragments on a polyacrylamide gel. In the presence of lac repressor, UV radiation failed to break at specific sites. We attribute this to a competing reaction in which the DNA crosslinks to the repressor rather than breaking. These crosslinkable sites thus define positions at which the lac repressor protein lies close to the methyl group of a thymine in the major groove of DNA. Images

Ogata, R; Gilbert, W

1977-01-01

109

Calculating optical water quality targets to restore and protect submersed aquatic vegetation: Overcoming problems in partitioning the diffuse attenuation coefficient for photosynthetically active radiation  

Microsoft Academic Search

Submersed aquatic vegetation (SAV) is an important component of shallow water estuarine systems that has declined drastically\\u000a in recent decades. SAV has particularly high light requirements, and losses of SAV have, in many cases, been attributed to\\u000a increased light attenuation in the water column, frequently due to coastal eutrophication. The desire to restore these valuable\\u000a habitats to their historical levels

Charles L. Gallegos

2001-01-01

110

SS Lac - the Effect of Cluster Environment  

NASA Astrophysics Data System (ADS)

We attempt to model in some detail the interesting triple system SS Lac located in the galactic cluster NGC 7209 which stopped eclipsing in about 1950. We find that our model of SS Lac is quite constrained by the relatively good observational data of this system and leads to a specific inclination (29°) of the outer orbit relative to the inner orbit at epoch zero (1912). We make some predictions about changes to system parameters in the short term (20-40 yr) and also in the medium term (up to ~3000 yr). Although the intrinsic spins of the stars have little effect on the orbit the converse is not true: the spin axes can vary their orientation relative to the close binary by up to 120° on a timescale of about a century. We discuss the processes in the cluster environment which whould produce a system with parameters similar to ones of SS Lac.

Kiseleva-Eggleton, Ludmila; Eggleton, Peter

111

SS Lac in Open Cluster NGC 7209  

NASA Astrophysics Data System (ADS)

We present IUE observations in far ultraviolet region for SS Lac in open cluster NGC 7209. The IUE short wavelength spectrum and long wavelength spectrum were merged to produce an energy distribution curve between 1200A and 3200A. The curve has been unreddened to take out reddening effect. Then the surface temperature, gravity and abundance of SS Lac were determined based on the Kurucz model atmosphere. The photographic light curve produced before cessation of eclipse were analyzed for photometric solutions. We confirmed SS Lac is a member of open cluster NGC 7209 based on its possible distance. The main reason for the cessation of eclipse is the change of the system's orbital inclination rather than collisional merger of two stars.

Kang, Young Woon

1997-12-01

112

Clustering environments of BL Lac objects  

NASA Technical Reports Server (NTRS)

We report measurements of the amplitude of the BL Lac galaxy spatial covariance function, B(gb), for the fields of five BL Lacertae objects. We present evidence for rich clusters around MS 1207+39 and MS 1407+59, and confirm high richness for the cluster containing H0414+009. We discuss the ease of 3C 66 A and find evidence for a poor cluster based on an uncertain redshift of z = 0.444. These data suggest that at least some BL Lac objects are consistent with being FR 1 radio galaxies in rich clusters.

Wurtz, Ronald; Ellingson, Erica; Stocke, John T.; Yee, H. K. C.

1993-01-01

113

Ultrasonic Attenuation in Lanthanum Monochalcogenides  

Microsoft Academic Search

Ultrasonic attenuation due to phonon-phonon interaction and thermoelastic relaxation are studied in Lanthanum Monochalcogenides in direction at different higher temperatures. For evaluation of ultrasonic absorption coefficients the second and third order elastic constants (SOEC) and (TOEC) are also calculated. Shear wave attenuation shows maximum along propagation direction with polarized along and the attenuation increases at higher temperatures. Thermo-elastic loss is

Raja Ram Yadav; Devraj Singh

2001-01-01

114

Meeting The Infrastructure Challenge In Lac  

Microsoft Academic Search

The World Development Report 1994 (New York: Oxford University Press) demonstrates that infrastructure can support economic growth, reduce poverty, and make development environmentally sustainable. The economic returns on infrastructure investment and rehabilitation are high. In Latin America and the Caribbean (LAC), economic growth has, in fact, always been underpinned by the development of infrastructure. When the debt crisis of the

1995-01-01

115

Bl Lac Population Study at High Energies  

NASA Astrophysics Data System (ADS)

In the framework of Active Galactic Nuclei (AGN) unification, BL Lacs and their parent population would share the same intrinsic characteristics, the observational differences being due to the orientation of the relativistic jet compared to the line of sight. BL Lacs would be the objects whose jet is oriented towards us, their emission being amplified by the relativistic Doppler boosting. Constraints arising from fast variability and/or large optical depth to pair production commonly imply large Lorentz factors. The growing number of BL Lacs detected at HE (> 100 MeV) and VHE (> 100 GeV) is a challenge for this unification scheme. Indeed, the high values of Doppler factor needed in the simplest radiative model to explain the emission of these sources imply a large density for the parent population. A possible solution to this Doppler factor crisis lies in considering different geometries for the jet. In this study, we use the BL Lacs detected at HE and VHE to investigate the intrinsic properties of the associated parent population. Using the results presented in Fermi's second AGN catalog and performing MC simulations of the parent population, we constrain the jet parameters: its intrinsic luminosity, Lorentz factor and geometric opening angle. The simulated density of parent population and Doppler factors of the objects detectable at HE within this population are presented according to the jet parameters.

Gérard, Lucie; Henri, Gilles; Pita, Santiago; Punch, Michael

2014-03-01

116

The 2QZ BL Lac survey - II  

NASA Astrophysics Data System (ADS)

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

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

2007-01-01

117

Design of the lac gene circuit revisited  

PubMed Central

The lactose (lac) operon of Escherichia coli serves as the paradigm for gene regulation, not only for bacteria, but also for all biological systems from simple phage to humans. The details of the systems may differ, but the key conceptual framework remains, and the original system continues to reveal deeper insights with continued experimental and theoretical study. Nearly as long lasting in impact as the pivotal work of Jacob and Monod is the classic experiment of Novick and Weiner in which they demonstrated all-or-none gene expression in response to an artificial inducer. These results are often cited in claims that normal gene expression is in fact a discontinuous bistable phenomenon. In this paper, I review several levels of analysis of the lac system and introduce another perspective based on the construction of the system design space. These represent variations on a theme, based on a simply stated design principle, that captures the key qualitative features of the system in a largely mechanism-independent fashion. Moreover, this principle can be readily interpreted in terms of specific mechanisms to make predictions regarding monostable vs. bistable behavior. The regions of design space representing bifurcations are compared with the corresponding regions identified through bifurcation analysis. I present evidence based on biological considerations as well as modeling and analysis to suggest that induction of the lac system in its natural setting is a monostable continuously graded phenomenon. Nevertheless, it must be acknowledged that the lac stability question remains unsettled, and it undoubtedly will remain so until there are definitive experimental results.

Savageau, Michael A.

2011-01-01

118

The role of genes LAC1 and LAC2 in the biosynthesis of lactose metabolism enzymes by Kluyveromyces lactis.  

PubMed

By crossing different Kluyveromyces lactis strains, the role of genes LAC1, LAC2 and of gene C were analyzed. These genes are involved in the biosynthesis of enzymes for the metabolism of lactose and galactose. They control the biosynthesis of the lactose and galactose transport, of beta-galactosidase and of the three enzymes of the Leloir pathway. The presence of at least one of the LAC gene is required for the biosynthesis to occur. The gene C seems to code for a negative factor which blocks the expression of the LAC1 and LAC2 genes in the absence of an inducer. PMID:3115053

Boze, H; Nicol, D; Moulin, G; Galzy, P

1987-01-01

119

Origin of Bistability in the lac Operon  

PubMed Central

Multistability is an emergent dynamic property that has been invoked to explain multiple coexisting biological states. In this work, we investigate the origin of bistability in the lac operon. To do this, we develop a mathematical model for the regulatory pathway in this system and compare the model predictions with other experimental results in which a nonmetabolizable inducer was employed. We investigate the effect of lactose metabolism using this model, and show that it greatly modifies the bistable region in the external lactose (Le) versus external glucose (Ge) parameter space. The model also predicts that lactose metabolism can cause bistability to disappear for very low Ge. We have also carried out stochastic numerical simulations of the model for several values of Ge and Le. Our results indicate that bistability can help guarantee that Escherichia coli consumes glucose and lactose in the most efficient possible way. Namely, the lac operon is induced only when there is almost no glucose in the growing medium, but if Le is high, the operon induction level increases abruptly when the levels of glucose in the environment decrease to very low values. We demonstrate that this behavior could not be obtained without bistability if the stability of the induced and uninduced states is to be preserved. Finally, we point out that the present methods and results may be useful to study the emergence of multistability in biological systems other than the lac operon.

Santillan, M.; Mackey, M. C.; Zeron, E. S.

2007-01-01

120

[Testicular function in mice of inbred strains BALB/cLac, PT, and CBA/Lac].  

PubMed

The main features of male fertility: sperm production and abnormalities, testosterone serum concentration and its testicular content after hCG injections, weights of the testes and cauda epididymes, were studied in adult males of three inbred mice strains BALB/cLac, PT, and CBA/Lac. The CBA/Lac males were characterized by lower value of the epididymal sperm number, as well as lower weights of reproductive organs in comparison with males of other inbred strains. The lower number of sperm is accompanied in the CBA/Lac males with lower proportion of morphologically abnormal spermatozoa as compared to other strains that could compensate its decreased count and improve fertility. The baseline testosterone concentration and its testicular content did not differ among the three strains but the testosterone response to injection of 10 IU of hCG was weaker in the CBA/Lac males than in the others. The results indicate significant interstrain differences in testicular traits implicated in male fertility which may be correlated and compensate to each other. PMID:20432726

Osadchuk, L V

2010-02-01

121

Photostimulated attenuation of hypersound in superlattice.  

National Technical Information Service (NTIS)

Photostimulated attenuation of hypersound in semiconductor superlattice has been investigated. It is shown that the attenuation coefficient depends on the phonon wave vector q in an oscillatory manner and that from this oscillation the band width (Delta) ...

S. Y. Mensah, F. K. Allotey, S. K. Adjepong

1992-01-01

122

BL Lac Candidates for TeV Observations  

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, thereby identifying 41 potential TeV emitters. We then perform a search over a more extended sample combining the ROSAT bright source catalog and the WISE all-sky survey, 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.

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

2013-07-01

123

The Lac Cinquante Uranium Deposit, Nunavut, Canada  

NASA Astrophysics Data System (ADS)

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

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

2009-12-01

124

The flare energy spectrum of EV Lac  

NASA Astrophysics Data System (ADS)

A study is made of the flare energy spectrum of the flare star EV Lac for the period 1974 - 79, based on the homogeneous series of observational data obtained at the Stephanion Observatory. The spectrum varies significantly during the 5-year activity cycle of the star. Analogous variation is also observed in the time-averaged rate of flare energy release of the star, which becomes at least twice as high during the years of maximum flare activity than during the rest of the cycle. Arguments are presented which show that the validity of the power law for the flare energy spectrum should be considered with due caution.

Mavridis, L. N.; Avgoloupis, S.

1987-12-01

125

Synthesis and identification of endohedral metallofullerenes La@C 82  

Microsoft Academic Search

The effect of the procedure of preparation of lanthanum-graphite electrodes and the regime of their evaporation in the electric\\u000a arc on the yield of endometallofullerene La@C82 has been studied. La@C82 was identified by ESR spectroscopy, optical spectroscopy, and mass spectrometry. The fractional extraction of the fullerene-containing\\u000a soot witho-xylene makes it possible to separate La@C82 from higher fullerenes containing no metal

V. P. Bubnov; V. K. Kol'tover; E. E. Laukhina; Ya. I. Estrin; E. B. Yagubskii

1997-01-01

126

Analysis of Capacitance Characteristics of C60, C70, and La@C82  

NASA Astrophysics Data System (ADS)

Fullerenes and their derivatives are promising materials for supercapacitor devices due to their unique nanostructure that combines the reversible redox charge storage with the high surface area. In this article, the reversible redox charge storage of C60, C70, and La@C82 in liquid ammonia solution is reported. An electrochemical analysis of these species using cyclic voltammetry is presented in conjunction with the theoretical interpretation. The relative magnitudes of transfer coefficients, which represent a measure of the symmetry of the energy barrier for oxidation and reduction of the monoanionic species of these fullerenes, suggest that the availability of the surface area permitting delocalization of ? electrons is a determining factor of their first reduction potential. The relationship between these transfer coefficients and fullerene geometry also support previous conclusions that the La atom is located within the fullerene cage of La@C82. The electrochemical measurements analyzed were made using a modified three-compartment cell. Advantages associated with this modified cell for analysis of capacitance characteristics of C60, C70, and La@C82 are discussed.

Tran, Nick E.; Lambrakos, Samuel G.; Lagowski, Joseph J.

2009-02-01

127

Gamma-ray luminosity function of BL Lac objects  

NASA Astrophysics Data System (ADS)

The gamma-ray luminosity function (GLF) of BL Lac objects is constructed by using a sample of BL Lac objects with redshifts selected from the Second LAT AGN catalog. The GLFs of BL Lacs in the frame of the pure density evolution (PDE), the pure luminosity evolution (PLE), and the luminosity-dependent density (LDDE) models are determined by using the Markov Chain Monte Carlo (MCMC) technique, respectively. Our results suggest that the PDE model can give best description for BL Lac GLF based on the combination of constraints of model parameters and good fits to the observed data of Fermi-Large Area Telescope (LAT) BL Lacs, but other two models (PLE and LDDE) cannot be excluded. Based on our constructed GLFs, the contribution to the extragalactic diffuse gamma-ray background (EGRB) from BL Lacs is estimated, and ˜1-5 per cent of the EGRB in the 0.1-100 GeV band is found to come from unresolved BL Lacs (including the cascade emission). In addition, it is found that the BL Lac GLF is very different from flat spectrum radio quasar GLF and then the contribution of blazars to the EGRB should be estimated separately.

Zeng, Houdun; Yan, Dahai; Zhang, Li

2014-06-01

128

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

129

Organ fusion and defective cuticle function in a lacs1 lacs2 double mutant of Arabidopsis  

Microsoft Academic Search

As the outermost layer on aerial tissues of the primary plant body, the cuticle plays important roles in plant development\\u000a and physiology. The major components of the cuticle are cutin and cuticular wax, both of which are composed primarily of fatty\\u000a acid derivatives synthesized in the epidermal cells. Long-chain acyl-CoA synthetases (LACS) catalyze the formation of long-chain\\u000a acyl-CoAs and the

Hua Weng; Isabel Molina; Jay Shockey; John Browse

2010-01-01

130

Determination of OM/OC ratios and specific attenuation coefficients (SAC) in ambient fine PM at a rural site in southern Ontario: implications for emission sources, particle aging, and radiative forcing  

NASA Astrophysics Data System (ADS)

Ambient particulate matter (PM) samples were collected on quartz filters at a rural site in southern Ontario during intensive studies in 2005 and 2007. The concentrations of organic carbon (OC), pyrolysis organic carbon (POC), and elemental carbon (EC) were determined by thermal analysis. These results were compared to the organic aerosol mass concentration (OM) measured by an Aerodyne Aerosol Mass Spectrometer (AMS) and to the particle absorption coefficient (b_asp) obtained from a Radiance Research Particle Soot Absorption Photometer (PSAP). The total organic mass to organic carbon ratios (OM/OC) and specific attenuation coefficients (SAC) were also derived. According to the results, the POC mass is proportional to the approximated oxygen mass in the aerosols and OM/OC ratios can be estimated directly from thermal measurements. The study also suggests that the air masses from the south, with relatively low OC/EC ratios, high EC, sulphate contents and OM/OC ratios, were originated from urban and industrial emissions and subsequently experienced photo-oxidations in the atmosphere, implying that the oxygenated organics could come from both primary and secondary sources. Whereas the air masses from the north, with relatively high OC/EC ratios, low EC, sulphate contents and OM/OC ratios, were dominant by the background clean air with relatively larger contributions from biogenic emissions. The mean SAC derived from the 2005 and 2007 studies are 4.9 m2 g-1 and 3.8 m2 g-1, respectively. When POC mass approaching zero (i.e. the impact of atmospheric aging is minimized), the SAC for primary emitted soot is estimated to be 5.8 m2 g-1 and 6.3 m2 g-1 for the northern and southern air masses, respectively, supported by the corresponding values when particulate sulphate concentration approaches zero. A decreasing trend in the SAC value with atmospheric aging of the aerosol was observed at the site, suggesting that during the study, the light absorption enhancement due to the presence of coating on particles was likely to be offset by the decrease in light absorption caused by increasing soot particle diameter and collapsing of soot particle structure. This result may imply that model simulations of atmospheric warming by BC could be 50% too high.

Chan, T. W.; Huang, L.; Leaitch, W. R.; Sharma, S.; Brook, J. R.; Slowik, J. G.; Abbatt, J. P. D.; Brickell, P. C.; Liggio, J.; Li, S.-M.; Moosmüller, H.

2009-07-01

131

Ultrasonic attenuation spectroscopy of industrial slurries  

Microsoft Academic Search

Using measurements of attenuation coefficients over a wide frequency range one can obtain particle size distribution (PSD) functions for concentrated colloidal suspensions. This paper deals with experimental aspects of ultrasonic spectroscopy. Recent activity in instrumentation for ultrasonic spectroscopy of emulsions and suspensions is briefly reviewed. The measurement issues related to calculations of attenuation coefficients using tone-burst signals are outlined showing

A. Sharma; H. P. Pendse

1997-01-01

132

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

133

AVHRR-LAC estimates of forest area in Madagascar, 1990  

Microsoft Academic Search

Three AVHRR-LAC data sets acquired in September 1990 and January 1991 were used to map the forest resources of Madagascar. The island was partitioned into four strata to include: (1) the western hardwoods, (2) the central grasslands, (3) the eastern rainforest, and (4) spiny forest. Each stratum was classified separately using AVHRR-LAC data in conjunction with 1984-1988 Landsat-MSS photoproducts. The

R. Nelson; N. Horning

1993-01-01

134

Photoacoustic imaging of lacZ gene expression in vivo  

Microsoft Academic Search

In the postgenomic era, imaging techniques are playing an important role in visualizing gene expression in vivo. This work represents the first demonstration of pho- toacoustic tomography PAT for reporter gene imaging. Rats inoculated with 9L\\/lacZ gliosarcoma tumor cells are imaged with PAT before and after injection of X-gal, a colorimetric assay for the lacZ-encoded enzyme -galactosidase. Using far-red optical

Li Li; Roger J. Zemp; Gina Lungu; George Stoica; Lihong V. Wang

2007-01-01

135

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

136

Lac Courte Oreilles Energy Analysis Project  

SciTech Connect

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

Leslie Isham; Denise Johnson

2009-04-01

137

Attenuation of terahertz transmission through rain  

NASA Astrophysics Data System (ADS)

Based on the Marshall-Palmer, Weibull raindrop size distribution and Mie electromagnetic scattering model, the relationships of attenuation coefficient of terahertz (THz) atmospheric window waves with precipitation rate and temperature are studied. Furthermore, combined with the loss of electromagnetic wave transmission in free space, the attenuation of THz communication and the transmission of current mobile communication signals through rain are compared and analyzed. The results show that the attenuation coefficient of THz transmission is increased with increasing precipitation rate, the difference of attenuation coefficient at different THz window waves is small, and the maximum difference is about 3 dB. The rain attenuation of THz wave is first decreased and then increased with increasing temperature, but the temperature has little effect on it. The attenuation of THz wave through rain is much larger than that of mobile communication signal.

Luo, Yi; Huang, Wan-xia; Luo, Zi-yi

2012-07-01

138

lac operon induction in Escherichia coli: Systematic comparison of IPTG and TMG induction and influence of the transacetylase LacA.  

PubMed

Most commonly used expression systems in bacteria are based on the Escherichia coli lac promoter. Furthermore, lac operon elements are used today in systems and synthetic biology. In the majority of the cases the gratuitous inducers IPTG or TMG are used. Here we report a systematic comparison of lac promoter induction by TMG and IPTG which focuses on the aspects inducer uptake, population heterogeneity and a potential influence of the transacetylase, LacA. We provide induction curves in E. coli LJ110 and in isogenic lacY and lacA mutant strains and we show that both inducers are substrates of the lactose permease at low inducer concentrations but can also enter cells independently of lactose permease if present at higher concentrations. Using a gfp reporter strain we compared TMG and IPTG induction at single cell level and showed that bimodal induction with IPTG occurred at approximately ten-fold lower concentrations than with TMG. Furthermore, we observed that lac operon induction is influenced by the transacetylase, LacA. By comparing two Plac-gfp reporter strains with and without a lacA deletion we could show that in the lacA(+) strain the fluorescence level decreased after few hours while the fluorescence further increased in the lacA(-) strain. The results indicate that through the activity of LacA the IPTG concentration can be reduced below an inducing threshold concentration-an influence that should be considered if low inducer amounts are used. PMID:22079752

Marbach, Anja; Bettenbrock, Katja

2012-01-01

139

X-Ray Form Factor, Attenuation and Scattering Tables  

National Institute of Standards and Technology Data Gateway

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

140

Natural Attenuation  

Microsoft Academic Search

\\u000a Natural Attenuation (NA) has emerged during the last 10–15 years as a useful and cost-efficient alternative approach for contaminated\\u000a site management. It refers to the naturally occurring processes like dispersion, diffusion, sorption, volatilization, degradation\\u000a and transformation, all of which can substantially decrease contaminant concentration, mass, toxicity and\\/or mobility within\\u000a soil and groundwater. The efficiency of Natural Attenuation processes depends to

Anita Peter; Thomas Held; Norbert Hüsers; Frank A. Swartjes

141

Ultrasonic Attenuation in Lanthanum Monochalcogenides  

NASA Astrophysics Data System (ADS)

Ultrasonic attenuation due to phonon-phonon interaction and thermoelastic relaxation are studied in Lanthanum Monochalcogenides in <110> direction at different higher temperatures. For evaluation of ultrasonic absorption coefficients the second and third order elastic constants (SOEC) and (TOEC) are also calculated. Shear wave attenuation shows maximum along <110> propagation direction with polarized along <110> and the attenuation increases at higher temperatures. Thermo-elastic loss is very small compared to phonon-viscosity loss. Behavior of temperature dependence of the absorption is the same as in case of pure metals and dielectric crystals.

Yadav, Raja; Singh, Devraj

2001-06-01

142

Mechanism of promoter repression by Lac repressor-DNA loops  

PubMed Central

The Escherichia coli lactose (lac) operon encodes the first genetic switch to be discovered, and lac remains a paradigm for studying negative and positive control of gene expression. Negative control is believed to involve competition of RNA polymerase and Lac repressor for overlapping binding sites. Contributions to the local Lac repressor concentration come from free repressor and repressor delivered to the operator from remote auxiliary operators by DNA looping. Long-standing questions persist concerning the actual role of DNA looping in the mechanism of promoter repression. Here, we use experiments in living bacteria to resolve four of these questions. We show that the distance dependence of repression enhancement is comparable for upstream and downstream auxiliary operators, confirming the hypothesis that repressor concentration increase is the principal mechanism of repression loops. We find that as few as four turns of DNA can be constrained in a stable loop by Lac repressor. We show that RNA polymerase is not trapped at repressed promoters. Finally, we show that constraining a promoter in a tight DNA loop is sufficient for repression even when promoter and operator do not overlap.

Becker, Nicole A.; Peters, Justin P.; Lionberger, Troy A.; Maher, L. James

2013-01-01

143

Arabidopsis CER8 encodes LONG-CHAIN ACYL-COA SYNTHETASE 1 (LACS1) that has overlapping functions with LACS2 in plant wax and cutin synthesis.  

PubMed

Plant cuticle is an extracellular lipid-based matrix of cutin and waxes, which covers aerial organs and protects them from many forms of environmental stress. We report here the characterization of CER8/LACS1, one of nine Arabidopsis long-chain acyl-CoA synthetases thought to activate acyl chains. Mutations in LACS1 reduced the amount of wax in all chemical classes on the stem and leaf, except in the very long-chain fatty acid (VLCFA) class wherein acids longer than 24 carbons (C(24)) were elevated more than 155%. The C(16) cutin monomers on lacs1 were reduced by 37% and 22%, whereas the C(18) monomers were increased by 28% and 20% on stem and leaf, respectively. Amounts of wax and cutin on a lacs1-1 lacs2-3 double mutant were much lower than on either parent, and lacs1-1 lacs2-3 had much higher cuticular permeability than either parent. These additive effects indicate that LACS1 and LACS2 have overlapping functions in both wax and cutin synthesis. We demonstrated that LACS1 has synthetase activity for VLCFAs C(20)-C(30), with highest activity for C(30) acids. LACS1 thus appears to function as a very long-chain acyl-CoA synthetase in wax metabolism. Since C(16) but not C(18) cutin monomers are reduced in lacs1, and C(16) acids are the next most preferred acid (behind C(30)) by LACS1 in our assays, LACS1 also appears to be important for the incorporation of C(16) monomers into cutin polyester. As such, LACS1 defines a functionally novel acyl-CoA synthetase that preferentially modifies both VLCFAs for wax synthesis and long-chain (C(16)) fatty acids for cutin synthesis. PMID:19392700

Lü, Shiyou; Song, Tao; Kosma, Dylan K; Parsons, Eugene P; Rowland, Owen; Jenks, Matthew A

2009-08-01

144

Construction of Tn5 lac, a transposon that fuses lacZ expression to exogenous promoters, and its introduction into Myxococcus xanthus.  

PubMed

A promoterless trp-lac fusion fragment was inserted near one end of the bacterial transposon Tn5 in the correct orientation to fuse lacZ gene expression to promoters outside Tn5. The resulting transposon, Tn5 lac, retains the kanamycin-resistance gene of Tn5 and transposes in Escherichia coli at 6% the frequency of Tn5 to many different sites in a bacteriophage lambda target. Expression of beta-galactosidase, the product of the lacZ gene, from Tn5 lac insertions in phage lambda depends both on insertion into a transcription unit in the correct orientation and on the regulation of the promoter of the transcription unit, verifying that by transposition Tn5 lac can fuse lacZ expression to outside promoters. An insertion of Tn5 lac in bacteriophage P1 was isolated and used to introduce Tn5 lac into Myxococcus xanthus, a bacterium that undergoes multicellular development. Stable kanamycin-resistant transductants are obtained that contain no P1 DNA sequences but have Tn5 lac inserted at different sites in the Myxococcus chromosome. Individual transductants express different levels of beta-galactosidase. A chromogenic substrate of beta-galactosidase, 5-bromo-4-chloro-3-indolyl beta-D-galactoside, is toxic in Myxococcus when cleaved in large amounts. In principle, Tn5 lac could be used to assay transcription in any bacterium in which Tn5 can transpose and beta-galactosidase can be measured. PMID:6091110

Kroos, L; Kaiser, D

1984-09-01

145

Role of protons in sugar binding to LacY  

PubMed Central

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

Smirnova, Irina; Kasho, Vladimir; Sugihara, Junichi; Vazquez-Ibar, Jose Luis; Kaback, H. Ronald

2012-01-01

146

Method for Estimating Total Attenuation from a Spatial Map of Attenuation Slope for Quantitative Ultrasound Imaging  

PubMed Central

Estimating total ultrasound attenuation from backscatter data is essential in the field of quantitative ultrasound (QUS) because of the need to compensate for attenuation when estimating the backscatter coefficient and QUS parameters. This work uses a reference phantom method of attenuation estimation to create a spatial map of attenuation slope (AS) from backscatter radio-frequency (RF) data of three phantoms and a rat mammary adenocarcinoma tumor (MAT). The attenuation maps show changes in attenuation between different regions of the phantoms and the MAT tumor. Analyses of the attenuation maps of the phantoms suggest that the AS estimates are in good quantitative agreement with the known values for the phantoms. Furthermore, estimates of total attenuation from the attenuation maps are likewise in good quantitative agreement with known values.

Pawlicki, Alexander D.; O'Brien, William D.

2013-01-01

147

Diffuse ?-Ray Emission from Unresolved BL Lac Objects  

NASA Astrophysics Data System (ADS)

Blazars, active galactic nuclei with a jet pointing toward the Earth, represent the most abundant class of high-energy extragalactic ?-ray sources. The subset of blazars known as BL Lac objects is on average closer to Earth (i.e., younger) and characterized by harder spectra at high energy than the whole sample. The fraction of BL Lacs that is too dim to be detected and resolved by current ?-ray telescopes is therefore expected to contribute to the high-energy isotropic diffuse ?-ray background (IGRB). The IGRB has been recently measured over a wide energy range by the Large Area Telescope (LAT) on board the Gamma-ray Space Telescope (Fermi). We present a new prediction of the diffuse ?-ray flux due to the unresolved BL Lac blazar population. The model is built upon the spectral energy distribution and the luminosity function derived from the fraction of BL Lacs detected (and spectrally characterized) in the ?-ray energy range. We focus our attention on the {\\cal O}(100) GeV energy range, predicting the emission up to the TeV scale and taking into account the absorption on the extragalactic background light. In order to better shape the BL Lac spectral energy distribution, we combine the Fermi-LAT data with Imaging Atmospheric Cerenkov Telescope measurements of the most energetic sources. Our analysis is carried on separately for low- and intermediate-synchrotron-peaked BL Lacs on the one hand and high-synchrotron-peaked BL Lacs on the other hand: we find in fact statistically different features for the two. The diffuse emission from the sum of both BL Lac classes increases from about 10% of the measured IGRB at 100 MeV to ~100% of the data level at 100 GeV. At energies greater than 100 GeV, our predictions naturally explain the IGRB data, accommodating their softening with increasing energy. Uncertainties are estimated to be within of a factor of two of the best-fit flux up to 500 GeV.

Di Mauro, M.; Donato, F.; Lamanna, G.; Sanchez, D. A.; Serpico, P. D.

2014-05-01

148

Photostimulated attenuation of hypersound in superlattices  

NASA Astrophysics Data System (ADS)

Photostimulated attenuation of hypersound in semiconductor superlattices has been investigated theoretically. It is shown that the attenuation coefficient depends on the phonon wave vector qin an oscillatory manner and that from this oscillation the band width ? of the superlattice can be found.

Mensah, S. Y.; Allotey, F. K.; Adjepong, S. K.; Mensah, N. G.

1997-12-01

149

Photostimulated attenuation of hypersound in superlattice  

NASA Astrophysics Data System (ADS)

Photostimulated attenuation of hypersound in a semiconductor superlattice has been investigated. It is shown that the attenuation coefficient depends on the phonon wave vector q in an oscillatory manner and that from this oscillation the band width of superlattice can be found.

Mensah, S. Y.; Allotey, F. K.; Adjepong, S. K.

1992-10-01

150

Attenuation in very narrow photon beams  

Microsoft Academic Search

When one measures the half-value layer (HVL) or the attenuation coefficient (mu) in a high-energy photon beam, it is necessary to use a narrow beam to eliminate the scattered photons produced in the attenuator. However, lateral electron equilibrium will be compromised if the beam is too small. If the HVL and mu are based on measurements of absorbed dose, the

B. E. T. Bjaerngard; J. S. Tsai; R. K. Rice

1989-01-01

151

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

152

Boundary method for attenuation correction in positron computed tomography  

Microsoft Academic Search

A new method for attenuation correction in positron computed tomography (PCT) has been developed, and it can improve the quality of PCT images. The method requires a short transmission scan by the PCT system. Then boundaries between tissues with significantly different attenuation coefficients are determined from the transmission image by edge-finding techniques. Attenuation correction factors (ACF) are then calculated using

S. C. Huang; R. E. Carson; M. E. Phelps; E. J. Hoff-man; H. R. Schelbert; D. E. Kuhl

1981-01-01

153

Technique of Measurements of Elastic Wave Attenuation Parameters  

Microsoft Academic Search

Certain methodical aspects of using one of the active methods of acoustic testing of materials and products, namely, measurements of the frequency dependence of the attenuation coefficient are considered when the dependence of recorded results on the physical differences between the measurement channels is eliminated. The attenuation coefficients of transverse and longitudinal ultrasonic waves are estimated under the laboratory conditions

S. B. Teodorovich

2003-01-01

154

Effect of ultrasonic attenuation on the feasibility of acoustic tweezers  

Microsoft Academic Search

A modified mathematical formulation for the calculation of axial radiation force was developed to incorporate the effect of ultrasonic attenuation. Axial forces, Fresnel coefficients, average internal attenuation factors and effective internal reflection coefficients were calculated. Thermal and mechanical indices were also computed to address the safety issues in the implementation of acoustic tweezers and were found to be negligible. The

Jungwoo Lee; K. Kirk Shung

2006-01-01

155

Chandra X-ray Scrutiny of New Radio-Shy BL Lac Candidates  

NASA Astrophysics Data System (ADS)

BL Lacs are rare X-ray emitting AGN, oft-unified with FR I radio galaxies viewed along a jet. Despite decades of study it is still uncertain whether all BL Lacs are strong radio sources: venerable BL Lac samples include just dozens of objects, too few to test for an even rarer radio-quiet subset. But, recent large area surveys have found a few intriguing BL Lacs lying on the radio faint tail; SDSS alone provides hundreds of new BL Lacs, with several dozen potentially radio-shy cases. We propose brief Chandra images of 3 such BL Lac candidates having deep VLA data but lacking X-ray constraints. Chandra scrutiny is a prerequisite to claiming them as radio quiet BL Lacs; confirmation would provide fascinating challenges to our understanding of this peculiar AGN subclass.

Anderson, Scott

2008-09-01

156

First photometric study of W UMa binary star LU Lac  

NASA Astrophysics Data System (ADS)

LU Lac is a neglected W UMa binary star in photometric investigations. In this paper, we present BVRI CCD photometric light curves obtained on one night in 2012. The first photometric solutions of this system are computed by using the Wilson-Devinney code. It is shown that LU Lac is a marginal contact W-type system with a degree of contact factor of f=8.9%, a mass ratio of q=2.085 and a high inclination of i=82°.20. From the first analyses of orbital period changes, we found the period variation of the system includes an oscillation (A3=0.0125 days and T3=51.92 years). The cyclic change may be attributed to the light-travel time effect through the presence of a third body.

Liao, W.-P.; Qian, S.-B.; Zhao, E.-G.; Jiang, L.-Q.

2014-08-01

157

Period of Light Variability in BL Lac ON 231  

NASA Astrophysics Data System (ADS)

In this paper, the authors have compiled the data of about 100 years in B-band of the BL Lac ON 231 and used this database to analyze periodicity signals in the optical light curve. Two different methods were applied: the wavelet analysis and the Discrete Correlation Function (DCF) method. We revealed the existence of periods of 13.5 years in the source variability.

Bing, Xu Yun; Jing, Zhang Hao; Xiong, Zhang; Ming, Mao Wei; Tong, Dong Fu

2011-06-01

158

Deep VLA Maps of the Complete EMSS BL Lac Sample  

NASA Astrophysics Data System (ADS)

Most BL Lacs are believed to be low-luminosity Fanaroff-Riley class I radio galaxies (FR-1s) whose jet axes are oriented towards the observer such that their emission is dominated by relativistically-boosted synchrotron and inverse-Compton emission, making them ideal laboratories for understanding the physics of beaming and relativistic jet propogation. Currently there are only two statistically-complete samples of BL Lacs: the radio-selected 1Jy sample (RBLs) and the X-ray-selected EMSS sample (XBLs). While once extremely rare, new X-ray and radio surveys are increasing the number of known BL Lacs dramatically, creating an impetus to understand their nature. In the unified model both RBLs and XBLs are believed to be beamed FR-1s and that XBLs are either viewed farther from the jet axis than RBLs. Alternatively, it has been suggested that their difference lies not in orientation but in the high-energy cutoff in their energy distributions, where XBLs and RBLs represent a single family of objects with a smooth energy distribution followed by a sharp cutoff. For RBLs this cutoff occurs in the near-IR/optical and for XBLs this cutoff is at UV/X-ray or higher energies. Padovani & Giommi have argued against the unified model on the basis that the radio structure of XBLs is more core dominated than predicted. However, their conclusions are drawn from VLA observations of a subset of the EMSS sample which includes only the brighter radio sources (Perlman & Stocke); a subset which, due to Doppler boosting, is biased towards more core-dominated sources. To eliminate this bias we have completed deep, 20cm observations with the VLA of the remaining objects in the EMSS sample. We will present these observations as well as discuss their implications for both the unified and energy-cutoff models for BL Lacs. These results will also be used to constrain beaming parameters for the XBL population.

Rector, T. A.; Stocke, J. T.

1998-09-01

159

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

PubMed

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

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

2014-01-01

160

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

PubMed Central

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

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

2014-01-01

161

Structure of sugar-bound LacY.  

PubMed

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

2014-02-01

162

AVHRR-LAC estimates of forest area in Madagascar, 1990  

NASA Technical Reports Server (NTRS)

Three AVHRR-LAC data sets acquired in September 1990 and January 1991 were used to map the forest resources of Madagascar. The island was partitioned into four strata to include: (1) the western hardwoods, (2) the central grasslands, (3) the eastern rainforest, and (4) spiny forest. Each stratum was classified separately using AVHRR-LAC data in conjunction with 1984-1988 Landsat-MSS photoproducts. The results of AVHRR classification indicate that approximately 11 percent of the island is covered by forest. Estimates of forest area, by stratum, are as follows: western hardwoods, 6697 sq km; central grasslands, 2830 sq km; eastern rainforest 34,167 sq km; and spiny forest, 17,224 sq km. The total forest area on the 587,041 sq km island is estimated to be 60,918 sq km. The AVHRR forest map was compared to a mid-1970s land cover map which was developed using Landsat-MSS photoproducts. The average class agreement between the mid 1970s ground reference map and the 1990 AVHRR-LAC map was 78.2 percent, the overall accuracy was 81.1 percent. Much of the per-pixel disagreement between the ground reference and AVHRR maps involved areas identified as forest in the 1970s and as nonforest in 1990.

Nelson, R.; Horning, N.

1993-01-01

163

The Side-chain of the Amino Acid Residue in Position 110 of the Lac Repressor Influences its Allosteric Equilibrium  

Microsoft Academic Search

Binding of the Lac repressor to its operator DNA controls the expression of the genes of thelacoperon ofEscherichia coli. Lac repressor's affinity for thelacoperator is diminished by an inducer that affects the structure of the repressor tetramer. Here we report the cloning and sequencing of the mutant Lac repressoritgene, whose product, the LacRtrepressor, shows a higher affinity for the inducer

Herbert Müller-Hartmann; Benno Müller-Hill

1996-01-01

164

Repression of lac Promoter as a Function of Distance, Phase and Quality of an Auxiliary lac Operator  

Microsoft Academic Search

The tetrameric Lac repressor can bind simultaneously to twolacoperators on the same DNA molecule, thereby including the formation of a DNA loop. We investigated the phasing dependence of DNA loop formation betweenlacoperator O1and an auxiliary ideallacoperator (Oid) on the bacterial chromosome, with inter-operator distances varying from 57.5 to 1493.5 bp. Repression of a CAP-independentlacUV5 promoter by O1at its natural position

Johannes Müller; Stefan Oehler; Benno Müller-Hill

1996-01-01

165

Genetic Transfer of Episomic Elements Among Erwinia Species and Other Enterobacteria: F?lac+  

PubMed Central

The episomic element F?lac+ was transferred, probably by conjugation, from Escherichia coli to Lac? strains of Erwinia herbicola, Erwinia amylovora, and Erwinia chrysanthemi (but not to several other Erwinia spp. In preliminary trials). The lac genes in the exconjugants of the Erwinia spp. showed varying degrees of stability depending on the strain (stable in E. herbicola strains Y46 and Y74 and E. amylovora strain EA178, but markedly unstable in E. chrysanthemi strain EC16). The lac genes and the sex factor (F) were eliminated from the exconjugants by treatment with acridine orange, thus suggesting that both lac and F are not integrated in the Erwinia exconjugants. All of the tested Lac+ exconjugants of E. herbicola strains Y46 and Y74 and E. amylovora strain EA178, but not of E. chrysanthemi strain EC 16, were sensitive to the F-specific phage M13. The heterogenotes (which harbored F?lac+) of E. herbicola strains Y46 and Y74, E. amylovora strain EA178, and E. chrysanthemi strain EC16 were able to transfer lac genes by conjugation to strains of E. herbicola, E. amylovora, E. chrysanthemi, Escherichia coli, and Shigella dysenteriae. The frequency of such transfer from Lac+ exconjugants of Erwinia spp. was comparable to that achieved by using E. coli F?lac+ as donors, thus indicating the stability, expression, and restriction-and-modification properties of the sex factor (F) in Erwinia spp.

Chatterjee, Arun K.; Starr, Mortimer P.

1972-01-01

166

Chemo-enzymatic modification of poly-N-acetyllactosamine (LacNAc) oligomers and N,N-diacetyllactosamine (LacDiNAc) based on galactose oxidase treatment  

PubMed Central

Summary The importance of glycans in biological systems is highlighted by their various functions in physiological and pathological processes. Many glycan epitopes on glycoproteins and glycolipids are based on N-acetyllactosamine units (LacNAc; Gal?1,4GlcNAc) and often present on extended poly-LacNAc glycans ([Gal?1,4GlcNAc]n). Poly-LacNAc itself has been identified as a binding motif of galectins, an important class of lectins with functions in immune response and tumorigenesis. Therefore, the synthesis of natural and modified poly-LacNAc glycans is of specific interest for binding studies with galectins as well as for studies of their possible therapeutic applications. We present the oxidation by galactose oxidase and subsequent chemical or enzymatic modification of terminal galactose and N-acetylgalactosamine residues of poly-N-acetyllactosamine (poly-LacNAc) oligomers and N,N-diacetyllactosamine (LacDiNAc) by galactose oxidase. Product formation starting from different poly-LacNAc oligomers was characterised and optimised regarding formation of the C6-aldo product. Further modification of the aldehyde containing glycans, either by chemical conversion or enzymatic elongation, was established. Base-catalysed ?-elimination, coupling of biotin–hydrazide with subsequent reduction to the corresponding hydrazine linkage, and coupling by reductive amination to an amino-functionalised poly-LacNAc oligomer were performed and the products characterised by LC–MS and NMR analysis. Remarkably, elongation of terminally oxidised poly-LacNAc glycans by ?3GlcNAc- and ?4Gal-transferase was also successful. In this way, a set of novel, modified poly-LacNAc oligomers containing terminally and/or internally modified galactose residues were obtained, which can be used for binding studies and various other applications.

Kupper, Christiane E; Rosencrantz, Ruben R; Henssen, Birgit; Pelantova, Helena; Thones, Stephan; Drozdova, Anna; Kren, Vladimir

2012-01-01

167

Relation of sound absorption and shallow water modal attenuation to plane wave attenuation.  

PubMed

Prediction of attenuation of acoustic fields in weakly absorbing media often uses the substitution of (omega/c)-->(omega/c)+ialpha(pw) into the idealized equations for constant frequency, with alpha(pw) representing the local plane wave attenuation coefficient. This assumption is flawed whenever the local absorption of sound is proportional to the square of the gradient of the acoustic pressure, as is the case when the absorption is caused by fluid velocity relaxation. A realistic analysis yields an improved weighting function over depth for determination of guided mode attenuation coefficients. PMID:19894791

Pierce, Allan D

2009-11-01

168

Applying Echoes Mean Frequency Shift for Attenuation Imaging in Tissue  

NASA Astrophysics Data System (ADS)

The purpose of this study was to develop the attenuation parametric imaging technique and to apply it for in vivo characterization of tissue. Local attenuation coefficient was determined by evaluating the frequency downshift that encounters the amplitude spectrum of the interrogating ultrasonic pulse during propagation in the absorbing tissue. Operation and accuracy of the processing methods were verified by assessing the size-independent region of interest (ROI) for attenuation determination and calculating the attenuation coefficient distribution for experimentally recorded tissue-phantom scattered waveforms. The Siemens Antares scanner equipped with Ultrasound Research Interface unit allowing for direct radiofrequency (RF) signals recording was used for B-scan imaging of the tissue- mimicking phantom in vitro and liver in vivo. RF data were processed to determine attenuation coefficient along the B-scan lines. Also, the preliminary studies of backscattered signals from skin recorded using a skin scanner were performed to calculate parametric-attenuation images.

Litniewski, J.; Klimonda, Z.; Nowicki, A.

169

BL Lacs from the EMSS: Number-counts and implications for the luminosity function  

NASA Technical Reports Server (NTRS)

BL Lac objects, extracted from the Einstein Extended Medium Sensitivity Survey (EMSS), are examined. X-ray selection proved to be a powerful tool to find new BL Lacs, and allows the creation of complete, well defined and sizable samples. X-ray selected BL Lac objects (XBL) have in general more starlight in the optical spectra than radio selected BL Lacs. Redshifts for a significant fraction of objects in samples of XBL can be determined. It is thus possible to study the cosmological properties of BL Lac objects. Different models of luminosity functions of BL Lacs, including relativistic beaming, are considered and integrated over luminosity and redshift. The results are compared with the observed number-counts. The observed redshift distribution and the models' predictions are analyzed.

Wolter, Anna; Gioia, Isabella M.; Maccacaro, Tommaso; Schild, Rudy E.; Morris, Simon L.; Stocke, John T.

1989-01-01

170

lac repressor: 3-fluorotyrosine substitution for nuclear magnetic resonance studies.  

PubMed Central

This paper describes the isolation of 3-fluorotyrosine-substituted lac repressor, and its 19F nuclear magnetic resonance spectrum. From the spectrum, one can conclude that for each of the four identical subunits of the repressor there are four or five surface tyrosines, two buried or internal tyrosines, and one tyrosine with an phenolic group ionized or involved in a hydrogen bond. Conditions are described that can be used for the 3-fluorotyrosine substitution of a variety of Escherichia coli proteins for 19F nuclear magnetic resonance studies.

Lu, P; Jarema, M; Mosser, K; Daniel, W E

1976-01-01

171

Fusions of the lac and trp Regions of the Escherichia coli Chromosome1  

PubMed Central

Two classes of strains were studied in which the lac operon is transposed to a chromosomal site close to the tonB and trp loci. The two classes differ in the orientation of the lac region on the chromosome. In both types of strains, tonB mutants were selected in which deletions removing the tonB locus also caused a fusion of the lac and trp regions. The study of the properties of such fusion strains provides information on the control of both the lac and trp operons.

Miller, Jeffrey H.; Reznikoff, William S.; Silverstone, Allan E.; Ippen, Karin; Signer, Ethan R.; Beckwith, Jonathan R.

1970-01-01

172

Electrophysiological characterization of uncoupled mutants of LacY.  

PubMed

In this study of the lactose permease of Escherichia coli (LacY), five functionally irreplaceable residues involved specifically in H(+) translocation (Arg302 and Glu325) or in the coupling between protonation and sugar binding (Tyr236, Glu269, and His322) were mutated individually or together with mutant Glu325 ? Ala. The wild type and each mutant were purified and reconstituted into proteoliposomes, which were then examined using solid-supported-membrane-based electrophysiology. Mutants Glu325 ? Ala or Arg302 ? Ala, in which H(+) symport is abolished, exhibit a weakly electrogenic rapid reaction triggered by sugar binding. The reaction is essentially absent in mutant Tyr236 ? Phe, Glu269 ? Ala, and His322 ? Ala, and each of these mutations blocks the electrogenic reaction observed in the Glu325 ? Ala mutant. The findings are consistent with the interpretation that the electrogenic reaction induced by sugar binding is due to rearrangement of charged residues in LacY and that this reaction is blocked by mutation of each member of the Tyr236/Glu269/His322 triad. In addition, further support is provided for the conclusion that deprotonation is rate limiting for downhill lactose/H(+) symport. PMID:24152072

Gaiko, Olga; Bazzone, Andre; Fendler, Klaus; Kaback, H Ronald

2013-11-19

173

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

174

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

PubMed

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

175

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.

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

176

Simultaneous activity and attenuation reconstruction in PET: applying partially known attenuation  

NASA Astrophysics Data System (ADS)

Simultaneous reconstruction of activity and attenuation in positron emission tomography without transmission data presents significant degradation due to crosstalk effect. The objective of this work is to investigate the effect of applying a priori knowledge, such as known attenuation coefficients, in some regions of the image, into a simultaneous activity and attenuation reconstruction algorithm (EM-AA). The methodology consists of applying, after each iteration, a global correction (addition) on the attenuation map, based on the difference between the known attenuation coefficient and the average of the estimated coefficients in the region. We also applied a correction factor that decreases with iteration number. The assessments were carried out via phantoms emulating 3D PET that presented specific features for crosstalk and structural accuracy measurements. We obtained three figures of merit for activity and three for attenuation. The results showed that, in the case of noiseless projections, the proposed correction improved the estimation of both activity and attenuation. On the other hand, while structural accuracy improved with iterations, the crosstalk effects become worse. The improvements were more pronounced for structural accuracy than for crosstalk effects. However, the errors are still too high, and more research is needed in this area.

Furuie, Sergio S.

2009-02-01

177

Structural and Enzymatic characterization of the lactonase SisLac from Sulfolobus islandicus  

PubMed Central

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

Chabriere, Eric; Elias, Mikael

2012-01-01

178

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

179

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

180

BL Lacs from the EMSS: Number-Counts and Implications for the Luminosity Function.  

National Technical Information Service (NTIS)

BL Lac objects, extracted from the Einstein Extended Medium Sensitivity Survey (EMSS), are examined. X-ray selection proved to be a powerful tool to find new BL Lacs, and allows the creation of complete, well defined and sizable samples. X-ray selected BL...

A. Wolter I. M. Gioia T. Maccacaro R. E. Schild S. L. Morris

1989-01-01

181

BL Lac objects from the extended medium sensitivity survey: The surface density  

Microsoft Academic Search

We present here the first sizeable sample of x-ray selected BL Lac objects. The sample has been extracted from the Einstein Observatory Extended Medium Sensitivity Survey. It contains some 30 previously unknown BL Lacs which have been found by virtue of their x-ray emission. The sample is homogeneous and statistically well defined. We can thus use it to derive the

Tommaso Maccacarol; I. Gioia; R. Schild; A. Wolter; S. Morris; J. Stocke

182

Dehyrogenation of Ethylene: Spectroscopy and Structures of La(C_2H_2) and La(C_4H_6) Complexes  

NASA Astrophysics Data System (ADS)

Hydrogen elimination is observed in the reaction of laser-ablated La atoms and ethylene (C_2H_4) in a pulsed molecular beam source. Dehydrogenated products, La(C_2H_2) and La(C_4H_6), are identified by time-of-flight mass spectrometry and studied by pulsed-field-ionization zero-electron kinetic energy spectroscopy and density functional theory calculations. La(C_2H_2) is determined as a triangle (C2v) in the ^2A_2 ground electronic state, where La binds with C_2H_2 in a two-fold mode (?^2). La(C_4H_6) is identified as a diligand species with La being sandwiched between C_2H_2 and C_2H_4, each in a two-fold binding mode, and the complex is in the ^2A_1 ground electronic state. The adiabatic ionization energies of La(?^2-C_2H_2) and La(?^2-C_2H_2)(?^2-C_2H_4) are measured to be 41174(5) and 39405(5) Cm-1, respectively. La^+-C_2H_2 and La^+-C_4H_6 stretching and C-H bending frequencies of the corresponding ions are also determined, and the vibrational assignments are confirmed with deuterated ethylene measurements.

Kumari, Sudesh; Roudjane, Mourad; Yang, Dong-Sheng

2011-06-01

183

Midperiod Rayleigh wave attenuation model for Asia  

NASA Astrophysics Data System (ADS)

We present an attenuation model for midperiod Rayleigh waves in Central Asia and surrounding regions. This model is defined by maps of attenuation coefficient across the region of study in the period band 14-24 s. The model is constructed to characterize the regional variations in attenuation of seismic waves in the crust, which are related to the tectonic history of the studied territory, to calibrate the regional surface-wave magnitude scale, and to extend the teleseismic 'surface-wave magnitude - body wave magnitude' (Ms-mb) discriminant to regional distances. The construction of the model proceeds in three stages. The first stage in model construction is the measurement of Rayleigh wave spectral amplitudes. We collected and processed waveform data for 200 earthquakes occurring from 2003 to 2006 inside and around Eurasia, and used records of about 135 broadband permanent and temporary stations. This data set provided a sufficient number of spectral amplitude measurements between 14 and 24 s periods for the construction of two-dimensional tomographic maps of attenuation coefficients. At the second stage of the work, the integral of attenuation coefficients along given paths is estimated using both inter-station measurements and single-station measurements corrected for source and receiver terms. The third stage includes the refining of source parameters, recalculation of attenuation coefficient integrals after this refinement, grooming of resulting coefficients, and multistage tomographic inversion of the data. Tomographic maps for the set of periods from 14 to 24 s, which exhibit clear correlation with geology and tectonics of the territory under study, were obtained. Validation of these maps using the inter-station measurements confirms their accuracy in predicting the observations.

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

2010-08-01

184

Dissociation of Lac Messenger Ribonucleic Acid Transcription from Translation During Recovery from Inhibition of Protein Synthesis  

PubMed Central

Studies were made of the synthesis of Lac messenger ribonucleic acid (mRNA) by Escherichia coli in the absence of protein synthesis and of the coupling of transcription of lac operon to translation. Lac mRNA was not synthesized in the presence of chloramphenicol, and its synthesis steadily decreased during K+ deprivation and treatment with puromycin. Since under these conditions total mRNA synthesis is not inhibited it is suggested that the control of Lac mRNA is distinct from that which regulates total mRNA synthesis. Lac mRNA synthesized during recovery from K+ starvation or from chloramphenicol inhibition is not translated into functional enzyme, suggesting translational control over ?-galactosidase synthesis.

Artman, Michael; Ennis, Herbert L.

1972-01-01

185

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

186

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

187

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

188

Geology and Geochemistry of the Lac Cinquante Uranium Deposit, Nunavut  

NASA Astrophysics Data System (ADS)

The Lac Cinquante Uranium Deposit, is located in the Kivalliq district of Nunavut approximately 350 km west of Rankin Inlet, and is centered on approximately Latitude 62°34'33"N, Longitude 98°41'41"W. Geologically it is located within the Baker Lake Basin of the Churchill province, one of several northeast- trending Proterozoic basins in the Western Churchill Province that lie unconformably on top of Archean volcanics. Mineralization is found within basement volcanics that have undergone hydrothermal alteration and mineralization in fault zones. Previous studies of this area document two major zones of mineralization: the Main zone and the South zone; with three dominant styles of mineralization in the Archean greenstones including: disseminated pitchblende with base metals in tuffaceous metasediments, discrete pitchblende veins that cut across the metasediments, and quartz, carbonate, sulphides, and pitchblende in gash veins on 040 to 060 trending cross fractures. Additionally, mineralized zones hosting uranium are also present in the overlying Proterozoic sediments. Field based mapping completed in the summer of 2008 at 1:5000 has revealed a more detailed and complicated geological history than previously reported. The newly acquired map and historical data have been combined in an attempt to develop a comparative data collection. Geochemical data has aided in a more developed interpretation for the formation of the greenstone belt within which the Lac Cinquante uranium deposit is hosted. Current analytical techniques complementing the geological observations include X-ray diffraction to determine mineral assemblages and X-ray fluorescence for major and trace element information. Other analytical techniques will be utilised including electron microprobe to understand precise mineral chemistry of uranium bearing minerals, oxygen stable isotopes to understand fluid migration and ore forming reservoirs, and further stable isotope analyses to understand the temperature and mineral-fluid interactions leading to uranium mineralization are planned.

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

2009-05-01

189

Adaptive Evolution of the Streptococcus pyogenes Regulatory Aldolase LacD.1  

PubMed Central

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

Cusumano, Zachary

2013-01-01

190

Feasibility Study of Grain Size Estimation of S45C by Attenuation Measurement of 40 MHz Surface Acoustic Wave Generated by Phase Velocity Scanning of Laser Interference Fringes  

Microsoft Academic Search

Structural change in 0.45 mass % carbon steel during tempering was measured nondestructively as a change in the attenuation coefficient of 40 MHz surface acoustic waves (SAW) generated by scanning interference fringes (SIF). The SIF selectively generate the SAW at an adequate center frequency, which is useful to distinguish the attenuation coefficients between slightly different structures. The attenuation coefficient at

Hideo Nishino; Tsutomu Furukawa; Sunao Takashina; Mikio Takemoto

2000-01-01

191

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

192

Attenuation Measurements in Solutions of Some Carbohydrates  

SciTech Connect

The linear attenuation coefficients in aqueous solutions of three carbohydrates, glucose (C{sub 6}H{sub 12}O{sub 6}), maltose monohydrate (C{sub 12}H{sub 22}O{sub 11}.H{sub 2}O), and sucrose (C{sub 12}H{sub 22}O{sub 11}), were determined at 81, 356, 511, 662, 1173, and 1332 keV by the gamma-ray transmission method in a good geometry setup. From the precisely measured densities of these solutions, mass attenuation coefficients were then obtained that varied systematically with the corresponding changes in the concentrations (g/cm{sup 3}) of these solutions. The experimental results were used in terms of effective atomic numbers and electron densities. A comparison between experimental and theoretical values of attenuation coefficients has proven that the study has a potential application for the determination of attenuation coefficients of solid solutes from their solutions without obtaining them in pure crystalline form.

Gagandeep [Guru Nanak Dev University (India); Singh, Kulwant [Guru Nanak Dev University (India); Lark, B.S. [Guru Nanak Dev University (India); Sahota, H.S. [Punjabi University (India)

2000-02-15

193

Electromagnetic Attenuation by Solid Particle Aerosols  

Microsoft Academic Search

Theories of electromagnetic attenuation by absorption and scattering from aerosols of solid particles were evaluated and experimentally verified. Particles having specific physical and morphological properties were tested to maximize the mass extinction coefficients of the aerosols in several bands of the electromagnetic spectrum. Particulate materials were chosen based on theoretical predictions and compatible aerosolization schemes were developed for each material.

Erica Ray Petersen

1991-01-01

194

Attenuation of ultrasonic waves in rolled metals  

Microsoft Academic Search

Scattering of ultrasonic waves in polycrystals with texture is studied in this article. The attenuations of the three wave modes are determined as a function of dimensionless frequency and propagation direction, respectively, for given orientation distribution coefficients (ODCs). The calculation is done in the case of a statistically orthorhombic sample made up of cubic crystallites. The wave propagation and scattering

Liyong Yang; Joseph A. Turner

2004-01-01

195

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

196

Extension of the Lac du Bouchet palaeomagnetic record over the last 120,000 years  

NASA Astrophysics Data System (ADS)

A high-resolution profile of the palaeomagnetic variations recorded in the upper 20 m of the Lac du Bouchet sedimentary sequence has been reconstructed from several parallel Mackereth and "Livingstone" type cores. Inter-core correlations were established by comparing individual core profiles of magnetic susceptibility. Individual records of AF cleaned directions were then "stretched" to a common depth scale and merged; the mean record was then filtered and smoothed in order to reduce the background noise. Accelerator radiocarbon determinations and pollen analyses show that the sequence covers the last interglacial/glacial cycle (back to ca. 120 kyr B.P.), and allow to perform a depth to time transformation. There is a noted absence of widely divergent directions back to 90 kyr B.P. It is estimated that the recorded signal (a PDRM signal) represents the geomagnetic input signal, attenuated by about 19%. It follows that the excursions reported for the Laschamp and Olby lavas, if they existed at all, must have been of rather short duration. Two durable excursions appear in narrow diameter sections at the base of three independent cores (B, C and D), while a reverse to normal transition is possibly documented in the lowermost meter (core D). This part of the sequence is dated from the recognition of major climatic events related to the 18O isotopic stages defined in the oceanic record between 116 and 95 kyr. This introduces the possibility of new excursions at ca. 104 and 95 kyr, i.e, immediately after the recovery of normal polarity documenting the end of the Blake event.

Thouveny, N.; Creer, K. M.; Blunk, I.

1990-02-01

197

Live Attenuated Coronavirus Vaccines.  

National Technical Information Service (NTIS)

The present invention is directed live, attenuated coronavirus vaccines. The vaccine comprises a viral genome encoding a p59 protein having at mutation at a specific tyrosine residue, and may include other attenuating mutations. Such viruses show reduced ...

M. Denison

2005-01-01

198

Attenuation of external Bremsstrahlung in metallic absorbers  

SciTech Connect

In this paper attenuation of bremsstrahlung from {sup 147}Pm and {sup 170}Tm beta emitters has been studied in aluminum, copper, tin, and lead metallic absorbers. Bremsstrahlung spectra and mass attenuation coefficients for monoenergetic gamma rays are used to calculate theoretical attenuation curves. Magnetic deflection and beta stopping techniques are used to measure the integral bremsstrahlung intensities above 30 keV in different target thicknesses. Comparison of measured and calculated attenuation curves shows a good agreement for various absorbers, thus providing a test of this technique, which may be useful in understanding bremsstrahlung intensity buildup and in the design of optimum shielding for bremsstrahlung sources. It is found that the absorption of bremsstrahlung in metallic absorbers does not obey an exponential law and that absorbers act as energy filters.

Dhaliwal, A.S.; Powar, M.S.; Singh, M. (Punjabi Univ., Physics Dept., Patiala 147002 (IN))

1990-12-01

199

Intramolecular dislocation of the COOH terminus of the lac carrier protein in reconstituted proteoliposomes.  

PubMed Central

A dodecapeptide corresponding to the carboxyl terminus of the lac carrier of Escherichia coli was synthesized, coupled to thyroglobulin, and the conjugate was used to generate site-directed polyclonal antibodies. The antibodies react with the carboxyl-terminal peptide and with the lac carrier protein, while monoclonal antibody 4B1 reacts with intact lac carrier protein, but not with the carboxyl-terminal peptide. Antibody 4B1 binds preferentially to right-side-out membrane vesicles relative to inside-out vesicles, confirming the presence of the 4B1 epitope on the periplasmic surface of the membrane. Alternatively, anti-carboxyl-terminal antibody binds preferentially to inside-out vesicles, demonstrating that the carboxyl terminus of the lac carrier protein is on the cytoplasmic surface. Surprisingly, both antibodies bind to proteoliposomes reconstituted with purified lac carrier protein, and quantitative binding assays indicate that the epitopes are equally accessible. When proteoliposomes containing purified lac carrier protein are digested with carboxypeptidases A and B, binding of anti-carboxyl-terminal antibodies decreases by greater than 80%, while binding of antibody 4B1 and various transport activities remain essentially unchanged. It is suggested that during reconstitution, the lac carrier protein undergoes intramolecular dislocation of the carboxyl terminus with no significant effect on its catalytic activity. Images

Carrasco, N; Herzlinger, D; Mitchell, R; DeChiara, S; Danho, W; Gabriel, T F; Kaback, H R

1984-01-01

200

Systematic Search for VHE Gamma-Ray Emission from X-Ray-bright High-Frequency BL Lac Objects  

NASA Astrophysics Data System (ADS)

All but three (M87, BL Lac, and 3C 279) extragalactic sources detected so far at very high energy ?-rays belong to the class of high-frequency-peaked BL Lac objects. This suggested to us a systematic scan of candidate sources with the MAGIC telescope, based on the Donato et al. compilation of X-ray blazars. The observations took place from 2004 December to 2006 March and cover northern sky sources visible under small zenith distances zd<30deg at culmination, constraining the declination to -2° to +58°. The sensitivity of the search was planned for detecting X-ray-bright [F(1 keV)>2 ?Jy] sources emitting at least the same energy flux at 200 GeV as at 1 keV. To avoid strong ?-ray attenuation close to the energy threshold, source redshift was constrained to z<0.3. Of the 14 sources observed, 1ES 1218+304 (for the first time at VHE) and 1ES 2344+514 (strong detection in a low flux state) were detected in addition to the known bright TeV blazars Mrk 421 and Mrk 501. A marginal excess of 3.5 ? from the position of 1ES 1011+496 was observed and then confirmed as a VHE ?-ray source by a second MAGIC observation triggered by a high optical state. For the remaining sources, we present 99% c.l. upper limits on the integral flux >~200 GeV. We characterize the HBL sample (including all HBLs detected at VHE so far) by looking for correlations between their multifrequency spectral indices determined from simultaneous optical, archival X-ray, and radio luminosities, finding that VHE-emitting HBLs do not seem to constitute a unique subclass. The HBLs' absorption-corrected ?-ray luminosities at 200 GeV are generally not higher than their X-ray luminosities at 1 keV.

Albert, J.; Aliu, E.; Anderhub, H.; Antoranz, P.; Baixeras, C.; Barrio, J. A.; Bartko, H.; Bastieri, D.; Becker, J. K.; Bednarek, W.; Berger, K.; Bigongiari, C.; Biland, A.; Bock, R. K.; Bordas, P.; Bosch-Ramon, V.; Bretz, T.; Britvitch, I.; Camara, M.; Carmona, E.; Chilingarian, A.; Coarasa, J. A.; Commichau, S.; Contreras, J. L.; Cortina, J.; Costado, M. T.; Curtef, V.; Danielyan, V.; Dazzi, F.; De Angelis, A.; Delgado, C.; de los Reyes, R.; De Lotto, B.; Dorner, D.; Doro, M.; Errando, M.; Fagiolini, M.; Ferenc, D.; Fernández, E.; Firpo, R.; Fonseca, M. V.; Font, L.; Fuchs, M.; Galante, N.; García-López, R. J.; Garczarczyk, M.; Gaug, M.; Giller, M.; Goebel, F.; Hakobyan, D.; Hayashida, M.; Hengstebeck, T.; Herrero, A.; Höhne, D.; Hose, J.; Huber, S.; Hsu, C. C.; Jacon, P.; Jogler, T.; Kosyra, R.; Kranich, D.; Kritzer, R.; Laille, A.; Lindfors, E.; Lombardi, S.; Longo, F.; López, M.; Lorenz, E.; Majumdar, P.; Maneva, G.; Mannheim, K.; Mariotti, M.; Martínez, M.; Mazin, D.; Merck, C.; Meucci, M.; Meyer, M.; Miranda, J. M.; Mirzoyan, R.; Mizobuchi, S.; Moralejo, A.; Nieto, D.; Nilsson, K.; Ninkovic, J.; Oña-Wilhelmi, E.; Otte, N.; Oya, I.; Panniello, M.; Paoletti, R.; Paredes, J. M.; Pasanen, M.; Pascoli, D.; Pauss, F.; Pegna, R.; Persic, M.; Peruzzo, L.; Piccioli, A.; Prandini, E.; Puchades, N.; Raymers, A.; Rhode, W.; Ribó, M.; Rico, J.; Rissi, M.; Robert, A.; Rügamer, S.; Saggion, A.; Saito, T. Y.; Sánchez, A.; Sartori, P.; Scalzotto, V.; Scapin, V.; Schmitt, R.; Schweizer, T.; Shayduk, M.; Shinozaki, K.; Shore, S. N.; Sidro, N.; Sillanpää, A.; Sobczynska, D.; Spanier, F.; Stamerra, A.; Stark, L. S.; Takalo, L.; Temnikov, P.; Tescaro, D.; Teshima, M.; Torres, D. F.; Turini, N.; Vankov, H.; Venturini, A.; Vitale, V.; Wagner, R. M.; Wibig, T.; Wittek, W.; Zandanel, F.; Zanin, R.; Zapatero, J.

2008-07-01

201

Evaluation of spontaneous and chemical-induced lacI mutations in germ cells from lambda/lacI transgenic mice.  

PubMed

The spontaneous mutant frequency in germ cells isolated from seminiferous tubules of two lambda/lacI transgenic mouse strains, C57BL/6 and B6C3F1 was evaluated. At least 500 000 phage were screened for mutation at lacI for each animal using standardized assay procedures. The germ cell spontaneous lacI mutant frequency was 17.8 +/- 8.1 x 10(-6) in C57BL/6 mice and 17.0 +/- 10.0 x 10(-6) in B6C3F1 mice. The induction of germ cell mutations by three well characterized alkylating agents were also evaluated in C57BL/6 mice on day 3 after a single dose administration. The lacI mutant frequencies were significantly elevated in transgenic mice dosed with ENU at 150 mg/kg (2-fold increase above control) and iPMS at 200 mg/kg (3-fold increase above control) but not in those receiving MMS at 40 mg/kg. These findings suggest that single dose studies using the lambda/lacI transgenic system may be capable of detecting germ mutations induced by chemicals characterized either by point mutations or small, intragenic deletions but not those characterized by a predominance of multi-locus deletions. PMID:9057874

Putman, D L; Ritter, A P; Carr, G J; Young, R R

1997-02-14

202

Untargeted mutagenesis induced by UV in the lacI gene of Escherichia coli.  

PubMed

Using a nonselective method, we have estimated the proportion of untargeted mutations in the lacI gene of E. coli by transferring either irradiated or unirradiated F' pro lac plasmids from an excision deficient donor to an excision deficient pro lac deleted recipient that had been irradiated and allowed to induce recA dependent functions for 30 min. We find that about 10 percent of the mutations induced by either 3.5 Jm-2 or 7 Jm-2 UV are untargeted. PMID:2997580

Christensen, R B; Christensen, J R; Koenig, I; Lawrence, C W

1985-01-01

203

Experimental Investigation of Wave Attenuation Through Vegetation  

NASA Astrophysics Data System (ADS)

Wetlands and coastal vegetation can reduce the surge and wave impact on coastal areas. Yet, the primary mechanisms of wave mitigation by vegetation are still unclear. The objective of this study was to investigate and quantify the attenuation of waves through vegetation using laboratory experiments. The wave attenuation properties of artificial vegetation and live and dormant S. alterniflora and J. roemerianus were investigated under monochromatic and irregular wave conditions at full scale in a wave tank facility at the USDA-ARS-National Sedimentation Laboratory in Oxford, Mississippi. Water level sensors and a video camera were used to record water level data. Drag coefficients were estimated for artificial and natural plants and regression equations were derived for the drag coefficients as functions of both Reynolds and Keulegan-Carpenter number. It was observed that vertical variation of vegetation density had an important effect on the drag coefficient.

Ozeren, Y.; Wren, D. G.

2011-12-01

204

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

Rosey, E L; Stewart, G C

1992-01-01

205

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

206

[Transmission of F'lac plasmid from Escherichia coli K-12 to bacteria of the genus Erwinia].  

PubMed

The F'lac plasmid was transferred by conjugation from Escherichia coli K-12 W1655 to 21 lac- strains of Erwinia spp. (5.2 . 10(-6) to 6.8 . 10(-2) lac+ exconjugants per donor cell). Erw. herbicola and Erw. chrysanthemi were the better recipients than others. The degree of the stability of lac+ genes in Erwinia exconjugants depends on the strains. Stable exconjugants of Erwinia, which harbored F'lac plasmid, were able to utilize lactose, to transfer lac genes by conjugation to Erwinia spp. and E. coli, and were sensitive to the F-specific phages f1, f2, Qbeta. The F'lac plasmid was eliminated from the exconjugants by the treatment with acridine orange, which indicates that this genetic element is not integrated into the Erwinia chromosome. PMID:363511

Prokulevich, V A; Fomichev, Iu K

1978-11-01

207

Functional rules for lac repressor-operator associations and implications for protein-DNA interactions  

PubMed Central

The Lac repressor has been used as a tool to understand protein–DNA recognition for many years. Recent experiments have demonstrated the ability of the Lac repressor to control gene expression in various eukaryotic systems, making the quest for an arsenal of protein–DNA binding partners desirable for potential therapeutic applications. Here, we present the results of the most exhaustive screen of Lac repressor-DNA binding partners to date, resulting in the elucidation of functional rules for Lac–DNA binding. Even within the confines of a single protein–DNA scaffold, modes of binding of different protein–DNA partners are sufficiently diverse so as to prevent elucidation of generalized rules for recognition for a single protein, much less an entire protein family.

Milk, Leslie; Daber, Robert; Lewis, Mitchell

2010-01-01

208

Characteristic and development report SA3581/MC4196 lightning arrestor connector (LAC).  

National Technical Information Service (NTIS)

This report describes the design, development, manufacturing processes, acceptance equipment, test results, and conclusions for the SA3581/MC4196 LAC program. Four development groups (Identified as Groups 1 through 3 and a Proof of Development Build) prov...

G. Gabert, K. Bradley, P. J. Konnick, W. Washington

1993-01-01

209

Construction of a translational lacZ fusion system to study gene regulation in Neisseria gonorrhoeae  

Microsoft Academic Search

A translational lacZ reporter system to study gene regulation in Neisseria gonorrhoeae (Ng) was developed. The pUC18-based vector pLES94 transforms Ng and recombines into the Ng chromosome at the site of the proAB genes. The vector contains a restriction site for cloning promoters that will result in a lacZ gene fusion. Initial cloning and characterization of promoters can be done

Lin E. Silver; Virginia L. Clark

1995-01-01

210

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

Microsoft Academic Search

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

James A. Shapiro

1984-01-01

211

Copurification of the Lac Repressor with Polyhistidine-Tagged Proteins in Immobilized Metal Affinity Chromatography  

Microsoft Academic Search

One of the commonly used resins for immobilized metal affinity purification of polyhistidine-tagged recombinant proteins is TALON resin, a cobalt (II)-carboxymethylaspartate-based matrix linked to Sepharose CL-6B. Here, we show that TALON resin efficiently purifies the native form of Lac repressor, which represents the major contaminant when (His)6- tagged proteins are isolated from Escherichia coli host cells carrying the lacIq gene.

Róis??n M. Owens; Andrew Grant; Nicholas Davies; C. David O'Connor

2001-01-01

212

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

Microsoft Academic Search

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

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

1999-01-01

213

Conversion of the lac repressor into an allosterically regulated transcriptional activator for mammalian cells.  

PubMed Central

A novel mammalian regulatory system was created by using the Escherichia coli lac repressor. The lac repressor was converted into a mammalian transcriptional activator by modifying the lac repressor coding region to include a nuclear localization signal from the simian virus 40 (SV40) large tumor antigen and the transcription activation domain from the herpes simplex virus type 1 virion protein 16. The lac activator protein (LAP) fusions were potent activators of several promoters containing lac operator sequences positioned either upstream or downstream of the transcription unit. A single lac operator allowed for transactivation, whereas multiple operators acted synergistically when separated by a small distance. Promoters containing 14 or 21 operator sequences were induced at least 1,000-fold in response to LAP, reaching levels of activity 20 to 30 times greater than that of the SV40 early promoter in HeLa cells. Activation was strongly inhibited by isopropyl-beta-D-thiogalactoside (IPTG), indicating that LAP retained the functions needed for allosteric regulation. LAP was bifunctional, also acting as a repressor of expression of an SV40 promoter containing an operator immediately downstream of the TATA box. Finally, genetic selection schemes were developed such that LAP-expressing cell lines can be generated at high frequency from either established or primary cells in culture. Images

Labow, M A; Baim, S B; Shenk, T; Levine, A J

1990-01-01

214

Second coefficient of viscosity in air  

NASA Technical Reports Server (NTRS)

Acoustic attenuation measurements in air were analyzed in order to estimate the second coefficient of viscosity. Data over a temperature range of 11 C to 50 C and at relative humidities between 6 percent and 91 percent were used. This analysis showed that the second coefficient of viscosity varied between 1900 and 20,000 times larger than the dynamic or first coefficient of viscosity over the temperature and humidity range of the data. In addition, the data showed that the molecular relaxation effects, which are responsible for the magnitude of the second coefficient of viscosity, place severe limits on the use of time-independent, thermodynamic equations of state. Compressible flows containing large streamwise velocity gradients, like shock waves, which cause significant changes in particle properties to occur during time intervals shorter than hundredths of seconds, must be modeled using dynamic equations of state. The dynamic model approach is described briefly.

Ash, Robert L.; Zuckerwar, Allan J.; Zheng, Zhonquan

1991-01-01

215

Variable laser attenuator  

DOEpatents

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

Foltyn, Stephen R. (Los Alamos, NM)

1988-01-01

216

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

217

Regulatory pathways governing modulation of fungal gene expression by a virulence-attenuating mycovirus.  

PubMed Central

A viral double-stranded RNA associated with virulence attenuation (hypovirulence) in the chestnut blight fungus (Cryphonectria parasitica) has been shown by DNA-mediated transformation to be responsible for transmissible hypovirulence. In addition to reduced virulence, the fungal strain harboring this virus exhibits a diverse array of characteristics, termed hypovirulence-associated traits, which distinguish it from an isogenic virus-free strain. We have investigated one of these traits, suppressed lac-1 (laccase) transcript accumulation. Two different and opposing regulatory pathways appear to govern lac-1 transcript levels in the virus-free strain: a stimulatory pathway was found to be dependent on the inositol trisphosphate (IP3) and calcium second messenger systems. A second pathway limiting transcript accumulation was shown to require ongoing protein synthesis. Additionally, changes in the level of lac-1 transcript accumulation were found to be related to modulation of promoter activity and this activity was shown to be suppressed in the virus-containing strain. We conclude that this hypovirulence-associated virus interferes with transduction of an IP3-calcium-dependent signal that is required for stimulation of lac-1 transcription. The perturbation of such signal transduction pathways by hypovirulence-associated viruses may account for the manifold symptoms associated with transmissible hypovirulence. Images

Larson, T G; Choi, G H; Nuss, D L

1992-01-01

218

Laser radiation attenuator on the basis of four Dove's prisms  

NASA Astrophysics Data System (ADS)

This work examines an attenuator of laser radiation based on four Dove prisms, which is much more efficient in comparison with two cascades of a di-prismatic attenuator. In this case, not only is its alignment and assembly significantly simplified, but also the consistency of the construction becomes evident. It turns out that the most optimal configuration of a four-prismatic attenuator is a pair-parallel one. This configuration, compared with a pair-perpendicular one, provides exchangeability of the di- and the four-prismatic model of the attenuator, maintains the direction of propagation of the radiation, and has a reference beam to control an attenuation coefficient in the operation process of the attenuator.

Owsik, Jan; Liberman, Anatoly A.; Kovalev, Alexander A.; Mikryukov, Alexey S.; Moskalyuk, Sergey A.; Ulanovsky, Michail V.; Noga, Janusz; Rembieli?ska, Anna; Walczuk, Joanna

2014-03-01

219

Expression Cloning of Recombinant Escherichia coli lacZ Genes Encoding Cytoplasmic and Nuclear ?-galactosidase Variants  

PubMed Central

Objective(s) Nonviral vector can be an attractive alternative to gene delivery in experimental study. In spite of some advantages in comparison with the viral vectors, there are still some limitations for efficiency of gene delivery in nonviral vectors. To determine the effective expression, the recombinant Escherichia coli lacZ genes were cloned into the different variants of pcDNA3.1 and then the mammalian cells were transfected. Methods and Materials The coding sequences of cytoplasmic and nuclear variants of lacZ gene were inserted downstream of the human cytomegalovirus immediate-early gene promoter of plasmid pcDNA3.1/myc-His C. The new cytoplasmic and nuclear constricts of E. coli ?-galactosidase-coding sequences were introduced into HeLa cells with the aid of linear polyethylenimine and at 2 days post-transfection the cells were stained using 5-bromo-4-chloro-3-indolyl-?-D-galactopyranoside (X-gal). Results Restriction enzyme analyses revealed the proper insertion of E. coli ?-galactosidase-coding sequences into the multiple cloning site of pcDNA3.1/myc-His C. The functionality of the resulting constructs designated pcDNA3.1-cyt.lacZ and pcDNA3.1-nls.lacZ(+) was confirmed by X-gal staining of HeLa cells transfected with these recombinant plasmids. While pcDNA3.1-cyt.lacZ directed the synthesis of cytoplasmically located ?-galactosidase molecules, the ?-galactosidase protein encoded by pcDNA3.1-nls.lacZ(+) was predominantly detected in the cell nucleus. Conclusion The expression of cytoplasmic and nuclear variant of LacZ gene confirmed the ability of pcDNA3.1 as versatility nonviral vector for the experimental gene delivery study in mammalian cells

Naderian, Homayoun; Rezvani, Zahra; Atlasi, Mohammad Ali; Nikzad, Hossein; Antoine, AF de Vries

2011-01-01

220

Monitored Natural Attenuation  

Microsoft Academic Search

Monitored natural attenuation (MNA) is an in situ remediation technology that relies on naturally occurring and demonstrable processes in soil and groundwater which reduce the mass and concentration of the contaminants. Natural attenuation (NA) involves both aerobic and anaerobic degradation of the contaminants due to the fact that oxygen is used up near the core of the contaminant plume. The

Kirsten S. Jørgensen; Jani M. Salminen; Katarina Björklöf

2010-01-01

221

Attenuation characteristics of underwater target lidar signals  

NASA Astrophysics Data System (ADS)

The effective attenuation coefficient of underwater target signals and that of backscattered signals are considered same in the present discuss. By the experiments and simulations of underwater target lidar signals, it is found that they are different. A new Monte Carlo method is introduced in the paper, the scattering phase function is approximately by a distorted Henyey-Greenstein (H-G) function, and the expression of the scattering angle (theta) is obtained from H-G function. The calculation efficiency of this method is improved five times than the traditional Monte Carlo method. Various sizes of the target are simulated in the paper. From the calculation results it is concluded that the effective attenuation coefficient of underwater target signals is larger than that of backscattered signals.

Lu, Yimin; Du, Zhufeng; Huang, Tiexia

1998-11-01

222

Fluorescence-Activated Sorting of Totipotent Embryonic Stem Cells Expressing Developmentally Regulated lacZ Fusion Genes  

Microsoft Academic Search

Murine embryonic stem (ES) cells were infected with a retrovirus promoter trap vector, and clones expressing lacZ fusion genes (LacZ^+) were isolated by fluorescence-activated cell sorting (FACS). Of 12 fusion genes tested, 1 was repressed when ES cells were allowed to differentiate in vitro. Two of three lacZ fusion genes tested were passed into the germ line, indicating that FACS

Sita Reddy; Helen Rayburn; Harald von Melchner; H. Earl Ruley

1992-01-01

223

Single-molecule manipulation reveals supercoiling-dependent modulation of lac repressor-mediated DNA looping  

PubMed Central

Gene expression regulation is a fundamental biological process which deploys specific sets of genomic information depending on physiological or environmental conditions. Several transcription factors (including lac repressor, LacI) are present in the cell at very low copy number and increase their local concentration by binding to multiple sites on DNA and looping the intervening sequence. In this work, we employ single-molecule manipulation to experimentally address the role of DNA supercoiling in the dynamics and stability of LacI-mediated DNA looping. We performed measurements over a range of degrees of supercoiling between ?0.026 and +0.026, in the absence of axial stretching forces. A supercoiling-dependent modulation of the lifetimes of both the looped and unlooped states was observed. Our experiments also provide evidence for multiple structural conformations of the LacI–DNA complex, depending on torsional constraints. The supercoiling-dependent modulation demonstrated here adds an important element to the model of the lac operon. In fact, the complex network of proteins acting on the DNA in a living cell constantly modifies its topological and mechanical properties: our observations demonstrate the possibility of establishing a signaling pathway from factors affecting DNA supercoiling to transcription factors responsible for the regulation of specific sets of genes.

Normanno, Davide; Vanzi, Francesco; Pavone, Francesco Saverio

2008-01-01

224

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.

225

Chandra Scrutiny Of Radio-Shy BL Lac Candidates From The SDSS  

NASA Astrophysics Data System (ADS)

BL Lac objects are rare radio and X-ray emitting AGN unified with FR I radio galaxies with a jet pointed toward the observer. Recently, BL Lac samples from the SDSS have become large enough to reveal especially rare subclasses of AGN, in relatively large numbers, with weak-featured optical spectra that are also radio-quiet. For example, approximately 100 radio-quiet BL Lac candidates have been discovered at z<2.2. Here, we present follow-up Chandra X-ray imaging of a subset of SDSS radio-quiet BL Lac candidates. We also consider follow-up VLA radio observations and optical variability to help constrain the true nature of these peculiar objects. We conclude the SDSS has likely recovered at least two populations of weak-featured radio-quiet AGN. Some may be low-redshift analogs to weak line quasars, a class of high-redshift (z>2.2) AGN with unusually weak broad emission line regions, while others may indeed lie on the radio-faint tail of the much larger radio-loud BL Lac parent population.

Plotkin, Richard M.; Anderson, S. F.; Brandt, W. N.; Diamond-Stanic, A. M.; Fan, X.; Schneider, D. P.; Shemmer, O.; Voges, W.

2010-02-01

226

INFRARED SPECTRAL OBSERVATION OF EIGHT BL LAC OBJECTS FROM THE SPITZER INFRARED SPECTROGRAPH  

SciTech Connect

The Spitzer Infrared Spectrograph (IRS) low-resolution spectra for eight BL Lac objects are presented in this paper. It can be seen that the infrared spectrum of S5 0716+714 shows in the IRS region many emission features that would be from a nearby galaxy. It is also shown that, except for the silicate absorptions around 10 {mu}m for some sources, emission lines in the infrared spectra for the other seven BL Lac objects are indeed very weak or absent. In addition, ignoring the silicate feature, all spectra can be well fitted by a power-law distribution indicative of the emission mechanism of the synchrotron radiation for these BL Lac objects in the IRS region.

Chen, P. S.; Shan, H. G., E-mail: iraspsc@yahoo.com.cn [National Astronomical Observatories/Yunnan Observatory and Key Laboratory for the Structure and Evolution of Celestial Objects, Chinese Academy of Sciences, Kunming 650011 (China)

2011-05-01

227

Electronic structure of potassium-doped La@C82 metallofullerene studied with photoelectron spectroscopy  

NASA Astrophysics Data System (ADS)

The electronic structure of potassium-doped La@C82 has been studied with synchrotron-radiation photoelectron spectroscopy. Ultraviolet photoemission measurements indicate evolution of the valence-band states of La@C82 with increasing potassium content, but KxLa@C82 remains semiconducting for all x between 0 and 6, with a band gap of at least 0.4eV , in contrast to K-doped C60 . The valence-band features, including those which arise from the interactions of C82 cages with La and K, show oscillatory behavior of photoemission intensity with incident photon energy. The strength of the oscillations varies between the states, and we associate diminished oscillations with increased localization of electron density. Finally, although core and valence states of La@C82 change considerably with potassium dosage, the encapsulated La atom is well shielded from the outside chemical environment and its valency remains close to 3+ .

Ton-That, C.; Dowd, A.; Shard, A. G.; Dhanak, V. R.; Taninaka, A.; Shinohara, H.; Welland, M. E.

2007-10-01

228

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

229

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

SciTech Connect

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

Varier, K.M.; Kunju, S.N.; Madhusudanan, K.

1986-04-01

230

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

231

Initiation of in vitro mRNA synthesis from the wild-type lac promoter.  

PubMed Central

An in vitro transcription system, dependent on catabolite gene activator protein (CAP), utilizing a 200 base-pair restriction fragment, has been used to show that the initiation site of the wild-type Escherichia coli lac mRNA, and that of two mutants, 8d and ps, are identical to that previously reported for the CAP-independent promoter mutant UV5. Order of addition experiments are used to show that the binding of lac repressor to the operator is competitive with that of the RNA polymerase (nucleosidetriphosphate:RNA nucleotidyltransferase, EC 2.7.7.6) to the promoter, thus demonstrating functional overlap of the operator and promoter sites. Images

Majors, J

1975-01-01

232

?-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

233

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.

Ghoshal, Goutam; Oelze, Michael L.

2012-01-01

234

Evaluation of Impact Attenuators.  

National Technical Information Service (NTIS)

The report investigates the cost-effectiveness of various design alternatives and operating polices for crash attenuators. Methods are developed to determine the preferred designs, restoration priorities and inventory policies under various circumstances....

F. Khorsandian P. Schonfeld

1988-01-01

235

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

236

Attenuated Familial Adenomatous Polyposis  

MedlinePLUS

... has been reviewed and approved by the Cancer.Net Editorial Board , 4/2013 Overview What is attenuated ... 4% to 12% Pancreatic cancer 2% Stomach cancer 0.5% What are the screening options for AFAP? ...

237

Complexation in the LaC13-CuC12 and LaC13-CuC12-KC1 systems according to spectroscopic data  

SciTech Connect

This paper describes a study of the complexation processes in the LaC1/sub 3/-CuC1/sub 2/ and LaC1/sub 3/-CuC1/sub 2/-KC1 salt systems with the mole ratios LaC1/sub 3/:CuC1/sub 2/ = m (0.33, 0.5, 1, 1) and KC1: CuC1/sub 2/ = n (0.5, 1,2) at temperatures from 200 to 350 degrees C, both in the presence and absence of the original reactants in the oxidation of hydrogen chloride, which is catalyzed by them. On the basis of the electronic diffuse reflectance spectra recorded from the catalysts in an atmosphere of nitrogen, hydrogen chloride, and molecular oxygen, it has been concluded that the oxidation of hydrogen chloride to melocular chlorine is caused by the relaying of electrons from the C1- ions of lanthanum chloride and HC1 through a copper atom to oxygen.

Utorov, N.P.; Bakshi, Y.M.; Bazov, V.P.; GEl'bshtein, A.I.

1986-03-01

238

Generalized Gaunt coefficients  

Microsoft Academic Search

Solid-harmonic derivatives of solid-harmonic-Gaussian integrals are evaluated. Cross differentiation and the n-j generalized Gaunt coefficients are defined. The generalized Gaunt coefficients ensure that cross differentiation in uncoupled, n-center, solid-harmonic derivatives of rotationally invariant Gaussian matrix elements subtracts zero total angular momentum. This preserves the spherical-tensor properties of quantum-chemical matrix elements. The generalized Gaunt coefficients are (n-1)-dimensional objects because the sum

Brett I. Dunlap

2002-01-01

239

Fiber Optic Attenuators  

NASA Technical Reports Server (NTRS)

Mike Buzzetti designed a fiber optic attenuator while working at Jet Propulsion Laboratory, intended for use in NASA's Deep Space Network. Buzzetti subsequently patented and received an exclusive license to commercialize the device, and founded Nanometer Technologies to produce it. The attenuator functions without introducing measurable back-reflection or insertion loss, and is relatively insensitive to vibration and changes in temperature. Applications include cable television, telephone networks, other signal distribution networks, and laboratory instrumentation.

1995-01-01

240

Binomial Coefficient Model  

NSDL National Science Digital Library

The Binomial Coefficient model displays the number of ways k objects can be chosen from among n objects when order is irrelevant.   This number is known as a binomial coefficient and can be used to predict the the flipping of n coins with equal probability of heads and tails. The Binomial Coefficient model was created using the Easy Java Simulations (EJS) modeling tool. It is distributed as a ready-to-run (compiled) Java archive. Double clicking the ejs_stp_BinomialCoefficient.jar file will run the program if Java is installed.

Christian, Wolfgang

2010-04-11

241

Comparison of ultrasound attenuation tomography methods for breast imaging  

NASA Astrophysics Data System (ADS)

Ultrasound attenuation parameters of breast masses are closely related to their types and pathological states, therefore, it is essential to reliably estimate attenuation parameters for quantitative breast tissue characterization. We study the applicability of three different attenuation tomography methods for ultrasound breast imaging using a ring transducer array. The first method uses the amplitude decays of signals transmitted through the breast to reconstruct attenuation coefficients. The second method employs the spectral ratios between the pulse propagating through the breast and that through water to obtain attenuation parameters. The third method makes use of the complex energy ratios estimated using the amplitude envelopes of transmitted signals. We use in vitro and in vivo breast data acquired with a clinical ultrasound breast imaging system (CURE) to compare these tomography methods. Our results show that the amplitude decay method yields attenuation coefficients with more artifacts than the other two methods. There is bias and variability in the estimated attenuation using the spectral ratio due to its sensitivity to different temporal band-widths and signal-to-noise-ratios of the data. The method based on the complex signal energy ratio is more robust than the other two methods and yields images with fewer artifacts.

Li, Cuiping; Duric, Neb; Huang, Lianjie

2008-04-01

242

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

Microsoft Academic Search

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

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

1996-01-01

243

Laser Measurement Of Convective-Heat-Transfer Coefficient  

NASA Technical Reports Server (NTRS)

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

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

1994-01-01

244

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

245

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

246

Topology of the lac carrier protein in the membrane of Escherichia coli.  

PubMed Central

Proteolysis of topologically sealed right-side-out and inside-out membrane vesicles from Escherichia coli with chymotrypsin, trypsin, or papain inactivates lac carrier function in a symmetrical manner. Concomitantly, the electrophoretic mobility of lac carrier protein photoaffinity labeled in situ with p-nitro[2-3H]phenyl-alpha-D-galactopyranoside is altered from a relative Mr of 33,000 to 20,000, and the time course of proteolysis is almost identical in vesicles of opposite polarities. In contrast, solubilization of the vesicles in NaDodSO4 followed by proteolysis causes fragmentation of the Mr 33,000 band into material that electrophoreses at the solvent front. Notably, proteolysis has no effect whatsoever on the ability of the lac carrier protein to bind substrate, as judged by photoaffinity-labeling experiments. Furthermore, the electrophoretic patterns of samples proteolyzed prior to photoaffinity labeling are the same as those observed when the procedures are reversed. These results show that the lac carrier protein spans the membrane and indicate that the binding site resides within a segment that is embedded in the bilayer. Images

Goldkorn, T; Rimon, G; Kaback, H R

1983-01-01

247

Extension of the Lac du Bouchet palaeomagnetic record over the last 120,000 years  

Microsoft Academic Search

A high-resolution profile of the palaeomagnetic variations recorded in the upper 20 m of the Lac du Bouchet sedimentary sequence has been reconstructed from several parallel Mackereth and ``Livingstone'' type cores. Inter-core correlations were established by comparing individual core profiles of magnetic susceptibility. Individual records of AF cleaned directions were then ``stretched'' to a common depth scale and merged; the

N. Thouveny; K. M. Creer; I. Blunk

1990-01-01

248

Third Party Evaluations. Experience Based Career Education Project. Fond du Lac Public School System.  

ERIC Educational Resources Information Center

Evaluations of the three years of the Fond du Lac public school system experience-based career education (EBCE) project are described in this three-part report. The two major sections of each evaluation are assessments of the achievement of student outcome objectives and of process objectives based on data collected through the use of standardized…

Nelson, Orville; And Others

249

Confirmation of the emisison-line redshift of the BL Lac object PKS 0215 + 015  

Microsoft Academic Search

Spectroscopic observations of the BL Lac object PKS 0215 + 015 during a faint phase are presented. Lyman-alpha and C IV 1548, 1550 A broad emission lines are seen at a redshift z = 1.715. This observation confirms the earlier redshift estimate, which was based upon the absorption-line spectrum observed when the object was approximately three mag brighter. 8 references.

Craig B. Foltz

1987-01-01

250

Plant Species Checklist for the Lac des Allemands Swamp Area of Louisiana.  

National Technical Information Service (NTIS)

The publication is a compilation of a checklist of plants found in Lac Des Allemands Swamp area of Louisiana. The following list is composed of those plants personally observed by the authors. Within the swamp two forest types were studied--bottomland and...

W. H. Conner R. E. Noble J. W. Day

1975-01-01

251

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

252

Radio spectra of a sample of X-ray selected BL Lacs  

Microsoft Academic Search

We present simultaneous multifrequency radio observations for a complete subsample of 26 XBLs from the Einstein Extended Medium-Sensitivity Survey, obtained with the Very Large Array (VLA). Spectra are computed using fluxes at 20, 6 and 3.6 cm. Unlike many radio selected samples, the EMSS did not impose any criterion on the radio spectrum to identify BL Lac objects. It is

Francesca Cavallotti; Anna Wolter; J. T. Stocke; Travis Rector

2004-01-01

253

Through a Glass, Darkly:1 Reflections of Mutation From lacI Transgenic Mice  

Microsoft Academic Search

The study of mutational frequency (Mf) and specificity in aging Big Blue lacI transgenic mice provides a unique opportunity to determine mutation rates (MR) in vivo in different tissues. We found that MR are not static, but rather, vary with the age or developmental stage of the tissue. Although Mf increase more rapidly early in life, MR are actually lower

Gregory R. Stuart; Barry W. Glickman

254

A theoretical interpretation of the radio outbursts of BL Lac objects and other rapidly variable sources  

NASA Technical Reports Server (NTRS)

Relativistic kinematics and superluminal effects in compact extragalactic radio sources are considered. A relativistic blast-wave model is applied to an outburst observed in the BL Lac object AO 0235+164. It is shown that the model can explain in detail the observed nature of variable extragalactic radio sources.

Marscher, A. P.

1978-01-01

255

Activation of the lac Genes of Tn951 by Insertion Sequences from 'Pseudomonas cepacia'.  

National Technical Information Service (NTIS)

Several transposable gene-activating elements from Pseudomonas cepacia have been identified on the basis of their ability to increase expression of the lac genes of the broad-host-range plasmid pGC91.14. When introduced into auxotrophic derivatives of P. ...

M. S. Wood C. Lory T. G. Lessie

1990-01-01

256

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

257

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

NASA Technical Reports Server (NTRS)

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

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

1993-01-01

258

Development of new inbred transgenic strains of rats with LacZ or GFP  

Microsoft Academic Search

The ideal goal of regeneration medicine is to restore form and function to damaged tissues. While stem cell transplantation is considered a promising therapeutic approach, knowing the fate of transplanted cells using appropriate markers is essential. We developed new inbred transgenic rat strains with lacZ and GFP based on the transgenic (Tg) animal technique in rats. These Tg animals expressed

Hirokazu Inoue; Ichiro Ohsawa; Takashi Murakami; Atsushi Kimura; Yoji Hakamata; Yuki Sato; Takashi Kaneko; Masafumi Takahashi; Takashi Okada; Keiya Ozawa; Jeremy Francis; Paola Leone; Eiji Kobayashi

2005-01-01

259

Development of a LAC4 promoter-based gratuitous induction system in Kluyveromyces lactis.  

PubMed

A gratuitous induction system based on the strong, indigenous LAC4 promoter was developed for Kluyveromyces lactis. To prevent consumption of the inducer galactose, a strain with a gal1-209 mutation was employed; this mutation disables the galactokinase function but retains the regulatory function for induction. The Escherichia coli lacZ gene (encoding beta-galactosidase) is functional in K. lactis and was used as the reporter gene downstream of the LAC4 promoter on a multicopy plasmid. The gal1-209 strain exhibited several unexpected phenomena, including partial consumption of the inducer galactose (although at a much slower rate relative to GAL1 strains) and growth inhibition at high concentrations of galactose. These unusual characteristics, however, did not prevent the successful construction of a strong gratuitous induction system. Due to the low rate of inducer consumption for the gratuitous strain, very low concentrations of galactose (1:20 galactose:glucose) resulted in high-level induction. Under these conditions, beta-galactosidase specific and volumetric activities were 4.2- and 5.5-fold higher, respectively, than those for the "GAL1" nongratuitous strain. This research demonstrated the improved productivity possible via LAC4 promoter-based gratuitous induction (and thus a more stable inducer concentration). The effects of various carbon source concentrations on growth and induction were also determined. PMID:10620756

Hsieh, H B; Da Silva, N A

2000-02-20

260

Deterministic and stochastic population-level simulations of an artificial lac operon genetic network  

PubMed Central

Background The lac operon genetic switch is considered as a paradigm of genetic regulation. This system has a positive feedback loop due to the LacY permease boosting its own production by the facilitated transport of inducer into the cell and the subsequent de-repression of the lac operon genes. Previously, we have investigated the effect of stochasticity in an artificial lac operon network at the single cell level by comparing corresponding deterministic and stochastic kinetic models. Results This work focuses on the dynamics of cell populations by incorporating the above kinetic scheme into two Monte Carlo (MC) simulation frameworks. The first MC framework assumes stochastic reaction occurrence, accounts for stochastic DNA duplication, division and partitioning and tracks all daughter cells to obtain the statistics of the entire cell population. In order to better understand how stochastic effects shape cell population distributions, we develop a second framework that assumes deterministic reaction dynamics. By comparing the predictions of the two frameworks, we conclude that stochasticity can create or destroy bimodality, and may enhance phenotypic heterogeneity. Conclusions Our results show how various sources of stochasticity act in synergy with the positive feedback architecture, thereby shaping the behavior at the cell population level. Further, the insights obtained from the present study allow us to construct simpler and less computationally intensive models that can closely approximate the dynamics of heterogeneous cell populations.

2011-01-01

261

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

SciTech Connect

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

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

2013-02-20

262

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

Microsoft Academic Search

A multiproxy paleoecological investigation of Lac la Biche, a large boreal lake in northeastern Alberta, Canada, revealed that the lake was eutrophic before European settlement but has undergone additional cultural eutrophication in the past 30 to 50 years. Annual fluxes to sediments of phosphorus, nitrogen, carbon, and inorganic sediments have in- creased with time. A declining N-P ratio has increasingly

D. W. Schindler; Alexander P. Wolfe; Rolf Vinebrooke; Angela Crowe; Jules M. Blais; Brenda Miskimmin; Rina Freed; Bianca Perren

2008-01-01

263

Tracking micrometastasis to multiple organs with lacZ-tagged CWR22R prostate carcinoma cells.  

PubMed

Metastasis to organs other than lung is rarely observed in animal model systems 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 cell line isolated from the CWR22R xenograft (primary tumor). Three clones of varying lacZ-expression stability were analyzed for tumorigenicity and progression in athymic nude mice. Clones B and D were highly tumorigenic in the subcutis; however, lacZ expression was highly unstable. In contrast, clone H demonstrated highly stable lacZ expression for >25 passages in culture or in animals. Clone H, injected sc in a PBS vehicle, gave a 15-40% tumorigenic take. All primary tumor-bearing animals exhibited micrometastases in lung and other organs. Clone H injected in a Matrigel vehicle gave 100% tumorigenicity, with all animals displaying micrometastases in lung, liver, and/or bone (lower frequency in brain and kidney). Overall, the relative frequency of micrometastasis to multiple organs was lung>liver=bone>brain>kidney. Overt metastases were never observed in the lung or bone but were occasionally found in liver. lacZ-transfected clone H CWR22Rv1 cells represent a much more accurate model of metastasis of PCA to the organs normally involved in progression of the human disease. Use of marker gene-tagged cells and other high-resolution molecular techniques will now permit analyses of the earliest events in PCA progression and micrometastasis. PMID:10769048

Holleran, J L; Miller, C J; Culp, L A

2000-05-01

264

Radio to X-Ray distribution of BL Lac Objects (Giommi+, 1995)  

NASA Astrophysics Data System (ADS)

We present multifrequency spectra of a large number of radio and X-ray selected BL Lacertae objects constructed using non-simultaneous archival data. The data were obtained using the European Space Information System (ESIS) and are from several radio and optical catalogues, the IRAS Faint Source Catalogue, the Einstein and the EXOSAT databases. The sample includes 121 BL Lacs that have been extracted from the 1Jy (1991ApJ...374..431S) and the S4 (1994A&AS..103..349S) radio surveys, the Einstein IPC Slew Survey, the Einstein Extended Medium Sensitivity Survey (EMSS), the EXOSAT High Galactic Latitude Survey, and from the compilations of Giommi et al. (1990ApJ...356..432G) and Veron & Veron (1993ESOSR..13....1V). We find that the shape of the radio to infra-red spectrum of Radio Selected and X-ray Selected BL Lacs is very similar. The difference between these two classes of objects is instead evident in the optical/X-ray part of the spectrum. The classical radio discovered BL Lacs are characterized by an energy spectrum with a sharp cutoff in the IR/optical band while in most of the X-ray discovered objects the turnover is located near the UV/X-ray band or at higher frequencies. For a given X-ray flux this diversity can give rise to radio fluxes different by a factor of 100 or more. We argue that BL Lac objects may be a single population of sources characterized by a wide range of energy cutoffs. In this scenario BL Lacs discovered in radio surveys are representative of the entire population, while objects characterized by an energy break near the X-ray band, which are abundantly detected at X-ray frequencies, are intrinsically a small minority. (5 data files).

Giommi, P.; Ansari, S. G.; Micol, A.

1995-02-01

265

Substrate-induced changes in the structural properties of LacY.  

PubMed

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 Cys154Gly do not change upon sugar binding. It is also observed that the single mutation of Cys154Gly 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; Müller, Daniel J

2014-04-22

266

Coefficient Color Constancy  

NASA Astrophysics Data System (ADS)

The goal of color constancy is to take the color responses (for example camera rgb triplets) of surfaces viewed under nn unknown illuminant and map them to illuminant independent descriptors. In existing theories this mapping is either a general linear 3 times 3 matrix or a simple diagonal matrix of scaling coefficients. The general theories have the advantage that the illuminant can be accurately discounted but have the disadvantage that nine parameters must be recovered. Conversely while the coefficient theories have only three unknowns, a diagonal matrix may only partially discount the illuminant. My starting point in this thesis is to generalize the coefficient approach; the goal is to retain its inherent simplicity while at the same time increasing its expressive power. Under the generalized coefficient scheme, I propose that a visual system transforms responses to a new sensor basis before applying the scaling coefficients. I present methods for choosing the best coefficient basis for a variety of statistical models of color responses. These models are rich enough that the generalized coefficient approach suffices for almost all possible sensor sets. To achieve color constancy the correct coefficients must be recovered. Existing algorithms can do so only when strong constraints are satisfied. For example it is often assumed that there is a white reflectance in every scene. In the second part of any thesis, I develop a new coefficient algorithm, which I call color in perspective, based on very weak (and very reasonable) assumptions about the world. I assume only that the range of color responses induced by different reflectances varies with a change in illumination and that illumination itself can vary only within certain bounds. I tested the algorithm on real images taken with a color video camera--extremely good constancy is delivered. Indeed the degree of constancy compares favorably with the best which is theoretically possible. The methods developed in this thesis can be applied to a variety of other areas: including color graphics, color reproduction and color appearance models.

Finlayson, Graham David

1995-01-01

267

Radiofrequency attenuator and method  

DOEpatents

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

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

2009-01-20

268

Strength Coefficient of Materials.  

National Technical Information Service (NTIS)

South Dakota's, previously conducted, Flexible Pavement Study indicated a relationship between Strength and Effective Thickness. It was apparent that a simple slope formula used for any two points on the curve produced strength coefficients. The slope of ...

R. A. Crawford

1971-01-01

269

Drag Coefficients of Cones.  

National Technical Information Service (NTIS)

The objective was to provide experimental values for cone drag coefficients in the near free molecule and transitional flow regimes including an examination of the effects of Mach number, wall speed ratio, bluntness, and specific heat ratio. A modulated f...

J. F. Wendt

1972-01-01

270

Coefficients of Effective Length.  

ERIC Educational Resources Information Center

Under certain conditions, a validity Coefficient of Effective Length (CEL) can produce highly misleading results. A modified coefficent is suggested for use when empirical studies indicate that underlying assumptions have been violated. (Author/BW)

Edwards, Roger H.

1981-01-01

271

Statistical Model for Diffusion Attenuated MR Signal  

PubMed Central

A general statistical model that can describe a rather large number of experimental results related to the structure of the diffusion-attenuated MR signal in biological systems is introduced. The theoretical framework relies on a phenomenological model that introduces a distribution function for tissue apparent diffusion coefficients (ADC). It is shown that at least two parameters—the position of distribution maxima (ADC) and the distribution width (?)—are needed to describe the MR signal in most regions of a human brain. A substantial distribution width, on the order of 36% of the ADC, was found for practically all brain regions examined. This method of modeling the MR diffusion measurement allows determination of an intrinsic tissue-specific ADC for a given diffusion time independent of the strength of diffusion sensitizing gradients. The model accounts for the previously found biexponential behavior of the diffusion-attenuated MR signal in CNS.

Yablonskiy, Dmitriy A.; Bretthorst, G. Larry; Ackerman, Joseph J.H.

2007-01-01

272

Enhanced Bacterial Protein Expression During Auto-induction Obtained by Alteration of Lac Repressor Dosage and Medium Composition  

PubMed Central

The auto-induction method of protein expression in E. coli is based on diauxic growth resulting from dynamic function of lac operon regulatory elements (lacO and LacI) in mixtures of glucose, glycerol and lactose. The results show that successful execution of auto-induction is strongly dependent on the plasmid promoter and repressor construction, on the oxygenation state of the culture, and on the composition of the auto-induction medium. Thus expression hosts expressing high levels of LacI during aerobic growth exhibit reduced ability to effectively complete the auto-induction process. Manipulation of the promoter to decrease the expression of LacI altered the preference for lactose consumption in a manner that led to increased protein expression and partially relieved the sensitivity of the auto-induction process to the oxygenation state of the culture. Factorial design methods were used to optimize the chemically defined growth medium used for expression of two model proteins, Photinus luciferase and enhanced green fluorescent protein, including variations for production of both unlabeled and selenomethionine-labeled samples. The optimization included studies of the expression from T7 and T7-lacI promoter plasmids and from T5 phage promoter plasmids expressing two levels of LacI. Upon the basis of the analysis of over 500 independent expression results, combinations of optimized expression media and expression plasmids that gave protein yields of greater than 1000 ?g/mL of expression culture were identified.

Blommel, Paul G.; Becker, Katie J.; Duvnjak, Petar

2009-01-01

273

[Ultrasound attenuation in calcaneus and bone density].  

PubMed

Broadband ultrasound attenuation (BUA) is a new technique for investigating bone status. We evaluated its use in osteoporosis. To assess in vivo reproducibility, we determined the coefficient of variation (cv) on the basis of five measurements (with repositioning) of the same foot in 50 women. The cv was 2.8 +/- 1.7%. BUA values were similar in the right feet and left foot and were correlated with bone density in the calcaneal area investigated (r = 0.8, p < 10(-4). BUA of the calcaneus was correlated with bone density in the lumbar spine, femur, and forearm in 240 healthy postmenopausal women (correlation coefficients 0.36 to 0.55; p < 10(-4)). BUA decreased with age, with a sharper drop during the first years following menopause. Mean broadband ultrasonic attenuation in 37 females with osteoporosis (58.92 +/- 11.59 dB/MHz) is lower than controls (66.10 +/- 15.29 dB/MHz, p = 0.04). Areas under receiver operating characteristic curves, used to evaluate the discriminating value of BUA in osteoporosis and osteopenia, were 0.79 and 0.72, respectively. The kappa coefficient of concordance between BUA and spinal density was 0.59. These data demonstrate that BUA cannot replace bone density measurements. Prospective studies are needed to investigate the potential role of this technique for identifying women at high risk for osteoporotic fractures. PMID:8012315

Roux, C; Lemonnier, E; Kolta, S; Charpentier, E; Dougados, M; Amor, B; Viens-Bitker, C

1993-12-01

274

Stress wave attenuation in shock-damaged rock  

NASA Astrophysics Data System (ADS)

The velocity and attenuation of ultrasonic stress waves in gabbroic rock samples (San Marcos, California) subjected to shock loading in the 2 GPa range were studied. Prom P wave velocity measurements we determined the damage parameter Dp and crack density ? of the samples and related these to the attenuation coefficient (quality factor) under dynamic strains of 2×10-7 and at a frequency of 2 MHz using the ultrasonic pulse-echo method. A fit to the data yields the P wave spatial attenuation coefficient at a frequency of 2 MHz, ?p(Dp) = 1.1 + 28.2DP (decibels per centimeter). From the relation between the attenuation coefficient and quality factor, the quality factor Q is given by Q-1 = 0.011(1 + 25.6Dp)(1 - Dp)½. Using O'Connell-Budiansky theory relating crack density to velocity, the parameter in Walsh's theory was determined based on experimental data. An approximate method is also proposed to estimate the average half-length of cracks based on the attenuation measurements.

Liu, Cangli; Ahrens, Thomas J.

1997-03-01

275

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

276

Use of Urea and Glycine Betaine to Quantify Coupled Folding and Probe the Burial of DNA Phosphates in Lac Repressor - Lac Operator Binding  

PubMed Central

Thermodynamic analysis of urea-biopolymer interactions and urea effects on folding of proteins and ?-helical peptides shows that urea interacts primarily with polar amide surface. Urea is therefore predicted to be a quantitative probe of coupled folding, remodeling and other large-scale changes in the amount of water-accessible polar amide surface in protein processes. A parallel analysis indicates that glycine betaine (N,N,N-trimethyl glycine; GB) can be used to detect burial or exposure of anionic (carboxylate, phosphate) biopolymer surface. To test these predictions, we have investigated the effects of these solutes (0 to 3 molal) on the formation of 1:1 complexes between lac repressor (LacI) and its symmetric operator site (SymL) at constant KCl molality. Urea reduces the binding constant KTO (initial slope dln KTO/dmurea = ?1.7 ± 0.2) and GB increases KTO (initial slope dln KTO/dmGB = + 2.1 ± 0.2). For both solutes, this derivative decreases with increasing solute concentration. Analysis of these initial slopes predicts that (1.5 ± 0.3) × 103 Å2 of polar amide surface and (4.5 ± 1.0) × 102 Å2 of anionic surface are buried in the association process. Analysis of published structural data, together with modeling of unfolded regions of free LacI as extended chains, indicates that 1.5 × 103 Å2 of polar amide surface and 6.3 × 102 Å2 of anionic surface are buried in complexation. Quantitative agreement between structural and thermodynamic results is obtained for amide surface (urea); for anionic surface (GB), the experimental value is ~70% of the structural value. For LacI-SymL binding, two thirds of the structurally-predicted change in amide surface (1.0 × 103 Å2) occurs outside the protein-DNA interface in protein-protein interfaces formed by folding of the hinge helices and interactions of the DNA binding domain (DBD) with the core of repressor. Since urea interacts principally with amide surface, it is particularly well-suited to detect and quantify the extent of coupled folding and other large-scale remodeling events in the steps of protein-nucleic acid interactions and other protein associations.

Hong, Jiang; Capp, Mike W.; Saecker, Ruth M.; Record, M. Thomas

2008-01-01

277

Monte Carlo-based down-scatter correction of SPECT attenuation maps  

Microsoft Academic Search

Combined acquisition of transmission and emission data in single-photon emission computed tomography (SPECT) can be used for correction of non-uniform photon attenuation. However, down-scatter from a higher energy isotope (e.g. 99mTc) contaminates lower energy transmission data (e.g. 153Gd, 100 keV), resulting in underestimation of reconstructed attenuation coefficients. Window-based corrections are often not very accurate and increase noise in attenuation maps. We

Tomislav Bokuli?; Brendan Vastenhouw; Hugo W. A. M. de Jong; Alice J. van Dongen; Peter P. van Rijk; Freek J. Beekman

2004-01-01

278

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

279

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

NASA Astrophysics Data System (ADS)

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

Karttunen, Jaana; Shastri, Nilabh

1991-05-01

280

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

281

Rain Attenuation Studies.  

National Technical Information Service (NTIS)

The statistical properties of rain attenuation which dominate propogation at frequencies above 10 GHz are required for planning radio systems at these frequencies. These properties are studied for three frequencies, 11.2, 12.7 and 18.76 GHz and various li...

G. Drufuca

1973-01-01

282

Relationships of ultrasonic backscatter with ultrasonic attenuation, sound speed and bone mineral density in human calcaneus  

Microsoft Academic Search

Ultrasonic attenuation and sound speed have been investigated in trabecular bone by numerous authors. Ultrasonic backscatter has received much less attention. To investigate relationships among these three ultrasonic parameters and bone mineral density (BMD), 30 defatted human calcanei were investigated in vitro. Normalized broadband ultrasonic attenuation (nBUA), sound speed (SOS), and logarithm of ultrasonic backscatter coefficient (LBC) were measured. Bone

Keith A Wear; Angela P Stuber; James C Reynolds

2000-01-01

283

The effect of structural disorder on anomalous critical attenuation of ultrasound by solids  

NASA Astrophysics Data System (ADS)

A field-theory description of dynamic effects of acoustic wave propagation in solids under phase transition is performed. The effects of structure defects on critical attenuation of ultrasound in Ising-like three-dimensional systems is discussed. Calculations of the attenuation coefficient and scaling function are carried out in a two-loop approximation for regular and disordered systems.

Prudnikov, P. V.; Prudnikov, V. V.

2007-05-01

284

Testing the FR I/BL Lac unifying model with HST observations  

NASA Astrophysics Data System (ADS)

Hubble Space Telescope (HST) observations provide a novel way of testing unified models for FR I radio sources and BL Lac objects. The detection of extended dust discs in some radio galaxies provides information on their jet orientation. Given this, the strength of the compact nuclear sources of FR I and BL Lacs can be compared with model predictions. As a pilot project towards using HST information in testing unified models, we selected five radio galaxies that show extended nuclear discs in the HST images. The relative orientation of the projected radio jets and of the extended nuclear discs indicates that they are not perpendicular, as the simplest geometrical model would suggest, but that they form an angle of ~20-40 with the symmetry axis of the disc: a significant change of orientation occurs between the innermost AGN structure and the kiloparsec scale. Nevertheless, the discs appear to be useful indicators of the orientation of the radio source, since the angles formed by the disc axis and the jet with the line of sight differ by only ~10-20. At the centre of each disc an unresolved nuclear source is present. We compared its luminosity with the optical core luminosity of BL Lacs selected for having similar host galaxy magnitude and extended radio luminosity. The BL Lac cores are between 2x10^2 and 3x10^5 times brighter than the corresponding radio galaxy ones. The FR I/BL Lac core luminosity ratio shows a suggestive correlation with the orientation of the radio galaxies with respect to the line of sight. The behaviour of this ratio is quantitatively consistent with a scenario in which the emission in the FR I and BL Lac sources is dominated by the beamed radiation from a relativistic jet with Doppler factor ~5-10, thus supporting the basic features of the proposed unification schemes. Several observational tests, based on the method proposed here, can strengthen our conclusions and improve the statistical significance of the findings presented.

Capetti, Alessandro; Celotti, Annalisa

1999-04-01

285

Performance Evaluation of Light Emission Models in Light Attenuating Media  

Microsoft Academic Search

The light distribution models developed in the literature have been mostly tested by conducting experiments in an annular reactor full of either air or deionized water, where the attenuating coefficients of the media were assumed to be zero. Although many of these models have predictive capability of the effect of absorbing media according to the Beer–Lambert law, their real performance

Quan Yang; Simo O. Pehkonen; Madhumita B. Ray

2005-01-01

286

X-Ray Attenuation and Absorption for Materials of Dosimetric Interest  

National Institute of Standards and Technology Data Gateway

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

287

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

Microsoft Academic Search

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

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

1999-01-01

288

Attenuation compensation in mesh-domain OSEM SPECT reconstruction  

NASA Astrophysics Data System (ADS)

A new method for attenuation compensation (AC) in mesh-domain SPECT OSEM reconstruction using strip-area approximation (SAAC) is introduced and compared to single-ray AC (SRAC). SAAC uses the polygonal area of the intersection of a mesh element (ME) and a tube-of-response (TOR) for defining an effective length of photon transit and an effective attenuation coefficient. This approach to AC is compared to SRAC, which defines the effective length of photon transit as the intersection of a single ray and a ME and the effective attenuation coefficient as the mean along the ray path. Comparative quantitative and qualitative analysis demonstrated that SAAC outperformed SRAC in terms of reconstruction image accuracy and quality.

Vogelsang, Levon; Lu, Yao; Yu, Bo; Krol, Andrzej; Xu, Yuesheng; Hu, Xiaofei; Feiglin, David; Lipson, Edward

2009-02-01

289

The effect of spo0 mutations on the expression of spo0A - and spo0F-lacZ fusions  

Microsoft Academic Search

Summary  We have constructedspo0A-lacZ andspo0F-lacZ fusions with a temperate phage vector and have investigated howspo0 gene products are involved in the expression of each of these genes. The expression ofspo0A-lacZ andspo0F-lacZ was stimulated at about the time of cessation of vegetative growth in Spo+ cells. This stimulation ofspo0A-lacZ was impaired by mutations in thespo0B, D, E, F orH genes but was

Shinya Yamashita; Hirofumi Yoshikawa; Fujio Kawamura; Hideo Takahashi; Tatsuo Yamamoto; Yasuo Kobayashi; Hiuga Saito

1986-01-01

290

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

291

Frequency Dependent Attenuation in Rocks.  

National Technical Information Service (NTIS)

An inconsistency in experimental stress-strain data for attenuation determinations is investigated. Attenuation (1/Q) calculated from the integrated areas of plotted hysteresis loops depend on the definition of maximum strain energy. If maximum strain ene...

K. B. Coyner R. J. Martin

1990-01-01

292

Radiation and attenuation of waves in a random medium  

NASA Technical Reports Server (NTRS)

The physical mechanisms of excess attenuation are analyzed on the basis of a one-dimensional time-independent model of propagation in a random medium. Attenuation is regarded as the rate of decrease in the mean intensity and the mean energy flux within a propagation range. A source function is assumed to be determinate, appropriate statistical properties are chosen for the sound speed, and specified statistical properties are found for the wave functions, i.e., the mean intensity and the mean energy flux. The medium is considered to be weakly homogeneous, and expansions are developed for the intensity and mean energy flux, along with an attenuation coefficient in two parts, the second of which defines the excess attenuation. The mean radiated power is defined, and backscattering by the random inhomogeneities in the medium is modeled as redistributing the mean intensity and energy flux, with a resultant decay which occurs more quickly than with randomness.

Wenzel, A. R.

1982-01-01

293

Attenuation Measurements of Cell Pellets Using Through Transmission  

NASA Astrophysics Data System (ADS)

A better understanding of differences in ultrasound tissue characteristics (such as speed of sound, attenuation, and backscatter coefficients) of benign compared to malignant cells could lead to improved cancer detection and diagnosis. A narrow band technique for measuring ultrasonic speed of sound and attenuation of small biological materials was developed and tested. Several mechanical improvements were made to the system to drastically improve alignment, allowing for accurate measurements of small cell pellets. Narrow band attenuation measurements were made first with tissue-mimicking phantoms and then with three different types of cell pellets: Chinese hamster ovary cells, healthy human prostate cells, and cancerous human prostate cells. Attenuation and speed of sound results for all three cell types, as well as the culture medium and tissue mimicking phantoms, are presented for a frequency range of 5 to 25 MHz.

Vadas, Justin; Greene, Claudia; Grygotis, Emma; Kuhn, Stephen; Mahlalela, Sanele; Newland, Tinisha; Ovutmen, Idil; Herd, Maria-Teresa

2011-10-01

294

A closer view of the conformation of the Lac repressor bound to operator.  

PubMed

Crystal structures of the Lac repressor, with and without isopropyithiogalactoside (IPTG), and the repressor bound to operator have provided a model for how the binding of the inducer reduces the affinity of the repressor for the operator. However, because of the low resolution of the operator-bound structure (4.8 A), the model for the allosteric transition was presented in terms of structural elements rather than in terms of side chain interactions. Here we have constructed a dimeric Lac repressor and determined its structure at 2.6 A resolution in complex with a symmetric operator and the anti-inducer orthonitrophenylfucoside (ONPF). The structure enables the induced (IPTG-bound) and repressed (operator-bound) conformations of the repressor to be compared in atomic detail. An extensive network of interactions between the DNA-binding and core domains of the repressor suggests a possible mechanism for the allosteric transition. PMID:10700279

Bell, C E; Lewis, M

2000-03-01

295

BeppoSAX spectral survey of BL Lacs - New spectra and results  

NASA Astrophysics Data System (ADS)

We present BeppoSAX LECS, MECS, and PDS spectra of eleven X-ray selected BL Lacertae objects. Combining these sources with the ones presented elsewhere we have a sample of 21 BL Lacs from the Einstein Medium Sensitivity and Einstein Slew Survey. The sample shows strong correlations of several physical parameters with the peak frequency of the synchrotron branch of the spectral energy distribution. In particular the peak frequency is correlated with the X-ray spectral shape: objects with the peak near to the X-ray band show harder and straighter X-ray spectra than those of the low energy peaked sources. This work shows that the recently proposed unification scenario for different types of blazars can hold also within the class of high frequency peaked BL Lac objects.

Beckmann, V.; Wolter, A.; Celotti, A.; Costamante, L.; Ghisellini, G.; Maccacaro, T.; Tagliaferri, G.

2002-02-01

296

The LCLS Gas Attenuator Revisited  

Microsoft Academic Search

In the report ''X-ray attenuation cell'' [1] a preliminary analysis of the gas attenuator for the Linac Coherent Light Source (LCLS) was presented. This analysis was carried out for extremely stringent set of specifications. In particular, a very large diameter for the unobstructed beam was set (1 cm) to accommodate the spontaneous radiation; the attenuator was supposed to cover the

Ryutov

2005-01-01

297

Microinjection of HSV-1 amplicon vector-mediated human proenkephalin into the periaqueductal grey attenuates neuropathic pain in rats.  

PubMed

We investigated the antinociceptive effect of microinjection of HSV-1 amplicon vector-mediated human proenkephalin (hPPE) into the ventral periaqueductal grey (PAG) on neuropathic pain in rats. Male Sprague-Dawley rats with chronic constriction injury (CCI)-induced neuropathic pain were microinjected into the ventral PAG with normal saline (NS), pHSVIRES-lacZ (SHZ), or HSV-1 amplicon vector pHSVIRES-hPPE-lacZ (SHPZ), respectively. Pain thresholds in the SHPZ-treated rats were significantly higher at day 3, then reached peak at day 14 and lasted until day 35 after PAG administration, and these effects were reversed by naloxone. In contrast, NS or SHZ-treated rats did not significantly affect pain thresholds. These results demonstrated that microinjection of HSV-1 amplicon vector-mediated hPPE into the ventral PAG attenuates neuropathic pain in rats. PMID:22082315

Zou, Wangyuan; Huang, Changshen; Yang, Yong; Pan, Yundan; Yan, Jianqin; Guo, Qulian

2012-04-01

298

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

299

Influence of Catabolite Repression and Inducer Exclusion on the Bistable Behavior of the lac Operon  

PubMed Central

A mathematical model of the lac operon which includes all of the known regulatory mechanisms, including external-glucose-dependent catabolite repression and inducer exclusion, as well as the time delays inherent to transcription and translation, is presented. With this model we investigate the influence of external glucose, by means of catabolite repression and the regulation of lactose uptake, on the bistable behavior of this system.

Santillan, Moises; Mackey, Michael C.

2004-01-01

300

lacZ fusions to genes that specify exported proteins: A general technique  

Microsoft Academic Search

We have devised a general, one-step technique for isolation of strains in which the gene coding for an exported protein is fused to the gene for ß-galactosidase (lacZ). These fusions specify a hybrid protein comprised of an NH2-terminal portion of the exported protein and a large functional COOH-terminal portion of ß-galactosidase. The fusions are constructed with a derivative of the

E. Tapio Palva; Thomas J. Silhavy

1984-01-01

301

A set of Hansenula polymorpha integrative vectors to construct lacZ fusions  

Microsoft Academic Search

A set of YEp Saccharomyces cerevisiae-based, integrative Hansenula polymorpha plasmids was constructed to express lacZ gene under yeast gene promoters. The HpLEU2 and HpURA3 genes were used both as markers and to target the integration of plasmids into the corresponding H. polymorpha genome locus. The frequency of transformation reached with these plasmids linearised either in HpLEU2 or HpURA3 was around

N. Brito; M. D. Pérez; G. Perdomo; C. González; P. García-Lugo; J. M. Siverio

1999-01-01

302

RpoS-Regulated Genes of Escherichia coli Identified by Random lacZ Fusion Mutagenesis  

Microsoft Academic Search

RpoS is a conserved alternative sigma factor that regulates the expression of many stress response genes in Escherichia coli. The RpoS regulon is large but has not yet been completely characterized. In this study, we report the identification of over 100 RpoS-dependent fusions in a genetic screen based on the differential expression of an operon-lacZ fusion bank in rpoS mutant

Somalinga R. V. Vijayakumar; Mark G. Kirchhof; Cheryl L. Patten; Herb E. Schellhorn

2004-01-01

303

Defects in fruiting body development caused by Tn5 lac insertions in Myxococcus xanthus.  

PubMed Central

Mutations caused by insertions of Tn5 lac that block development are rare. At least six of the eight mutations examined appeared to be regulatory. Three of these were found to disrupt social motility, suggesting a particular importance for this function. One other occurred in a known cell-cell interaction gene, bsgA, and the remaining two were located in genes operative early in the developmental program. Images FIG. 1 FIG. 2

Kroos, L; Kuspa, A; Kaiser, D

1990-01-01

304

Defects in fruiting body development caused by Tn5 lac insertions in Myxococcus xanthus.  

PubMed

Mutations caused by insertions of Tn5 lac that block development are rare. At least six of the eight mutations examined appeared to be regulatory. Three of these were found to disrupt social motility, suggesting a particular importance for this function. One other occurred in a known cell-cell interaction gene, bsgA, and the remaining two were located in genes operative early in the developmental program. PMID:2152913

Kroos, L; Kuspa, A; Kaiser, D

1990-01-01

305

Clinical and Molecular Aspects of Juvenile Hemochromatosis in Saguenay–Lac-Saint-Jean (Quebec, Canada)  

Microsoft Academic Search

ABSTRACT:We report the clinical, biochemical, and genetic characteristics of 13 hemochromatosis patients from Saguenay–Lac-Saint-Jean in whom the first symptoms appeared before age 30. Although the mean age at onset of the first symptoms was 21.5 years, their mean age at diagnosis was 23.8 years; the diagnosis was particularly delayed among women. Seventy-seven percent of the patients had hypogonadotrophic hypogonadism and

Sylvain R Rivard; Catherine Mura; Hervé Simard; Raynald Simard; Doria Grimard; Gérald Le Gac; Odile Raguenes; Claude Férec; Marc De Braekeleer

2000-01-01

306

Hydrogeologic characteristics of domains of sparsely fractured rock in the granitic Lac Du Bonnet Batholith, southeastern Manitoba, Canada.  

National Technical Information Service (NTIS)

The hydrogeologic characteristics of the granitic Lac du Bonnet batholith in southeastern Manitoba have been studied since 1978, as part of AECL's program to assess the concept of disposing of Canada's nuclear fuel waste deep within plutonic rocks of the ...

D. R. Stevenson E. T. Kozak C. C. Davison M. Gascoyne R. A. Broadfoot

1996-01-01

307

Computational analysis of looping of a large family of highly bent DNA by LacI.  

PubMed

Sequence-dependent intrinsic curvature of DNA influences looping by regulatory proteins such as LacI and NtrC. Curvature can enhance stability and control shape, as observed in LacI loops formed with three designed sequences with operators bracketing an A-tract bend. We explore geometric, topological, and energetic effects of curvature with an analysis of a family of highly bent sequences, using the elastic rod model from previous work. A unifying straight-helical-straight representation uses two phasing parameters to describe sequences composed of two straight segments that flank a common helically supercoiled segment. We exercise the rod model over this two-dimensional space of phasing parameters to evaluate looping behaviors. This design space is found to comprise two subspaces that prefer parallel versus anti-parallel binding topologies. The energetic cost of looping varies from 4 to 12 kT. Molecules can be designed to yield distinct binding topologies as well as hyperstable or hypostable loops and potentially loops that can switch conformations. Loop switching could be a mechanism for control of gene expression. Model predictions for linking numbers and sizes of LacI-DNA loops can be tested using multiple experimental approaches, which coupled with theory could address whether proteins or DNA provide the observed flexibility of protein-DNA loops. PMID:18931251

Lillian, Todd D; Goyal, Sachin; Kahn, Jason D; Meyhöfer, Edgar; Perkins, N C

2008-12-15

308

Two helix DNA binding motif of CAP found in lac repressor and gal repressor.  

PubMed Central

Comparison of both the DNA and protein sequences of catabolite gene activator protein (CAP) with the sequences of lac and gal repressors shows significant homologies between a sequence that forms a two alpha-helix motif in CAP and sequences near the amino terminus of both repressors. This two-helix motif is thought to be involved in specific DNA sequence recognition by CAP. The region in lac repressor to which CAP is homologous contains many i-d mutations that are defective in DNA binding. Less significant sequence homologies between CAP and phage repressors and activators are also shown. The amino acid residues that are critical to the formation of the two-helix motif are conserved, while those residues expected to interact with DNA are variable. These observations suggest the lac and gal repressors also have a two alpha-helix structural motif which is involved in DNA binding and that this two helix motif may be generally found in many bacterial and phage repressors. We conclude that one major mechanism by which proteins can recognize specific base sequences in double stranded DNA is via the amino acid side chains of alpha-helices fitting into the major groove of B-DNA.

Weber, I T; McKay, D B; Steitz, T A

1982-01-01

309

DNA looping increases the range of bistability in a stochastic model of the lac genetic switch  

NASA Astrophysics Data System (ADS)

Conditions and parameters affecting the range of bistability of the lac genetic switch in Escherichia coli are examined for a model which includes DNA looping interactions with the lac repressor and a lactose analogue. This stochastic gene–mRNA–protein model of the lac switch describes DNA looping using a third transcriptional state. We exploit the fast bursting dynamics of mRNA by combining a novel geometric burst extension with the finite state projection method. This limits the number of protein/mRNA states, allowing for an accelerated search of the model's parameter space. We evaluate how the addition of the third state changes the bistability properties of the model and find a critical region of parameter space where the phenotypic switching occurs in a range seen in single molecule fluorescence studies. Stochastic simulations show induction in the looping model is preceded by a rare complete dissociation of the loop followed by an immediate burst of mRNA rather than a slower build up of mRNA as in the two-state model. The overall effect of the looped state is to allow for faster switching times while at the same time further differentiating the uninduced and induced phenotypes. Furthermore, the kinetic parameters are consistent with free energies derived from thermodynamic studies suggesting that this minimal model of DNA looping could have a broader range of application.

Earnest, Tyler M.; Roberts, Elijah; Assaf, Michael; Dahmen, Karin; Luthey-Schulten, Zaida

2013-04-01

310

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

PubMed Central

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

Yu, Pulan; Wild, David J.

2012-01-01

311

'Muprints' of the lac operon demonstrate physiological control over the randomness of in vivo transposition.  

PubMed

A method called Muprinting has been developed that uses PCR to generate a detailed picture of the bacteriophage Mu transposition sites in chosen domains of the bacterial chromosome. Muprinting experiments in Escherichia coli show that the frequency of phage integration changes dramatically near two repressor binding sites in the lac operon. When the lac operon was repressed, hotspots for Mu transposition were found near the O1 and O2 operators that are proposed to make a repression loop. When cells were grown in lactose, Mu transposition near these operators was greatly diminished. Striking changes in transposition frequencies were limited to the control region and were not found in a region of the lacZ gene lying beyond the O2 operator. Muprints of the bgl operon showed a different pattern; hotspots for Mu transposition detected in sequences upstream of the bglC promoter when the operon was silenced changed when the operon became activated by mutation. By targeting transposition to the regulatory regions around non-expressed genes, Mu may demonstrate a self-restraint mechanism that allows the virus to move through its host genome without disrupting the functions that contribute to a healthy cell physiology. PMID:7934890

Wang, X; Higgins, N P

1994-05-01

312

C-band attenuation by tropical rainfall in Darwin, Australia, using climatologically tuned Z(e)-R relations  

NASA Technical Reports Server (NTRS)

The probability matching method (PMM) is used as a basis for estimating attenuation in tropical rains near Darwin, Australia. PMM provides a climatological relationship between measured radar reflectivity and rain rate, which includes the effects of rain and cloud attenuation. When the radar sample is representative, PMM estimates the rainfall without bias. When the data are stratified for greater than average rates, the method no longer compensates for the higher attenuation and the radar rainfall estimates are biased low. The uncompensated attenuation is used to estimate the climatological attenuation coefficient. The two-way attenuation coefficient was found to be 0.0085 dB/km ( mm/h) exp -1.08 for the tropical rains and associated clouds in Darwin for the first two months of the year for horizontally polarized radiation at 5.63 GHz. This unusually large value is discussed. The risks of making real-time corrections for attenuation are also treated.

Atlas, David; Rosenfeld, Daniel; Wolff, David B.

1993-01-01

313

Monitored natural attenuation.  

PubMed

Monitored natural attenuation (MNA) is an in situ remediation technology that relies on naturally occurring and demonstrable processes in soil and groundwater which reduce the mass and concentration of the contaminants. Natural attenuation (NA) involves both aerobic and anaerobic degradation of the contaminants due to the fact that oxygen is used up near the core of the contaminant plume. The aerobic and anaerobic microbial processes can be assessed by microbial activity measurements and molecular biology methods in combination with chemical analyses. The sampling and knowledge on the site conditions are of major importance for the linkage of the results obtained to the conditions in situ. Rates obtained from activity measurements can, with certain limitations, be used in modeling of the fate of contaminants whereas most molecular methods mainly give qualitative information on the microbial community and gene abundances. However, molecular biology methods are fast and describe the in situ communities and avoid the biases inherent to activity assays requiring laboratory incubations. PMID:19882289

Jørgensen, Kirsten S; Salminen, Jani M; Björklöf, Katarina

2010-01-01

314

Natural Attenuation Tool Kit  

NSDL National Science Digital Library

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

315

Differential experimental micrometastasis to lung, liver, and bone with lacZ -tagged CWR22R prostate carcinoma cells  

Microsoft Academic Search

LacZ-tagged human prostate carcinoma CWR22Rv1 cells metastasize spontaneously to lung, liver, and bone from subcutaneous primary tumors in athymic nude mice; these organs are ‘natural’ targets of metastasis for the human disease. To evaluate the mechanism(s) of metastasis to these organs, an experimental metastasis model was used by taking advantage of the ultrasensitive detection of lacZ. Within 1 h after

Julianne L. Holleran; Carson J. Miller; Nancy L. Edgehouse; Theresa P. Pretlow; Lloyd A. Culp

2002-01-01

316

glnF-lacZ fusions in Escherichia coli : studies on glnF expression and its chromosomal orientation  

Microsoft Academic Search

The regulatory gene, glnF, of Escherichia coli was fused to the structural genes of the lac operon by use of the hybrid Mu phage derivative Mudl (Ap lac). Analysis of two of these fusions showed that the glnF gene is expressed constitutively, i.e., independent of either the nitrogen source in the growth medium or the availability of the glnA, glnL,

Irene Castafio; Fernando Bastarrachea

1984-01-01

317

P Regulatory Products Repress in vivo the P Promoter Activity in P-lacZ Fusion Genes  

Microsoft Academic Search

The transposition of P elements in Drosophila melanogaster is regulated by products encoded by the P elements themselves. The molecular mechanisms of this regulation are complex and still unclear. We have assayed in vivo the effects of P regulatory products on the P promoter itself by using P-lacZ fusion genes. We have found that all the P-lacZ insertions are repressed

Bruno Lemaitre; Dario Coen

1991-01-01

318

Regulation of a fos-lacZ Fusion Gene: A Paradigm for Quantitative Analysis of Stimulus-Transcription Coupling  

Microsoft Academic Search

Expression of the c-fos protooncogene is induced by a great variety of extracellular stimuli. A fos-lacZ fusion gene has been constructed that recapitulates this regulation. The fos-lacZ gene was introduced into B104 neuroblastoma cells for use in a quantitative assay for stimulus-transcription coupling. Both alpha- and beta-adrenergic agonists, dibutyryl cAMP, and phorbol ester induced beta-galactosidase activity in a dose-dependent manner.

Karl Schilling; Daniel Luk; James I. Morgan; Tom Curran

1991-01-01

319

Sensorimotor functions in transgenic mice expressing the neurofilament\\/heavy-LacZ fusion protein on two genetic backgrounds  

Microsoft Academic Search

NFH-LacZ transgenic mice are characterized by expression of a non-endogenous fusion protein between a truncated form of mouse NFH (neurofilament of heavy molecular weight) and the complete Escherichia coli ?-galactosidase protein. These transgenic mice were compared to their respective controls on two background strains (C3H and FVB) in several sensorimotor tests. NFH-LacZ mice were deficient in tests requiring balance and

M. Dubois; C. Strazielle; J. Eyer; R. Lalonde

2002-01-01

320

Pearson's Correlation Coefficient  

NSDL National Science Digital Library

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

2009-01-09

321

Point Biserial Correlation Coefficient  

NSDL National Science Digital Library

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

Lowry, Richard, 1940-

2008-06-26

322

Predicting protein diffusion coefficients.  

PubMed Central

Diffusion coefficients for proteins in water are predicted. The numerical method developed is general enough to be applied to a wide range of protein surface shapes, from rodlike to globular. Results are presented for lysozyme and tobacco mosaic virus, and they are compared with actual data and with predictions made by less general methods. Images Fig. 2

Brune, D; Kim, S

1993-01-01

323

Axonal regeneration is compromised in NFH-LacZ transgenic mice but not in NFH-GFP mice.  

PubMed

To investigate neurofilament (NF) dynamics during the cytoskeleton reorganization in regenerating axons, and their electrophysiological and histological consequences, we used two transgenic lines of mice: neurofilament high (NFH)-LacZ and NFH-green fluorescent protein (GFP). In NFH-LacZ mice, NFs are retained in cell bodies and deficient in axons (Eyer and Peterson, 1994), while in NFH-GFP mice the fluorescent fusion protein is normally transported along axons (Letournel et al., 2006). Following a crush of the sciatic nerve, conduction recovery in NFH-GFP mice is similar to wild-type (wt) mice, but it is reduced in NFH-LacZ mice. Moreover, changes of axonal calibres following regeneration are similar between NFH-GFP and wt mice, but they are systematically reduced in NFH-LacZ mice. Finally, the axonal transport of NFH-GFP fusion protein and NFs is re-initiated after the crush as evidenced by the fluorescent and immunolabelling of axons distal from the crushed point, but NFs and the fusion protein are not transported along axons during regeneration in NFH-LacZ mice. Together, these results argue that the absence of axonal NFs in NFH-LacZ mice compromises the axonal regeneration, and that the NFH-GFP reporter fusion protein represents an efficient model to evaluate the NF dynamics during axonal regeneration. PMID:23079625

Cassereau, J; Nicolas, G; Lonchampt, P; Pinier, M; Barthelaix, A; Eyer, J; Letournel, F

2013-01-01

324

Gamma ray attenuation in a developed borate glassy system  

NASA Astrophysics Data System (ADS)

Measurements and calculations of gamma ray attenuation coefficients in glass barriers of xBaO-5ZnO-5MgO-14Na2O--1Li2O-(75-x)B2O3, previously prepared by the melt-quenching technique [1], were performed for ?-ray of energies 121.8, 244.7, 344.14, 661.66, 778.7, 974, 1086.7, 1173.24, 1332.5, and 1407.9 keV; which emitted from 152Eu, 137Cs, and 60Co radioactive gamma ray sources. The transmitted ?-rays were detected by 3?×3? and 5?×5? NaI (Tl) scintillation ?-ray spectrometers, and a highly calibrated survey meter. The mass attenuation coefficients of ?-rays (?(E) were deduced from the attenuation curves, while the WinXCom computer program (version 3.1) was used to calculate the mass attenuation coefficients of ?-rays for such energies at different barium concentrations of a glassy system. A good agreement between both experimental and theoretical results was achieved as well as results obtained by other workers in similar field.

Saeed, Aly; El shazly, R. M.; Elbashar, Y. H.; Abou El-azm, A. M.; El-Okr, M. M.; Comsan, M. N. H.; Osman, A. M.; Abdal-monem, A. M.; El-Sersy, A. R.

2014-09-01

325

Comparison of nitrate attenuation characterization methods at the Uranium mill tailing site in Monument Valley, Arizona  

NASA Astrophysics Data System (ADS)

SummarySeveral methods for characterizing the occurrence and rate of nitrate attenuation were tested at a field site near Monument Valley, Arizona. Spatial and temporal nitrate concentration data collected from a transect of monitoring wells located along the plume centerline were analyzed to evaluate the overall rates of natural attenuation. The occurrence and rate of denitrification was evaluated through microcosm experiments, nitrogen isotopic fractionation analysis, and solute-transport modeling. First-order denitrification-rate coefficients calculated with each method were comparable. In addition, the composite natural attenuation rate coefficient was similar to the denitrification-rate coefficients, which suggests that microbially induced decay primarily controls nitrate attenuation at the site. This

Carroll, Kenneth C.; Jordan, Fiona L.; Glenn, Edward P.; Jody Waugh, W.; Brusseau, Mark L.

2009-11-01

326

Statistical Inference for Coefficient Alpha  

Microsoft Academic Search

Rigorous comparison of the reliability coefficients of several tests or measurement procedures requires a sampling theory for the coefficients. This paper sum marizes the important aspects of the sampling theory for Cronbach's (1951) coefficient alpha, a widely used internal consistency coefficient. This theory enables researchers to test a specific numerical hypothesis about the population alpha and to obtain confidence intervals

Leonard S. Feldt; David J. Woodruff; Fathi A. Salih

1987-01-01

327

Investigation of the use of X-ray CT images for attenuation compensation in SPECT  

SciTech Connect

This study investigates the general use of single-beam X-ray computed tomography (CT) images for generating attenuation maps for compensation of photon attenuation in SPECT images. A 3D mathematical thorax phantom is used to simulate both emission and transmission projection data for monoenergetic and polyenergetic sources. Polyenergetic transmission projection data are simulated for a standard X-ray spectrum and fan-beam geometry. The projection data are reconstructed using filtered backprojection to form an X-ray CT image which is then scaled to produce an estimate of the attenuation map at the energy of the emission radionuclide. Emission projection data are simulated for a fan-beam geometry at the energies of [sup 201]Tl and [sup 99m]Tc, two radionuclides commonly used in cardiac SPECT. Detector response and scatter are not included in the model. Noiseless, emission projection data are iteratively reconstructed using the ML-EM algorithm with nonuniform attenuation compensation and attenuation maps derived from both the simulated X-ray CT image and from a simulated monoenergetic transmission CT image. The attenuation maps generated from the X-ray CT images accurately estimate the attenuation coefficient for muscle and lung tissues, but not for bone tissues, which show error in the attenuation coefficient of 21--42% for spinal bone and 34--58% for rib bone. However, despite the inaccurate estimate of bone attenuation, the reconstructed SPECT images provide estimates of myocardial radioactivity concentration to within 9% and show few artifacts.

LaCroix, K.J.; Tsui, B.M.W. (Univ. of North Carolina, Chapel Hill, NC (United States)); Hasegawa, B.H.; Brown, J.K. (Univ. of California, San Francisco, CA (United States))

1994-12-01

328

Influence of modal attenuation on shallow water propagation  

NASA Astrophysics Data System (ADS)

A recent simplification of Biot theory is used to illustrate relationships between the intrinsic sediment attenuation, the attenuation of individual modes (as expressed by the modal attenuation coefficients or MACs), and the energy loss of the total field. The simplest two-layer, isospeed waveguides yield MACs that decrease from f-2 to f-1 as frequency f becomes large. A heuristic modification of the environment suggests how a change in the magnitude and frequency behavior of the MACs may arise. We demonstrate how the MACs increase with the incorporation of a fluid-saturated porous layer in the waveguide by using a convenient parameterization and numerical results. The frequency power-law behavior observed increases from f0.7 to f1.7 as the thickness of this layer increases from 2% to 15% of the water depth. Numerical calculations for more realistic waveguides use sandy bottom sediments and isospeed, linear, and piecewise linear water depth profiles. These are environmental simplifications that preserve key features of waveguides from experiments near the New Jersey continental shelf. Principal characteristics of the calculated MACs at frequencies up to 2 kHz include: increased magnitude in the presence of near-interface gradients, reordering of least-attenuated modes for downward refracting water sound speed profiles, and variations of frequency behavior from f-1 to f1. We also demonstrate the sensitivity of the MACs to experimentally-determined upward, isospeed, and downward-refracting sound speed profiles in a shallow water environment with sandy, depositional layers located in the Gulf of Mexico. A comparison of these results with previous numerical studies shows good agreement with water sound speed profiles for nearly isospeed and weakly downward refracting cases. Water sound speed has a significant influence on modal attenuation and, consequently, on the effective attenuation coefficient, which estimates the average transmission decrease with range. The effective attenuation coefficients behave with frequency from f0.0 for isospeed to f0.9 for strongly downward refracting water. Analysis demonstrates how a band of least-attenuated modes contribute to this rate of decrease with range. For a strongly downward refracting linear water sound speed profile, very good approximations of effective attenuation coefficients are shown. At 500, 1000, 1500, and 2000 Hz, the least-attenuated modes, which contribute 90% or more of the effective attenuation coefficient, are modes 1--17, 1--26, 5--21, and 13--31. At large frequencies a parallel trend is apparent between the envelope of the family of MAC curves and EAC. These new results may help interpretation and prediction of data when seasonal changes occur and provide insights into the influence of depth structures and frequency-dependent characteristics of the upper sediment layer on field attenuation.

Saintval, Wendy

329

The Transport Coefficients  

NASA Astrophysics Data System (ADS)

In this section we wish to give a detailed account of all the transport coefficients related to the vectorial fluxes discussed in the previous chapters. These are the mass flux Ja (=-Jb ), the corresponding charge flux or electrical current Jc , closely related to Ja , and J^'q the heat flux. In every case the magnetic field is chosen as the direction of the z-axis, B=Bhat{k} so that for any vector, its different components respect to B will follow from the decomposition illustrated in Fig. (4.1).

García-Colín, Leopoldo S.; Dagdug, Leonardo

330

Natural attenuation of contaminated soils.  

PubMed

Natural attenuation is increasing in use as a low cost means of remediating contaminated soil and groundwater. Modelling of contaminant migration plays a key role in evaluating natural attenuation as a remediation option and in ensuring that there will be no adverse impact on humans and the environment. During natural attenuation, the contamination must be characterized thoroughly and monitored through the process. In this paper, attenuation mechanisms for both organic and inorganic contaminants, use of models and protocols, role of monitoring and field case studies will be reviewed. PMID:15031019

Mulligan, Catherine N; Yong, Raymond N

2004-06-01

331

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

332

Genetic assignment of resonances in the NMR spectrum of a protein: lac repressor.  

PubMed Central

By using a systematic genetic approach, the resonances in the 19F NMR spectrum of 3-fluorotyrosine-substituted lac repressor protein have been assigned. The NMR data indicate that each monomer of the repressor consists of two distinct and independent domains. One domain, the NH2-terminal sixth of the primary sequence, which has been shown to be very important for DNA binding, is very mobile. The remaining COOH-terminal sequence is more rigid. Ligands of the repressor, which affect its DNA binding capability, lead to conformational changes in the COOH-terminal domain. The approach to the assignment of spectral features taken here can be extended to other systems.

Jarema, M A; Lu, P; Miller, J H

1981-01-01

333

The optical periodic analysis of BL Lac object AO 0235+164  

NASA Astrophysics Data System (ADS)

BL Lac object AO 0235+164 is a well-known object. We collect a large number of effective observation in B, V, R and I band from historical literatures. The possible periods are analyzed by means of discrete correlation function (DCF) method, structure function (SF) method and Jurkevich (J-K) method. The results show that there are possible periodic variations of 2.63-2.66 years in B band, 2.79-2.84 years in V band, 2.57-2.87 years in R band, 2.62-2.88 years in I band, respectively.

Wang, Hongtao

2014-05-01

334

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

335

VSOP Monitoring of the Compact BL Lac Object AO 0235+164  

NASA Astrophysics Data System (ADS)

In 1999, the highly compact and variable BL Lac object AO 0235+ 164 was identified as the highest brightness temperature active galactic nucleus observed with the VLBI Space Observatory Programme (VSOP), with TB > 5.8 × 1013 K (Frey et al. 2000). The sub-milliarcsec radio structure of this source has been studied with dual-frequency (1.6 and 5GHz), polarization-sensitive VSOP observations during 2001 and 2002. Here we present the results of this monitoring campaign. At the time of these observations, the source was weakly polarized and characterized by a radio core that is clearly resolved on space-ground baselines.

Frey, Sándor; Gurvits, Leonid I.; Gabuzda, Denise C.; Salter, Chris J.; Altschuler, Daniel R.; Perillat, Phil; Aller, Margo F.; Aller, Hugh D.; Hirabayashi, Hisashi; Davis, Michael M.

2006-04-01

336

BeppoSAX observations of the BL Lac object 1E1207.9+3945  

NASA Astrophysics Data System (ADS)

We present the results of four X-ray observations of the BL Lac object 1E1207.9+3945 performed in 1996 with the MECS instrument onboard BeppoSAX. The source shows an unabsorbed flux in 2-10 keV range of (3.39 +/- 0.08) x 10-12 erg s-1 cm-2 with a photon spectral index of 2.12 +/- 0.06. No temporal variations during BeppoSAX observation have been detected. From the comparison with previous PSPC and EXOSAT observations, a secular variation in the 2-10 keV flux has been revealed.

Cusumano, G.; Mineo, T.; Giommi, P.

337

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

338

The functional stability of the lacZ transcript is sensitive towards sequence alterations immediately downstream of the ribosome binding site  

Microsoft Academic Search

Various synthetic DNA sequences were inserted downstream of the fourth codon of the Escherichia coli lacZ gene on plasmids containing a hybrid lacZ-galK operon. Several different sequences, one as short as 10 bp, reduced the functional stability of the lacZ message three- to fourfold, whereas others had little or no effect. Introduction of synthetic sequences into a plasmid containing the

Carsten Petersen

1987-01-01

339

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

340

Bacterial species specificity in proU osmoinducibility and nptII and lacZ expression.  

PubMed

Reporter gene-based transcriptional fusions are increasingly being used to address questions in microbial ecology, with constitutively expressed fusions enabling microbe tracking and inducible fusions reporting the presence of environmental signals. To more readily apply this technology to a variety of bacterial species, we examined species specificity in the expression of three promoters of interest. A comparison of two potentially constitutive promoters, each fused to the reporter gene gfp, showed that the nptII promoter (P(nptII)) was expressed in a broader range of species (100% of 11 tested) than the lacZ promoter (P(lacZ)) (75% of 11 tested), and thus has broader applicability for marking bacteria than P(lacZ). For the species that expressed P(lacZ), however,P(lacZ) was expressed 3-fold more than P(nptII), on average. The Escherichia coli proU promoter, which is induced by low water potential in E. coli, Salmonella typhimurium, Pantoea agglomerans, and Pseudomonas syringae, was shown to be similarly responsive to water potential in strains of Clavibacter michiganensis, Enterobacter aerogenes, Pseudomonas fluorescens, Pseudomonas putida, and Sinorhizobium meliloti, as well as mildly osmoresponsive in Agrobacterium tumefaciens, supporting its broad use as a reporter of water potential. Surprisingly, this promoter was not regulated by water potential in strains of Staphylococcus aureus and Erwinia amylovora, illustrating heretofore unrecognized species specificity in proU inducibility, as well as potential limitations in the species that can serve as bioreporters of water potential. PMID:16179797

Wright, Catherine A; Beattie, Gwyn A

2004-01-01

341

The roles of starvation and selective substrates in the emergence of araB-lacZ fusion clones.  

PubMed Central

The araB-lacZ fusion system has been a key case in the 'directed mutation' controversy. Fusions did not occur detectably during normal growth but formed readily after prolonged incubation on selective Ara-Lac medium. To distinguish the roles of starvation stress and selective substrates in coding sequence fusions, we applied sib selection and PCR technologies. Sib selection of the prefusion strain, MCS2, starved under aerobic conditions permitted us to isolate active fusion clones which had never been in contact with arabinose or lactose. Hence, a directive role for selective substrates is not essential. Aerobiosis was necessary for fusions to appear in glucose-starved cultures. The difference in fusion formation between normal and starved conditions is best explained by the response of a signal transduction network to physiological stimuli to activate Mu prophage joining of araB and lacZ sequences. PCR analysis revealed that direct plating on selective Ara-Lac agar yielded mostly a single class of 'standard' fusions, while sib selection yielded a broader spectrum of fusion structures. Standard fusions were found to occur within a narrow 9 bp window in lacZ. The high frequency of standard fusions in glucose-starved cultures suggested efficient and/or specific Mu action. Images

Maenhaut-Michel, G; Shapiro, J A

1994-01-01

342

A new method for retrieval of the extinction coefficient of water clouds by using the tail of the CALIOP signal  

Microsoft Academic Search

A method is developed based on Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) level 1 attenuated backscatter profile data for deriving the mean extinction coefficient of water droplets close to cloud top. The method is applicable to low level (cloud top <2 km), opaque water clouds in which the lidar signal is completely attenuated beyond about 100 m of

J. Li; Y. Hu; J. Huang; K. Stamnes; Y. Yi; S. Stamnes

2011-01-01

343

A new method for retrieval of the extinction coefficient of water clouds by using the tail of the CALIOP signal  

Microsoft Academic Search

A method is developed based on Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) level 1 attenuated backscatter profile data for deriving the mean extinction coefficient of water droplets close to cloud top. The method is applicable to low level (cloud top < 2 km), opaque water clouds in which the lidar signal is completely attenuated beyond about 100 m

J. Li; Y. Hu; J. Huang; K. Stamnes; Y. Yi

2010-01-01

344

An attenuated philosophical gentleman.  

PubMed

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

Christie, John R R

2014-06-20

345

Molar extinction coefficients of some fatty acids  

NASA Astrophysics Data System (ADS)

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

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

2002-10-01

346

Measurement of acoustic attenuation in South Pole ice  

NASA Astrophysics Data System (ADS)

Using the South Pole Acoustic Test Setup (SPATS) and a retrievable transmitter deployed in holes drilled for the IceCube experiment, we have measured the attenuation of acoustic signals by South Pole ice at depths between 190 m and 500 m. Three data sets, using different acoustic sources, have been analyzed and give consistent results. The method with the smallest systematic uncertainties yields an amplitude attenuation coefficient ? = 3.20 ± 0.57 km-1 between 10 and 30 kHz, considerably larger than previous theoretical estimates. Expressed as an attenuation length, the analyses give a consistent result for ? ? 1/? of ˜300 m with 20% uncertainty. No significant depth or frequency dependence has been found.

IceCube Collaboration; Abbasi, R.; Abdou, Y.; Abu-Zayyad, T.; Adams, J.; Aguilar, J. A.; Ahlers, M.; Andeen, K.; Auffenberg, J.; Bai, X.; Baker, M.; Barwick, S. W.; Bay, R.; Bazo Alba, J. L.; Beattie, K.; Beatty, J. J.; Bechet, S.; Becker, J. K.; Becker, K.-H.; Benabderrahmane, M. L.; Berdermann, J.; Berghaus, P.; Berley, D.; Bernardini, E.; Bertrand, D.; Besson, D. Z.; Bissok, M.; Blaufuss, E.; Boersma, D. J.; Bohm, C.; Böser, S.; Botner, O.; Bradley, L.; Braun, J.; Buitink, S.; Carson, M.; Chirkin, D.; Christy, B.; Clem, J.; Clevermann, F.; Cohen, S.; Colnard, C.; Cowen, D. F.; D'Agostino, M. V.; Danninger, M.; de Clercq, C.; Demirörs, L.; Depaepe, O.; Descamps, F.; Desiati, P.; de Vries-Uiterweerd, G.; Deyoung, T.; Díaz-Vélez, J. C.; Dreyer, J.; Dumm, J. P.; Duvoort, M. R.; Ehrlich, R.; Eisch, J.; Ellsworth, R. W.; Engdegård, O.; Euler, S.; Evenson, P. A.; Fadiran, O.; Fazely, A. R.; Feusels, T.; Filimonov, K.; Finley, C.; Foerster, M. M.; Fox, B. D.; Franckowiak, A.; Franke, R.; Gaisser, T. K.; Gallagher, J.; Ganugapati, R.; Geisler, M.; Gerhardt, L.; Gladstone, L.; Glüsenkamp, T.; Goldschmidt, A.; Goodman, J. A.; Grant, D.; Griesel, T.; Groß, A.; Grullon, S.; Gunasingha, R. M.; Gurtner, M.; Gustafsson, L.; Ha, C.; Hallgren, A.; Halzen, F.; Han, K.; Hanson, K.; Helbing, K.; Herquet, P.; Hickford, S.; Hill, G. C.; Hoffman, K. D.; Homeier, A.; Hoshina, K.; Hubert, D.; Huelsnitz, W.; Hülß, J.-P.; Hulth, P. O.; Hultqvist, K.; Hussain, S.; Imlay, R. L.; Ishihara, A.; Jacobsen, J.; Japaridze, G. S.; Johansson, H.; Joseph, J. M.; Kampert, K.-H.; Kappes, A.; Karg, T.; Karle, A.; Kelley, J. L.; Kemming, N.; Kenny, P.; Kiryluk, J.; Kislat, F.; Klein, S. R.; Knops, S.; Köhne, J.-H.; Kohnen, G.; Kolanoski, H.; Köpke, L.; Koskinen, D. J.; Kowalski, M.; Kowarik, T.; Krasberg, M.; Krings, T.; Kroll, G.; Kuehn, K.; Kuwabara, T.; Labare, M.; Lafebre, S.; Laihem, K.; Landsman, H.; Lauer, R.; Lehmann, R.; Lennarz, D.; Lünemann, J.; Madsen, J.; Majumdar, P.; Maruyama, R.; Mase, K.; Matis, H. S.; Matusik, M.; Meagher, K.; Merck, M.; Mészáros, P.; Meures, T.; Middell, E.; Milke, N.; Montaruli, T.; Morse, R.; Movit, S. M.; Nahnhauer, R.; Nam, J. W.; Naumann, U.; Nießen, P.; Nygren, D. R.; Odrowski, S.; Olivas, A.; Olivo, M.; Ono, M.; Panknin, S.; Paul, L.; Pérez de Los Heros, C.; Petrovic, J.; Piegsa, A.; Pieloth, D.; Porrata, R.; Posselt, J.; Price, P. B.; Prikockis, M.; Przybylski, G. T.; Rawlins, K.; Redl, P.; Resconi, E.; Rhode, W.; Ribordy, M.; Rizzo, A.; Rodrigues, J. P.; Roth, P.; Rothmaier, F.; Rott, C.; Roucelle, C.; Ruhe, T.; Rutledge, D.; Ruzybayev, B.; Ryckbosch, D.; Sander, H.-G.; Sarkar, S.; Schatto, K.; Schlenstedt, S.; Schmidt, T.; Schneider, D.; Schukraft, A.; Schultes, A.; Schulz, O.; Schunck, M.; Seckel, D.; Semburg, B.; Seo, S. H.; Sestayo, Y.; Seunarine, S.; Silvestri, A.; Slipak, A.; Spiczak, G. M.; Spiering, C.; Stamatikos, M.; Stanev, T.; Stephens, G.; Stezelberger, T.; Stokstad, R. G.; Stoyanov, S.; Strahler, E. A.; Straszheim, T.; Sullivan, G. W.; Swillens, Q.; Taboada, I.; Tamburro, A.; Tarasova, O.; Tepe, A.; Ter-Antonyan, S.; Tilav, S.; Toale, P. A.; Tosi, D.; Tur?an, D.; van Eijndhoven, N.; Vandenbroucke, J.; van Overloop, A.; van Santen, J.; Voigt, B.; Walck, C.; Waldenmaier, T.; Wallraff, M.; Walter, M.; Wendt, C.; Westerhoff, S.; Whitehorn, N.; Wiebe, K.; Wiebusch, C. H.; Wikström, G.; Williams, D. R.; Wischnewski, R.; Wissing, H.; Woschnagg, K.; Xu, C.; Xu, X. W.; Yanez, J. P.; Yodh, G.; Yoshida, S.; Zarzhitsky, P.; IceCube Collaboration

2011-01-01

347

Wave Attenuation by Artificial Seaweed.  

National Technical Information Service (NTIS)

A series of wave tank tests was conducted at this Center (CERC) to determine the ability of a field of low specific gravity artificial seaweed to attenuate wave action. Wave gages were located on both sides of the seaweed field to measure wave attenuation...

J. P. Ahrens

1976-01-01

348

Monitored Natural Attenuation of Explosives  

Microsoft Academic Search

Explosives are subject to several attenuation processes that potentially reduce concentrations in groundwater over time. Some of these processes are well defined, while others are poorly understood. The objective of the project was to optimize data collection and processing procedures for evaluation and implementation of monitored natural attenuation of explosives. After conducting experiments to optimize data quality, a protocol was

Judith C. Pennington; James M. Brannon; Douglas Gunnison; D. W. Harrelson; M. Zakikhani; Paul Miyares; Thomas F. Jenkins; Joan Clarke; Charolett Hayes; David Ringleberg; Ed Perkins; Herb Fredrickson

2001-01-01

349

Radar attenuation in desert soil  

Microsoft Academic Search

Soil properties make a significant impact in the observed responses of various sensors for subsurface target detection. Ground penetrating radars (GPRs) have been extensively researched as a tool for subsurface target detection. A key soil parameter of interest for evaluating GPR performance is the soil attenuation rate. The information about the soil attenuation rate coupled with target properties (size, shape,

Gary Koh

2008-01-01

350

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

351

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

352

Intelligent Local Avoided Collision (iLAC) MAC Protocol for Very High Speed Wireless Network  

NASA Astrophysics Data System (ADS)

Future wireless communication systems aim at very high data rates. As the medium access control (MAC) protocol plays the central role in determining the overall performance of the wireless system, designing a suitable MAC protocol is critical to fully exploit the benefit of high speed transmission that the physical layer (PHY) offers. In the latest 802.11n standard [2], the problem of long overhead has been addressed adequately but the issue of excessive colliding transmissions, especially in congested situation, remains untouched. The procedure of setting the backoff value is the heart of the 802.11 distributed coordination function (DCF) to avoid collision in which each station makes its own decision on how to avoid collision in the next transmission. However, collision avoidance is a problem that can not be solved by a single station. In this paper, we introduce a new MAC protocol called Intelligent Local Avoided Collision (iLAC) that redefines individual rationality in choosing the backoff counter value to avoid a colliding transmission. The distinguishing feature of iLAC is that it fundamentally changes this decision making process from collision avoidance to collaborative collision prevention. As a result, stations can avoid colliding transmissions with much greater precision. Analytical solution confirms the validity of this proposal and simulation results show that the proposed algorithm outperforms the conventional algorithms by a large margin.

Hieu, Dinh Chi; Masuda, Akeo; Rabarijaona, Verotiana Hanitriniala; Shimamoto, Shigeru

353

A plasmid-based lacZ? gene assay for DNA polymerase fidelity measurement  

PubMed Central

A significantly improved DNA polymerase fidelity assay, based on a gapped plasmid containing the lacZ? reporter gene in a single-stranded region, is described. Nicking at two sites flanking lacZ?, and removing the excised strand by thermocycling in the presence of complementary competitor DNA, is used to generate the gap. Simple methods are presented for preparing the single-stranded competitor. The gapped plasmid can be purified, in high amounts and in a very pure state, using benzoylated–naphthoylated DEAE–cellulose, resulting in a low background mutation frequency (?1 × 10?4). Two key parameters, the number of detectable sites and the expression frequency, necessary for measuring polymerase error rates have been determined. DNA polymerase fidelity is measured by gap filling in vitro, followed by transformation into Escherichia coli and scoring of blue/white colonies and converting the ratio to error rate. Several DNA polymerases have been used to fully validate this straightforward and highly sensitive system.

Keith, Brian J.; Jozwiakowski, Stanislaw K.; Connolly, Bernard A.

2013-01-01

354

LacCore: Support for the terrestrial sediment core research community  

NASA Astrophysics Data System (ADS)

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 procedures, and core and data curation. The user base has increased from perhaps 20 users and a handful of projects in the first year to 621 users and 250 projects in 2008. The community served is diverse, with topics including invasive species, eutrophication, salinization, tectonics, geomicrobiology, evolutionary biology, isostatic rebound, stream bank erosion, glaciology, hydrogeology, atmospheric chemistry, carbon cycling, and rock magnetics, as well as paleoenvironment and paleoclimate. The changing needs of projects drive innovation in procedures and equipment, all of which become available to subsequent researchers. Among the newest additions to the lab is a benchtop scanning electron microscope with electron-dispersive x-ray spectrometry (SEM-EDX or -EDS) capability for sediment characterization. This instrument allows rapid imaging of sedimentary components and determination of their elemental composition without substantial sample preparation, lead time, or user training. These images and data augment the initial core description process, filling a void between existing smear slide and scanning micro XRF capabilities.

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

2009-12-01

355

Bistable Behavior in a Model of the lac Operon in Escherichia coli with Variable Growth Rate  

PubMed Central

This work is a continuation from another study previously published in this journal. Both the former and the present works are dedicated to investigating the bistable behavior of the lac operon in Escherichia coli from a mathematical modeling point of view. In the previous article, we developed a detailed mathematical model that accounts for all of the known regulatory mechanisms in this system, and studied the effect of inducing the operon with lactose instead of an artificial inducer. In this article, the model is improved to account, in a more detailed way, for the interaction of the repressor molecules with the three lac operators. A recently discovered cooperative interaction between the CAP molecule (an activator of the lactose operon) and Operator 3 (which influences DNA folding) is also included in this new version of the model. The growth rate dependence on the rate of energy entering the bacteria (in the form of transported glucose molecules and of metabolized lactose molecules) is also considered. A large number of numerical experiments is carried out with this improved model. The results are discussed in regard to the bistable behavior of the lactose operon. Special attention is paid to the effect that a variable growth rate has on the system dynamics.

Santillan, M.

2008-01-01

356

Dynamics and bistability in a reduced model of the lac operon.  

PubMed

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 beta-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 beta-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. PMID:15189056

Yildirim, Necmettin; Santillan, Moises; Horike, Daisuke; Mackey, Michael C

2004-06-01

357

From binary to multivalued to continuous models: the lac operon as a case study.  

PubMed

Using the lac operon as a paradigmatic example for a gene regulatory system in prokaryotes, we demonstrate how qualitative knowledge can be initially captured using simple discrete (Boolean) models and then stepwise refined to multivalued logical models and finally to continuous (ODE) models. At all stages, signal transduction and transcriptional regulation is integrated in the model description. We first show the potential benefit of a discrete binary approach and discuss then problems and limitations due to indeterminacy arising in cyclic networks. These limitations can be partially circumvented by using multilevel logic as generalization of the Boolean framework enabling one to formulate a more realistic model of the lac operon. Ultimately a dynamic description is needed to fully appreciate the potential dynamic behavior that can be induced by regulatory feedback loops. As a very promising method we show how the use of multivariate polynomial interpolation allows transformation of the logical network into a system of ordinary differential equations (ODEs), which then enables the analysis of key features of the dynamic behavior. PMID:21200084

Franke, Raimo; Theis, Fabian J; Klamt, Steffen

2010-01-01

358

Local Gene Regulation Details a Recognition Code within the LacI Transcriptional Factor Family  

PubMed Central

The specific binding of regulatory proteins to DNA sequences exhibits no clear patterns of association between amino acids (AAs) and nucleotides (NTs). This complexity of protein-DNA interactions raises the question of whether a simple set of wide-coverage recognition rules can ever be identified. Here, we analyzed this issue using the extensive LacI family of transcriptional factors (TFs). We searched for recognition patterns by introducing a new approach to phylogenetic footprinting, based on the pervasive presence of local regulation in prokaryotic transcriptional networks. We identified a set of specificity correlations –determined by two AAs of the TFs and two NTs in the binding sites– that is conserved throughout a dominant subgroup within the family regardless of the evolutionary distance, and that act as a relatively consistent recognition code. The proposed rules are confirmed with data of previous experimental studies and by events of convergent evolution in the phylogenetic tree. The presence of a code emphasizes the stable structural context of the LacI family, while defining a precise blueprint to reprogram TF specificity with many practical applications.

Camas, Francisco M.; Alm, Eric J.; Poyatos, Juan F.

2010-01-01

359

Protein-induced unwinding of DNA: measurement by gel electrophoresis of complexes with DNA minicircles. Application to restriction endonuclease EcoRI, catabolite gene activator protein and lac repressor.  

PubMed Central

An electrophoretic procedure for the measurement of the helix unwinding induced by a sequence-specific protein is described. The method, which was applied here to EcoR I, CAP and lac repressor, involved the migration of the complexes with positively and negatively supercoiled DNA minicircles carrying a single protein binding site. Mobility shifts of complexes relative to naked DNAs appeared to be a result of i) the unwinding; of ii) an increase in the molecular frictional coefficient, which led to a retardation; of iii) bending, in the particular case of CAP, which induced an acceleration; and of iv) looping, in the case of lac repressor, which also resulted in an acceleration. Under conditions where the migration of the naked topoisomers was V-like (topoisomer mobility showed the same linear increase with both negative and positive supercoilings; Zivanovic et al. (1986) J. Mol. Biol., 192, 645-660), the protein unwinding contribution to mobility was assumed to be identical to that experimentally observed in the case of a thermal unwinding: all negatively supercoiled topoisomers were retarded and all positively supercoiled topoisomers were accelerated to the same extent. In contrast, the mobility contribution of the frictional term, as well as those of bending and looping, appeared to vary strongly with the magnitude of the supercoiling, but only weakly with its polarity. As a consequence, these latter contributions may approximately cancel when one is measuring the difference between the shifts observed for two comigrating, negatively and positively supercoiled, topoisomers, allowing the unwinding to be calculated. While estimates obtained for EcoR I, 23 +/- 3 degrees, and CAP, about 29 degrees, were in good agreement with previous measurements using topoisomerase I, the value found for lac repressor, 13 to 16 degrees, was significantly smaller. Images

Douc-Rasy, S; Kolb, A; Prunell, A

1989-01-01

360

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

361

Recursive calculation of hansen coefficients  

Microsoft Academic Search

Hansen coefficients are used in expansions of the elliptic motion. Three methods for calculating the coefficients are studied: Tisserand's method, the Von Zeipel-Andoyer (VZA) method with explicit representation of the polynomials required to compute the Hansen coefficients, and the VZA method with the values of the polynomials calculated recursively. The VZA method with explicit polynomials is by far the most

Richard L. Branham

1990-01-01

362

Attenuation of diagnostic energy photons by polymer gel dosimeters  

Microsoft Academic Search

Post-irradiation changes in the linear attenuation coefficient, mu, of polymer gel dosimeters give rise to a change which can be measured with x-ray computed tomography. Polymer gel dosimeters were manufactured consisting of 3% (by weight) acrylamide and 3% N,N'-methylene-bis-acrylamide comonomers dissolved in aqueous gelatin (5% gelatin by total weight and 89% de-ionized distilled water). mu was measured in a collimated

J. V. Trapp; G. Michael; Y. de Deene; C. Baldock

2002-01-01

363

Regulation of fos-lacZ fusion gene expression in primary mouse epidermal keratinocytes isolated from transgenic mice.  

PubMed Central

The expression of a fos-lacZ fusion gene was studied in primary mouse epidermal keratinocytes obtained from transgenic mice. This gene construct contains the entire upstream regulatory sequence of c-fos, and expression of the endogenous and fusion gene was shown by Northern analysis to correlate upon induction with the phorbol ester 12-O-tetradecanoylphorbol 13-acetate (TPA). Using a chromogenic substrate of beta-galactosidase, we also demonstrated that expression of the fusion gene product, like that of Fos, was localized to the cell nucleus. In addition, we showed that epidermal keratinocytes responded to dialysed fetal bovine serum (FBS), TPA and high-calcium medium with enhanced Fos-lacZ expression and an inhibition of proliferation. The time course of induction of Fos-lacZ expression was similar for dialysed FBS and TPA, with a peak approximately 2 h after exposure. Exposure for approximately 24 h to an elevated extracellular calcium concentration was required to elicit an increase in Fos-lacZ expression. The lack of an immediate effect of raising medium calcium levels on Fos-lacZ expression contrasted with the rapidity of its effect on DNA synthesis, which was significantly inhibited within 6-8 h. In addition, we found that the protein kinase C inhibitor Ro 31-7549 blocked Fos-lacZ expression induced by TPA but had little or no effect on that elicited by high calcium levels. Thus, although our results indicate that the fos gene product may be involved in mediating epidermal keratinocyte growth arrest in response to differentiative agents such as FBS, TPA and high medium calcium levels, the exact role of this gene product remains unclear. Images Figure 1 Figure 2

Bollag, W B; Xiong, Y; Ducote, J; Harmon, C S

1994-01-01

364

Fine-tuning function: Correlation of hinge domain interactions with functional distinctions between LacI and PurR  

PubMed Central

LacI and PurR are highly homologous proteins. Their functional units are homodimers, with an N-terminal DNA binding domain that comprises the helix-turn-helix (HTH), N-linker, and hinge regions from both monomers. Hinge structural changes are known to occur upon DNA dissociation but are difficult to monitor experimentally. The initial steps of hinge unfolding were therefore examined using molecular dynamics simulations, utilizing a truncated, chimeric protein comprising the LacI HTH/N-linker and PurR hinge. A terminal Gly-Cys-Gly was added to allow "dimerization" through disulfide bond formation. Simulations indicate that differences in LacI and PurR hinge primary sequence affect the quaternary structure of the hinge•hinge` interface. However, these alternate hinge orientations would be sterically restricted by the core domain. These results prompted detailed comparison of recently available DNA-bound structures for LacI and truncated LacI(1–62) with the PurR structure. Examination revealed that different N-linker and hinge contacts to the core domain of the partner monomer (which binds effector molecule) affect the juxtapositions of the HTH, N-linker, and hinge regions in the DNA binding domain. In addition, the two full-length repressors exhibit significant differences in the interactions between the core and the C-linker connection to the DNA binding domain. Both linkers and the hinge have been implicated in the allosteric response of these repressors. Intriguingly, one functional difference between these two proteins is that they exhibit opposite allosteric response to effector. Simulations and observed structural distinctions are correlated with mutational analysis and sequence information from the LacI/GalR family to formulate a mechanism for fine-tuning individual repressor function.

Swint-Kruse, Liskin; Larson, Christopher; Pettitt, B. Montgomery; Matthews, Kathleen Shive

2002-01-01

365

Mutation spectrum in the lacI gene, induced by gamma-radiation in aqueous solution under oxic conditions.  

PubMed

Irradiation of DNA in a cellular environment leads to many types of DNA damage, resulting from various effects of gamma-radiation. One of these effects is the formation of water-derived radicals (e.g., .OH radicals), which are formed in the vicinity of DNA (indirect effect). To study the influence of the indirect effect on gamma-radiation-induced mutations, a newly constructed plasmid, containing the lacI gene as a target gene, was irradiated with 60Co gamma-radiation in aqueous solution, in the presence of oxygen. Under these circumstances, only .OH radicals will be responsible for the induced mutations. Sequence analysis of the gamma-radiation-induced mutations showed that 96% of all mutations were base pair substitutions, 87% of which occurred in the lacI gene, the others are formed in the lac operator part. All gamma-radiation-induced mutations in the lacI gene occurred exclusively on G:C base pairs, and no mutations at A:T base pairs could be detected. In the spontaneous mutation spectrum, 83% of all mutations were base pair substitutions, 35% of which occurred in the lacI gene and 48% in the lac operator part. Base pair substitutions on G:C base pairs were very similar in the gamma-radiation-induced and in the spontaneous mutation spectrum, implying a high contribution of .OH radicals to spontaneous mutagenesis. A:T to G:C transitions accounted for 10% of all spontaneous base pair substitutions in the lacI gene and are probably the result of effects, other than just .OH radicals. It can be concluded that .OH radicals are an important source for mutations at G:C base pairs. In this paper, the extracellular gamma-radiation-induced mutation spectrum is also compared to the previously obtained, intracellular gamma-radiation-induced mutation spectrum of the lacI gene. Comparison shows some differences, such as relative high amounts of mutations at A:T base pairs, G:C to T:A transversions and frameshift mutations in the intracellular gamma-radiation-induced mutation spectrum, as compared to the extracellular gamma-radiation-induced mutation spectrum. Since the extracellular gamma-radiation-induced mutation spectrum shows that .OH radicals are mainly responsible for base pair substitutions on G:C base pairs, mutations at A:T base pairs in the intracellular gamma-radiation-induced mutation spectrum are apparently the result of additional or other factors. PMID:9726014

Wijker, C A; Wientjes, N M; Lafleur, V M

1998-07-17

366

GB6 J1058+5628: A NEW QUASI-PERIODIC BL LAC OBJECT FROM THE ASIAGO PLATE ARCHIVE  

SciTech Connect

We present the historic photographic light curves of three little known blazars (two BL Lac objects and one FSRQ), GB6 J1058+5628, GB6 J1148+5254, and GB6 J1209+4119, spanning a time interval of about 50 years, mostly built using the Asiago plate archive. All objects show evident long-term variability, over which short-term variations are superposed. One source, GB6 J1058+5628, showed a marked quasi-periodic variability of 1 mag on timescale of about 6.3 years, making it one of the few BL Lac objects with a quasi-periodic behavior.

Nesci, R., E-mail: roberto.nesci@uniroma1.i [Physics Department, University of Roma La Sapienza, Piazzale A. Moro 2, I-00185 Roma (Italy)

2010-06-15

367

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

368

Functional Consequences of Exchanging Domains Between LacI and PurR are Mediated by the Intervening Linker Sequence  

PubMed Central

Homologue function can be differentiated by changing residues that affect binding sites or long-range interactions. LacI and PurR are two proteins that represent the LacI/GalR family (>500 members) of bacterial transcription regulators. All members have distinct DNA-binding and regulatory domains linked by ~18 amino acids. Each homologue has specificity for different DNA and regulatory effector ligands; LacI and PurR also exhibit differences in allosteric communication between DNA and effector binding sites. A comparative study of LacI and PurR suggested that alterations in the interface between the regulatory domain and linker are important for differentiating their functions. Four residues (equivalent to LacI positions 48, 55, 58, and 61) appear particularly important for creating a unique interface and were predicted to be necessary for allosteric regulation. However, nearby residues in the linker interact with DNA ligand. Thus, differences observed in interactions between linker and regulatory domain may be the cause of altered function or an effect of the two proteins binding different DNA ligands. To separate these possibilities, we created a chimeric protein with the LacI DNA-binding domain/linker and the PurR regulatory domain (LLhP). If the interface requires homologue-specific interactions in order to propagate the signal from effector binding, then LLhP repression should not be allosterically regulated by effector binding. Experiments show that LLhP is capable of repression from lacO1 and, contrary to expectation, allosteric response is intact. Further, restoring the potential for PurR-like interactions via substitutions in the LLhP linker tends to diminish repression. These effects are especially pronounced for residues 58 and 61. Clearly, binding affinity of LLhP for the lacO1 DNA site is sensitive to long-range changes in the linker. This result also raises the possibility that mutations at positions 58 and 61 co-evolved with changes in the DNA-binding site. In addition, repression measured in the absence and presence of effector ligand shows that allosteric response increases for several LLhP variants with substitutions at positions 48 and 55. Thus, while side chain variation at these sites does not generally dictate the presence or absence of allostery, the nature of the amino acid can modulate the response to effector.

Tungtur, Sudheer; Egan, Susan M.; Swint-Kruse, Liskin

2007-01-01

369

Fate Tracing of neurogenin2-Expressing Cells in the Mouse Retina Using CreER™: LacZ  

PubMed Central

Delineating the final fate of progenitor cells that transiently express a regulatory gene may shed light on how the gene participates in regulating retinal development. We describe the steps in tracing final fates of progenitor cells that once transiently express neurogenin2 (ngn2) during mouse retinal development with the binary, conditional Ngn2-CreER™—LacZ reporter system. Ngn2-CreER™ mice (Zirlinger et al. Proc Natl Acad Sci USA 99:8084–8089, 2002), in which ngn2 promoter drives the expression of Cre-estrogen receptor CreER™ (Littlewood et al. Nuc Acid Res 23:1686–1690, 1995; Hayashi and McMahon Dev Biol 244:305–318, 2002), are crossed with Rosa26-LoxP-LacZ reporter mice (Soriano Nat Genet 21:70–71, 1999), in which the expression of lacZ requires the removal of “stop” by Cre recombinase (Wagner et al. Transgenic Res 10:545–553, 2001). 4-hydroxytamoxifen (4-OHT), a synthetic ligand with high affinity for ER™, is administered to double transgenic embryos and/or neonatal mice. Binding of 4-OHT to Cre-ER™ activates Cre recombinase, which then catalyzes the removal of the “stop” sequence from the LoxP-LacZ transgene, leading to lacZ expression in cells that express ngn2. Retinal tissues are fixed at different time points after 4-OHT treatment and analyzed for LacZ activities by colorimetric reaction. Double-labeling with a cell type-specific marker can be used to define the identity of a LacZ+ cell. Combining persisted lacZ expression through the life of the cell and the short half-life (0.5–2 h) of 4-OHT (Danielian et al. Curr Biol 8:1323–1326, 1998), this system offers the opportunity to track the final fates of cells that have expressed ngn2 during the brief presence of 4-OHT administered during retinal development.

Ma, Wenxin; Wang, Shu-Zhen

2012-01-01

370

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

371

Pressure wave attenuation and dispersion in two-phase flow  

SciTech Connect

The pressure shock wave propagation behavior in three vapor-liquid systems, steam-water, ethanol-ethanol, and Freon-Freon, has been investigated over a void fraction, ..cap alpha.., range from zero to 30%. Attenuation and dispersion behavior seems relatively insensitive (no order-of-magnitude deviations) to differences in system physical properties. The attenuation coefficient of water, BETA/sub H/2/sub O/ ranged from 0.021 cm/sup -1/ at 5% void to 0.072 cm/sup -1/ at 30% void fraction. BETA/sub F113/ was as much as 40% lower than BETA/sub ETOH/ or BETA/sub H/2/sub O/ for void fractions less than 20% where the initial wave amplitude, ..delta..P/sub o/ was 2.90 bar. Larger amplitude waves (4.14 bar) demonstrated a greater rate of attenuation throughout the void fraction range, more pronounced in the lower regions: 80% greater for 5% steam-water and 120% greater for 5% Freon-113. The attenuation data from the present investigation tend to lie between one- and two-component acoustic attenuation theories and data. However, near the resonant bubble frequency, the two component results approach the one-component region. As the void fraction is decreased, the one- and two-component acoustic theories and data (small and finite amplitude, including the present experimentation) smoothly converge.

Kovarik, F.S.; Bankoff, S.G.

1987-01-01

372

Effects of Pressure on Attenuation of Seismic Waves Through Sedimentary Rocks  

NASA Astrophysics Data System (ADS)

The research focuses on the effects of pressure on the Attenuation of Seismic waves propagating three different rock samples from the upper crust. The frequency used ranges from 1Hz to 1000Hz while the pressure was varied from atmospheric to 27,960 Nm -1. The research was carried out in Year 1 Laboratory of the Department of Physics of the Lagos State University Ojo, Nigeria. The Continuous wave Transmission and spectral Amplitude wave ratio technique was employed to determine the Attenuation Coefficient K for each rock sample. Attenuation Coefficients were plotted against frequency on scatter diagram and bar charts were constructed. Result shows sandstone attenuated most of the three rock types used.

Olorode, D. O.; Aregbede, O. S.; Olorode, G. T.

2009-05-01

373

Attenuation of an electromagnetic wave by charged dust particles in a sandstorm.  

PubMed

We calculate the light scattering properties of the partially charged dust particles with the Mie theory for electromagnetic waves with different frequencies, and the attenuation coefficients of an electromagnetic wave propagating in a sandstorm are also calculated. The results show that the electric charges distributed on the sand surface have a significant effect on the attenuation of the electromagnetic wave, especially for a frequency lower than 40 GHz, and attenuation coefficients increase with the magnitude of charges carried by the dust particles (expressed by the charge-to-mass ratio in this paper). For the higher frequency electromagnetic wave, such as visible light, the effect of charges carried by sand particles on its attenuation is very little, which can be ignored. PMID:21151232

Xie, Li; Li, Xingcai; Zheng, Xiaojing

2010-12-10

374

Decadal to millennial scale geomagnetic field variations in the Levantine archaeointensity curve (LAC): methodology and applications  

NASA Astrophysics Data System (ADS)

Recovering the absolute intensity of the geomagnetic field on historical and archaeological timescale (archaeointensity) in a sufficient resolution is a fundamental effort in the paleomagnetic research. However, it is a complicated task hampered by some serious methodological difficulties. First, paleointensity experiments should be carefully designed using sufficient number of specimens, and accurate correction for remanence anisotropy, cooling rate effects, and non-linear TRM (NLT). Second, the basic assumption of the paleointensity method - that the natural remanence magnetization (NRM) is a stable thermoremanent magnetization (TRM) carried by single domain (SD) like particles - is hard to test using non-destructive methods. Third, the interpretation of the experimental results is non-unique leading to uncertainty in the final paleointensity calculation. These experimental difficulties compound with dating problems, which are not always easy to overcome. Here, we address each of the issues pointed above in order to construct a high-resolution archaeointensity curve of the Levant using a comprehensive dataset consisting of more than 2000 specimens from over 400 samples. The experimental difficulties are overcome by applying the same treatments to all specimens: Thellier-type IZZI protocol with pTRM checks every second step, and additional anisotropy, cooling rate, and NLT experiments. To ensure consistency, comparability, and objectivity of the interpretations we apply an automatic data analysis technique using a recently published open code computer program (PmagPy Thellier-GUI). We use strict selection criteria for the specimens/samples level and for the correction to screen out any unreliable data. For transparency, we make all the raw data, which include over 80,000 individual measurements, available in the MagIC database for the use of other researchers. We treat the dating problems by assigning a six-level quality scale (form controversial to excellent) according to the dating method employed (archaeological, historical, radiocarbon). In addition, we cross check results from multiple archaeological sites using different source materials dated using different methodologies. The results of this effort are summarized in a regional compilation namely Levantine Archaeomagnetic Curve - LAC. The initial version of the LAC includes recently published data from ancient copper production sites, and new data from two important biblical archaeological mounds in Israel - Tel Megiddo ("Armageddon") and Tel Hazor. In this talk we review our working methodologies, report the current status of the LAC, and discuss its implications on our understanding of geomagnetic secular variations.

Shaar, Ron; Tauxe, Lisa; Ron, Hagai; Agnon, Amotz; Ben-Yosef, Erez; Finkelstein, Israel; Zuckerman, Sharon; Levy, Thomas E.

2014-05-01

375

Perturbation from a distance: mutations that alter LacI function through long-range effects.  

PubMed

Allosteric modification of ligand binding is central to LacI transcription control. Recently, the conformational change between LacI operator- and inducer-bound states was simulated with targeted molecular dynamics (TMD) [Flynn, T. C., Swint-Kruse, L., Kong, Y., Booth, C., Matthews, K. S., and Ma, J. (2003) Protein Sci., 12, 2523-2541]. Atomic-level analyses of TMD results indicate the structural importance of the core pivot region that connects the N- and C-subdomains flanking the inducer-binding site. Further, a number of LacI mutations in the core pivot have been identified recently by their altered behaviors in phenotypic screens. Biochemical characterization of three of these variants-L148F, S151P, and P320A-provides an opportunity to directly explore the role of the core pivot in repressor function. For L148F, inducer IPTG binding affinity is strengthened, whereas O(1) operator DNA binding is diminished approximately 30-fold. In contrast, O(1) binding is increased for S151P, whereas IPTG binding is decreased. UV-difference spectroscopy and urea denaturation indicate long-range effects in both variants. Interestingly, P320A binds to DNA approximately 4-fold more tightly than wild-type, yet inducer binding is unaffected. To examine linkage between the core pivot and DNA binding domains, the L148F substitution was combined with Q60G, a previously known mutant with enhanced operator affinity. The double mutant exhibits the properties of both parent proteins, resulting in near wild-type DNA binding affinity and enhanced inducer sensitivity. These features may render Q60G/L148F more cost-effective in technological applications than wild-type repressor. As a group, the behaviors of the core pivot mutants are consistent with the allosteric structural role predicted for this region by TMD and reflect the significant long-range impact that single substitutions can elicit on protein function. PMID:14636069

Swint-Kruse, Liskin; Zhan, Hongli; Fairbanks, Bonnie M; Maheshwari, Atul; Matthews, Kathleen S

2003-12-01

376

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

377

Monte Carlo based down-scatter correction of SPECT attenuation maps  

Microsoft Academic Search

Combined acquisition of transmission and emission data in SPECT can be used for accurate correction of non-uniform photon attenuation. However, down-scatter from a higher energy isotope (e.g. Tc-99m, 140 keV) contaminates lower energy transmission data (e.g. Gd-153, 100 keV), resulting in under-estimation of reconstructed attenuation coefficients. Correction for down-scatter by subtraction of down-scatter projections (for example collected in a separate

Brendan Vastenhouw; P. P. van Rijk; F. J. Beekman

2002-01-01

378

LETTER TO THE EDITOR: The influence of disorder on the critical sound attenuation in solids  

NASA Astrophysics Data System (ADS)

The field-theoretic description of dynamical critical effects of the influence of disorder on acoustic anomalies near the temperature of the second-order phase transition is considered for three-dimensional Ising-like systems. Calculations of the sound attenuation in pure and dilute Ising-like systems near the critical point are presented. The dynamical scaling function for the critical attenuation coefficient is calculated. The influence of quenched disorder on the asymptotic behaviour of the critical ultrasonic anomalies is discussed.

Prudnikov, P. V.; Prudnikov, V. V.

2005-11-01

379

Antibody biodistribution coefficients  

PubMed Central

Tissue vs. plasma concentration profiles have been generated from a physiologically-based pharmacokinetic model of monoclonal antibody (mAb). Based on the profiles, we hypothesized that a linear relationship between the plasma and tissue concentrations of non-binding mAbs could exist; and that the relationship may be generally constant irrespective of the absolute mAb concentration, time, and animal species being analyzed. The hypothesis was verified for various tissues in mice, rat, monkey, and human using mAb or antibody-drug conjugate tissue distribution data collected from diverse literature. The relationship between the plasma and various tissue concentrations was mathematically characterized using the antibody biodistribution coefficient (ABC). Estimated ABC values suggest that typically the concentration of mAb in lung is 14.9%, heart 10.2%, kidney 13.7%, muscle 3.97%, skin 15.7%, small intestine 5.22%, large intestine 5.03%, spleen 12.8%, liver 12.1%, bone 7.27%, stomach 4.98%, lymph node 8.46%, adipose 4.78%, brain 0.351%, pancreas 6.4%, testes 5.88%, thyroid 67.5% and thymus is 6.62% of the plasma concentration. The validity of using the ABC to predict mAb concentrations in different tissues of mouse, rat, monkey, and human species was evaluated by generating validation data sets, which demonstrated that predicted concentrations were within 2-fold of the observed concentrations. The use of ABC to infer tissue concentrations of mAbs and related molecules provides a valuable tool for investigating preclinical or clinical disposition of these molecules. It can also help eliminate or optimize biodistribution studies, and interpret efficacy or toxicity of the drug in a particular tissue.

Shah, Dhaval K.; Betts, Alison M.

2013-01-01

380

Development of a LacZ-based transcriptional reporter system for use with Moraxella catarrhalis.  

PubMed

The lack of a transcriptional reporter system for use in Moraxella catarrhalis has hindered studies of gene regulation in this pathogen. PCR and recombinant DNA methods were used to insert a multicloning site (MCS) and promoterless full-length Escherichia coli lacZ gene, flanked by transcriptional terminators both immediately upstream and downstream, into the M. catarrhalis recombinant plasmid pWW115. Insertion into the MCS in the newly constructed plasmid pASE222 of M. catarrhalis promoter regions controlled by either a repressor (i.e., NsrR) or activator (i.e., PhoB) yielded transcriptional fusion constructs that were appropriately responsive to signal inputs dependent on the host strain genotype, as measured quantitatively by means of a Miller ?-galactosidase assay. The transcriptional reporter plasmid pASE222 should prove to be a useful tool for rapid screening of factors affecting gene expression in M. catarrhalis. PMID:23219721

Evans, Amanda S; Pybus, Christine; Hansen, Eric J

2013-03-01

381

lac repressor changes conformation upon binding to poly[dA-T)  

PubMed Central

N-(Iodoacetylaminoethyl)-1-naphthylamine-5-sulfonate reacts with Escherichia coli lac repressor to selectively label cysteine-140 with the fluorescent N-(acetylaminoethyl)-1-naphthylamine-5-sulfonate group. The fluorescence intensity of this label decreases by 20% when labeled repressor associates with poly[d(A-T)]. Fifteen base pairs of poly[d(A-T)] per repressor tetramer are required to complete this decrease. Stopped-flow experiments have shown that the repressor undergoes at least two conformational changes as it binds to poly[d(A-T)], with half-lives of 5.0 +/- 1.2 msec and 3.5 +/- 1.0 sex. Quite likely, these conformational changes serve to strengthen the interaction of repressor with DNA.

Kelsey, D E; Rounds, T C; York, S S

1979-01-01

382

Multiwavelength Observations of 6 BL Lac Objects in 2008-2012  

NASA Astrophysics Data System (ADS)

We present results of 4 years of VLBA monitoring along with ?-ray and optical R-band photometric observations of 6 BL Lac objects (3C 66A, S5 0716+71, PKS 0735+17, S4 0954+68, W Com, and OT 081). We have analyzed total intensity images obtained with the VLBA at 43 GHz and investigated the kinematic evolution of the parsec scale jets of the sources. For all sources we compare flux variations in the VLBI core and bright superluminal knots with ?-ray and optical light curves. The majority of ?-ray flares have optical counterparts. 67% of the ?-ray events are coincident with the appearance of new superluminal knots and/or flares in the millimeter-wave core. These results support the conclusion that for many flares in blazars the region of the ?-ray and optical emission is located in the vicinity or downstream of the mm-wave VLBI core.

Morozova, D. A.; Jorstad, S. G.; Marscher, A. P.; Larionov, V. M.; Troitskiy, I. S.; Blinov, D. A.; Agudo, I.; Smith, P. S.

2013-12-01

383

Development of a LacZ-Based Transcriptional Reporter System for Use with Moraxella catarrhalis  

PubMed Central

The lack of a transcriptional reporter system for use in Moraxella catarrhalis has hindered studies of gene regulation in this pathogen. PCR and recombinant DNA methods were used to insert a multicloning site (MCS) and promoterless full-length E. coli lacZ gene, flanked by transcriptional terminators both immediately upstream and downstream, into the M. catarrhalis recombinant plasmid pWW115. Insertion into the MCS in the newly constructed plasmid pASE222 of M. catarrhalis promoter regions controlled by either a repressor (i.e., NsrR) or activator (i.e., PhoB) yielded transcriptional fusion constructs that were appropriately responsive to signal inputs dependent on the host strain genotype, as measured quantitatively by means of a Miller ?-galactosidase assay. The transcriptional reporter plasmid pASE222 should prove to be a useful tool for rapid screening of factors affecting gene expression in M. catarrhalis.

Evans, Amanda S.; Pybus, Christine; Hansen, Eric J.

2012-01-01

384

Gene fusions with lacZ by duplication insertion in the radioresistant bacterium Deinococcus radiodurans  

SciTech Connect

Deinococcus radiodurans is the most-studied species of a eubacterial family characterized by extreme resistance to DNA damage. We have focused on developing molecular biological techniques to investigate the genetics of this organism. We report construction of lacZ gene fusions by a method involving both in vitro splicing and the natural transformation of D. radiodurans. Numerous fusion strains were identified by expression of beta-galactosidase. Among these fusion strains, several were inducible by exposure to the DNA-damaging agent mitomycin C, and four of the inducible fusion constructs were cloned in Escherichia coli. Hybridization studies indicate that one of the damage-inducible genes contains a sequence reiterated throughout the D. radiodurans chromosome. Survival measurements show that two of the fusion strains have increased sensitivity to mitomycin C, suggesting that the fusions within these strains inactivate repair functions.

Lennon, E.; Minton, K.W. (Uniformed Services Univ. of the Health Sciences, Bethesda, MD (USA))

1990-06-01

385

Sensitive biological detection method for tetracyclines using a tetA-lacZ fusion system.  

PubMed Central

A sensitive microbiological detection system for tetracyclines, utilizing an Escherichia coli strain containing a cloned tetA-lacZ gene fusion, is described. Expression of beta-galactosidase by the fusion plasmid pUB3610 remained subject to regulatory control by the TetR repressor protein, with the presence of tetracyclines in the growth medium leading to a 12-fold induction of beta-galactosidase synthesis. Because synthesis of beta-galactosidase was influenced to a small extent by the carbon source and the addition of cyclic AMP to the medium, cells were grown in the presence of cyclic AMP to enhance the sensitivity of the assay. All commonly marketed tetracyclines and some derivatives at concentrations as low as 0.1 ng/ml could be detected in the growth medium. A plate assay utilizing the fusion plasmid that detects 1 ng of tetracycline has also been developed. Images

Chopra, I; Hacker, K; Misulovin, Z; Rothstein, D M

1990-01-01

386

Analysis of Optical Variations of BL Lac Object AO 0235+164  

NASA Astrophysics Data System (ADS)

Historical optical BVRI band data are combined on the BL Lac object AO 0235 + 164. In order to examine the possible existence of lags and correlations between variations in different optical bands from this source, a statistical analysis is performed through the Discrete Correlation Function (DCF) method. Monte Carlo simulations called Flux Redistribution/Random Subset Selection (FR/RSS) are performed to obtain statistically meaningful values for the cross-correlation time lags and their related uncertainties. The analysis confirms that the variations in different optical light curves are strongly correlated, with no or very weak lag within the errors. Long term variability of color indices are also analysed. No color variabilities are found.

Hong-tao, Wang

2014-03-01

387

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

388

Interplay of Protein and DNA Structure Revealed in Simulations of the lac Operon  

PubMed Central

The E. coli Lac repressor is the classic textbook example of a protein that attaches to widely spaced sites along a genome and forces the intervening DNA into a loop. The short loops implicated in the regulation of the lac operon suggest the involvement of factors other than DNA and repressor in gene control. The molecular simulations presented here examine two likely structural contributions to the in-vivo looping of bacterial DNA: the distortions of the double helix introduced upon association of the highly abundant, nonspecific nucleoid protein HU and the large-scale deformations of the repressor detected in low-resolution experiments. The computations take account of the three-dimensional arrangements of nucleotides and amino acids found in crystal structures of DNA with the two proteins, the natural rest state and deformational properties of protein-free DNA, and the constraints on looping imposed by the conformation of the repressor and the orientation of bound DNA. The predicted looping propensities capture the complex, chain-length-dependent variation in repression efficacy extracted from gene expression studies and in vitro experiments and reveal unexpected chain-length-dependent variations in the uptake of HU, the deformation of repressor, and the folding of DNA. Both the opening of repressor and the presence of HU, at levels approximating those found in vivo, enhance the probability of loop formation. HU affects the global organization of the repressor and the opening of repressor influences the levels of HU binding to DNA. The length of the loop determines whether the DNA adopts antiparallel or parallel orientations on the repressor, whether the repressor is opened or closed, and how many HU molecules bind to the loop. The collective behavior of proteins and DNA is greater than the sum of the parts and hints of ways in which multiple proteins may coordinate the packaging and processing of genetic information.

Czapla, Luke; Grosner, Michael A.; Swigon, David; Olson, Wilma K.

2013-01-01

389

Interplay of protein and DNA structure revealed in simulations of the lac operon.  

PubMed

The E. coli Lac repressor is the classic textbook example of a protein that attaches to widely spaced sites along a genome and forces the intervening DNA into a loop. The short loops implicated in the regulation of the lac operon suggest the involvement of factors other than DNA and repressor in gene control. The molecular simulations presented here examine two likely structural contributions to the in-vivo looping of bacterial DNA: the distortions of the double helix introduced upon association of the highly abundant, nonspecific nucleoid protein HU and the large-scale deformations of the repressor detected in low-resolution experiments. The computations take account of the three-dimensional arrangements of nucleotides and amino acids found in crystal structures of DNA with the two proteins, the natural rest state and deformational properties of protein-free DNA, and the constraints on looping imposed by the conformation of the repressor and the orientation of bound DNA. The predicted looping propensities capture the complex, chain-length-dependent variation in repression efficacy extracted from gene expression studies and in vitro experiments and reveal unexpected chain-length-dependent variations in the uptake of HU, the deformation of repressor, and the folding of DNA. Both the opening of repressor and the presence of HU, at levels approximating those found in vivo, enhance the probability of loop formation. HU affects the global organization of the repressor and the opening of repressor influences the levels of HU binding to DNA. The length of the loop determines whether the DNA adopts antiparallel or parallel orientations on the repressor, whether the repressor is opened or closed, and how many HU molecules bind to the loop. The collective behavior of proteins and DNA is greater than the sum of the parts and hints of ways in which multiple proteins may coordinate the packaging and processing of genetic information. PMID:23457581

Czapla, Luke; Grosner, Michael A; Swigon, David; Olson, Wilma K

2013-01-01

390

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.

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

2012-01-01

391

Activation of silent gal genes in the lac-gal regulon of Streptococcus thermophilus.  

PubMed

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, E E; van den Bogaard, P T; Catzeddu, P; Kuipers, O P; de Vos, W M

2001-02-01

392

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.

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

2014-01-01

393

Measurement of ultrasonic attenuation in diabetic neuropathic sciatic nerves for diagnostic and therapeutic applications.  

PubMed

Measurements of ultrasonic attenuation in the sciatic nerves of rats were performed to verify the feasibility of ultrasound diagnosis of peripheral neuropathy and to avoid damage to the nerves caused by overheating in pain management applications. A rat model of diabetic peripheral neuropathy was established. The proximal-segment and middle-segment sciatic nerves of control and neuropathic rats were dissected for the attenuation measurement. Two commercial ultrasound transducers and a self-developed experimental platform were used in the measurements. Using H&E staining and transmission electron (TE) microscopy, morphological analysis of the control and neuropathic nerves was performed to determine the relationship between attenuation and the histology of the nerves. The experimental results showed that the attenuation coefficients of the control, second-week, fourth-week, and eighth-week neuropathic nerves were -6.68 ± 0.50, -5.61 ± 0.34, -6.27 ± 0.40, and -7.10 ± 0.35 dB/cm at 2.68 MHz, respectively. The respective values at 7.50 MHz were -14.96 ± 0.79, -12.65 ± 0.28, -13.98 ± 1.07, and -16.00 ± 0.54 dB/cm. The changes in the attenuation coefficients were significantly different among the second-week, fourth-week, and eighth-week DN nerves. Additionally, the ultrasonic attenuation coefficient of the rat sciatic nerve was fourfold that of the cat brain and cow liver and twofold that of human muscle. PMID:24566928

Chen, Gin-Shin; Lee, Yee-Fun; Cheng, Jung-Sung

2014-08-01

394

Two Lactococcus lactis genes, including lacX, cooperate to trigger an SOS response in a recA-negative background.  

PubMed

A 4.3-kb EcoRI fragment from a Lactococcus lactis genomic library alleviates the methyl methanesulfonate, mitomycin C, and UV sensitivities of an Escherichia coli recA mutant (M. Novel, X. F. Huang, and G. Novel, FEMS Microbiol. Lett. 72:309-314, 1990). It complements recA1 and delta recA mutations but not recA13. Three proteins (with molecular masses of 20, 35, and 23 kDa) were produced from this fragment in a T7-directed system, and three corresponding genes were detected by DNA sequencing, namely, ISS1CH;lacX, which is the distal gene of the lac operon; and a third open reading frame, named lacN, which encodes 211 amino acids. Mutations produced in either lacX or in lacN resulted in the loss of the resistance to DNA-damaging agents. Thus, these two genes appeared to be involved in this activity. Introduction of pUCB214 carrying the 4.3-kb fragment into a lexA+ delta recA306 sfiA::lacZ strain resulted in UV-inducible synthesis of beta-galactosidase. A uvrA strain or a lexA (Ind-) strain containing pUCB214 did not support any DNA repair. However, a lexA (Def-) strain carrying pUCB214 could partly repair UV damage. We discuss possible targets for LacX and LacN products, and we speculate that LacX and LacN may constitute a two-component regulatory system that is able to respond to SOS signals, and then to act in the SOS response, bypassing the RecA-activated function. PMID:7814316

Huang, X F; Huang, D C; Novel, G; Novel, M

1995-01-01

395

Differential experimental micrometastasis to lung, liver, and bone with lacZ-tagged CWR22R prostate carcinoma cells.  

PubMed

LacZ-tagged human prostate carcinoma CWR22Rv1 cells metastasize spontaneously to lung, liver, and bone from subcutaneous primary tumors in athymic nude mice; these organs are 'natural' targets of metastasis for the human disease. To evaluate the mechanism(s) of metastasis to these organs, an experimental metastasis model was used by taking advantage of the ultrasensitive detection of lacZ. Within I h after tail vein injection, micrometastases were forming in lung, liver, bone, kidney, and brain with very different quantitative levels. The kinetics of loss of unstable micrometastases and retention of stable ones were also very different in these organs. After injecting suspensions of single cells, both whole-organ and serial-section staining for lacZ revealed considerable heterogeneity in cell number of individual lung micrometastases while micrometastases in liver contained only I or 2 cells. The size of individual bone micrometastases also suggested only 1 or 2 cells. Tumor cells could also be detected in the small blood vessels of the lung within minutes after injection. These studies indicate that lacZ-tagged CWR22Rv1 cells after tissue culturing contain subsets of cells capable of establishing transient micrometastases in lung, liver, and bone after direct injection into the animal's circulation. Moreover, the quantitative and qualitative properties of the micrometastases in the three organs differ significantly, suggesting different mechanisms for stabilization and fates of micrometastases in these organs. PMID:11918079

Holleran, Julianne L; Miller, Carson J; Edgehouse, Nancy L; Pretlow, Theresa P; Culp, Lloyd A

2002-01-01

396

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

397

DIETS OF MICROPTERUS SALMOIDES LAC. AND ESOX LUCIUS L. IN LAKE TRASIMENO (UMBRIA, ITALY) AND THEIR DIET OVERLAP  

Microsoft Academic Search

The aim of this study was to gather information about the feeding habits of Micropterus salmoides Lac., an exotic species recently introduced into Lake Trasimeno and Esox lucius L., in order to determine the degree of overlap between the two diets. The stomachs of 179 largemouth basses and 125 pikes were examined. The index of diet overlap (?) was determined

M. LORENZONI; M. CORBOLI; A. J. M. DÖRR; G. GIOVINAZZO; S. SELVI; M. MEARELLI

2002-01-01

398

Structure-Based Rational Design to Enhance the Solubility and Thermostability of a Bacterial Laccase Lac15  

PubMed Central

Bacterial laccases are ideal alternatives of fungal laccases for specific industrial applications due to specific characteristics such as alkalescence dependence and high chloride tolerance. However, some bacterial laccases presented as inclusion bodies when expressing in Escherichia coli and showed thermal instability. In this study, rational design was employed to enhance the solubility and the thermostablity of the bacterial laccase Lac15-His6 based on the crystal structure obtained previously. After deletion of His-tag and residues323–332, the obtained Lac15D was completely expressed in soluble form even at a higher temperature of 28°C, compared to only 50% of Lac15-His6 expressed solubly at 16°C. It showed a two-time higher activity at temperatures lower than 35°C and a half-life increasing from 72 min to 150 min at 45°C. When used in chromogenic reactions, Lac15D showed constant activity toward dye precursors and their combinations under alkaline conditions, demonstrating its application potential in hair coloring biotechnology.

Fang, Zemin; Zhou, Peng; Chang, Fei; Yin, Qiang; Fang, Wei; Yuan, Jing; Zhang, Xuecheng; Xiao, Yazhong

2014-01-01

399

Progressive microcrack development in tests in Lac du Bonnet granite—I. Acoustic emission source location and velocity measurements  

Microsoft Academic Search

Three large blocks (52 × 52 × 22 cm) of Lac du Bonnet granite from the Cold Springs Quarry were tested under various load conditions to investigate the effect of stress path on the formation of damage around holes. Two blocks had throughgoing central holes, and were subjected to uniaxial and biaxial loads, respectively. Acoustic emission (AE) count rates were

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

1995-01-01

400

Fibronectin-binding proteins are required for biofilm formation by community-associated methicillin-resistant Staphylococcus aureus strain LAC.  

PubMed

Community-associated methicillin-resistant Staphylococcus aureus of the USA300 lineage is emerging as an important cause of medical device-related infection. However, few factors required for biofilm accumulation by USA300 strains have been identified, and the processes involved are poorly understood. Here, we identify S. aureus proteins required for the USA300 isolate LAC to form biofilm. A mutant with a deletion of the fnbA and fnbB genes did not express the fibronectin-binding proteins FnBPA and FnBPB and lacked the ability to adhere to fibronectin or to form biofilm. Biofilm formation by the mutant LAC?fnbAfnbB could be restored by expression of FnBPA or FnBPB from a plasmid demonstrating that both of these proteins can mediate biofilm formation when expressed by LAC. Expression of FnBPA and FnBPB increased bacterial aggregation suggesting that fibronectin-binding proteins can promote the accumulation phase of biofilm. Loss of fibronectin-binding proteins reduced the initial adherence of bacteria, indicating that these proteins are also involved in primary attachment. In summary, these findings improve our understanding of biofilm formation by the USA300 strain LAC by demonstrating that the fibronectin-binding proteins are required. PMID:24628034

McCourt, Jennifer; O'Halloran, Dara P; McCarthy, Hannah; O'Gara, James P; Geoghegan, Joan A

2014-04-01

401

The addition of a coarse-grained looping state enhances bistability in a gene expression model of lac  

NASA Astrophysics Data System (ADS)

Bistability of the lac genetic switch in Escherichia coli is known to depend on its ability to form DNA loops with the lac repressor. Here we present a stochastic gene--mRNA--protein model of the lac switch that includes a third transcriptional state describing the DNA loop. We introduce a novel geometric burst extension to the finite state projection method, which allows us to eliminate mRNA as an independent species and rapidly search the parameter space of the model. We evaluate how the addition of the third state changes the model's bistability properties and find a region of parameter space where the system behaves in a way consistent to that seen experimentally for lac. Induction in the looping model is preceded by a rare complete dissociation of the loop followed by an immediate burst of mRNA rather than a slower build up of mRNA as in the two-state model. The overall effect of the looped state is to allow for faster switching times while at the same time further separating the uninduced and induced phenotypes from each other. These properties of loop regulatory elements give them intriguing implications for use in synthetic biology.

Earnest, Tyler; Roberts, Elijah; Assaf, Michael; Dahmen, Karin; Luthey-Schulten, Zaida

2013-03-01

402

FRACTIONAL WAVE EQUATIONS WITH ATTENUATION  

PubMed Central

Fractional wave equations with attenuation have been proposed by Caputo [5], Szabo [27], Chen and Holm [7], and Kelly et al. [11]. These equations capture the power-law attenuation with frequency observed in many experimental settings when sound waves travel through inhomogeneous media. In particular, these models are useful for medical ultrasound. This paper develops stochastic solutions and weak solutions to the power law wave equation of Kelly et al. [11].

Straka, Peter; Meerschaert, Mark M.; McGough, Robert J.; Zhou, Yuzhen

2013-01-01

403

Use of the tac promoter and lacIq for the controlled expression of Zymomonas mobilis fermentative genes in Escherichia coli and Zymomonas mobilis.  

PubMed Central

The Zymomonas mobilis genes encoding alcohol dehydrogenase I (adhA), alcohol dehydrogenase II (adhB), and pyruvate decarboxylase (pdc) were overexpressed in Escherichia coli and Z. mobilis by using a broad-host-range vector containing the tac promoter and the lacIq repressor gene. Maximal IPTG (isopropyl-beta-D-thiogalactopyranoside) induction of these plasmid-borne genes in Z. mobilis resulted in a 35-fold increase in alcohol dehydrogenase I activity, a 16.7-fold increase in alcohol dehydrogenase II activity, and a 6.3-fold increase in pyruvate decarboxylase activity. Small changes in the activities of these enzymes did not affect glycolytic flux in cells which are at maximal metabolic activity, indicating that flux under these conditions is controlled at some other point in metabolism. Expression of adhA, adhB, or pdc at high specific activities (above 8 IU/mg of cell protein) resulted in a decrease in glycolytic flux (negative flux control coefficients), which was most pronounced for pyruvate decarboxylase. Growth rate and flux are imperfectly coupled in this organism. Neither a twofold increase in flux nor a 50% decline from maximal flux caused any immediate change in growth rate. Thus, the rates of biosynthesis and growth in this organism are not limited by energy generation in rich medium. Images

Arfman, N; Worrell, V; Ingram, L O

1992-01-01

404

Attenuation correction for small animal SPECT imaging using x-ray CT data  

SciTech Connect

Photon attenuation in small animal nuclear medicine scans can be significant when using isotopes that emit lower energy photons such as iodine-125. We have developed a method to use microCT data to perform attenuation corrected small animal single-photon emission computed tomography (SPECT). A microCT calibration phantom was first imaged, and the resulting calibration curve was used to convert microCT image values to linear attenuation coefficient values that were then used in an iterative SPECT reconstruction algorithm. This method was applied to reconstruct a SPECT image of a uniform phantom filled with {sup 125}I-NaI. Without attenuation correction, the image suffered a 30% decrease in intensity in the center of the image, which was removed with the addition of attenuation correction. This reduced the relative standard deviation in the region of interest from 10% to 6%.

Hwang, Andrew B.; Hasegawa, Bruce H. [Bioengineering Graduate Group, University of California at Berkeley and University of California, San Francisco, Berkeley, California 94720 (United States); Bioengineering Graduate Group, University of California at Berkeley and University of California, San Francisco, Berkeley, California 94720 and Department of Radiology, University of California, 185 Berry Street, Suite 350, San Francisco, San Francisco, California 94143-0943 (United States)

2005-09-15

405

Radar attenuation in desert soil  

NASA Astrophysics Data System (ADS)

Soil properties make a significant impact in the observed responses of various sensors for subsurface target detection. Ground penetrating radars (GPRs) have been extensively researched as a tool for subsurface target detection. A key soil parameter of interest for evaluating GPR performance is the soil attenuation rate. The information about the soil attenuation rate coupled with target properties (size, shape, material properties and depth of burial) can be used to estimate the effectiveness of radar sensors in a particular soil environment. Radar attenuation in desert soil is of interest in today's political and military climate. Laboratory measurements of desert soil attenuation were conducted using samples collected from a desert in Southwestern United States and in Iraq. These measurements were made in a coaxial waveguide over the frequency ranging from 250 MHz to 4 GHz. The soil grain size distribution, mineralogy, moisture and salinity were also measured. This report describes the experimental procedure and presents the radar attenuation rates observed in desert soils. The results show that the soluble salt content is an important parameter affecting the attenuation behavior of desert soils.

Koh, Gary

2008-05-01

406

Table for determining phi coefficients  

Microsoft Academic Search

A table is presented which directly gives phi coefficients accurate to three places when entered by the proportion of one sub-group responding in a specified manner and the proportion of a second sub-group responding in the same manner. The table gives coefficients identical with those obtained by formula if the sub-groups are equal in number. The phi coefficients can readily

C. E. Jurgensen

1947-01-01

407

The Bethe lattice treatment of sound attenuation for a spin- 3/2 Ising model  

NASA Astrophysics Data System (ADS)

The sound attenuation phenomena is investigated for a spin- 3/2 Ising model on the Bethe lattice in terms of the recursion relations by using the Onsager theory of irreversible thermodynamics. The dependencies of sound attenuation on the temperature (T), frequency (w), Onsager coefficient (?) and external magnetic field (H) near the second-order (Tc) and first-order (Tt) phase transition temperatures are examined for given coordination numbers q on the Bethe lattice. It is assumed that the sound wave couples to the order-parameter fluctuations which decay mainly via the order-parameter relaxation process, thus two relaxation times are obtained and which are used to obtain an expression for the sound attenuation coefficient (?). Our investigations revealed that only one peak is obtained near Tt and three peaks are found near Tc when the Onsager coefficient is varied at a given constant frequency for q=3. Fixing the Onsager coefficient and varying the frequency always leads to two peaks for q=3,4 and 6 near Tc. The sound attenuation peaks are observed near Tt at lower values of external magnetic field, but as it increases the sound attenuation peaks decrease and eventually disappear.

Cengiz, Tunç; Albayrak, Erhan

2012-05-01

408

Effects of shock-induced cracks on the ultrasonic velocity and attenuation in granite  

NASA Astrophysics Data System (ADS)

Measurements of the compressional wave velocity and the attenuation coefficients of 1-cm cubes were conducted. Samples were taken at various radii and depths beneath a 20 × 20 × 15 cm San Marcos granite block, impacted by a lead bullet at a velocity of 1200 m/s. The damage parameters of the cubes are calculated from the measured preimpact and postimpact P wave velocities, Vp0 and Vp, and the crack density is inverted from the measured P wave velocities. The anisotropic orientation of cracks is more obvious from the attenuation than crack density and damage parameters calculated from the ultrasonic velocity. P wave velocity and the normalized distance from the impact point follow an exponential decay relation. Other properties, such as the damage parameter, crack density, and attenuation coefficient, are expressed by a power law decay with distance. The damage parameter and attenuation coefficients are approximately linearly related. The slope of the linear fitting results in directions normal to the crack orientation is about twice the value in direction along the crack orientation. The attenuation coefficient is found to be a more useful parameter than elastic velocity in describing the anisotropic orientation of cracks.

Ai, Huirong A.; Ahrens, Thomas J.

2007-01-01

409

The AAPM/RSNA physics tutorial for residents. X-ray attenuation.  

PubMed

Attenuation is the reduction of the intensity of an x-ray beam as it traverses matter. The reduction may be caused by absorption or by deflection (scatter) of photons from the beam and can be affected by different factors such as beam energy and atomic number of the absorber. An attenuation coefficient is a measure of the quantity of radiation attenuation by a given thickness of absorber. Linear and mass attenuation coefficients are the coefficients used most often. The equation I = Ioe-mu x expresses the exponential relationship between incident primary photons and transmitted photons for a monoenergetic beam with respect to the thickness of the absorber and thus may be used to calculate the attenuation by any thickness of material. The quality or penetrating ability of an x-ray beam is usually described by stating its half-value layer (HVL). Another parameter used to describe the penetrating ability of a beam is the homogeneity coefficient. Among other things, use of added filtration reduces the intensity of the x-ray beam, increases the HVL, decreases patient exposure, and improves image quality for a given radiation dose. PMID:9460114

McKetty, M H

1998-01-01

410

STP Second Virial Coefficient Program  

NSDL National Science Digital Library

The STP SecondVirialCoefficient program numerically evaluates the second virial coefficient for the Lennard-Jones potential at various temperatures. The default is temperature range is 0.5 to 5. STP SecondVirialCoefficient is part of a suite of Open Source Physics programs that model aspects of Statistical and Thermal Physics (STP). The program is distributed as a ready-to-run (compiled) Java archive. Double clicking the stp_SecondVirialCoefficient.jar file will run the program if Java is installed on your computer. Additional programs can be found by searching ComPADRE for Open Source Physics, STP, or Statistical and Thermal Physics.

Gould, Harvey; Tobochnik, Jan; Christian, Wolfgang; Cox, Anne

2009-02-18

411

The crystal field effects on sound attenuation for a spin-1 Ising model on the Bethe lattice  

NASA Astrophysics Data System (ADS)

The sound attenuation phenomenon is investigated by using the Onsager theory of irreversible thermodynamics for a spin-1 Ising model with the inclusion of the crystal field effects on the Bethe lattice. The recursion relations are calculated in a transcendental form to obtain the order-parameters and then the sound attenuation is analyzed. The relationships of sound attenuation with temperature, frequency and Onsager coefficient are examined near the second- and first-order phase transition temperatures, Tc and Tt respectively, for given negative crystal field values and coordination numbers on the Bethe lattice. The sound wave couples to the order-parameter fluctuations which decay mainly via the order-parameter relaxation process. Thus, two relaxation times are obtained which are used to find an expression for the sound attenuation coefficient. The attenuation maxima are found near the second- and first-order phase transition temperatures in the ferromagnetic and quadrupole phase regions, respectively, for the coordination numbers q = 3,4 and 6. The attenuation peaks are observed at the same temperature before Tt and are found to be shifted to lower (higher) temperatures with increasing value of frequency (Onsager coefficient) before Tc for any crystal field values. The attenuation peaks are found at lower values and at higher temperatures with negatively increasing crystal field values in the quadrupolar phase regions. In addition, the sound attenuation peaks are also studied at some tricritical points for q = 3,4 and 6 for some critical values of the crystal field.

Cengiz, Tunç; Albayrak, Erhan

2012-07-01

412

Attenuation correction for PET/MR: problems, novel approaches and practical solutions.  

PubMed

Attenuation correction in PET is the primary prerequisite for quantification of the radiotracer's signal. Absolute quantification is the key to improve diagnostic performance, to enable comparisons between follow-up examinations and to perform pharmacokinetic modeling. A large fraction of the 511 keV annihilation photons from the positron emitters are scattered by the patient's body. Thus, they are discarded or do not even reach the PET detectors, while others are identified at the wrong location after being scattered. To account for these effects and thus generate quantitative PET images showing the actual activity distribution, it is necessary to determine an attenuation map with the appropriate attenuation coefficients for 511 keV photons at each voxel. In hybrid PET/CT systems, this is achieved using the information about the tissue electron density provided by the CT and adjusting it for the difference in photon energy. In PET/MR systems, there is no mechanism to directly measure the attenuation coefficients of the tissue. Determining the attenuation map in PET/MR is an important challenge involving two problems: the determination of the patient's attenuation map and the determination of the attenuation introduced by additional hardware components. We describe the approaches investigated to deal with these problems and, based on the experience with a fully integrated PET/MR system, we finally discuss potential solutions and limitations in a close to routine setting. PMID:22925653

Martinez-Möller, Axel; Nekolla, Stephan G

2012-12-01

413

Feasibility Study of Grain Size Estimation of S45C by Attenuation Measurement of 40 MHz Surface Acoustic Wave Generated by Phase Velocity Scanning of Laser Interference Fringes  

NASA Astrophysics Data System (ADS)

Structural change in 0.45 mass % carbon steel during tempering was measured nondestructively as a change in the attenuation coefficient of 40 MHz surface acoustic waves (SAW) generated by scanning interference fringes (SIF). The SIF selectively generate the SAW at an adequate center frequency, which is useful to distinguish the attenuation coefficients between slightly different structures. The attenuation coefficient at 40 MHz increased linearly with heating time (30, 60 and 90 min) at 750°C, representing a minute change in the structure of ferrite and pearlite grains. The method revealed a minute structural change in the ferrite-pearlite ratio and in grain size growth due to the heat treatment.

Nishino, Hideo; Furukawa, Tsutomu; Takashina, Sunao; Takemoto, Mikio

2000-05-01

414

Graph characterization via Ihara coefficients.  

PubMed

The novel contributions of this paper are twofold. First, we demonstrate how to characterize unweighted graphs in a permutation-invariant manner using the polynomial coefficients from the Ihara zeta function, i.e., the Ihara coefficients. Second, we generalize the definition of the Ihara coefficients to edge-weighted graphs. For an unweighted graph, the Ihara zeta function is the reciprocal of a quasi characteristic polynomial of the adjacency matrix of the associated oriented line graph. Since the Ihara zeta function has poles that give rise to infinities, the most convenient numerically stable representation is to work with the coefficients of the quasi characteristic polynomial. Moreover, the polynomial coefficients are invariant to vertex order permutations and also convey information concerning the cycle structure of the graph. To generalize the representation to edge-weighted graphs, we make use of the reduced Bartholdi zeta function. We prove that the computation of the Ihara coefficients for unweighted graphs is a special case of our proposed method for unit edge weights. We also present a spectral analysis of the Ihara coefficients and indicate their advantages over other graph spectral methods. We apply the proposed graph characterization method to capturing graph-class structure and clustering graphs. Experimental results reveal that the Ihara coefficients are more effective than methods based on Laplacian spectra. PMID:21118772

Ren, Peng; Wilson, Richard C; Hancock, Edwin R

2011-02-01

415

Extinction Coefficient at Zero Concentration  

Microsoft Academic Search

THE use of extinction coefficients to characterize substances depends on the validity of Lambert-Beer's law. The following shows that a constant-extinction coefficient at zero concentration-which is the tangent to the extinction-concentration curve at zero concentration, may be calculated even if Lambert-Beer's law is not followed.

J. Fog

1962-01-01

416

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

PubMed

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 +3.5mV, 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

2013-06-28

417

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.

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

2013-01-01

418

Prediction of spectral acceleration response ordinates based on PGA attenuation  

USGS Publications Warehouse

Developed herein is a new peak ground acceleration (PGA)-based predictive model for 5% damped pseudospectral acceleration (SA) ordinates of free-field horizontal component of ground motion from shallow-crustal earthquakes. The predictive model of ground motion spectral shape (i.e., normalized spectrum) is generated as a continuous function of few parameters. The proposed model eliminates the classical exhausted matrix of estimator coefficients, and provides significant ease in its implementation. It is structured on the Next Generation Attenuation (NGA) database with a number of additions from recent Californian events including 2003 San Simeon and 2004 Parkfield earthquakes. A unique feature of the model is its new functional form explicitly integrating PGA as a scaling factor. The spectral shape model is parameterized within an approximation function using moment magnitude, closest distance to the fault (fault distance) and VS30 (average shear-wave velocity in the upper 30 m) as independent variables. Mean values of its estimator coefficients were computed by fitting an approximation function to spectral shape of each record using robust nonlinear optimization. Proposed spectral shape model is independent of the PGA attenuation, allowing utilization of various PGA attenuation relations to estimate the response spectrum of earthquake recordings.

Graizer, V.; Kalkan, E.

2009-01-01

419

UVR attenuation in lakes: relative contibutions of dissolved and particulate material  

NASA Astrophysics Data System (ADS)

Solar radiation in lakes is attenuated by dissolved material, especially dissolved organic material (DOC), particulate material (PM), and water. DOC is a strong predictor of the attenuation of Ultraviolet Radiation (UVR) in lakes. Phytoplankton and detritus are known to contribute substantially to PAR attenuation but relatively little is known about their role in attenuation of UVR. This study investigated the relative contributions of dissolved and particulate material to the attenuation of UVR in lakes by combining an adapted Quantitative Filter Technique (QFT) with laboratory measurements of absorption by DOC and field measurements of UVR diffuse attenuation. The absorption of filtrate and PM filtered onto glass fiber filters were scanned by a UV-visible dual beam spectrophotometer. Total absorption coefficient (at) was computed as the sum of the absorption coefficients for water (aw), dissolved material (ad), and PM (ap). The value of at was compared with the diffuse attenuation coefficient (Kd) measured directly in the lakes by a Profiling UV radiometer. The ratio at/Kd ranged between 0.9 and 1.3 for UVR. Ratios less than unity may be attributed to scattering and to sun angle effects, especially at the longer UVR wavelengths. Ratios occasionally were measured above unity, suggesting errors in estimating at. Particles played a significant and seasonally-varying role in lake UVR attenuation. Within oligotrophic, low DOC Lake Giles, the relative contribution of ap varied from 30 percent to 53 percent for 320 nm UVR. In mesotrophic, higher DOC Lake Lacawac the seasonal range was 7.6 percent to 57 percent. In each case, the highest contribution of PM was found during early spring and late fall.

Ayoub, L. M.; Hargreaves, B. R.; Morris, D. P.

1997-02-01

420

KDR-LacZ-expressing cells are involved in ovarian and testis-specific vascular development, suggesting a role for VEGFA in the regulation of this vasculature.  

PubMed

Our objectives were to evaluate kinase insert domain protein receptor (KDR)-?-galactosidase (LacZ) expression as a marker for vascular development during gonadal morphogenesis and to determine whether any novel non-angiogenic KDR-LacZ expression was present in mouse testes or ovaries. Gonads were collected from mice expressing LacZ driven by the Kdr promoter (KDR-LacZ) from embryonic day 11 (E11) through postnatal day 60 (P60). At E11.5, mesonephric cells expressing KDR-LacZ seemed to migrate into the developing testis and surrounded developing seminiferous cords. Cells expressing KDR-LacZ appeared in the ovary with no apparent migration from the adjacent mesonephros, suggesting a different origin of endothelial cells. Testis organ cultures from E11 mice were treated with 8 ?M VEGFR-TKI, a vascular endothelial growth factor A signal transduction inhibitor; subsequently, the amount of KDR-LacZ staining was reduced by 66%-99% (P<0.002), and the ability of KDR-expressing cells to form a densely organized vascular network was inhibited. Novel non-angiogenic KDR-LacZ staining was detected in the testis on specific subsets of germ cells at E16, E17, P4, P20, P30, and P60. In ovaries, staining was present on oocytes within oocyte cysts at E17 and within late secondary follicles of postnatal mice. Thus, KDR is an excellent marker for analyzing vascular development in the gonads. Inhibition of VEGFA signal transduction prevents the development of testis-specific vasculature. Furthermore, non-vascular KDR-LacZ staining suggests that KDR directly affects both spermatogenesis and somatic-oocyte interactions during gametogenesis. PMID:20848132

Bott, Rebecca C; Clopton, Debra T; Fuller, Anna M; McFee, Ryann M; Lu, Ningxia; McFee, Renee M; Cupp, Andrea S

2010-10-01

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