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1

Attenuation coefficients of Rayleigh and Lg waves  

Microsoft Academic Search

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

Igor B. Morozov

2010-01-01

2

Investigation of photon attenuation coefficients for marble.  

PubMed

The total linear attenuation coefficients micro (cm(-1)) have been obtained using the XCOM program at photon energies of 1 keV to 1 GeV for six different natural marbles produced in different places in Turkey. The individual contribution of photon interaction processes to the total linear attenuation coefficients for marble has been investigated. The calculated results were also compared with the measurements. The results obtained for marble were also compared with concrete. PMID:15942062

Basyigit, C; Akkurt, I; Kilincarslan, S; Akkurt, A

2005-06-07

3

Gamma ray attenuation coefficient measurement for neutron-absorbent materials  

NASA Astrophysics Data System (ADS)

The compounds Na2B4O7, H3BO3, CdCl2 and NaCl and their solutions attenuate gamma rays in addition to neutron absorption. These compounds are widely used in the shielding of neutron sources, reactor control and neutron converters. Mass attenuation coefficients of gamma related to the four compounds aforementioned, in energies 662, 778.9, 867.38, 964.1, 1085.9, 1173, 1212.9, 1299.1,1332 and 1408 keV, have been determined by the ? rays transmission method in a good geometry setup; also, these coefficients were calculated by MCNP code. A comparison between experiments, simulations and Xcom code has shown that the study has potential application for determining the attenuation coefficient of various compound materials. Experiment and computation show that H3BO3 with the lowest average Z has the highest gamma ray attenuation coefficient among the aforementioned compounds.

Jalali, Majid; Mohammadi, Ali

2008-05-01

4

A model for the diffuse attenuation coefficient of downwelling irradiance  

Microsoft Academic Search

The diffuse attenuation coefficient for downwelling irradiance (Kd) is an important parameter for ocean studies. For the vast ocean the only feasible means to get fine-scale measurements of Kd is by ocean color remote sensing. At present, values of Kd from remote sensing are estimated using empirical algorithms. Such an approach is insufficient to provide an understanding regarding the variation

Zhong-Ping Lee; Ke-Ping Du; Robert Arnone

2005-01-01

5

Gamma-ray attenuation coefficients in bismuth borate glasses  

NASA Astrophysics Data System (ADS)

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 samples, which were found to be constant with bismuth concentration and energy.

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

2002-07-01

6

Gamma ray attenuation coefficient measurement for neutron-absorbent materials  

Microsoft Academic Search

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

Majid Jalali; Ali Mohammadi

2008-01-01

7

Temporal variations of coda Q: An attenuation-coefficient view  

NASA Astrophysics Data System (ADS)

Spatial and temporal variations of coda wave attenuation were identified in many studies, and particularly in relation to major earthquakes and volcanic eruptions. Both the coda quality factor, Qc, and its frequency dependence often change following such events, which is often attributed to variations in the properties of large volumes of the subsurface. However, Qc is also strongly sensitive to the assumed theoretical models, which are usually insufficiently accurate for constraining the actual relationships between the geometrical spreading, anelastic dissipation, and scattering. This inaccuracy often leads to significant exaggeration of attenuation effects and complicates the interpretation of temporal variations. To resolve this problem, this study uses a phenomenological approach based on the temporal attenuation coefficient ? instead of Qc. The attenuation coefficient often linearly depends on frequency f, with intercept ?=?(0) related to the geometrical spreading and slope giving the "effective quality" factor Qe as d?/df=?Qe-1. Two published examples of temporal variations of local-earthquake coda are revisited: a non-volcanic (Stone Canyon in central California) and volcanic area (Mount St. Helens, Washington). In both cases, linear ?(f) patterns are found, with the effects of ? on coda decay rates being significantly stronger than those of Qe-1. At Stone Canyon, ? ranged from 0.035 to 0.06 s -1 and Qe varied from 3000 to 10,000, with ? increasing and Qe decreasing during the winter season. At Mount St. Helens, ? remained constant at ˜0.18 s -1, and Qe changed from 400 before the eruption to 750 after it. The observed temporal variations are explained by the near-surface changes caused by seasonal variations in the non-volcanic case and gas-, magma-, and geothermal-system related in the volcanic case. Scattering attenuation does not appear to be a significant factor in these areas, or otherwise it may be indistinguishable due to its fundamental trade-off with the background structure and anelastic attenuation in the data.

Morozov, Igor B.

2011-07-01

8

Attenuation Coefficient of Single-Mode Periodic Waveguides  

NASA Astrophysics Data System (ADS)

It is widely accepted that, on ensemble average, the transmission T of guided modes decays exponentially with the waveguide length L due to small imperfections, leading to the important figure of merit defined as the attenuation-rate coefficient ?=-?ln?(T)?/L. In this Letter, we evidence that the exponential-damping law is not valid in general for periodic monomode waveguides, especially as the group velocity decreases. This result, that contradicts common beliefs and experimental practices aiming at measuring ?, is supported by a theoretical study of light transport in the limit of very small imperfections, and by numerical results obtained for two waveguide geometries that offer contrasted damping behaviors.

Baron, A.; Mazoyer, S.; Smigaj, W.; Lalanne, P.

2011-10-01

9

Reference Materials for the Measurement of Acoustic Attenuation Coefficients  

NASA Astrophysics Data System (ADS)

In this work, we present a reference material for measuring the acoustic attenuation coefficient of biological tissues or tissue-mimicking materials by a transmission method. Accurate measurements by the method require a reference material that has the same acoustic velocity and density as the biological tissue. The newly developed reference material was prepared from NaCl and MgSO4 aqueous solutions. The inorganic material is stable through time. To formulate materials with the desired acoustic velocity and density, the ratio of three constituents (i.e., water, NaCl, and MgSO4) can be determined depending on the method of experiments with mixtures by Scheffe.

Yoshida, Tomoji; Gotow, Akari; Tanaka, Kouhei; Kondo, Toshio

2011-07-01

10

Apparent Linear Attenuation Coefficients in Phase Contrast X-Ray Tomography  

PubMed Central

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

Yan, Aimin; Wu, Xizeng

2011-01-01

11

Vertical profiles of beam attenuation coefficients in East China Sea  

NASA Astrophysics Data System (ADS)

The vertical profiles of beam attenuation coefficient (c) can provide information about the distribution and variability of suspended particles in the water column. Vertical profiles of particulate beam attenuation coefficient at 660 nm (cp(660)), Chlorophyll a (chla) and Particulate Organic Carbon(POC) were analyzed to examine patterns and controlling factors of vertical distributions in the East China Sea (ECS), based on two cruises in summer and late autumn. In late autumn, the cp(660) profiles showed uniform distribution with depth in most of shelf regions, and high value of cp(660) was observed in some inshore stations caused by strong resuspension. In summer, cp(660) exhibited weak subsurface maxima phenomenon in outer shelf, while with the well vertical mixed structures in the northern coast areas of ECS. The variability of cp(660) between summer and autumn were mainly influenced by the changes of thermocline distribution in the ECS. In the late autumn, water potential density were characterized as fully vertical mixed, on the contrary, the strong stratifications of water column were observed in summer. Except for several inshore stations with highly influenced by terrestrial input, significant relationships between POC and cP(660) were observed in both late autumn and summer. The close relationship between POC and cp(660) could be an potential application to retrieve the POC profiles from in situ cP(660) measurements, and be applied to the surface POC estimated from space.

Liu, Qiong; Pan, Delu; Bai, Yan; Zhang, Xuan; Zhang, Lin; Zhu, Qiankun

2012-09-01

12

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

13

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

14

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

15

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

16

Measurement of atomic number and mass attenuation coefficient in magnesium ferrite  

Microsoft Academic Search

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

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

2007-01-01

17

Study on Z dependence of partial and total mass attenuation coefficients  

NASA Astrophysics Data System (ADS)

The partial and total mass attenuation coefficients ?/?(cmg) of photons at energy of 1 keV 100 GeV have been calculated as a function of atomic number and photon energies using the XCOM program (version 3.1) and data base and the calculated results were compared with the measurement. The results show that the mass attenuation coefficients (?/?) depend on incoming photon energies and Z numbers of the target nuclei.

Akkurt, I.; Mavi, B.; Akkurt, A.; Basyigit, C.; Kilincarslan, S.; Yalim, H. A.

2005-09-01

18

Experimental X-ray attenuation coefficients at low photon energies for substances of medical importance.  

PubMed

Recent experimental values of X-ray mass attenuation coefficients for the elements zota = 6 to zota = 18 in the energy range from 4 to 25 keV suggest improvements to the data set presented in the ICRU Report 17. The results are, however, in excellent agreement with the theoretical data of Storm and Israel (1970). Values of mass attenuation coefficient for these elements and for a selection of materials of medical and biological importance are presented. PMID:1202514

Millar, R H

1975-11-01

19

Ultrasonic computed tomography reconstruction of the attenuation coefficient using a linear array.  

PubMed

The attenuation coefficient distribution and sound velocity distribution in the breast can be used to complement B-mode ultrasound imaging in the detection of breast cancer. This study investigated an approach for reconstructing the attenuation coefficient distribution in the breast using a linear array. The imaging setup was identical to that for conventional B-mode breast imaging, and the same setup has been used for reconstruction of sound velocity distributions in previous studies. In this study, we further developed a reconstruction method for the attenuation coefficient distribution. In particular, the proposed method incorporates the segmentation information from B-mode images and uses the sound velocity distribution to compensate for refraction effects. Experiments were conducted with a setup consisting of a 5-MHz, 128-channel linear array, a programmable digital array system, a phantom, and a computer. The constructed phantom contained materials mimicking the following breast tissues: glandular tissue, fat, cysts, high-attenuation tumors, and irregular tumors. Application of the proposed technique resulted in all the cysts and tumors (including high-attenuation and irregular tumors) being distinguished by thresholding the reconstructed attenuation coefficients. We have demonstrated that it is possible to use the same imaging setup to acquire data for B-mode image, sound velocity distribution, and attenuation coefficient distribution simultaneously. Moreover, the experimental data indicate its potential in improving the detection of breast cancer. PMID:16422413

Huang, Sheng-Wen; Li, Pai-Chi

2005-11-01

20

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, Yury V.

1994-10-01

21

Measurement of the attenuation coefficient for Livermore Thoracic Phantom lungs fabricated using contemporary materials.  

PubMed

The University of Cincinnati has reproduced the original formulation for the Livermore Thoracic Phantom lungs using contemporary materials and has adopted the linear attenuation coefficient as the primary quality assurance parameter for evaluating the performance capabilities of these new lung phantoms. The Livermore Thoracic Phantom was originally fabricated in 1978 to intercalibrate detector systems used to measure plutonium and other low-energy, photon emitting radionuclides deposited in the respiratory tract. The linear attenuation coefficient is a critical performance indicator for these phantom lungs since the presence of any material with a high effective atomic number (where Z > or = 20) will make a significant change in the photoelectric cross section, the predominant mode of interaction for plutonium x rays. A set of test lungs was fabricated with KCl to introduce a known quantity of 40K in the phantom and to determine, by measurement and calculations, what change would be made to the attenuation coefficient at photon energies below 100 keV as a result of the modified formulation. The KCl increased the linear attenuation coefficient below 60 keV by more than a factor of two, which would produce a substantial systematic error in any subsequent calibration measurements performed with these modified phantom lungs. These results support use of the attenuation coefficient as an important performance indicator for the Livermore Thoracic Phantom lungs and also suggest that KCl not be added to the lung tissue substitute formulation as a means to incorporate 40K in the phantom for low energy calibrations. PMID:8200800

Spitz, H; Glover, S; Liu, N; Smith, B; Hickman, D; Kruchten, D; Anderson, L

1994-07-01

22

Measurement of atomic number and mass attenuation coefficient in magnesium ferrite  

NASA Astrophysics Data System (ADS)

Pure magnesium ferrite sample was prepared by standard ceramic technique and characterized by X-ray diffraction method. XRD pattern revealed that the sample possess single-phase cubic spinel structure. The linear attenuation coefficient (?), mass attenuation coefficient (?/?), total atomic cross-section (?_{tot}), total electronic cross-section (?_{ele}) and the effective atomic number (Z_{eff}) were calculated for pure magnesium ferrite (MgFe_{2}O_{4}). The values of ?-ray mass attenuation coefficient were obtained using a NaI energy selective scintillation counter with radioactive ?-ray sources having energy 0.36, 0.511, 0.662, 1.17 and 1.28 MeV. The experimentally obtained values of ?/? and Z_{eff} agreed fairly well with those obtained theoretically.

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

2007-05-01

23

Trends in attenuation coefficients in Athens, Greece, from 1954 to 1991  

SciTech Connect

Unsworth and Monteith`s attenuation coefficient T{sub UM} was calculated from midday cloudless sky data in Athens, Greece, for the period 1954 to 1991. An interdependence between T{sub UM} and the Linke factor T{sub L} was found and is expressed as a mathematical function. It was also shown that the minimum turbidity levels occur during the winter and maximum levels occur during summer. An analysis of the long-term variation of the attenuation coefficients depicts the deterioration of air quality during the same period. The dependence of the ratio of diffuse to global radiation on the attenuation coefficient T{sub UM}, is also presented. 26 refs., 4 figs., 1 tab.

Jacovides, C.P.; Kaltsounides, N.A.; Giannourakos, G.P.; Kallos, G.B. [Univ. of Athens (Greece)

1995-06-01

24

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

25

Measurement of atomic number and mass attenuation coefficient in magnesium ferrite  

Microsoft Academic Search

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

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

2007-01-01

26

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

2011-11-28

27

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

28

Measurements of rain drop size distributions and estimation of radio-wave attenuation coefficients  

NASA Astrophysics Data System (ADS)

Results of photoelectron-detector measurements of rain drop size distributions carried out near Dubna, USSR during May-September, 1987 are presented. It is shown that, for large and small drop diameters, these distributions differ from the Marshall-Palmer ones. Radio-wave attenuation coefficients are evaluated for such distributions.

Zakharian, M. V.; Kornilov, L. N.; Pozhidaev, V. N.

1989-10-01

29

Comparison of dual-window scatter correction and effective attenuation coefficients for quantification in dedicated breast SPECT  

Microsoft Academic Search

Correction for scattered and attenuated photons is necessary for accurate quantification in dedicated breast SPECT. An implemented dual energy window (DEW) scatter correction method along with attenuation correction has been shown to be accurate to within 10% of true values; however, the DEW method requires multiple processing steps, and thus more time, than an effective attenuation coefficient (EAC) method. This

Steve Mann; Kristy Perez; Martin Tornai

2011-01-01

30

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

31

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

32

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

SciTech Connect

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

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

1987-09-01

33

Total mass attenuation coefficient evaluation of ten materials commonly used to simulate human tissue  

NASA Astrophysics Data System (ADS)

To study the doses received by patient submitted to ionizing radiation, several materials are used to simulate the human tissue and organs. The total mass attenuation coefficient is a reasonable way for evaluating the usage in dosimetry of these materials. The total mass attenuation coefficient is determined by photon energy and constituent elements of the material. Currently, the human phantoms are composed by a unique material that presents characteristics similar to the mean proprieties of the different tissues within the region. Therefore, the phantoms are usually homogeneous and filled with a material similar to soft tissue. We studied ten materials used as soft tissue-simulating. These materials were named: bolus, nylon®, orange articulation wax, red articulation wax, PMMA, modelling clay, bee wax, paraffin 1, paraffin 2 and pitch. The objective of this study was to verify the best material to simulate the human cerebral tissue. We determined the elementary composition, mass density and, therefore, calculated the total mass attenuation coefficient of each material. The results were compared to the values established by the International Commission on Radiation Units and Measurements - ICRU, report n° 44, and by the International Commission on Radiation Protection - ICRP, report n° 89, to determine the best material for this energy interval. These results indicate that new head phantoms can be constructed with nylon®.

Ferreira, C. C.; Ximenes, R. E.; Garcia, C. A. B.; Vieira, J. W.; Maia, A. F.

2010-11-01

34

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

PubMed

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

Concannon, B M; Davis, J P

1999-08-20

35

Determination of mass attenuation coefficients, effective atomic numbers, effective electron numbers and kermas for Earth and Martian soils  

NASA Astrophysics Data System (ADS)

Total mass attenuation coefficients, effective atomic numbers, effective electron numbers and kerma values for Earth and Martian soils are calculated in the energy range from 1 keV to 100 GeV. The values of mass attenuation and absorption coefficients used in calculations are taken from the WinXCOM program and correct data base. Contributions of different scatterings on the total mass attenuation coefficients of the soils are presented. In addition, the obtained results for Martian soils are compared with the results for Earth soils. The similarities of Earth and Martian soils are also investigated.

Un, A.; Sahin, Y.

2012-10-01

36

An Instrument for the Measurement of Spectral Attenuation Coefficient and Narrow Angle Volume Scattering Function of Ocean Waters.  

National Technical Information Service (NTIS)

A new instrument has been developed for the study of those optical properties of ocean water that affect the transmission of image-forming light. The instrument performs simultaneous measurements of the volume attenuation coefficient and the volume scatte...

R. W. Austin T. J. Petzold

1975-01-01

37

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

38

Relationships between water attenuation coefficients derived from active and passive remote sensing: a case study from two coastal environments.  

PubMed

Relationships between the satellite-derived diffuse attenuation coefficient of downwelling irradiance (K(d)) and airborne-based vertical attenuation of lidar volume backscattering (?) were examined in two coastal environments. At 1.1 km resolution and a wavelength of 532 nm, we found a greater connection between ? and K(d) when ? was computed below 2 m depth (Spearman rank correlation coefficient up to 0.96), and a larger contribution of K(d) to ? with respect to the beam attenuation coefficient as estimated from lidar measurements and K(d) models. Our results suggest that concurrent passive and active optical measurements can be used to estimate total scattering coefficient and backscattering efficiency in waters without optical vertical structure. PMID:21691366

Montes, Martin A; Churnside, James; Lee, Zhongping; Gould, Richard; Arnone, Robert; Weidemann, Alan

2011-06-20

39

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

SciTech Connect

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

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

1999-05-01

40

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

NASA Astrophysics Data System (ADS)

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

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

2010-03-01

41

Attenuation coefficients and absorbed gamma radiation energy of different varieties of potato, mango and prawn at different storage time and physiological condition.  

PubMed

Attenuation coefficients of different varieties of gamma irradiated potato (Kufri Chandramukhi, Kufri Jyoti, and Kufri Sindhuri), mango (Himsagar, Langra, Dashehri and Fazli) and prawn (Tiger prawn and Fresh water prawn) of different storage time and physiological stages were determined. After six months storage attenuation coefficient of Kufri Chandramukhi was decreased by 30.8% with decrease of density and moisture content. Decreasing trend of attenuation coefficient during storage was more prominent (almost 50%) in other two varieties of potato. On the other hand in all four varieties, unripe mango consisted of significantly less (p?0.05) attenuation coefficient (around 11-14%) than the ripe one due to changes in physiological properties and density. Different varieties of prawn had different attenuation coefficients due to subtle differences in their proximate composition. Due to having different attenuation coefficients, different food components, even different varieties of same food component absorbed different gamma radiation energy though exposed to same radiation dose. PMID:24128533

Ghosh, Sayanti; Das, M K

2013-09-04

42

Mass attenuation coefficients, effective atomic numbers and effective electron densities for some polymers.  

PubMed

In this study, the total mass attenuation coefficients (?(m)) for some homo- and hetero-chain polymers, namely polyamide-6 (PA-6), poly-methyl methacrylate (PMMA), low-density polyethylene (LDPE), polypropylene (PP) and polystyrene (PS) were measured at 59.5, 511, 661.6, 1173.2, 1274.5 and 1332.5 keV photon energies. The samples were separately irradiated with (241)Am, (22)Na, (137)Cs and (60)Co (638 kBq) radioactive gamma sources. The measurements were made by performing transmission experiments with a 2?×2? NaI(Tl) scintillation detector having an energy resolution of 7 % at 662 keV gamma ray from the decay of (137)Cs. The effective atomic numbers (Z(eff)) and the effective electron densities (N(eff)) were determined experimentally and theoretically using the obtained ?(m) values for the investigated samples. Furthermore, Z(eff) and N(eff) of each polymer were computed for total photon interaction cross-sections using theoretical data over a wide energy region from 1 keV to 10 MeV. The experimental values of the selected polymers were found to be in good agreement with the theoretical values. PMID:22645382

Kucuk, Nil; Cakir, Merve; Isitman, Nihat Ali

2012-05-29

43

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

2009-12-16

44

Development of in vivo characterization of breast tissues through absolute attenuation coefficients using dedicated cone-beam CT  

NASA Astrophysics Data System (ADS)

With advances in 3D in vivo imaging technology, non-invasive procedures can be used to characterize tissues to identify tumors and monitor changes over time. Using a dedicated breast CT system with a quasi-monochromatic cone-beam x-ray source and flat-panel digital detector, this study was performed in an effort to directly characterize different materials in vivo based on their absolute attenuation coefficients. CT acquisitions were first acquired using a multi-material rod phantom with acrylic, delrin, polyethylene, fat-equivalent, and glandular-equivalent plastic rods, and also with a human cadaver breast. Projections were collected with and without a beam stop array for scatter correction. For each projection, the 2D scatter was estimated with cubic spline interpolation of the average values behind the shadow of each beam stop overlapping the object. Scatter-corrected projections were subsequently calculated by subtracting the scatter images containing only the region of the object from corresponding projections (consisting of primary and scatter x-rays) without the beam stop array. Iterative OSTR was used to reconstruct the data and estimate the non-uniform attenuation distribution. Preliminary results show that with reduced beam hardening from the x-ray beam, scatter correction further reduces the cupping artifact, improves image contrast, and yields attenuation coefficients < 8% of narrow-beam values of the known materials (range 1.2 - 7.8%). Peaks in the histogram showed clear separation between the different material attenuation coefficients. These findings indicate that minimizing beam hardening and applying scatter correction make it practical to directly characterize different tissues in vivo using absolute attenuation coefficients.

Madhav, Priti; Li, Christina M.; Tornai, Martin P.

2010-03-01

45

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

Microsoft Academic Search

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

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

2010-01-01

46

Validation of CALIPSO space-borne-derived attenuated backscatter coefficient profiles using a ground-based lidar in Athens, Greece  

Microsoft Academic Search

We present initial aerosol validation results of the space-borne lidar CALIOP -onboard the CALIPSO satellite- Level 1 attenuated backscatter coefficient profiles, using coincident observations performed with a ground-based lidar in Athens, Greece (37.9° N, 23.6° E). A multi-wavelength ground-based backscatter\\/Raman lidar system is operating since 2000 at the National Technical University of Athens (NTUA) in the framework of the European

R. E. Mamouri; V. Amiridis; A. Papayannis; E. Giannakaki; G. Tsaknakis; D. S. Balis

2009-01-01

47

Parametrization of the total photon mass attenuation coefficients in the energy range 0.1-1000 keV  

NASA Astrophysics Data System (ADS)

It is convenient to generate mass attenuation coefficients using semi-empirical schemes. The validity of most of the existing schemes is limited to a relatively narrow energy interval (1-40 keV) and their accuracies are poor in some energy regions. In this work, a semi-empirical scheme flexible enough to give a good fit to data in a very wide photon energy range (0.1-1000 keV) was employed. Fitting coefficients for the entire range were obtained by utilizing mass attenuation data from two sources: (1) semi-empirical data of Henke et al. in the low photon energy region, and (2) theoretical values generated with the XCOM code for fitting in the high energy region. The root mean square of the fit is generally less than 0.2% except for energies below 1 keV where the available data are scattered. A computer code for generating mass attenuation coefficients based on the proposed scheme has been developed.

Orlic, I.; Loh, K. K.; Sow, C. H.; Tang, S. M.; Thong, P.

1993-05-01

48

Deriving attenuation coefficients from 3D CT data for SPECT Monte Carlo simulations  

Microsoft Academic Search

Quantitation of nuclear medicine data is a major goal in medical imaging. It implies that photon attenuation, scatter and depth dependent spatial resolution be corrected for. Realistic, anthropomorphic numerical phantoms are needed to understand how these phenomena degrade nuclear medicine images, and to validate correction methods. We developed a Monte Carlo simulator which simulates photon transport in an anthropomorphic phantom.

Veronique Baccarne; A. Turzo; Y. Bizais; M. Farine

1997-01-01

49

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

50

Bibliography of photon total cross section (attenuation coefficient) measurements 10 eV to 13. 5 Gev  

SciTech Connect

The authors present a bibliography 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 eV to above 10 GeV. The papers are part of the reference collection of the National Bureau of Standards Photon and Charged Particle Data Center. They cover the period from 1907 to March 1986. Included with each reference are annotations specifying the substances studied and the duplicative references to a total of about 20,000 data points. All these data are available in machine-readable form.

Hubbell, J.H.; Gerstenberg, H.M.; Saloman, E.B.

1986-10-01

51

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

52

Vertical diffuse attenuation coefficient (Kd) based optical classification of IRS-P3 MOS-B satellite ocean colour data  

NASA Astrophysics Data System (ADS)

The optical classification of the different water types provides vital input for studies related to primary productivity, water clarity and determination of euphotic depth. Image data of the IRSP3 MOS-B, for Path 90 of 27th February, 1998 was used for deriving vertical diffuse attenuation coefficient (Kd) and an optical classification based on K d values was performed. An atmospheric correction scheme was used for retrieving water leaving radiances in blue and green channels of 412, 443, 490 and 550 nm. The upwelling radiances from 443 nm and 550 nm spectral channels were used for computation of vertical diffuse attenuation coefficient K d at 490 nm. The waters off the Gujarat coast were classified into different water types based on Jerlov classification scheme. The oceanic water type IA ( K d range 0.035-0.040m-1), type IB (0.042-0.065 m-1), type II (0.07-0.1m-1) and type III (0.115-0.14m-1) were identified. For the coastal waters along Gujarat coast and Gulf of Kachchh, Kd( 490) values ranged between 0.15 m-1 and 0.35 m-1. The depth of 1% of surface light for water type IA, IB, II and III corresponds to 88, 68, 58 and 34 meters respectively. Classification of oceanic and coastal waters based on K d is useful in understanding the light transmission characteristics for sub-marine navigation and under-water imaging.

Sarangi, R. K.; Chauhan, Prakash; Nayak, S. R.

2002-09-01

53

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

2012-05-22

54

Mass attenuation coefficients of natural Rhizophora spp. wood for X-rays in the 15.77-25.27 keV range.  

PubMed

The mass attenuation coefficients (mu/rho) of Rhizophora spp. were determined for photons in the energy range of 15.77-25.27 keV. This was carried out by studying the attenuation of X-ray fluorescent photons from zirconium, molybdenum, palladium, silver, indium and tin targets. The results were compared with theoretical values for average breast tissues in young-age, middle-age and old-age groups calculated using photon cross section database (XCOM), the well-known code for calculating attenuation coefficients and interaction cross-sections. The measured mass attenuation coefficients were found to be very close to the calculated XCOM values in breasts of young-age group. PMID:19482883

Shakhreet, B Z; Bauk, S; Tajuddin, A A; Shukri, A

2009-05-29

55

Comparison of photon attenuation coefficients (2-150 KeV) for diagnostic imaging simulations  

NASA Astrophysics Data System (ADS)

The Radiology Research Laboratory at the Henry Ford Hospital has been involved in modeling x-ray units in order to predict image quality. A critical part of that modeling process is the accurate choice of interaction coefficients. This paper serves as a review and comparison of existing interaction models. Our objective was to obtain accurate and easily calculated interaction coefficients, at diagnostically relevant energies. We obtained data from: McMaster, Lawrence Berkeley Lab data (LBL), XCOM and FFAST Data from NIST, and the EPDL-97 database via LLNL. Our studies involve low energy photons; therefore, comparisons were limited to Coherent (Rayleigh), Incoherent (Compton) and Photoelectric effects, which were summed to determine a total interaction cross section. Without measured data, it becomes difficult to definitively choose the most accurate method. However, known limitations in the McMaster data and smoothing of photo-edge transitions can be used as a guide to establish more valid approaches. Each method was compared to one another graphically and at individual points. We found that agreement between all methods was excellent when away from photo-edges. Near photo-edges and at low energies, most methods were less accurate. Only the Chanter (FFAST) data seems to have consistently and accurately predicted the placement of edges (through M-shell), while minimizing smoothing errors. The EPDL-97 data by LLNL was the best over method in predicting coherent and incoherent cross sections.

Dodge, Charles W., III; Flynn, Michael J.

2004-05-01

56

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

57

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

Microsoft Academic Search

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

Jalali; Majid

2006-01-01

58

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

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

59

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

PubMed

Dual energy computed tomography (DECT) can provide simultaneous estimation of relative electron density ?e and effective atomic number Zeff. The ability to obtain these quantities (?e, Zeff) has been shown to benefit selected radiotherapy applications where tissue characterization is required. The conventional analysis method (spectral method) relies on knowledge of the CT scanner photon spectra which may be difficult to obtain accurately. Furthermore an approximate empirical attenuation correction of the photon spectrum through the patient is necessary. We present an alternative approach based on a parameterization of the measured ratio of low and high kVp linear attenuation coefficients for deriving Zeff which does not require the estimation of the CT scanner spectra. In a first approach, the tissue substitute method (TSM), the Rutherford parameterization of the linear attenuation coefficients was employed to derive a relation between Zeff and the ratio of the linear attenuation coefficients measured at the low and high kVp of the CT scanner. A phantom containing 16 tissue mimicking inserts was scanned with a dual source DECT scanner at 80 and 140 kVp. The data from the 16 inserts phantom was used to obtain model parameters for the relation between Zeff and [Formula: see text]. The accuracy of the method was evaluated with a second phantom containing 4 tissue mimicking inserts. The TSM was compared to a more complex approach, the reference tissue method (RTM), which requires the derivation of stoichiometric fit parameters. These were derived from the 16 inserts phantom scans and used to calculate CT numbers at 80 and 140 kVp for a set of tabulated reference human tissues. Model parameters for the parameterization of [Formula: see text] were estimated for this reference tissue dataset and compared to the results of the TSM. Residuals on Zeff for the reference tissue dataset for both TSM and RTM were compared to those obtained from the spectral method. The tissue substitutes were well fitted by the TSM with R(2) = 0.9930. Residuals on Zeff for the phantoms were similar between the TSM and spectral methods for Zeff < 8 while they were improved by the TSM for higher Zeff. The RTM fitted the reference tissue dataset well with R(2) = 0.9999. Comparing the Zeff extracted from TSM and the more complex RTM to the known values from the reference tissue dataset yielded errors of up to 0.3 and 0.15 units of Zeff respectively. The parameterization approach yielded standard deviations which were up to 0.3 units of Zeff higher than those observed with the spectral method for Zeff around 7.5. Procedures for the DECT estimation of Zeff removing the need for estimates of the CT scanner spectra have been presented. Both the TSM and the more complex RTM performed better than the spectral method. The RTM yielded the best results for the reference human tissue dataset reducing errors from up to 0.3 to 0.15 units of Zeff compared to the simpler TSM. Both TSM and RTM are simpler to implement than the spectral method which requires estimates of the CT scanner spectra. PMID:24025623

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

2013-09-11

60

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, Zeff, effective electron number, Neff, 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

61

Dual beam pulse laser experimental set-up for measuring attenuation coefficients of liquids: application to distilled water in the 414-662 nm spectral range  

Microsoft Academic Search

A double beam laser method for measuring attenuation coefficients of sea-water throughout the 414-662 nm wavelength region is presented. The radiant source is a pulsed wavelength-tunable dye laser, with a spectral width of 0.01 nm. A test with de-ionised filtered distilled water is described.

H. Mercier; F. Gaillard; J. Cariou; J. Lotrian

1982-01-01

62

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

SciTech Connect

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

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

2010-11-12

63

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

NASA Astrophysics Data System (ADS)

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

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

2010-02-01

64

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

65

Estimation of surface-wave phase velocities and attenuation coefficients in southern Korea from spatial coherency of the ambient seismic noise  

NASA Astrophysics Data System (ADS)

The measurements of the spatial coherency of the ambient seismic noise as a function of interstation distance produce distribution of surface-wave phase velocities and attenuation coefficients in southern Korea. The coherency pairs from 43 broadband stations are used for the estimation of phase velocity and attenuation coefficient in the period band of 5 - 20 seconds. From these measurements we simultaneously invert 1-D shear wave velocity and Q as a function of depth beneath southern Korea. To investigate localized velocities and attenuations associated with tectonic units, we subdivide the measurements according to the interstation paths. We retrieve lower-wave velocities and lower-quality factors in the Gyeongsang basin, Cretaceous nonmarine basin in the southeastern area.

Cho, H.; Shin, J.

2011-12-01

66

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

67

The lac operon galactoside acetyltransferase  

Microsoft Academic Search

Of the proteins encoded by the three structural genes of the lac operon, the galactoside acetyltransferase (thiogalactoside transacetylase, LacA, GAT) encoded by lacA is the only protein whose biological role remains in doubt. Here, we briefly note the classical literature that led to the identification and initial characterization of GAT, and focus on more recent results which have revealed its

Steven L. Roderick

2005-01-01

68

Wave intensity amplification and attenuation in non-linear flow: implications for the calculation of local reflection coefficients.  

PubMed

Local reflection coefficients (R) provide important insights into the influence of wave reflection on vascular haemodynamics. Using the relatively new time-domain method of wave intensity analysis, R has been calculated as the ratio of the peak intensities (R(PI)) or areas (R(CI)) of incident and reflected waves, or as the ratio of the changes in pressure caused by these waves (R(DeltaP)). While these methods have not yet been compared, it is likely that elastic non-linearities present in large arteries will lead to changes in the size of waves as they propagate and thus errors in the calculation of R(PI) and R(CI). To test this proposition, R(PI), R(CI) and R(DeltaP) were calculated in a non-linear computer model of a single vessel with various degrees of elastic non-linearity, determined by wave speed and pulse amplitude (DeltaP(+)), and a terminal admittance to produce reflections. Results obtained from this model demonstrated that under linear flow conditions (i.e. as DeltaP(+)-->0), R(DeltaP) is equivalent to the square-root of R(PI) and R(CI) (denoted by R(PI)(p) and R(CI)(p)). However for non-linear flow, pressure-increasing (compression) waves undergo amplification while pressure-reducing (expansion) waves undergo attenuation as they propagate. Consequently, significant errors related to the degree of elastic non-linearity arise in R(PI) and R(CI), and also R(PI)(p) and R(CI)(p), with greater errors associated with larger reflections. Conversely, R(Delta)(P) is unaffected by the degree of non-linearity and is thus more accurate than R(PI) and R(CI). PMID:19019371

Mynard, Jonathan; Penny, Daniel J; Smolich, Joseph J

2008-11-18

69

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

70

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

71

The diffuse attenuation coefficient model in the Yellow Sea for the Korean Geostationary Ocean Color Imager (GOCI)  

NASA Astrophysics Data System (ADS)

The first geostationary ocean color sensor, Geostationary Ocean Color Imager (GOCI), on board the Korean Communication Ocean and Meteorological Satellite (COMS), was successfully launched on June 26 of 2010. GOCI includes 8 spectral bands in visible and near-infrared wavelengths with a coverage area of 2,500×2,500 km2 centered at 36°N and 130°E over the Korean seas. GOCI will provide an important capability to monitor ocean phenomenon with one hour temporal and 500 m spatial resolutions for a better understanding of biogeochemical processes in the Korean seas. However, there are uncertainties in estimating bio-optical properties since water properties in large areas of Koreans are optically characterized as Case-2 waters due to strong tidal mixing and large amount of river discharges. The newly-developed semi-analytical algorithm of diffusion attenuation coefficient at the wavelength of 490 nm, Kd(490), for the turbid coastal waters was assessed using in situ radiometric and Kd(490) measurement obtained from clear and turbid waters over the global ocean. Results of the Kd(490) data using the new model is well correlated with the in situ Kd(490) measurements. Synoptic maps of Kd(490) data from the Moderate Resolution Imaging Spectroradiometer (MODIS) onboard the Aqua satellite using the new model were derived in the Yellow Sea and East China Sea. The MODIS-derived Kd(490) data show significant increased values along the turbid coastal waters including the Bohai Sea and the Yangtze River Estuary. In general, the highest Kd(490) appeared in winter and the lowest Kd(490) are presented in summer over the all area. Interannual variability of Kd(490) in timing and magnitude is apparent, but there is no consistent trend of interannual variability across all areas.

Son, Seunghyun; Wang, Menghua

2010-10-01

72

BL Lac Reunification  

NASA Astrophysics Data System (ADS)

X-ray-selected BL Lacs (XBLs) are generally thought to outnumber the more extreme radio-selected objects (RBLs), on the grounds that their properties could be understood if the X-ray jet were broader than the radio one. Here we present an alternative explanation: RBLs and XBLs may well be two aspects of the same population, whose main difference is the frequency of the high-energy cut-off in their energy distribution, with XBLs constituting the small subclass with cut-offs at X-ray (or higher) energies. Under this assumption, we are able to reproduce the X-ray number counts of XBLs starting from the radio counts of RBLs. We also calculate the distribution of radio fluxes of BL Lacs in current and future (deeper) X-ray surveys (e.g ROSAT), wherein we predict that a strong selection effect arising from radio constraints will lead to the preferential discovery of objects of the RBL kind. our hypothesis implies that there is a single family of BL Lacs and that, within this family, XBL-like objects are a small minority, contrary to the common belief that they represent the most numerous class.

Giommi, P.; Padovani, P.

1994-05-01

73

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

74

Gene Machine: The Lac Operon  

NSDL National Science Digital Library

Build a gene network! The lac operon is a set of genes which are responsible for the metabolism of lactose in some bacterial cells. Explore the effects of mutations within the lac operon by adding or removing genes from the DNA.

Simulations, Phet I.; Blanco, John; Perkins, Kathy; Podolefsky, Noah; Spiegelman, George; Taylor, Jared

2010-05-01

75

Estimation of Production of Lac.  

National Technical Information Service (NTIS)

A pilot sample survey for the estimation of lac production was carried out in the Palamau district of Bihar State during the years 1975-77. The main objective of the survey was to develop a suitable sampling technique for the estimation of number of lac h...

D. V. S. Rao S. D. Bokil

1978-01-01

76

Indian Americans at Mille Lacs.  

ERIC Educational Resources Information Center

|The Training Center for Community Programs prepared a report on the Mille Lacs (Chippewa) Reservation in Minnesota. Data for the report were from 2 separate sources: a survey conducted by the Training Center with the assistance of the Mille Lacs community action program (1967) and an attitudinal survey conducted by Victoria Holbert during 1969.…

Holbert, Victoria L.; And Others

77

Effect of sample thickness on the measured mass attenuation coefficients of some compounds and elements for 59.54, 661.6 and 1332.5 keV ?-rays  

Microsoft Academic Search

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

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

2000-01-01

78

Mass attenuation coefficient of the Earth, Moon and Mars samples over 1keV-100GeV energy range.  

PubMed

This work presents the calculation of the mass attenuation coefficient (micro) of lunar, Martian and terrestrial samples in function of the energy. WinXCOM software was employed to determine the micro values for the samples in the range from 1 keV to 100 GeV. The obtained values were practically the same for energies larger than 100 keV, but marked differences among the samples were observed for energies below 25 keV, which is the energy range of interest for the XRF system used in space probes. PMID:16725330

Camargo Moreira, Anderson; Roberto Appoloni, Carlos

2006-05-24

79

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

Microsoft Academic Search

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

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

2003-01-01

80

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

Microsoft Academic Search

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 (?Ci) 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

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

1989-01-01

81

Measurement of the mass attenuation coefficient for elemental materials in the range 6 < or = Z < or = 82 using X-rays from 13 up to 50 kev.  

PubMed

The mass attenuation coefficients for 22 high purity elemental materials (C, Al, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Rh, Pd, Ag, Cd, In, Ta, Pt, Au, Pb) were measured in the X-ray energy range from 13 up to 50 keV using a high purity germanium detector with thin (50 microm) Be window and a variable-energy X-ray source. The measured values are compared with the theoretical ones obtained using the XCOM code and data base, as well as with other experimental data showing a general agreement within +/- 5%. The mass attenuation cross-sections were thus derived and compared with other experimental data available on the 1988 NBS database of X-ray attenuation cross-sections. The agreement is always within +/- 8%, but for a few points the discrepancies are up to +/- 18%. The data analysis has also shown that some measurements performed at 50.65 keV as well as at 36.65 keV are to be considered as new data for most of the measured materials. PMID:11545503

Angelone, M; Bubba, T; Esposito, A

2001-10-01

82

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

NASA Astrophysics Data System (ADS)

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

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

2012-10-01

83

Environments of BL Lac Objects  

NASA Astrophysics Data System (ADS)

In current theory, BL Lac objects arise from one of two processes: relativistically beamed jets nearly in the line of sight, or gravitationally lensed or microlensed subregions of background QSOs. To better explore these possibilities, we used the Canada-France-Hawaii Telescope to obtain high resolution two-color optical images of a complete sample of x-ray selected BL Lac objects (XBLs) from the Einstein Medium Sensitivity Survey, as well as a large comparison sample of radio-selected BL Lac objects (RBLs). >From these images we extracted the isophotal profiles of the host galaxies of the two samples and found them to be generally consistent with brightest cluster galaxies (BCGs), first rank elliptical galaxies, and Fanaroff-Riley type 1 radio galaxies, arguing in favor of the jet hypothesis. Both the XBL and RBL samples include a subset of ``peculiar objects'' which warrant further observation. It is possible that these objects are more consistent with the gravitational lens theory. We also examined galaxies in the region around the objects to study the clustering properties around BL Lacs. If some of the objects reside in BCGs, then we should be able to find clusters surrounding them. We determined the amplitude of the BL Lac-galaxy spatial covariance function (Bgb) of the surrounding galaxies. Several BL Lac fields have a Bgb comparable with that of Abell class 1 or 2 clusters, but other images show no evidence for rich clustering.

Wurtz, R.

1992-12-01

84

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

NASA Astrophysics Data System (ADS)

The X-ray linear attenuation coefficient was measured for materials containing elements hydrogen to calcium. Characteristic X-rays with energies 32-66keV were produced by X-ray fluorescence using a secondary target system, and 140keV gamma rays were obtained from an unsealed 99mTc source. The photon beams were highly collimated and recorded using energy dispersive detection. A high-purity germanium detector was utilised to distinguish between measurements with K? and K? characteristic X-rays, and the gamma ray measurements used a sodium iodide detector. Samples were selected on the basis of having known composition and mass densities were measured using a pycnometer. The samples comprised six plastics, seven crystalline materials, three tissue substitute materials, three liquids and six salt solutions. Our results have an uncertainty of less than 2% and are a few percent lower than values predicted by the tabulations.

Midgley, S. M.

2005-03-01

85

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

NASA Astrophysics Data System (ADS)

The K-shell absorption jump factors and jump ratios were derived from new mass attenuation coefficients measured using an energy dispersive X-ray fluorescence (EDXRF) spectrometer for Tm, Yb elements being Tm2O3, Yb2O3 compounds and pure Lu, Hf, Ta, W, Re and Os. The measurements, in the region 56 77 keV, were done in a transmission geometry utilizing the K?1, K?2, K?1 and K?2 X- rays from different secondary source targets (Yb, Ta, Os, W, Re and Ir, etc.) excited by the 123.6 keV ?-photons from an 57Co annular source and detected by an Ultra-LEGe solid state detector with a resolution of 150 eV at 5.9 keV. Experimental results have been compared with theoretically calculated values. The measured values of Tm, Yb, Lu, Hf, Ta, W, Re and Os are reported here for the first time.

Kaya, Necati; T?ra?o?lu, Engin; Apayd?n, Gökhan; Ayl?kc?, Volkan; Cengiz, Erhan

2007-08-01

86

Bibliography of photon total cross section (attenuation coefficient) measurements 10 eV to 13. 5 GeV, 1907-1993  

SciTech Connect

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 eV to above 10 GeV. These papers are part of the reference collection of the National Institute of Standards and Technology Photon and Charged Particle Data Center. They cover the period from 1907 through 1993 and into 1994. Thus this report is an update of the 1986 earlier report NBSIR 86-3461 (PB87-116141), and also includes additional papers dating back as far as 1966 which have since been found or brought to the attention of the author. Included with each reference are annotations specifying the energy range covered and the substances studied. This updated bibliography now includes 573 non-duplicative references to available measured data, plus 42 references to critical evaluations and review articles.

Hubbell, J.H.

1994-05-01

87

Influence of atmospheric forcing and freshwater discharge on interannual variability of the vertical diffuse attenuation coefficient at 490 nm in the Baltic Sea  

NASA Astrophysics Data System (ADS)

Each year spatial patterns of ocean color in the Baltic Sea differ in temporal evolution and magnitude. We have investigated the interannual variability of the spatially averaged vertical diffuse attenuation coefficient at 490 nm, Kd(490), in response to atmospheric forcing and river discharge. Our results indicate that atmospheric forcing does not have a significant influence on the interannual anomalies of Kd(490) in the Baltic Sea. This is in contrast to the North Atlantic site located at similar latitudes, were interannual variability of phytoplankton blooms (and ocean color) is to a large degree controlled by a local weather. Instead, in the Baltic Sea, the interannual variability of Kd(490) is significantly influenced by the river runoff. Higher values of Kd(490) are observed in years with larger inflow of water from rivers. Without an access to more detailed information about the concentrations of various optically significant water components, we can only speculate about the possible reasons for this correlation, but it is most likely a combination of several factors. These include: development of more intense phytoplankton blooms associated with larger supply of nutrients delivered by rivers, advection of optically important material with river water, as well as different physical condition for phytoplankton growth due to more stable water stratification. The diffuse attenuation coefficient plays a critical role in many oceanographic processes. For example, Kd is essential for quantification of radiative heating of the ocean, in models of primary production and other photoprocesses, and in studies discussing water turbidity and water quality. Better understanding of the variability of Kd in the Baltic Sea can impove our knowledge of this marine environment.

Stramska, Malgorzata

2013-04-01

88

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

89

Fifty years fused to lac.  

PubMed

I recount the history of how I became interested in the use of gene fusions for studying biological problems. Initially, selections for mutations that would restore function to an inactivated lac operon unexpectedly yielded fusions in which lac was expressed from the controlling elements of upstream genes. Subsequently, by chance, I generated strains in which the lac operon was transposed from its normal position on the chromosome to a position close to the trp operon, thus facilitating sets of useful fusions of the two operons. The development of a more generalized technique for obtaining fusions by my student Malcolm Casadaban opened up a much broader set of biological problems that could be approached with fusions. Work on these problems included the study of protein translocation across membranes, the analysis of membrane protein topology, and the discovery of the pathway of electron transfer that leads to disulfide bond formation in proteins. PMID:24024632

Beckwith, Jonathan

2013-09-01

90

[Effects of lac insect honeydew on the diversity of ground-dwelling ants in lac plantation].  

PubMed

By the method of pitfall trapping, an investigation was conducted on the diversity of ground-dwelling ants in a lac plantation in Yayi Town of Mojiang County, Yunnan Province of Southwest China in December 2009-May 2010, aimed to understand the effects of lac insect honeydew on the diversity of ground-dwelling ants. The presence or absence of lac insect honeydew and its dynamics all affected the species composition, abundance, and diversity of ground-dwelling ants. In the lac plantation with lac insect hosting, a total of 4953 ant individuals were collected, belonging to 34 species, 23 genera, and 5 subfamilies of Formicidae; whereas in the lac plantation without lac insect hosting, a total of 2416 ant individuals were collected, belonging to 30 species, 20 genera, and 5 subfamilies of Formicidae. The relative abundance, species richness (S), and ACE index in the lac plantation with lac insect hosting were higher than those in the lac plantation without lac insect hosting, and the common species and indicator species of ground-dwelling ants in the lac plantation with lac insect hosting differed from those in the lac plantation without lac insect hosting, suggesting that lac insect hosting altered the community structure of ground-dwelling ants. The adult lac insects excreted larger quantity of honeydew than the larval lac insects, and the relative abundance, S, and ACE index of ground-dwelling ants were higher at the adult stage than at the larval stage of lac insects. The common species and indicator species of ground-dwelling ants also had great differences between the two stages of lac insects. PMID:22803483

Lu, Zhi-Xing; Chen, You-Qing; Li, Qiao; Wang, Si-Ming; Liu, Chun-Ju; Zhang, Wei

2012-04-01

91

Energy spectrum based calculation of the half and the tenth value layers for brachytherapy sources using a semiempirical parametrized mass attenuation coefficient formulism  

SciTech Connect

As different types of radionuclides (e.g., {sup 131}Cs source) are introduced for clinical use in brachytherapy, the question is raised regarding whether a relatively simple method exists for the derivation of values of the half value layer (HVL) or the tenth value layer (TVL). For the radionuclide that has been clinically used for years, such as {sup 125}I and {sup 103}Pd, the sources have been manufactured and marketed by several vendors with different designs and structures. Because of the nature of emission of low energy photons for these radionuclides, energy spectra of the sources are very dependent on their individual designs. Though values of the HVL or the TVL in certain commonly used shielding materials are relatively small for these low energy photon emitting sources, the question remains how the variations in energy spectra affect the HVL (or TVL) values and whether these values can be calculated with a relatively simple method. A more fundamental question is whether a method can be established to derive the HVL (TVL) values for any brachytherapy sources and for different materials in a relatively straightforward fashion. This study was undertaken to answer these questions. Based on energy spectra, a well established semiempirical mass attenuation coefficient computing scheme was utilized to derive the HVL (TVL) values of different materials for different types of brachytherapy sources. The method presented in this study may be useful to estimate HVL (TVL) values of different materials for brachytherapy sources of different designs and containing different radionuclides.

Yue, Ning J. [Department of Radiation Oncology, Cancer Institute of New Jersey, UMDNJ-Robert Wood Johnson Medical School, New Brunswick, New Jersey 08903 (United States)

2008-06-15

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

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

Microsoft Academic Search

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

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

2001-01-01

94

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

2012-07-25

95

Mass attenuation coefficients of Clear-Pb{reg_sign} for photons from {sup 125}I, {sup 103}Pd, {sup 99m}Tc, {sup 192}Ir, {sup 137}Cs, and {sup 60}Co  

SciTech Connect

The mass attenuation coefficients, {mu}/{rho}, for Clear-Pb{reg_sign} for photon energies ranging from 10 keV to 10 MeV were determined using Monte Carlo methods and simple equations used to manipulate elemental mass attenuation coefficients. It was determined that the effectiveness of Clear-Pb{reg_sign} as a radiation shielding material was greater than plain acrylic for all photon energies, especially those less than 150 keV, and for deep penetration problems where the differences in {mu}/{rho} between Clear-Pb{reg_sign} as a shielding material when compared with acrylic was determined for the following commonly used radionuclides: {sup 125}I, {sup 103}Pd, {sup 99m}Tc, {sup 192}Ir, {sup 137}Cs, and {sup 60}Co.

Rivard, M.J. [Tufts Univ. School of Medicine, Boston, MA (United States). Dept. of Radiation Oncology; Waid, D.S. [Hackley Hospital, Muskegon, MI (United States). Radiation Oncology Dept.; Wierzbicki, J.G. [St. Mary`s Medical Center, Saginaw, MI (United States). Cancer Treatment Center

1999-11-01

96

Mass attenuation coefficients of Clear-Pb[reg sign] for photons from [sup 125]I, [sup 103]Pd, [sup 99m]Tc, [sup 192]Ir, [sup 137]Cs, and [sup 60]Co  

SciTech Connect

The mass attenuation coefficients, [mu]/[rho], for Clear-Pb[reg sign] for photon energies ranging from 10 keV to 10 MeV were determined using Monte Carlo methods and simple equations used to manipulate elemental mass attenuation coefficients. It was determined that the effectiveness of Clear-Pb[reg sign] as a radiation shielding material was greater than plain acrylic for all photon energies, especially those less than 150 keV, and for deep penetration problems where the differences in [mu]/[rho] between Clear-Pb[reg sign] as a shielding material when compared with acrylic was determined for the following commonly used radionuclides: [sup 125]I, [sup 103]Pd, [sup 99m]Tc, [sup 192]Ir, [sup 137]Cs, and [sup 60]Co.

Rivard, M.J. (Tufts Univ. School of Medicine, Boston, MA (United States). Dept. of Radiation Oncology); Waid, D.S. (Hackley Hospital, Muskegon, MI (United States). Radiation Oncology Dept.); Wierzbicki, J.G. (St. Mary's Medical Center, Saginaw, MI (United States). Cancer Treatment Center)

1999-11-01

97

Measurement of mass attenuation coefficients for holmium doped and undoped layered semiconductors InSe at different energies and the validity of mixture rule for crystals around the absorption edge  

NASA Astrophysics Data System (ADS)

The mass attenuation coefficients of InSe and InSe having different holmium concentrations were measured in the energy region 15.746 40.930 keV using a Si(Li) detector. InSe and InSe:holmium(0.0025), InSe:holmium(0.0050), InSe:holmium(0.025) and InSe:holmium(0.05) crystals were grown by the Bridgman Stocbarger method. The measured values are compared with the theoretical ones obtained using WinXcom which is a Windows version of XCOM. The measurement of mass attenuation coefficients of ternary semiconductors is very important because of its use in technology.

Erzeneo?lu, S.; Içelli, O.; Gürbulak, B.; Ate?, A.

2006-12-01

98

Low frequency variability of BL Lac  

Microsoft Academic Search

Observations of the variability of BL Lac at relatively long radio wavelengths are reported which were made at Jodrell Bank at 31 and 74 cm and conflict with the models of Van der Laan (1966) and Ozernoy and Sazonov (1969). It is noted that BL Lac is completely unresolvable at 31 and 74 cm and that significant variations of about

D. Stannard; A. M. Treverton; R. W. Porcas; R. J. Davis

1975-01-01

99

Lac repressor with the helix-turn-helix motif of lambda cro binds to lac operator.  

PubMed Central

Lac repressor, lambda cro protein and their operator complexes are structurally, biochemically and genetically well analysed. Both proteins contain a helix-turn-helix (HTH) motif which they use to bind specifically to their operators. The DNA sequences 5'-GTGA-3' and 5'-TCAC-3' recognized in palindromic lac operator are the same as in lambda operator but their order is inverted form head to head to tail to tail. Different modes of aggregation of the monomers of the two proteins determine the different arrangements of the HTH motifs. Here we show that the HTH motif of lambda cro protein can replace the HTH motif of Lac repressor without changing its specificity. Such hybrid Lac repressor is unstable. It binds in vitro more weakly than Lac repressor but with the same specificity to ideal lac operator. It does not bind to consensus lambda operator. Images

Kolkhof, P; Teichmann, D; Kisters-Woike, B; von Wilcken-Bergmann, B; Muller-Hill, B

1992-01-01

100

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

101

The role of cis-acting sequences governing catabolite repression control of lacS expression in the archaeon Sulfolobus solfataricus.  

PubMed

The archaeon Sulfolobus solfataricus uses a catabolite repression-like system to control production of several glycoside hydrolases. To better understand this regulatory system, studies of the regulation of expression of the beta-glycosidase gene (lacS) were conducted. Expression of lacS varies in response to medium composition and to mutations at an unlinked gene called car. Despite gene overlap, expression of the lacS promoter proximal gene, SSO3017, exhibited coregulation but not cotranscription with lacS. Measurements of mRNA half-life excluded differential stability as a factor in lacS regulation. Chromosomal repositioning by homologous recombination of a lacS deletion series clarified critical cis-acting sequences required for lacS regulation. lacS repositioned at amyA exhibited increased lacS expression and compromised the response to medium composition independently of lacS 5' flanking sequence composition. In contrast, regulation of lacS by the car mutation was dependent on sequences upstream of the archaeal TATA box. Expression of a promoter fusion between lacS and the car-independent malA promoter integrated either at amyA or at the natural lacS locus was insensitive to the allelic state of car. In contrast, the promoter fusion retained a response to medium composition only at the lacS locus. These results indicate that car acts at the lacS promoter and that the response to medium composition involves locus-specific sequences exclusive of those present 5' to lacS or within the lacS transcription unit. PMID:15342498

Hoang, Viet; Bini, Elisabetta; Dixit, Vidula; Drozda, Melissa; Blum, Paul

2004-08-01

102

The role of cis-acting sequences governing catabolite repression control of lacS expression in the archaeon Sulfolobus solfataricus.  

PubMed Central

The archaeon Sulfolobus solfataricus uses a catabolite repression-like system to control production of several glycoside hydrolases. To better understand this regulatory system, studies of the regulation of expression of the beta-glycosidase gene (lacS) were conducted. Expression of lacS varies in response to medium composition and to mutations at an unlinked gene called car. Despite gene overlap, expression of the lacS promoter proximal gene, SSO3017, exhibited coregulation but not cotranscription with lacS. Measurements of mRNA half-life excluded differential stability as a factor in lacS regulation. Chromosomal repositioning by homologous recombination of a lacS deletion series clarified critical cis-acting sequences required for lacS regulation. lacS repositioned at amyA exhibited increased lacS expression and compromised the response to medium composition independently of lacS 5' flanking sequence composition. In contrast, regulation of lacS by the car mutation was dependent on sequences upstream of the archaeal TATA box. Expression of a promoter fusion between lacS and the car-independent malA promoter integrated either at amyA or at the natural lacS locus was insensitive to the allelic state of car. In contrast, the promoter fusion retained a response to medium composition only at the lacS locus. These results indicate that car acts at the lacS promoter and that the response to medium composition involves locus-specific sequences exclusive of those present 5' to lacS or within the lacS transcription unit.

Hoang, Viet; Bini, Elisabetta; Dixit, Vidula; Drozda, Melissa; Blum, Paul

2004-01-01

103

Apsidal motion elements of six eccentric eclipsing binaries: V799 Cas, CO Cep, V1136 Cyg, V345 Lac, V364 Lac and V402 Lac  

NASA Astrophysics Data System (ADS)

The apsidal motion analysis of the eccentric eclipsing binaries: V799 Cas, CO Cep, V1136 Cyg, V345 Lac, V364 Lac and V402 Lac have been presented. The method described by Lacy (1992) has been used for the apsidal motion analysis. The apsidal motion periods have been found to be 1229 ± 235, 64,600 ± 20,000, 586 ± 6, 14,240 ± 2800, 3502 ± 582 and 242 ± 60 yr for V799 Cas, CO Cep, V1136 Cyg, V345 Lac, V364 Lac and V402 Lac, respectively. The corresponding internal structure constant, logk, for V799 Cas, V364 Lac and V402 Lac have been derived and compared to the theoretical values.

Bulut, ?brahim

2013-07-01

104

Multiband Microvariability of BL Lac During Outburst  

NASA Astrophysics Data System (ADS)

The blazar BL Lac recently underwent a major outburst. A search for microvariability was made with the 0.76 m telescope at the University of Florida's Rosemary Hill Observatory. Nearly 300 CCD observations in V and R were made over ten nights in July. During that time, BL Lac varied by more than 1.5 magnitudes and exhibited substantial microvariability. In fact, it exhibited microvariability each of the eight nights multiple exposures were made, being most active when brightest on July 29. On this night, four mini-flares were seen within 7 hours. During one of these flares, BL Lac brightened by more than 0.5 magnitude in less than 2.5 hours. The variations in V and R were simultaneous within the limits of the observations. However, the V and R magnitudes did not always change at the same rate. On July 3, BL Lac brightened in R faster than in V. Then on July 4, it dimmed in V faster than in R. Yet over the ten nights observed, BL Lac became bluer as it brightened. Another interesting difference between the V and R data was seen on July 4 when a mini-flare was seen in V but not in R. Clearly, while the V and R variations are highly correlated, there are compelling differences. Here we present these observations and discuss them in relation to models intended to explain microvariability. The authors gratefully acknowledge the support of NASA grant NCC5-228.

Clements, S. D.; Carini, M. T.; Noble, J. C.

1998-01-01

105

Modeling the Lac repressor-operator assembly: the influence of DNA looping on Lac repressor conformation.  

PubMed

Repression of transcription of the Escherichia coli Lac operon by the Lac repressor (LacR) is accompanied by the simultaneous binding of LacR to two operators and the formation of a DNA loop. A recently developed theory of sequence-dependent DNA elasticity enables one to relate the fine structure of the LacR-DNA complex to a wide range of heretofore-unconnected experimental observations. Here, that theory is used to calculate the configuration and free energy of the DNA loop as a function of its length and base-pair sequence, its linking number, and the end conditions imposed by the LacR tetramer. The tetramer can assume two types of conformations. Whereas a rigid V-shaped structure is observed in the crystal, EM images show extended forms in which two dimer subunits are flexibly joined. Upon comparing our computed loop configurations with published experimental observations of permanganate sensitivities, DNase I cutting patterns, and loop stabilities, we conclude that linear DNA segments of short-to-medium chain length (50-180 bp) give rise to loops with the extended form of LacR and that loops formed within negatively supercoiled plasmids induce the V-shaped structure. PMID:16785444

Swigon, David; Coleman, Bernard D; Olson, Wilma K

2006-06-19

106

Lac Courte Oreilles Energy Analysis Project  

Microsoft Academic Search

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

Leslie Isham; Denise Johnson

2009-01-01

107

Regulatory Revolution- Evolving the "Anti-LacI" Repressor  

PubMed Central

Much of adaptation is based upon changes in gene expression, but the emergence of new regulatory logic has not been observed directly. Now Poelwijk et al. report evolving the lac repressor (LacI) to reverse its regulatory logic, resulting in an “anti-LacI” that represses transcription when bound to its “inducer.”

Marx, Christopher J.

2011-01-01

108

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

109

The Role of cis-acting Sequences Governing Catabolite Repression Control of lacS Expression in the Archaeon Sulfolobus solfataricus  

Microsoft Academic Search

The archaeon Sulfolobus solfataricus uses a catabolite repression-like system to control production of several glycoside hydrolases. To better understand this regulatory system, studies of the regulation of expression of the -glycosidase gene (lacS) were conducted. Expression of lacS varies in response to medium composition and to mutations at an unlinked gene called car. Despite gene overlap, expression of the lacS

Viet Hoang; Elisabetta Bini; Vidula Dixit; Melissa Drozda; Paul Blum

2004-01-01

110

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

111

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

112

Polarization microvariability studies of BL Lac objects  

NASA Astrophysics Data System (ADS)

We report the results of a systematic campaign devoted to determine the incidence of microvariability in the optical polarization of BL Lac objects. We have observed a sample formed by 8 X-ray selected (XBL) and 10 radio-selected (RBL) sources, in addition to the quasar 3C279, searching for rapid changes in both the degree of linear polarization and the corresponding polarization angle. The statistical properties of both classes of objects are compared and some general conclusions on the nature of these phenomena are drawn.

Andruchow, I.; Cellone, S. A.; Romero, G. E.

113

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

114

The New BL Lac Candidaties from the FBS  

NASA Astrophysics Data System (ADS)

The optical spectra of BL Lac objects are the most distinguishable characteristic for them. But there are only ten objects classified as BL Lac objects from optical surveys. Three of them are the well known Markarian galaxies from FBS (First Byurakan Survey) and two candidates of BL Lacs - from SBS (Second Byurakan Survey). The fundamental part of them are selected from radio or X-Ray surveys and are called RBL and XBL. The number of BL Lac objects are increasing now by tens or hundreds on account of X-Ray sources. The Markarian galaxies are the type of extragalactic objects having the most typical characteristics of BL Lacs. The completeness of BL Lacs is estimated by the well known relation: lg N(mv) = 0.6 mv + C The inclination of this relation is about 0.57 for brighter objects (mv=16.0) and only 0.3 for the objects with 16.0=mv=17.0 in the regions of FBS survey: the number of BL Lacs is less than 27% from expected numbers in this part of the sky. The list of new possible candidates of BL Lacs was selected on the basis of the most important and necessary characteristics for these objects from the catalog of Markarian galaxies. The list of nine Markarian galaxies from the 103 possible candidates of BL Lacs is presented in this work, three of them are well known BL Lacs - Mkn 180, Mkn 421, Mkn 501, and one candidate of RBL - Mkn 514 was classified as candidate of BL Lacs by the authors of the Radiosurvey of Markarian galaxies in 1989.

Torosyan, Ofelia Kh.

115

The Energy Landscape of Hyperstable LacI-DNA Loops  

NASA Astrophysics Data System (ADS)

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

Kahn, Jason

2009-03-01

116

Proposed Rice Lake and Mille Lacs Islands, Wilderness Areas, Minnesota.  

National Technical Information Service (NTIS)

The proposal recommends that 1,406 acres of the Rice Lake National Wildlife Refuge, Aitkin County, Minnesota and .6 acre Mille Lacs National Wildlife Refuge (two small islands) in Mille Lacs County, Minnesota, be designated as wilderness within the Nation...

1973-01-01

117

Specificities of three tight-binding Lac repressors.  

PubMed Central

Tight binding mutants of Lac repressor exhibit complex repression phenomena. In this work, in vivo Lac operator binding of three such mutants of E. coli Lac repressor (X86: ser 61-leu, l12: pro 3-tyr and the double mutant l12X86: pro 3-tyr, ser 61-leu) was analyzed. Repression of beta-galactosidase synthesis controlled by ideal lac operator and its 27 symmetric operator variants containing each possible base-pair at each single half-operator position in the presence of the tight-binding Lac repressor mutants was determined. The average increase of repression with all operator variants was about 3 fold with the X86 mutant. It was about 4 fold with the l12 mutant and about 2 fold with the double mutant l12X86 as compared to wildtype Lac repressor. The X86 mutant showed the same increase of affinity to all operator variants, whereas the l12 and l12X86 mutants exhibited lower repression with some variants than with most others. These results suggest that the X86 mutant has gained no additional specificity. In contrast the l12 mutant and the l12X86 mutant exhibit a relaxed specificity for certain base pairs in positions 1 and 3 of lac operator. This suggests that the extreme N-terminus of Lac repressor may interact with the inner base-pairs in the minor groove.

Kolkhof, P

1992-01-01

118

Intranight Variability During the 1997 Outburst of BL Lac  

NASA Astrophysics Data System (ADS)

The blazar BL Lac underwent a major outburst this summer. To search for intranight variability during the outburst, observations of BL Lac were made with the 30 inch telescope at the University of Florida's Rosemary Hill Observatory. During ten nights in July, nearly 300 CCD observations were made. BL Lac was seen to vary by more than 1.5 magnitudes over those ten nights. Substantial intranight variability was also observed. For example, on July 29, BL Lac increased in brightness by more than 0.5 magnitude in less than 2.5 hours. The observations of BL Lac taken in July are reported here and discussed in relation to the models intended to explain intranight variability.

Clements, Sandra D.; Carini, Michael T.; Noble, John C.

1998-02-01

119

BATSE Observations of BL Lac objects  

NASA Astrophysics Data System (ADS)

The Burst And Transient Source Experiment (BATSE) on the Compton Gamma-Ray Observatory has been shown to be sensitive to non-transient hard X-ray sources in our galaxy, down to flux levels of 100 mCrab for daily measurements, 3 mCrab for integrations over several years. We use the continuous 7-year BATSE database and the Earth Occultation technique to extract average flux values between 20 and 200 keV from complete X-ray and radio selected BL Lac samples, and to measure their variability over periods of months to years. We compare the behaviour and the spectral characteristics of the objects in the XBL and RBL classes.

Connaughton, V.; McCollough, M.; Robinson, C. R.; Laurent-Muehleisen, S.

120

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

121

Polarimetric Identification of the RGB BL Lac Candidates  

NASA Astrophysics Data System (ADS)

We present preliminary results on our programme "Identification of new RGB BL LAC objects". The original sample was selected by crosscorrelating the ROSAT All Sky Survey and Green Bank 5 Ghz radio survey. In the flux ratio distribution log(S_x/S_r) RGB sample is intermediate between XBLs and RBLs. Preliminary results suggest that about 60% of the objects have high (P > 3%) polarization, confirming their identification as BL Lacs. The results will be discussed in connecting RBL and XBL subsamples and compared to previous polarimetric studies of BL Lacs.

Pursimo, T.; Nilsson, K.; Heinämäki, P.; Katajainen, S.; Sillanpää, A.; Takalo, L. O.; Laurent-Muehleisen, S. A.; Brinkmann, W.

122

Ultrasonic attenuation measurements in Egyptian dry compact rocks  

Microsoft Academic Search

The attenuation of ultrasonic waves in specific dry rocks is measured in laboratory. The pulse echo technique is used to determine attenuation coefficients (?) and quality factor (Q) values of different kinds of rocks in the frequency range of 1-5 MHz. The laboratory measurements showed that, the attenuation coefficients are linearly proportional to frequency (constant Q) in the considered frequency

S. M. El-Sherbiny; A. G. Hassanin; H. A. Nofal; S. M. Abd-Alkader

2003-01-01

123

A computational study of ?-lac mutants  

NASA Astrophysics Data System (ADS)

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

Werner, Maria; Aurell, Erik

2009-12-01

124

Optimising HIFU Lesion Formation with Backscatter Attenuation Estimation (BAE)  

Microsoft Academic Search

Ultrasound attenuation is an important dosimetric factor for HIFU treatments of soft tissue tumours. During clinical HIFU treatments ultrasound attenuation in the tissue overlying the focal volume leads to a loss in intensity. In clinical treatments at the Royal Marsden Hospital (UK), ultrasound attenuation is currently estimated using published tissue attenuation coefficients and the thickness of tissue layers determined from

John Civale; Jeff Bamber; Ian Rivens; Gail Ter Haar

2006-01-01

125

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

126

Tetramer opening in LacI-mediated DNA looping.  

PubMed

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

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

2009-09-21

127

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

128

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

129

Sugar recognition by CscB and LacY  

PubMed Central

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

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

2011-01-01

130

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

131

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

132

Method for estimating total attenuation from a spatial map of attenuation slope for quantitative ultrasound imaging.  

PubMed

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. PMID:23493614

Pawlicki, Alexander D; O'Brien, William D

2013-04-01

133

Hematoxylin-lac-curcuma polychrome stain for mucin.  

PubMed

A polychrome method for detection of mucin substance in paraffin section is produced by sequential stepwise staining of hematoxylin, crude lac extract (Laccifer lacca), and crude curcuma extract (khamin shan-Curcuma longa). The name LacCur stain is proposed. After a tissue section is deparaffinized and rehydrated, it is stained with Weigert's hematoxylin for 7 minutes. After a quick wash, it is stained for at least 3 hours with lac dye mordanted with aluminum chloride. Washed again and premordanted with ferric chloride for 1 minute, in the last step, it is counterstained with curcuma dye for 5 minutes. With this staining method, the nuclei are stained black, mucin deep red, and organelles and ground substances brownish yellow. The method and outcome colors are comparable to the widely used Mayer's mucicarmine staining method. It costs less than the Mayer's mucicarmine staining method and the procedure is not complicated. PMID:7543924

Sriplung, H; Kietthubthew, S; Boonyaphiphat, P

1995-03-01

134

Complete samples of radio-selected BL Lac objects  

SciTech Connect

A uniform sample of 43 BL Lacertae objects selected from two flux-limited radio surveys is presented. From confirming optical polarimetric observations, it is clear that the combination of a flat high-frequency radio spectrum (11-6 cm) and featureless optical continuum are very effective at isolating classical BL Lacs, with 95 percent of sources satisfying these criteria also proving to be strongly polarized on at least one occasion. Variability is also a general characteristic of the sample, with a typical radio-selected BL Lac spending 60 percent of the time in a state of high polarization (P greater than 3 percent). The completeness of this sample of BL Lac objects and the relationship between the radio-selected nuclei and their more docile X-ray-selected counterparts are discussed. 26 refs.

Kuehr, H.; Schmidt, G.D. (Max-Plank-Institut fuer Astronomie, Heidelberg (Germany, F.R.) Steward Observatory, Tucson, AZ (USA))

1990-01-01

135

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

136

Dynamic model of gene regulation for the lac operon  

NASA Astrophysics Data System (ADS)

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

Angelova, Maia; Ben-Halim, Asma

2011-03-01

137

LacCur stain for detection of mucin in adenocarcinoma.  

PubMed

Identification of cytoplasmic mucin, usually by Mayer's mucicarmine stain, is one of the criteria to diagnose adenocarcinoma. The inexpensive LacCur stain, made up of Curcuma longa (khamin-shan) and secreta of Laccifer lacca (krang) has been introduced. The aim of this study was to compare the Mayer's mucicarmine and LacCur stains in the detection of mucin material. The specimens included 17 adenocarcinomas of the stomach, 16 of the colon, 18 of the lung, 16 of the breast, and 12 of the bile duct. Squamous cell carcinoma and hepatocellular carcinoma (altogether 20 cases) were set as negative control. Like Mayer's mucicarmine, LacCur was capable of detecting of intracytoplasmic mucin in all adenocarcinomas of the stomach, colon and bile duct, and revealed mucin substance in 15/18 and 11/16 cases of specimens from the lung and breast, respectively. The negative control group showed a negative result. Although a little more time required in preparation, the LacCur stain is simple and very economical. PMID:14971540

Wattanasirmkit, Vanee; Tanboon, Jantima; Shuangshoti, Somruetai; Shuangshoti, Shanop

2004-01-01

138

CGRO Observations of BL Lac Objects and Other Blazars  

NASA Astrophysics Data System (ADS)

Among the roughly 60 blazars detected by EGRET, about a quarter are classified as BL Lac objects. Although most are of the RBL subspecies, a small number of XBLs have now been detected. In general, the BL Lacs appear to have slightly harder spectra than the other blazars. One BL Lac object, BL Lacertae itself, received exceptionally good optical coverage during an EGRET target-of-opportunity flare observation in 1997 July. During a 1-day miniflare in the middle of the EGRET observation, the optical and gamma-ray fluxes appeared to peak very close in time, with the gamma rays possibly peaking a few hours earlier than optical flux. In the only other blazar flare with comparable coverage, that of 3C 279 in 1996 Feb, there is little evidence for 1-day-scale gamma/optical correlation, although both were bright. Other gamma-ray characteristics of BL Lac objects, and comparisons with flat-spectrum radio quasars detected by EGRET, will be presented.

Hartman, R. C.

139

X-Ray Variability of BL Lac Objects  

NASA Astrophysics Data System (ADS)

I present an overview of the X-ray temporal and spectral variability of BL Lacs on both short and long timescales. The previously observed behaviour of short (~days) flares superimposed on a relatively steady `quiescent' level is still broadly correct. However, for the brighter BL Lacs, the well sampled lightcurves from the RXTE ASM show that the `quiescent' level also varies considerably on timescales of ~100 days in a manner similar to that seen in Optically Violently Variable Quasars (OVVs) such as 3C279 and 3C273. Possible reasons for this behaviour are discussed. For the large majority of BL Lacs the soft and medium energy X-ray bands are dominated by synchrotron emission and, unlike the case of OVVs, the emission mechanism is not in doubt. Most interest then centres on the structure of the emitting region, and the electron acceleration processes, particularly during outbursts. That structure, and the acceleration processes, can be investigated by consideration of the spectral variability during flares, which is not simple. I review the observations of spectral variability and consider the evidence for and against homogeneous models. I also briefly compare the X-ray spectral variability of BL Lacs with that of OVVs such as 3C273.

McHardy, Ian

140

Activation of the Lac Repressor in the Transgenic Mouse  

PubMed Central

We have introduced sequences encoding the lac repressor of Escherichia coli into the genome of the mouse. One sequence was derived from the bacterial lac operon and the other was created by re-encoding the amino acid sequence of lacI with mammalian codons. Both versions are driven by an identical promoter fragment derived from the human ?-actin locus and were microinjected into genetically identical pronuclear stage embryos. All transgenes utilizing the bacterial coding sequence were transcriptionally silent in all somatic tissues tested. The sequence re-encoded with mammalian codons was transcriptionally active at all transgene loci and expressed ubiquitously. Using methylation-sensitive enzymes, we have determined the methylation status of lac repressor transgenes encoded by either the bacterial or mammalian sequence. The highly divergent bacterial sequence was hypermethylated at all transgene loci, while the mammalian sequence was only hypermethylated at a high copy number locus. This may reflect a normal process that protects the genome from acquiring new material that has an abnormally divergent sequence or structure.

Scrable, H.; Stambrook, P. J.

1997-01-01

141

Purification and characterization of two phospho-?-galactosidases, LacG1 and LacG2, from Lactobacillus gasseri ATCC33323(T).  

PubMed

Lactobacillus gasseri ATCC33323(T) expresses four enzymes showing phospho-?-galactosidase activity (LacG1, LacG2, Pbg1 and Pbg2). We previously reported the purification and characterization of two phospho-?-galactosidases (Pbg1 and Pbg2) from Lactobacillus gasseri JCM1031 cultured in lactose medium. Here we aimed to characterize LacG1 and LacG2, and classify the four enzymes into 'phospho-?-galactosidase' or 'phospho-?-glucosidase.' LacG1 and recombinant LacG2 (rLacG2), from Lb. gasseri ATCC33323(T), were purified to homogeneity using column chromatography. Kinetic experiments were performed using sugar substrates, o-nitrophenyl-?-D-galactopyranoside 6-phosphate (ONPGal-6P) and o-nitrophenyl-?-D-glucopyranoside 6-phosphate (ONPGlc-6P), synthesized in our laboratory. LacG1 and rLacG2 exhibited high k(cat)/K(m) values for ONPGal-6P as compared with Pbg1 and Pbg2. The V(max) values for ONPGal-6P were higher than phospho-?-galactosidases previously purified and characterized from several lactic acid bacteria. A phylogenetic tree analysis showed that LacG1 and LacG2 belong to the phospho-?-galactosidase cluster and Pbg1 and Pbg2 belong to the phospho-?-glucosidase cluster. Our data suggest two phospho-?-galactosidase, LacG1 and LacG2, are the primary enzymes for lactose utilization in Lb. gasseri ATCC33323(T). We propose a reclassification of Pbg1 and Pbg2 as phospho-?-glucosidase. PMID:22449746

Honda, Hiroyuki; Nagaoka, Seiji; Kawai, Yasushi; Kemperman, Robèr; Kok, Jan; Yamazaki, Yukiko; Tateno, Yoshio; Kitazawa, Haruki; Saito, Tadao

2012-01-01

142

76 FR 78974 - Wisconsin Central Ltd.-Abandonment Exemption-in Fond Du Lac County, WI  

Federal Register 2010, 2011, 2012, 2013

...Central Ltd.--Abandonment Exemption--in Fond Du Lac County, WI Wisconsin Central Ltd. (WCL) \\1\\ filed...line between mileposts 175.40 and 176.00, in Fond Du Lac, Fond Du Lac County, Wis. The line traverses United States...

2011-12-20

143

77 FR 2774 - Notice of Intent To Prepare a Supplemental Environmental Impact Statement: Fond du Lac...  

Federal Register 2010, 2011, 2012, 2013

...Environmental Impact Statement: Fond du Lac & Sheboygan Counties, WI AGENCY: Federal...Highway 151 to County Highway P in Fond du Lac and Sheboygan Counties, Wisconsin. FOR...S. Highway 151 in the City of Fond du Lac to County Highway P in the City of...

2012-01-19

144

Attenuation inversions in the East China Sea  

NASA Astrophysics Data System (ADS)

Data from the ASIAEX East China Sea (ECS) experiment is used to estimate sediment attenuation coefficients as a function of frequency and depth. The ECS experiment offers a number of independent measures of sediment parameters using seismic and chirp surveys, gravity and piston cores and historic data. Modal amplitude ratios for modes 1 to 3 are used to obtain the modal attenuation coefficient and attenuation profiles. These inversions use broad-band data from Wide Band Sources (WBS) in the frequency range 20-100 Hz. The modes are detected, identified and their amplitudes measured using a time-frequency wavelet analysis. A joint inversion for modal attenuation coefficients, water depth, source and receiver depths, range and Empirical Orthogonal Functions in the water column is performed. The results will be compared with core data and frequency and depth dependence will be examined. [Work supported by ONR.

Potty, Gopu; Miller, James

2003-10-01

145

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

Microsoft Academic Search

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

Lee Kroos; Dale Kaiser

1984-01-01

146

Mass attenuation coefficients in the range 3.8?E?11keV, K fluorescence yield and K?/K? relative X-ray emission rate for Ti, V, Fe, Co, Ni, Cu and Zn measured with a tunable monochromatic X-ray source  

NASA Astrophysics Data System (ADS)

This work presents new measurements of mass attenuation coefficients in the range 3.8?E?11keV, K-absorption jump-ratios, K? and K? fluorescence yields for Ti, V, Fe, Co, Ni, Cu and Zn. We use the experimental facility SOLEX, a tunable monochromatic X-ray source combined with an energy-dispersive high-purity germanium detector. The results are compared with theoretical values as well as with other experimental data and show a relatively good agreement. However, the derived K-jump-ratios appear larger than those widely used in the XCOM database. The K? and K? fluorescence yields and the corresponding relative emission rates K?/K? are also derived, which was made possible by the use of energy-dispersive detectors with good spectral resolution.

Ménesguen, Y.; Lépy, M.-C.

2010-08-01

147

Computed structure and energetics of La@C60  

NASA Astrophysics Data System (ADS)

Computations are carried out using density functional theory for the endohedral system La@C60, i.e., the very first metallofullerene observed in gas phase (although not yet isolated in a solid form). The computations offer data on the molecular and electronic structure of the species. In particular, it is shown that the encapsulated atom is not located in the cage center, but is shifted toward the wall. There is a substantial charge transfer from the metal to the cage, at some levels of theory amounting roughly to three electrons. It is shown that there is a relatively large energy stabilization upon encapsulation. However, the entropy term also influences the association equilibrium significantly, so that the standard Gibbs-energy change depends strongly on temperature. The reasons why La@C60 could not be isolated yet are briefly discussed, as well as a possible relationship to superconductivity. Content:text/plain; charset="UTF-8"

Slanina, Zdenêk; Lee, Shyi-Long; Adamowicz, Ludwik; Uhlík, Filip; Nagase, Shigeru

148

Intrinsic curvature of DNA influences LacR-mediated looping.  

PubMed

Protein-mediated DNA looping is a common mechanism for regulating gene expression. Loops occur when a protein binds to two operators on the same DNA molecule. The probability of looping is controlled, in part, by the basepair sequence of inter-operator DNA, which influences its structural properties. One structural property is the intrinsic or stress-free curvature. In this article, we explore the influence of sequence-dependent intrinsic curvature by exercising a computational rod model for the inter-operator DNA as applied to looping of the LacR-DNA complex. Starting with known sequences for the inter-operator DNA, we first compute the intrinsic curvature of the helical axis as input to the rod model. The crystal structure of the LacR (with bound operators) then defines the requisite boundary conditions needed for the dynamic rod model that predicts the energetics and topology of the intervening DNA loop. A major contribution of this model is its ability to predict a broad range of published experimental data for highly bent (designed) sequences. The model successfully predicts the loop topologies known from fluorescence resonance energy transfer measurements, the linking number distribution known from cyclization assays with the LacR-DNA complex, the relative loop stability known from competition assays, and the relative loop size known from gel mobility assays. In addition, the computations reveal that highly curved sequences tend to lower the energetic cost of loop formation, widen the energy distribution among stable and meta-stable looped states, and substantially alter loop topology. The inclusion of sequence-dependent intrinsic curvature also leads to nonuniform twist and necessitates consideration of eight distinct binding topologies from the known crystal structure of the LacR-DNA complex. PMID:17766355

Goyal, Sachin; Lillian, Todd; Blumberg, Seth; Meiners, Jens-Christian; Meyhöfer, Edgar; Perkins, N C

2007-08-31

149

Integration host factor alters LacI-induced DNA looping  

Microsoft Academic Search

The integration host factor protein of Escherichia coli, which sharply bends DNA at specific sites and non-specifically compacts the bacterial genome, can also alter looping of DNA in an artificial system based on the lactose repressor protein of E. coli. In single molecule experiments, we show that both specific bending and non-specific compaction alter LacI-mediated looping of DNA. Our results

Chiara Zurla; Tomas Samuely; Giovanni Bertoni; Francesco Valle; Giovanni Dietler; Laura Finzi; David D. Dunlap

2007-01-01

150

Limits On Selected BL Lac objects with the CAT Telescope  

NASA Astrophysics Data System (ADS)

We report here limits on the gamma-ray emission above 250 Gev for three hard X-ray selected BL Lacs, 1ES2344+514, 1ES1959+650, 1ES1426+428 and the RBL BL Lacertae. These objects were observed by the CAT imaging telescope respectively for 15 hours (September 1997 - January 1998 and July 1998 - September 1998), 10 hours (June 1998 - September 1998), 8 hours (March 1998 - April 1998) and 9 hours (August 1997 - September 1997).

Piron, Frederic; CAT Collaboration

1998-12-01

151

Ion effects on the lac repressor-operator interaction  

SciTech Connect

The effects of ions on the binding of lac repressor protein and operator DNA have been studied using the membrane filter technique. The association and dissociation rate constants were measured, and the equilibrium association constants calculated, as a function of monovalent and divalent cation concentrations, anions, and pH. The salt dependence of the binding parameters is interpreted in light of recent theoretical analyses based on Manning's counterion condensation model.

Barkley, M.D.; Lewis, P.A.; Sullivan, G.E.

1980-10-01

152

Transcription and decay of the lac messenger: role of an intergenic terminator.  

PubMed

Prior work has indicated that the polycistronic lacZYA mRNA of Escherichia coli is cleaved during decay at approximately intergenic sites (L. W. Lim and D. Kennell, J. Mol. Biol. 135: 369-390, 1979). In this work, we characterized the products by using probes specific for the different cistrons. This analysis indicated that six lac mRNA species are present in the following order of decreasing abundance: lacZ, -A, -ZYA, -ZY, -YA, and -Y. Very little lacYA and lacY mRNAs were present, whereas in cells induced to steady state, there was 10 times more lacZ than lacZYA mRNA. The lacZ mRNA appeared as a discrete species extending to a site in the lacZ-Y intergenic space (ca. residue 3150). This site is just distal to a potential rho-independent termination sequence. We examined the function of this sequence to determine whether it contributes to the distribution of the mRNAs. Although the termination sequence was shown to function in vitro, when it was recloned into an expression vector, no termination was seen in vivo. Moreover, direct examination of the kinetics of lac messenger synthesis revealed that after initiation, most transcription continued to the end of the operon. We conclude that during normal growth, the operon is transcribed in its entirety and that the individual lac mRNAs are formed by cleavage. These results confirm earlier work implying that the lac operon is transcribed in its entirety but are in conflict with several recent reports suggesting that internal termination occurs. Our findings indicate that the natural polarity of the operon (lacZ is expressed sixfold more strongly than lacA) is based on posttranslational effects and not on polarity of transcription. PMID:1702782

Murakawa, G J; Kwan, C; Yamashita, J; Nierlich, D P

1991-01-01

153

Transcription and decay of the lac messenger: role of an intergenic terminator.  

PubMed Central

Prior work has indicated that the polycistronic lacZYA mRNA of Escherichia coli is cleaved during decay at approximately intergenic sites (L. W. Lim and D. Kennell, J. Mol. Biol. 135: 369-390, 1979). In this work, we characterized the products by using probes specific for the different cistrons. This analysis indicated that six lac mRNA species are present in the following order of decreasing abundance: lacZ, -A, -ZYA, -ZY, -YA, and -Y. Very little lacYA and lacY mRNAs were present, whereas in cells induced to steady state, there was 10 times more lacZ than lacZYA mRNA. The lacZ mRNA appeared as a discrete species extending to a site in the lacZ-Y intergenic space (ca. residue 3150). This site is just distal to a potential rho-independent termination sequence. We examined the function of this sequence to determine whether it contributes to the distribution of the mRNAs. Although the termination sequence was shown to function in vitro, when it was recloned into an expression vector, no termination was seen in vivo. Moreover, direct examination of the kinetics of lac messenger synthesis revealed that after initiation, most transcription continued to the end of the operon. We conclude that during normal growth, the operon is transcribed in its entirety and that the individual lac mRNAs are formed by cleavage. These results confirm earlier work implying that the lac operon is transcribed in its entirety but are in conflict with several recent reports suggesting that internal termination occurs. Our findings indicate that the natural polarity of the operon (lacZ is expressed sixfold more strongly than lacA) is based on posttranslational effects and not on polarity of transcription. Images

Murakawa, G J; Kwan, C; Yamashita, J; Nierlich, D P

1991-01-01

154

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

PubMed

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

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

2013-02-15

155

Wrapped-Around Models for the Lac Operon Complex  

PubMed Central

Abstract The protein-DNA complex, involved in the lac operon of enteric bacteria, is paradigmatic in understanding the extent of DNA bending and plasticity due to interactions with protein assemblies acting as DNA regulators. For the lac operon, two classes of structures have been proposed: 1), with the protein tetramer lying away from the DNA loop (wrapped-away model); and 2), with the protein tetramer lying inside the DNA loop (wrapped-around model). A recently developed electrostatic analytical model shows that the size and net charge of the Lac protein tetramer allow the bending of DNA, which is consistent with another wrapped-around model from the literature. Coarse-grained models, designed based on this observation, are extensively investigated and show three kinds of wrapped-around arrangements of DNA and a lower propensity for wrapped-away configurations. Molecular dynamics simulations of an all-atom model, built on the basis of the most tightly collapsed coarse-grained model, show that most of the DNA double-helical architecture is maintained in the region between O3 and O1 DNA operators, that the DNA distortion is concentrated in the chain beyond the O1 operator, and that the protein tetramer can adapt the N-terminal domains to the DNA tension.

La Penna, Giovanni; Perico, Angelo

2010-01-01

156

Ultra-wideband P-3 and CARABAS II foliage attenuation and backscatter analysis  

Microsoft Academic Search

Two-way foliage attenuation measurements from UHF and VHF SAR images collected from several USA forests and an empirical model of two-way attenuation versus center frequency are presented. Comparisons of UHF and VHF clutter backscatter coefficient distributions are made for different forest areas and terrain slopes. UHF two-way attenuation and backscatter coefficient statistics are presented for different polarization channels

L. A. Bessette; S. Ayasli

2001-01-01

157

The construction of ? transducing phages containing deletions defining regulatory elements of the lac and trp operons in E. coli  

Microsoft Academic Search

Two sets of plaque-forming ? transducing phages have been isolated which carry parts of the tryptophan (trp) and lactose (lac) operons. The ?ptrp-lac set of phages carry the trp and lac operons in the same orientation connected by deletions which enter the lac regulatory region from the i side. These deletions start at various sites in or near the trp

Wayne M. Barnes; Ruth B. Siegel; William S. Reznikoff

1974-01-01

158

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

Microsoft Academic Search

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

Fernand DAVID; Geneviève FARJANEL; URA CNRS

2000-01-01

159

H NMR study of a complex between the lac repressor headpiece and a 22 base pair symmetric lac operator.  

PubMed

A complex between the lac repressor headpiece and a fully symmetric tight-binding 22 bp lac operator was studied by 2D NMR. Several 2D NOE spectra were recorded for the complex in both H2O and 2H2O. Many NOE cross-peaks between the headpiece and DNA could be identified, and changes in the chemical shift of the DNA protons upon complex formation were analyzed. Comparison of these data with those obtained for a complex between the headpiece and a 14 bp half-operator, studied previously [Boelens, R., Scheek, R. M., Lamerichs, R. M. J. N., de Vlieg, J., van Boom, J. H., & Kaptein, R. (1987) in DNA-ligand interactions (Guschlbauer, W., & Saenger, W., Eds.) pp 191-215, Plenum, New York], shows that two headpieces form a specific complex with the 22 bp lac operator in which each headpiece binds in the same way as found for the 14 bp complex. The orientation of the recognition helix in the major groove of DNA in these complexes is opposite with respect to the dyad axis to that found for other repressors. PMID:2742823

Lamerichs, R M; Boelens, R; van der Marel, G A; van Boom, J H; Kaptein, R; Buck, F; Fera, B; Rüterjans, H

1989-04-01

160

Infection of Salmonella typhimurium with coliphage Mu d1 (Apr lac): construction of pyr::lac gene fusions.  

PubMed Central

A procedure was developed for introducing the coliphage Mu d1 (Apr lac) into Salmonella typhimurium in order to construct gene fusions that place the structural genes of the lac operon under the control of the promoter-regulatory region of other genes. To introduce Mu d1 from Escherichia coli K-12 into S. typhimurium, which is normally not a host for Mu, we first constructed an E. coli double lysogen carrying the defective Mu d1 phage and a Mu-P1 hybrid helper phage (MuhP1) that confers the P1 host range. A lysate prepared from this strain was used to infect a P1-sensitive (i.e., galE), restriction-deficient, modification-proficient strain of S. typhimurium, and a double lysogen carrying Mu d1 and MuhP1 was isolated. Induction of the latter strain produced lysates capable of infecting and generating gene fusions in P1-sensitive strains of S. typhimurium. In this paper we describe the construction of pyr::lac fusions by this technique.

Csonka, L N; Howe, M M; Ingraham, J L; Pierson, L S; Turnbough, C L

1981-01-01

161

DNA sequence of the lactose operon: the lacA gene and the transcriptional termination region.  

PubMed Central

The lac operon of Escherichia coli spans approximately 5300 base pairs and includes the lacZ, lacY, and lacA genes in addition to the operator, promoter, and transcription termination regions. We report here the sequence of the lacA gene and the region distal to it, confirming the sequence of thiogalactoside transacetylase and completing the sequence of the lac operon. The lacA gene is characterized by use of rare codons, suggesting an origin from a plasmid, transposon, or virus gene. UUG is the translation initiation codon. A preliminary examination of 3' end of the lac messenger in the region distal to the lacA gene indicates several endpoints. A predominant one is located at the 3' end of a G + C-rich hairpin structure, which may be involved in termination of transcription or in post-transcriptional processing. An open reading frame of 702 base pairs is present on the complementary strand downstream from lacA. Images

Hediger, M A; Johnson, D F; Nierlich, D P; Zabin, I

1985-01-01

162

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

163

Attenuated Influenza A Virus.  

National Technical Information Service (NTIS)

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

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

1992-01-01

164

Orientation of the Lac repressor DNA binding domain in complex with the left lac operator half site characterized by affinity cleaving.  

PubMed Central

Lac repressor (LacR) is a helix-turn-helix motif sequence-specific DNA binding protein. Based on proton NMR spectroscopic investigations, Kaptein and co-workers have proposed that the helix-turn-helix motif of LacR binds to DNA in an orientation opposite to that of the helix-turn-helix motifs of lambda repressor, lambda cro, 434 repressor, 434 cro, and CAP [Boelens, R., Scheek, R., van Boom, J. and Kaptein, R., J. Mol. Biol. 193, 1987, 213-216]. In the present work, we have determined the orientation of the helix-turn-helix motif of LacR in the LacR-DNA complex by the affinity cleaving method. The DNA cleaving moiety EDTA.Fe was attached to the N-terminus of a 56-residue synthetic protein corresponding to the DNA binding domain of LacR. We have formed the complex between the modified protein and the left DNA half site for LacR. The locations of the resulting DNA cleavage positions relative to the left DNA half site provide strong support for the proposal of Kaptein and co-workers. Images

Shin, J A; Ebright, R H; Dervan, P B

1991-01-01

165

Fluorescence resonance energy transfer over approximately 130 basepairs in hyperstable lac repressor-DNA loops.  

PubMed

Lac repressor (LacI) binds two operator DNA sites, looping the intervening DNA. DNA molecules containing two lac operators bracketing a sequence-directed bend were previously shown to form hyperstable LacI-looped complexes. Biochemical studies suggested that orienting the operators outward relative to the bend direction (in construct 9C14) stabilizes a positively supercoiled closed form, with a V-shaped LacI, but that the most stable loop construct (11C12) is a more open form. Here, fluorescence resonance energy transfer (FRET) is measured on DNA loops, between fluorescein and TAMRA attached near the two operators, approximately 130 basepairs apart. For 9C14, efficient LacI-induced energy transfer ( approximately 74% based on donor quenching) confirms that the designed DNA shape can force the looped complex into a closed form. From enhanced acceptor emission, correcting for observed donor-dependent quenching of acceptor fluorescence, approximately 52% transfer was observed. Time-resolved FRET suggests that this complex exists in both closed- and open form populations. Less efficient transfer, approximately 10%, was detected for DNA-LacI sandwiches and 11C12-LacI, consistent with an open form loop. This demonstration of long-range FRET in large DNA loops confirms that appropriate DNA design can control loop geometry. LacI flexibility may allow it to maintain looping with other proteins bound or under different intracellular conditions. PMID:12547794

Edelman, Laurence M; Cheong, Raymond; Kahn, Jason D

2003-02-01

166

Excess attenuation of an acoustic beam by turbulence.  

PubMed

A theory based on the concept of a spatial sinusoidal diffraction grating is presented for the estimation of the excess attenuation in an acoustic beam. The equation of the excess attenuation coefficient shows that the excess attenuation of acoustic beam not only depends on the turbulence but also depends on the application parameters such as the beam width, the beam orientation and whether for forward propagation or back scatter propagation. Analysis shows that the excess attenuation appears to have a frequency dependence of cube-root. The expression for the excess attenuation coefficient has been used in the estimations of the temperature structure coefficient, C(T)2, in sodar sounding. The correction of C(T)2 values for excess attenuation reduces their errors greatly. Published profiles of temperature structure coefficient and the velocity structure coefficient in convective conditions are used to test our theory, which is compared with the theory by Brown and Clifford. The excess attenuation due to scattering from turbulence and atmospheric absorption are both taken into account in sodar data processing for deducing the contribution of the lower atmosphere to seeing, which is the sharpness of a telescope image determined by the degree of turbulence in the Earth's atmosphere. The comparison between the contributions of the lowest 300-m layer to seeing with that of the whole atmosphere supports the reasonableness of our estimation of excess attenuation. PMID:14714792

Pan, Naixian

2003-12-01

167

A Multiwavelength Study of BL Lacs: Implications for Unification  

NASA Astrophysics Data System (ADS)

New multi-wavelength observations, including X-ray, optical and radio (VLA and VLBA) imaging and spectroscopy, for both the EMSS XBL and 1Jy RBL complete samples will be presented. Many of the differences between XBLs and RBLs are consistent with the beaming hypothesis; i.e., BL Lacs are highly-beamed FR-1 radio galaxies, and XBLs are seen further off-axis than RBLs. But results that I will present reveal differences in the spatial distributions and physical properties (e.g., emission-line and extended-radio lumin- osities) of the two samples, suggesting a more complex picture. While most XBLs are consistent with being highly-beamed FR-1s, half of the 1Jy RBLs are more consistent with being beamed high-luminosity FR-2s. Further, primarily in the 1Jy sample we find evidence for BL Lacs which are gravitationally-lensed quasars. The implications of these observations for unification models will be discussed.

Rector, Travis A.; Stocke, J.

168

Lactose metabolism by Staphylococcus aureus: characterization of lacABCD, the structural genes of the tagatose 6-phosphate pathway.  

PubMed

The nucleotide and deduced amino acid sequences of the lacA and lacB genes of the Staphylococcus aureus lactose operon (lacABCDFEG) are presented. The primary translation products are polypeptides of 142 (Mr = 15,425) and 171 (Mr = 18,953) amino acids, respectively. The lacABCD loci were shown to encode enzymes of the tagatose 6-phosphate pathway through both in vitro studies and complementation analysis in Escherichia coli. A serum aldolase assay, modified to allow detection of the tagatose 6-phosphate pathway enzymes utilizing galactose 6-phosphate or fructose phosphate analogs as substrate, is described. Expression of both lacA and lacB was required for galactose 6-phosphate isomerase activity. LacC (34 kDa) demonstrated tagatose 6-phosphate kinase activity and was found to share significant homology with LacC from Lactococcus lactis and with both the minor 6-phosphofructokinase (PfkB) and 1-phosphofructokinase (FruK) from E. coli. Detection of tagatose 1,6-bisphosphate aldolase activity was dependent on expression of the 36-kDa protein specified by lacD. The LacD protein is highly homologous with LacD of L. lactis. Thus, the lacABCD genes comprise the tagatose 6-phosphate pathway and are cotranscribed with genes lacFEG, which specify proteins for transport and cleavage of lactose in S. aureus. PMID:1655695

Rosey, E L; Oskouian, B; Stewart, G C

1991-10-01

169

Retro-reaction of singly bonded La@C82 derivatives.  

PubMed

Retro-reaction of radical monoadducts of a paramagnetic endohedral metallofullerene, La@C(2v)-C(82), is shown using thermal reaction in the presence of a radical trapping reagent, affording pristine La@C(2v)-C(82) in high yield (96%). PMID:20862446

Takano, Yuta; Ishitsuka, Midori O; Tsuchiya, Takahiro; Akasaka, Takeshi; Kato, Tatsuhisa; Nagase, Shigeru

2010-09-23

170

Radical coupling reaction of paramagnetic endohedral metallofullerene La@C82.  

PubMed

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

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

2008-12-01

171

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

172

lacZ Transgenic mice to monitor gene expression in embryo and adult  

Microsoft Academic Search

In transgenic experiments, lacZ can be used as a reporter gene for activity of a given promoter. Its main advantage is the ease of visualization in situ, on sections or in whole mount preparations, and the availability of simple protocols. In the following, we describe our procedure for detecting promoter activity in transgenic mice, including choice of lacZ vectors, generation

Andrea Schmidt; Kirsten Tief; Alessandro Foletti; Agnès Hunziker; Doris Penna; Edith Hummler; Friedrich Beermann

1998-01-01

173

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

2012-09-27

174

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

Microsoft Academic Search

Gene expression regulation is a fundamental bio- logical 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

Davide Normanno; Francesco Vanzi; Francesco Saverio Pavone

2008-01-01

175

The lac operator-repressor system is functional in the mouse  

Microsoft Academic Search

We report the successful transfer of a fully functional lac operator-repressor gene regulatory system to the mouse. The key component is a lac repressor transgene that resembles a typical mammalian gene both in codon usage and structure and expresses functional levels of repressor protein in the animal. We used the repressor to regulate the expression of a mammalian reporter gene

Carolyn A. Cronin; Wendy Gluba; Heidi Scrable

2001-01-01

176

Study of thermal behaviour of lac resin using specular reflectance spectroscopy  

Microsoft Academic Search

Purpose – To determine molecular level changes occurring in lac resin, due to the effect of thermal stress at different levels of temperature and baking times. Design\\/methodology\\/approach – Films of lac resin were applied on tin panels and baked at 100 and 200°C for different time intervals. The baked films were examined by specular reflectance spectroscopy, as they were otherwise

D. Bhatia; P. C. Sarkar; M. Alam

2006-01-01

177

Ultrasound attenuation dependence on air compression or expansion processes  

Microsoft Academic Search

In this work variation of ultrasonic attenuation coefficient is analyzed in terms of air compression or expansion processes. In\\u000aclosed spaces changing air volume, the ultrasound attenuation coefficient depends on thermodynamic processes which occur\\u000aduring the air volume change. Two limiting cases are possible: 1) if the change of air volume is very slow or intensive heat\\u000aexchange occurs between

L. Jakevicius; A. Demcenko; R. Mardosaite

2010-01-01

178

Light attenuators for plastic scintillation detectors  

Microsoft Academic Search

The need for light filters to attenuate flashes in plastic scintillators arose in designing apparatus for measurement of the charge composition of primary cosmic rays. Eight photomultipliers, each of which required a light filter, were arranged horizontally over a length of 50 cm in each of 10 rows of an ionization calorimeter. It was required that the absorption coefficients of

Tretyakova; Ch. A

1987-01-01

179

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

180

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

181

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

182

Photometry and radial velocities of 16 Lac (Chapellier+, 1995)  

NASA Astrophysics Data System (ADS)

Photometric and spectroscopic observations of the ? Cephei star 16 Lacertae obtained in 1983 and 1984 are presented and analysed. Using all the published maxima we have computed ephemerides for each of the three pulsational modes. No period variation is detected from 1950 to 1983. In order to identify the pulsational modes corresponding to the three main periods of 16 Lac we have applied different methods based on photometric and radial velocity variations. All give the same results: the mode corresponding to the largest amplitude P1 (016917d) is radial, P2 (017079d) is a nonradial mode of degree l=2. For P3 (018171d) the results are more dubious, but P3 is probably a l=1 nonradial mode. We have also studied the interaction between pulsation and binarity in 16 Lac. We confirm the existence of a resonance phenomenon between the radial and nonradial modes: the ratios between the beat frequencies of the pulsational modes and the orbital frequency are close but significantly different from simple rational numbers. According to Kato (1974) that means that the nonradial modes might be excited or at least enhanced by tidal effects. They would have been selected among all the possible modes because their ability to be resonant with the radial mode. The photometric amplitude of P3 in both filters appears to be variable from night to night in correlation with the orbital phase but despite its rapid and irregular fluctuations, the P3 amplitude stayed in constant average over 80 years. The present observations confirm the decrease of P1 and P2 amplitudes since 1950 but an analysis of older radial velocity data shows that the amplitude of the P1 mode went through a maximum around the middle of the century before the observed decrease of the last thirty years. (2 data files).

Chapellier, E.; Le Contel, J. M.; Le Contel, D.; Sareyan, J. P.; Valtier, J. C.

1995-06-01

183

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

184

Optimising HIFU Lesion Formation with Backscatter Attenuation Estimation (BAE)  

NASA Astrophysics Data System (ADS)

Ultrasound attenuation is an important dosimetric factor for HIFU treatments of soft tissue tumours. During clinical HIFU treatments ultrasound attenuation in the tissue overlying the focal volume leads to a loss in intensity. In clinical treatments at the Royal Marsden Hospital (UK), ultrasound attenuation is currently estimated using published tissue attenuation coefficients and the thickness of tissue layers determined from diagnostic ultrasound images. This method gives an inaccurate estimate of attenuation. Therefore to improve the delivery of HIFU, a better measurement of attenuation is required. Methods have been investigated for eventual clinical use in estimating the attenuation coefficient of the liver in vivo, immediately prior to HIFU treatment, using backscattered ultrasound pulses. Radio frequency (RF) echo signals were acquired using a clinical ultrasound scanner working with a linear array probe. The data required for diffraction correction of these estimates is a set of RF images obtained where the sample is axially translated with respect to the imaging transducer. These data were used to compute the diffraction corrected attenuation coefficient at each frequency using two methods: a substitution method and an inverse diffraction filtering process. In preliminary experiments, a homogeneous sponge material was used to test the data acquisition and processing techniques. Attenuation measurements were also made on ex vivo bovine liver tissue samples where the time since excision and the level of degassing were varied.

Civale, John; Bamber, Jeff; Rivens, Ian; Ter Haar, Gail

2006-05-01

185

Global teleseismic S wave attenuation  

NASA Astrophysics Data System (ADS)

We have measured 140,000 teleseismic S wave spectra from 150 deep (focal depth > 200 km) earthquakes recorded at 890 broadband global and regional network stations up to 0.7 Hz. We have analyzed these data to constrain the (1) epicentral distance and (2) spatial variation of the shear wave attenuation parameter tS*. tS* increases by about 2 s between 30° and 98°. The increase in tS* is consistent (correlation coefficient of 0.9) with global QS profiles (Dziewonski and Anderson, 1981; Durek and Ekström, 1996; Lawrence and Wysession, 2006). However, there are well resolved departures in the distance dependence of tS*. Most notably, tS* is lower than PREM-predicted values between 58°-64°. This indicates a reduction in shear attenuation from the global average at ~1600 km depth beneath Central America, eastern Asia, and Alaska. These regions have previously been identified as downwelling mantle regions on the basis of seismic tomography (Grand et al., 1997), plate reconstructions (Ricard et al., 1993), and waveform analysis (Lay et al., 2004). Stations terms of tS* represent the spatial variation of attenuation in the upper mantle. Using multi-channel cross-correlation and least-squares inversion of differential spectra we resolve high attenuation in the upper mantle beneath western North America, western Europe, and eastern Africa. Attenuation is low beneath eastern North America, the Baltic regions, and central and southern Africa. This variation correlates well with global variations in heat flow (Pollack et al., 1993) and crustal age (Mooney et al., 1995).

Hwang, Y.; Ritsema, J. E.

2009-12-01

186

THE LOBATE LAC SCALE, A NEW INSECT PEST OF TREES AND SHRUBS IN FLORIDA: IMPLICATIONS OF THE CARIBBEAN REGION  

Technology Transfer Automated Retrieval System (TEKTRAN)

The lobate lac scale, Paratachardina lobata, was first detected in the Western Hemisphere in southern Florida in 1999. Subsequent examination of specimens collected from New Providence Island in the Bahamas in 1992, determined these as the lobate lac scale. The lobate lac scale, which attacks woody ...

187

Generation of Nkx2.2:lacZ mice using recombination-mediated cassette exchange technology.  

PubMed

Nkx2.2 encodes a homeodomain transcription factor required for the correct specification and/or differentiation of cells in the pancreas, intestine, and central nervous system (CNS). To follow the fate of cells deleted for Nkx2.2 within these tissues, we generated Nkx2.2:lacZ knockin mice using a recombination-mediated cassette exchange (RMCE) approach. Expression analysis of lacZ and/or ?-galactosidase in Nkx2.2(lacZ/+) heterozygote embryos and adults demonstrates that lacZ faithfully recapitulates endogenous Nkx2.2 expression. Furthermore, the Nkx2.2(lacZ/lacZ) homozygous embryos display phenotypes indistinguishable from the previously characterized Nkx2.2(-/-) strain. LacZ expression analyses in the Nkx2.2(lacZ/lacZ) homozygous embryos indicate that Nkx2.2-expressing progenitor cells within the pancreas are generated in their normal numbers and are not mislocalized within the pancreatic ductal epithelium or developing islets. In the CNS of Nkx2.2(lacZ/lacZ) embryos, LacZ-expressing cells within the ventral P3 progenitor domain display different migration properties depending on the developmental stage and their respective differentiation potential. PMID:22539496

Arnes, Luis; Leclerc, Kevin; Friel, Jessica M; Hipkens, Susan B; Magnuson, Mark A; Sussel, Lori

2012-05-19

188

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

189

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

190

Live Attenuated Influenza Vaccine  

Microsoft Academic Search

\\u000a The development of the live, attenuated influenza vaccine (LAIV), based on the cold-adapted (ca), attenuated ca A\\/Ann Arbor\\/6\\/60 and ca B\\/Ann Arbor\\/1\\/66 backbones, has spanned several decades. The vaccine contains three vaccine strains, two attenuated influenza\\u000a A strains and one attenuated influenza B strain; these vaccine strains are genetic reassortants, each harboring two gene segments\\u000a from the currently circulating wild

Harry Greenberg; George Kemble

191

The interaction of lac repressor headpiece with its operator: an NMR view.  

PubMed

Analysis of nuclear Overhauser enhancements in two-dimensional NMR spectra of the complex of lac repressor headpiece with a 14 base pair lac operator fragment shows that the second helix of the headpiece binds in the major groove of DNA, as has been suggested. The orientation of this helix is approximately 180 degrees different from the proposed models and from that found in the X-ray structure of the 434 repressor-operator complex. The model of the lac headpiece-operator complex provides a good explanation for a large amount of biochemical, genetic and physical data. PMID:3064080

Boelens, R; Lamerichs, R M; Rullmann, J A; van Boom, J H; Kaptein, R

1988-01-01

192

Wave Attenuation in Effective Models Describing Porous and Fractured Media Saturated by a Fluid  

Microsoft Academic Search

Wave attenuation is introduced in the effective model of media that consists of alternating elastic and fluid layers. This attenuation is due to the friction on the boundaries between elastic and fluid layers and is described by additional terms in equations of the effective model. An investigation of these equations allows one to derive expressions of the attenuation coefficients for

L. A. Molotkov

2005-01-01

193

Attenuation Map Segmentation without Reconstruction Using a Level Set Method in Nuclear Medicine Imaging  

Microsoft Academic Search

In nuclear medical imaging, attenuation maps are images of the set of the linear attenuation coefficients of the observed body region. They are reconstructed from transmission SPECT (single photon emission computed tomography) acquisitions (the projections). The geometrical information of attenuation maps is crucial. We make the reasonable hypothesis that they are composed of homogeneous regions limited by straight edges. Thus,

Eric Debreuve; Michel Barlaud; Gilles Aubert; Jacques Darcourt

1998-01-01

194

Measurement of velocity and attenuation of shear waves in bovine compact bone using ultrasonic spectroscopy  

Microsoft Academic Search

The ultrasonic spectroscopy (broadband pulse) technique was applied to simultaneously measure phase velocity and attenuation coefficient of shear waves in bovine compact bone at frequencies ranging from 4.0–10.0 MHz. It was found that the ratio of attenuation coefficient of shear waves to that of longitudinal waves at a particular frequency for bovine compact bone was smaller than that of other

Junru Wu; Frances Cubberley

1997-01-01

195

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

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. PMID:1400164

Rosey, E L; Stewart, G C

1992-10-01

196

Boundary method for attenuation correction in positron computed tomography  

SciTech Connect

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 these boundaries and the average attenuation coefficients within the enclosed regions. The method has been tested on computer-simulated data, on scans of phantoms, and on patient studies, and has been found effective in reducing the random noise in transmission measurements and in providing more accurate ACFs than the method using geometric attenuation correction. As a result, transmission scan times can be shortened, inconvenience to patients is reduced, and PCT images are improved.

Huang, S.C.; Carson, R.E.; Phelps, M.E.; Hoffman, E.J.; Schelbert, H.R.; Kuhl, D.E.

1981-07-01

197

LAC2 encoding a secreted laccase is involved in appressorial melanization and conidial pigmentation in Colletotrichum orbiculare.  

PubMed

Both Colletotrichum and Magnaporthe spp. develop appressoria pigmented with melanin, which is essential for fungal pathogenicity. 1,8-Dihydroxynaphthalene (1,8-DHN) is believed to be polymerized to yield melanin around the appresorial cell wall through the oxidative activity of laccases. However, no 1,8-DHN laccase has yet been identified in either Colletotrichum or Magnaporthe spp. Here, we report a laccase gene, LAC2, that is involved in the appressorial melanization of Colletotrichum orbiculare, which causes cucumber anthracnose. LAC2 encodes a protein with a signal peptide and has high homology to fungal laccases. The conidial color of lac2 mutants is distinct from that of the C. orbiculare wild type, and the mutants are nonpathogenic. Notably, the mutant appressoria are defective in melanization, and a host invasion assay showed that the appressoria are nonfunctional. LAC2 was induced during appressorial melanization. These results suggest that LAC2 oxidizes 1,8-DHN in the appressoria. The LAC2 homologues of other fungi located in the same phylogenetic clade as LAC2 fully complemented the lac2 mutants. Interestingly, a LAC2 homologue, located in a different clade, complemented the conidial pigmentation but not appressorial melanization of the mutants, suggesting that the LAC2 function in appressorial melanization might only be conserved in laccases of the LAC2 clade. PMID:22934563

Lin, Shao Yu; Okuda, Shiho; Ikeda, Kyoko; Okuno, Tetsuro; Takano, Yoshitaka

2012-12-01

198

Chromatic aberration coefficients  

NASA Astrophysics Data System (ADS)

Our work deals with the influence of the wavelength of light on values of wave aberration coefficients. It is proposed a technique for calculation of the dependence of aberration coefficients on the wavelength, their interpretation and the connection to chromatic aberrations. It is also shown the calculation of the Strehl definition using chromatic aberration coefficients and the tolerance limits are given. The proposed method for calculation of chromatic aberration coefficients is shown for the case of the imaging of axial point by the rotationally symmetrical optical system. Relations that enable calculation of chromatic aberration coefficients up to fifth order are carried out. These relations are accurate enough for most optical systems in practice.

Miks, Antonin; Novak, Jiri; Novak, Pavel

2007-05-01

199

Unification of bl lac objects and fr i radio galaxies  

NASA Astrophysics Data System (ADS)

To understand the unification scheme for BL Lac objects with FR I radio galax-ies and Flat spetrum radio quasars (FSRQ), here the correlations of the bolometric luminosi-ties with redshifts and brightness temperatures of these objects are studied. The bolometric luminosity versus brightness temperature distribution shows a good correlation except a few scattered objects, mostly RBLs. The bolometric luminosities vary linearly with redshifts but here also a few scattered objects at high redshift. The FSRQs are at high redshifts and the bolometric luminosities and brightness temperatures of these objects are also high relative to XBLs and RBLs. The bolometric luminosities and brightness temperatures of FR I radio galax-ies with low redshift (< 0.1) and low Spectral index (?rx < 0.75) are comparable to those of XBLs and those characteristics of FR I radio galaxies, with relatively high redshift (> 0.2) and high spectral index, can be comparable with RBLs with low redshift (< 0.5) and low bolmetric luminosity. Those scattered RBLs with high redshifts (> 0.5) are believed to be in complex environment with companion galaxies, most of these objects are still unresolved. The bolomet-ric luminosity and brightness temperature of these objects are comparable to those of quasars. These results support the unification scheme. It suggests that, the FR I radio galaxies with high redshifts and spectral indices and those with low redshifts and spectral indices may be the parent populations of the RBL and XBL objects respectively.

Seal Braun, P.

200

Insertion mutagenesis of the lac repressor and its implications for structure-function analysis.  

PubMed Central

We recently developed a simple technique for the generation of relatively large (31-codon) insertion mutations in cloned genes. To test whether the analysis of such mutations could provide insight into structure-function relationships in proteins, we examined a set of insertion mutants of the Escherichia coli lac repressor (LacI). Representatives of several LacI mutant classes were recovered, including mutants which exhibit fully active, inducer-insensitive, or weak dominant-negative phenotypes. The various properties of the recovered mutants agree with previous biophysical, biochemical, and genetic data for the protein. In particular, the results support the prior designation of mutationally tolerant spacer regions of LacI as well as proposed differences in dimerization interactions among regions of the protein core domain. These findings suggest that the analysis of 31-codon insertion mutations may provide a simple approach for characterizing structure-function relationships in proteins for which high-resolution structures are not available.

Nelson, B D; Manoil, C; Traxler, B

1997-01-01

201

Structures and Spectra of Hot Gas around Nearby BL Lac Objects  

NASA Astrophysics Data System (ADS)

If FR I radio galaxies and BL Lac objects are parts of a single population, and only their orientation causes them to appear different (the BL Lac ``unification'' scheme), then they should have the same isotropic properties. We recently extended existing radio and optical tests to the X-ray by searching near BL Lacs for X-ray emission which matches the X-ray envelopes of FR I objects found by Worrall & Birkinshaw (1994). The well-known object PKS 0521-365 shows an unexpectedly strong halo when observed with the ROSAT HRI. Here we propose to use ACIS-I to obtain images and spectroscopy for PKS 0521-365 and three other BL Lacs. The data will determine the physical relationship between halos and their AGN and test the unification scheme.

Birkinshaw, Mark

1999-09-01

202

Ground-Water Resources of the Mille Lacs Lake Area, East-Central Minnesota.  

National Technical Information Service (NTIS)

The purposes of this report are: (1) describe groundwater occurrence and quality in the surficial and uppermost buried aquifers of the Mille Lacs Lake area, (2) define the interaction between ground water and Lake Onamia, and (3) describe susceptibility t...

L. C. Trotta T. K. Cowdery

1998-01-01

203

Secretion of LamB-LacZ by the signal recognition particle pathway of Escherichia coli.  

PubMed

LamB-LacZ fusion proteins have classically been used in studies of the general secretion pathway of Escherichia coli. Here we describe how increasing signal sequence hydrophobicity routes LamB-LacZ Hyb42-1 to the signal recognition particle (SRP) pathway. Secretion of this hydrophobic fusion variant (H*LamB-LacZ) was reduced in the absence of fully functional Ffh and Ffs, and the translocator jamming caused by Hyb42-1 was prevented by efficient delivery of the fusion to the periplasm. Finally, we found that in the absence of the ribosome-associated chaperone, trigger factor (Tig), LamB-LacZ localized to the periplasm in a SecA-dependent, SRP-independent fashion. Collectively, our results provide compelling in vivo evidence that there is an SRP-dependent cotranslational targeting mechanism in E. coli and argue against a role for trigger factor in pathway discrimination. PMID:13129940

Bowers, Christina Wilson; Lau, Fion; Silhavy, Thomas J

2003-10-01

204

Quality and position of the three lac operators of E. coli define efficiency of repression.  

PubMed Central

Repression of the lac promoter may be achieved in two different ways: either by interference with the action of RNA polymerase or by interference with CAP activation. We investigated cooperative repression of the Escherichia coli lac operon by systematic conversion of its three natural operators (O1, O2 and O3) on the chromosome. We find that cooperative repression by tetrameric Lac repressor increases with both quality and proximity of the interacting operators. A short distance of 92 bp allows effective repression by two very weak operators (O3, O3). The cooperativity of lac operators is discussed in terms of a local increase of repressor concentration. This increase in concentration depends on flexible DNA which allows loop formation.

Oehler, S; Amouyal, M; Kolkhof, P; von Wilcken-Bergmann, B; Muller-Hill, B

1994-01-01

205

Plasmid insertion mutagenesis and lac gene fusion with mini-mu bacteriophage transposons.  

PubMed Central

Small bacteriophage Mu transposable elements containing the lac operon structural genes were constructed to facilitate the isolation and use of Mu insertions and lac gene fusions. These mini-Mu elements have selectable genes for either ampicillin or kanamycin resistance and can be used to form both transcriptional and translational lac gene fusions. Some of the mini-Mu-lac elements constructed are deleted for the Mu A and B transposition genes and form stable insertions that cannot undergo transposition unless complemented for these functions. A procedure was developed for selecting mini-Mu insertions specifically into plasmids, including commonly used high-copy-number cloning vectors such as pBR322. Mu insertions in pBR322 were found to be distributed around the plasmid, but insertions in certain regions occurred more frequently than in others.

Castilho, B A; Olfson, P; Casadaban, M J

1984-01-01

206

Specular reflectance and derivative spectrometric studies on lac-epoxy resin blends  

Microsoft Academic Search

Purpose – This paper aims to gain a greater insight into the molecular level changes occurring in lac-epoxy blends, at elevated temperatures for different intervals of time. It is also to determine the changes in key physico-chemical parameters of these blends, before and after applying thermal stress on these blends. Design\\/methodology\\/approach – Films of lac-epoxy blends, applied on tin panels,

Deepika Bhatia; M. Alam; P. C. Sarkar

2007-01-01

207

Studies on thermal stress of lac-polyvinyl butyral resin blends through specular reflectance spectra  

Microsoft Academic Search

Purpose – To study the changes occurring in lac-polyvinyl butyral (PVB) resin blends at molecular levels on baking the blends at 200°C for different intervals of time. It was also to ascertain the changes in key physico-chemical parameters of these blends, before and after applying thermal stress on these blends. Design\\/methodology\\/approach – Films of lac-PVB blends, applied on tin panels

D. Bhatia; M. Alam; P. C. Sarkar

2007-01-01

208

Spatial monitoring of toxicity in HMOX-LacZ transgenic mice  

Microsoft Academic Search

Transgenic reporter mice can contribute in the development of less toxic and more selective drugs to treat disease. In this\\u000a brief communication we describe the generation and initial validation of transgenic mice that provide a visual spatial readout\\u000a of oxidative stress. These mice carry a LacZ reporter transgene driven by the human haem oxygenase 1 promoter. The induction\\u000a of LacZ

Rachel YoungC; C. Roland Wolf; Ken Brown; John D. Hayes; C. Bruce A. Whitelaw

2010-01-01

209

The Study of Rain Specific Attenuation for the Prediction of Satellite Propagation in Malaysia  

NASA Astrophysics Data System (ADS)

Specific attenuation is the fundamental quantity in the calculation of rain attenuation for terrestrial path and slant paths representing as rain attenuation per unit distance (dB/km). Specific attenuation is an important element in developing the predicted rain attenuation model. This paper deals with the empirical determination of the power law coefficients which allow calculating the specific attenuation in dB/km from the knowledge of the rain rate in mm/h. The main purpose of the paper is to obtain the coefficients of k and ? of power law relationship between specific attenuation. Three years (from 1st January 2006 until 31st December 2008) rain gauge and beacon data taken from USM, Nibong Tebal have been used to do the empirical procedure analysis of rain specific attenuation. The data presented are semi-empirical in nature. A year-to-year variation of the coefficients has been indicated and the empirical measured data was compared with ITU-R provided regression coefficient. The result indicated that the USM empirical measured data was significantly vary from ITU-R predicted value. Hence, ITU-R recommendation for regression coefficients of rain specific attenuation is not suitable for predicting rain attenuation at Malaysia.

Mandeep, J. S.; Ng, Y. Y.; Abdullah, H.; Abdullah, M.

2010-06-01

210

Comparison of Advanced Radar Polarimetric Techniques for Operational Attenuation Correction at C Band  

Microsoft Academic Search

ABSTRACT Rain path attenuation correction is a challenging task for quantitative use of weather,radar measurements at frequencies higher than S band. The proportionality,relationship between,specific attenuation,hh (spe- cific differential attenuation,dp) and specific differential phase Kdp is the basis for simple path-integrated attenuation correction using differential phase dp. However, the coefficients of proportionality are known to be dependent upon temperature, on the

Gianfranco Vulpiani; Pierre Tabary; Jacques Parent du Chatelet; Frank S. Marzano

2008-01-01

211

Comparison of Nitrate Attenuation Characterization Methods for Groundwater Remediation  

NASA Astrophysics Data System (ADS)

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

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

2008-12-01

212

Wearable Sound Attenuating Enclosure.  

National Technical Information Service (NTIS)

The patent application discloses a lightweight noise attenuating enclosure shaped to cover the head, neck and upper thorax. A rigid outer shell and a sound attenuation layer block up to 10 db of ambient noise and a number of pads mounted along the mouth o...

R. S. Gales

1974-01-01

213

Ferromagnetic spin coupling between endohedral metallofullerene La@C82 and a cyclodimeric copper porphyrin upon inclusion.  

PubMed

The cyclic host cyclo-[P(Cu)](2) carrying two covalently connected Cu(II) porphyrin units can accommodate La@C(82), a paramagnetic endohedral metallofullerene, in its cavity to form the inclusion complex cyclo-[P(Cu)](2)?La@C(82), which can be transformed into the caged complex cage-[P(Cu)](2)?La@C(82) by ring-closing olefin metathesis of its side-chain olefinic termini. On the basis of electron spin resonance (ESR) and electron spin transient nutation (ESTN) studies, cyclo-[P(Cu)](2)?La@C(82) is the first ferromagnetically coupled inclusion complex featuring La@C(82), whereas cage-[P(Cu)](2)?La@C(82) is ferrimagnetic. PMID:21599021

Hajjaj, Fatin; Tashiro, Kentaro; Nikawa, Hidefumi; Mizorogi, Naomi; Akasaka, Takeshi; Nagase, Shigeru; Furukawa, Ko; Kato, Tatsuhisa; Aida, Takuzo

2011-06-01

214

YidC Protein, a Molecular Chaperone for LacY Protein Folding via the SecYEG Protein Machinery.  

PubMed

To understand how YidC and SecYEG function together in membrane protein topogenesis, insertion and folding of the lactose permease of Escherichia coli (LacY), a 12-transmembrane helix protein LacY that catalyzes symport of a galactoside and an H(+), was studied. Although both the SecYEG machinery and signal recognition particle are required for insertion of LacY into the membrane, YidC is not required for translocation of the six periplasmic loops in LacY. Rather, YidC acts as a chaperone, facilitating LacY folding. Upon YidC depletion, the conformation of LacY is perturbed, as judged by monoclonal antibody binding studies and by in vivo cross-linking between introduced Cys pairs. Disulfide cross-linking also demonstrates that YidC interacts with multiple transmembrane segments of LacY during membrane biogenesis. Moreover, YidC is strictly required for insertion of M13 procoat protein fused into the middle cytoplasmic loop of LacY. In contrast, the loops preceding and following the inserted procoat domain are dependent on SecYEG for insertion. These studies demonstrate close cooperation between the two complexes in membrane biogenesis and that YidC functions primarily as a foldase for LacY. PMID:23928306

Zhu, Lu; Kaback, H Ronald; Dalbey, Ross E

2013-08-08

215

In Vivo Cloning of lac Genes in Streptococcus lactis ML3 †  

PubMed Central

The isolation and characterization of a Streptococcus lactis ML3 strain which possessed a recombinant lactose plasmid is described. The recombination events generating this plasmid occurred in vivo in a recombination-deficient strain and appeared to be mediated by transposition events. Restriction mapping revealed that the recombinant plasmid, pDA0307, contained a region of the lactose plasmid, pSK08, linked to another resident plasmid, pSK07. Copy number determinations indicated that the lac genes were present at approximately 20 copies per cell in pDA0307, whereas the lac genes are normally present at approximately 10 copies per cell in pSK08. The strain containing pDA0307 displayed a 21 to 54% increase in the expression of the Lac enzyme phospho-?-d-galactosidase. However, the strain containing pDA0307 both grew and produced lactic acid in milk at rates identical to that of a strain containing pSK08. This result suggests that lac gene dosage of plasmid-linked lac genes was not limiting the rate at which these derivatives of S. lactis ML3 fermented milk. Images

Anderson, Douglas G.; McKay, Larry L.

1984-01-01

216

Bl Lac Population Study: Early Results Using the Fermi 11-MONTH Catalog  

NASA Astrophysics Data System (ADS)

In the framework of AGN unification, BL Lacs and their parent population would share the same intrinsic characteristics, the observational differences being due to the orientation of the jet compared to our line of sight. BL Lacs would be those objects whose jet is oriented towards us, Doppler boosting the emission. The growing number of BL Lacs detected at HE (> 100 MeV) and VHE (> 100 GeV) is a challenge for this scheme, since the high values of Doppler factors needed to explain the emission of these sources imply a large density for the parent population. We studied the BL Lac source sample detected by Fermi after 11 months of observation. Using the data presented in Fermi's first AGN catalog, we put constraints on the intrinsic characteristics of this BL Lac population, such as the intrinsic luminosity and Lorentz factor distributions. Based on these results, we used Monte Carlo simulations to constrain the space density of the parent population and the jet opening angle.

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

217

The attenuation of microwave radiation by fog and rain  

NASA Astrophysics Data System (ADS)

In this report, the equations which describe the attenuation of long-wavelength electromagnetic radiation by water fogs and rain are briefly reviewed and explained under the assumption that the aerosol droplets are spherical and that the irradiance of the beam is in the 'linear' regime. Calculations of water fog attenuation coefficients are made using the Rayleigh approximation, and an approximate error analysis of this approximation is made by comparing Rayleigh approximation calculations of absorption efficiency with exact Mie theory calculations of extinction efficiency. Numerical integration of the Mie extinction efficiency is used to compute the attenuation coefficient for rain with a Marshall-Palmer drop size distribution for various rain rates and temperatures. These results are compared with those given by a power law relationship with coefficients given by Olsen, Rogers, and Hodge which was used in the Near Milimeter Wave (NMMW) Module of the Electro- Optical Systems Atmospheric Effects Library (EOSAEL).

Pendleton, J. D.; Niles, Stanley

1994-08-01

218

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

219

RADIO FREQUENCY ATTENUATOR  

DOEpatents

A high peak power level r-f attenuator that is readily and easily insertable along a coaxial cable having an inner conductor and an outer annular conductor without breaking the ends thereof is presented. Spaced first and second flares in the outer conductor face each other with a slidable cylindrical outer conductor portion therebetween. Dielectric means, such as water, contact the cable between the flares to attenuate the radio-frequency energy received thereby. The cylindrical outer conductor portion is slidable to adjust the voltage standing wave ratio to a low level, and one of the flares is slidable to adjust the attenuation level. An integral dielectric container is also provided. (AFC)

Giordano, S.

1963-11-12

220

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

221

Lac repressor: Crystallization of intact tetramer and its complexes with inducer and operator DNA  

SciTech Connect

The intact lac repressor tetramer, which regulates expression of the lac operon in Escherichia coli, has been crystallized in the native form, with an inducer, and in a ternary complex with operator DNA and an anti-inducer. The crystals without DNA diffract to better than 3.5 {angstrom}. They belong to the monoclinic space group C2 and have cell dimensions a = 164.7 {angstrom}, b = 75.6 {angstrom}, and c = 161.2 {angstrom}, with {alpha} = {gamma} = 90{degree} and {beta} = 125.5{degree}. Cocrystals have been obtained with a number of different lac operator-related DNA fragments. The complex with a blunt-ended 16-base-pair strand yielded tetragonal bipyramids that diffract to 6.5 {angstrom}. These protein-DNA cocrystals crack upon exposure to the gratuitous inducer isopropyl {beta}-D-thiogalactoside, suggesting a conformational change in the repressor-operator complex.

Pace, H.C.; Lu, P. (Univ. of Pennsylvania, Philadelphia (USA)); Lewis, M. (Univ. of Pennsylvania, Philadelphia, (USA) Smith Kline and French Labs., King of Prussia, PA (USA))

1990-03-01

222

A model of the lac repressor-operator complex based on physical and genetic data.  

PubMed

Computer graphics were used to build a molecular model of the complex of Lac repressor and lac operator. The model is based (a) on the NMR data of the Kaptein group [Boelens, R., Lamerichs, R. M. J. N., Rullmann, J. A. C., van Boom, J. H. & Kaptein, R. (1988) Protein Sequence Data Anal. 1, 487-498] and (b) on our genetic and biochemical data including specificity changes [Lehming, N., Sartorius, J., Kisters-Woike, B., von Wilcken-Bergmann, B. & Müller-Hill, B. (1990) EMBO J. 9, 615-621]. Effects of amino acid exchanges in the recognition helix could be predicted by the model and were subsequently tested and confirmed by genetic experiments. Comparison of the modelled lac complex with the known crystallographic structures of several helix-turn-helix DNA complexes reveals striking similarities and suggests rules which govern the recognition between particular amino acid side chains and particular base pairs in these systems. PMID:2040302

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

1991-06-01

223

Isolation of pseudorevertants of lac oc mutants: selection system for superoperator mutations.  

PubMed Central

A selection procedure and rapid screening test are described that allow the isolation of rarely occurring pseudorevertants of lac oc mutants. These techniques were developed with the aim of isolating superoperator (os) mutants in which a secondary mutation in the operator would increase the affinity of the repressor of superoperator, thereby overcoming the effect of the oc mutation. The occurrence of superoperator mutants is predicted on the basis of a probable twofold symmetry in the lac repressor-operator recognition. Over 2,300 oc pseudorevertants were isolated and screened. In vitro measurements of the affinity of lac repressor for the operator region indicate that, among these, one oc pseudorevertant probably results from an oc mutation. The selection procedure also yielded other types of regulatory mutants that behave as promoter mutants and as i gene mutants in which the repressor is capable of overcoming an oc mutation.

Pfahl, M; Bourgeois, S

1976-01-01

224

Improvement of quantitation in SPECT: Attenuation and scatter correction using non-uniform attenuation data  

SciTech Connect

Quantitative assessment of tracer distribution with single photon emission computed tomography (SPECT) is difficult because of attenuation and scattering of gamma rays within the object. A method considering the source geometry was developed, and effects of attenuation and scatter on SPECT quantitation were studied using phantoms with non-uniform attenuation. The distribution of attenuation coefficients (..mu..) within the source were obtained by transmission CT. The attenuation correction was performed by an iterative reprojection technique. The scatter correction was done by convolution of the attenuation corrected image and an appropriate filter made by line source studies. The filter characteristics depended on ..mu.. and SPEC measurement at each pixel. The SPECT obtained by this method showed the most reasonable results than the images reconstructed by other methods. The scatter correction could compensate completely for a 28% scatter components from a long line source, and a 61% component for thick and extended source. Consideration of source geometries was necessary for effective corrections. The present method is expected to be valuable for the quantitative assessment of regional tracer activity.

Mukai, T.; Torizuka, K.; Douglass, K.H.; Wagner, H.N.

1985-05-01

225

Spectral characterization of 4 MV Bremsstrahlung by attenuation analysis.  

PubMed

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

Huang, P H; Kase, K R; Bjärngard, B E

226

Determinants of bistability in induction of the Escherichia coli lac operon.  

PubMed

The authors have developed a mathematical model of regulation of expression of the Escherichia coli lac operon, and have investigated bistability in its steady-state induction behaviour in the absence of external glucose. Numerical analysis of equations describing regulation by artificial inducers revealed two natural bistability parameters that can be used to control the range of inducer concentrations over which the model exhibits bistability. By tuning these bistability parameters, the authors found a family of biophysically reasonable systems that are consistent with an experimentally determined bistable region for induction by thio-methylgalactoside (TMG) (in Ozbudak et al. Nature, 2004, 427; p. 737). To model regulation by lactose, the authors developed similar equations in which allolactose, a metabolic intermediate in lactose metabolism and a natural inducer of lac, is the inducer. For biophysically reasonable parameter values, these equations yield no bistability in response to induction by lactose - only systems with an unphysically small permease-dependent export effect can exhibit small amounts of bistability for limited ranges of parameter values. These results cast doubt on the relevance of bistability in the lac operon within the natural context of E. coli, and help shed light on the controversy among existing theoretical studies that address this issue. The results also motivate a deeper experimental characterisation of permease-independent transport of lac inducers, and suggest an experimental approach to address the relevance of bistability in the lac operon within the natural context of E. coli. The sensitivity of lac bistability to the type of inducer emphasises the importance of metabolism in determining the functions of genetic regulatory networks. PMID:19045824

Dreisigmeyer, D W; Stajic, J; Nemenman, I; Hlavacek, W S; Wall, M E

2008-09-01

227

Attenuated Measles Virus as a Vaccine Vector  

PubMed Central

Live attenuated measles virus (MV) vaccines have an impressive record of safety, efficacy and ability to induce life-long immunity against measles infection. Using reverse genetics technology, such negative-strand RNA viruses can now be rescued from cloned DNA. This technology allows the insertion of exogenous genes encoding foreign antigens into the MV genome in such a way that they can be expressed by the MV vaccine strain, without affecting virus structure, propagation and cell targeting. Recombinant viruses rescued from cloned cDNA induce immune responses against both measles virus and the cloned antigens. The tolerability of MV to gene(s) insertion makes it an attractive flexible vector system, especially if broad immune responses are required. The fact that measles replication strictly occurs in the cytoplasm of infected cells without DNA intermediate has important biosafety implications and adds to the attractiveness of MV as a vector. In this article we report the characteristics of reporter gene expression (GFP, LacZ and CAT) and the biochemical, biophysical and immunological properties of recombinant MV expressing heterologous antigens of simian immunogeficiency virus (SIV).

Zuniga, Armando; Wang, ZiLi; Liniger, Matthias; Hangartner, Lars; Caballero, Michael; Pavlovic, Jovan; Wild, Peter; Viret, Jean Francois; Glueck, Reinhard; Billeter, Martin A.; Naim, Hussein Y.

2013-01-01

228

Attenuated measles virus as a vaccine vector.  

PubMed

Live attenuated measles virus (MV) vaccines have an impressive record of safety, efficacy and ability to induce life-long immunity against measles infection. Using reverse genetics technology, such negative-strand RNA viruses can now be rescued from cloned DNA. This technology allows the insertion of exogenous genes encoding foreign antigens into the MV genome in such a way that they can be expressed by the MV vaccine strain, without affecting virus structure, propagation and cell targeting. Recombinant viruses rescued from cloned cDNA induce immune responses against both measles virus and the cloned antigens. The tolerability of MV to gene(s) insertion makes it an attractive flexible vector system, especially if broad immune responses are required. The fact that measles replication strictly occurs in the cytoplasm of infected cells without DNA intermediate has important biosafety implications and adds to the attractiveness of MV as a vector. In this article we report the characteristics of reporter gene expression (GFP, LacZ and CAT) and the biochemical, biophysical and immunological properties of recombinant MV expressing heterologous antigens of simian immunogeficiency virus (SIV). PMID:17303293

Zuniga, Armando; Wang, Zili; Liniger, Matthias; Hangartner, Lars; Caballero, Michael; Pavlovic, Jovan; Wild, Peter; Viret, Jean Francois; Glueck, Reinhard; Billeter, Martin A; Naim, Hussein Y

2007-02-02

229

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

PubMed Central

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

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

1990-01-01

230

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

231

Characterization of hematopoietic progenitor cells that express the transcription factor SCL, using a lacZ "knock-in" strategy  

PubMed Central

Gene targeting experiments have demonstrated that the transcription factor SCL is essential for primitive and definitive hematopoiesis in the mouse. To study the functional properties of hematopoietic cells expressing SCL, we have generated mutant mice (SCLlacZ/w) in which the Escherichia coli lacZ reporter gene has been “knocked in” to the SCL locus, thereby linking ?-galactosidase expression to transcription from the SCL promoter. Bone marrow cells from heterozygous SCLlacZ/w mice were sorted into fractions expressing high, intermediate and low levels of ?-galactosidase (designated lacZhigh, lacZint, and lacZneg). Cells that were lacZhigh or lacZint were enriched for day 12 spleen colony-forming units and myeloid and erythroid colony-forming cells (CFCs). These fractions included >99% of the erythroid and >90% of the myeloid CFCs. Culture of sorted bone marrow populations on stromal cells secreting interleukin-7 or in fetal thymic organ cultures showed that B and T lymphoid progenitors were also present in the lacZhigh and lacZint fractions. These data provide a functional correlation between SCL expression and colony-forming ability in immature hematopoietic cells. Our data also suggested that expression of SCL was transient and confined to hematopoietic stem and/or progenitor cells, because the differentiated progeny of most lineages (except the erythroid) were ?-galactosidase-negative.

Elefanty, Andrew G.; Begley, C. Glenn; Metcalf, Donald; Barnett, Louise; Kontgen, Frank; Robb, Lorraine

1998-01-01

232

Bounding the Bogoliubov coefficients  

SciTech Connect

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

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

2008-11-15

233

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

Microsoft Academic Search

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

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

1995-01-01

234

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

Microsoft Academic Search

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

Achim Brauer; Joël Casanova

2001-01-01

235

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

Microsoft Academic Search

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

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

2001-01-01

236

Mineralogy of primary carbonate-bearing hypabyssal kimberlite, Lac de Gras, Slave Province, Northwest Territories, Canada  

Microsoft Academic Search

A suite of fresh, Late Cretaceous to Eocene hypabyssal kimberlites from the Lac de Gras field were studied in order to understand better carbonate, silicate and oxide paragenesis. The samples have excellent preservation of textures and primary mineralogy and are archetypal or Group 1 kimberlite. Five kimberlite localities are identified as calcite-bearing based on the presence of high Sr–Ba calcite

John P. Armstrong; Mark Wilson; Robert L. Barnett; Tom Nowicki; Bruce A. Kjarsgaard

2004-01-01

237

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

238

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

Technology Transfer Automated Retrieval System (TEKTRAN)

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

239

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

NASA Astrophysics Data System (ADS)

We report on spectroscopic observations covering most of the 475 BL Lacs in the second Fermi Large Area Telescope (LAT) catalog of active galactic nuclei (AGNs). Including archival measurements (correcting several erroneous literature values) we now have spectroscopic redshifts for 44% of the BL Lacs. We establish firm lower redshift limits via intervening absorption systems and statistical lower limits via searches for host galaxies for an additional 51% of the sample leaving only 5% of the BL Lacs unconstrained. The new redshifts raise the median spectroscopic \\tilde{z} from 0.23 to 0.33 and include redshifts as large as z = 2.471. Spectroscopic redshift minima from intervening absorbers have \\tilde{z}= 0.70, showing a substantial fraction at large z and arguing against strong negative evolution. We find that detected BL Lac hosts are bright ellipticals with black hole masses M • ~ 108.5 - 109, substantially larger than the mean of optical AGNs and LAT Flat Spectrum Radio Quasar samples. A slow increase in M • with z may be due to selection bias. We find that the power-law dominance of the optical spectrum extends to extreme values, but this does not strongly correlate with the ?-ray properties, suggesting that strong beaming is the primary cause of the range in continuum dominance.

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

2013-02-01

240

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

241

Exploring the sequence-function relationship in transcriptional regulation by the lac O1 operator.  

PubMed

Understanding how binding of a transcription factor to an operator is influenced by the operator sequence is an ongoing quest. It facilitates discovery of alternative binding sites as well as tuning of transcriptional regulation. We investigated the behavior of the Escherichia coli Lac repressor (LacI) protein with a large set of lac O(1) operator variants. The 114 variants examined contained a mean of 2.9 (range 0-4) mutations at positions -4, -2, +2 and +4 in the minimally required 17 bp operator. The relative affinity of LacI for the operators was examined by quantifying expression of a GFP reporter gene and Rosetta structural modeling. The combinations of mutations in the operator sequence created a wide range of regulatory behaviors. We observed variations in the GFP fluorescent signal among the operator variants of more than an order of magnitude under both uninduced and induced conditions. We found that a single nucleotide change may result in changes of up to six- and 12-fold in uninduced and induced GFP signals, respectively. Among the four positions mutated, we found that nucleotide G at position -4 is strongly correlated with strong repression. By Rosetta modeling, we found a significant correlation between the calculated binding energy and the experimentally observed transcriptional repression strength for many operators. However, exceptions were also observed, underscoring the necessity for further improvement in biophysical models of protein-DNA interactions. PMID:22594825

Maity, Tuhin S; Jha, Ramesh K; Strauss, Charlie E M; Dunbar, John

2012-06-15

242

Develop a Detailed Map of Mille Lacs Lake Shoal Areas, Aitkin Area Fisheries, 1996. Completion Report.  

National Technical Information Service (NTIS)

Substrate and aquatic vegetation in the shoal areas of Mille Lacs Lake were mapped during the summers from 1992 through 1996 to document existing physical and environmental conditions. One-thousand and seventy transects were established, including 1,015 t...

1996-01-01

243

Large Lake Sampling Program Assessment Report for Mille Lacs Lake 1994 and 1995.  

National Technical Information Service (NTIS)

The walleye fishery in Mille Lacs is presently less dependent on strong year classes that have provided a majority of the catch in recent years. The present fishery consists of several average year classes (1991, 1992, 1993, and possibly 1994). The combin...

R. Bruesewitz

1996-01-01

244

Period Change, Spot Migration and Orbital Solution for the Eclipsing Binary AR Lac  

Microsoft Academic Search

We present a new large set of photoelectric photometric measurements (1806 in V and 1367 in B passbands) of the eclipsing RS CVn-type system AR Lac covering the period 2000 June 28 to 2005 October 13. 13 new epochs of minima have been derived that allows us to update the complex O--C pattern of this binary, now monitored for more

A. Siviero; S. Dallaporta; U. Munari

2006-01-01

245

Genetic analysis of Mu or mini-Mu containing F? pro lac episomes after prophage induction  

Microsoft Academic Search

We have investigated the fate of different F pro lac episomes carrying a Mu or mini-Mu, after induction of the Mu or mini-Mu prophage, by looking at the frequencies of transfer of the episome and of one chromosomal marker. During the first 10 min after induction the frequency of chromosome mobilization increases while the frequency of episome transfer decreases. This

A. Toussaint; L. Desmet; F. van Gijsegem; M. Faelen

1981-01-01

246

The Rosat-Green Bank Sample of Intermediate BL Lac Objects  

NASA Astrophysics Data System (ADS)

The Rosat-Green Bank BL Lac sample consists of 119 objects and smoothly bridges the gap between the previously disparate subclasses of radio- and X-ray-selected objects. Further study of this sample should provide useful constraints to the unified scheme and help determine if modifications are necessary.

Laurent-Muehleisen, S. A.; Kollgaard, R. I.; Feigelson, E. D.

247

Ultra-Violet and X-ray Observations of BL Lac Type Objects.  

National Technical Information Service (NTIS)

The BL Lac type objects Mrk 421, Mrk 501, Mrk 180 and 1218+304 were studied in the ultraviolet and X-ray bands. In the UV, these objects typically exhibit slow drifts in flux (on a timescale of weeks or longer) with little change in spectral index. Such b...

I. M. George R. S. Warwick G. E. Bromage

1988-01-01

248

Development of a VSV-G protein pseudotyped retroviral vector system expressing dominant oncogenes from a lacO-modified inducible LTR promoter  

Microsoft Academic Search

We report the development of a retroviral vector system in which two dominant oncogenes are expressed inducibly in human cells using the lac repressor\\/lac operator regulatable promoter system. First, the parent vector, pLoCRNLo, was constructed to contain a retroviral long terminal repeat (LTR) promoter that has been modified by incorporation of a lac operator sequence (lacO). This promoter, LTRo, was

Sijian Wang; Gillian M. Beattie; Alberto Hayek; Fred Levine

1996-01-01

249

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

250

Isolating LacZ-expressing cells from mouse inner ear tissues using flow cytometry.  

PubMed

Isolation of specific cell types allows one to analyze rare cell populations such as stem/progenitor cells. Such an approach to studying inner ear tissues presents a unique challenge because of the paucity of cells of interest and few transgenic reporter mouse models. Here, we describe a protocol using fluorescence-conjugated probes to selectively label LacZ-positive cells from the neonatal cochleae. The most common underlying pathology of sensorineural hearing loss is the irreversible damage and loss of cochlear sensory hair cells, which are required to transduce sound waves to neural impulses. Recent evidence suggests that the murine auditory and vestibular organs harbor stem/progenitor cells that may have regenerative potential. These findings warrant further investigation, including identifying specific cell types with stem/progenitor cell characteristics. The Wnt signaling pathway has been demonstrated to play a critical role in maintaining stem/progenitor cell populations in several organ systems. We have recently identified Wnt-responsive Axin2-expressing cells in the neonatal cochlea, but their function is largely unknown. To better understand the behavior of these Wnt-responsive cells in vitro, we have developed a method of isolating Axin2-expressing cells from cochleae of Axin2-LacZ reporter mice. Using flow cytometry to isolate Axin2-LacZ positive cells from the neonatal cochleae, we could in turn execute a variety of experiments on live cells to interrogate their behavior as stem/progenitor cells. Here, we describe in detail the steps for the microdissection of neonatal cochlea, dissociation of these tissues, labeling of the LacZ-positive cells using a fluorogenic substrate, and cell sorting. Techniques for dissociating cochleae into single cells and isolating cochlear cells via flow cytometry have been described. We have made modifications to these techniques to establish a novel protocol to isolate LacZ-expressing cells from the neonatal cochlea. PMID:22217925

Jan, Taha A; Chai, Renjie; Sayyid, Zahra N; Cheng, Alan G

2011-12-23

251

Isolating LacZ-expressing Cells from Mouse Inner Ear Tissues using Flow Cytometry  

PubMed Central

Isolation of specific cell types allows one to analyze rare cell populations such as stem/progenitor cells. Such an approach to studying inner ear tissues presents a unique challenge because of the paucity of cells of interest and few transgenic reporter mouse models. Here, we describe a protocol using fluorescence-conjugated probes to selectively label LacZ-positive cells from the neonatal cochleae. The most common underlying pathology of sensorineural hearing loss is the irreversible damage and loss of cochlear sensory hair cells, which are required to transduce sound waves to neural impulses. Recent evidence suggests that the murine auditory and vestibular organs harbor stem/progenitor cells that may have regenerative potential1,2. These findings warrant further investigation, including identifying specific cell types with stem/progenitor cell characteristics. The Wnt signaling pathway has been demonstrated to play a critical role in maintaining stem/progenitor cell populations in several organ systems3-7. We have recently identified Wnt-responsive Axin2-expressing cells in the neonatal cochlea, but their function is largely unknown8. To better understand the behavior of these Wnt-responsive cells in vitro, we have developed a method of isolating Axin2-expressing cells from cochleae of Axin2-LacZ reporter mice9. Using flow cytometry to isolate Axin2-LacZ positive cells from the neonatal cochleae, we could in turn execute a variety of experiments on live cells to interrogate their behavior as stem/progenitor cells. Here, we describe in detail the steps for the microdissection of neonatal cochlea, dissociation of these tissues, labeling of the LacZ-positive cells using a fluorogenic substrate, and cell sorting. Techniques for dissociating cochleae into single cells and isolating cochlear cells via flow cytometry have been described2,10-12. We have made modifications to these techniques to establish a novel protocol to isolate LacZ-expressing cells from the neonatal cochlea.

Jan, Taha A.; Chai, Renjie; Sayyid, Zahra N.; Cheng, Alan G.

2011-01-01

252

Investigation of Radiation Attenuation Properties for Baryte Concrete  

NASA Astrophysics Data System (ADS)

In the present work the authors have studied the attenuation properties of baryte concrete as a biological shield for nuclear power plants, particle accelerators, research reactors, laboratory hot cells and different radiation sources. Investigation has been performed by measuring the transmitted fast neutron and gamma ray spectra through cylindrical samples of baryte concrete (?=3.49 g\\cdotcm-3). A reactor-collimated beam and neutron-gamma spectrometer with stilbene scintillator were used during measurements. A pulse shape discriminating technique based on zero cross over method was used to discriminate between neutron and gamma pulses. Removal cross-section ?R,eff and total attenuation coefficient ?eff of neutrons and gamma rays were evaluated from the obtained results. Also, slow neutron fluxes have been measured using a collimated reactor beam and BF3 counter, where the macroscopic cross section ?(En) has been evaluated using the attenuation relation. The total macroscopic cross sections ?T(En) and total attenuation coefficient ?(Eg) of neutrons and gamma rays have been calculated based on the database cross sections. Also, the total mass attenuation coefficient ?eff(Eg)/? and ?(Eg)/? of gamma ray have been estimated and calculated using the measured results and XCOM code respectively. Measured and calculated results were compared and a reasonable agreement was found.

Abdo, A. El-Sayed; Kansouh, W. A.; Megahid, R. M.

2002-12-01

253

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

254

Effect of selected pesticides on larval mortality of the neuropteran predator, Chrysopa lacciperda Kimmins, of the lac insect, Kerria lacca (Kerr)  

Microsoft Academic Search

Laboratory bioassays were carried out to evaluate the bioefficacy of some pesticides against larval Chrysopa lacciperda Kimmins, a lac insect predator, to develop a suitable strategy for field management of this serious neuropteran pest of Indian lac insect, Kerria lacca (Kerr). Seven insecticides (lambdacyhalothrin, carbosulfan, spinosad, indoxacarb, fipronil, alphamethrin and ethofenprox) were identified based on field trials against the lac

J. P. Singh; A. K. Jaiswal; M. Monobrullah; A. Bhattacharya

2010-01-01

255

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.

256

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

Microsoft Academic Search

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

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

2007-01-01

257

P-Element repression in Drosophila melanogaster by variegating clusters of P-lacZ-white transgenes.  

PubMed Central

In Drosophila, clusters of P transgenes (P-lac-w) display a variegating phenotype for the w marker. In addition, X-ray-induced rearrangements of chromosomes bearing such clusters may lead to enhancement of the variegated phenotype. Since P-lacZ transgenes in subtelomeric heterochromatin have some P-element repression abilities, we tested whether P-lac-w clusters also have the capacity to repress P-element activity in the germline. One cluster (T-1), located on a rearranged chromosome (T2;3) and derived from a line bearing a variegating tandem array of seven P-lac-w elements, partially represses the dysgenic sterility (GD sterility) induced by P elements. This cluster also strongly represses in trans the expression of P-lacZ elements in the germline. This latter suppression shows a maternal effect. Finally, the combination of variegating P-lac-w clusters and a single P-lacZ reporter inserted in subtelomeric heterochromatic sequences at the X chromosome telomere (cytological site 1A) leads to strong repression of dysgenic sterility. These results show that repression of P-induced dysgenic sterility can be elicited in the absence of P elements encoding a polypeptide repressor and that a transgene cluster can repress the expression of a single homologous transgene at a nonallelic position. Implications for models of transposable element silencing are discussed.

Ronsseray, S; Boivin, A; Anxolabehere, D

2001-01-01

258

Airblast Attenuation and Flow Loss Performance of Passive Attenuators.  

National Technical Information Service (NTIS)

An analytical/experimental program was conducted for Waterways Experiment Station (WES) to develop a passive airblast attenuator to protect hardened shelters from conventional weapon attack. The role of a passive attenuator is to provide protection throug...

J. P. Harrell Q. A. Baker

1992-01-01

259

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

260

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

261

Attenuation and scattering of axisymmetrical modes in a fluid-filled round pipe with internally rough walls.  

PubMed

The attenuation of axisymmetric eigenmodes in a cylindrical, elastic, fluid-filled waveguide with a statistically rough elastic wall is studied. It is shown that small perturbation theory can be used to relate explicitly the statistical characteristics of the internal wall surface roughness of an elastic pipe to the attenuation and scattering coefficients of the acoustic modes in the filling fluid. Analytical expressions for modal attenuation coefficients are obtained. The analysis of the frequency dependent attenuation coefficients and the ratio between the roughness correlation length and the inner radius of the pipe is made for different correlation functions of the roughness. It is shown that two scale parameters control the overall behavior of the modal attenuation coefficients. These are the ratios of the roughness correlation length and the inner pipe radius to the acoustic wavelength. The numerical results for sound propagation in a pipe and in a borehole with statistically rough, elastic walls are obtained and discussed. PMID:18345814

Maximov, German A; Podjachev, Eugenii V; Horoshenkov, Kirill V

2008-03-01

262

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

263

Broad beam attenuation of cobalt-60 gamma rays and 6-, 18-, and 25-MV x rays by lead  

SciTech Connect

The measurement of photon attenuation by absorbing materials in radiation beams is usually performed using narrow beam geometry. However, radiotherapy treatments rarely simulate narrow beam conditions. The effect of broad beams on the attenuation of cobalt-60 gamma rays and 6-, 18-, and 25-MV x rays by lead is considered both theoretically and experimentally. The theoretical calculations are based on first-scatter considerations and indicate a dependence on treatment geometry (i.e., maximum scattering angle). Measured attenuation coefficients vary by as much as 16%, comparing narrow and broad beam data for typical treatment conditions. Broad beam attenuation coefficients, calculated from the measured zero-area values agree with the measured results to within 2% on average with a maximum deviation of 5%. A very simple empirical procedure is proposed to determine attenuation coefficients for a wide range of field sizes. This agrees with the measured data to within 0.5% on average and 4% at worst. With irregularly shaped absorbers, a sector integration technique is considered in combination with a first-scatter calculation. For a long rectangular field, the agreement between measured and calculated attenuation coefficients is better than 1.5% for all energies. The question of accuracy in attenuation coefficients needed to give an accuracy of 3% in relative transmission is addressed and shows a dependence on absorber thickness. For 75% transmission, the required accuracy in attenuation coefficient is 10%, whereas for 25% transmission, it should be improved to 2%.

Van Dyk, J.

1986-01-01

264

Analysis of natural coloring matters in food. III. Application of methylation with diazomethane for the detection of lac color.  

PubMed

A new method has been proposed for detection of lac color in food. Lac color is a natural color additive derived from a secretion of the insect Coccus Laccae (Laccifer lacca Kerr). It is extracted from food with methanolic oxalic acid and eluted from a column of Amberlite XAD-2 with the same solvent. The fraction containing the lac color is treated with diazomethane to produce 2 reddish-orange markers. The marker species in the reaction mixture are detected by both thin-layer chromatography and reverse-phase liquid chromatography. PMID:2715136

Yamada, S; Noda, N; Mikami, E; Hayakawa, J; Yamada, M

265

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

266

Ultrasonic Attenuation in Zircaloy4  

Microsoft Academic Search

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

M. P. Go´mez; A. D. Banchik; M. I. Lo´pez Pumarega; J. E. Ruzzante

2005-01-01

267

Ultrasonic Attenuation in Zircaloy4  

Microsoft Academic Search

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

M. P. Gómez; A. D. Banchik; M. I. López Pumarega; J. E. Ruzzante

2005-01-01

268

Absorption filter correction by spectral shifts of ultrasonic propagation in nonlinear attenuating media  

NASA Astrophysics Data System (ADS)

A closed form solution of the general case of frequency shift of a Gaussian pulse in a nonlinear power law attenuating medium of arbitrary exponent including the effect of transient radiation coupling process is presented. Also, this paper describes a simulation of the spectrum pathway in an ultrasonic A-scan. It includes transducer response, frequency dependent absorption in the test medium and radiation coupling transfer function. The measurement and simulation result has been used with the closed form solution to correct the absorption filter (attenuation coefficient). The attenuation coefficient correction for castor oil to fit the simulation result with recorded data is examined.

Ali, M. G. S.; El-Sayed, N. Z.; Kamel, N. A.; Raouf Mohamed, A.

2002-11-01

269

Isolation of gene fusions (soi::lacZ) inducible by oxidative stress in Escherichia coli.  

PubMed Central

Mu dX phage was used to isolate three gene fusions to the lacZ gene (soi::lacZ; soi for superoxide radical inducible) that were induced by treatment with superoxide radical anion generators such as paraquat and plumbagin. The induction of beta-galactosidase in these fusion strains with the superoxide radical generating agents required aerobic metabolism. Hyperoxygenation (i.e., bubbling of cultures with oxygen gas) also induced the fusions. On the other hand, hydrogen peroxide did not induce the fusions at concentrations that are known to invoke an adaptive response. Introduction of oxyR, htpR, or recA mutations did not affect the induction. Two of the fusion strains exhibited increased sensitivity to paraquat but not to hydrogen peroxide. The third fusion strain showed no increased sensitivity to either agent. All three fusions were located in the 45- to 61-min region of the Escherichia coli chromosome.

Kogoma, T; Farr, S B; Joyce, K M; Natvig, D O

1988-01-01

270

Dynamics and bistability in a reduced model of the lac operon  

NASA Astrophysics Data System (ADS)

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

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

2004-06-01

271

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

PubMed Central

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

Santillan, Moises; Mackey, Michael C.

2008-01-01

272

The REX Survey: How to Find a Large and Complete Sample of BL Lacs  

NASA Astrophysics Data System (ADS)

The number of known BL Lacs is not large, if compared to that of other classes of AGN, and in particular the statistically complete samples are made of a few tens of objects. This fact makes any quantitative derivation of the global properties of the class subject to large uncertainties. We have started a project to find a sizable, complete and deep sample of Radio Emitting X-ray sources (REXs) using the available data from a VLA survey (NVSS) and the ROSAT PSPC archive. We expect that the sample will contain, by the end of the identification process, about 200 BL Lacs, enabling us to better study their statistical properties, like the X-ray, radio and optical luminosity functions and their cosmological evolution, and to address the apparent dichotomy of RBL and XBL using a unique sample to test the two classes at the same time. We will describe the project and its current status.

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

273

Monitored Natural Attenuation  

NASA Astrophysics Data System (ADS)

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.

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

274

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

275

The City Manager Experience in the U.S.: Perspectives on Improving Local Government in LAC  

Microsoft Academic Search

The City (or Council) Manager--a career professional who handles budget, personnel, and implementation, leaving political matters to elected officials--has been adopted in more than a score of cities in LAC. City managers are found in more than 2,000 U.S. cities, making it the most widely used form of management in the country. This paper reviews the origins of the Council-Manager

Travis Katz; Tim Campbell

1995-01-01

276

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

Microsoft Academic Search

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

Leonard Guarente; Mark Ptashne

1981-01-01

277

H0323+022: Classification as a BL Lac and EXOSAT coordinated observations  

Microsoft Academic Search

The object H0323+022 (Doxsey et al. 1983) has been shown to be a BL Lac object by virtue of a diversity of observational characteristics at radio, optical, and x-ray wavelengths, in agreement with the conclusion of Margon and Jacoby (1984). Multi-frequency coordinated observations of this highly variable object with EXOSAT in September 1984 found it to be in a faint

H. Bradt; J. Baldwin; E. Feigelson; B. Geldzahler; G. Madejski; P. Massey; J. McClintock; I. McHardy; R. McMahan; T. Ohashi; R. Remillard; W. Romanishin; C. Salter; B. Schaefer; D. Schwartz; S. Tapia; J. Thorstensen; C. M. Urry; P. Wehinger; A. Wilson; S. Wyckoff

1985-01-01

278

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

Microsoft Academic Search

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

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

2008-01-01

279

Prolonged Intranight Optical Quiescence of the Classical BL Lac Object PKS 0735+178  

Microsoft Academic Search

We report our extensive intranight optical monitoring of the well known low-energy peaked (LBL) BL Lac object PKS 0735+178. This long-term follow-up consists of R-band monitoring for a minimum duration of ˜ 4 hours, on 17 nights spanning the past 11 years (1998-2008). Intra-night optical variability (INOV) amplitude of >= 3% on hour-like time scale was not observed in any

A. Goyal; Gopal-Krishna; G. C. Anupama; D. K. Sahu; R. Sagar; S. Britzen; M. Karazous; M. F. Aller; H. D. Aller

2009-01-01

280

Isolation and characterization of Bacillus subtilis genomic lacZ fusions induced during partial purine starvation.  

PubMed Central

Random genomic Bacillus subtilis lacZ fusions were screened in order to identify the possible existence of regulons responding to the stimuli generated by partial purine starvation. A leaky pur mutation (purL8) was isolated and used to generate the partial purine starvation conditions in the host strain used for screening. On the basis of their induction during partial purine starvation, seven genomic lacZ fusions were isolated. None of the fusions map in loci previously reported to contain purine-regulated genes. One fusion maps very close to the citB locus and may very well be a citB fusion. The fusions were divided into two types on the basis of their response to complete starvation for either ATP or GTP or both components at the same time. Except for one, type 2 fusions were induced by specific starvation for ATP and by simultaneous starvation for ATP and GTP, but not by specific GTP starvation in a gua strain or by GTP starvation induced by the addition of decoyinine. Type 1 fusions were equally well induced by all three kinds of purine starvation including GTP starvation induced by decoyinine. Further subdivisions of the fusions were obtained on the basis of their responses to the spo0A gene product. A total of five fusions showed that spo0A affected expression. One class was unable to induce lacZ expression in the absence of the spo0A gene product, whereas the other class had increased lacZ expression during partial purine starvation in a spo0A background.

Saxild, H H; Jensen, C L; Hubrechts, P; Hammer, K

1994-01-01

281

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

SciTech Connect

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

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

1985-01-01

282

V340 Ser and V448 Lac light curves (Arkhipova+, 2011)  

NASA Astrophysics Data System (ADS)

We performed our UBV observations of two program stars, V340 Ser and V448 Lac, at the Crimean Station of the Sternberg Astronomical Institute using a 60-cm Zeiss reflector with a photoelectric photometer designed by Lyuty (1971, Soobshch. GAISh 172, 30) with a 27 aperture. The accuracy of the observations was from 0.01mag to 0.02mag. The photometric system of the photometer is close to Johnson's standard UBV system. (2 data files).

Arkhipova, V. P.; Ikonnikova, N. P.; Komissarova, G. V.

2011-09-01

283

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.

284

NIOSH Health Hazard Evaluation Report: HETA No. 2005-0243-3016, ACH Foam Technologies, Fond du Lac, Wisconsin, September 2006.  

National Technical Information Service (NTIS)

On May 17, 2005, the National Institute for Occupational Safety and Health (NIOSH) received a confidential request from three employees at ACH Foam Technologies in Fond du Lac, Wisconsin. The requestors expressed concerns about potential long-term effects...

M. Rodriguez C. Achutan

2006-01-01

285

An Early Event in the Transport Mechanism of LacY Protein  

PubMed Central

Helix V in LacY, which abuts and crosses helix I in the N-terminal helix bundle of LacY, contains Arg144 and Trp151, two residues that play direct roles in sugar recognition and binding, as well as Cys154, which is important for conformational flexibility. In this study, paired Cys replacement mutants in helices V and I were strategically constructed with tandem factor Xa protease cleavage sites in the loop between the two helices to test cross-linking. None of the mutants form disulfides spontaneously; however, three mutants (Pro28 ? Cys/Cys154, Pro28 ? Cys/Val158 ? Cys, and Phe29 ? Cys/Val158 ? Cys) exhibit cross-linking after treatment with copper/1,10-phenanthroline (Cu/Ph) or 1,1-methanediyl bismethanethiosulfonate ((MTS)2-1), 3–4 ?), and cross-linking is quantitative in the presence of ligand. Remarkably, with one mutant, complete cross-linking with (MTS)2-1 has no effect on lactose transport, whereas quantitative disulfide cross-linking catalyzed by Cu/Ph markedly inhibits transport activity. The findings are consistant with a number of previous conclusions suggesting that sugar binding to LacY causes a localized scissors-like movement between helices V and I near the point where the two helices cross in the middle of the membrane. This ligand-induced movement may act to initiate the global conformational change resulting from sugar binding.

Zhou, Yonggang; Madej, M. Gregor; Guan, Lan; Nie, Yiling; Kaback, H. Ronald

2011-01-01

286

Engineering a portable riboswitch-LacP hybrid device for two-way gene regulation  

PubMed Central

Riboswitches are RNA-based regulatory devices that mediate ligand-dependent control of gene expression. However, there has been limited success in rationally designing riboswitches. Moreover, most previous riboswitches are confined to a particular gene and only perform one-way regulation. Here, we used a library screening strategy for efficient creation of ON and OFF riboswitches of lacI on the chromosome of Escherichia coli. We then engineered a riboswitch-LacP hybrid device to achieve portable gene control in response to theophylline and IPTG. Moreover, this device regulated target expression in a ‘two-way’ manner: the default state of target expression was ON; the expression was switched off by adding theophylline and restored to the ON state by adding IPTG without changing growth medium. We showcased the portability and two-way regulation of this device by applying it to the small RNA CsrB and the RpoS protein. Finally, the use of the hybrid device uncovered an inhibitory role of RpoS in acetate assimilation, a function which is otherwise neglected using conventional genetic approaches. Overall, this work establishes a portable riboswitch-LacP device that achieves sequential OFF-and-ON gene regulation. The two-way control of gene expression has various potential scientific and biotechnological applications and helps reveal novel gene functions.

Jin, Ye; Huang, Jian-Dong

2011-01-01

287

Color Variations of Two Blazars: BL Lac and PKS 0736+017  

NASA Astrophysics Data System (ADS)

Multi-night campaigns to monitor sources for microvariability were undertaken in the summer of 1997 for BL Lac and in early 2002 for PKS 0736+017. BL Lac was observed at Rosemary Hill Observatory in Bronson, Florida and PKS 0736+017 was observed with the SARA telescope on Kitt Peak in Arizona. Both sources underwent dramatic flares and exhibited substantial microvariability. During each campaign, the source was observed alternately through V and R filters so that color variations could be monitored as well. The most commonly reported behavior for such objects is that they become redder when fainter. This is observed in the BL Lac data. These data do not indicate that the point source varies in color however. Instead, they support the notion that the underlying host galaxy contributes a larger fraction of the total flux when the source is faint than when it is bright. More unusual was the observation that PKS 0736+017 was observed to be redder when brighter. The data support the notion that the observed color variation may be related more to the nature of the variation (flaring, subsiding, or quiescent) than to the flux level.

Clements, S. D.

2002-12-01

288

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

289

Flavonoid-responsive nodY-lacZ expression in three phylogenetically different Bradyrhizobium groups.  

PubMed

Previously, restriction fragment length polymorphism analysis using the nodD1YABC gene probe showed the genetic diversity of common nodD1ABC gene regions of Bradyrhizobium japonicum, Bradyrhizobium elkanii, and the Thai soybean Bradyrhizobium. The nodD1 sequences of representative strains of the 3 groups differed phylogenetically, suggesting that responses of NodD1 proteins of the 3 Bradyrhizobium groups to diverse flavonoids may differ. To confirm this hypothesis, 6 representative strains were chosen from the 3 Bradyrhizobium groups. Six reporter strains were constructed, all carrying the pZB32 plasmid, which contains a nod box and the nodY-lacZ fusion of B. japonicum USDA 110. Differences in nodY-lacZ expression among the strains in response to 37 flavonoid compounds at various concentrations were evaluated. Of those compounds, prunetin (4',5-dihydroxy-7-methoxyisoflavone) and esculetin (6,7-dihydroxycoumarin) were identified as Bradyrhizobium group-specific nod gene inducers. Esculetin showed nod gene induction activities unique to Thai Bradyrhizobium strains. The levels of nodY-lacZ induction among B. japonicum and Thai Bradyrhizobium strains increased with increasing concentration of prunetin, whereas, those in B. elkanii strains did not. PMID:18449225

Yokoyama, Tadashi

2008-05-01

290

SIMULTANEOUS BACKSCATTER AND ATTENUATION ESTIMATION USING A LEAST SQUARES METHOD WITH CONSTRAINTS  

PubMed Central

Backscatter and attenuation variations are essential contrast mechanisms in ultrasound B-mode imaging. Emerging Quantitative Ultrasound methods extract and display absolute values of these tissue properties. However, in clinical applications, backscatter and attenuation parameters sometimes are not easily measured because of tissues inhomogeneities above the region of interest. We describe a least squares method (LSM) that fits the echo signal power spectra from a region of interest (ROI) to a 3-parameter tissue model that simultaneously yields estimates of attenuation losses and backscatter coefficients. To test the method, tissue-mimicking phantoms with backscatter and attenuation contrast as well as uniform phantoms were scanned with linear array transducers on a Siemens S2000. Attenuation and backscatter coefficients estimated by the LSM were compared with those derived using a reference phantom method (Yao et al. 1990). Results show that the LSM yields effective attenuation coefficients for uniform phantoms comparable to values derived using the reference phantom method. For layered phantoms exhibiting non-uniform backscatter, the LSM resulted in smaller attenuation estimation errors than the reference phantom method. Backscatter coefficients derived using the LSM were in excellent agreement with values obtained from laboratory measurements on test samples and with theory. The LSM is more immune to depth-dependent backscatter changes than commonly used reference phantom methods.

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

2011-01-01

291

Characterization of pLAC1, a cryptic plasmid isolated from Lactobacillus acidipiscis and comparative analysis with its related plasmids.  

PubMed

The pLAC1 plasmid of Lactobacillus acidipiscis ACA-DC 1533, a strain isolated from traditional Kopanisti cheese, was characterised. Nucleotide sequence analysis revealed a circular molecule of 3478bp with a G+C content of 37.2%. Ab initio annotation indicated four putative open reading frames (orfs). orf1 and orf4 were found to encode a replication initiation protein (Rep) and a mobilization protein (Mob), respectively. The deduced products of orf2 and orf3 revealed no significant homology to other known proteins. However, in silico examination of the plasmid sequence supported the existence of a novel operon that includes rep, orf2 and orf3 in pLAC1 and that this operon is highly conserved also in plasmids pLB925A02, pSMA23, pLC88 and pC7. RT-PCR experiments allowed us to verify that these three genes are co-transcribed as a single polycistronic mRNA species. Furthermore, phylogenetic analysis of pLAC1 Rep and Mob proteins demonstrated that they may have derived from different plasmid origins, suggesting that pLAC1 is a product of a modular evolution process. Comparative analysis of full length nucleotide sequences of pLAC1 and related Lactobacillus plasmids showed that pLAC1 shares a very similar replication backbone with pLB925A02, pSMA23 and pLC88. In contrast, mob of pLAC1 was almost identical with the respective gene of plasmids pLAB1000, pLB4 and pPB1. These findings lead to the conclusion that pLAC1 acquired mob probably via an ancestral recombination event. Our overall work highlights the importance of characterizing plasmids deriving from non-starter 'wild' isolates in order to better appreciate plasmid divergence and evolution of lactic acid bacteria. PMID:20538362

Asteri, Ioanna-Areti; Papadimitriou, Konstantinos; Boutou, Effrossyni; Anastasiou, Rania; Pot, Bruno; Vorgias, Constantinos E; Tsakalidou, Effie

2010-05-25

292

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

PubMed

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

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

2012-06-15

293

OCT skin image enhancement through attenuation compensation.  

PubMed

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

Hojjatoleslami, Ali; Avanaki, Mohammad R N

2012-07-20

294

[Attenuation of photosynthetically available radiation (PAR) in Meiliang Bay under different winds and waves].  

PubMed

Based on the successive underwater irradiance measurement in situ from Jul. 12 to 17 in 2003, the attenuation of photosynthetically available radiation (PAR) and euphotic depth in Meiliang Bay were analyzed under different winds and waves. The results showed that the downward PAR attenuation coefficients ranged from 2.63 to 4.7 m(-1), with an average of 3.63 +/- 0.47 x m(-1), and the corresponding euphotic depth ranged from 0.98 to 1.75 m, with an average of 1.29 +/- 0.18 m, which demonstrated that phytoplankton and macrophyte could not grow below 1.5 m due to the lack of adequate solar radiation. The total suspended solids resulted from wind and wave increased the attenuation of light, with the downward attenuation coefficients of PAR being 2.63, 3.72 and 4.37 x m(-1) under small, medium and large wind and wave, respectively. Significant linear correlations were found between transparence, PAR attenuation coefficient, euphotic depth and total suspended solid, especially inorganic suspended solid, while chlorophyll a was the most nonsignificant light attenuator. Multiple stepwise linear regressions showed that inorganic suspended solid was the most important light attenuator dominating the light attenuation in wind-exposed Meiliang Bay. PMID:16180769

Zhang, Yunlin; Qin, Boqiang; Chen, Weimin; Hu, Weiping; Gao, Guang; Zhu, Guangwei; Luo, Liancong

2005-06-01

295

Effect of DNA looping on the induction kinetics of the lac operon.  

PubMed

The induction of the lac operon follows cooperative kinetics. The first mechanistic model of these kinetics is the de facto standard in the modeling literature [Yagil, G., Yagil, E., 1971. On the relation between effector concentration and the rate of induced enzyme synthesis. Biophys. J. 11, 11-17]. Yet, subsequent studies have shown that the model is based on incorrect assumptions. Specifically, the repressor is a tetramer with four (not two) inducer-binding sites, and the operon contains two auxiliary operators (in addition to the main operator). Furthermore, these structural features are crucial for the formation of DNA loops, the key determinants of lac repression and induction. Indeed, the repression is determined almost entirely (>95%) by the looped complexes [Oehler, S., Eismann, E.R., Krämer, H., Müller-Hill, B., 1990. The three operators of the lac operon cooperate in repression. EMBO J. 9(4), 973-979], and the pronounced cooperativity of the induction curve hinges upon the existence of the looped complexes [Oehler, S., Alberti, S., Müller-Hill, B., 2006. Induction of the lac promoter in the absence of DNA loops and the stoichiometry of induction. Nucleic Acids Res. 34(2), 606-612]. Here, we formulate a model of lac induction taking due account of the tetrameric structure of the repressor and the existence of looped complexes. We show that: (1) The kinetics are significantly more cooperative than those predicted by the Yagil and Yagil model. The cooperativity is higher because the formation of looped complexes is easily abolished by repressor-inducer binding. (2) The model provides good fits to the repression data for cells containing wild-type tetrameric or mutant dimeric repressor, as well as the induction curves for 6 different strains of Escherichia coli. It also implies that the ratios of certain looped and non-looped complexes are independent of inducer and repressor levels, a conclusion that can be rigorously tested by gel electrophoresis. (3) Repressor overexpression dramatically increases the cooperativity of the induction curve. This suggests that repressor overexpression can induce bistability in systems, such as growth of E. coli on lactose, that are otherwise monostable. PMID:17490688

Narang, Atul

2007-03-28

296

Light attenuation in a shallow, turbid reservoir, Lake Houston, Texas  

USGS Publications Warehouse

Results of measurements of light penetration at sites in Lake Houston near Houston, Texas, indicate that light-extinction coefficients during 1989?90 range from about 2.49 to 7.93 meters-1 and euphotic zone depth ranges from about 0.61 to 1.85 meters. The coefficients are largest near the inflow site of West Fork San Jacinto River (upstream) and decrease slightly toward the dam (downstream). Total suspended solids and total organic carbon concentrations also are largest at the upstream end. Chlorophyll a+b concentrations are smallest near the dam, increase slightly upstream, and are largest during growing-season months. Color and turbidity show the strongest correlations with light-extinction coefficients in Lake Houston. Dissolved phosphorus and nitrogen concentrations are greater than growth-limiting concentrations during the study period, indicating that nutrient availability did not limit primary productivity or the phytoplankton biomass in Lake Houston. Light-extinction coefficients in relation to selected water-quality constituents indicate that more than one constituent affects the light-attenuating properties of Lake Houston. Attenuation of light in water depends on total suspended solids for predominant light scattering and on dissolved organic matter (color) and chlorophyll a+b for absorption of light. A statistical analytical model using Spearman rank order correlation shows that color and turbidity are the most useful water-quality constituents sampled to determine light-attenuating properties of water in Lake Houston. Multiple-regression analysis of measured light-extinction coefficients as the dependent variable and measured color and turbidity as independent variables for water from Lake Houston produced the relation: light-extinction coefficient (h) = 2.78 + 0.007 x color + 0.036 x turbidity, with an average error of the computed coefficient to measured value of ?13 percent. The model can be useful in computing the thickness of the euphotic zone to determine primary productivity in the reservoir.

Lee, Roger W.; Rast, Walter

1997-01-01

297

Multidimensional seismic noise attenuation  

NASA Astrophysics Data System (ADS)

This dissertation addresses the problem of seismic noise attenuation by using inversion. Two types of noise are considered. First, spiky noise, which is attenuated with a robust error measure called the Huber norm. This norm treats small residual with the ?2 norm and large residuals with the ?1 norm. It is continuous everywhere and can be minimized with a standard gradient-based solver. In this thesis, the well-known quasi-Newton method L-BFGS is used. The Huber norm and the L-BFGS solver are flexible enough to be used in many different situations, such as velocity analysis and regridding of noise bathymetry data. Another powerful application of the Huber norm is adaptive subtraction of surface-related multiples. In this case, weak multiples in the vicinity of strong primaries are better removed with the Huber norm than with ?2. Second, coherent noise, which is attenuated by making the residual components of any least-squares fitting of contaminated data independent and identically distributed (IID). To achieve this goal, a weighting and a modeling approach are introduced. The weighting approach aims at approximating the inverse data covariance operator (or matrix) with multidimensional prediction-error filters (PEFs). The modeling approach introduces a coherent noise modeling operator inside the inversion. The modeling technique converges usually better than the weighting approach and yields smaller residuals. One advantage of the weighting approach, however, is that it can be used to separate non-stationary signal and non-stationary noise with PEFs. In this case, the separation is called pattern-based because it involves the multivariate noise and signal spectra that PEFs approximate. For removal of surface-related multiples, this technique proves being more robust to modeling inadequacies than adaptive subtraction with the ?2 norm, as exemplified on marine 2-D and 3-D field data examples.

Guitton, Antoine

298

Viscothermal Coupling Effects on Sound Attenuation in Concentrated Colloidal Dispersions.  

NASA Astrophysics Data System (ADS)

This thesis describes a Unified Coupled Phase Continuum (UCPC) model to analyze sound propagation through aerosols, emulsions and suspensions in terms of frequency dependent attenuation coefficient and sound speed. Expressions for the viscous and thermal coupling coefficients explicitly account for the effects of particle size, shape factor, orientation as well as concentration and the sound frequency. The UCPC model also takes into account the intrinsic acoustic absorption within the fluid medium due to its viscosity and heat conductivity. The effective complex wave number as a function of frequency is derived. A frequency- and concentration-dependent complex Nusselt number for the interfacial thermal coupling coefficient is derived using an approximate similarity between the 'viscous skin drag' and 'heat conduction flux' associated with the discontinuous suspended phase, on the basis of a cell model. The theoretical predictions of attenuation spectra provide satisfactory agreement with reported experimental data on two concentrated suspensions (polystyrene latex and kaolin pigment), two concentrated emulsions (toluene -in-water, n-hexadecane-in-water), and two aerosols (oleic acid droplets-in-nitrogen, alumina-in-air), covering a wide range of relative magnitudes (from 10^ {-3} to 10^{3}) of thermal versus viscous contributions, for dispersed phase volume fractions as high as 50%. The relative differences between the additive result of separate viscous and thermal loss estimates and combined viscothermal absorption results are also presented. Effects of particle shape on viscous attenuation of sound in concentrated suspensions of non-spherical clay particles are studied. Attenuation spectra for 18 frequencies from 3 to 100 MHz are measured and analyzed for eleven kaolin clay slurries with solid concentrations ranging from 0.6% to 35% (w/w). A modified viscous drag coefficient that considers frequency, concentration, particle size, shape and orientation of spheroids, is developed and applied to estimate the viscous attenuation coefficients. With incorporation of particle size and shape distributions (PSSD), predictions agree quantitatively with observed attenuation coefficients. The effects of particle aspect ratio and orientation become more evident as particle concentrations and frequencies are increased. The UCPC model combined with the ultrasonic spectroscopy techniques can provide for theoretical and experimental frameworks in characterization of concentrated colloidal dispersions.

Han, Wei

299

[Influenza live attenuated vaccine].  

PubMed

Inactivated influenza vaccine has been widely used; however, its effectiveness is not always perfect. To create a much better vaccine, live vaccines have been extensively investigated. Among several candidate live vaccines, cold-adapted(Ca) vaccine is the only promising candidate. According to clinical studies recently conducted in the U.S., Ca vaccine was proven to be highly effective against laboratory confirmed influenza, both in adults and children. Furthermore, Ca vaccines for the H5N1 pandemic strains were generated and their attenuation and efficacy were confirmed in experimental animals. PMID:11225322

Kino, Y

2000-11-01

300

Radiation Imaging and Attenuation  

NASA Astrophysics Data System (ADS)

X-ray and neutron images are used to demonstrate materials' different radiation attenuation properties. This leads to discussion of applications in medicine, industry and research. The Penn State Radiation Science and Engineering Center (RSEC) uses neutron radioscopy to image the inside of a working hydrogen fuel cell. This is one of the many educational activities that are conducted when students visit the RSEC. To encourage pre-college students to apply these principles and learn more about nuclear technology, we are sponsoring a design competition. For more information visit www.rsec.psu.edu

Davison, Candace; Yocum, Douglas

2008-03-01

301

Drag Coefficient of Hexadecane Particles  

NASA Astrophysics Data System (ADS)

This paper deals with the drag coefficient of solidified hexadecane particles and their free rising velocity in liquid. The drag coefficient was experimentally investigated in Reynolds number range of about 40-300. The present experimental results are summarized in the following; (1) the drag coefficient of solidified hexadecane particles formed in liquid coolant by direct contact cooling is higher than that of a smooth surface sphere, this high drag coefficient seems to be attributed to the non-smooth surface of the solidified hexadecane particles, (2) experimental correlation for the drag coefficient of the solidified hexadecane particles was proposed, (3 ) the measured rising velocity of the solidified hexadecane particle agrees well with the calculated one, (4) the drag coefficients of hexadecane particles that were made by pouring hexadecane liquid into a solid hollow sphere agreed well with the drag coefficient of smooth surface sphere.

Nakao, Yoshinobu; Hishida, Makoto; Kajimoto, Sadaaki; Tanaka, Gaku

302

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

303

Optical solitons with time-dependent dispersion, nonlinearity and attenuation in a power-law media  

Microsoft Academic Search

This paper studies optical solitons in a power-law media with time-dependent coefficients of dispersion, nonlinearity and attenuation. The 1-soliton solution is obtained for the nonlinear Schrödinger’s equation with power-law nonlinearity. In addition, a relation between these coefficients is obtained for the solitons to exist. Finally, the velocity of the soliton is also obtained in terms of these coefficients.

Anjan Biswas

2009-01-01

304

LacR mutations are frequently observed in Streptococcus intermedius and are responsible for increased intermedilysin production and virulence.  

PubMed

Streptococcus intermedius secretes a human-specific cytolysin, intermedilysin (ILY), which is considered to be the major virulence factor of this pathogen. We screened for a repressor of ily expression by using random gene disruption in a low-ILY-producing strain (PC574). Three independent high-ILY-producing colonies that had plasmid insertions within a gene that has high homology to lacR were isolated. Validation of these observations was achieved through disruption of lacR in strain PC574 with an erythromycin cassette, which also led to higher hemolytic activity, increased transcription of ily, and higher cytotoxicity against HepG2 cells, compared to the parental strain. The direct binding of LacR within the ily promoter region was shown by a biotinylated DNA probe pulldown assay, and the amount of ILY secreted into the culture supernatant by PC574 cells was increased by adding lactose or galactose to the medium as a carbon source. Furthermore, we examined lacR nucleotide sequences and the hemolytic activity of 50 strains isolated from clinical infections and 7 strains isolated from dental plaque. Of the 50 strains isolated from infections, 13 showed high ILY production, 11 of these 13 strains had one or more point mutations and/or an insertion mutation in LacR, and almost all mutations were associated with a marked decline in LacR function. These results strongly suggest that mutation in lacR is required for the overproduction of ILY, which is associated with an increase in pathogenicity of S. intermedius. PMID:23798532

Tomoyasu, Toshifumi; Imaki, Hidenori; Masuda, Sachiko; Okamoto, Ayumi; Kim, Hyejin; Waite, Richard D; Whiley, Robert A; Kikuchi, Ken; Hiramatsu, Keiichi; Tabata, Atsushi; Nagamune, Hideaki

2013-06-24

305

Trp replacements for tightly interacting Gly-Gly pairs in LacY stabilize an outward-facing conformation.  

PubMed

Trp replacements for conserved Gly-Gly pairs between the N- and C-terminal six-helix bundles on the periplasmic side of lactose permease (LacY) cause complete loss of transport activity with little or no effect on sugar binding. Moreover, the detergent-solubilized mutants exhibit much greater thermal stability than WT LacY. A Cys replacement for Asn245, which is inaccessible/unreactive in WT LacY, alkylates readily in the Gly?Trp mutants, indicating that the periplasmic cavity is patent. Stopped-flow kinetic measurements of sugar binding with the Gly?Trp mutants in detergent reveal linear dependence of binding rates on sugar concentration, as observed with WT or the C154G mutant of LacY, and are compatible with free access to the sugar-binding site in the middle of the molecule. Remarkably, after reconstitution of the Gly?Trp mutants into proteoliposomes, the concentration dependence of sugar-binding rates increases sharply with even faster rates than measured in detergent. Such behavior is strikingly different from that observed for reconstituted WT LacY, in which sugar-binding rates are independent of sugar concentration because opening of the periplasmic cavity is limiting for sugar binding. The observations clearly indicate that Gly?Trp replacements, which introduce bulky residues into tight Gly-Gly interdomain interactions on the periplasmic side of LacY, prevent closure of the periplasmic cavity and, as a result, shift the distribution of LacY toward an outward-open conformation. PMID:23671103

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

2013-05-13

306

Ultrasonic Attenuation in Zircaloy-4  

NASA Astrophysics Data System (ADS)

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

Gómez, M. P.; Banchik, A. D.; López Pumarega, M. I.; Ruzzante, J. E.

2005-04-01

307

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

SciTech Connect

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

Gullberg, Grant T.

1980-03-01

308

The Effect of Stochasticity on the Lac Operon: An Evolutionary Perspective  

PubMed Central

The role of stochasticity on gene expression is widely discussed. Both potential advantages and disadvantages have been revealed. In some systems, noise in gene expression has been quantified, in among others the lac operon of Escherichia coli. Whether stochastic gene expression in this system is detrimental or beneficial for the cells is, however, still unclear. We are interested in the effects of stochasticity from an evolutionary point of view. We study this question in the lac operon, taking a computational approach: using a detailed, quantitative, spatial model, we evolve through a mutation–selection process the shape of the promoter function and therewith the effective amount of stochasticity. We find that noise values for lactose, the natural inducer, are much lower than for artificial, nonmetabolizable inducers, because these artificial inducers experience a stronger positive feedback. In the evolved promoter functions, noise due to stochasticity in gene expression, when induced by lactose, only plays a very minor role in short-term physiological adaptation, because other sources of population heterogeneity dominate. Finally, promoter functions evolved in the stochastic model evolve to higher repressed transcription rates than those evolved in a deterministic version of the model. This causes these promoter functions to experience less stochasticity in gene expression. We show that a high repression rate and hence high stochasticity increases the delay in lactose uptake in a variable environment. We conclude that the lac operon evolved such that the impact of stochastic gene expression is minor in its natural environment, but happens to respond with much stronger stochasticity when confronted with artificial inducers. In this particular system, we have shown that stochasticity is detrimental. Moreover, we demonstrate that in silico evolution in a quantitative model, by mutating the parameters of interest, is a promising way to unravel the functional properties of biological systems.

van Hoek, Milan; Hogeweg, Paulien

2007-01-01

309

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

310

Lactose Genes Fused to Exogenous Promoters in One Step Using a Mu-lac Bacteriophage: In vivo Probe for Transcriptional Control Sequences  

Microsoft Academic Search

The lactose structural genes, without the lactose promoter, have been incorporated into the bacteriophage Mu genome to form a Mu-lac specialized transducing phage. This phage also carries a gene encoding resistance to ampicillin (Ap) [Mu(Ap, lac)]. After infection and upon establishment of lysogeny, the Mu(Ap, lac) genome can integrate into apparently random sites in the Escherichia coli chromosome. When integration

Malcolm J. Casadaban; Stanley N. Cohen

1979-01-01

311

Quadrature formulas for Fourier coefficients  

NASA Astrophysics Data System (ADS)

We consider quadrature formulas of high degree of precision for the computation of the Fourier coefficients in expansions of functions with respect to a system of orthogonal polynomials. In particular, we show the uniqueness of a multiple node formula for the Fourier-Tchebycheff coefficients given by Micchelli and Sharma and construct new Gaussian formulas for the Fourier coefficients of a function, based on the values of the function and its derivatives.

Bojanov, Borislav; Petrova, Guergana

2009-09-01

312

[Machine learning study of DNA binding by transcription factors from the LacI family].  

PubMed

We studied 1372 LacI-family transcription factors and their 4484 DNA binding sites using machine learning algorithms and feature selection techniques. The Naive Bayes classifier and Logistic Regression were used to predict binding sites given transcription factor sequences and to classify factor-site pairs on binding and non-binding ones. Prediction accuracy was estimated using 10-fold cross-validation. Experiments showed that the best prediction of nucleotide densities at selected site positions is obtained using only a few key protein sequence positions. These positions are stably selected by the forward feature selection based on the mutual information of factor-site position pairs. PMID:21954606

Fedonin, G G; Rakhmaninova, A B; Korostelev, Iu D; La?kova, O N; Gel'fand, M S

313

Anti-correlation between the extended power and the core dominance parameter of BL Lac objects  

NASA Astrophysics Data System (ADS)

The XBL and RBL samples presented recently by Kollgaardet al. (1996) are employed to investigate whether the extended power of BL Lac objects is correlated with the core dominance parameter. The results show that the two quantities are statistically anti-corelated at a rather high level of confidence for both XBLs and RBLs. Since the core dominance parameter is generally used as a relative measure of orientation and the extended emission of radio sources is assumed unbeamed and isotropic, the results obviously contradict common inference from unified schemes. By adopting and combining some basic concepts of unified schemes and the different SED scenario, a possible explanation for the results is suggested.

Qin, Y. P.; Xie, G. Z.; Fan, J. H.

1996-03-01

314

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

315

Attenuation of an air shock wave by perforated baffles  

SciTech Connect

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

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

1984-03-01

316

Vertical light attenuation and phytoplankton development in Lake Zurich  

Microsoft Academic Search

Many light-depth profiles based on measurements of photosynthetically available radiation (PAR) in the 0-20-m zone ofLake Zurich were analyzed with respect to phytoplankton development in the epilimnion and the thermocline. Variations in the average value of the vertical attenuation coefficient with time were closely related to variations in biomass. Inspection of the depth distri- bution of the natural logarithms of

FERDINAND SCHANZ

1985-01-01

317

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

318

Six-Decibel Digital Attenuation  

Microsoft Academic Search

In the interest of future studies of digital echo suppressors operating directly on PCM words and of other possible future studies involving digital attenuation, a technique for 6-dB digital attenuation without linearization of the compressed PCM words from an 8-bit 15-segment compandor (? = 255 law) is presented. The compandor is assumed to have midtread form at the origin, and

W. Montgomery

1971-01-01

319

Power Coefficient Anomaly in JOYO.  

National Technical Information Service (NTIS)

Power Coefficient Anomaly appeared in JOYO, which occurred in 75MW Power Ascension Test, Summer 1979. The substance of this anomaly was the non-reproducible power coefficient during the initial power-up from 50MWt to 75MWt and the permanent reactivity los...

M. Ishikawa Y. Yamashita Y. Nara H. Yamamoto

1981-01-01

320

RADIONUCLIDE RISK COEFFICIENT UNCERTAINTY REPORT  

EPA Science Inventory

EPA has published excess cancer risk coefficients for the US population in Federal Guidance Report 13 (FGR 13). FGR 13 gives separate risk coefficients for food ingestion, water ingestion, inhalation, and external exposure for each of over 800 radionuclides. Some information on...

321

Calculate thermal-expansion coefficients  

Microsoft Academic Search

To properly design and use process equipment, an engineer needs a sound knowledge of physical and thermodynamic property data. A lack of such knowledge can lead to design or operating mistakes that can be dangerous, costly or even fatal. One useful type of property data is the thermal-expansion coefficient. This article presents equations and tables to find the thermal-expansion coefficients

Yaws

1995-01-01

322

Powerful High-energy Emission of the Remarkable BL Lac Object S5 0716+714  

NASA Astrophysics Data System (ADS)

BL Lac objects of the intermediate subclass (IBLs) are known to emit a substantial fraction of their power in the energy range 0.1-10 GeV. Detecting ?-ray emission from such sources provides therefore a direct probe of the emission mechanisms and of the underlying powerhouse. The ?-ray satellite, AGILE, detected the remarkable IBL S5 0716+714 (z sime 0.3) during a high state in the period from 2007 September-October, marked by two very intense flares reaching peak fluxes of 200 × 10-8 photons cm-2 s-1 above 100 MeV, with simultaneous optical and X-ray observations. We present here a theoretical model for the two major flares and discuss the overall energetics of the source. We conclude that 0716+714 is among the brightest BL Lac's ever detected at ?-ray energies. Because of its high power and lack of signs for ongoing accretion or surrounding gas, the source is an ideal candidate to test the maximal power extractable from a rotating supermassive black hole via the pure Blandford-Znajek (BZ) mechanism. We find that during the 2007 ?-ray flares 0716+714 approached or just exceeded the upper limit set by BZ for a black hole of mass 109 M sun.

Vittorini, V.; Tavani, M.; Paggi, A.; Cavaliere, A.; Bulgarelli, A.; Chen, A. W.; D'Ammando, F.; Donnarumma, I.; Giuliani, A.; Longo, F.; Pacciani, L.; Pucella, G.; Vercellone, S.; Ferrari, A.; Colafrancesco, S.; Giommi, P.

2009-12-01

323

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

324

Small-scale field test of the genetically engineered lacZY marker  

SciTech Connect

Commercial genetic engineering is advancing into areas that require the small-scale introduction of genetically engineered microorganisms (GEMs) to better quantify variables that affect microorganism distribution and survival and to document potential long-term consequences. A recombinant DNA marker system, the lacZY marker, developed by the Monsanto Agricultural Co., enables the distribution and fate of marked fluorescent pseudomonad organisms to be monitored under actual field conditions. Critical evaluation of GEMs under field conditions is imperative if plant-beneficial effects are to be correlated with organism release. This paper evaluates the effectiveness of this marker system and its ability to facilitate the assessment of risks associated with deliberate environmental introductions of genetically engineered microorganisms. Results of prerelease contained growth chamber and field experiments demonstrated that: (1) the scientific risk assessment methodology adopted by Monsanto and approved by the U.S. Environmental Protection Agency was appropriate and comprehensive; (2) the deliberate introduction of a GEM did not pose unacceptable or unforeseen risks to human health or the environment; (3) the lacZY marker is an effective environmental tracking tool; and (4) regulatory oversight should reflect the expected risk and not be excessively burdensome for all GEMs.

Hattemer-Frey, H.A.; Brandt, E.J.; Travis, C.C. (Oak Ridge National Laboratory, TN (USA))

1990-06-01

325

Role of the irreplaceable residues in the LacY alternating access mechanism  

PubMed Central

Few side chains in the galactoside/H+ symporter LacY (lactose permease of Escherichia coli) are irreplaceable for an alternating access mechanism in which sugar binding induces closing of the cytoplasmic cavity and reciprocal opening of a periplasmic cavity. In this study, each irreplaceable residue was mutated individually, and galactoside-induced opening or closing of periplasmic or cytoplasmic cavities was probed by site-directed alkylation. Mutation of Glu126 (helix IV) or Arg144 (helix V), which are essential for sugar binding, completely blocks sugar-induced periplasmic opening as expected. Remarkably, however, replacement of Glu269 (helix VIII), His322 (helix X), or Tyr236 (helix VII) causes spontaneous opening of the periplasmic cavity in the absence of sugar and decreased closing of the cytoplasmic cavity in the presence of galactoside. In contrast, mutation of Arg302 (helix IX) or Glu325 (helix X) has no such effect, and sugar binding induces normal opening and closing of periplasmic and cytoplasmic cavities. Possibly, Glu269, His322, and Tyr236 act in concert to coordinate opening and closing of the cavities by binding water, which also acts as a cofactor in H+ translocation. Mutation of the triad results in loss of the bound water, which destabilizes LacY, and the cavities open and close in an uncoordinated manner. Thus, the triad mutants exhibit poor affinity for sugar, and galactoside/H+ symport is abolished as well.

Zhou, Yonggang; Jiang, Xiaoxu; Kaback, H. Ronald

2012-01-01

326

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

327

POWERFUL HIGH-ENERGY EMISSION OF THE REMARKABLE BL Lac OBJECT S5 0716+714  

SciTech Connect

BL Lac objects of the intermediate subclass (IBLs) are known to emit a substantial fraction of their power in the energy range 0.1-10 GeV. Detecting gamma-ray emission from such sources provides therefore a direct probe of the emission mechanisms and of the underlying powerhouse. The gamma-ray satellite, AGILE, detected the remarkable IBL S5 0716+714 (z approx = 0.3) during a high state in the period from 2007 September-October, marked by two very intense flares reaching peak fluxes of 200 x 10{sup -8} photons cm{sup -2} s{sup -1} above 100 MeV, with simultaneous optical and X-ray observations. We present here a theoretical model for the two major flares and discuss the overall energetics of the source. We conclude that 0716+714 is among the brightest BL Lac's ever detected at gamma-ray energies. Because of its high power and lack of signs for ongoing accretion or surrounding gas, the source is an ideal candidate to test the maximal power extractable from a rotating supermassive black hole via the pure Blandford-Znajek (BZ) mechanism. We find that during the 2007 gamma-ray flares 0716+714 approached or just exceeded the upper limit set by BZ for a black hole of mass 10{sup 9} M{sub sun}.

Vittorini, V.; Chen, A. W.; Ferrari, A. [CIFS-Torino, Viale Settimio Severo 3, I-10133, Torino (Italy); Tavani, M.; D'Ammando, F.; Donnarumma, I.; Pacciani, L.; Pucella, G. [INAF/IASF-Roma, Via del Fosso del Cavaliere 100, I-00133 Roma (Italy); Paggi, A.; Cavaliere, A. [University of Rome, 'Tor Vergata', Via della Ricerca Scientifica 1, I-00133 Roma (Italy); Bulgarelli, A. [INAF/IASF-Bologna, Via Gobetti 101, I-40129 Bologna (Italy); Giuliani, A.; Vercellone, S. [INAF/IASF-Milano, Via E. Bassini 15, I-20133 Milano (Italy); Longo, F. [INFN-Trieste, Via Valerio 2, I-34127 Trieste (Italy); Colafrancesco, S.; Giommi, P., E-mail: vittorini@roma2.infn.i [ASDC c/o ESRIN, Via G. Galilei snc, I-00044 Frascati, Roma (Italy)

2009-12-01

328

Structure, energy, and spin characteristics of La@C60-Lu@C60 lanthanide endofullerenes  

NASA Astrophysics Data System (ADS)

Calculations of the equilibrium geometric and electronic structure of lanthanide endofullerenes are presented. Two types of the Ln@C60 structure are found. For endofullerenes of the first type (La@C60-Dy@C60), the stable position of the lanthanide atom is achieved at a distance of 0.67 R from the center of fullerene ( R is the fullerene radius); in endofullerenes of the second type (Ho@C60-Lu@C60), the character of the interaction between the lanthanide atom and fullerene changes because of the transfer of unpaired electrons from the corresponding atom to fullerene. It is found that in endofullerenes of the second type, metal atom mobility increases, and two minima of the potential energy appear, which corresponds to the Ln position in the center and at a distance of 0.5 R from the center. Based on the obtained spin density distribution for La@C60-Lu@C60 endofullerenes, we conclude that there is spin leakage.

Krisilov, A. V.; Zon, B. A.

2011-10-01

329

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

PubMed

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. PMID:23098700

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

2012-10-22

330

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

SciTech Connect

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

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

2004-09-30

331

Fate tracing of neurogenin2-expressing cells in the mouse retina using CreER™: LacZ.  

PubMed

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. PMID:22688703

Ma, Wenxin; Wang, Shu-Zhen

2012-01-01

332

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

333

Rocket engine nozzle attenuator  

NASA Astrophysics Data System (ADS)

The function of a rocket engine nozzle is to expand the hot engine exhaust gases down to ambient pressure, transforming thermal energy to directed kinetic energy in order to produce thrust. Considering nozzle design, there is an optimum nozzle shape and length, the bell-shaped or contour nozzle. The reason for this specific contour is that the nozzle must be designed in such a manner that the expansion shock waves emanating from the nozzle throat region coincide, and thus diminish the compression effects accompanying the reorientation of flow in the center region of the expansion section. A rocket nozzle must absorb a variety of loads caused by such shocks due to thermal expansion and contraction, as well as shocks from sudden pressurization at startup, and flight accelerations. A rocket engine nozzle is provided which is capable of attenuating nozzle vibrations generated therein during use. The nozzle includes an annular closed chamber surrounding the nozzle adjacent to its gas exhaust end. Within the chamber is a dense but unrestricted particulate mass capable of undergoing frictional movement within the chamber.

Lewis, David A.

1993-01-01

334

Cytoplasmic hydrogen ion diffusion coefficient.  

PubMed Central

The apparent cytoplasmic proton diffusion coefficient was measured using pH electrodes and samples of cytoplasm extracted from the giant neuron of a marine invertebrate. By suddenly changing the pH at one surface of the sample and recording the relaxation of pH within the sample, an apparent diffusion coefficient of 1.4 +/- 0.5 x 10(-6) cm2/s (N = 7) was measured in the acidic or neutral range of pH (6.0-7.2). This value is approximately 5x lower than the diffusion coefficient of the mobile pH buffers (approximately 8 x 10(-6) cm2/s) and approximately 68x lower than the diffusion coefficient of the hydronium ion (93 x 10(-6) cm2/s). A mobile pH buffer (approximately 15% of the buffering power) and an immobile buffer (approximately 85% of the buffering power) could quantitatively account for the results at acidic or neutral pH. At alkaline pH (8.2-8.6), the apparent proton diffusion coefficient increased to 4.1 +/- 0.8 x 10(-6) cm2/s (N = 7). This larger diffusion coefficient at alkaline pH could be explained quantitatively by the enhanced buffering power of the mobile amino acids. Under the conditions of these experiments, it is unlikely that hydroxide movement influences the apparent hydrogen ion diffusion coefficient.

al-Baldawi, N F; Abercrombie, R F

1992-01-01

335

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

Microsoft Academic Search

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

Li Zhai; Charles Tang; Trevor Platt; Shubha Sathyendranath

2011-01-01

336

The Relative Importance and Compositional Effects of Suspended Solids on Light Attenuation  

NASA Astrophysics Data System (ADS)

The relative contributions of suspended particles and colored dissolved organic matter (CDOM) to the attenuation of light at 400 to 700 nm was studied using laboratory analyses of samples from the Indian River Lagoon, Florida. Water samples were collected during spring and summer. The beam attenuation coefficient (c in m-1) was determined for whole water samples (cTotal) and for filtered samples (cCDOM) in the laboratory using an OOIBase32 Spectrometer. Attenuation due to suspended particles (cTSS) was calculated by subtracting cCDOM from cTotal where cTSS accounted for ~90% of cTotal. To evaluate the compositional effects to light attenuation, suspended solids were categorized as either organic matter (OM) or inorganic matter (IM) and then used as independent variables in a multi-variable analysis with cTSS serving as the dependent variable. The coefficients determined for the OM and IM fractions were significant (p<0.001) and indicate that IM was at least three times more effective in attenuating light than OM (r = 0.97). The OM fractions of suspended solids were further categorized as terrestrial and lagoonal organic matter (based on values for ?13C) and the IM was characterized as clay and other inorganic mineral matter (based on the Si/Al content) and again used as independent variables in a multi- variable analysis. The model produced a strong correlation coefficient (r = 0.98) and all coefficients were significant at the p<0.001 level. Results showed no significant difference between the effect of clay and other inorganic mineral matter to light attenuation (p>0.05). However, results confirm the effective difference between the IM and OM fractions to light attenuation (p<0.001), and indicate that terrestrial organic matter was 2.5 times more effective in attenuating light than lagoonal organic matter (p<0.001).

Woodall, D. W.; Trefry, J. H.; Trocine, R. P.

2006-12-01

337

Spatially resolved 2D attenuation image of a semi-infinite non-homogeneous tissue from diffuse reflectance  

NASA Astrophysics Data System (ADS)

Optical properties of biological tissue such as reduced scattering and absorption coefficients can be determined from the temporal or spatial reflectance curve of the diffusion process. Owing to its non-homogenous nature, the assumption of uniform optical parameters may not be valid in practice. We propose a new scheme to resolve the optical effective attenuation profile from the spatial reflectance curve of a non-homogeneous tissue. The algorithm reconstructs the linear attenuation profile along the line of measurement, rather than giving one single value for the coefficient for each reflectance curve. The technique was applied to the reconstruction of a 2-dimensional attenuation image.

Tse, Jorden; Chen, Lian-Kuan

2010-02-01

338

Negative coefficient of normal restitution  

NASA Astrophysics Data System (ADS)

This paper shows that negative coefficients of normal restitution occur inevitably when the interaction force between colliding particles is finite. We derive an explicit criterion showing that for any set of material properties there is always a collision geometry leading to negative restitution coefficients. While from a phenomenological point of view, negative coefficients of normal restitution appear rather artificial, this phenomenon is generic and implies an important overlooked limitation of the widely used hard sphere model. The criterion is explicitly applied to two paradigmatic situations: for the linear dashpot model and for viscoelastic particles. In addition, we show that for frictional particles the phenomenon is less pronounced than for smooth spheres.

Müller, Patric; Krengel, Dominik; Pöschel, Thorsten

2012-04-01

339

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

340

Attenuation correction of myocardial SPECT by scatter-photopeak window method in normal subjects  

Microsoft Academic Search

Objective  Segmentation with scatter and photopeak window data using attenuation correction (SSPAC) method can provide a patient-specific\\u000a non-uniform attenuation coefficient map only by using photopeak and scatter images without X-ray computed tomography (CT).\\u000a The purpose of this study is to evaluate the performance of attenuation correction (AC) by the SSPAC method on normal myocardial\\u000a perfusion database.\\u000a \\u000a \\u000a \\u000a Methods  A total of 32 sets

Koichi Okuda; Kenichi Nakajima; Nobutoku Motomura; Masahiro Kubota; Noriyasu Yamaki; Hisato Maeda; Shinro Matsuo; Seigo Kinuya

2009-01-01

341

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

NASA Astrophysics Data System (ADS)

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

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

2004-11-01

342

A set of lacZ mutations in Escherichia coli that allow rapid detection of each of the six base substitutions  

SciTech Connect

We describe the construction of six strains of Escherichia coli with different mutations at the same coding position in the lacZ gene, which specifies the active site glutamic acid residue at position 461 in beta'-galactosidase. Each strain is Lac- and reverts to Lac+ only by restoring the glutamic acid codon. The strains have been designed so that each reverts via one of the six base substitutions. The set of strains allows detection of each transition and transversion simply by monitoring the Lac- to Lac+ frequency, as demonstrated here with characterized mutagens and mutator alleles. These strains are useful for rapidly determining the mutagenic specificity of mutagens at a single site, for detecting low levels of stimulation of certain base substitutions, for monitoring specific base changes in response to various experimental conditions or strain backgrounds, and for isolating new mutator strains.

Cupples, C.G.; Miller, J.H.

1989-07-01

343

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

344

Electron spin coherence in metallofullerenes: Y, Sc, and La@C82  

NASA Astrophysics Data System (ADS)

Endohedral fullerenes encapsulating a spin-active atom or ion within a carbon cage offer a route to self-assembled arrays such as spin chains. In the case of metallofullerenes the charge transfer between the atom and the fullerene cage has been thought to limit the electron spin phase coherence time (T2) to the order of a few microseconds. We study electron spin relaxation in several species of metallofullerene as a function of temperature and solvent environment, yielding a maximum T2 in deuterated o-terphenyl greater than 200?s for Y, Sc, and La@C82 . The mechanisms governing relaxation ( T1 , T2 ) arise from metal-cage vibrational modes, spin-orbit coupling and the nuclear spin environment. The T2 times are over 2 orders of magnitude longer than previously reported and consequently make metallofullerenes of interest in areas such as spin labeling, spintronics, and quantum computing.

Brown, Richard M.; Ito, Yasuhiro; Warner, Jamie H.; Ardavan, Arzhang; Shinohara, Hisanori; Briggs, G. Andrew D.; Morton, John J. L.

2010-07-01

345

The Bingel monoadducts of La@C82: synthesis, characterization, and electrochemistry.  

PubMed

The reaction of La@C82 with diethyl bromomalonate in the presence of base (the Bingel reaction) generated five monoadducts which have been fully characterized. It was found that four of them (mono-A, -B, -C, and -D) are ESR-inactive, suggesting singly bonded regioisomers. In contrast, the fifth product (mono-E) is ESR-active, indicating that it possesses a cyclic moiety between the appended malonate group and the fullerene cage, analogous to conventional Bingel adducts. The differences in the molecular structures of mono-A, -B, -C, and -E result in varying thermal stabilities and electrochemical behavior. In particular, the singly bonded monoadducts undergo the retro-Bingel reaction either under thermal treatment or during electron transfer on the cyclic voltammetric timescale. However, mono-E shows remarkable thermal stability and perfect reversibility under the same experimental conditions. PMID:16637083

Feng, Lai; Wakahara, Takatsugu; Nakahodo, Tsukasa; Tsuchiya, Takahiro; Piao, Qiuyue; Maeda, Yutaka; Lian, Yongfu; Akasaka, Takeshi; Horn, Ernst; Yoza, Kenji; Kato, Tatsuhisa; Mizorogi, Naomi; Nagase, Shigeru

2006-07-17

346

H.E.S.S. observations of the distant BL Lac PKS 0301-243  

NASA Astrophysics Data System (ADS)

PKS 0301-243 is a distant (z=0.266) high-frequency-peaked BL Lac object, detected both at high and very high energies (VHE) with Fermi/LAT and H.E.S.S., and which experienced a flare in May 2010 in the GeV band. H.E.S.S. observations of PKS 0301-243 carried out between September 2009 and December 2011 result in a strong detection of VHE ?-rays from the source with a significance of 9.8 standard deviations. Multi-wavelength observations from optical to GeV gamma-rays are also presented. The VHE spectrum is used to derive an upper limit on the opacity of the universe to gamma-rays.

Wouters, Denis; Lenain, Jean-Philippe; Becherini, Yvonne; Harris, Jon; Brun, Pierre; Kaufmann, Sarah; Boisson, Catherine; Cerruti, Matteo; Sol, Hélène; Zech, Andreas; H. E. S. S. Collaboration

2012-12-01

347

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

348

The Correlated Multi-color Optical Variations of BL Lac Object S5 0716+714  

NASA Astrophysics Data System (ADS)

S5 0716+714 is a well-studied BL Lac object in the sky. Verifying the existence of correlations among the flux variations in different bands serves as an important tool to investigate the emission processes. To examine the possible existence of a lag between variations in different optical bands on this source, we employ a discrete correlation function analysis on the light curves. In order to obtain statistically meaningful values for the cross-correlation time lags and their related uncertainties, we perform Monte Carlo simulations called `flux redistribution/random subset selection'. Our analysis confirms that the variations in different optical light curves are strongly correlated. The time lags show a hint of the variations in high frequency band leading those in low frequency band of the order of a few minutes.

Zhang, Bingkai; Dai, Benzhong; Zhang, Li; Liu, Jiali; Cao, Zhen

2010-06-01

349

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

SciTech Connect

We study the spectral and temporal behavior of X-ray flares from the active M dwarf EV Lac in 200 ks of exposure with the Chandra/HETGS. We derive flare parameters by fitting an empirical function which characterizes the amplitude, shape, and scale. The flares range from very short (<1 ks) to long ({approx}10{sup 4} s) duration events with a range of shapes and amplitudes for all durations. We extract spectra for composite flares to study their mean evolution and to compare flares of different lengths. Evolution of spectral features in the density-temperature plane shows probable sustained heating. The short flares are significantly hotter than the longer flares. We determined an upper limit to the Fe K fluorescent flux, the best-fit value being close to what is expected for compact loops.

Huenemoerder, David P.; Schulz, Norbert S. [Massachusetts Institute of Technology, Kavli Institute for Astrophysics and Space Research, 77 Massachusetts Avenue, Cambridge, MA 02139 (United States); Testa, Paola; Drake, Jeremy J. [Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138 (United States); Osten, Rachel A. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Reale, Fabio [Universita di Palermo, Dipartimento di Scienze Fisiche and Astronomiche, Piazza del Parlamento 1, 90134 Palermo (Italy)

2010-11-10

350

Nutrient status of the lowbush blueberry, Lac-Saint-Jean area, Quebec, Canada. [Vaccinium angustifolium  

SciTech Connect

The lowbush blueberry (Vaccinium angustifolium Ait.) is an important commercial crop of the Lac-Saint-Jean area (Quebec, Canada). The major blueberry fields are located on sandy soils relatively poor in available mineral nutrients. The nutrients originate from a thin organic layer found on the top of these sandy soils. The leaf mineral contents (N, P, K, Mg, Ca, Mn, Fe, Cu, Zn and B) were measured in five blueberry fields during 1984 and 1985. Soil pH and soil available P, K, and Mg were also assessed. The results show that the leaf mineral contents are generally adequate. However, K and Zn might be occasionally deficient when compared to the actual established standards. The available Mg in soil was significantly correlated with the leaf Mg concentration. The data also suggest that the influence of the pH following the burn pruning seems to influence the nutrition of this species.

Bouchard, A.R.; Gagnon, M.J.

1987-01-01

351

Mouthparts and stylet penetration of the lac insect Kerria lacca (Kerr) (Hemiptera:Tachardiidae).  

PubMed

Hitherto less known aspects on mouthpart morphology and penetration mechanism of the lac insect Kerria lacca have been explored. Unique details of the mouthparts, i.e. morphology of labium and stylets and salivary sheath have been brought out. The gross morphology of the mouthparts though resembled other plant sucking homopterans; a two-segmented labium with symmetrically distributed six pairs of contact-chemoreceptors on its surface was distinct; the mandibular stylets had serrations on its extreme apical region, while the maxillary stylets had their external surface smooth with parallel longitudinal grooves on their inner surface. Formation of flanges, salivary sheath and penetration pathway observed along with probing and penetration of the stylets intracellularly up to the phloem cells, as illustrated herein, are the addition to the existing knowledge on the structural details of the mouthparts and the feeding behavior thereupon. PMID:22531548

Ahmad, Ayashaa; Kaushik, Sandeep; Ramamurthy, V V; Lakhanpaul, Suman; Ramani, R; Sharma, K K; Vidyarthi, A S

2012-04-22

352

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

Microsoft Academic Search

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

Manirupa Saha; Amarendra K. Sarma; Anjan Biswas

2009-01-01

353

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

354

RADIATION MECHANISMS AND PHYSICAL PROPERTIES OF GeV-TeV BL Lac OBJECTS  

SciTech Connect

BL Lac objects are the best candidates to study the jet properties since their spectral energy distributions (SEDs) are less contaminated by the emission from the accretion disk and external Compton processes. We compile the broadband SEDs observed with Fermi/LAT and other instruments from literature for 24 TeV BL Lac objects. Two SEDs, which are identified as a low or high state according to its flux density at 1 TeV, are available for each of 10 objects. These SEDs can be explained well with the synchrotron+synchrotron-self-Compton model. We constrain the magnetic field strength (B) and the Doppler factor ({delta}) of the radiation region by incorporating the {chi}{sup 2}-minimization technique and the {gamma}-ray transparency condition. Twenty-four out of the 34 SEDs can constrain B and {delta} in the 1{sigma} significance level, and others only present the limits for both B and {delta}. The typical values of B and {delta} are 0.1-0.6 G and 10-35, respectively. The derived values of {gamma}{sub b} are significantly different among sources and even among the low and high states of a given source. Prominent flux variations with a clear spectral shift are observed, and a tentative correlation between the ratio of the flux density at 1 TeV and the ratio of {gamma}{sub b} in the low and high states is presented, likely indicating that the relativistic shocks for the electron acceleration may be responsible for the flux variations and the spectral shift. A weak anti-correlation between the jet power and the mass of the central black hole is observed, i.e., P{sub jet}{proportional_to}M{sup -1}{sub BH}, which disfavors the scenario of a pure accretion-driven jet. Implications for the blazar sequence and the intergalactic magnetic field from our results are also briefly discussed.

Zhang Jin; Zhang Shuangnan [National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012 (China); Liang Enwei [Department of Physics and GXU-NAOC, Center for Astrophysics and Space Sciences, Guangxi University, Nanning 530004 (China); Bai, J. M., E-mail: zhang.jin@hotmail.com [National Astronomical Observatories/Yunnan Observatory, Chinese Academy of Sciences, Kunming 650011 (China)

2012-06-20

355

Radiation Mechanisms and Physical Properties of GeV-TeV BL Lac Objects  

NASA Astrophysics Data System (ADS)

BL Lac objects are the best candidates to study the jet properties since their spectral energy distributions (SEDs) are less contaminated by the emission from the accretion disk and external Compton processes. We compile the broadband SEDs observed with Fermi/LAT and other instruments from literature for 24 TeV BL Lac objects. Two SEDs, which are identified as a low or high state according to its flux density at 1 TeV, are available for each of 10 objects. These SEDs can be explained well with the synchrotron+synchrotron-self-Compton model. We constrain the magnetic field strength (B) and the Doppler factor (?) of the radiation region by incorporating the ?2-minimization technique and the ?-ray transparency condition. Twenty-four out of the 34 SEDs can constrain B and ? in the 1? significance level, and others only present the limits for both B and ?. The typical values of B and ? are 0.1-0.6 G and 10-35, respectively. The derived values of ?b are significantly different among sources and even among the low and high states of a given source. Prominent flux variations with a clear spectral shift are observed, and a tentative correlation between the ratio of the flux density at 1 TeV and the ratio of ?b in the low and high states is presented, likely indicating that the relativistic shocks for the electron acceleration may be responsible for the flux variations and the spectral shift. A weak anti-correlation between the jet power and the mass of the central black hole is observed, i.e., P jetvpropM -1 BH, which disfavors the scenario of a pure accretion-driven jet. Implications for the blazar sequence and the intergalactic magnetic field from our results are also briefly discussed.

Zhang, Jin; Liang, En-Wei; Zhang, Shuang-Nan; Bai, J. M.

2012-06-01

356

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

357

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

2013-02-14

358

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

PubMed

This review provides an overview of the structure, function, and catalytic mechanism of lacZ ?-galactosidase. The protein played a central role in Jacob and Monod's development of the operon model for the regulation of gene expression. Determination of the crystal structure made it possible to understand why deletion of certain residues toward the amino-terminus not only caused the full enzyme tetramer to dissociate into dimers but also abolished activity. It was also possible to rationalize ?-complementation, in which addition to the inactive dimers of peptides containing the "missing" N-terminal residues restored catalytic activity. The enzyme is well known to signal its presence by hydrolyzing X-gal to produce a blue product. That this reaction takes place in crystals of the protein confirms that the X-ray structure represents an active conformation. Individual tetramers of ?-galactosidase have been measured to catalyze 38,500 ± 900 reactions per minute. Extensive kinetic, biochemical, mutagenic, and crystallographic analyses have made it possible to develop a presumed mechanism of action. Substrate initially binds near the top of the active site but then moves deeper for reaction. The first catalytic step (called galactosylation) is a nucleophilic displacement by Glu537 to form a covalent bond with galactose. This is initiated by proton donation by Glu461. The second displacement (degalactosylation) by water or an acceptor is initiated by proton abstraction by Glu461. Both of these displacements occur via planar oxocarbenium ion-like transition states. The acceptor reaction with glucose is important for the formation of allolactose, the natural inducer of the lac operon. PMID:23011886

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

2012-11-13

359

Mini-mu bacteriophage with plasmid replicons for in vivo cloning and lac gene fusing.  

PubMed Central

New mini-Mu transposons with plasmid replicons were constructed with additional features for in vivo DNA cloning and lac gene fusing in Escherichia coli. These mini-Mu replicons can be used to clone DNA by growing them with a complementing Mu bacteriophage and by using the resulting lysate to transduce Mu-lysogenic cells. These mini-Mu phage have selectable genes for resistance to kanamycin, chloramphenicol, and spectinomycin-streptomycin, and replicons from the high-copy-number plasmids pMB1 and P15A and the low-copy, broad-host-range plasmid pSa. The most efficient of these elements can be used to clone genes 100 times more frequently than with the previously described mini-Mu replicon Mu dII4042, such that complete gene banks can be made with as little as 1 microliter of a lysate containing 10(6) helper phage. The 39-kilobase-pair Mu headful DNA packaging mechanism limits the size of the clones formed. The smallest of the mini-Mu elements is only 7.9 kilobase pairs long, allowing the cloning of DNA fragments of up to 31.1 kilobase pairs, and the largest of them is 21.7 kilobase pairs, requiring that clones carry insertions of less than 17.3 kilobase pairs. Elements have been constructed to form both transcriptional and translational types of lac gene fusions to promoters present in the cloned fragment. Two of these elements also contain the origin-of-transfer sequence oriT from the plasmid RK2, so that clones obtained with these mini-Mu bacteriophage can be efficiently mobilized by conjugation.

Groisman, E A; Casadaban, M J

1986-01-01

360

Study of ?-ray and X-ray emission from BL LAC objects  

NASA Astrophysics Data System (ADS)

This paper collects 18 ?-ray-loud BL Lacertae (BL Lac) objects with the observed X-ray and ?-ray flux densities (maximum, minimum, average) as well as the X-ray (1keV) and ?-ray (above 100MeV) average spectral indices.These flux densities and average spectral indices data came from 33 literatures. To analysis the character between X-ray and ?-ray flux densities in the maximum(, ) , minimum (, ) and average(, ) value and those average spectral indices( , ) , we employed the correlation analysis. We studied their correlations in detail, and our results show that:1) there is a strong correlation between and in the high, average and low state.This result affirmed Stickel et al. [53]model which supposed express a few dust around the black hole.2) there is a strong correlations between and in the average state.3) there is not a significant correlation between the average spectral indices and the flux densities in high and average state.4) there is a strong anti-correlation between the average ?-ray spectral indices and the X-ray flux densities in the low state, and also there is a weak correlation between the average X-ray spectral indices and the ?-ray flux densities in the low state.Our results are in agreement with the scenario that the X-ray and ?-ray emission from BL Lac objects are likely produced by the same population of relativistic electrons through synchrotron and synchrotron Self-Compton model (SSC) process, respectively.

Zhang, H. J.; Zhang, X.

2008-07-01

361

Genome Sequence of Pseudomonas stutzeri SDM-LAC, a Typical Strain for Studying the Molecular Mechanism of Lactate Utilization  

PubMed Central

Pseudomonas stutzeri SDM-LAC is an efficient lactate utilizer with various applications in biocatalysis. Here we present a 4.2-Mb assembly of its genome. The annotated four adjacent genes form a lactate utilization operon, which could provide further insights into the molecular mechanism of lactate utilization.

Jiang, Tianyi; Gao, Chao; Su, Fei; Zhang, Wen; Hu, Chunhui; Dou, Peipei; Zheng, Zhaojuan; Tao, Fei

2012-01-01

362

Individual flood events detected in the recent sediments of the Petit Lac d'Annecy, eastern France  

Microsoft Academic Search

A 90-cm long freeze core from the Petit Lac d'Annecy was sampled at 1-cm intervals and studied using magnetic measurements, chemical element and pollen analysis. The results reveal four distinctive horizons in each of which the different lines of evidence point to deposition during a single, major flood event. The magnetic evidence shows that the sediment deposited in each event

V. Thorndycraft; Y. Hu; F. Oldfield; P. R. J. Crooks; P. G. Appleby

1998-01-01

363

Late Glacial and Holocene chironomid assemblages in Lac Long Inférieur (southern France, 2090 m): palaeoenvironmental and palaeoclimatic implications  

Microsoft Academic Search

Changes in lake water temperature and trophic states were inferred using chironomid fossil assemblages from Lac Long Inférieur (Southern Alps, France). In the Late Glacial, a colder period, possibly analogous to the Younger Dryas, is characterised by a peak in Micropsectra, a cold stenothermic taxon. The increase in temperatures during the Late Glacial interstadial is indicated by a decrease in

Emmanuel Gandouin; Evelyne Franquet

2002-01-01

364

Palaeoclimatic significance of the 300 ka mineral magnetic record from the sediments of Lac du Bouchet, France  

Microsoft Academic Search

A set of three 50-metre sediment cores from a small crater lake, Lac du Bouchet, show down-core changes in the magnetic mineralogy which reflect the changing past environmental and climatic conditions around the lake over the last 300 ka. This work builds on studies of 20 metre and shorter cores from the same lake, extending both the time covered by

Trevor Williams; Nicolas Thouveny; K. M. Creer

1996-01-01

365

The lac Repressor Protein: Molecular Shape, Subunit Structure, and Proposed Model for Operator Interaction Based on Structural Studies of Microcrystals  

Microsoft Academic Search

Electron microscopic and powder x-ray diffraction studies of small crystals of the lac repressor protein provide evidence on its molecular shape and subunit structure which in turn suggests a possible mode of repressor-operator interaction. The crystals are probably orthorhombic space group P2221 with unit cell dimensions of a = 140, b = 91, c = 117 A. This tetrameric protein

Thomas A. Steitz; Timothy J. Richmond; David Wise; Donald Engelman

1974-01-01

366

LacZ Transgenic Mice and Immunoelectron Microscopy: An Ultrastructural Method for Dual Localization of ?-Galactosidase and Horseradish Peroxidase  

Microsoft Academic Search

Transgenic animals bearing the reporter gene, LacZ, encoding the histochemical enzyme, ?-galactosidase, are increasingly becoming available. Similarly, antibody conjugates consisting of specific IgGs coupled to horseradish peroxidase (HRP) are widely used for Western blotting, ELISA, and immunohistochemistry. Here we provide a detailed fixation and histochemical protocol for the simultaneous electron microscopic visualization and discrimination of ?-galactosidase and peroxidase reaction products

Patricia L. St. John; Dale R. Abrahamson

2007-01-01

367

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

NASA Astrophysics Data System (ADS)

The WARPS survey (Wide-Angle ROSAT Pointed Survey) has been constructed from the archive of all public ROSAT PSPC observations, and is a subset of the WGACAT catalog. WARPS will include a complete sample of >= 100 BL Lacs at F_x >= 10(-13) erg s(-1) cm(-2) . A second selection technique will identify ~ 100 clusters at 0.15Lacs are known and the largest complete samples are also small, with 20-50 objects each. Current data shows a discrepancy between XBL (X-ray selected BL Lac) and RBL (Radio-selected BL Lac) evolution, with = 0.304 +/- 0.062 for XBLs but = 0.60 +/- 0.05 for RBLs. Models of the X-ray luminosity function (XLF) are also poorly constrained. WARPS will allow us to compute an accurate XLF, decreasing the error bars above by over a factor of two. We will also test for low-luminosity BL Lacs, whose non-thermal nuclear sources are dim compared to the host galaxy. Browne and Marcha (1993) claim the EMSS missed most of these objects and is incomplete. If their predictions are correct, 20-40% of the BL Lacs we find will fall in this category, enabling us to probe the evolution and internal workings of BL Lacs at lower luminosities than ever before. By removing likely QSOs before optical spectroscopy, WARPS requires only modest amounts of telescope time. It will extend measurement of the cluster XLF both to higher redshifts (z>0.5) and lower luminosities (LX<1x10(44) erg s(-1) ) than previous measurements, confirming or rejecting the 3sigma detection of negative evolution found in the EMSS, and constraining Cold Dark Matter cosmologies. Faint NELGs are a recently discovered major contributor to the X-ray background. They are a mixture of Sy2s, starbursts and galaxies of unknown type. Detailed classification and evolution of their XLF will be determined for the first time.

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

1994-12-01

368

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

369

Transport coefficients of gluonic fluid  

SciTech Connect

The shear ({eta}) and bulk ({zeta}) viscous coefficients have been evaluated for a gluonic fluid. The elastic, gg{yields}gg and the inelastic, number nonconserving, gg{yields}ggg processes have been considered as the dominant perturbative processes in evaluating the viscous coefficients to entropy density (s) ratios. Recently the processes: gg{yields}ggg has been revisited and a correction to the widely used Gunion-Bertsch (GB) formula has been obtained. The {eta} and {zeta} have been evaluated for gluonic fluid with the formula recently derived. At large {alpha}{sub s} the value of {eta}/s approaches its lower bound, {approx}1/4{pi}.

Das, Santosh K.; Alam, Jan-e [Variable Energy Cyclotron Centre, 1/AF, Bidhan Nagar, Kolkata-700064 (India)

2011-06-01

370

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

2013-04-06

371

Identification of phosphate starvation-inducible genes in Escherichia coli K-12 by DNA sequence analysis of psi::lacZ(Mu d1) transcriptional fusions.  

PubMed Central

Twenty-four independent phosphate starvation-inducible (psi) transcriptional fusions made with Mu d1(lacZbla) were analyzed by sequencing the psi::lacZ(Mu d1) chromosomal junctions by using DNAs amplified with the polymerase chain reaction or mini-Mu cloning. Our DNA sequence analysis showed that the MuR DNA in Mu d1 has an unexpected structure that is comprised of 104 bases of MuR DNA in the form of a large inverted repeat, which we denoted Mu d1-R. Also, Mu d1s in the phoA and phn (psiD) loci of the phosphate regulon showed regional specificities for the insertion sites despite the randomness of Mu d1 insertions into the genome as a whole. Gene products or open reading frames were identified for seven unknown psi::lacZ(Mu d1) transcriptional fusions by searching DNA data bases with the sequences adjacent and upstream of the Mu d1s. One psiC::lacZ(Mu d1) lies in the ugpB gene of the ugpBAEC operon, which encodes a periplasmic sn-glycerol-3-phosphate-binding protein; two psiQ::lacZ(Mu d1)s lie in the gltB gene, and one psiQ::lacZ(Mu d1) lies in the gltD gene of the gltBDF operon, encoding the large and small subunits of glutamate synthase, respectively; and the psi-51::lacZ(Mu d1) lies in the glpB gene of the glpABC operon, which codes for the anaerobically regulated glycerol-3-phosphate dehydrogenase. psiE and psiF::lacZ(Mu d1)s lie in uncharacterized open reading frames near the xylE and phoA genes, respectively. Six other psi::lacZ(Mu d1)s lie in yet unreported Escherichia coli sequences.

Metcalf, W W; Steed, P M; Wanner, B L

1990-01-01

372

The Condensation Coefficient of Aln.  

National Technical Information Service (NTIS)

The condensation coefficient of AlN was measured by following the rate of exchange is isotopic N2 gas (N15) with AlN14(s) and that of N2 gas (N14) with AlN15(s) using a time-of-flight mass spectrometer. The isotopic N2 gas (N15) was generated by decomposi...

M. Hoch D. Ramakrishnan

1965-01-01

373

TOPAZ II Temperature Coefficient Analyses  

NASA Astrophysics Data System (ADS)

A two-dimensional model of the Topaz II reactor core suitable for neutronic analyses of temperature coefficients of reactivity is presented. The model is based on a 30° r-theta segment of the core. Results of TWODANT calculations are used to estimate temperature coefficients associated with fuel, electrodes, moderator, reflector, and tube plates over the range of temperatures anticipated during startup and operation. Results are presented to assess the reactivity effects associated with Doppler broadening, spectral effects and thermal expansion. Comparisons are made between the TWODANT results and empirical Russian curves used for simulating Topaz II system transients. TWODANT results indicate that the prompt temperature coefficients associated with temperature changes in fuel and emitters are negative. This is primarily because of Doppler broadening of the absorption resonances of uranium and molybdenum. The delayed effect of tube plate heating is also negative because fuel is moved radially outward in the core where it is less important. Temperature coefficients associated with delayed heating of the zirconium hydride moderator and the Beryllium reflector are positive, as the change in the neutron spectrum with moderator or reflector temperature decreases the rate of absorption in these components. The TWODANT results agree with the results obtained from the empirical Russian correlations.

Loaiza, David; Haskin, F. Eric; Marshall, Albert C.

1994-07-01

374

Geometrical content of Leslie coefficients.  

PubMed

In this work, we will study how the effective geometry acquired by nematic molecules under thermal vibration contribute to the determination of the Leslie coefficients. To do this, we will divide this work in two sections. In the first section, we present the geometrical fundamentals of the so-called Hess-Baalss (HB) approach [D. Baalss and S. Hess, Phys. Rev. Lett. 57, 86 (1986)] where we show that its basic assumptions can be understood as a geometrical interpretation of de Gennes' passage from the microscopic to the macroscopic order parameter. In the second section, we use an extended version of the HB approach [M. Simões, K. Yamaguti, and A. J. Palangana, Phys. Rev. E 80, 061701 (2009)] to obtain the geometrical contribution to each Leslie coefficient. Our results will be compared with experimental data, and we will show that the Miesowicz's coefficients are connected as long as the ratio ?(3)/?(4) between these Leslie coefficients can be considered small. PMID:21728551

Simões, M; da Silva, J L Correia

2011-05-10

375

Geometrical content of Leslie coefficients  

NASA Astrophysics Data System (ADS)

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

Simões, M.; da Silva, J. L. Correia

2011-05-01

376

Identities for generalized hypergeometric coefficients  

SciTech Connect

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

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

1991-01-01

377

Factoring Polynomials with Rational Coefficients.  

National Technical Information Service (NTIS)

A polynomial-time algorithm for the factorization of polynomials in one variable with rational coefficients is described. First a suitable small prime number p is found, a p-adic irreducible factor h of the polynomial f. This is done with Berlekamp's algo...

A. K. Lenstra H. W. Lenstra L. Lovasz

1982-01-01

378

Effective Viscosity Coefficient of Nanosuspensions  

NASA Astrophysics Data System (ADS)

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

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

2008-12-01

379

Composition of Partition Coefficients of  

Microsoft Academic Search

Partition coefficients (P) of tri-, tetra-, penta-, and hexa-chlorocyclohexene isomers were measured in an octanol\\/water system. These log P values and values previously determined for polychlorocy- clohexane isomers and some polychlorinated acyclic alkenes were analyzed by the summation of the hydrophobic fragment constants of their structural units and features. The introduction of new fragment constants, including interactive and conformational factors,

Norio KURIHARA

380

Prediction of stream volatilization coefficients  

USGS Publications Warehouse

Equations are developed for predicting the liquid-film and gas-film reference-substance parameters for quantifying volatilization of organic solutes from streams. Molecular weight and molecular-diffusion coefficients of the solute are used as correlating parameters. Equations for predicting molecular-diffusion coefficients of organic solutes in water and air are developed, with molecular weight and molal volume as parameters. Mean absolute errors of prediction for diffusion coefficients in water are 9.97% for the molecular-weight equation, 6.45% for the molal-volume equation. The mean absolute error for the diffusion coefficient in air is 5.79% for the molal-volume equation. Molecular weight is not a satisfactory correlating parameter for diffusion in air because two equations are necessary to describe the values in the data set. The best predictive equation for the liquid-film reference-substance parameter has a mean absolute error of 5.74%, with molal volume as the correlating parameter. The best equation for the gas-film parameter has a mean absolute error of 7.80%, with molecular weight as the correlating parameter.

Rathbun, Ronald, E.

1990-01-01

381

Random seismic noise attenuation using the Wavelet Transform  

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

382

Estimating contaminant attenuation half-lives in alluvial groundwater systems  

SciTech Connect

One aspect of describing contamination in an alluvial aquifer is estimating changes in concentrations over time. A variety of statistical methods are available for assessing trends in contaminant concentrations. We present a method that extends trend analysis to include estimating the coefficients for the exponential decay equation and calculating contaminant attenuation half-lives. The conceptual model for this approach assumes that the rate of decline is proportional to the contaminant concentration in an aquifer. Consequently, the amount of time to remove a unit quantity of the contaminant inventory from an aquifer lengthens as the concentration decreases. Support for this conceptual model is demonstrated empirically with log-transformed time series of contaminant data. Equations are provided for calculating system attenuation half-lives for non-radioactive contaminants.

Tardiff, Mark F.; Katzman, Danny

2007-03-13

383

Shape Minimization of Dendritic Attenuation  

SciTech Connect

What is the optimal shape of a dendrite? Of course, optimality refers to some particular criterion. In this paper, we look at the case of a dendrite sealed at one end and connected at the other end to a soma. The electrical potential in the fiber follows the classical cable equations as established by W. Rall. We are interested in the shape of the dendrite which minimizes either the attenuation in time of the potential or the attenuation in space. In both cases, we prove that the cylindrical shape is optimal.

Henrot, Antoine, E-mail: Antoine.Henrot@iecn.u-nancy.fr; Privat, Yannick [UMR 7502 Nancy-Universite-CNRS-INRIA, Institut Elie Cartan de Nancy (France)

2008-02-15

384

SEISMIC ATTENUATION FOR RESERVOIR CHARACTERIZATION  

SciTech Connect

In this report we will show results of seismic and well log derived attenuation attributes from a deep water Gulf of Mexico data set. This data was contributed by Burlington Resources and Seitel Inc. The data consists of ten square kilometers of 3D seismic data and three well penetrations. We have computed anomalous seismic absorption attributes on the seismic data and have computed Q from the well log curves. The results show a good correlation between the anomalous absorption (attenuation) attributes and the presence of gas as indicated by well logs.

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

2003-04-01

385

Comparison of mutant frequencies at the transgenic lambda LacI and cII/cI loci in control and ENU-treated Big Blue mice.  

PubMed

We compared the lambda cII/cI transgenic mutation assay described by Jakubczak et al. [(1996): Proc Natl Acad Sci USA 93:9073-9078] to the previously established Big Blue assay. Genomic DNA isolated from liver, spleen, and lung tissue of control or ethylnitrosourea (ENU)-treated Big Blue mice (100 mg/kg i.p., single dose) was packaged into phage (five animals, two packagings per DNA sample) which were simultaneously plated for lacI and cII/cI mutant frequency (MF) and titer. Mean MF of control animals was higher for cII/cI than lacI for all three tissues examined (spontaneous cII/cI MF divided by spontaneous lacI MF = 2.9, 3.1, and 1.7 for liver, spleen, and lung, respectively). The differences were statistically significant for liver and spleen, but not lung. The ENU-induced MF measured by subtracting control MFs from ENU-treated MFs was higher in the cII/cI assay than lacI (liver = 23.0 x 10(-5) for cII/cI vs. 15.1 x 10(-5) for lacI; spleen = 64.8 x 10(-5) for cII/cI vs. 36.1 x 10(-5) for lacI; lung = 17.1 x 10(-5) for cII/cI vs. 15.8 x 10(-5) for lacI). Fold increase over control values measured by dividing MF of ENU-treated animals by appropriate control values was higher for lacI than cII/cI (liver = 4.4-fold for lacI vs. 2.7 for cII/cI; spleen = 13.1-fold for lacI vs. 8.4 for cII/cI; and lung = 5.6-fold for lacI vs. 4.0 for cII/cI). Despite these differences, overall results were similar for the two mutational endpoints. These results suggest that the cII/cI assay may be an acceptable alternative to lacI where transgenic mutation studies are indicated. PMID:10334627

Zimmer, D M; Harbach, P R; Mattes, W B; Aaron, C S

1999-01-01

386

Cellular determinants of the mutational specificity of 1-nitroso-6-nitropyrene and 1-nitroso-8-nitropyrene in the lacI gene of Escherichia coli  

Microsoft Academic Search

We have characterized 202 lacI? mutations, and 158 dominant lacI?d mutations following treatment of Escherichiacoli strains NR6112 and EE125 with 1-nitroso-6-nitropyrene (1,6-NONP), an activated metabolite of the carcinogen 1,6-dinitropyrene. In all, 91% of the induced point mutations occurred at G:C residues. The ?(G:C) frameshifts were the dominant mutational class in the lacI? collections of both NR6112 and EE125, and in

I. B. Lambert; C. Carroll; N. Laycock; J. Koziarz; I. Lawford; L. Duval; G. Turner; R. Booth; S. Douville; J. Whiteway; M. R. Nokhbeh

2001-01-01

387

Next Generation - Monitored Natural Attenuation And Enhanced Attenuation - Chlorinated Solvents  

Microsoft Academic Search

Monitored Natural Attenuation (MNA) is a necessary part of the remedial action at most chlorinated solvent sites. As a result, site owners, stakeholders, and regulators are identifying and responding to MNAs technical challenges. For example, many contaminated plumes are not in anaerobic settings, making it unlikely the predominant mechanism embodied in existing protocols and guidance documents, reductive dechlorination, will be

Karen M. Vangelas

2005-01-01

388

Wave-induced fluid flow in random porous media: attenuation and dispersion of elastic waves.  

PubMed

A detailed analysis of the relationship between elastic waves in inhomogeneous, porous media and the effect of wave-induced fluid flow is presented. Based on the results of the poroelastic first-order statistical smoothing approximation applied to Biot's equations of poroelasticity, a model for elastic wave attenuation and dispersion due to wave-induced fluid flow in 3-D randomly inhomogeneous poroelastic media is developed. Attenuation and dispersion depend on linear combinations of the spatial correlations of the fluctuating poroelastic parameters. The observed frequency dependence is typical for a relaxation phenomenon. Further, the analytic properties of attenuation and dispersion are analyzed. It is shown that the low-frequency asymptote of the attenuation coefficient of a plane compressional wave is proportional to the square of frequency. At high frequencies the attenuation coefficient becomes proportional to the square root of frequency. A comparison with the 1-D theory shows that attenuation is of the same order but slightly larger in 3-D random media. Several modeling choices of the approach including the effect of cross correlations between fluid and solid phase properties are demonstrated. The potential application of the results to real porous materials is discussed. PMID:15957744

Müller, Tobias M; Gurevich, Boris

2005-05-01

389

Ultrasound characterization of red blood cell aggregation with intervening attenuating tissue-mimicking phantoms  

PubMed Central

The analysis of the ultrasonic frequency-dependent backscatter coefficient of aggregating red blood cells reveals information about blood structural properties. The difficulty in applying this technique in vivo is due to the frequency-dependent attenuation caused by intervening tissue layers that distorts the spectral content of signals backscattered by blood. An optimization method is proposed to simultaneously estimate tissue attenuation and blood structure properties, and was termed the structure factor size and attenuation estimator (SFSAE). An ultrasound scanner equipped with a wide-band 25 MHz probe was used to insonify porcine blood sheared in both Couette and tubular flow devices. Since skin is one of the most attenuating tissue layers during in vivo scanning, four skin-mimicking phantoms with different attenuation coefficients were introduced between the transducer and the blood flow. The SFSAE gave estimates with relative errors below 25% for attenuations between 0.115 and 0.411 dB?MHz and kR<2.08 (k being the wave number and R the aggregate radius). The SFSAE can be useful to examine in vivo and in situ abnormal blood conditions suspected to promote pathophysiological cardiovascular consequences.

Franceschini, Emilie; Yu, Francois T.H.; Destrempes, Francois; Cloutier, Guy

2010-01-01

390

Attenuation of strain waves in core samples of three types of rock  

Microsoft Academic Search

Dynamic photoelasticity was employed to determine the velocity of longitudinal stress waves, dynamic modulus of elasticity and attenuation coefficients in rockcore samples 1 in. (25 mm) in diameter, 18 in. (0.46 m) long. Birefringent strips bonded to the core samples of Salem limestone, Charcoal granite and Berea sandstone provided all the data needed for the dynamic characterization of these rock

W. L. Fourney; J. W. Dally; D. C. Holloway

1976-01-01

391

Acoustic characterization of echogenic liposomes: Frequency-dependent attenuation and backscatter  

PubMed Central

Ultrasound contrast agents (UCAs) are used clinically to aid detection and diagnosis of abnormal blood flow or perfusion. Characterization of UCAs can aid in the optimization of ultrasound parameters for enhanced image contrast. In this study echogenic liposomes (ELIPs) were characterized acoustically by measuring the frequency-dependent attenuation and backscatter coefficients at frequencies between 3 and 30 MHz using a broadband pulse-echo technique. The experimental methods were initially validated by comparing the attenuation and backscatter coefficients measured from 50-?m and 100-?m polystyrene microspheres with theoretical values. The size distribution of the ELIPs was measured and found to be polydisperse, ranging in size from 40 nm to 6 ?m in diameter, with the highest number observed at 65 nm. The ELIP attenuation coefficients ranged from 3.7?±?1.0 to 8.0?±?3.3 dB/cm between 3 and 25 MHz. The backscatter coefficients were 0.011?±?0.006 (cm str)?1 between 6 and 9 MHz and 0.023?±?0.006 (cm str)?1 between 13 and 30 MHz. The measured scattering-to-attenuation ratio ranged from 8% to 22% between 6 and 25 MHz. Thus ELIPs can provide enhanced contrast over a broad range of frequencies and the scattering properties are suitable for various ultrasound imaging applications including diagnostic and intravascular ultrasound.

Kopechek, Jonathan A.; Haworth, Kevin J.; Raymond, Jason L.; Douglas Mast, T.; Perrin, Stephen R.; Klegerman, Melvin E.; Huang, Shaoling; Porter, Tyrone M.; McPherson, David D.; Holland, Christy K.

2011-01-01

392

Attenuation of Body Waves and the Q Structure of the Mantle   

Microsoft Academic Search

eliminate the source effect and the effect of the wave front divergence. It is shown that, when instrumental and crustal effects are removed, the logarithm of the spectral ratio is a linear function of frequency. The coefficient of the linear term, called the differential attenuation, is used to invert for a Qdepth structure. Two possible Qa models are presented, both

Seismological Laborat

1968-01-01

393

Stability of RNA Virus Attenuation Approaches  

PubMed Central

The greatest risk from live-attenuated vaccines is reversion to virulence. Particular concerns arise for RNA viruses, which exhibit high mutation frequencies. We examined the stability of 3 attenuation strategies for the alphavirus, Venezuelan equine encephalitis virus (VEEV): a traditional, point mutation-dependent attenuation approach exemplified by TC-83; a rationally designed, targeted-mutation approach represented by V3526; and a chimeric vaccine, SIN/TC/ZPC. Our findings suggest that the chimeric strain combines the initial attenuation of TC-83 with the greater phenotypic stability of V3526, highlighting the importance of the both initial attenuation and stability for live-attenuated vaccines.

Kenney, Joan L.; Volk, Sara M.; Pandya, Jyotsna; Wang, Eryu; Liang, Xiaodong; Weaver, Scott C.

2011-01-01

394

The Effect of Attenuation Coefficient on Radiation Force Impulse Monitoring of Thermal Lesions  

NASA Astrophysics Data System (ADS)

Accurate monitoring of ultrasonically induced thermal lesions in biological tissue has been one of the challenges behind bringing focused ultrasound surgery to mainstream clinical use. Recent research has shown the potential of using radiation force impulses to monitor displacement changes that may be related to the formation of the lesion. It has been suggested that as the lesion forms a reduction in displacement should occur due to a stiffening of the tissue in the focal region, indicating the onset of ablation. More recent literature has reported initial increases in the displacements prior to stiffening which were explained by a softening in the tissue before denaturation took place. In this paper we present results supporting that initial increase, however here we propose that these changes are dominated by an increase in sound absorption in the tissue, rather than a tissue softening. The results show that a lesion may have already formed before decreases in displacement are observed. The measurement of displacement change using this method could provide valuable information not only about the onset of ablation but also the size of the induced lesion.

Haw, Christopher; Arora, Manish; Coussious, Constantin C.; Noble, Alison

2010-03-01

395

Research on the Signal Random Attenuation Coefficient Based on RSSI in WSN Localization Technology  

Microsoft Academic Search

Localization technology is the important supporting technology in wireless sensor networks. Positioning precision is largely determined by ranging precision in the localization technology based on the distance. Traditional RSSI ranging method exists some problems of path loss model complex, serious signal concussion caused by environmental changes, which leads to ranging error and so on. According to the above problems, the

Jijun Zhao; Hua Li; Xiang Sun

2009-01-01

396

Contrast enhancement procedure for digital images of dense breasts by using tissue attenuation coefficients  

Microsoft Academic Search

Computer-aided diagnosis (CAD) schemes are developed all over the world to aid radiologists in order to increase the probabilities of early detection of breast cancer. Among the challenges to overcome by these schemes, one is very important: the contrast enhancement in dense breast images, which frequently present poor contrast among the structures of clinical interest and the background due to

F. L. S. Nunes; H. Schiabel

2000-01-01

397

Assessment of satellite derived diffuse attenuation coefficients and euphotic depths in south Florida coastal waters  

EPA Science Inventory

Optical data collected in coastal waters off South Florida and in the Caribbean Sea between January 2009 and December 2010 were used to evaluate products derived with three bio-optical inversion algorithms applied to MOIDS/Aqua, MODIS/Terra, and SeaWiFS satellite observations. Th...

398

Transient attenuation in optical fibers  

SciTech Connect

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

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

1984-01-01

399

Attenuation Tomography in Eastern Russia  

Microsoft Academic Search

We are using catalog amplitude parameters to derive a 2D function that maps laterally-varying attenuation features for eastern Siberia and the Russian Far East. Our information is from the Michigan State University (MSU) Siberia database, compiled through cooperative efforts of MSU, Russian network operators and Los Alamos researchers. The database also includes information from teleseismic bulletins, such as those provided

C. A. Rowe; W. S. Phillips; H. E. Hartse; L. K. Steck; M. L. Begnaud; K. G. Mackey; K. Fujita

2006-01-01

400

SEISMIC ATTENUATION FOR RESERVOIR CHARACTERIZATION  

SciTech Connect

In fully-saturated rock and at ultrasonic frequencies, the microscopic squirt flow induced between the stiff and soft parts of the pore space by an elastic wave is responsible for velocity-frequency dispersion and attenuation. In the seismic frequency range, it is the macroscopic cross-flow between the stiffer and softer parts of the rock. We use the latter hypothesis to introduce simple approximate equations for velocity-frequency dispersion and attenuation in a fully water saturated reservoir. The equations are based on the assumption that in heterogeneous rock and at a very low frequency, the effective elastic modulus of the fully-saturated rock can be estimated by applying a fluid substitution procedure to the averaged (upscaled) dry frame whose effective porosity is the mean porosity and the effective elastic modulus is the Backus-average (geometric mean) of the individual dry-frame elastic moduli of parts of the rock. At a higher frequency, the effective elastic modulus of the saturated rock is the Backus-average of the individual fully-saturated-rock elastic moduli of parts of the rock. The difference between the effective elastic modulus calculated separately by these two methods determines the velocity-frequency dispersion. The corresponding attenuation is calculated from this dispersion by using (e.g.) the standard linear solid attenuation model.

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

2002-07-01

401

Semi-metallic single-component crystal of soluble La@C82 derivative with high electron mobility.  

PubMed

We prepared an organic conductor crystal having extremely high electron mobility, in which the adamantylidene (Ad) derivative of La@C(82) (an endohedral metallofullerene known as a n-type semiconductor) is aligned in an orderly fashion. The single-component crystal exhibits high electron mobility of ? > 10 cm(2) V(-1) s(-1) along the c axis under normal temperatures and pressures in the atmosphere, as shown by flash-photolysis time-resolved microwave conductivity (TRMC) measurements, which are the highest of reported organic conductors measured by TRMC. According to density functional calculations, the single crystal of La@C(82)Ad is semi-metallic, with a small band gap of 0.005 eV. PMID:21294573

Sato, Satoru; Seki, Shu; Honsho, Yoshihito; Wang, Lu; Nikawa, Hidefumi; Luo, Guangfu; Lu, Jing; Haranaka, Masayuki; Tsuchiya, Takahiro; Nagase, Shigeru; Akasaka, Takeshi

2011-02-04

402

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

PubMed

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

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

2012-11-23

403

THE 2001-2003 LOW STATE OF NOVA LACERTAE 1950 (DK LAC)  

SciTech Connect

We report on extensive photometry of DK Lac obtained during the interval 1990-2009, which includes a 2 mag low state during 2001-2003. Much of the photometry consists of exposures obtained with a typical spacing of several days, but also includes 26 sequences of continuous photometry each lasting 2-7 hr. We find no evidence for periodicities in our data. We do find that the random variations in the low state are approximately twice those in the high state, when expressed in magnitudes. The lack of orbital-timescale variations is attributed to the nearly face-on presentation of the disk. There is a 0.2 mag decline in the high-state brightness of the system over 19 years, which is consistent with the behavior of other old novae in the decades following outburst. High-state spectra are also presented and discussed. We find that the equivalent width of H{alpha} falls by about double from 1991 to 2008. The photometric properties are discussed in the context of the hibernation scenario for the behavior of novae between outbursts, in which we conclude that low states in old novae are probably unrelated to their possible entrance into hibernation.

Honeycutt, R. K.; Jacobson, H.; Hoffman, D.; Maxwell, T.; Croxall, K. [Astronomy Department, Indiana University, Swain Hall West, Bloomington, IN 47405 (United States); Kafka, S. [Department of Terrestrial Magnetism, Carnegie Institute of Washington, 5241 Broad Branch Rd. NW, Washington, DC 2001 (United States); Henden, A. A. [American Association of Variable Star Observers, 49 Bay State Rd., Cambridge, MA 02138-1203 (United States); Robertson, J. W., E-mail: honey@astro.indiana.edu, E-mail: jacob189@msu.edu, E-mail: dhoffman@nmsu.edu, E-mail: tmaxwell@astro.indiana.edu, E-mail: kevin.croxall@utoledo.edu, E-mail: skafka@dtm.ciw.edu, E-mail: arne@aavso.org, E-mail: Jeff.Robertson@atu.edu [Arkansas Tech University, Department of Physical Sciences, 1701 N. Boulder, Russellville, AR 72801-2222 (United States)

2011-04-15

404

CAP and RNA polymerase interactions with the lac promoter: binding stoichiometry and long range effects.  

PubMed Central

The binding stoichiometries of the complexes formed when the E. coli cyclic AMP receptor protein (CAP) binds to 203 bp lac promoter-operator restriction fragments have been determined. Under quantitative binding conditions, a single dimer of CAP occupies each of two sites in the promoter. Different electrophoretic mobilities are observed for 1:1 complexes formed with L8-UV5 mutant, L305 mutant, and wild type promoter fragments, indicating sequence-specific structural differences between the complexes. The differences in gel mobility between L8-UV5 and wild type complexes disappear when the promoter fragments are cleaved with Hpa II restriction endonuclease. Models in which CAP alters DNA conformation or in which CAP forms a transient intramolecular bridge between two domains of a DNA molecule could account for these observations. The selective binding of RNA polymerase to CAP-promoter complexes is demonstrated: the binding of a single CAP dimer to the promoter is sufficient to stimulate subsequent polymerase binding. Functional CAP molecules are not released from the promoter on polymerase binding. Images

Fried, M G; Crothers, D M

1983-01-01

405

GAMMA-RAY BURST AFTERGLOWS AS ANALOGS OF HIGH-FREQUENCY-PEAKED BL LAC OBJECTS  

SciTech Connect

The spectral properties from radio-to-optical bands are compared between the 18 optically bright gamma-ray burst (GRB) afterglows and the well-established power-spectrum sequence in blazars. The comparison shows that the afterglows are in well agreement with the well-known blazar sequence (i.e., the {nu}L{sub {nu}}(5 GHz)-{alpha}{sub RO} correlation, where {alpha}{sub RO} is the broadband spectral slope from radio-to-optical bands). The afterglows are, however, clustered at the low-luminosity end of the sequence, which is typically occupied by high-frequency-peaked BL Lac objects (HBLs). The correlation suggests that GRB afterglows share a similar emission process with HBLs. We further identify a deviation at a significance level larger than 2{sigma} from the sequence for three typical optically 'dark' bursts. The deviation favors a heavy extinction in optical bands for the 'dark' bursts. The extinction A{sub V} is estimated to be larger than 0.5-0.6 mag from the {nu}L{sub {nu}}(5 GHz)-{alpha}{sub RO} sequence.

Wang, J.; Wei, J. Y., E-mail: wj@bao.ac.cn [National Astronomical Observatories, Chinese Academy of Science, 20A Datun Road, Chaoyang District, Beijing 100012 (China)

2011-01-01

406

Long-term optical and infrared variability of the BL Lac object PKS 0537 - 441  

NASA Astrophysics Data System (ADS)

The long-term optical and infrared variability of the BL Lac object PKS 0537 - 441 has been studied. The source exhibits strong variability in the optical and infrared bands, and long-term variations of spectral indices have been analysed. The results indicate that there is a complex relationship between the spectral index and the brightness. In the low state, a redder-when-brighter chromatism has been found, in the sense that the spectrum steepens as the brightness increases, whereas in the high state, the source shows an opposite trend. The correlations between different bands have been investigated by means of the discrete correlation function method. The results show that the variations in the various optical and infrared bands are strongly correlated, but with no significant lags. It is, however, expected that there will be time lags of minutes to hours between the bands. Therefore, any attempt to detect the time lag needs a much denser monitoring of the source. Structure function analysis suggests that the source varies with a short-term time-scale of 34-46 d. An intra-day variability with a 24.5-min time-scale has been detected in the optical V band. The optical emission diameter is estimated to be 4.33 × 1014 cm, and the mass of the central black hole is estimated to be 2.3 × 108 M?.

Zhang, Bing-Kai; Wang, Sen; Zhao, Xiao-Yun; Dai, Ben-Zhong; Zha, Min

2013-02-01

407

Colorimetry of two large flares of EV Lac according to UBVRI observations in 1996-1998  

NASA Astrophysics Data System (ADS)

According to the data of fast UBVRI photometry of the red flaring dwarf star EV Lac obtained in the course of international cooperative observations, a fine temporal structure of two large flares (15 Oct 1996 and 10 Oct 1998) with amplitudes of 3.73 and 2.72 magnitudes in the U band have been studied. A detailed colorimetric analysis allowed us to trace variations in the flare plasma characteristics such as the optical thickness, electron density, and temperature during the development of the flare. It was revealed that, in the time period up to the maximum brightness, both flares are in the state of hydrogen plasma, which is optically thin in the Balmer continuum. In the region of the brightness maximum, both flares emit for about 1 min as an absolutely black body (ABB), the temperature of which varies from 20000 to 12000 K and 16000 to 14000 K, respectively. Then, these flares pass to the plasma state, is optically thick in the Balmer continuum. At the brightness maximum, the flares emitted as an ABB with a temperature of about 15000 and 16000 K. In the ABB approximation, the linear sizes of the flares are approximately 5 and 3% of the stellar radius at luminosity maximum. The area is 5.1 × 1018 cm2 and 1.6 × 1018 cm2.

Lovkaya, M. N.

2012-06-01

408

BL Lac Object PKS B1144-379: An Extreme Scintillator  

NASA Astrophysics Data System (ADS)

Rapid variability in the radio flux density of the BL Lac object PKS B1144-379 has been observed at four frequencies, ranging from 1.5 to 15 GHz, with the Very Large Array and the University of Tasmania's Ceduna antenna. Intrinsic and line-of-sight effects were examined as possible causes of this variability, with interstellar scintillation best explaining the frequency dependence of the variability timescales and modulation indices. This scintillation is consistent with a compact source 20-40 ?as or 0.15-0.3 pc in size. The inferred brightness temperature for PKS B1144-379 (assuming that the observed variations are due to scintillation) is 6.2 × 1012 K at 4.9 GHz, with approximately 10% of the total flux in the scintillating component. We show that scintillation surveys aimed at identifying variability timescales of days to weeks are an effective way to identify the active galactic nuclei with the highest brightness temperatures.

Turner, R. J.; Ellingsen, S. P.; Shabala, S. S.; Blanchard, J.; Lovell, J. E. J.; McCallum, J. N.; Cimò, G.

2012-08-01

409

X-RAY AND TeV EMISSIONS FROM HIGH-FREQUENCY-PEAKED BL LAC OBJECTS  

SciTech Connect

The majority of the extragalactic sources yet detected at TeV photon energies belong to the class of 'high-frequency-peaked BL Lac objects' (HBLs) that exhibit a spectral energy distribution with a lower peak in the X-ray band. Such spectra are well described in terms of a log-parabolic shape with considerable curvature, and widely interpreted as synchrotron emission from ultrarelativistic electrons outflowing in a relativistic jet; these are expected to radiate also in {gamma}-rays through the inverse Compton process. Recently, we have compared the X-ray spectral parameter distributions of TeV detected HBLs (TBLs) with those undetected (UBLs), and found that the distributions of the peak energies E{sub p} are similarly symmetric around a value of a few keVs for both subclasses, while the X-ray spectra are broader for TBLs than for UBLs. Here we propose an acceleration scenario to interpret both the E{sub p} and the spectral curvature distributions in terms of a coherent and a stochastic acceleration mechanisms, respectively. We show how the curvature parameter b {approx_equal} 0.3-0.7 of the synchrotron X-rays, which depends only on the latter acceleration component, can be related to the inverse Compton luminosity in {gamma}-rays, thus introducing a link between the X-ray and the TeV observations of HBLs.

Massaro, F.; Paggi, A. [Harvard-Smithsonian Astrophysical Observatory, 60 Garden Street, Cambridge, MA 02138 (United States); Cavaliere, A. [Dipartimento di Fisica, Universita di Roma Tor Vergata, Via della Ricerca Scientifica 1, I-00133 Roma (Italy)

2011-12-15

410

Yeast extract mediated autoinduction of lacUV5 promoter: an insight.  

PubMed

We report a simple and cost-effective autoinducible media component responsible for the autoinduction of proteins in Escherichia coli under lacUV5 promoter system. Yeast extract (YE) at high concentration was found to stimulate the expression of T7 RNA polymerase in BL21(DE3) cells while such an effect was not seen in BL21A1 cells. A systematic study on the effect of varying concentrations of YE indicated several folds higher expression of genes viz., human granulocyte colony stimulating factor (rhGCSF), human interferon alpha 2b (rhIFN-alpha2b) and Staphylokinase (rSAK) in BL21(DE3) cells in the absence of any specific inducer like IPTG or additional lactose. Additional investigations on the inducible component of the YE revealed the presence of significant amount of endogenous lactose as the contributory factor for the observed autoinduction phenomenon. This paper highlights the easy scalability of the use of the present media component for large-scale production in biotechnology industry. PMID:19666150

Nair, Rahul; Salvi, Pankaj; Banerjee, Sampali; Raiker, Veena A; Bandyopadhyay, Suman; Soorapaneni, Sudheerbabu; Kotwal, Prakash; Padmanabhan, Sriram

2009-08-08

411

Is Low-Frequency-Peaked BL Lac Object OJ 287 a TeV Emitter?  

NASA Astrophysics Data System (ADS)

It is well known that there are only two low-frequency-peaked BL Lac objects (LBLs: BL Lacertae and S5 0716+714) and one flat spectrum radio quasar (FSRQ: 3C 279) among more than 30 active galactic nuclei (AGNs) with detected TeV emissions. We study the spectral energy distribution (SED) of a famous LBL OJ 287, whose light curve has a 12-y period. Using a homogeneous one-zone synchrotron + synchrotron-self Compton model, we model the quasi-simultaneous broad-band SED of OJ 287. With some reasonable assumptions, we extrapolate the model to the high state of OJ 287 and predict its ?-ray emissions. Taking into account the absorption of ?-ray by the extragalactic background light (EBL), we find that the TeV emission of OJ 287 in high state is slightly higher than the sensitivity of H.E.S.S. The study on SEDs of OJ 287 has implications to unveil the origin of jet activity during its 12-y period and the properties of EBL.

Chen, Liang; Bai, Jin-Ming

2010-11-01

412

Portable vapor diffusion coefficient meter  

DOEpatents

An apparatus for measuring the effective vapor diffusion coefficient of a test vapor diffusing through a sample of porous media contained within a test chamber. A chemical sensor measures the time-varying concentration of vapor that has diffused a known distance through the porous media. A data processor contained within the apparatus compares the measured sensor data with analytical predictions of the response curve based on the transient diffusion equation using Fick's Law, iterating on the choice of an effective vapor diffusion coefficient until the difference between the predicted and measured curves is minimized. Optionally, a purge fluid can forced through the porous media, permitting the apparatus to also measure a gas-phase permeability. The apparatus can be made lightweight, self-powered, and portable for use in the field.

Ho, Clifford K. (Albuquerque, NM)

2007-06-12

413

Elastic coefficients of animal bone.  

PubMed

The elastic stiffness coefficients of dried bovine phalanx and femur and of fresh bovine phalanx were measured by an ultrasonic technique. An analysis of the crystallographic structure of the principal components of bone and its piezoelectric and pyroelectric behavior showed that bone is a texture that has the same elastic coeffcient matrix as a hexagonal single crystal. The five elastic stiffness coefficients of fresh phalanx are: C(1l), 1.97; C(12), 1.21; C(13), 1.26; C(33), 3.20; and C(44), 0.54 (all in units of 10(11) dynes per square centimeter). Value of axial and transverse Young's and shear moduli, compressibility, and the three Poisson's ratios were calculated. PMID:5787984

Lang, S B

1969-07-18

414

High temperature Seebeck coefficient metrology  

SciTech Connect

We present an overview of the challenges and practices of thermoelectric metrology on bulk materials at high temperature (300 to 1300 K). The Seebeck coefficient, when combined with thermal and electrical conductivity, is an essential property measurement for evaluating the potential performance of novel thermoelectric materials. However, there is some question as to which measurement technique(s) provides the most accurate determination of the Seebeck coefficient at high temperature. This has led to the implementation of nonideal practices that have further complicated the confirmation of reported high ZT materials. To ensure meaningful interlaboratory comparison of data, thermoelectric measurements must be reliable, accurate, and consistent. This article will summarize and compare the relevant measurement techniques and apparatus designs required to effectively manage uncertainty, while also providing a reference resource of previous advances in high temperature thermoelectric metrology.

Martin, J. [Materials Science and Engineering Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (United States); Tritt, T. [Department of Physics and Astronomy, Clemson University, Clemson, South Carolina 29634 (United States); Uher, C. [Department of Physics, University of Michigan, Ann Arbor, Michigan 48109 (United States)

2010-12-15

415

Factoring polynomials with rational coefficients  

Microsoft Academic Search

In this paper we present a polynomial-time algorithm to solve the following problem: given a non-zero polynomial fe Q(X) in one variable with rational coefficients, find the decomposition of f into irreducible factors in Q(X). It is well known that this is equivalent to factoring primitive polynomials feZ(X) into irreducible factors in Z(X). Here we call f~ Z(X) primitive if

A. K. Lenstra; H. W. Lenstra; L. Lovfiasz

1982-01-01

416

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

Microsoft Academic Search

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

François Bonnieux; Gérard Miclet; Pierre Rainelli

1978-01-01

417

Mutational spectrum of bleomycin in lacZ mouse kidney: a possible model for mutational spectrum of reactive oxygen species  

Microsoft Academic Search

The mutational spectrum of bleomycin was compared with the spontaneous mutational spectrum in lacZ mouse kidney. Mice were treated with four 20mg\\/kg of doses of bleomycin over a two-week period, leading to a mutant fraction several times greater than that of controls. The major class of bleomycin-induced mutations consisted of small deletions, in particular ?1 deletions at AT base pairs

Joseph B. Guttenplan; Michael Khmelnitsky; Roderick Haesevoets; Wieslawa Kosinska

2004-01-01

418

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

PubMed Central

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

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

2010-01-01

419

Lac Télé structure, Republic of Congo: Geological setting of a cryptozoological and biodiversity hotspot, and evidence against an impact origin  

Microsoft Academic Search

Lac Télé is a large lake, ?5.6km 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

Sharad Master

2010-01-01

420

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

Microsoft Academic Search

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

Tibor Torok; Gabriella Tick; Martha Alvarado; Istvan Kiss

1993-01-01

421

Application of Fluorescence Energy Transfer and Polarization to Monitor Escherichia Coli cAMP Receptor Protein and lac Promoter Interaction  

Microsoft Academic Search

A fluorescence method was developed to study DNA-protein interactions in solution. A 32-base-pair (bp) DNA fragment of the lac promoter containing the primary binding site for Escherichia coli cAMP receptor protein (CRP) was chemically synthesized and labeled specifically at the 5' end with fluorescent probe. Binding of cAMP receptor protein to this fragment can be conveniently followed by measuring changes

Tomasz Heyduk; James C. Lee

1990-01-01

422

Unusual optical quiescence of the classical BL Lac object PKS 0735+178 on intranight time-scale  

Microsoft Academic Search

We present the result of our extensive intranight optical monitoring of the well-known low-energy peaked BL Lac (LBL) object PKS 0735+178. This long-term follow-up consists of R-band monitoring for a minimum duration of ~4 hours, on 17 nights spanning 11 years (1998-2008). Using the CCD as an N-star photometer, a detection limit of around 1 per cent was attained for

Arti Goyal; Gopal-Krishna; G. C. Anupama; D. K. Sahu; R. Sagar; S. Britzen; M. Karouzos; M. F. Aller; H. D. Aller

2009-01-01

423

Origins of the Highly Ionized Gas toward the X-ray Bright BL Lac Object Mrk 421  

Microsoft Academic Search

The X-ray bright BL Lac object Mrk 421 is one of the small number of extragalactic objects for which it is possible to study the highly ionized gas in the ISM and Local Group using the full diagnostic power of UV, far-UV and X-ray observatories. High quality far-UV observations of OVI and other ions have been obtained by FUSE, whereas

Blair Savage

2004-01-01

424

Spectroscopic orbit of the ex-eclipsing binain the young open cluster NGC 7209ry SS Lac  

Microsoft Academic Search

The no-longer-eclipsing system SS Lac in the young open cluster NGC 7209 has\\u000abeen recently announced to show a constant radial velocity. Puzzled by this\\u000afinding, we have monitored the system during 1997 obtaining 24 Echelle+CCD\\u000aspectra over 8 orbital revolutions. Our spectra reveal a nice orbital motion\\u000awith periodic splitting and merging of spectral lines from both components. An

Lina Tomasella; Ulisse Munari

1998-01-01

425

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

Microsoft Academic Search

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

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

2010-01-01

426

Ionization coefficients in gas mixtures  

NASA Astrophysics Data System (ADS)

We have tested the application of the common E/N (E—electric field, N—gas number density) or Wieland approximation [Van Brunt, R.J., 1987. Common parametrizations of electron transport, collision cross section, and dielectric strength data for binary gas mixtures. J. Appl. Phys. 61 (5), 1773 1787.] and the common mean energy (CME) combination of the data for pure gases to obtain ionization coefficients for mixtures. Test calculations were made for Ar CH4, Ar N2, He Xe and CH4 N2 mixtures. Standard combination procedure gives poor results in general, due to the fact that the electron energy distribution is considerably different in mixtures and in individual gases at the same values of E/N. The CME method may be used for mixtures of gases with ionization coefficients that do not differ by more than two orders of magnitude which is better than any other technique that was proposed [Mari?, D., Radmilovi?-Ra?enovi?, M., Petrovi?, Z.Lj., 2005. On parametrization and mixture laws for electron ionization coefficients. Eur. Phys. J. D 35, 313 321.].

Mari?, D.; Šaši?, O.; Jovanovi?, J.; Radmilovi?-Ra?enovi?, M.; Petrovi?, Z. Lj.

2007-03-01

427

Analysis of site parameters affecting natural attenuation in saturated soil. Master's thesis  

SciTech Connect

This study investigated the natural attenuation mechanisms and some of the parameters affecting those mechanisms in the saturated zone. A literature search revealed numerous studies of various attenuation and the associated parameters. Much of the literature emphasized biodegradation as the most promising attenuation mechanism. BIOPLUME II(TM), a fate and transport model, was used to simulate the fate and transport of contaminant plume. The effects of the model parameters were investigated by observing the distance a contaminant plume was expected to migrate over a fifty year period. The investigation was limited by the model which excludes chemical reactions and some physical and physiochemical reactions. The model simulations indicated that parameters which exhibited significant influence on natural attenuation include hydraulic conductivity, reaeration, and coefficient of anaerobic biodegradation.

Potts, W.H.

1993-09-01

428

Estimating contaminant attenuation half-lives in alluvial groundwater systems.  

PubMed

One aspect of describing contamination in an alluvial aquifer is estimating changes in concentrations over time. A variety of statistical methods are available for assessing trends in contaminant concentrations. We present a method that extends trend analysis to include estimating the coefficients for the exponential decay equation and calculating contaminant attenuation half-lives. The conceptual model for this approach assumes that the rate of decline is proportional to the contaminant concentration in an aquifer. Consequently, the amount of time to remove a unit quantity of the contaminant inventory from an aquifer lengthens as the concentration decreases. Support for this conceptual model is demonstrated empirically with log-transformed time series of contaminant data. Equations are provided for calculating system attenuation half-lives for non-radioactive contaminants. For radioactive contaminants, the system attenuation half-life is partitioned into the intrinsic radioactive decay and the concentration reduction caused by aquifer processes. Examples are presented that provide the details of this approach. In addition to gaining an understanding of aquifer characteristics and changes in constituent concentrations, this method can be used to assess compliance with regulatory standards and to estimate the time to compliance when natural attenuation is being considered as a remediation strategy. A special application of this method is also provided that estimates the half-life of the residence time for groundwater in the aquifer by estimating the half life for a conservative contaminant that is no longer being released into the aquifer. Finally, the ratio of the half-life for groundwater residence time to the attenuation half-life for a contaminant is discussed as a system-scale retardation factor which can be used in analytical and numerical modeling. PMID:17344953

Tardiff, Mark F; Katzman, Danny

2007-02-09

429

Uruguay Round of Multilateral Trade Negotiations: Report of the Labor Advisory Committee (LAC) on the Uruguay Round of Multilateral Trade Negotiations.  

National Technical Information Service (NTIS)

The Labor Advisory Committee for Trade Negotiations and Trade Policy (LAC) believes that the proposed trade agreements resulting from the Uruguay Round of Multilateral Trade Negotiations offer little, if anything positive to U.S. workers, and in certain r...

1994-01-01

430

The Multiple-Partial Correlation Coefficient  

Microsoft Academic Search

A partial correlation coefficient which is also a multiple correlation coefficient is discussed. Its relationship with other well-known coefficients is explained. Computational methods for computing the estimating equation and the correlation coefficient are suggested.* The writer wishes to thank Professors Harold Hotelling, George E. Nicholson, and John H. Smith for critically reading the manuscript and offering valuable comments. Professor Hotelling

Dudley J. Cowden

1952-01-01

431

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

SciTech Connect

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

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

1997-10-01

432

Analysis of neural crest cell fate during cardiovascular development using Cre-activated lacZ/?-galactosidase staining.  

PubMed

It is important to identify the mechanisms regulating cardiovascular development. However, complex genetic tools are often required, including transgenic animals that express the lacZ transgene encoding the ?-galactosidase enzyme under the control of a specific promoter or following recombination with the Cre recombinase. The latter can be useful for identifying specific cell populations of the developing cardiovascular system, including neural crest cells. The tracking of these cells can help clarify their fate in mutant embryos and elucidate the etiology of some congenital cardiovascular birth defects. This chapter highlights the methods used to stain embryonic tissues in whole mount or sections to detect the expression of the lacZ transgene with a focus on tracking cardiac neural crest cells using the Wnt1-Cre and R26R mouse lines. We also provide a protocol using fluorescence-activated cell sorting for collecting neural crest cells for further analysis. These protocols can be used with any embryos expressing Cre and lacZ. PMID:22222527

Zhang, Yanping; Ruest, L Bruno

2012-01-01

433

Two-dimensional NMR study of a protein-DNA complex. lac repressor headpiece-operator interaction.  

PubMed

The interaction of the N-terminal DNA-binding domain (56 amino acid residues) of the lac repressor with lac operator DNA was analyzed using two-dimensional NMR spectroscopy. Both half-operators (11 and 14 bp) and a complete fully symmetric 22 bp operator were studied. Two-dimensional nuclear Overhauser effect (2D NOE) spectra of headpiece-operator complexes were taken in both D2O and H2O solutions. Special attention was given to the problem of 1H resonance assignments. Based on an analysis of the proton-proton NOEs, a model for the headpiece-operator complex could be derived. In this model, most of the protein-DNA contracts occur between amino acid residues in the second helix (recognition helix) of the lac headpiece and DNA bases in the major groove. The orientation of this helix with respect to the dyad axis of the operator is opposite to that found in the X-ray structures of several other repressor-operator complexes. PMID:2372315

Kaptein, R; Lamerichs, R M; Boelens, R; Rullmann, J A

1990-07-01