These are representative sample records from Science.gov related to your search topic.
For comprehensive and current results, perform a real-time search at Science.gov.
1

Attenuation coefficients for water quality trading.  

PubMed

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

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

2014-06-17

2

FREQUENCY DEPENDENT ULTRASONIC ATTENUATION COEFFICIENT ASSESSMENT IN FRESH  

E-print Network

dependency of the ultrasonic attenuation coefficient ranges from f * e to fl.3 6 and its magnitude at 1 MHzFREQUENCY DEPENDENT ULTRASONIC ATTENUATION COEFFICIENT ASSESSMENT IN FRESH TISSUE Laurie A . Segal 61801 Abstract Ultrasonic attenuation coefficient measurements were made at 1.4, 4.2, 7.0 and 9.8 MHz

Illinois at Urbana-Champaign, University of

3

Gamma ray attenuation coefficient measurement for neutron-absorbent materials  

NASA Astrophysics Data System (ADS)

The compounds Na 2B 4O 7, H 3BO 3, CdCl 2 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 H 3BO 3 with the lowest average Z has the highest gamma ray attenuation coefficient among the aforementioned compounds.

Jalali, Majid; Mohammadi, Ali

2008-05-01

4

Attenuation coefficients of body tissues using principal-components analysis  

Microsoft Academic Search

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

J. B. Weaver; A. L. Huddleston

2009-01-01

5

Measurements of spectral attenuation coefficients in the lower Chesapeake Bay  

NASA Technical Reports Server (NTRS)

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

Houghton, W. M.

1983-01-01

6

Temporal Variations of Seismic Coda: Attenuation-Coefficient View  

NASA Astrophysics Data System (ADS)

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

Morozov, I. B.

2010-12-01

7

Apparent Linear Attenuation Coefficients in Phase Contrast X-Ray Tomography  

PubMed Central

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

Yan, Aimin; Wu, Xizeng

2011-01-01

8

Representative Elementary Length to Measure Soil Mass Attenuation Coefficient  

PubMed Central

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

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

2014-01-01

9

Effect of atmospheric environment on the attenuation coefficient of light in water  

E-print Network

The attenuation coefficient of 532 nm light in water under different atmospheric conditions was investigated. Measurements were made over a two-year period at the same location and show that the attenuation coefficient is significantly influenced by the atmospheric environment. It is lowest when the atmospheric pressure is high and temperature is low, and is highest when the atmospheric pressure is low and temperature is high. The maximum attenuation coefficient of pure water in these studies was about three times the minimum value. The mechanism of the phenomena is discussed. These results are also important in underwater acoustics.

Liu, Juan; Tang, Yijun; Zhu, Kaixing; Ge, Yuan; Chen, Xuegang; He, Xingdao; Liu, Dahe

2014-01-01

10

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

NASA Astrophysics Data System (ADS)

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

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

2010-11-01

11

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

Microsoft Academic Search

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

A. M. El-Khayatt

2011-01-01

12

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

13

Measurements of linear attenuation coefficients of irregular shaped samples by two media method  

NASA Astrophysics Data System (ADS)

The linear attenuation coefficient values of regular and irregular shaped flyash materials have been measured without knowing the thickness of a sample using a new technique namely "two media method". These values have also been measured with a standard gamma ray transmission method and obtained theoretically with winXCOM computer code. From the comparison it is reported that the two media method has given accurate results of attenuation coefficients of flyash materials.

Singh, Sukhpal; Kumar, Ashok; Thind, Kulwant Singh; Mudahar, Gurmel S.

2008-04-01

14

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

NASA Technical Reports Server (NTRS)

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

Generazio, E. R.

1984-01-01

15

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

Microsoft Academic Search

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

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

2004-01-01

16

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

17

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

18

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

PubMed

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

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

2012-07-01

19

Measurement of x-ray attenuation coefficients of aqueous solutions of indocyanine green and glycated chitosan  

E-print Network

and glycated chitosan Fang Xu and Hong Liua) Department of Radiology and Biomedical Engineering, University of a light absorbing dye, indocyanine green, and an immunoadjuvant, glycated chitosan. In the treatment results show that glycated chitosan has a higher attenuation coefficient compared to indocyanine green

Jiang, Hangyi

20

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

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

21

The attenuation coefficient of ammonium chloride for 662 keV gamma radiation, measured for dilute solutions  

NASA Astrophysics Data System (ADS)

The technique developed for the direct measurement of linear attenuation and mass attenuation (or absorption) coefficients of dilute solutions of salts has been applied to the attenuation of 662 keV gamma rays from 137Cs in dilute NH 4Cl solution.

Teli, M. T.; Chaudhari, L. M.

1996-04-01

22

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

NASA Astrophysics Data System (ADS)

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

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

2014-02-01

23

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. PMID:22312589

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

24

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

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

25

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

Microsoft Academic Search

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

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

2005-01-01

26

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

NASA Astrophysics Data System (ADS)

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

Rettschlag, M.; Berndt, R.; Mortreau, P.

2007-11-01

27

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

28

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

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

29

Attenuation coefficients of soils and some building materials of Bangladesh in the energy range 276-1332 keV.  

PubMed

The linear and mass attenuation coefficients of different types of soil, sand, building materials and heavy beach mineral samples from the Chittagong and Cox's Bazar area of Bangladesh were measured using a high-resolution HPGe detector and the gamma-ray energies 276.1, 302.8, 356.0, 383.8, 661.6 and 1173.2 and 1332.5 keV emitted from point sources of 133Ba, 137Cs and 60Co, respectively. The linear attenuation coefficients show a linear relationship with the corresponding densities of the samples studied. The variations of the mass attenuation coefficient with gamma-ray energy were exponential in nature. The measured mass attenuation coefficient values were compared with measurements made in other countries for similar kinds of materials. The values are in good agreement with each other in most cases. PMID:11300413

Alam, M N; Miah, M M; Chowdhury, M I; Kamal, M; Ghose, S; Rahman, R

2001-06-01

30

Parameterization of X-ray mass attenuation coefficients in the energy range of 1-150 keV  

Microsoft Academic Search

Knowledge of X-ray mass attenuation coefficients is necessary when the thick target PIXE method is applied for quantitative elemental analysis of materials. For this purpose, the X-ray mass attenuation coefficients of Veigele [Atom. Data Tables 5 (1973) 51] ave been parameterized in the photon energy range of 1-150 keV for all elements from hydrogen to plutonium (Z = 1-94), taking

J. Braziewicz; E. Braziewicz; M. Pajek

1993-01-01

31

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

Microsoft Academic Search

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

Menghua Wang; SeungHyun Son; Lawrence W. Harding Jr

2009-01-01

32

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

PubMed Central

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

2013-01-01

33

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

NASA Astrophysics Data System (ADS)

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

Kore, Prashant S.; Pawar, Pravina P.

2014-05-01

34

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

2010-04-01

35

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

PubMed

As banked human tissues are not widely available, the development of new non-destructive and contactless techniques to evaluate the quality of allografts before distribution for transplantation is very important. Also, tissues will be processed accordingly to standard procedures and to minimize disease transmission most tissue banks will include a decontamination or sterilization step such as ionizing radiation. In this work, we present a new method to evaluate the internal structure of frozen or glycerol processed human cartilages, submitted to various dosis of irradiation, using the total optical attenuation coefficient retrieved from optical coherence tomography (OCT) images. Our results show a close relationship between tensile properties and the total optical attenuation coefficient of cartilages. Therefore, OCT associated with the total optical attenuation coefficient open a new window to evaluate quantitatively biological changes in processed tissues. PMID:23887800

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

2014-09-01

36

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

PubMed

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

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

2015-05-01

37

The determination of the effective attenuation coefficient from effective organ depth and modulation transfer function in gamma camera imaging.  

PubMed

Absolute measurement of activity implies a determination of effective depths and effective attenuation coefficients. In order to define restoration filters, it is necessary to measure the transfer function, i.e. position a line source at an effective depth for the specific measurement situation. A phantom was designed which can simulate an organ with a certain thickness at a certain depth. The phantom was used to measure transfer functions and a comparison was made with transfer functions from a line source to determine effective depths. Effective attenuation coefficients were calculated for 99mTc, 111In and 201Tl for different organ thicknesses and depths of simulated organs. The effective attenuation coefficient for 99mTc was found to be 0.124 +/- 0.006 cm-1, in good agreement with previously published values. For 111In, the attenuation coefficient decreased with the depth of an organ due to the use of two energy windows in the measurements and a corresponding change in mean photon energy by depth. For 201Tl, the attenuation coefficient decreased with increasing organ thickness due to the increasing fraction of scattered radiation in the 40% energy window used. Using attenuation coefficients of 0.124, 0.184 and 0.11 cm-1 for 99mTc, 201Tl and 111In respectively, the derived equations can be used to calculate the position of a conventional line source for measurements of transfer functions for a specific organ with a certain thickness at a certain depth for definition of different types of restoration filter. PMID:9364591

Starck, S A; Carlsson, S

1997-10-01

38

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

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

39

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

2014-02-15

40

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

NASA Astrophysics Data System (ADS)

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

Kheireddine, Malika; Antoine, David

2014-08-01

41

Measurement of mass attenuation coefficients for YBaCuO superconductor at different energies  

NASA Astrophysics Data System (ADS)

The mass attenuation coefficients for Y2O3, BaCO3, CuO compounds, and solid-state forms of YBa2Cu3O7 superconductor were determined at energies of 57.5, 59.5, 65.2, 74.8, 77.1, 87.3, 94.6, 98.4, 122, and 136 keV. The samples were irradiated using a 241Am point source emitting 59.5 keV photon energies and a 57Co point source emitting 122 and 136 keV photon energies. The other energies were obtained using secondary targets such as Ta, Bi2O3, and (CH3COO)2UO22H2O. The gamma- and x-rays were counted by a Si(Li) detector with a resolution of 160 eV at 5.9 keV. Samples were selected on the basis of known composition and mass densities were measured using a densitometer. The experimental results obtained in this study are compared with theoretical values.

Çevik, U.; Baltas, H.; Çelik, S.; Karaca, I.; Kopya, I.

2005-01-01

42

Theoretical explanation of the relationship between backscattered electron and x-ray linear attenuation coefficients in calcified tissues.  

PubMed

X-ray absorption and backscattered electron (BSE) microscopies are two commonly used techniques for estimating mineral contents in calcified tissues. The resolution in BSE images is usually higher than in x-ray images, but due to the previous lack of good standards to quantify the grey levels in BSE images of bones and teeth, x-ray microtomography (XMT) images of the same specimens have been used for calibration. However, the physics of these two techniques is different: for a specimen with a given composition, the x-ray linear attenuation coefficient is proportional to density, but there is no such relation with the BSE coefficient. To understand the reason that this calibration appears to be valid, the behaviour of simulated bone samples was investigated. In this, the bone samples were modelled as having three phases: hydroxyapatite (Ca10(PO4)6(OH)2), protein, and void (either empty or completely filled with polymethylmethacrylate (PMMA), a resin which is usually used for embedding bones and teeth in microscopic studies). The x-ray linear attenuation coefficients (calculated using published data) and the BSE coefficients (calculated using Monte Carlo simulation) were compared for samples of various phase proportions. It was found that the BSE coefficient correlated only with the x-ray attenuation coefficient for samples with PMMA infiltration. This was attributed to the properties of PMMA (density and mean atomic number) being very similar to those of the protein; therefore, the sample behaves like a two-phase system which allows the establishment of a monotonic relation between density and BSE coefficient. With the newly developed standards (brominated and iodinated dimethacrylate esters) for BSE microscopy of bone, grey levels can be converted to absolute BSE coefficients by linear interpolation, from which equivalent densities can be determined. PMID:9418207

Wong, F S; Elliott, J C

1997-11-01

43

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.

2010-04-01

44

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

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

45

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

NASA Technical Reports Server (NTRS)

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

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

1981-01-01

46

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

NASA Astrophysics Data System (ADS)

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

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

2006-11-01

47

Exploring mediated reality to approximate x-ray attenuation coefficients from radiographs  

NASA Astrophysics Data System (ADS)

Estimation of the x-ray attenuation properties of an object with respect to the energy emitted from the source is a challenging task for traditional Bremsstrahlung sources. This exploratory work attempts to estimate the x-ray attenuation profile for the energy range of a given Bremsstrahlung profile. Previous work has shown that calculating a single effective attenuation value for a polychromatic source is not accurate due to the non-linearities associated with the image formation process. Instead, we completely characterize the imaging system virtually and utilize an iterative search method/constrained optimization technique to approximate the attenuation profile of the object of interest. This work presents preliminary results from various approaches that were investigated. The early results illustrate the challenges associated with these techniques and the potential for obtaining an accurate estimate of the attenuation profile for objects composed of homogeneous materials.

Jimenez, Edward S.; Orr, Laurel J.; Morgan, Megan L.; Thompson, Kyle R.

2014-09-01

48

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

PubMed

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

Trunova, Valentina; Sidorina, Anna; Kriventsov, Vladimir

2014-10-17

49

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

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

50

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

51

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

NASA Astrophysics Data System (ADS)

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

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

2011-01-01

52

The effective attenuation coefficient of soft tissue in the presence of Compton scattering from bone: experiments on models.  

PubMed

Calibration methods are investigated for the determination of bone density by the Compton scattering method. The scattered radiation from materials of different densities and dimensions is measured for this purpose. A function for the dependence of the intensity on these parameters is derived and compared with the experimental results. The influence of the surrounding soft tissue is studied by simulation experiments with water. It is found that the 'effective attenuation coefficient' of water for the incident and scattered radiation depends on the thickness of the surrounding water layer itself, as well as on the density of the scattering material. The implications of these findings for the evaluation of bone density measurements are discussed. PMID:7454760

Leichter, I; Weinreb, A; Hazan, G

1980-07-01

53

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

NASA Astrophysics Data System (ADS)

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

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

2010-02-01

54

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

PubMed Central

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

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

2010-01-01

55

Optical coherence tomography can assess skeletal muscle tissue from mouse models of muscular dystrophy by parametric imaging of the attenuation coefficient  

PubMed Central

We present the assessment of ex vivo mouse muscle tissue by quantitative parametric imaging of the near-infrared attenuation coefficient µt using optical coherence tomography. The resulting values of the local total attenuation coefficient µt (mean ± standard error) from necrotic lesions in the dystrophic skeletal muscle tissue of mdx mice are higher (9.6 ± 0.3 mm?1) than regions from the same tissue containing only necrotic myofibers (7.0 ± 0.6 mm?1), and significantly higher than values from intact myofibers, whether from an adjacent region of the same sample (4.8 ± 0.3 mm?1) or from healthy tissue of the wild-type C57 mouse (3.9 ± 0.2 mm?1) used as a control. Our results suggest that the attenuation coefficient could be used as a quantitative means to identify necrotic lesions and assess skeletal muscle tissue in mouse models of human Duchenne muscular dystrophy. PMID:24761302

Klyen, Blake R.; Scolaro, Loretta; Shavlakadze, Tea; Grounds, Miranda D.; Sampson, David D.

2014-01-01

56

Determination of Linear X-Ray Attenuation Coefficients of Pathological Brain Tissues and Use of Filters in Tissue Contrast Enhancement in Computed Tomography  

PubMed Central

Objective: X-ray attenuation coefficients are used in common radiological, pathological and spectroscopic examinations and in the determination of the radiation dose distribution in biological tissues. In radiology, these coefficients enable diagnosis by differentiating the abnormal tissues from the normal ones using their morphological structure and contrast differences. In this study, our aim is to precisely determine the linear x-ray attenuation coefficients of pathological brain tissues and to use x-ray beam filters to enhance the tissue contrast in computed tomography. Materials and Methods: To directly measure the relative linear attenuation coefficients, an energy dispersive x-ray spectroscopy system (EDXRS-Canberra, Si(Li) with DSA-1000 spectrum analyzer 1998; CT, USA) was used with collimators and a medical-purpose x-ray tube (Siemens, Siremobil, 1985; Erlangen, Germany) in a linear geometry. Results: Using a Mo filter with Computed Tomography CT and photon energies from 15 to 25 keV, EDXRS acquisitions were found to significantly distinguish grades of brain tumors (p<0.05). For the data acquired from CT systems with the decreasing filtered photon mean energy, the x-ray attenuation coefficients (i.e., the Hounsfield units) show that the ratio of EDXRS to CT for water’s attenuation coefficient are increased. With our suggested x-ray filters, the tissue contrast has been found to be increased in ex vivo brain tumor slices compared with slices scanned in conventional CT scanners. Conclusion: X-ray attenuations measured with the EDXRS are found to be statistically more reliable because of the length of acquisition times in this study.

Sagsoz, M. Erdem; Erdogan, Fazl?; Erzeneoglu, Salih Z.; Yuce, ?hsan

2010-01-01

57

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

58

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

2013-10-01

59

Towards a quantitative, measurement-based estimate of the uncertainty in photon mass attenuation coefficients at radiation therapy energies.  

PubMed

In this study, a quantitative estimate is derived for the uncertainty in the XCOM photon mass attenuation coefficients in the energy range of interest to external beam radiation therapy-i.e. 100 keV (orthovoltage) to 25 MeV-using direct comparisons of experimental data against Monte Carlo models and theoretical XCOM data. Two independent datasets are used. The first dataset is from our recent transmission measurements and the corresponding EGSnrc calculations (Ali et al 2012 Med. Phys. 39 5990-6003) for 10-30 MV photon beams from the research linac at the National Research Council Canada. The attenuators are graphite and lead, with a total of 140 data points and an experimental uncertainty of ?0.5% (k = 1). An optimum energy-independent cross section scaling factor that minimizes the discrepancies between measurements and calculations is used to deduce cross section uncertainty. The second dataset is from the aggregate of cross section measurements in the literature for graphite and lead (49 experiments, 288 data points). The dataset is compared to the sum of the XCOM data plus the IAEA photonuclear data. Again, an optimum energy-independent cross section scaling factor is used to deduce the cross section uncertainty. Using the average result from the two datasets, the energy-independent cross section uncertainty estimate is 0.5% (68% confidence) and 0.7% (95% confidence). The potential for energy-dependent errors is discussed. Photon cross section uncertainty is shown to be smaller than the current qualitative 'envelope of uncertainty' of the order of 1-2%, as given by Hubbell (1999 Phys. Med. Biol 44 R1-22). PMID:25622289

Ali, E S M; Spencer, B; McEwen, M R; Rogers, D W O

2015-02-21

60

Towards a quantitative, measurement-based estimate of the uncertainty in photon mass attenuation coefficients at radiation therapy energies  

NASA Astrophysics Data System (ADS)

In this study, a quantitative estimate is derived for the uncertainty in the XCOM photon mass attenuation coefficients in the energy range of interest to external beam radiation therapy—i.e. 100 keV (orthovoltage) to 25 MeV—using direct comparisons of experimental data against Monte Carlo models and theoretical XCOM data. Two independent datasets are used. The first dataset is from our recent transmission measurements and the corresponding EGSnrc calculations (Ali et al 2012 Med. Phys. 39 5990–6003) for 10–30 MV photon beams from the research linac at the National Research Council Canada. The attenuators are graphite and lead, with a total of 140 data points and an experimental uncertainty of ?0.5% (k = 1). An optimum energy-independent cross section scaling factor that minimizes the discrepancies between measurements and calculations is used to deduce cross section uncertainty. The second dataset is from the aggregate of cross section measurements in the literature for graphite and lead (49 experiments, 288 data points). The dataset is compared to the sum of the XCOM data plus the IAEA photonuclear data. Again, an optimum energy-independent cross section scaling factor is used to deduce the cross section uncertainty. Using the average result from the two datasets, the energy-independent cross section uncertainty estimate is 0.5% (68% confidence) and 0.7% (95% confidence). The potential for energy-dependent errors is discussed. Photon cross section uncertainty is shown to be smaller than the current qualitative ‘envelope of uncertainty’ of the order of 1–2%, as given by Hubbell (1999 Phys. Med. Biol 44 R1–22).

Ali, E. S. M.; Spencer, B.; McEwen, M. R.; Rogers, D. W. O.

2015-02-01

61

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

PubMed

Gamma-ray transmission methods have been used accurately for the study of the properties of soil in the agricultural purposes. In this study, photon attenuation coefficient, porosity and field capacity of soil are determined by using gamma-ray transmission method. To this end, the soil sample was collected from Erzurum and a 2 x 2 in NaI (Tl) scintillation detector measured the attenuation of strongly collimated monoenergetic gamma beam through soil sample. The radioactive sources used in the experiment were (241)Am, (133)Ba and (137)Cs. The mass attenuation coefficients of dry soil samples were calculated from the transmission measurements. The soil samples were irrigated by adding known quantities of water and the soil-water properties were examined. It was observed that gamma-ray transmission method for determination of the soil parameters has advantages such as practical, inexpensive, non-destructive and fast analysis. PMID:18554919

Demir, D; Un, A; Ozgül, M; Sahin, Y

2008-12-01

62

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

NASA Astrophysics Data System (ADS)

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

Sokoletsky, Leonid; Yang, Xianping; Shen, Fang

2014-11-01

63

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

PubMed Central

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

Okunade, Akintunde A.

2007-01-01

64

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

65

Estimate of the attenuation coefficient using a clinical array transducer for the detection of cervical ripening in human pregnancy  

E-print Network

of cervical ripening in human pregnancy Yassin Labyed a,*, Timothy A. Bigelow a , Barbara L. McFarlin b online 19 May 2010 Keywords: Quantitative ultrasound Attenuation estimation Cervical ripening a b s t r to diagnose symptoms prior to uterine contractions. Cervical ripening is a long period that precedes

Illinois at Urbana-Champaign, University of

66

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

67

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

NASA Astrophysics Data System (ADS)

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

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

2012-10-01

68

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

69

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

NASA Astrophysics Data System (ADS)

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

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

2001-08-01

70

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

NASA Astrophysics Data System (ADS)

The total mass attenuation coefficients for elements Cr, Co and Fe and compounds CrCl_{2}, CrCl_{3}, Cr_{2}(SO_{4})_{3}K_{2}SO_{4}\\cdot24H_{2}O, CoO, CoCl_{2}, Co(CH_{3}COO)_{2}, FePO_{4}, FeCl_{3}\\cdot6H_{2}O, Fe(SO_{4})_{2}NH_{4}\\cdot12H_{2}O were measured at different energies between 4.508 and 14.142 keV using secondary excitation method. Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Br, Rb, Sr were chosen as secondary exciters. 59.5 keV ?-rays emitted from a ^{241}Am annular source were used to excite a secondary exciter and K_{?}(K-L_{3}, L_{2}) lines emitted by the secondary exciter were counted by a Si(Li) detector with a resolution of 160 eV at 5.9 keV. It was observed that mixture rule method is not a suitable method for determination of the mass attenuation coefficients of compounds, especially at an energy that is near the absorption edge. The obtained values were compared with theoretical values.

Turgut, U.; Simsek, O.; Büyükkasap, E.

2007-08-01

71

Loss of the lac Operon Contributes to Salmonella Invasion of Epithelial Cells Through Derepression of Flagellar Synthesis.  

PubMed

Salmonella, a genus that is closely related to Escherichia coli, includes many pathogens of humans and other animals. A notable feature that distinguishes Salmonella from E. coli is lactose negativity, because the lac operon is lost in most Salmonella genomes. Here, we expressed the lac operon in Salmonella enterica serovar Typhimurium and compared the virulence of the Lac(+) strain to that of the wild-type strain in a murine model, invasion assays, and macrophage replication assays. We showed that the Lac(+) strain is attenuated in vivo and the attenuation of virulence is caused by its defect in epithelial cell invasion. However, the invasion-defective phenotype is unrelated to lactose utilization. Through sequencing and the comparison of the transcriptome profile between the Lac(+) and wild-type strains during invasion, we found that most flagellar genes were markedly downregulated in the Lac(+) strain, while other genes associated with invasion, such as the majority of genes encoded in Salmonella pathogenicity island 1, were not differentially expressed. Moreover, we discovered that lacA is the major repressor of flagellar gene expression in the lac operon. In conclusion, these data demonstrate that the lac operon decreases Salmonella invasion of epithelial cells through repression of flagellar biosynthesis. As the ability to invade epithelial cells is a critical virulence determinant of Salmonella, our results provide important evidence that the loss of the lac operon contributes to the evolution of Salmonella pathogenicity. PMID:25362512

Jiang, Lingyan; Ni, Zhiwei; Wang, Lei; Feng, Lu; Liu, Bin

2015-03-01

72

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

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

73

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

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- 66 keV were produced by X-ray fluorescence using a secondary target system, and 140 keV gamma rays were obtained from an unsealed 99 mTc 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

74

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

PubMed

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

Simon, Arthi; Shanmugam, Palanisamy

2013-12-01

75

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

76

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

2013-01-01

77

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

SciTech Connect

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

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

2010-02-15

78

JOURNAL DE PHYSIQUE Colloque C4, supplkment au no 10, Tome 32, Octobre 1971, page C4-21 ATTENUATION COEFFICIENTS OF GASES FOR 4.5 TO 145 keV PHOTONS(*)  

E-print Network

beam mass attenuation coefficient pip, with units of cm2/g is defined by the relation where I of 30 torr to 3 600 torr were used. The solid angle subtended by the detector at the source varied intervals between the source and the detector to minimize scattering from the walls of the pipe and from

Paris-Sud XI, Université de

79

Comparative analysis of radiative transfer approaches for calculation of plane transmittance and diffuse attenuation coefficient of plane-parallel light scattering layers.  

PubMed

We present an analysis of a number of different approximations for the plane transmittance Tp and diffuse attenuation coefficient Kd of a semi-infinite, unbounded, plane-parallel, and optically homogeneous layer. The maximally wide optical conditions (from the full absorption to the full scattering and from the fully forward to the fully backward scattering) were considered. The approximations were analyzed from the point of view of their physical limitations and closeness to the numerical solution of the radiative transfer equation for the plane transmittance. The main criterion for inclusion of the models for analysis was the possibility of practical use, i.e., approximations were well parameterized and included only easily measured or estimated parameters. A detailed analysis of errors for different Tp and Kd models showed that the two-stream radiative transfer Ben-David model yields the best results over all optical conditions and depths. However, the quasi-single-scattering and polynomial Gordon's approximations proved to be the best for the depths close to zero. PMID:24514134

Sokoletsky, Leonid G; Budak, Vladimir P; Shen, Fang; Kokhanovsky, Alexander A

2014-01-20

80

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 Tm 2O 3, Yb 2O 3 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

81

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

NASA Astrophysics Data System (ADS)

The mass attenuation coefficients for Bi, Pb, Sr, Ca, Cu metals, Bi 2O 3, PbO, SrCO 3, CaO, CuO compounds and solid-state forms of Bi 1.7Pb 0.3Sr 2Ca 2Cu 3O 10 superconductor were determined at 57.5, 65.2, 77.1, 87.3, 94.6, 122 and 136 keV energies. The samples were irradiated using a 57Co point source emitted 122 and 136 keV ?-ray energies. The X-ray energies were obtained using secondary targets such as Ta, Bi 2O 3 and (CH 3COO) 2UO 22H 2O. The ?- and X-rays were counted by a Si(Li) detector with a resolution of 0.16 keV at 5.9 keV. The effect of absorption edges on electron density, effective atomic numbers and their variation with photon energy in composite superconductor samples was discussed. Obtained values were compared with theoretical values.

Çevik, U.; Balta?, H.

2007-03-01

82

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  

NASA Astrophysics Data System (ADS)

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 for these chosen materials ( ?/ ?) remains constant in good agreement with the theoretical values up to 3 mean free paths and after that ( ?/ ?) values for Cu, Pb and Hg decrease with further increase in the absorber thickness. This result may be attributed to the increase in the number of coherent small-angle scattering photons which reach the detector.

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

2000-06-01

83

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

SciTech Connect

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

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

2007-01-01

84

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

PubMed

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

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

2012-04-01

85

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

PubMed Central

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

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

2013-01-01

86

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

SciTech Connect

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

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

2013-12-15

87

The Coronae of AR Lac  

E-print Network

We observed the coronally active eclipsing binary, AR Lac, with the High Energy Transmission Grating on Chandra for a total of 97 ks, spaced over five orbits, at quadratures and conjunctions. Contemporaneous and simultaneous EUV spectra and photometry were also obtained with the Extreme Ultraviolet Explorer. Significant variability in both X-ray and EUV fluxes were observed, dominated by at least one X-ray flare and one EUV flare. We saw no evidence of primary or secondary eclipses. X-ray flux modulation was largest at high temperature, indicative of flare heating of coronal plasma. Line widths interpreted in terms of Doppler broadening suggest that both binary stellar components are active. From line fluxes obtained from total integrated spectra, we have modeled the emission measure and abundance distributions. A strong maximum was found in the differential emission measure, characterized by peaks at log T = 6.9 and 7.4, together with a weak but significant cooler maximum near log T=6.2, and a moderately strong hot tail from log T= 7.6-8.2. Coronal abundances have a broad distribution and show no simple correlation with first ionization potential. While the resulting model spectrum generally agrees very well with the observed spectrum, there are some significant discrepancies, especially among the many Fe L-lines. Both the emission measure and abundance distributions are qualitatively similar to prior determinations from other X-ray and ultraviolet spectra, indicating some long-term stability in the overall coronal structure.

David P. Huenemoerder; Claude R. Canizares; Jeremy J. Drake; Jorge Sanz-Forcada

2003-06-18

88

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

89

Bl Lac Population Study at High Energies  

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

90

Sound Attenuation in Magnetic Metals  

Microsoft Academic Search

The anomalous sound attenuation due to spin fluctuations near the magnetic phase transition temperatures in itinerant magnets and the rare earth metals is theoretically studied. By applying Tsuneto and Kadanoff and Falko's formulas, the attenuation coefficient is calculated. The calculated results explain the critical anomalies observed in magnetic metals such as Ni and Gd. By comparing the results with that

Sadamichi Maekawa; Masashi Tachiki

1977-01-01

91

Ultrasonic attenuation in pearlitic steel.  

PubMed

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

Du, Hualong; Turner, Joseph A

2014-03-01

92

Folding LacZ in the periplasm of Escherichia coli.  

PubMed

Targeted, translational LacZ fusions provided the initial support for the signal sequence hypothesis in prokaryotes and allowed for selection of the mutations that identified the Sec translocon. Many of these selections relied on the fact that expression of targeted, translational lacZ fusions like malE-lacZ and lamB-lacZ42-1 causes lethal toxicity as folded LacZ jams the translocation pore. However, there is another class of targeted LacZ fusions that do not jam the translocon. These targeted, nonjamming fusions also show toxic phenotypes that may be useful for selecting mutations in genes involved in posttranslocational protein folding and targeting; however, they have not been investigated to the same extent as their jamming counterparts. In fact, it is still unclear whether LacZ can be fully translocated in these fusions. It may be that they simply partition into the inner membrane where they can no longer participate in folding or assembly. In the present study, we systematically characterize the nonjamming fusions and determine their ultimate localization. We report that LacZ can be fully translocated into the periplasm, where it is toxic. We show that this toxicity is likely due to LacZ misfolding and that, in the absence of the periplasmic disulfide bond catalyst DsbA, LacZ folds in the periplasm. Using the novel phenotype of periplasmic ?-galactosidase activity, we show that the periplasmic chaperone FkpA contributes to LacZ folding in this nonnative compartment. We propose that targeted, nonjamming LacZ fusions may be used to further study folding and targeting in the periplasm of Escherichia coli. PMID:25002543

Dwyer, Robert S; Malinverni, Juliana C; Boyd, Dana; Beckwith, Jon; Silhavy, Thomas J

2014-09-01

93

Au Chalet du LacAu Chalet du Lac Samedi 23 septembre 1995  

E-print Network

dans le bois de Vincennes, au Chalet du Lac de Saint- Mandé, un dancing à l'ancienne, avec parquet ciré foulard bariolé, un arbre à planter avant la Sainte-Catherine. Il y eut même de la musique... et Colette

Paris-Sud XI, Université de

94

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

95

Evidence that selected amplification of a bacterial lac frameshift allele stimulates Lac(+) reversion (adaptive mutation) with or without general hypermutability.  

PubMed Central

In the genetic system of Cairns and Foster, a nongrowing population of an E. coli lac frameshift mutant appears to specifically accumulate Lac(+) revertants when starved on medium including lactose (adaptive mutation). This behavior has been attributed to stress-induced general mutagenesis in a subpopulation of starved cells (the hypermutable state model). We have suggested that, on the contrary, stress has no direct effect on mutability but favors only growth of cells that amplify their leaky mutant lac region (the amplification mutagenesis model). Selection enhances reversion primarily by increasing the mutant lac copy number within each developing clone on the selection plate. The observed general mutagenesis is attributed to a side effect of growth with an amplification-induction of SOS by DNA fragments released from a tandem array of lac copies. Here we show that the S. enterica version of the Cairns system shows SOS-dependent general mutagenesis and behaves in every way like the original E. coli system. In both systems, lac revertants are mutagenized during selection. Eliminating the 35-fold increase in mutation rate reduces revertant number only 2- to 4-fold. This discrepancy is due to continued growth of amplification cells until some clones manage to revert without mutagenesis solely by increasing their lac copy number. Reversion in the absence of mutagenesis is still dependent on RecA function, as expected if it depends on lac amplification (a recombination-dependent process). These observations support the amplification mutagenesis model. PMID:12136002

Slechta, E Susan; Liu, Jing; Andersson, Dan I; Roth, John R

2002-01-01

96

The physical properties of Fermi BL Lac objects jets  

NASA Astrophysics Data System (ADS)

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

Yan, Dahai; Zeng, Houdun; Zhang, Li

2014-04-01

97

Natural LacI from E. coli Yields Faster Response and Higher Level of Expression than the LVA-Tagged LacI.  

PubMed

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

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

2014-12-19

98

The lac operon of Lactobacillus casei contains lacT, a gene coding for a protein of the Bg1G family of transcriptional antiterminators.  

PubMed

The 5' region of the lac operon of Lactobacillus casei has been investigated. An open reading frame of 293 codons, designated lacT, was identified upstream of lacE. The gene product encoded by lacT is related to the family of transcriptional antiterminator proteins, which includes BglG from Escherichia coli, ArbG from Erwinia chrysanthemi, SacT, SacY, and LicT from Bacillus subtilis, and BglR from Lactococcus lactis. Amino acid sequence identities range from 35 to 24%, while similarities range from 56 to 47%. The transcriptional start site of the lac operon was identified upstream of lacT. The corresponding mRNA would contain in the 5' region a sequence with high similarity to the consensus RNA binding site of transcriptional antiterminators overlapping a sequence capable of folding into a structure that resembles a rho-independent terminator. LacT was shown to be active as an antiterminator in a B. subtilis test system using the sacB target sequence. lacT directly precedes lacEGF, the genes coding for enzyme IICB, phospho-beta-galactosidase, and enzyme IIA, and these genes are followed by a sequence that appears to encode a second rho-independent transcription terminator-like structure. Northern hybridizations with probes against lacT, lacE, and lacF revealed transcripts of similar sizes for the lac mRNAs of several L. casei strains. Since the length of the lac mRNA is just sufficient to contain lacTEGF, we conclude that the lac operon of L. casei does not contain the genes of the accessory tagatose-6-phosphate pathway as occurs in the lac operons of Lactococcus lactis, Streptococcus mutans, or Staphylococcus aureus. PMID:9045813

Alpert, C A; Siebers, U

1997-03-01

99

The lac operon of Lactobacillus casei contains lacT, a gene coding for a protein of the Bg1G family of transcriptional antiterminators.  

PubMed Central

The 5' region of the lac operon of Lactobacillus casei has been investigated. An open reading frame of 293 codons, designated lacT, was identified upstream of lacE. The gene product encoded by lacT is related to the family of transcriptional antiterminator proteins, which includes BglG from Escherichia coli, ArbG from Erwinia chrysanthemi, SacT, SacY, and LicT from Bacillus subtilis, and BglR from Lactococcus lactis. Amino acid sequence identities range from 35 to 24%, while similarities range from 56 to 47%. The transcriptional start site of the lac operon was identified upstream of lacT. The corresponding mRNA would contain in the 5' region a sequence with high similarity to the consensus RNA binding site of transcriptional antiterminators overlapping a sequence capable of folding into a structure that resembles a rho-independent terminator. LacT was shown to be active as an antiterminator in a B. subtilis test system using the sacB target sequence. lacT directly precedes lacEGF, the genes coding for enzyme IICB, phospho-beta-galactosidase, and enzyme IIA, and these genes are followed by a sequence that appears to encode a second rho-independent transcription terminator-like structure. Northern hybridizations with probes against lacT, lacE, and lacF revealed transcripts of similar sizes for the lac mRNAs of several L. casei strains. Since the length of the lac mRNA is just sufficient to contain lacTEGF, we conclude that the lac operon of L. casei does not contain the genes of the accessory tagatose-6-phosphate pathway as occurs in the lac operons of Lactococcus lactis, Streptococcus mutans, or Staphylococcus aureus. PMID:9045813

Alpert, C A; Siebers, U

1997-01-01

100

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

101

Computational Data Analysis and Simulation in Cosmology: The LAC Experience  

E-print Network

FÍSICA COMPUTACIONAL E COMPUTA��O CIENTÍFICA Laboratório Associado de Computação e Matemática Aplicada@lac.inpe.br / reinaldo.rosa@pq.cnpq.br #12;1. Escopo da Cosmologia Computacional Observação FÍSICA COMPUTACIONAL E COMPUTA��O CIENTÍFICA - LAC Computação Aplicada ao Estudo da Formação de Padrões

102

Generating attenuation maps using differential attenuation data  

Microsoft Academic Search

A method is proposed to estimate attenuation from differential attenuation information (DAI) contained solely in SPECT emission data produced by 201Tl or other multiple emission isotopes. The total attenuation along each projection line is shown to be related to the difference in attenuation for two emissions at distinct energies (low energy gamma rays are attenuated more than high energy gamma

M. S. Kaplan; D. R. Haynor; R. S. Miyaoka; T. K. Lewellen

1996-01-01

103

Attenuation of \\  

Microsoft Academic Search

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

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

1975-01-01

104

Characterization of growth and enzymes produced by prt+lac+ and prt-lac- Lactococcus lactis cells  

Microsoft Academic Search

Lactococcus lactis subsp.cremoris strains KH (prt+lac+) and KHA (prt?lac?) are used as starter cultures in manufacture of ripened cheeses. The growth characteristics and the dipeptidases produced\\u000a by these cells have been investigated in this study. A new semisynthetic medium was developed for growth of the cells. Growth\\u000a on this medium was as good as or better than that on milk,

Joong Kim; Rakesh Bajpai; Robert T. Marshall

1993-01-01

105

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

106

Attenuation correction for the NIH ATLAS small animal PET scanner  

Microsoft Academic Search

We evaluated an analytic attenuation correction method for the National Institutes of Health (NIH) Advanced Technology Laboratory Animal Scanner (ATLAS) small animal positron emission tomography (PET) scanner. This method is based on the body outline of emission images and an average empirical ? (linear attenuation coefficient) value. We evaluated this method using a computed tomography (CT)-based attenuation correction (ACs) as

Rutao Yao; Jürgen Seidel; Jeih-San Liow; Michael V. Green

2005-01-01

107

VLBI observations of seven BL Lac objects from RGB sample  

E-print Network

We present EVN observations of seven BL Lac objects selected from the RGB sample. To investigate the intrinsic radiation property of BL Lac objects, we estimated the Doppler factor with the VLA or MERLIN core and the total 408 MHz luminosity for a sample of 170 BL Lac objects. The intrinsic (comoving) synchrotron peak frequency was then calculated by using the estimated Doppler factor. Assuming a Lorentz factor of 5, the viewing angle of jets was constrained. The high-resolution VLBI images of seven sources all show a core-jet structure. We estimated the proper motions of three sources with the VLBI archive data, and find that the apparent speed increases with the distance of components to the core for all of them. In our BL Lacs sample, the Doppler factor of LBLs is systematically larger than that of IBLs and HBLs. We find a significant anti-correlation between the total 408 MHz luminosity and the intrinsic synchrotron peak frequency. However, the scatter is much larger than for the blazar sequence. Moreover, we find a significant positive correlation between the viewing angle and the intrinsic synchrotron peak frequency. The BL Lac objects show a continuous distribution on the viewing angle. While LBLs have a smaller viewing angle than that of IBLs and HBLs, IBLs are comparable to HBLs. We conclude that the intrinsic synchrotron peak frequency is not only related to the intrinsic radio power (though with a large scatter), but also to the viewing angle for the present sample.

Zhongzu Wu; D. R. Jiang; Minfeng Gu; Yi Liu

2007-06-01

108

X-ray emission computed tomography with attenuation correction for ICF research  

NASA Astrophysics Data System (ADS)

An attenuation correction method was proposed for laser-produced plasma emission computed tomography (ECT), which is based on relation of attenuation coefficient and emission coefficient in plasma. Simulation results show that the reconstructed images are dramatically improved in comparison to reconstructions without attenuation correction.

Chen, Yen-Wei

1996-05-01

109

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

PubMed Central

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

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

2013-01-01

110

LUNSORT list of lunar orbiter data by LAC area  

NASA Technical Reports Server (NTRS)

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

Hixon, S.

1976-01-01

111

Properties of optically selected BL Lac candidates from the SDSS  

E-print Network

\\textbf{Context.} Deep optical surveys open the avenue for find large numbers of BL Lac objects that are hard to identify because they lack the unique properties classifying them as such. While radio or X-ray surveys typically reveal dozens of sources, recent compilations based on optical criteria alone have increased the number of BL Lac candidates considerably. However, these compilations are subject to biases and may contain a substantial number of contaminating sources. \\textbf{Aims.} In this paper we extend our analysis of 182 optically selected BL Lac object candidates from the SDSS with respect to an earlier study. The main goal is to determine the number of bona fide BL Lac objects in this sample. \\textbf{Methods.} We examine their variability characteristics, determine their broad-band radio-UV SEDs, and search for the presence of a host galaxy. In addition we present new optical spectra for 27 targets with improved S/N with respect to the SDSS spectra. \\textbf{Results.} At least 59% of our targets h...

Kügler, S D; Heidt, J; Esser, J; Schultz, T

2014-01-01

112

Mechanism of negative thermal expansion in LaC2 from first-principles prediction  

NASA Astrophysics Data System (ADS)

Based on density functional theory and quasiharmonic approximation, the coefficients of thermal expansion (CTE) and negative thermal expansion (NTE) mechanism of tetragonal LaC2 are studied. Numerical results show that there is an obvious NTE parallel to c-axis, and the CTE is approximately ?c = - 1.67 ×10-6K-1, which coincides with the experimental data - 1.0 ×10-6K-1. In particular, a tiny NTE phenomenon along a-axis below 10 K has been predicted. The vibrational modes Eu and Eg at ? (0 , 0 , 0), and other three modes at M (0.5 , 0.5 , 0) and Z (0 , 0 , 0.5), give rise to negative Grüneisen parameters and therefore contribute to the NTE along a- and c-axis. Additionally, the bulk CTE was calculated to be positive, our CTE values and temperature intervals agree well with the presented experiments.

Liu, Yaming; Jia, Yu; Sun, Qiang; Liang, Erjun

2015-01-01

113

Light attenuation characteristics of glacially-fed lakes  

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

114

Wind Resource Assessment Report: Mille Lacs Indian Reservation, Minnesota  

SciTech Connect

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

Jimenez, A. C.

2013-12-01

115

Radio and Gamma-ray emission in nearby BL Lacs  

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

116

Structure of sugar-bound LacY  

PubMed Central

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

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

2014-01-01

117

Electromagnetic Attenuation by Solid Particle Aerosols  

Microsoft Academic Search

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

Erica Ray Petersen

1991-01-01

118

Pressure surge attenuator  

DOEpatents

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

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

1985-01-01

119

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

NASA Astrophysics Data System (ADS)

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

Gardner, Emma; Done, Chris

2014-02-01

120

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

121

Tracer attenuation in groundwater  

NASA Astrophysics Data System (ADS)

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

Cvetkovic, Vladimir

2011-12-01

122

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

PubMed Central

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

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

2014-01-01

123

Thermal Conductivity and Element Fractionation in EV Lac  

NASA Astrophysics Data System (ADS)

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

Laming, J. Martin; Hwang, Una

2009-12-01

124

An SPM8-based Approach for Attenuation Correction Combining Segmentation and Non-rigid Template Formation: Application to Simultaneous PET/MR Brain Imaging  

PubMed Central

We present an approach for head MR-based attenuation correction (MR-AC) based on the Statistical Parametric Mapping (SPM8) software that combines segmentation- and atlas-based features to provide a robust technique to generate attenuation maps (µ-maps) from MR data in integrated PET/MR scanners. Methods Coregistered anatomical MR and CT images acquired in 15 glioblastoma subjects were used to generate the templates. The MR images from these subjects were first segmented into 6 tissue classes (gray and white matter, cerebro-spinal fluid, bone and soft tissue, and air), which were then non-rigidly coregistered using a diffeomorphic approach. A similar procedure was used to coregister the anatomical MR data for a new subject to the template. Finally, the CT-like images obtained by applying the inverse transformations were converted to linear attenuation coefficients (LACs) to be used for AC of PET data. The method was validated on sixteen new subjects with brain tumors (N=12) or mild cognitive impairment (N=4) who underwent CT and PET/MR scans. The µ-maps and corresponding reconstructed PET images were compared to those obtained using the gold standard CT-based approach and the Dixon-based method available on the Siemens Biograph mMR scanner. Relative change (RC) images were generated in each case and voxel- and region of interest (ROI)-based analyses were performed. Results The leave-one-out cross-validation analysis of the data from the 15 atlas-generation subjects showed small errors in brain LACs (RC=1.38%±4.52%) compared to the gold standard. Similar results (RC=1.86±4.06%) were obtained from the analysis of the atlas-validation datasets. The voxel- and ROI-based analysis of the corresponding reconstructed PET images revealed quantification errors of 3.87±5.0% and 2.74±2.28%, respectively. The Dixon-based method performed substantially worse (the mean RC values were 13.0±10.25% and 9.38±4.97%, respectively). Areas closer to skull showed the largest improvement. Conclusion We have presented an SPM8-based approach for deriving the head µ-map from MR data to be used for PET AC in integrated PET/MR scanners. Its implementation is straightforward and only requires the morphological data acquired with a single MR sequence. The method is very accurate and robust, combining the strengths of both segmentation- and atlas-based approaches while minimizing their drawbacks. PMID:25278515

Izquierdo-Garcia, David; Hansen, Adam E.; Förster, Stefan; Benoit, Didier; Schachoff, Sylvia; Fürst, Sebastian; Chen, Kevin T.; Chonde, Daniel B.; Catana, Ciprian

2014-01-01

125

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

PubMed Central

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

2014-01-01

126

Yellowstone Attenuation Tomography from Ambient Seismic Noise  

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

127

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

E-print Network

1 Les méandres du développement agricole au Lac Alaotra, Madagascar Entre inconstance politique et, principal grenier à riz de Madagascar, région à forte immigration et zone de prédilection de l'aide publique, innovation, Lac Alaotra, Madagascar Summary The animated history of the evolution of agriculture of the Lake

Paris-Sud XI, Université de

128

Structural and Enzymatic characterization of the lactonase SisLac from Sulfolobus islandicus  

PubMed Central

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

Chabriere, Eric; Elias, Mikael

2012-01-01

129

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

130

Controlling intermolecular spin interactions of La@C(82) in empty fullerene matrices.  

PubMed

The ESR properties and crystal structures of solid-state La@C(82) in empty fullerene matrices were investigated by changing the concentration of La@C(82) and the species of an empty fullerene matrix: C(60), C(70), C(78)(C(2v)(3)), C(82)(C(2)) and C(84)(D(2d)(4)). The rotational correlation time of La@C(82) molecules tended to be shorter when La@C(82) is dispersed in larger fullerene matrices because large C(2n) molecules provide more space for La@C(82) molecules for rotating. La@C(82) dispersed in a hcp-C(82) matrix showed the narrowest hyperfine structure (hfs) due to the ordered nature of La@C(82) molecules in the C(82) crystal. On the other hand, in a C(60) matrix, La@C(82) molecules formed clusters because of the large different solubility, which leads to the ESR spectra being broad sloping features due to strong dipole-dipole and exchange interactions. PMID:20126778

Ito, Yasuhiro; Warner, Jamie H; Brown, Richard; Zaka, Mujtaba; Pfeiffer, Rudolf; Aono, Takayuki; Izumi, Noriko; Okimoto, Haruya; Morton, John J L; Ardavan, Arzhang; Shinohara, Hisanori; Kuzmany, Hans; Peterlik, Herwig; Briggs, G Andrew D

2010-02-21

131

The lac Operon Section of DNA that acts as an ON/OFF  

E-print Network

feedback mechanism. Their model assumed · transcription/translation require 1 time unit · m binds to initiate transcription of the lac genes. The lac Operon Section of DNA that acts as an ON to the promoter. Transcription of the 3 structural genes does not occur. Source: http://ghs.gresham.k12.or

Robbiano, Lorenzo

132

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

133

Variable laser attenuator  

DOEpatents

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

Foltyn, Stephen R. (Los Alamos, NM)

1988-01-01

134

Variable laser attenuator  

DOEpatents

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

Foltyn, S.R.

1987-05-29

135

X-ray observations of BL Lac objects  

NASA Technical Reports Server (NTRS)

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

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

1978-01-01

136

Extended radio emission in BL Lac objects - I: the images  

E-print Network

We have observed 28 sources selected from the 1Jy sample of BL Lac objects (Stickel et al. 1991) with the Very Large Array (VLA) in A, B and D configurations at 1.36, 1.66 and 4.85 GHz, and/or with the Westerbork Synthesis Radio Telescope (WSRT) at 1.40 GHz. In this paper we present high sensitivity images at arcsecond resolution of the 18 objects showing extended structure in our images, and of another source from the FIRST (Faint Images of the Radio Sky at Twenty-cm) survey (Becker et al. 1995). In general our high sensitivity images reveal an amount of extended emission larger than previously reported. In some objects the luminosity of the extended structure is comparable with that of FR~II radio sources. A future paper will be devoted to the interpretation of these results.

P. Cassaro; C. Stanghellini; M. Bondi; D. Dallacasa; R. Della Ceca; R. A. Zappala`

1999-10-12

137

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

138

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

Microsoft Academic Search

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

John G. Hinchey; Kéiko H. Hattori

2005-01-01

139

Compensation for non-uniform attenuation in SPECT brain imaging  

SciTech Connect

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

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

1994-05-01

140

Bound Lac repressor protein differentially inhibits the unwinding reactions catalyzed by DNA helicases.  

PubMed Central

A partial duplex DNA substrate containing the Lac repressor binding site, within the duplex region, was constructed to examine the effect of bound Lac repressor on the unwinding reaction catalyzed by several DNA helicases. The substrate contained 90 base pairs of double-stranded DNA and, in the absence of Lac repressor, was effectively unwound by each of the seven helicases tested. The unwinding reactions catalyzed by Escherichia coli Rep protein, bacteriophage T4 Dda protein and E. coli DNA helicase I were not inhibited by the presence of bound Lac repressor. Both SV40 T antigen and E. coli helicase II were partially inhibited by bound repressor at the highest repressor concentrations tested. The helicase reactions catalyzed by E. coli DnaB protein and helicase IV were substantially inhibited by the presence of bound protein. When the length of the duplex region was increased to 323 base pairs the inhibition spectrum caused by bound Lac repressor on the unwinding reactions catalyzed by DnaB protein, helicase I and helicase II was essentially the same as that observed using the shorter partial duplex molecule. Inhibition of the unwinding reaction was due to the presence of bound Lac repressor as evidenced by the substantially weaker inhibition of helicase IV by Lac repressor in the presence of IPTG. In addition, we have shown that Rep protein displaces the bound repressor protein during the course of an unwinding reaction. Images PMID:1336182

Yancey-Wrona, J E; Matson, S W

1992-01-01

141

MAXIMUM MULTIPLE ATTENUATION  

Microsoft Academic Search

Recently Common Depth Point Stacking has become the general rule for seismic evaluation. Stack shooting is carried out to enhance the' primary event as well as to attenuate the multiple. Actual multiple attenuation can only take place providing the multiple event is stacked out of phase. Such out of stacking can only take place providing there is an increase of

W. HRYHOR

142

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

E-print Network

is itself formed from lactose by ?-galactosidase; ii) LacI regulates the expression of proteins essential for uptake (by lactose permease) as * Correspondence: fh111@cam.ac.ukCellular metabolism has evolved to be energy efficient,Background: The lac operon... I function of mutations at position 220, saturation muta- genesis was performed at this position by means of whole plasmid amplification with degenerate oligonucleotides bearing an NNS codon. E. coli BL21(DE3) colonies carry- ing a mutated LacI were grouped...

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

2013-07-08

143

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

PubMed

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

Prokulevich, V A; Fomichev, Iu K

1978-11-01

144

A numeric evaluation of attenuation from ambient noise correlation functions  

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

145

Second coefficient of viscosity in air  

NASA Technical Reports Server (NTRS)

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

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

1991-01-01

146

Landing gear noise attenuation  

NASA Technical Reports Server (NTRS)

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

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

2011-01-01

147

78 FR 48224 - Lac-Mégantic Railroad Accident Discussion and DOT Safety Recommendations  

Federal Register 2010, 2011, 2012, 2013, 2014

...DEPARTMENT OF TRANSPORTATION Federal Railroad Administration [Safety Advisory 2013-06...13-13] Lac-M[eacute]gantic Railroad Accident Discussion and DOT Safety Recommendations AGENCY: Federal Railroad Administration (FRA) and...

2013-08-07

148

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

PubMed Central

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

Diolez, A; Coleno, A

1985-01-01

149

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

SciTech Connect

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

Isham, Leslie; Weaver, Jason

2013-09-30

150

Absorption coefficient instrument for turbid natural waters  

NASA Technical Reports Server (NTRS)

The paper presents an instrument that directly measures multispectral absorption coefficient of turbid natural water. Attention is given to the design, which is shown to incorporate methods for the compensation of variation in the internal light source intensity, correction of the spectrally dependent nature of the optical elements, and correction for variation in the background light level. In addition, when used in conjunction with a spectrally matched total attenuation instrument, the spectrally dependent scattering coefficient can also be derived. Finally, it is reported that systematic errors associated with multiple scattering have been estimated using Monte Carlo techniques.

Friedman, E.; Cherdak, A.; Poole, L.; Houghton, W.

1980-01-01

151

Effect of finite absorber dimensions on ?-ray attenuation measurements  

NASA Astrophysics Data System (ADS)

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

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

1986-04-01

152

Implications of NGA for NEHRP site coefficients  

USGS Publications Warehouse

Three proposals are provided to update tables 11.4-1 and 11.4-2 of Minimum Design Loads for Buildings and Other Structures (7-10), by the American Society of Civil Engineers (2010) (ASCE/SEI 7-10), with site coefficients implied directly by NGA (Next Generation Attenuation) ground motion prediction equations (GMPEs). Proposals include a recommendation to use straight-line interpolation to infer site coefficients at intermediate values of ?vs (average shear velocity). Site coefficients are recommended to ensure consistency with ASCE/SEI 7-10 MCER (Maximum Considered Earthquake) seismic-design maps and simplified site-specific design spectra procedures requiring site classes with associated tabulated site coefficients and a reference site class with unity site coefficients. Recommended site coefficients are confirmed by independent observations of average site amplification coefficients inferred with respect to an average ground condition consistent with that used for the MCER maps. The NGA coefficients recommended for consideration are implied directly by the NGA GMPEs and do not require introduction of additional models.

Borcherdt, Roger D.

2012-01-01

153

Backscatter and attenuation properties of mammalian brain tissues  

NASA Astrophysics Data System (ADS)

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

Wijekularatne, Pushpani Vihara

154

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

155

A direct measurement of skull attenuation for quantitative SPECT  

SciTech Connect

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

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

1993-08-01

156

Factor Scores, Structure Coefficients, and Communality Coefficients  

ERIC Educational Resources Information Center

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

Goodwyn, Fara

2012-01-01

157

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

PubMed Central

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

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

2014-01-01

158

Attenuator And Conditioner  

DOEpatents

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

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

2006-04-04

159

Ultrasonic attenuation in superconducting borocarbides YNi 2B 2C  

NASA Astrophysics Data System (ADS)

Recently we have proposed s+g-wave superconductor in order to describe unusual superconductivity in borocarbides YNi 2B 2C and LuNi 2B 2C. In the present paper we study both the longitudinal and the transverse ultrasonic attenuation coefficients in the hydrodynamic limit. Indeed, such experiments have been reported very recently. The present model appears to describe the attenuation coefficients of L100, L001, T110 and T001 modes in the superconducting YNi 2B 2C very well. On the other hand, for L110 and T100 modes, the experimental results are somewhat different from the theoretical prediction.

Won, H.; Maki, K.

2004-08-01

160

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

Microsoft Academic Search

The auto-induction method of protein expression in E. coli is based on diauxic growth resulting from dynamic function of lac operon regulatory elements (lacO and LacI) in mixtures of glucose, glycerol, and lactose. The results show that successful execution of auto-induction is strongly dependent on the plasmid promoter and repressor construction, on the oxygenation state of the culture, and on

Paul G. Blommel; Katie J. Becker; Petar Duvnjak; Brian G. Fox

2007-01-01

161

Depth dependent seismic scattering attenuation in the Nuevo Cuyo region (southern central Andes)  

NASA Astrophysics Data System (ADS)

In the present work we separated intrinsic from scattering attenuation coefficients both for the crust and the upper mantle in the tectonically highly active areas of the Southern-Central Andes - Nuevo Cuyo region, analyzing two groups of earthquakes, well separated in depth. This region is characterized by the presence of flat subduction. We apply MLTWA (Multiple Lapse Time Window Analysis), coda normalization and Q-coda techniques to measure the scattering and intrinsic attenuation coefficient and the total Q for S waves. We find that intrinsic attenuation does not decrease with depth whereas scattering attenuation is higher in the crust than in the upper mantle, and that intrinsic attenuation predominates over scattering attenuation. We interpret this observation in terms of the release of water and other fluids into the overlying lithosphere due to the dynamics of the subduction process, in agreement with most of the prevalent geodynamic models.

Badi, G.; Del Pezzo, E.; Ibanez, J. M.; Bianco, F.; Sabbione, N.; Araujo, M.

2009-12-01

162

Radiofrequency attenuator and method  

DOEpatents

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

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

2009-11-10

163

Vortex attenuation flight experiments  

NASA Technical Reports Server (NTRS)

Flight tests evaluating the effects of altered span loading, turbulence ingestion, combinations of mass and turbulence ingestion, and combinations of altered span loading turbulance ingestion on trailed wake vortex attenuation were conducted. Span loadings were altered in flight by varying the deflections of the inboard and outboard flaps on a B-747 aircraft. Turbulence ingestion was achieved in flight by mounting splines on a C-54G aircraft. Mass and turbulence ingestion was achieved in flight by varying the thrust on the B-747 aircraft. Combinations of altered span loading and turbulence ingestion were achieved in flight by installing a spoiler on a CV-990 aircraft and by deflecting the existing spoilers on a B-747 aircraft. The characteristics of the attenuated and unattenuated vortexes were determined by probing them with smaller aircraft. Acceptable separation distances for encounters with the attenuated and unattenuated vortexes are presented.

Barber, M. R.; Hastings, E. C., Jr.; Champine, R. A.; Tymczyszyn, J. J.

1977-01-01

164

Radiofrequency attenuator and method  

DOEpatents

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

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

2009-01-20

165

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

E-print Network

possibilities using subfamilies in the LacI/GalR transcription regulators as a model system. The LacI/GalR family is experimentally well- characterized for both wild-type (reviewed in [2,3]) and synthetic homologs [4–6] and is often used to develop and evaluate...% sequence identity [18,21,33]. These two proteins respectively bind the lacO and pur operators [2,3,34–36], and are respectively regulated by binding allolactose and purines [3,37–39]. Thus, the LacI/GalR sequence clusters appear to correspond to groups...

Parente, Daniel J.; Swint-Kruse, Liskin

2013-12-31

166

Frequency Dependent Attenuation Revisited  

E-print Network

The work is inspired by thermo-and photoacoustic imaging, where recent efforts are devoted to take into account attenuation and varying wave speed parameters. In this paper we study causal equations describing propagation of attenuated pressure waves. We review standard models like frequency power laws and and the thermo-viscous equation. The lack of causality of standard models in the parameter range relevant for photoacoustic imaging requires to derive novel equations. The main ingredients for deriving causal equations are the Kramers-Kronig relation and the mathematical concept of linear system theory. The theoretical results of this work are underpined by numerical experiments.

Richard, Kowar; Xavier, Bonnefond

2009-01-01

167

Outward-facing conformers of LacY stabilized by nanobodies.  

PubMed

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

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

2014-12-30

168

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

PubMed

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

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

2014-09-21

169

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

NASA Astrophysics Data System (ADS)

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

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

1999-11-01

170

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

171

Electromagnetic Attenuation by Solid Particle Aerosols.  

NASA Astrophysics Data System (ADS)

Theories of electromagnetic attenuation by absorption and scattering from aerosols of solid particles were evaluated and experimentally verified. Particles having specific physical and morphological properties were tested to maximize the mass extinction coefficients of the aerosols in several bands of the electromagnetic spectrum. Particulate materials were chosen based on theoretical predictions and compatible aerosolization schemes were developed for each material. Direct measurements of attenuation by the resulting aerosols were conducted in instrumented cloud chambers and a new measurement system using "stationary aerosols" was developed. The method of producing the stationary aerosols was optimized experimentally and results of the two measurement techniques were compared, validating the stationary aerosol approach as a viable alternative to chamber testing. Theoretical results were used to determine ideal particles for maximizing attenuation and particles with the appropriate parameters were designed and produced in the laboratory. A combination of aerosol and stationary aerosol testing was used to measure attenuations and extinction coefficients were computed as the figures of merit in evaluating the efficacy of each material. Materials with less than ideal parameters were tested to further validate the theoretical predictions. Materials produced as testing particulates included deflagrated graphitic oxides, charge transfer salts, iron whiskers, and aluminum flake with varying levels of passivation. Product characterizations were done using electron microscopies and image analysis, x-ray spectroscopies and electron spectroscopies. The same methods were used to verify manufacturers' specifications for commercially available materials tested. Characterization results were used to calculate theoretical predictions. Dissemination schemes investigated included sonic velocity pneumatic nozzles, mechanical systems, magnetic systems and material specific reaction systems. Figures of merit for dissemination systems were determined in terms of aerosolized yields, fall rates, and extents of agglomeration.

Petersen, Erica Ray

1991-02-01

172

Laser Measurement Of Convective-Heat-Transfer Coefficient  

NASA Technical Reports Server (NTRS)

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

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

1994-01-01

173

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

NASA Astrophysics Data System (ADS)

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

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

1999-11-01

174

Attenuated yaws in Surinam.  

PubMed

Results of a pilot survey in the central, northern region of Surinam indicate that yaws is prevalent (hypoendemic) in this part of the country. No classical symptoms of yaws were seen. The observed lesions were scanty or solitary, dry papillomatous, or macular and scaly, which fits into the clinical picture of attenuated endemic treponematosis. PMID:445127

Niemel, P L; Brunings, E A; Menke, H E

1979-04-01

175

NEUTRON ATTENUATION IN CONCRETE  

Microsoft Academic Search

The observed behavior of the penetrating neutrons in a concrete shield ; is accounted for by a simple theory making use of a calculated transport' cross ; section for fast neutrons. This method is then linked with conventional age ; theory in an empirical manner so that a good fit is obtained to the observed ; neutron attenuation at all

Spinney

1955-01-01

176

Extended X-ray emission from the BL Lac object PKS 0521-365  

E-print Network

Models that seek to unify BL Lacs and low-power radio galaxies predict that the two types of object should show similar isotropically emitted X-ray emission. Testing this is usually limited by difficulties in separating strong X-ray emission from a BL Lac nucleus and surrounding low-surface brightness emission. In this paper we report ROSAT HRI observations of the z=0.055 BL Lac object PKS 0521-365. We are able to separate a luminous extended X-ray component from the bright nucleus. Using a new radio map, we show that it is unlikely that the extended emission is due to inverse-Compton scattering of photons from the active nucleus, and instead interpret it as thermal emission from dense, rapidly cooling gas. This is a more extreme environment than is found in typical FRI radio galaxies, and may pose a problem for unified models.

M. J. Hardcastle; D. M. Worrall; M. Birkinshaw

1998-12-08

177

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

178

Doppler Boosting and Orientation Effects in BL Lacs and Other AGNs  

NASA Astrophysics Data System (ADS)

We have used the observed variability brightness temperatures of AGN monitored at Mets=E4hovi to derive the Doppler boosting factors for a large sample of BL Lacs and other classes of compact radio sources. A comparison between the boosting factors derived by this new method and values derived by traditional methods (e.g., synchrotron self-Compton and equipartition estimates) will be presented. The variability Doppler boosting factors and the VLBI expansion speeds are used to derive the viewing angles and the Lorentz factors of the sources. A comparison of these parameters for BL Lacs and for other AGN will be presented.

Valtaoja, Esko; Lähteenmäki, A.; Teräsranta, H.; Lainela, M.

179

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

NASA Technical Reports Server (NTRS)

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

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

1993-01-01

180

Live attenuated tetravalent dengue vaccine  

Microsoft Academic Search

The development of a live attenuated tetravalent dengue vaccine is currently the best strategy to obtain a vaccine against dengue viruses. The Mahidol University group developed candidate live attenuated vaccines by attenuation through serial passages in certified primary cell cultures. Dengue serotype 1, 2 and 4 viruses were developed in primary dog kidney cells, whereas dengue serotype 3 was serially

N Bhamarapravati; Y Sutee

2000-01-01

181

Control algorithms for dynamic attenuators  

SciTech Connect

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

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

2014-06-15

182

Flexible graphene based microwave attenuators.  

PubMed

We demonstrate flexible 3 dB and 6 dB microwave attenuators using multilayer graphene grown by the chemical vapor deposition method. On the basis of the characterized results of multilayer graphene and graphene-Au ohmic contacts, the graphene attenuators are designed and measured. The flexible graphene-based attenuators have 3 dB and 6 dB attenuation with a return loss of less than -15 dB at higher than 5 GHz. The devices have shown durability in a bending cycling test of 100 times. The circuit model of the attenuator based on the characterized results matches the experimental results well. PMID:25590144

Byun, Kisik; Ju Park, Yong; Ahn, Jong-Hyun; Min, Byung-Wook

2015-02-01

183

Flexible graphene based microwave attenuators  

NASA Astrophysics Data System (ADS)

We demonstrate flexible 3 dB and 6 dB microwave attenuators using multilayer graphene grown by the chemical vapor deposition method. On the basis of the characterized results of multilayer graphene and graphene–Au ohmic contacts, the graphene attenuators are designed and measured. The flexible graphene-based attenuators have 3 dB and 6 dB attenuation with a return loss of less than ?15 dB at higher than 5 GHz. The devices have shown durability in a bending cycling test of 100 times. The circuit model of the attenuator based on the characterized results matches the experimental results well.

Byun, Kisik; Park, Yong Ju; Ahn, Jong-Hyun; Min, Byung-Wook

2015-02-01

184

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

NSDL National Science Digital Library

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

2008-10-06

185

In vivo role of the relA+ gene in regulation of the lac operon.  

PubMed Central

Under conditions of amino acid limitation, beta-galactosidase was produced at a 70-fold higher rate in a relA+ strain than in an isogenic relA strain of Escherichia coli K-12. Under identical conditions with the relA+ and relA strains carrying various lac promoter mutations, rates of beta-galactosidase synthesis in relA+ (relative to relA) ranged from 26-fold higher (promoter mutant Pr 13) to only 5-fold higher (promoter mutant PrL8uv5). This promoter specificity was independent of strain background and the means of eliciting amino acid limitation. Addition of cyclic AMP to the growth medium altered the relA+/relA difference for beta-galactosidase synthesis from the wild-type lac promoter. The experiments suggest that the relA+/relA difference in lac expression arises primarily at the point of transcription initiation. The results are discussed in relation to recent in vitro data showing a promoter-specific guanosine 5'-diphosphate 3'-diphosphate stimulation of lac transcription (P. Primakoff and S. W. Artz, Proc. Natl. Acad. Sci. U.S.A. 76:1726-1730). PMID:6257637

Primakoff, P

1981-01-01

186

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

Microsoft Academic Search

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

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

2003-01-01

187

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

PubMed

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

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

2013-10-01

188

Gamma ray attenuation in a developed borate glassy system  

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

189

Substrate-induced changes in the structural properties of LacY  

PubMed Central

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

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

2014-01-01

190

Inversion for the attenuated radon transform with constant attenuation  

SciTech Connect

An exact form of the inversion formula for the attenuated Radon transform with constant attenuation in a convex domain for use in Single-Photon Computerized Tomography is presented. This problem is reduced to solving a generalized Abel integral equation and the conditions for the existence of a unique continuous solution are given. Implementation of this method involves a preprocessing step (modified attenuated Radon transform), a convolution by an attenuation-dependent function and a weighted backprojection. Therefore, only slight modifications of existing reconstruction algorithms are needed. If the attenuation is zero, this formula reduces to Radon's original inversion formula. When attenuation is not constant, the conditions for a unique continuous solution can be established with a similar approach. Many results found empirically by previous authors are consistent with this theory.

Kim, K.I.; Bizais, Y.; Rowe, R.W.; Tewarson, R.P.

1984-02-01

191

Inversion for the attenuated radon transform with constant attenuation  

SciTech Connect

An exact form of the inversion formula for the attenuated Radon transform with constant attenuation in a convex domain for use in Single-Photon Computerized Tomography is presented. This problem is reduced to solving a generalized Abel integral equation and the conditions for the existence of a unique continuous solution are given. Implementation of this method involves a preprocessing step (modified attenuated Radon transform), a convolution by an attenuation-dependent function and a weighted backprojection. Therefore, only slight modifications of existing reconstruction algorithms are needed. If the attenuation is zero, this formula reduces to Radon's original inversion formula. When attenuation is not constant, the conditions for a unique continuous solution can be established with a similar approach. Many results found empirically by previous authors are consistent with this theory.

Kim, K.I.; Tewarson, R.P.; Bizais, Y.; Rowe, R.W.

1983-01-01

192

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

NASA Astrophysics Data System (ADS)

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

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

2015-02-01

193

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

2008-12-01

194

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

195

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

PubMed Central

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

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

2013-01-01

196

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

PubMed Central

Thermodynamic analysis of urea-biopolymer interactions and urea effects on folding of proteins and ?-helical peptides shows that urea interacts primarily with polar amide surface. Urea is therefore predicted to be a quantitative probe of coupled folding, remodeling and other large-scale changes in the amount of water-accessible polar amide surface in protein processes. A parallel analysis indicates that glycine betaine (N,N,N-trimethyl glycine; GB) can be used to detect burial or exposure of anionic (carboxylate, phosphate) biopolymer surface. To test these predictions, we have investigated the effects of these solutes (0 to 3 molal) on the formation of 1:1 complexes between lac repressor (LacI) and its symmetric operator site (SymL) at constant KCl molality. Urea reduces the binding constant KTO (initial slope dln KTO/dmurea = ?1.7 ± 0.2) and GB increases KTO (initial slope dln KTO/dmGB = + 2.1 ± 0.2). For both solutes, this derivative decreases with increasing solute concentration. Analysis of these initial slopes predicts that (1.5 ± 0.3) × 103 Å2 of polar amide surface and (4.5 ± 1.0) × 102 Å2 of anionic surface are buried in the association process. Analysis of published structural data, together with modeling of unfolded regions of free LacI as extended chains, indicates that 1.5 × 103 Å2 of polar amide surface and 6.3 × 102 Å2 of anionic surface are buried in complexation. Quantitative agreement between structural and thermodynamic results is obtained for amide surface (urea); for anionic surface (GB), the experimental value is ~70% of the structural value. For LacI-SymL binding, two thirds of the structurally-predicted change in amide surface (1.0 × 103 Å2) occurs outside the protein-DNA interface in protein-protein interfaces formed by folding of the hinge helices and interactions of the DNA binding domain (DBD) with the core of repressor. Since urea interacts principally with amide surface, it is particularly well-suited to detect and quantify the extent of coupled folding and other large-scale remodeling events in the steps of protein-nucleic acid interactions and other protein associations. PMID:16363803

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

2008-01-01

197

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

198

Inversion for the attenuated radon transform with constant attenuation  

Microsoft Academic Search

An exact form of the inversion formula for the attenuated Radon transform with constant attenuation in a convex domain for use in Single-Photon Computerized Tomography is presented. This problem is reduced to solving a generalized Abel integral equation and the conditions for the existence of a unique continuous solution are given. Implementation of this method involves a preprocessing step (modified

K. I. Kim; Y. Bizais; R. W. Rowe; R. P. Tewarson

1984-01-01

199

Inversion for the attenuated radon transform with constant attenuation  

Microsoft Academic Search

An exact form of the inversion formula for the attenuated Radon transform with constant attenuation in a convex domain for use in Single-Photon Computerized Tomography is presented. This problem is reduced to solving a generalized Abel integral equation and the conditions for the existence of a unique continuous solution are given. Implementation of this method involves a preprocessing step (modified

K. I. Kim; R. P. Tewarson; Y. Bizais; R. W. Rowe

1983-01-01

200

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. PMID:18426771

Santillán, Moisés; Mackey, Michael C.

2008-01-01

201

VERITAS observations and spectral energy distribution of H 1426+428 BL Lac  

NASA Astrophysics Data System (ADS)

The VERITAS array of 12-m atmospheric-Cherenkov telescopes in southern Arizona is one of the world's most sensitive detectors of astrophysical very high energy (VHE) ?-rays above 100 GeV. We present results from VERITAS observations of the BL Lac object H 1426+428. The VERITAS array has been monitoring this source since 2007 and has accumulated over 35 hours of data. The source was first detected in the VHE range by the Whipple 10-m ?-ray telescope in 2002 during a flaring state. It is classified as an extreme high-frequency peaked BL Lac (HBL), with the peak of the synchrotron emission lying above 100 keV, even during low states. The spectral energy distribution of H 1426+428, including contemporaneous VERITAS, Fermi-LAT, Swift XRT/UVOT and optical data, will be presented.

Khassen, Y.

2014-07-01

202

The debeamed luminosity, sychrotron peak frequency and black hole mass of BL Lac objects  

E-print Network

We estimate the intrinsic luminosities and synchrotron peak frequency using the derived Doppler factor for a sample of 170 BL Lac objects, of which the synchrotron peak frequency are derived by fitting the SED constructed with the collected multi-band data from literatures. We find that the debeamed radio and optical core luminosities follow the same correlation found for FR I radio galaxies, which is in support of the unification of the BL Lac objects and the FR I galaxies based on orientation. For the debeamed luminosity at synchrotron peak frequency, we find a significant positive correlation between the luminosity and intrinsic synchrotron peak frequency. This implies that the more powerful sources may have the majority of jet emission at higher frequency. At synchrotron peak frequency, the intrinsic luminosity and black hole mass show strong positive correlation, while mild correlation is found in the case of jet power, indicating that the more powerful sources may have heavier black hole.

Zhongzu Wu; Minfeng Gu; D. R. Jiang

2008-04-08

203

Live attenuated influenza vaccine.  

PubMed

Cold-adapted Ann Arbor based live attenuated influenza vaccine (LAIV) has been available in the USA since 2003. The vaccine is efficacious against influenza infection. Features of LAIV include: easy administration suitable for mass immunization, cross-reactivity to drifted strains for broader coverage, and establishment of herd immunity for control of influenza spread. Annual seasonal LAIV now contains four strains against influenza A H1N1, H3N2, influenza B-Victoria, and B-Yamagata lineages that are co-circulating in humans. LAIV played a significant role in protecting the public from the 2009 H1N1 pandemic and has been evaluated for pandemic preparedness. Pandemic vaccines including influenza H2, H5, H6, H7, and H9 subtypes have been produced and evaluated in preclinical and small-scale phase I clinical studies. This review summarizes the current status and perspectives of seasonal and pandemic LAIV. PMID:25059893

Jin, Hong; Subbarao, Kanta

2015-01-01

204

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

E-print Network

1 Les méandres du développement agricole au Lac Alaotra, Madagascar Entre inconstance politique et Antananarivo, Madagascar Discipline ; socio-économie Téléphone : 00 261 (0) 34 044 63 29 Penot@cirad.fr Résumé Madagascar, région à forte immigration et zone de prédilection de l'aide publique au développement, est

Paris-Sud XI, Université de

205

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

Microsoft Academic Search

The specific binding of regulatory proteins to DNA sequences exhibits no clear patterns of association between amino acids (AAs) and nucleotides (NTs). This complexity of protein-DNA interactions raises the question of whether a simple set of wide-coverage recognition rules can ever be identified. Here, we analyzed this issue using the extensive LacI family of transcriptional factors (TFs). We searched for

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

2010-01-01

206

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

207

Suicide Risk: Amplifiers and Attenuators.  

ERIC Educational Resources Information Center

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

Plutchik, Robert; Van Praag, Herman M.

1994-01-01

208

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

209

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

NASA Astrophysics Data System (ADS)

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

Tavecchio, Fabrizio; Ghisellini, Gabriele; Guetta, Dafne

2014-09-01

210

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

211

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. PMID:23227228

Yu, Pulan; Wild, David J.

2012-01-01

212

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

PubMed Central

Comparison of both the DNA and protein sequences of catabolite gene activator protein (CAP) with the sequences of lac and gal repressors shows significant homologies between a sequence that forms a two alpha-helix motif in CAP and sequences near the amino terminus of both repressors. This two-helix motif is thought to be involved in specific DNA sequence recognition by CAP. The region in lac repressor to which CAP is homologous contains many i-d mutations that are defective in DNA binding. Less significant sequence homologies between CAP and phage repressors and activators are also shown. The amino acid residues that are critical to the formation of the two-helix motif are conserved, while those residues expected to interact with DNA are variable. These observations suggest the lac and gal repressors also have a two alpha-helix structural motif which is involved in DNA binding and that this two helix motif may be generally found in many bacterial and phage repressors. We conclude that one major mechanism by which proteins can recognize specific base sequences in double stranded DNA is via the amino acid side chains of alpha-helices fitting into the major groove of B-DNA. PMID:6897114

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

1982-01-01

213

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

SciTech Connect

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

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

1985-01-01

214

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

PubMed Central

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

Solanki, Manu; Garg, Faquir C.

2014-01-01

215

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

2010-07-15

216

Pearson's Correlation Coefficient  

NSDL National Science Digital Library

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

2009-01-09

217

Zero-Coefficient Cuts  

NASA Astrophysics Data System (ADS)

Many cuts used in practice to solve mixed integer programs are derived from a basis of the linear relaxation. Every such cut is of the form ? T x ? 1, where x ? 0 is the vector of non-basic variables and ? ? 0. For a point bar{x} of the linear relaxation, we call ? T x ? 1 a zero-coefficient cut wrt. bar{x} if ?^T bar{x} = 0, since this implies ? j = 0 when bar{x}_j > 0. We consider the following problem: Given a point bar{x} of the linear relaxation, find a basis, and a zero-coefficient cut wrt. bar{x} derived from this basis, or provide a certificate that shows no such cut exists. We show that this problem can be solved in polynomial time. We also test the performance of zero-coefficient cuts on a number of test problems. For several instances zero-coefficient cuts provide a substantial strengthening of the linear relaxation.

Andersen, Kent; Weismantel, Robert

218

Inverse problems of ultrasound tomography in models with attenuation.  

PubMed

We develop efficient methods for solving inverse problems of ultrasound tomography in models with attenuation. We treat the inverse problem as a coefficient inverse problem for unknown coordinate-dependent functions that characterize both the speed cross section and the coefficients of the wave equation describing attenuation in the diagnosed region. We derive exact formulas for the gradient of the residual functional in models with attenuation, and develop efficient algorithms for minimizing the gradient of the residual by solving the conjugate problem. These algorithms are easy to parallelize when implemented on supercomputers, allowing the computation time to be reduced by a factor of several hundred compared to a PC. The numerical analysis of model problems shows that it is possible to reconstruct not only the speed cross section, but also the properties of the attenuating medium. We investigate the choice of the initial approximation for iterative algorithms used to solve inverse problems. The algorithms considered are primarily meant for the development of ultrasound tomographs for differential diagnosis of breast cancer. PMID:24694653

Goncharsky, Alexander V; Romanov, Sergey Y

2014-04-21

219

Inverse problems of ultrasound tomography in models with attenuation  

NASA Astrophysics Data System (ADS)

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

Goncharsky, Alexander V.; Romanov, Sergey Y.

2014-04-01

220

Modeling ultrasonic noise and attenuation in elongated duplex polycrystalline materials  

NASA Astrophysics Data System (ADS)

The interaction between ultrasonic waves and the polycrystalline microstructure of metals leads to structural noise and attenuation, which can cause significant losses in detection performances. Taking these phenomena into account in UT simulation can help designing suitable inspection procedures. It is possible to model them based on the intrinsic scattering coefficients of a material. Expressions of this coefficient valid for duplex elongated materials and for any mode and scattering direction are given in this communication. Structural noise from a titanium alloy was computed based on these expressions and is compared to measurement.

Dorval, V.; Ganjehi, L.; Chatillon, S.; Jenson, F.

2013-01-01

221

New inverses of the attenuated Abel integral equation  

Microsoft Academic Search

Abel's integral equation relates the line-of-sight radiance to the emission coefficient distribution function of an extended, cylindrically symmetric transparent radiation source. In the presence of absorption this equation is modified. The author presents two new inversion formulae for this attenuated Abel equation for the case of constant absorption throughout the source. As one of them is completely derivative-free and the

M. Deutsch

1984-01-01

222

The maraging-steel blades of the Virgo super attenuator  

Microsoft Academic Search

The blades are crucial components of the Virgo super attenuators. The material used for their construction is maraging steel, a low-carbon-content alloy with high ultimate tensile strength and low creep under stress. Young's modulus, the shear modulus, the Poisson ratio and the corresponding elastic energy-loss coefficients have been measured. The measurements have been performed on specimens subjected to the same

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

2000-01-01

223

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

E-print Network

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

Ri, Yong-Wu; Im, Song-Jin

2014-01-01

224

Seismic attenuation in fractured media  

NASA Astrophysics Data System (ADS)

The prime objective of this paper is to quantitatively estimate seismic attenuation caused by fractures with different physical parameters. In seismic wave simulation, the fractured media are treated as the anisotropic media and fractures are represented by frequency-dependent elastic constants. Based on numerical experiments with three different parameters, namely viscosity, porosity and the Lamé parameters, this paper has the following observations. First, seismic attenuation is not affected by the viscosity within fractures, although it increases with the increase of porosity and decreases with the increase of the Lamé parameters within fractures. Among the latter two parameters, seismic attenuation is more sensitive to the Lamé parameters than to the porosity. Second, for the attenuation anisotropy, low frequencies have more anisotropic effect than high frequencies. For example, a 50?Hz wavefield has the strongest anisotropy effect if compared to 100 and 150?Hz wavefields. The attenuation anisotropy for low frequency (say 50?Hz) is more sensitive to the viscosity than the porosity and the Lamé parameters have the weakest effect among these three parameters. These observations suggest that low-frequency seismic attenuation, and especially the attenuation anisotropy in low frequency, would have great potential for fluid discrimination within fractured media.

Rao, Ying; Wang, Yanghua

2015-02-01

225

SEISMIC ATTENUATION FOR RESERVOIR CHARACTERIZATION  

SciTech Connect

Wave-induced variations of pore pressure in a partially-saturated reservoir result in oscillatory liquid flow. The viscous losses during this flow are responsible for wave attenuation. The same viscous effects determine the changes in the dynamic bulk modulus of the system versus frequency. These changes are necessarily linked to attenuation via the causality condition. We analytically quantify the frequency dependence of the bulk modulus of a partially saturated rock by assuming that saturation is patchy and then link these changes to the inverse quality factor. As a result, the P-wave attenuation is quantitatively linked to saturation and thus can serve as a saturation indicator.

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

2002-04-01

226

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

SciTech Connect

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

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

2005-09-15

227

Dual energy CT for attenuation correction with PET/CT  

PubMed Central

Purpose: The authors evaluate the energy dependent noise and bias properties of monoenergetic images synthesized from dual-energy CT (DECT) acquisitions. These monoenergetic images can be used to estimate attenuation coefficients at energies suitable for positron emission tomography (PET) and single-photon emission computed tomography (SPECT) imaging. This is becoming more relevant with the increased use of quantitative imaging by PET/CT and SPECT/CT scanners. There are, however, potential variations in the noise and bias of synthesized monoenergetic images as a function of energy. Methods: The authors used analytic approximations and simulations to estimate the noise and bias of synthesized monoenergetic images of water-filled cylinders with different shapes and the NURBS-based cardiac-torso (NCAT) phantom from 40 to 520 keV, the range of SPECT and PET energies. The dual-kVp spectra were based on the GE Lightspeed VCT scanner at 80 and 140 kVp with added filtration of 0.5 mm Cu. The authors evaluated strategies of noise suppression with sinogram smoothing and dose minimization with reduction of tube currents at the two kVp settings. The authors compared the impact of DECT-based attenuation correction with single-kVp CT-based attenuation correction on PET quantitation for the NCAT phantom for soft tissue and high-Z materials of bone and iodine contrast enhancement. Results: Both analytic calculations and simulations displayed the expected minimum noise value for a synthesized monoenergetic image at an energy between the mean energies of the two spectra. In addition the authors found that the normalized coefficient of variation in the synthesized attenuation map increased with energy but reached a plateau near 160 keV, and then remained constant with increasing energy up to 511 keV and beyond. The bias was minimal, as the linear attenuation coefficients of the synthesized monoenergetic images were within 2.4% of the known true values across the entire energy range. Compared with no sinogram smoothing, sinogram smoothing can dramatically reduce noise in the DECT-derived attenuation map. Through appropriate selection of tube currents for high and low kVp scans, DECT can deliver roughly the same amount of radiation dose as that of a single kVp CT scan, but could be used for PET attenuation correction with reduced bias in contrast agent regions by a factor of ?2.6 and slightly reduced RMSE for the total image. Conclusions: When DECT is used for attenuation correction at higher energies, there is a noise amplification that is dependent on the energy of the synthesized monoenergetic image of linear attenuation coefficients. Sinogram smoothing reduces the noise amplification in DECT-derived attenuation maps without increasing bias. With an appropriate selection of CT techniques, a DECT scan with the same radiation dose as a single CT scan can result in a PET image with improved quantitative accuracy. PMID:24387525

Xia, Ting; Alessio, Adam M.; Kinahan, Paul E.

2014-01-01

228

Dual energy CT for attenuation correction with PET/CT  

SciTech Connect

Purpose: The authors evaluate the energy dependent noise and bias properties of monoenergetic images synthesized from dual-energy CT (DECT) acquisitions. These monoenergetic images can be used to estimate attenuation coefficients at energies suitable for positron emission tomography (PET) and single-photon emission computed tomography (SPECT) imaging. This is becoming more relevant with the increased use of quantitative imaging by PET/CT and SPECT/CT scanners. There are, however, potential variations in the noise and bias of synthesized monoenergetic images as a function of energy. Methods: The authors used analytic approximations and simulations to estimate the noise and bias of synthesized monoenergetic images of water-filled cylinders with different shapes and the NURBS-based cardiac-torso (NCAT) phantom from 40 to 520 keV, the range of SPECT and PET energies. The dual-kVp spectra were based on the GE Lightspeed VCT scanner at 80 and 140 kVp with added filtration of 0.5 mm Cu. The authors evaluated strategies of noise suppression with sinogram smoothing and dose minimization with reduction of tube currents at the two kVp settings. The authors compared the impact of DECT-based attenuation correction with single-kVp CT-based attenuation correction on PET quantitation for the NCAT phantom for soft tissue and high-Z materials of bone and iodine contrast enhancement. Results: Both analytic calculations and simulations displayed the expected minimum noise value for a synthesized monoenergetic image at an energy between the mean energies of the two spectra. In addition the authors found that the normalized coefficient of variation in the synthesized attenuation map increased with energy but reached a plateau near 160 keV, and then remained constant with increasing energy up to 511 keV and beyond. The bias was minimal, as the linear attenuation coefficients of the synthesized monoenergetic images were within 2.4% of the known true values across the entire energy range. Compared with no sinogram smoothing, sinogram smoothing can dramatically reduce noise in the DECT-derived attenuation map. Through appropriate selection of tube currents for high and low kVp scans, DECT can deliver roughly the same amount of radiation dose as that of a single kVp CT scan, but could be used for PET attenuation correction with reduced bias in contrast agent regions by a factor of ?2.6 and slightly reduced RMSE for the total image. Conclusions: When DECT is used for attenuation correction at higher energies, there is a noise amplification that is dependent on the energy of the synthesized monoenergetic image of linear attenuation coefficients. Sinogram smoothing reduces the noise amplification in DECT-derived attenuation maps without increasing bias. With an appropriate selection of CT techniques, a DECT scan with the same radiation dose as a single CT scan can result in a PET image with improved quantitative accuracy.

Xia, Ting [Department of Bioengineering, University of Washington, Seattle, Washington 98105 (United States)] [Department of Bioengineering, University of Washington, Seattle, Washington 98105 (United States); Alessio, Adam M. [Department of Radiology, University of Washington, Seattle, Washington 98105 (United States)] [Department of Radiology, University of Washington, Seattle, Washington 98105 (United States); Kinahan, Paul E., E-mail: kinahan@uw.edu [Departments of Radiology and Bioengineering, University of Washington, Seattle, Washington 98105 (United States)

2014-01-15

229

Comprehensive study of photon attenuation through different construction matters by Monte Carlo Simulation  

NASA Astrophysics Data System (ADS)

The main goal of this work is focused on testing the applicability of Geant4 electromagnetic models for studying mass attenuations for different types of composite materials at 59.5, 80, 356, 661.6, 1173.2 and 1332.5 keV photon energies. The simulated results of mass attenuation coefficients were compared with the experimental and theoretical data for the same samples and a good agreement has been observed. The results indicate that this process can be followed to determine the data on the attenuation of gamma-rays with the several energies in different materials.

Medhat, M. E.

2015-02-01

230

FRACTIONAL WAVE EQUATIONS WITH ATTENUATION  

PubMed Central

Fractional wave equations with attenuation have been proposed by Caputo [5], Szabo [27], Chen and Holm [7], and Kelly et al. [11]. These equations capture the power-law attenuation with frequency observed in many experimental settings when sound waves travel through inhomogeneous media. In particular, these models are useful for medical ultrasound. This paper develops stochastic solutions and weak solutions to the power law wave equation of Kelly et al. [11]. PMID:25045309

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

2013-01-01

231

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

NASA Astrophysics Data System (ADS)

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

Cengiz, Tunç; Albayrak, Erhan

2012-07-01

232

Activation of the Escherichia coli lacZ promoter by the Klebsiella aerogenes nitrogen assimilation control protein (NAC), a LysR family transcription factor.  

PubMed Central

A chimeric promoter with the nitrogen assimilation control protein binding site from hutUp of Klebsiella aerogenes fused to the lacZ core promoter from Escherichia coli was built and cloned in a lacZ reporter plasmid. This construct showed a 14-fold increase of beta-galactosidase activity upon nitrogen limitation. Primer extension experiments showed that the nitrogen assimilation control protein activates lacZp1 in a position-dependent manner. PMID:7642513

Pomposiello, P J; Bender, R A

1995-01-01

233

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

NASA Astrophysics Data System (ADS)

In the 21 st century, an increasing number of astronauts will visit the International Space Station (ISS) for prolonged times. Therefore it is of utmost importance to provide necessary basic knowledge concerning risks to their health and their ability to work on the station and during extravehicular activities (EVA) in free space. It is the aim of one experiment of the German project TRIPLE-LUX (to be flown on the ISS) to provide an estimation of health risk resulting from exposure of the astronauts to the radiation in space inside the station as well as during extravehicular activities on one hand, and of exposure of astronauts to unavoidable or as yet unknown ISS-environmental genotoxic substances on the other. The project will (i) provide increased knowledge of the biological action of space radiation and enzymatic repair of DNA damage, (ii) uncover cellular mechanisms of synergistic interaction of microgravity and space radiation and (iii) examine the space craft milieu with highly specific biosensors. For these investigations, the bacterial biosensor SOS-LUX-LAC-FLUORO-Toxicity-test will be used, combining the SOS-LUX-Test invented at DLR Germany (Patent) with the commercially available LAC-FLUORO-Test. The SOS-LUX-Test comprises genetically modified bacteria transformed with the pBR322-derived plasmid pPLS-1. This plasmid carries the promoterless lux operon of Photobacterium leiognathi as a reporter element under control of the DNA-damage dependent SOS promoter of ColD as sensor element. This system reacts to radiation and other agents that induce DNA damages with a dose dependent measurable emission of bioluminescence of the transformed bacteria. The analogous LAC-FLUORO-Test has been developed for the detection of cellular responses to cytotoxins. It is based on the constitutive expression of green fluorescent protein (GFP) mediated by the bacterial protein expression vector pGFPuv (Clontech, Palo Alto, USA). In response to cytotoxic agents, this system reacts with a dose-dependent reduction of GFP-fluorescence. Currently, a fully automated miniaturized hardware system for the bacterial set up, which includes measurements of luminescence and fluorescence or absorption and the image analysis based evaluation is under development. During the first mission of the SOS-LUX-LAC-FLUORO-Toxicity-Test on the ISS, a standardized, DNA-damaging radiation source still to be determined will be used as a genotoxic inducer. A panel of recombinant Salmonella typhimurium strains carrying either the SOS-LUX plasmid or the fluorescence-mediating lac-GFPuv plasmid will be used to determine in parallel on one microplate the genotoxic and the cytotoxic action of the applied radiation in combination with microgravity. Either in addition to or in place of the fluorometric measurements of the cytotoxic agents, photometric measurements will simultaneously monitor cell growth, giving additional data on survival of the cells. The obtained data will be available on line during the TRIPLE-LUX mission time. Though it is the main goal during the TRIPLE-LUX mission to measure the radiation effect in microgravity, the SOS-LUX-LAC-FLUORO-Toxicity-test in principle is also applicable as a biomonitor for the detection and measurement of genotoxic substances in air or in the (recycled) water system on the ISS or on earth in general.

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

234

Confirmed Identification of the BL Lac Object 3EG J0433+2908  

NASA Astrophysics Data System (ADS)

We present a formal multiwavelength examination of the EGRET source 3EG J0433+2908 and conclude that the source is a BL Lac type blazar. Dingus et al. 1996 hypothesized that this EGRET source belongs to the blazar class of AGN; they further noted that the most likely radio counterpart is 87GB 0430+2859. The EGRET data for 3EG J0433+2908 suggest time variability typical of BL Lac objects. Archival radio data confirms that 87GB 0430+2859 is by far the brightest flat-spectrum radio source within the 95% confidence contour of J0433+2908; data taken at GBI incicate that this radio source is variable on a timescale of 1 month at 2.25 GHz and 8.3 GHz. The ROSAT all-sky survey reports a hard X-ray source within one degree of the center of the EGRET 95% confidence contour; this X-ray source is within 5" of the candidate radio source's position as listed in the NVSS catalog. The 2MASS Point Source Catalog contains one infrared source that lies within 1" of the NVSS position and associates this infrared source with an optical counterpart that also lies within 1" of the NVSS position, according to the USNO-A catalog. Spectroscopy indicates that the optical counterpart exhibits a red, featureless spectrum typical of BL Lac type blazars. Together, these multiwavelength data trace out a bimodal spectral energy distribution--a signature of members of the blazar class of AGN. This is the first blazar identification to be prompted by gamma-ray observations.

Foreman, J. V.; Eracleous, M.; Halpern, J. P.; Thompson, D. J.; Wallace, P. M.

2001-12-01

235

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

PubMed Central

The major facilitator superfamily (MFS) transporter lactose permease (LacY) alternates between cytoplasmic and periplasmic open conformations to co-transport a sugar molecule together with a proton across the plasma membrane. Indirect experimental evidence suggested the existence of an occluded transition intermediate of LacY, which would prevent leaking of the proton gradient. As no experimental structure is known, the conformational transition is not fully understood in atomic detail. We simulated transition events from a cytoplasmic open conformation to a periplasmic open conformation with the dynamic importance sampling molecular dynamics method and observed occluded intermediates. Analysis of water permeation pathways and the electrostatic free-energy landscape of a solvated proton indicated that the occluded state contains a solvated central cavity inaccessible from either side of the membrane. We propose a pair of geometric order parameters that capture the state of the pathway through the MFS transporters as shown by a survey of available crystal structures and models. We present a model for the occluded state of apo-LacY, which is similar to the occluded crystal structures of the MFS transporters EmrD, PepTSo, NarU, PiPT and XylE. Our simulations are consistent with experimental double electron spin–spin distance measurements that have been interpreted to show occluded conformations. During the simulations, a salt bridge that has been postulated to be involved in driving the conformational transition formed. Our results argue against a simple rigid-body domain motion as implied by a strict “rocker-switch mechanism” and instead hint at an intricate coupling between two flexible gates. PMID:24513108

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

2014-01-01

236

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

NASA Astrophysics Data System (ADS)

Lac Télé is a large lake, ˜5.6 km in diameter, with an ovoid shape, situated at 17°10'E, 1°20'N, in the great tropical rain forest region of the Republic of Congo. This lake has attracted widespread attention, mainly because of the legends among the local people that it harbours a strange animal known as the Mokele-Mbembe, but also because it is situated in a region that is a hotbed of biodiversity and conservation efforts with respect to various endangered mammalian species, including gorillas and chimpanzees. Because of its appearance, Lac Télé has been regarded as a possible meteorite impact structure. Various expeditions, studying cryptozoology, conservation ecology, biodiversity, and the impact hypothesis, have visited Lac Télé in the past several decades. The Lac Télé structure is located in the NW part of the intracratonic Congo Basin, in a region dominated by Holocene alluvium, dense tropical rain forest, and swamps which form part of the basin of the Likouala aux Herbes, a multi-branched meandering river flowing over very low gradients into the Sangha river, a major tributary of the Congo river. Previous bathymetric studies have shown that the average depth of Lac Télé is only 4 m, including organic-rich silty sediments. The structure is that of a flat-bottomed dish. Modelling of the Lac Télé as an impact structure indicates a number of features which ought to be present. The absence of any of these features, coupled with the irregular ovoid shape, the palynological record, and the location of the structure at the intersection of major regional lineaments, is regarded as evidence against the impact hypothesis. Lac Télé as an isolated lake ecosystem is not unique in the Congo Basin, and there are several other similar small shallow isolated lakes surrounded by rain forest and marshes, some of which formed by damming of drainage systems by neotectonic faults. It is suggested that the formation of Lac Télé may be related to its location over neotectonically reactivated regional lineaments, which are also seismically active. Lac Télé and other similar hydrologic systems may be biodiversity hotspots because they acted as refugia following neotectonic hydrological re-organization of the Congo Basin.

Master, Sharad

2010-11-01

237

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

NASA Astrophysics Data System (ADS)

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

Yuan, Yu-hai; Liu, Fu-qing

2014-07-01

238

Evaluation of critical indicators in the process of acquiring supplies and services LAC-UFPE  

NASA Astrophysics Data System (ADS)

In laboratories linked to public universities and accredited by the NBR ISO/IEC 17025, to meet efficiently item 4.6 (procurement of supplies and services) is a challenge that can be accomplished by programming based on historical purchases and services. In this study, we evaluated the critical procurement items to meet the quality management system of the LAC-UFPE: reagents, certified reference material, of equipment parts, maintenance and calibration of equipment and instruments. It was found that the most critical item is the certified reference material, the purchase or repair of which must be expedited within 125 days prior to the receipt to occur within the desired period.

Caetano, V. F.; Ferreira, C. V.; dos Santos, M. J.; Honorato, F. A.

2015-01-01

239

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

PubMed Central

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

Semsey, Szabolcs; Jauffred, Liselotte; Csiszovszki, Zsolt; Erd?ssy, János; Stéger, Viktor; Hansen, Sabine; Krishna, Sandeep

2013-01-01

240

Crystal structure of VmoLac, a tentative quorum quenching lactonase from the extremophilic crenarchaeon Vulcanisaeta moutnovskia  

PubMed Central

A new representative of the Phosphotriesterase-Like Lactonases (PLLs) family from the hyperthermophilic crenarchaeon Vulcanisaeta moutnovskia has been characterized and crystallized. VmoLac is a native, proficient lactonase with promiscuous, low phosphotriesterase activity. VmoLac therefore represents an interesting candidate for engineering studies, with the aim of developing an efficient bacterial quorum-quenching agent. Here, we provide an extensive biochemical and kinetic characterization of VmoLac and describe the X-ray structures of the enzyme bound to a fatty acid and to its cognate substrate 3-oxo-C10 AHL (Acyl-Homoserine Lactone). The structures highlight possible structural determinants that may be involved in its extreme thermal stability (Tm = 128°C). Moreover, the structure reveals that the substrate binding mode of VmoLac significantly differs from those of its close homologues, possibly explaining the substrate specificity of the enzyme. Finally, we describe the specific interactions between the enzyme and its substrate, and discuss the possible lactone hydrolysis mechanism of VmoLac. PMID:25670483

Hiblot, Julien; Bzdrenga, Janek; Champion, Charlotte; Chabriere, Eric; Elias, Mikael

2015-01-01

241

Crystal structure of VmoLac, a tentative quorum quenching lactonase from the extremophilic crenarchaeon Vulcanisaeta moutnovskia.  

PubMed

A new representative of the Phosphotriesterase-Like Lactonases (PLLs) family from the hyperthermophilic crenarchaeon Vulcanisaeta moutnovskia has been characterized and crystallized. VmoLac is a native, proficient lactonase with promiscuous, low phosphotriesterase activity. VmoLac therefore represents an interesting candidate for engineering studies, with the aim of developing an efficient bacterial quorum-quenching agent. Here, we provide an extensive biochemical and kinetic characterization of VmoLac and describe the X-ray structures of the enzyme bound to a fatty acid and to its cognate substrate 3-oxo-C10 AHL (Acyl-Homoserine Lactone). The structures highlight possible structural determinants that may be involved in its extreme thermal stability (Tm = 128°C). Moreover, the structure reveals that the substrate binding mode of VmoLac significantly differs from those of its close homologues, possibly explaining the substrate specificity of the enzyme. Finally, we describe the specific interactions between the enzyme and its substrate, and discuss the possible lactone hydrolysis mechanism of VmoLac. PMID:25670483

Hiblot, Julien; Bzdrenga, Janek; Champion, Charlotte; Chabriere, Eric; Elias, Mikael

2015-01-01

242

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

PubMed

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

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

2013-07-01

243

The attenuation mechanism of S-waves in the source zone of the 1999 Chamoli earthquake  

NASA Astrophysics Data System (ADS)

In the present study the attenuation mechanism of seismic wave energy in and around the source area of the Chamoli earthquake of 29th March 1999 is estimated using the aftershock data. Most of the analyzed events are from the vicinity of the Main Central Thrust (MCT), which is a well-defined tectonic discontinuity in the Himalayas. Separation of intrinsic (Qi-1) and scattering (Qs-1) attenuation coefficient is done over the frequencies 1, 2, 4, 8 and 16 Hz using Multiple Lapse Time Window Analysis (MLTWA) method. It is observed that S-waves and their coda are primarily attenuated due to scattering attenuation and seismic albedo is very high at all the frequencies. A comparison of attenuation characteristics obtained using these aftershock data with those obtained using data of general seismicity of this region reveal that at lower frequencies both intrinsic and scattering attenuation for Chamoli was much higher compared to those for Garwhal-Kumaun region using general seismicity data. At higher frequencies intrinsic attenuation for Chamoli is lower than and scattering attenuation is comparable to those obtained using general seismicity data of Garwhal-Kumaun region.

Mukhopadhyay, S.; Kumar, A.; Garg, A.; Del-Pezzo, E.; Kayal, J. R.

2014-01-01

244

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

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

245

Occurrence and in-stream attenuation of wastewater-derived pharmaceuticals in Iberian rivers.  

PubMed

A multitude of pharmaceuticals enter surface waters via discharges of wastewater treatment plants (WWTPs), and many raise environmental and health concerns. Chemical fate models predict their concentrations using estimates of mass loading, dilution and in-stream attenuation. However, current comprehension of the attenuation rates remains a limiting factor for predictive models. We assessed in-stream attenuation of 75 pharmaceuticals in 4 river segments, aiming to characterize in-stream attenuation variability among different pharmaceutical compounds, as well as among river segments differing in environmental conditions. Our study revealed that in-stream attenuation was highly variable among pharmaceuticals and river segments and that none of the considered pharmaceutical physicochemical and molecular properties proved to be relevant in determining the mean attenuation rates. Instead, the octanol-water partition coefficient (Kow) influenced the variability of rates among river segments, likely due to its effect on sorption to sediments and suspended particles, and therefore influencing the balance between the different attenuation mechanisms (biotransformation, photolysis, sorption, and volatilization). The magnitude of the measured attenuation rates urges scientists to consider them as important as dilution when aiming to predict concentrations in freshwater ecosystems. PMID:24908335

Acuña, Vicenç; von Schiller, Daniel; García-Galán, Maria Jesús; Rodríguez-Mozaz, Sara; Corominas, Lluís; Petrovic, Mira; Poch, Manel; Barceló, Damià; Sabater, Sergi

2015-01-15

246

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

247

Abundance Gradients in Cooling Flow Clusters: Ginga Lac & Einstein SSS Spectra of A496, A1795, A2142 & A2199  

E-print Network

We analyze the Ginga LAC and Einstein SSS spectra of four cooling flow clusters, A496, A1795, A2142 and A2199, each of which shows firm evidence of a relatively cool component. The inclusion of such cool spectral components in joint fits of SSS and LAC data leads to somewhat higher global temperatures than are derived from the high energy LAC data alone. We find little evidence of cool emission outside the SSS field of view. Metal abundances appear to be centrally enhanced in all four cluster, with varying degrees of model dependence and statistical significance: the evidence is statistically strongest for A496 and A2142, somewhat weaker for A2199 and weakest for A1795. We also explore the model-dependence in the amount of cold, X-ray absorbing matter discovered in these clusters by White et al. (1991).

Raymond E. White III; C. S. R. Day; Isamu Hatsukade; John P. Hughes

1994-04-26

248

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

249

Adaptation of a Luciferase Gene Reporter and lac Expression System to Borrelia burgdorferi? †  

PubMed Central

The development of new genetic systems for studying the complex regulatory events that occur within Borrelia burgdorferi is an important goal of contemporary Lyme disease research. Although recent advancements have been made in the genetic manipulation of B. burgdorferi, there still remains a paucity of basic molecular systems for assessing differential gene expression in this pathogen. Herein, we describe the adaptation of two powerful genetic tools for use in B. burgdorferi. The first is a Photinus pyralis firefly luciferase gene reporter that was codon optimized to enhance translation in B. burgdorferi. Using this modified reporter, we demonstrated an increase in luciferase expression when B. burgdorferi transformed with a shuttle vector encoding the outer surface protein C (OspC) promoter fused to the luciferase reporter was cultivated in the presence of fresh rabbit blood. The second is a lac operator/repressor system that was optimized to achieve the tightest degree of regulation. Using the aforementioned luciferase reporter, we assessed the kinetics and maximal level of isopropyl-?-d-thiogalactopyranoside (IPTG)-dependent gene expression. This lac-inducible expression system also was used to express the gene carried on lp25 required for borrelial persistence in ticks (bptA). These advancements should be generally applicable for assessing further the regulation of other genes potentially involved in virulence expression by B. burgdorferi. PMID:17220265

Blevins, Jon S.; Revel, Andrew T.; Smith, Alexandra H.; Bachlani, Gulnaz N.; Norgard, Michael V.

2007-01-01

250

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

251

Comparison of Radio and EGRET ?-ray Properties between BL Lacs and other AGN  

NASA Astrophysics Data System (ADS)

We have compared EGRET Phase 1+2+3 gamma-ray data with Mets=E4hovi radio monitoring data of AGN at 22 and 37 GHz. The most probable gamma-ray AGN to be detected is a high polarization quasar (HPQ) with an ongoing and rising high frequency radio flare and a large associated variability brightness temperature T(b,var) (or Doppler boosting factor D). BL Lacs have a low detection rate compared even to 'non-blazar', low polarization quasars (LPQs). The detection probability depends on T(b,var) and, during a single EGRET pointing, the phase of the radio flare. The strength of the gamma-ray emission depends also on T(b,var) and on the strength of the radio flare. The gamma-ray properties of BL Lacs as well as other AGN are closely related both to the average radio properties and to the individual radio outbursts (shocks) growing in the source. Natural explanation is that the gamma emission is produced in the same shocks, induced by the synchrotron self-Compton mechanism.

Lähteenmäki, A.; Valtaoja, E.

252

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

NASA Astrophysics Data System (ADS)

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

Xiong, Dingrong; Zhang, Xiong; Zheng, Yonggang

2014-11-01

253

3.39-um laser beam attenuator  

NASA Astrophysics Data System (ADS)

Light beam attenuator is one kind of optical element which has been widely used in optical technique. According to beam attenuation principle, it can be divided into two kinds, one is absorbing type attenuator, the other is non-absorbing type attenuator. There has been considerable attention paid to study visible attenuator, but there are few ways to attenuate 3.39 micrometer laser beam. In this article we have introduced a series new type 3.39 micrometer laser beam attenuator made by using birefringent crystal. Some is absorbing type attenuator, the other is non-absorbing type attenuator. Such as: two calcite parallel plates type, two yttrium orthovanadate prism type, two yttrium orthovanadate parallel plates plus lambda/2 waveplate type, etc.

Xu, Fuyun; Chi, Zongtao

1996-11-01

254

The LCLS Gas Attenuator Revisited  

SciTech Connect

In the report ''X-ray attenuation cell'' [1] a preliminary analysis of the gas attenuator for the Linac Coherent Light Source (LCLS) was presented. This analysis was carried out for extremely stringent set of specifications. In particular, a very large diameter for the unobstructed beam was set (1 cm) to accommodate the spontaneous radiation; the attenuator was supposed to cover the whole range of energies of the coherent radiation, from 800 eV to 8000 eV; the maximum attenuation was set at the level of 10{sup 4}; the use of solid attenuators was not allowed, as well as the use of rotating shutters. The need to reach a sufficient absorption at the high-energy end of the spectrum predetermined the choice of Xe as the working gas (in order to have a reasonable absorption at a not-too-high pressure). A sophisticated differential pumping system that included a Penning-type ion pump was suggested in order to minimize the gas leak into the undulator/accelerator part of the facility. A high cost of xenon meant also that an efficient (and expensive) gas-recovery system would have to be installed. The main parameter that determined the high cost and the complexity of the system was a large radius of the orifice. The present viewpoint allows for much smaller size of the orifice, r{sub 0} = 1.5 mm. (1) The use of solid attenuators is also allowed (R.M. Bionta, private communication). It is, therefore, worthwhile to reconsider various parameters of the gas attenuator for these much less stringent conditions. This brief study should be considered as a physics input for the engineering design. As a working gas we consider now the argon, which, on the one hand, provides a reasonable absorption lengths and, on the other hand, is inexpensive enough to be exhausted into the atmosphere (no recovery). The absorption properties of argon are illustrated by Fig.1 where the attenuation factor A is shown for various beam energies, based on Ref. [2]. The other relevant parameters for argon are presented in Table 1.

Ryutov, D

2005-06-07

255

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

PubMed

The capabilities of some building materials used in Jordan to attenuate gamma radiation were tested. Measurements of the attenuation coefficients of limestone, bricks and concrete have been carried out using a HPGe-spectrometer. Narrow beam technique was used, with a multiple gamma radiation source of different energy lines. Results indicate that variations in the attenuation coefficient for all limestone samples, at the same energy line, are within the experimental uncertainties. On the basis of the results achieved, an empirical formula mu(m)=AE(-0.44) was proposed to calculate attenuation at various incident energies. Limestone of average thickness 7cm was found to stop 75% of a gamma beam of energy 662keV. Meanwhile a brick of effective thickness 7cm was found to stop 60% of the same beam. The total attenuation coefficient of concrete calculated at 1333keV was 11.2m(-1), which is less than that of limestone and bricks. PMID:17368884

Awadallah, Mohammad I; Imran, Mousa M A

2007-01-01

256

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

Microsoft Academic Search

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

Reinhard Pienitz; Karine Roberge; Warwick F. Vincent

2006-01-01

257

Anisotropy of magnetic susceptibility versus lattice-and shape-preferred orientation in the Lac Tio hemo-ilmenite ore body  

E-print Network

Keywords: Magnetic fabric EBSD Image analysis Iron­titanium ore Anorthosite The Lac Tio hemo-ilmenite ore body crops out in the outer portion of the 1.06 Ga Lac Allard anorthosite, a member of the Havre-Saint-Pierre anorthosite suite from the Grenville province of North America. It is made up of ilmenitite (commonly

Bascou, Jérôme

258

Ultrasonic attenuation and speed of sound of cornstarch suspensions.  

PubMed

The goal of this study is to contribute to the physics underlying the material properties of suspensions that exhibit shear thickening through the ultrasonic characterization of suspensions of cornstarch in a density-matched solution. Ultrasonic measurements at frequencies in the range of 4 to 8?MHz of the speed of sound and the frequency-dependent attenuation properties are reported for concentrations of cornstarch in a density-matched aqueous (cesium chloride brine) suspension, ranging up to 40% cornstarch. The speed of sound is found to range from 1483?±?10?m/s in pure brine to 1765?±?9?m/s in the 40% cornstarch suspension. The bulk modulus of a granule of cornstarch is inferred to be 1.2(±?0.1) × 10(10)?Pa. The attenuation coefficient at 5?MHz increases from essentially zero in brine to 12.0?±?1.2?dB/cm at 40% cornstarch. PMID:23464011

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

2013-03-01

259

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

260

NATURAL ATTENUATION OF CHLORINATED SOLVENTS  

EPA Science Inventory

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

261

White matter attenuation and megalencephaly.  

PubMed Central

The computed tomogram of a 6 month old girl with familial megalencephaly showed widespread attenuation throughout the white matter. She continued to be developmentally and neurologically normal. Her scan at age 3 years was normal apart from the megalencephaly. A tentative explanation for this unusual series of events is offered. Images Fig. 1 Fig. 2 PMID:4073939

Robinson, R O

1985-01-01

262

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. PMID:22088022

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

263

A New Approach for Detecting Attenuation Changes During High-Intensity Focused  

E-print Network

resulting from heating. To date, parametric images of attenuation coefficient from backscattered ultrasound to thermal damage [2]. Furthermore, knowledge of acoustic absorption is required to accurately predict heat have been associated with acoustic cavitation [3], which can make controlling HIFU difficult. Current

Illinois at Urbana-Champaign, University of

264

Antibody biodistribution coefficients  

PubMed Central

Tissue vs. plasma concentration profiles have been generated from a physiologically-based pharmacokinetic model of monoclonal antibody (mAb). Based on the profiles, we hypothesized that a linear relationship between the plasma and tissue concentrations of non-binding mAbs could exist; and that the relationship may be generally constant irrespective of the absolute mAb concentration, time, and animal species being analyzed. The hypothesis was verified for various tissues in mice, rat, monkey, and human using mAb or antibody-drug conjugate tissue distribution data collected from diverse literature. The relationship between the plasma and various tissue concentrations was mathematically characterized using the antibody biodistribution coefficient (ABC). Estimated ABC values suggest that typically the concentration of mAb in lung is 14.9%, heart 10.2%, kidney 13.7%, muscle 3.97%, skin 15.7%, small intestine 5.22%, large intestine 5.03%, spleen 12.8%, liver 12.1%, bone 7.27%, stomach 4.98%, lymph node 8.46%, adipose 4.78%, brain 0.351%, pancreas 6.4%, testes 5.88%, thyroid 67.5% and thymus is 6.62% of the plasma concentration. The validity of using the ABC to predict mAb concentrations in different tissues of mouse, rat, monkey, and human species was evaluated by generating validation data sets, which demonstrated that predicted concentrations were within 2-fold of the observed concentrations. The use of ABC to infer tissue concentrations of mAbs and related molecules provides a valuable tool for investigating preclinical or clinical disposition of these molecules. It can also help eliminate or optimize biodistribution studies, and interpret efficacy or toxicity of the drug in a particular tissue. PMID:23406896

Shah, Dhaval K.; Betts, Alison M.

2013-01-01

265

A Maximum Likelihood Approach to Determine Sensor Radiometric Response Coefficients for NPP VIIRS Reflective Solar Bands  

NASA Technical Reports Server (NTRS)

Optical sensors aboard Earth orbiting satellites such as the next generation Visible/Infrared Imager/Radiometer Suite (VIIRS) assume that the sensors radiometric response in the Reflective Solar Bands (RSB) is described by a quadratic polynomial, in relating the aperture spectral radiance to the sensor Digital Number (DN) readout. For VIIRS Flight Unit 1, the coefficients are to be determined before launch by an attenuation method, although the linear coefficient will be further determined on-orbit through observing the Solar Diffuser. In determining the quadratic polynomial coefficients by the attenuation method, a Maximum Likelihood approach is applied in carrying out the least-squares procedure. Crucial to the Maximum Likelihood least-squares procedure is the computation of the weight. The weight not only has a contribution from the noise of the sensor s digital count, with an important contribution from digitization error, but also is affected heavily by the mathematical expression used to predict the value of the dependent variable, because both the independent and the dependent variables contain random noise. In addition, model errors have a major impact on the uncertainties of the coefficients. The Maximum Likelihood approach demonstrates the inadequacy of the attenuation method model with a quadratic polynomial for the retrieved spectral radiance. We show that using the inadequate model dramatically increases the uncertainties of the coefficients. We compute the coefficient values and their uncertainties, considering both measurement and model errors.

Lei, Ning; Chiang, Kwo-Fu; Oudrari, Hassan; Xiong, Xiaoxiong

2011-01-01

266

Numerical solution of the identification problem for the attenuated Radon transform  

NASA Astrophysics Data System (ADS)

The attenuated Radon transform serves as a mathematical tool for single-photon emission computerized tomography (SPECT). The identification problem for the attenuated Radon transform is to find the attenuation coefficient, which is a parameter of the transform, from the values of the transform alone. Previous attempts to solve this problem used range theorems for the continuous attenuated/exponential Radon transform. We consider a matrix representation of the transform and formulate the corresponding discrete consistency conditions in the form of the orthogonal projection of the data vector onto the orthogonal complement of the column space of the matrix. The singular value decomposition is applied to compute the orthogonal projector and its Fréchet derivative. The numerical algorithm suggested is based on the Newton method with the Tikhonov regularization. Results of numerical experiments and inversion of the measured SPECT data are considered.

Bronnikov, A. V.

1999-10-01

267

Ferrite attenuator modulation improves antenna performance  

NASA Technical Reports Server (NTRS)

Ferrite attenuator inserted into appropriate waveguide reduces the gain of the antenna element which is causing interference. Modulating the ferrite attenuator to change the antenna gain at the receive frequency permits ground tracking until the antenna is no longer needed.

Hooks, J. C.; Larson, S. G.; Shorkley, F. H.; Williams, B. T.

1970-01-01

268

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

E-print Network

to automatically create (reverse engineer) a computer program representing the logic underlying the genetic network "reverse engineer" the logic underlying a genetic network. This reverse engineering entails creating bothAUTOMATIC CREATION OF A GENETIC NETWORK FOR THE lac OPERON FROM OBSERVED DATA BY MEANS OF GENETIC

Fernandez, Thomas

269

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

270

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

SciTech Connect

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

NONE

1996-06-01

271

4U1722 + 11 - The discovery of an X-ray selected BL Lac object  

NASA Technical Reports Server (NTRS)

The Uhuru X-ray source 4U1722 + 11 was observed using the microchannel-plate detector (High Resolution Imager) on the Einstein Observatory, and its coordinates measured to a precision of about 5 arcsec. A 16th-magnitude stellar object within the error circle was observed spectroscopically at CTIO, and at the AAT, and found to have a featureless continuum. Subsequent radio observations at the VLA have established that the object is a radio source at the level of 60 mJy, and optical polarization measurements have determined that the source exhibits variable polarization at the level of 10 percent. On the basis of these observations, it is concluded that 4U1722 + 11 is a member of the class of objects known as X-ray selected blazars of BL Lac objects.

Griffiths, R. E.; Wilson, A. S.; Ward, M. J.; Tapia, S.; Ulvestad, J. S.

1989-01-01

272

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

273

Spatial Diagnostics of Potential X-ray Remnants in Old Novae T Aur and DK Lac  

NASA Astrophysics Data System (ADS)

We propose 5 and 3 ks ACIS-S snapshots of potentially extended X-ray remnants of two old classical novae, T Aur and DK Lac. They are the likely counterparts of X-ray sources discovered in our Swift survey of old classical novae, and each target has a spatially-resolved optical remnant with a size of order arcseconds. The additional short Chandra snapshots will confirm or reject the tentative Swift identifications through pinpoint astrometry, and will distinguish between extended remnant emission or rejuvenated accretion. Both are important for understanding binary evolution and also potential post-outburst hibernation, while detection of extended emission will represent extremely rare additions to the exclusive club of X-ray emitting classical nova remnants.

Drake, Jeremy

2013-09-01

274

Modelling gene expression control using P systems: The Lac Operon, a case study.  

PubMed

In this paper P systems are used as a formal framework for the specification and simulation of biological systems. In particular, we will deal with gene regulation systems consisting of protein-protein and protein-DNA interactions that take place in different compartments of the hierarchical structure of the living cell or in different individual cells from a colony. We will explicitly model transcription and translation as concurrent and discrete processes using rewriting rules on multisets of objects and strings. Our approach takes into account the discrete character of the components of the system, its random behaviour and the key role played by membranes in processes involving signalling at the cell surface and selective uptake of substances from the environment. Our systems will evolve according to an extension of Gillespie's algorithm, called Multicompartmental Gillespie's Algorithm. The well known gene regulation system in the Lac Operon in Escherichia coli will be modelled as a case study to benchmark our approach. PMID:17822838

Romero-Campero, Francisco José; Pérez-Jiménez, Mario J

2008-03-01

275

STP Second Virial Coefficient Program  

NSDL National Science Digital Library

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

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

2009-02-18

276

Generation of attenuation map for MR-based attenuation correction of PET data in the head area employing 3D short echo time MR imaging  

NASA Astrophysics Data System (ADS)

Attenuation correction is a crucial step to get accurate quantification of Positron Emission Tomography (PET) data. An attenuation map to provide attenuation coefficients at 511 keV can be generated using Magnetic Resonance Images (MRI). One of the main steps involved in MR-based attenuation correction (MRAC) of PET data is to separate bone from air. Low signal intensity of bone in conventional MRI makes it difficult to separate bone from air in the head area, while their attenuation coefficients are very different. In literature, several groups proposed ultrashort echo-time (UTE) sequences to differentiate bone from air [4,5,7], because these sequences are capable of imaging tissues with short T2* relaxation time, such as cortical bone; however, they are difficult to use, expensive and time-consuming. Employing short echo-time (STE) MRI in combination with long echo-time (LTE) MRI, and along with high performance image processing algorithms is a good substitute for UTE-based PET attenuation correction; they are widely available, easy to use, inexpensive and much faster than UTE pulse sequences. In this work, we propose the use of STE sequences along with LTE ones, as well as a dedicated image processing method to differentiate bone from air cavities in the head area by creating contrast between the tissues. Attenuation coefficients at 511 kev, relying on literature [5], will then be assigned to the voxels. Acquisition was performed on a clinical 3T Tim Trio scanner (Siemens Medical Solution, Erlangen, Germany), employing a dual echo sequence. To achieve an optimized protocol with the best result for discrimination of bone and air, two types of acquisitions were performed, with and without fat suppression; the acquisition parameters were as follows: TE=1.21/5 ms, TR=5/17, FA=30, and TE=1.12/3.16 ms, TR=5/5, FA=12 for non-fat-suppressed and fat-suppressed protocol, respectively. Contrast enhancement and tissue segmentation were applied as processing steps, to successfully classify voxels into bone, air and soft tissue classes, yielding accuracy, sensitivity and specificity of 88%, 77% and 94%, for non-fat suppressed acquisition, respectively. This method could potentially be as an efficient method for generation of attenuation map in 511 keV for MR-based attenuation correction of PET data in clinical PET/MR applications with mixed air and bone signals.

Khateri, Parisa; Salighe Rad, Hamidreza; Fathi, Anahita; Ay, Mohammad Reza

2013-02-01

277

Study on laser and infrared attenuation performance of carbon nanotubes  

NASA Astrophysics Data System (ADS)

In recent years, the weapon systems of laser and infrared (IR) imaging guidance have been widely used in modern warfare because of their high precision and strong anti-interference. However, military smoke, a rapid and effective passive jamming method, can effectively counteract the attack of precision-guided weapons by their scattering and absorbing effects. The traditional smoke has good visible light (0.4-0.76?m) obscurant performance, but hardly any effects to other electromagnetic wave bands while the weapon systems of laser and IR imaging guidance usually work in broad band, including the near-infrared (1-3?m), middle-infrared (3-5?m), far-infrared (8-14?m), and so on. Accordingly, exploiting new effective obscurant materials has attracted tremendous interest worldwide nowadays. As is known, the nano-structured materials have lots of unique properties comparing with the traditional materials suggesting that they might be the perfect alternatives to solve the problems above. Carbon nanotubes (CNTs) are well-ordered, all-carbon hollow graphitic nano-structured materials with a high aspect ratio, lengths from several hundred nanometers to several millimeters. CNTs possess many unique intrinsic physical-chemical properties and are investigated in many areas reported by the previous studies. However, no application research about CNTs in smoke technology field is reported yet. In this paper, the attenuation performances of CNTs smoke to laser and IR were assessed in 20m3 smoke chamber. The testing wavebands employed in experiments are 1.06?m and 10.6?m laser, 3-5?m and 8-14?m IR radiation. The main parameters were obtained included the attenuation rate, transmission rate, mass extinction coefficient, etc. The experimental results suggest that CNTs smoke exhibits excellent attenuation ability to the broadband IR radiation. Their mass extinction coefficients are all above 1m2·g-1. Nevertheless, the mass extinction coefficients vary with the sampling time and smoke particles concentrations, even in the same testing waveband. With the time going the mass extinction coefficients will increase gradually. Based on the above results, theoretical calculations are also carried out for further exploitations. In general, CNTs smoke behaves excellent attenuation ability toward laser and IR under the experimental conditions. Therefore, they have great potentials to develop new smoke obscurant materials which could effectively interfere with broadband IR radiation including 1.06?m, 10.6?m, 3-5?m and 8-12?m IR waveband.

Liu, Xiang-cui; Liu, Qing-hai; Dai, Meng-yan; Cheng, Xiang; Fang, Guo-feng; Zhang, Tong; Liu, Haifeng

2014-11-01

278

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

ERIC Educational Resources Information Center

Coefficient alpha is almost universally applied to assess reliability of scales in psychology. We argue that researchers should consider alternatives to coefficient alpha. Our preference is for structural equation modeling (SEM) estimates of reliability because they are informative and allow for an empirical evaluation of the assumptions…

Yang, Yanyun; Green, Samuel B.

2011-01-01

279

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

280

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

PubMed Central

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

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

2012-01-01

281

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

PubMed Central

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

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

2014-01-01

282

Calculation of the X-Ray Bremsstrahlung Transmission Coefficient of Test Filter  

Microsoft Academic Search

The qualitative composition of the Xray brems? strahlung is characterized by parameters of Xray radia? tion attenuation during its transmission through absorb? ing material. One parameter is effective radiation energy determined using exposure radiation dose extinction (or exposure dose power) of a test filter (1). Effective energy is determined indirectly from transmission coefficient K of the test filter using a

M. G. Petrushanskii

2008-01-01

283

ENHANCEMENTS TO NATURAL ATTENUATION: SELECTED CASE STUDIES  

SciTech Connect

In 2003 the US Department of Energy (DOE) embarked on a project to explore an innovative approach to remediation of subsurface contaminant plumes that focused on introducing mechanisms for augmenting natural attenuation to achieve site closure. Termed enhanced attenuation (EA), this approach has drawn its inspiration from the concept of monitored natural attenuation (MNA).

Vangelas, K; W. H. Albright, W; E. S. Becvar, E; C. H. Benson, C; T. O. Early, T; E. Hood, E; P. M. Jardine, P; M. Lorah, M; E. Majche, E; D. Major, D; W. J. Waugh, W; G. Wein, G; O. R. West, O

2007-05-15

284

A Stochastic Dynamic Model of Rain Attenuation  

Microsoft Academic Search

A dynamic mathematical model of rain attenuation has been developed and is presented in this paper. This model permits the expression of analytic relationships between parameters commonly used to describe the properties of interest for communication. The dynamic model is based on the lognormal distribution of rain attenuation and utilizes a memoryless nonlinear device to transform attenuation and rain intensity

T. Maseng; P. Bakken

1981-01-01

285

trp RNA-binding attenuation protein-5' stem-loop RNA interaction is required for proper transcription attenuation control of the Bacillus subtilis trpEDCFBA operon.  

PubMed

The trp RNA-binding attenuation protein (TRAP) regulates expression of the Bacillus subtilis trpEDCFBA operon by a novel transcription attenuation mechanism. Tryptophan-activated TRAP binds to the nascent trp leader transcript by interacting with 11 (G/U)AG repeats, 6 of which are present in an antiterminator structure. TRAP binding to these repeats prevents formation of the antiterminator, thereby promoting formation of an overlapping intrinsic terminator. A third stem-loop structure that forms at the extreme 5' end of the trp leader transcript also plays a role in the transcription attenuation mechanism. The 5' stem-loop increases the affinity of TRAP for trp leader RNA. Results from RNA structure mapping experiments demonstrate that the 5' stem-loop consists of a 3-bp lower stem, a 5-by-2 asymmetric internal loop, a 6-bp upper stem, and a hexaloop at the apex of the structure. Footprinting results indicate that TRAP interacts with the 5' stem-loop and that this interaction differs depending on the number of downstream (G/U)AG repeats present in the transcript. Expression studies with trpE'-'lacZ translational fusions demonstrate that TRAP-5' stem-loop interaction is required for proper regulation of the trp operon. 3' RNA boundary experiments indicate that the 5' structure reduces the number of (G/U)AG repeats required for stable TRAP-trp leader RNA association. Thus, TRAP-5' stem-loop interaction may increase the likelihood that TRAP will bind to the (G/U)AG repeats in time to block antiterminator formation. PMID:10714985

Du, H; Yakhnin, A V; Dharmaraj, S; Babitzke, P

2000-04-01

286

Semiparametric Estimation of Index Coefficients  

Microsoft Academic Search

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

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

1989-01-01

287

Study of DCT coefficient distributions  

Microsoft Academic Search

Many image and video compression schemes perform the discrete cosine transform (DCT) to represent image data in frequency space. An analysis of a broad suite of images confirms previous finding that a Laplacian distribution can be used to model the luminance AC coefficients. This model is expanded and applied to color space (Cr\\/Cb) coefficients. In MPEG, the DCT is used

Stephen Smoot

1996-01-01

288

SEISMIC ATTENUATION FOR RESERVOIR CHARACTERIZATION  

SciTech Connect

In Section 1 of this first report we will describe the work we are doing to collect and analyze rock physics data for the purpose of modeling seismic attenuation from other measurable quantities such as porosity, water saturation, clay content and net stress. This work and other empirical methods to be presented later, will form the basis for ''Q pseudo-well modeling'' that is a key part of this project. In Section 2 of this report, we will show the fundamentals of a new method to extract Q, dispersion, and attenuation from field seismic data. The method is called Gabor-Morlet time-frequency decomposition. This technique has a number of advantages including greater stability and better time resolution than spectral ratio methods.

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

2002-01-01

289

The beta-globin locus control region enhances transcription of but does not confer position-independent expression onto the lacZ gene in transgenic mice.  

PubMed Central

The beta-globin locus control region (LCR) confers high levels of position-independent, copy number-dependent expression onto globin transgenes. Here > 40 independent transgenic mouse lines and founders that carried the LCR in cis with the beta-globin gene promoter driving a lacZ reporter gene were studied. Expression of the lacZ transgene was assayed by measuring beta-galactosidase enzyme activity in fetal liver extracts, the levels of which correlated with the quantity of lacZ mRNA determined using RNase protection assays. Unexpectedly, expression of the lacZ transgene was found to show strong position effects, varying as much as 700-fold per transgene copy. These position effects occurred even if the whole beta-globin gene was incorporated as part of the lacZ reporter gene. Moreover, DNase I-hypersensitive sites appeared in the transgene LCR in high expressing but not in low expressing lines, suggesting that the LCR itself was position dependent. In contrast, MEL cell clones, in which transcriptionally active integration sites were selected for, gave < 13-fold variation in expression per copy of an LCR-lacZ construct. These results show that the lacZ reporter affects the ability of the LCR to activate chromatin in mice and that culture cells are not an adequate model for position-independent gene expression studies. Images PMID:8670875

Guy, L G; Kothary, R; DeRepentigny, Y; Delvoye, N; Ellis, J; Wall, L

1996-01-01

290

A variable mechanical optical attenuator  

NASA Astrophysics Data System (ADS)

A new design of a variable mechanical optical attenuator is proposed in this paper. Mechanical attenuators are extensively important in designing optical communication systems. It is also highly used in testing and training purposes. The design consists a novel fiber optic splitter-combiner setup. Each branch of the splitter meets a specific branch of the combiner. A fixed distanced multi-window rotary wheel slides between them. Upon rotation the light is either blocked or allowed to pass from a splitter branch to a combiner branch. By changing the number of open gates, the amount of yielded light can be controlled. There is only one moving part. So, the design is easy to manufacture, use or repair. The basic design and work flow is explained. The formula for calculating the attenuation and calibration guideline is also discussed. Then the design is compared with the other design standards based on the areas of application. The possible effects of linear and non-linear properties of light is also discussed. The primary concerns that should be taken if this design is to be fabricated in photonic integrated circuits is also mentioned briefly.

Shehab, Omar

2012-06-01

291

Modification of atmospheric extinction coefficient of non-line-of-sight ultraviolet communication under weak turbulence  

NASA Astrophysics Data System (ADS)

A calculation method of scintillation attenuation (SA) for non-line-of-sight (NLOS) ultraviolet (UV) communication is proposed on the basis of weak turbulence theory. To improve the channel model under turbulent environment, the atmospheric extinction coefficient in combination with UV single-scatter approximation model is modified based on SA. The in-depth analysis and interesting conclusion of atmospheric extinction coefficient named the turbulence coefficient versus different factors, including refractive-index structure parameter at the ground with measurement data, transceiver range and transceiver apex angles, are conducted.

Li, Bifeng; Wang, Hongxing; Wu, Xiaojun; Song, Bo; Hu, Hao

2015-03-01

292

Underwater optical wireless communications: depth dependent variations in attenuation.  

PubMed

Depth variations in the attenuation coefficient for light in the ocean were calculated using a one-parameter model based on the chlorophyll-a concentration C(c) and experimentally-determined Gaussian chlorophyll-depth profiles. The depth profiles were related to surface chlorophyll levels for the range 0-4??mg/m², representing clear, open ocean. The depth where C(c) became negligible was calculated to be shallower for places of high surface chlorophyll; 111.5 m for surface chlorophyll 0.8attenuation for underwater ocean communication links, calculated to be 0.0092??m?¹ at a wavelength of 430 nm. By combining this with satellite surface-chlorophyll data, it is possible to quantify the attenuation between any two locations in the ocean, with applications for low-noise or secure underwater communications and vertical links from the ocean surface. PMID:24513735

Johnson, Laura J; Green, Roger J; Leeson, Mark S

2013-11-20

293

Methods of Attenuation Correction for Dual-Wavelength and Dual-Polarization Weather Radar Data  

NASA Technical Reports Server (NTRS)

In writing the integral equations for the median mass diameter and number concentration, or comparable parameters of the raindrop size distribution, it is apparent that the forms of the equations for dual-polarization and dual-wavelength radar data are identical when attenuation effects are included. The differential backscattering and extinction coefficients appear in both sets of equations: for the dual-polarization equations, the differences are taken with respect to polarization at a fixed frequency while for the dual-wavelength equations, the differences are taken with respect to frequency at a fixed polarization. An alternative to the integral equation formulation is that based on the k-Z (attenuation coefficient-radar reflectivity factor) parameterization. This-technique was originally developed for attenuating single-wavelength radars, a variation of which has been applied to the TRMM Precipitation Radar data (PR). Extensions of this method have also been applied to dual-polarization data. In fact, it is not difficult to show that nearly identical equations are applicable as well to dualwavelength radar data. In this case, the equations for median mass diameter and number concentration take the form of coupled, but non-integral equations. Differences between this and the integral equation formulation are a consequence of the different ways in which attenuation correction is performed under the two formulations. For both techniques, the equations can be solved either forward from the radar outward or backward from the final range gate toward the radar. Although the forward-going solutions tend to be unstable as the attenuation out to the range of interest becomes large in some sense, an independent estimate of path attenuation is not required. This is analogous to the case of an attenuating single-wavelength radar where the forward solution to the Hitschfeld-Bordan equation becomes unstable as the attenuation increases. To circumvent this problem, the equations can be expressed in the form of a final-value problem so that the recursion begins at the far range gate and proceeds inward towards the radar. Solving the problem in this way traditionally requires estimates of path attenuation to the final gate: in the case of orthogonal linear polarizations, the attenuations at horizontal and vertical polarizations (same frequency) are required while in the dual-wavelength case, attenuations at the two frequencies (same polarization) are required.

Meneghini, R.; Liao, L.

2007-01-01

294

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

NASA Astrophysics Data System (ADS)

This platform, called the Hydrology and Climate Change in Latin America and The Caribbean, or "HC-LAC", is an integrated quantitative simulation of hydrology and climate change. The HC-LAC is composed of two principal components: the Analytical Hydrography Dataset (AHD) and an enhanced version of the Generalized Watershed Loading Function (GWLF). The AHD is a spatially explicit surface water data layer of Central and South America derived from digital elevation data from the Shuttle Radar Topography Mission (SRTM) and modified by the USGS to provide more accurate flow between cells in the raster data. For the LAC area, AHD consists 230, 000 catchments and stream segments with an average area of 100 km2 and length of 10 km, respectively. The AHD data structure is patterned after the US National Hydrography Dataset Plus (NHDPlus), thus providing a proven structure for flexible data integration and analyses necessary for spatial models like the HC-LAC. The structure of the AHD enables the implementation of water balance modeling and general routing of flows through the stream network thus supporting a range of environmental models. GWLF is applied on each AHD catchment which is characterized by multiple land use and soil type. The response of each land use in a given catchment is modeled separately in generating stream flow as well as recharge to soil storage. The stream flows generated from each catchment are routed through stream networks, providing total flow at any point in the stream network. A pilot implementation of the HC-LAC was established for the Rio Grande basin in North West Argentina (drainage area 6,700 km2). The model was parameterized and calibrated using readily available data. Three stream flow time series were generated using a reference climate case and two climate change projections. The reference case was based on historical records and assumes no climate change. The two climate change projections were generated using the IPCC "A2" high emissions scenario with two general circulation models: the UKMO Hadley CM3 (used frequently in Argentina) and the CSIRO Mk3 (the "dry" scenario used by World Bank) for the period 2012-2060. The three stream flow time series were used to calculate unmet water demand for urban water supply and irrigation, taking into account various measures to adopt to climate change. The HC-LAC was also used to generate a complete surface flow database for the Rio Grande basin, which is proving useful for analysis of a variety of current and future water resource management issues by the local governmental agencies.

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

2013-05-01

295

Molar extinction coefficients of solutions of some organic compounds  

NASA Astrophysics Data System (ADS)

Molar extinction coefficients of aqueous solutions of some organic compounds, viz. formamide (CH_{3}NO), N-methylformamide (C_{2}H_{5}NO), NN-dimethylformamide (C_{3}H_{7}NO), NN-dimethylacetamide (C_{4}H_{9}NO), 1,4-dioxane (C_{4}H_{8}O_{2}), succinimide (C_{4}H_{5}NO_{2}) and solutions of acetamide (C_{2}H_{5}NO) and benzoic acid (C_{7}H_{6}O_{2}) in 1,4-dioxane (C_{4}H_{8}O_{2}) have been determined by narrow beam gamma-ray transmission method at 81, 356, 511, 662, 1173 and 1332 keV. The experimental values of mass attenuation coefficients of these compounds have been used to calculate effective atomic numbers and electron densities. The additivity rule earlier used for aqueous solution has been extended to non-aqueous (1,4-dioxane) solutions.

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

2004-05-01

296

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

NASA Astrophysics Data System (ADS)

Lead silicate glasses (LSGs) have high gamma-ray attenuation but low chemical durability properties. In this work, LSGs with (55.5-68.5 wt%) PbO content containing ZrO 2 and TiO 2 additions were produced. The chemical corrosion of various produced LSGs in 0.5 N HNO 3 aqueous solution and determination of their gamma-ray attenuation coefficients for 60Co and 137Cs sources were investigated. The weight loss measurements, the SEM micrographs, the EDS analysis of the sample surfaces and the ICP analysis of solution were used to characterize the dissolution process. The effects of PbO content, ZrO 2 and TiO 2 additives on chemical corrosion, and also the effect of PbO on gamma-ray attenuation coefficient, glass transition temperature (Tg), and density of LSG glasses were determined. The results showed that by increasing the lead content of glass the gamma-ray attenuation coefficient, chemical corrosion and density were increased, but the Tg decreased. One of the samples with PbO contents of 65.4 wt% and SiO 2 content of 26.9 wt% showed a very low chemical corrosion behavior and good gamma-ray absorption property.

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

2009-04-01

297

An elastic plate model for wave attenuation and ice floe breaking in the marginal ice zone  

NASA Astrophysics Data System (ADS)

We present a model for wave attenuation in the marginal ice zone (MIZ) based on a two-dimensional (one horizontal and one vertical dimension) multiple floating elastic plate solution in the frequency domain, which is solved exactly using a matched eigenfunction expansion. The only physical parameters that enter the model are length, mass, and elastic stiffness (of which, the latter two depend primarily on thickness) of the ice floes. The model neglects all nonlinear effects as well as floe collisions or ice creep and is therefore most applicable to floes which are large compared to the thickness and to wave conditions which are not extreme. The solution for a given arrangement of floes is fully coherent, and the results are therefore dependent on the exact geometry. We firstly show that this dependence can be removed by averaging over a distribution of floe lengths (we choose the Rayleigh distribution). We then show that after this averaging, the attenuation coefficient is a function of floe number and independent of floe length, provided the floe lengths are sufficiently large. The model predicts an exponential decay of energy, just as is shown experimentally. This enables us to provide explicit values for the attenuation coefficient, as a function of the average floe thickness and wave period. We compare our theoretical predictions of the wave attenuation with measured data and other scattering models. The limited data allows us to conclude that our model is applicable to large floes for short to medium wave periods (6 to 15 seconds). We also derive a floe breaking model, based on our wave attenuation model, which indicates that we are under-predicting the attenuation coefficients at long periods.

Kohout, A. L.; Meylan, M. H.

2008-09-01

298

The relationship between phytoplankton concentration and light attenuation in ocean waters  

NASA Technical Reports Server (NTRS)

The accuracy of chlorophyll estimates by ocean color algorithms is affected by the variability of particulate attenuation; the presence of dissolved organic matter; and the nonlinear inverse relationship between the attenuation coefficient, K, and chlorophyll. Data collected during the Warm Core Rings Program were used to model the downwelling light field and determine the impact of these errors. A possible mechanism for the nonlinearity of K and chlorophyll is suggested; namely, that changing substrate from nitrate-nitrogen to ammonium causes enhanced blue absorption by photosynthetic phytoplankton in oligotrophic surface waters.

Phinney, David A.; Yentsch, Charles S.

1986-01-01

299

An All-Optical Diode Based on Plasmonic Attenuation and Nonlinear Frequency Conversion  

NASA Astrophysics Data System (ADS)

We present the design of an all-optical diode in a metal-dielectric structure where plasmonic attenuation and quasi-phase-matching are harnessed to greatly improve its performance. Due to the asymmetric design of the second-order nonlinear coefficient, different incident directions will ignite different plasmonic nonlinear processes, which compensate or accelerate plasmonic attenuation. As a result, a unidirectional output of plasmonic signal is achieved. This designed all-optical diode shows advantages of low power consumption, short sample length, high isolation contrast, wide acceptance of structural and initial conditions, and tunable unidirectionality, and becomes of practical interest.

Ren, Ming-Liang; Zhong, Xiao-Lan; Chen, Bao-Qin; Li, Zhi-Yuan

2013-09-01

300

On the validity and improvement of the ultrasonic pulse-echo immersion technique to measure real attenuation.  

PubMed

A fundamental assumption embraced in conventional use of the ultrasonic pulse-echo immersion technique to measure attenuation in solid materials is revisited. The cited assumption relies on perfect and immutable adhesion at the water to sample interface, a necessary condition that allows calculating the reflection coefficient at any interface from elastic wave propagation theory. This parameter is then used to correct the measured signal and obtain the real attenuation coefficient of the sample under scrutiny. In this paper, cases in which the perfectly cohesive interfacial condition is not satisfied are presented. It is shown also that in those cases, the repeatability of the conditions at the interface is always uncertain. This implies that the reflection coefficients are unknown, even when density is known. A new method of simultaneously measuring the reflection coefficients for both exposed interfaces that are normal to the transducer, and the attenuation coefficient of the specimen is developed and is presented here. The robustness of the new method is proven, as we demonstrate that the proper value of attenuation is achieved independently of the continuously varying interfacial conditions of these non-ideal cases. PMID:23998204

Goñi, Miguel A; Rousseau, Carl-Ernst

2014-02-01

301

Advanced reconstruction of attenuation maps using SPECT emission data only  

NASA Astrophysics Data System (ADS)

Today, attenuation corrected SPECT, typically performed using CT or Gadolinium line source based transmission scans, is more and more becoming standard in many medical applications. Moreover, the information about the material density distribution provided by these scans is key for other artifact compensation approaches in advanced SPECT reconstruction. Major drawbacks of these approaches are the additional patient radiation and hardware/maintenance costs as well as the additional workflow effort, e.g. if the CT scans are not performed on a hybrid scanner. It has been investigated in the past, whether it is possible to recover this structural information solely from the SPECT scan data. However, the investigated methods often result in noticeable image artifacts due to cross-dependences between attenuation and activity distribution estimation. With the simultaneous reconstruction method presented in this paper, we aim to effectively prevent these typical cross-talk artifacts using a-priori known atlas information of a human body. At first, an initial 3D shape model is coarsely registered to the SPECT data using anatomical landmarks and each organ structure within the model is identified with its typical attenuation coefficient. During the iterative reconstruction based on a modified ML-EM scheme, the algorithm simultaneously adapts both, the local activity estimation and the 3D shape model in order to improve the overall consistency between measured and estimated sinogram data. By explicitly avoiding topology modifications resulting in a non-anatomical state, we ensure that the estimated attenuation map remains realistic. Several tests with simulated as well as real patient SPECT data were performed to test the proposed algorithm, which demonstrated reliable convergence behaviour in both cases. Comparing the achieved results with available reference data, an overall good agreement for both cold as well as hot activity regions could be observed (mean deviation: -5.98%).

Salomon, André; Goedicke, Andreas; Aach, Til

2009-02-01

302

Escherichia coli-mycobacteria shuttle vectors for operon and gene fusions to lacZ: the pJEM series.  

PubMed Central

A series of Escherichia coli-mycobacteria shuttle plasmids for the isolation and study of gene regulatory sequences was constructed. These pJEM vectors contain an efficient transcription terminator and multiple cloning sites and allow either operon or gene fusions to lacZ. By constructing operon fusions with pJEM15, we assessed various previously characterized mycobacterial promoters in the fast-growing species Mycobacterium smegmatis and the slow-growing species M. bovis BCG. Our results suggest that M. smegmatis and M. bovis BCG RNA polymerases do not share the same specificity. To isolate new mycobacterial promoters, an M. tuberculosis DNA library was generated, using pJEM13, and screened in M. smegmatis. Several Lac+ clones were isolated, and the beta-galactosidase activity was measured. Images PMID:7961429

Timm, J; Lim, E M; Gicquel, B

1994-01-01

303

D-Ala-D-lac binding is not required for the high activity of vancomycin dimers against vancomycin resistant enterococci.  

PubMed

Covalent dimerization and oligomerization of vancomycin is an important and extensively used strategy to develop analogues active against vancomycin resistant enteroccoci (VRE). Here, we have carried out investigations to probe the role of peptide binding (Lys-d-Ala-d-Lac) in the high anti-VRE activities of covalently linked vancomycin dimers. Covalent dimers of damaged vancomycin (desleucyl) were prepared, and their anti-VRE activities and binding affinities toward various model peptides were measured. Despite the dramatic loss in affinity toward several model peptides in comparison to the corresponding intact vancomycin dimers, these damaged dimers maintained good activity against VRE. These results strongly suggest that the high anti-VRE activities of covalent vancomycin dimers are conferred from mechanisms other than Lys-d-Ala-d-Lac binding. PMID:12862465

Jain, Rishi K; Trias, Joaquim; Ellman, Jonathan A

2003-07-23

304

In vivo ultrasonographic exposimetry: Human tissuespecific attenuation coefficients in the gynecologic examination  

E-print Network

. We wanted to validate the "homogeneous" tissue model-based Food and Drug Administration derating comprising the anterior abdominal wall, uterus, and vagina and validated the Food and Drug Administration definite and biologically harmful, even lethal, effects.2 Whether clinical instruments with lower power

Illinois at Urbana-Champaign, University of

305

Characterizing the vertical diffuse attenuation coefficient for downwelling irradiance in coastal waters: Implications for water  

E-print Network

.503 m- 1 , respectively. Error analysis revealed a significantly high uncertainty in the red region (600­700 nm) and, as expected, low estimation uncertainty in blue and green. When compared with IKONOS derived can be accom- plished by incorporating accurate bathymetric informa- tion in the classification

Rundquist, Donald C.

306

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

PubMed

Ultrasonic inverse problems such as spike train deconvolution, synthetic aperture focusing, or tomography attempt to reconstruct spatial properties of an object (discontinuities, delaminations, flaws, etc.) from noisy and incomplete measurements. They require an accurate description of the data acquisition process. Dealing with frequency-dependent attenuation and dispersion is therefore crucial because both phenomena modify the wave shape as the travel distance increases. In an inversion context, this paper proposes to exploit a linear model of ultrasonic data taking into account attenuation and dispersion. The propagation distance is discretized to build a finite set of radiation impulse responses. Attenuation is modeled with a frequency power law and then dispersion is computed to yield physically consistent responses. Using experimental data acquired from attenuative materials, this model outperforms the standard attenuation-free model and other models of the literature. Because of model linearity, robust estimation methods can be implemented. When matched filtering is employed for single echo detection, the model that we propose yields precise estimation of the attenuation coefficient and of the sound velocity. A thickness estimation problem is also addressed through spike deconvolution, for which the proposed model also achieves accurate results. PMID:24960708

Carcreff, Ewen; Bourguignon, Sébastien; Idier, Jérôme; Simon, Laurent

2014-07-01

307

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

E-print Network

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

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

2012-09-08

308

Converting Sabine absorption coefficients to random incidence absorption coefficients.  

PubMed

Absorption coefficients measured by the chamber method are referred to as Sabine absorption coefficients, which sometimes exceed unity due to the finite size of a sample and non-uniform intensity in the reverberation chambers under test. In this study, conversion methods from Sabine absorption coefficients to random incidence absorption coefficients are proposed. The overestimations of the Sabine absorption coefficient are investigated theoretically based on Miki's model for porous absorbers backed by a rigid wall or an air cavity, resulting in conversion factors. Additionally, three optimizations are suggested: An optimization method for the surface impedances for locally reacting absorbers, the flow resistivity for extendedly reacting absorbers, and the flow resistance for fabrics. With four porous type absorbers, the conversion methods are validated. For absorbers backed by a rigid wall, the surface impedance optimization produces the best results, while the flow resistivity optimization also yields reasonable results. The flow resistivity and flow resistance optimization for extendedly reacting absorbers are also found to be successful. However, the theoretical conversion factors based on Miki's model do not guarantee reliable estimations, particularly at frequencies below 250 Hz and beyond 2500?Hz. PMID:23742349

Jeong, Cheol-Ho

2013-06-01

309

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

310

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

311

Q-structure beneath the Tibetan Plateau from the inversion of Love- and Rayleigh-wave attenuation data  

NASA Astrophysics Data System (ADS)

The fundamental mode Love and Rayleigh waves generated by ten earthquakes and recorded across the Tibet Plateau, at QUE, LAH, NDI, NIL, KBL, SHL, CHG, SNG and HKG are analysed. Love- and Rayleigh-wave attenuation coefficients are obtained at time periods of 5-120 s using the spectral amplitudes of these waves for 23 different paths. Love wave attenuation coefficient varies from 0.0021 km -1, at a period of 10 s, to 0.0002 km -1 at a period of 90 s, attaining two maxima at time periods of 10 and 115 s, and two minima at time periods of 25 and 90 s. The Rayleigh-wave attenuation coefficient also shows a similar trend. The very low value for the dissipation factor, Q?, obtained in this study suggests high dissipation across the Tibetan paths. Backus-Gilbert inversion theory is applied to these surface wave attenuation data to obtain average Q?-1 models for the crust and uppermost mantle beneath the Tibetan Plateau. Independent inversion of Love- and Rayleigh-wave attenuation data shows very high attenuation at a depth of ˜50-120 km ( Q ? ? 10 ). The simultaneous inversion of the Love and Rayleigh wave data yields a model which includes alternating regions of high and low Q?-1 values. This model also shows a zone of high attenuating material at a depth of ˜40-120 km. The very high inferred attenuation at a depth of ˜40-120 km supports the hypothesis that the Tibetan Plateau was formed by horizontal compression, and that thickening occurred after the collision of the Indian and Eurasian plates.

Singh, D. D.; Gupta, Harsh K.

1982-08-01

312

A LacI-Family Regulator Activates Maltodextrin Metabolism of Enterococcus faecium  

PubMed Central

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

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

2013-01-01

313

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

314

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

315

Peculiar Optical Variability in BL Lac object S5 0716+714  

NASA Astrophysics Data System (ADS)

Blazars are very well known for flux variations over complete energy spectrum ranging from radio to very high energy gamma-rays (TeV). The different timescales of variations represents different emission mechanism responsible. The violent activities in the jets are directly manifested in the form of flux variations. Here, we report a very peculiar nature of optical intranight variability (INV) in BL Lac object S5 0716+714. The preliminary results from the seven year optical observations of this source, monitored using MIRO, revealed completely unexpected scenario of intranight variations during different brightness state of this object. The duty cycle of INV corresponding to the continuous monitoring of 2 hours or more turned to well in agreement with the literature (84 %). However, the amplitudes of INV are seen to highly dependent of the brightness state. The highest amplitude is seen when source was in relatively fainter state which again questions the traditional internal shock model which emphasize the maximum activity when source in most turbulent state. This clearly indicate the significant contribution of emission due to disk instabilities, reflecting such a rapid and strong flux variations.

Chandra, Sunil; Ganesh, Shashikiran; Baliyan, Kiran

316

Search for X-ray Spectral Features in Two BL Lac Objects  

NASA Technical Reports Server (NTRS)

This grant covered the analysis and interpretation of astrophysical data obtained with the XMM-Newton satellite mission. BL Lac objects are active galactic nuclei that exhibit unusually strong polarization and variability, and are also missing the usual strong optical/ultraviolet emission lines. They are typically strong X-ray sources, but this is the first survey gathering high-quality spectral data from a significant number of these objects. The observations were successful, and all data (for objects in this proposal as well as that of Dr. Perlman s) were of very good quality, as expected. We find that the X-ray spectra of most of these objects are well described by a power-law after allowing for low-energy absorption that can be attributed to neutral gas in the line of sight, presumably located in our own Galaxy. However, in some cases we see indications of a deviation from power-law behavior in the sense that the spectrum appears to be steepening (softening) to higher energies. We are developing a theoretical model in which the steepening is a result of energy-dependent cooling of the radiating particles.We searched for discrete spectral features that might be intrinsic to the objects or their host galaxies, but we found none at the level of sensitivity provided by these data. These are interestingly strong upper bounds.

2003-01-01

317

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

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

318

Activity of Lac repressor anchored to the Escherichia coli inner membrane  

PubMed Central

The transient inactivation of gene regulatory proteins by their sequestration to the cytoplasmic membrane in response to cognate signals is an increasingly recognized mechanism of gene regulation in bacteria. It remained to be shown, however, whether tethering to the membrane per se could be responsible for inactivation, i.e. whether such relocation leads to a spatial separation from the chromosome that results in inactivity or whether other mechanisms are involved. We, therefore, investigated the activity of Lac repressor artificially attached to the Escherichia coli cytoplasmic membrane. We demonstrate that this chimeric protein perfectly represses transcription initiated at the tac operator–promoter present on a plasmid and even in the chromosome. Moreover, this repression is inducible as normal. The data suggest that proteins localized to the inner face of the cytoplasmic membrane in principle have unrestricted access to the chromosome. Thus sequestration to the membrane in terms of physical separation from the chromosome cannot account alone for the inactivation of regulatory proteins. Other mechanisms, like induction of a conformational change or masking of binding domains are required additionally. PMID:15867195

Görke, Boris; Reinhardt, Jana; Rak, Bodo

2005-01-01

319

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 PMID:6306561

Fried, M G; Crothers, D M

1983-01-01

320

Polymer Gels as Temperature-responsive Attenuator  

NASA Astrophysics Data System (ADS)

The ultrasonic attenuation in N-isopropylacrylamide (NIPA) gel has been measured as a function of temperature at various frequencies. It is found that at room temperature, the attenuation of a longitudinal ultrasonic wave in the gel is small and close to that of pure water. However, as the temperature increases above the spinodal phase transition point of the gel, the attenuation increases drastically. This change of the attenuation is completely reversible and due to the micro-domains formed in the NIPA gel above its phase transition temperature. The change of attenuation at 15 MHz in the temperature range between 26 and 45 ^0C is about 26 dB/cm. The rate of attenuation change is within 5 minutes for a sample with diameter 1 cm and height 0.8 cm. The results reported here may have potential applications from ultrasonic assistant drug-release to a switch for ultrasonic signals.

Yuan, Kaihua; Hu, Zhibing; Li, Yong

1998-10-01

321

An emerging population of BL Lacs with extreme properties: towards a class of EBL and cosmic magnetic field probes?  

E-print Network

High energy observations of extreme BL Lac objects, such as 1ES 0229+200 or 1ES 0347-121, recently focused interest both for blazar and jet physics and for the implication on the extragalactic background light and intergalactic magnetic field estimate. However, the number of these extreme highly peaked BL Lac objects (EHBL) is still rather small. Aiming at increase their number, we selected a group of EHBL candidates starting from the BL Lac sample of Plotkin et al. (2011), considering those undetected (or only barely detected) by the Large Area Telescope onboard Fermi and characterized by a high X-ray vs. radio flux ratio. We assembled the multi-wavelength spectral energy distribution of the resulting 9 sources, profiting of publicly available archival observations performed by the Swift, Galex and Fermi satellites, confirming their nature. Through a simple one-zone synchrotron self-Compton model we estimate the expected VHE flux, finding that in the majority of cases it is within the reach of present genera...

Bonnoli, Giacomo; Ghisellini, Gabriele; Sbarrato, Tullia

2015-01-01

322

Colloque ECLIPSE II, 15 et 16 octobre 2007, CNRS Paris 1 Culture du millet et rosion des sols depuis l'Age du Bronze autour du Lac  

E-print Network

depuis l'Age du Bronze autour du Lac du Bourget : Apport des lipides sédimentaires au projet APHRODYTE Néolithique au Moyen Age. L'analyse des lipides préservés dans les sédiments du Lac du Bourget révèle la'�ge du Bronze est caractérisé par de fortes concentrations en miliacine, traduisant la culture intensive

Paris-Sud XI, Université de

323

Salmonella Enterica Serovar Typhimurium HilA-LacZY Fusion Gene Response to Iron Chelation or Supplementation in Rich and Minimal Media  

Microsoft Academic Search

Virulence expression of Salmonella enterica serovar Typhimurium under iron limited condition was measured by ?-galactosidase (?-gal) assay using a hilA-lacZY fusion strain and calculated as Miller units. hilA-lacZY?-galactosidase assays were performed in brain heart infusion (BHI) and minimal media (M9), after iron chelation with 2, 2-dipridyl and iron-supplementation respectively. Before performing virulence assays, concentrations of iron in the media were

P. Rishi; C. L. Woodward; W.-K. Kim; S. C. Ricke

2004-01-01

324

Dust Attenuation at High Redshift  

NASA Astrophysics Data System (ADS)

In this work we study the dust distribution of the 100 most massive systems in the Vulcan simulation, a new state of the art cosmological simulation of a 25 Mpc per side volume, with unprecedented spatial resolution. The galaxies in our sample have typical stellar masses of 10**8.5-10.5 solar masses and star formation rates in the range 1-100 solar masses per year, typical of galaxies observed in the CANDELS survey. Interstellar dust remarkably affects how we observe galaxies - it comprises only ~ 0.1% of the total mass in a galaxy yet absorbs nearly 50% of it's starlight and reradiates it as far infrared continuum emission. Here we use a complete set of resolved systems to study how this attenuation varies with halo mass and metallicity, as well as star formation history, and orientation at high redshift. To measure the effects of dust we use Sunrise, a 3D radiative transfer code, which processes stellar light through dust in arbitrary geometries, and calculates the SED of every resolution element, from the far-UV to far-infrared. Using Sunrise, we can realistically calculate the attenuation of each resolved galaxy to quantify its variation with physical quantities. In addition, with these 'simulated observations', we compare our sample to the high redshift IRX-beta relationship observed in Lyman break galaxies, and investigate the cause of its intrinsic scatter.

Skinner, Danielle; Anderson, Lauren M.; Quinn, Thomas R.; Governato, Fabio; Tremmel, Michael J.

2015-01-01

325

SEISMIC ATTENUATION FOR RESERVOIR CHARACTERIZATION  

SciTech Connect

We have developed and tested technology for a new type of direct hydrocarbon detection. The method uses inelastic rock properties to greatly enhance the sensitivity of surface seismic methods to the presence of oil and gas saturation. These methods include use of energy absorption, dispersion, and attenuation (Q) along with traditional seismic attributes like velocity, impedance, and AVO. Our approach is to combine three elements: (1) a synthesis of the latest rock physics understanding of how rock inelasticity is related to rock type, pore fluid types, and pore microstructure, (2) synthetic seismic modeling that will help identify the relative contributions of scattering and intrinsic inelasticity to apparent Q attributes, and (3) robust algorithms that extract relative wave attenuation attributes from seismic data. This project provides: (1) Additional petrophysical insight from acquired data; (2) Increased understanding of rock and fluid properties; (3) New techniques to measure reservoir properties that are not currently available; and (4) Provide tools to more accurately describe the reservoir and predict oil location and volumes. These methodologies will improve the industry's ability to predict and quantify oil and gas saturation distribution, and to apply this information through geologic models to enhance reservoir simulation. We have applied for two separate patents relating to work that was completed as part of this project.

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

2003-12-01

326

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

SciTech Connect

A systematic assessment of a variety of physics issues affecting the performance of the LCLS X-ray beam attenuator is presented. Detailed analysis of the gas flow in the gas attenuator and in the apertures is performed. A lot of attention is directed towards the gas ionization and heating by intense X-ray pulses. The role of these phenomena in possible deviations of the attenuation coefficient from its 'dialed in' value is evaluated and found small in most cases. Other sources of systematic and statistical errors are also discussed. The regimes where the errors may reach a few percent correspond to the lower X-ray energies (less than 2 keV) and highest beam intensities. Other effects discussed include chemical interaction of the gas with apertures, shock formation in the transonic flow in the apertures of the attenuator, generation of electromagnetic wakes in the gas, and head-to-tail variation of the attenuation caused by the ionization of gas or solid. Possible experimental tests of the consistency of the physics assumptions used in the concept of the gas attenuator are discussed. Interaction of X-rays with the solid attenuator (that will be used at higher X-ray energies, from 2.5 to 8 keV) is considered and thermo-mechanical effects caused by the beam heating are evaluated. Wave-front distortions induced by non-uniform heating of both the solid and the gas are found to be small. An overall conclusion drawn from the analysis presented is that the attenuator will be a reliable and highly versatile device, provided that some caution is exercised in its use for highest beam intensities at lowest X-ray energies.

Ryutov, D.D.; Bionta, R.M.; Hau-Riege, S.P.; Kishiyama, K.I.; McMahon, D.; Roeben, M.D.; Shen, S.; /LLNL, Livermore; Stefan, P.M.; /SLAC; ,

2011-02-07

327

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

328

Seebeck coefficient of one electron  

SciTech Connect

The Seebeck coefficient of one electron, driven thermally into a semiconductor single-electron box, is investigated theoretically. With a finite temperature difference ?T between the source and charging island, a single electron can charge the island in equilibrium, directly generating a Seebeck effect. Seebeck coefficients for small and finite ?T are calculated and a thermally driven Coulomb staircase is predicted. Single-electron Seebeck oscillations occur with increasing ?T, as one electron at a time charges the box. A method is proposed for experimental verification of these effects.

Durrani, Zahid A. K., E-mail: z.durrani@imperial.ac.uk [Department of Electrical and Electronic Engineering, Imperial College London, South Kensington Campus, London SW7 2AZ (United Kingdom)

2014-03-07

329

Analysis of frequency dependent attenuation in shallow water  

NASA Astrophysics Data System (ADS)

This thesis is motivated by the experiments conducted near the site of AMCOR Borehole 6010 on the New Jersey Continental Shelf in 1988 and 1993. A major objective of these experiments was the evaluation of propagation predictability in sandy shallow water environments. In this thesis we use a non-linear frequency dependence of the sediment volume attenuation to determine estimates for the site specific surficial attenuation coefficient and the power-law exponent in the uppermost sediment layer. Previous studies in the literature determined that a site specific frequency power exponent of 1.5, relative to a reference frequency of 50 Hz over the frequency interval 50-1000 Hz, provided the best comparison with the measurements. In our approach we use 1 kHz as an attenuation reference frequency and employ different parameter ranges and optimization criteria. A metric of transmission loss variation with range is an effective attenuation coefficient (EAC) that can be extracted from the range and depth averaged transmission loss, both for measurements and for calculated data with the parabolic equation. Once we have determined the EAC for both measured and calculated data, preliminary parameter ranges are found based on a normalized standard deviation analysis. Then we fit measured-computed EAC pairs by the least square fit (LS). If the agreement were perfect, then the slope of the straight line fit through all the points given by the measured-computed pairs would be one. Finally, the frequency exponent in the power-law dependance is allowed to vary until agreement between measured and calculated EACs is achieved within acceptable bounds and the hypothesis that the LS slope is one is tested. For 400-1000 Hz, this procedure leads to a power exponent, in the range 1.7-2.0, which is consistent with other sand-silt regions. The estimates are robust with respect to variations in the water and sediment sound-speed profiles and the sediment layer thickness. The influence of measured range dependence on sound speed and bathymetry is examined. Signal time spread calculation code is checked on the Pekeris type waveguide. We provide further application, such as estimates of signal time spread for a recent experiment in the same ocean region.

Dediu, Simona M.

330

Measurements of Wave Attenuation Through Model and Live Vegetation in a Wave Tank  

NASA Astrophysics Data System (ADS)

It is well accepted that wetlands have an important role in shoreline protection against wave damage. However, there is still a lack of knowledge on primary mechanisms of wave attenuation though wetland vegetation. The purpose of this study was to understand these mechanisms and quantify the impact of vegetation on the waves through a series of laboratory experiments. Experiments were conducted in a wave tank at the USDA-ARS-National Sedimentation Laboratory to measure the rate of wave attenuation through emergent and submerged rigid and flexible cylindrical stems, and live vegetation. Dormant and healthy Spartina alterniflora and healthy Juncus romerianus, two common plant species in coastal areas, were used during the tests. The time series water surface elevation at five locations was recorded by wave probes and the water surface profile through the vegetation field was recorded using a digital video camera. The recorded data were analyzed with imaging techniques to identify the wave attenuation characteristic of wetland vegetation and drag coefficients.

Ozeren, Y.; Wren, D. G.

2010-12-01

331

Live attenuated vaccines against pertussis.  

PubMed

The intensive use of pertussis vaccines has dramatically reduced the incidence of whooping cough during the 20th century. However, recent outbreaks in countries with high vaccination coverage illustrate the shortcomings of current vaccination regimens, and immunity induced by the most recent, acellular vaccines wanes much faster than anticipated. As an alternative, live attenuated vaccine candidates have recently been developed in order to mimic natural infection, which induces long-lasting immunity. One of them has successfully completed a Phase I trial in humans and is now undergoing further product and clinical developments. This article describes the development of such vaccines, discusses their advantages over existing vaccines and their interesting bystander properties as powerful anti-inflammatory agents, which widens their potential use far beyond that for protection against whooping cough. PMID:25085735

Locht, Camille; Mielcarek, Nathalie

2014-09-01

332

Attenuation of skeletal muscle and strength in the elderly: The Health ABC Study.  

PubMed

Although loss of muscle mass is considered a cause of diminished muscle strength with aging, little is known regarding whether composition of aging muscle affects strength. The skeletal muscle attenuation coefficient, as determined by computed tomography, is a noninvasive measure of muscle density, and lower values reflect increased muscle lipid content. This investigation examined the hypothesis that lower values for muscle attenuation are associated with lower voluntary isokinetic knee extensor strength at 60 degrees/s in 2,627 men and women aged 70-79 yr participating in baseline studies of the Health ABC Study, a longitudinal study of health, aging, and body composition. Strength was higher in men than in women (132.3 +/- 34.5 vs. 81.4 +/- 22.0 N x m, P < 0.01). Men had greater muscle attenuation values (37.3 +/- 6.5 vs. 34.7 +/- 7.0 Hounsfield units) and muscle cross-sectional area (CSA) at the midthigh than women (132.7 +/- 22.4 vs. 93.3 +/- 17.5 cm(2), P < 0.01 for both). The strength per muscle CSA (specific force) was also higher in men (1.00 +/- 0.21 vs. 0.88 +/- 0.21 N x m x cm(-2)). The attenuation coefficient was significantly lower for hamstrings than for quadriceps (28.7 +/- 8.7 vs. 41.1 +/- 6.9 Hounsfield units, P < 0.01). Midthigh muscle attenuation values were lowest (P < 0.01) in the eldest men and women and were negatively associated with total body fat (r = -0.53, P < 0.01). Higher muscle attenuation values were also associated with greater specific force production (r = 0.26, P < 0.01). Multivariate regression analysis revealed that the attenuation coefficient of muscle was independently associated with muscle strength after adjustment for muscle CSA and midthigh adipose tissue in men and women. These results demonstrate that the attenuation values of muscle on computed tomography in older persons can account for differences in muscle strength not attributed to muscle quantity. PMID:11356778

Goodpaster, B H; Carlson, C L; Visser, M; Kelley, D E; Scherzinger, A; Harris, T B; Stamm, E; Newman, A B

2001-06-01

333

VERITAS Observations of the BL Lac Object PG 1553+113  

NASA Astrophysics Data System (ADS)

We present results from VERITAS observations of the BL Lac object PG 1553+113 spanning the years 2010, 2011, and 2012. The time-averaged spectrum, measured between 160 and 560 GeV, is well described by a power law with a spectral index of 4.33 ± 0.09. The time-averaged integral flux above 200 GeV measured for this period was (1.69 ± 0.06) × 10-11 photons cm-2 s-1, corresponding to 6.9% of the Crab Nebula flux. We also present the combined ?-ray spectrum from the Fermi Large Area Telescope and VERITAS covering an energy range from 100 MeV to 560 GeV. The data are well fit by a power law with an exponential cutoff at 101.9 ± 3.2 GeV. The origin of the cutoff could be intrinsic to PG 1553+113 or be due to the ?-ray opacity of our universe through pair production off the extragalactic background light (EBL). Given lower limits to the redshift of z > 0.395 based on optical/UV observations of PG 1553+113, the cutoff would be dominated by EBL absorption. Conversely, the small statistical uncertainties of the VERITAS energy spectrum have allowed us to provide a robust upper limit on the redshift of PG 1553+113 of z <= 0.62. A strongly elevated mean flux of (2.50 ± 0.14) × 10-11 photons cm-2 s-1 (10.3% of the Crab Nebula flux) was observed during 2012, with the daily flux reaching as high as (4.44 +/- 0.71) × 10-11 {photons} {cm}-2 {s}-1 (18.3% of the Crab Nebula flux) on MJD 56048. The light curve measured during the 2012 observing season is marginally inconsistent with a steady flux, giving a ?2 probability for a steady flux of 0.03%.

Aliu, E.; Archer, A.; Aune, T.; Barnacka, A.; Behera, B.; Beilicke, M.; Benbow, W.; Berger, K.; Bird, R.; Buckley, J. H.; Bugaev, V.; Byrum, K.; Cardenzana, J. V.; Cerruti, M.; Chen, X.; Ciupik, L.; Connolly, M. P.; Cui, W.; Dickinson, H. J.; Dumm, J.; Eisch, J. D.; Errando, M.; Falcone, A.; Federici, S.; Feng, Q.; Finley, J. P.; Fortin, P.; Fortson, L.; Furniss, A.; Galante, N.; Gillanders, G. H.; Griffin, S.; Griffiths, S. T.; Grube, J.; Gyuk, G.; Håkansson, N.; Hanna, D.; Holder, J.; Hughes, G.; Humensky, T. B.; Johnson, C. A.; Kaaret, P.; Kar, P.; Kertzman, M.; Khassen, Y.; Kieda, D.; Krawczynski, H.; Krennrich, F.; Kumar, S.; Lang, M. J.; Madhavan, A.; McArthur, S.; McCann, A.; Meagher, K.; Millis, J.; Moriarty, P.; Nieto, D.; O'Faoláin de Bhróithe, A.; Ong, R. A.; Orr, M.; Otte, A. N.; Park, N.; Perkins, J. S.; Pohl, M.; Popkow, A.; Prokoph, H.; Pueschel, E.; Quinn, J.; Ragan, K.; Rajotte, J.; Reyes, L. C.; Reynolds, P. T.; Richards, G. T.; Roache, E.; Sembroski, G. H.; Shahinyan, K.; Staszak, D.; Telezhinsky, I.; Tucci, J. V.; Tyler, J.; Varlotta, A.; Vassiliev, V. V.; Wakely, S. P.; Weinstein, A.; Welsing, R.; Wilhelm, A.; Williams, D. A.; Zitzer, B.

2015-01-01

334

Jacob's lac operon drawing, still imageSite: DNA Interactive (www.dnai.org)  

NSDL National Science Digital Library

small image of Francois Jacob's lac operon drawing. So by comparing the system of the viruses, the lysogenic bacteria on the one hand and the induced synthesis of galactosidase, it was clear that it was two very similar system, and by comparing this system we came to a model which I am trying to describe now, the idea what you had a gene controlling the structure of proteins, which we called structural gene, and we can call that SG-1, SG-2, cloned to each other, for instance the Z gene of galactosidase and the Y gene permease. And somewhere else, which could be either far or close to the other, a regulatory gene, that is a gene, which control the expression of these two structural genes. So the idea were that from this you had a messenger, that the gene which is, it's DNA, a messenger which was RNA, and from this messenger proteins were done. So that goes like that. Now the regulation was by, what we call this negative system, that is a regulatory gene made a product, which at first we thought was RNA but finally was protein, so it made a protein which we called a repressor. And this repressor was acting on a small sequence of DNA adjacent to the structure, which we called the operator. So there was here, so the regulatory gene produced a repressor, a protein, which binds to a specific sequence, which is the operator, which control the initiation of messenger production. And the lactose that is the inducer, was supposed to interact with the repressor and prevent him from attaching to the operator. So the repressor was a double-sided structure, one which recognize the operator and the other which recognize the small molecule, the lactose. And this we call the negative system because it blocked, so that was the model, which we call operon, 'ron', with 'on'.

2008-10-06

335

Bone marrow and liver mutagenesis in lacZ transgenic mice treated with hexavalent chromium.  

PubMed

The mutagenic effects of the hexavalent chromium compound K2CrO4 in lacZ transgenic mice (Muta Mouse) were investigated at two sampling times. K2CrO4 was administered intraperitoneally to five male mice per treatment group at a single dose of 40 mg/kg. The animals were sacrificed on days 1 and 7 after the treatment. Mutant frequencies in the bone marrow and liver were analyzed by the positive selection method using Escherichia coli C (galE-) strain and phenyl beta-D-galactoside. K2CrO4 induced a significant increase in mutant frequency in the bone marrow on day 1, but not on day 7 after the treatment. In the liver, on the other hand, a significant induction in the mutant frequency was seen on day 7, whereas no induction was observed on day 1. The reason for the different responses to the mutagenic activity of K2CrO4 between these organs may be related to their cell turnover rates. The mutations induced by K2CrO4 in the bone marrow may have occurred in more differentiated cells than stem cells, and the rapid proliferative activity may have caused a rapid decrease in mutated cells by day 7. These results suggest that experiments on mutagenesis should be done with more than one sampling point, a short expression time in addition to a longer one, so as to detect mutations induced in organ with high cell proliferation. PMID:9508365

Itoh, S; Shimada, H

1998-01-13

336

Attenuation of landfill leachate pollutants in aquifers  

Microsoft Academic Search

Landfill leachate contains a variety of pollutants that may potentially contaminate the ground water and affect the quality of surface waters and well waters. The literature has been critically reviewed in order to assess the attenuation processes governing the contaminants in leachate?affected aquifers. After an introductory section on leachate composition, the physical and chemical frameworks for the attenuation processes are

Thomas H. Christensen; Peter Kjeldsen; Gorm Heron; Per H. Nielsen; Poul L. Bjerg; Peter E. Holm

1994-01-01

337

Scatter and attenuation correction for 111In based on energy spectrum fitting.  

PubMed

A combined scatter and attenuation correction that does not require a transmission scan is proposed for 111In imaging. Estimates of the unscattered intensity at both 171 and 245 keV are obtained by fitting the observed energy spectrum at each pixel or region of interest using the measured scatter-free spectrum and a simple model for scatter. The scatter model for the 171 keV peak accounts for scatter contributed by both the 171 and 245 keV emissions. After correcting for scatter, the attenuation is estimated from the observed ratio of photopeak intensities using the known difference in attenuation at the two emission energies and a model based on a point source in water. Accurate scatter correction is a prerequisite for the success of this method because scatter from the higher energy emission will otherwise contaminate the lower photopeak. This differential attenuation method (DAM) of estimating attenuation is demonstrated and calibrated using a series of point source measurements with a wedge-shaped attenuator. The observed absolute and differential attenuation are in good agreement with the narrow-beam linear attenuation coefficients for water. Estimates of precision suggest a depth resolution of 1.0-2.5 cm for realistic count densities over the clinically relevant depth range (0-25 cm). The accuracy of DAM in a more realistic attenuation environment is assessed using a hot sphere inside the anthropomorphic data spectrum torso phantom viewed from several angles (with differing attenuation). Finally, the potential of DAM for SPECT attenuation correction was investigated by computer simulation using the SIMSET Monte Carlo software. Preliminary results based on measured planar data and simulated SPECT data indicate that DAM can improve the quality and quantitative accuracy of 111In images. In one SPECT simulation study, the average error in tumor to soft-tissue ratios was reduced from 32% for uncorrected data to 8% for data corrected with DAM. However, the technique is susceptible to significant noise amplification and can cause substantial streak artifacts in low-count SPECT studies if sufficient smoothing of the depth estimates is not performed. PMID:8839424

Kaplan, M S; Miyaoka, R S; Kohlmyer, S K; Haynor, D R; Harrison, R L; Lewellen, T K

1996-07-01

338

Using nearest neighbors for accurate estimation of ultrasonic attenuation in the spectral domain.  

PubMed

Attenuation is a key diagnostic parameter of tissue pathology change and thus may play a vital role in the quantitative discrimination of malignant and benign tumors in soft tissue. In this paper, two novel techniques are proposed for estimating the average ultrasonic attenuation in soft tissue using the spectral domain weighted nearest neighbor method. Because the attenuation coefficient of soft tissues can be considered to be a continuous function in a small neighborhood, we directly estimate an average value of it from the slope of the regression line fitted to the 1) modified average midband fit value and 2) the average center frequency shift along the depth. To calculate the average midband fit value, an average regression line computed from the exponentially weighted short-time Fourier transform (STFT) of the neighboring 1-D signal blocks, in the axial and lateral directions, is fitted over the usable bandwidth of the normalized power spectrum. The average center frequency downshift is computed from the maximization of a cost function defined from the normalized spectral cross-correlation (NSCC) of exponentially weighted nearest neighbors in both directions. Different from the large spatial signal-block-based spectral stability approach, a costfunction- based approach incorporating NSCC functions of neighboring 1-D signal blocks is introduced. This paves the way for using comparatively smaller spatial area along the lateral direction, a necessity for producing more realistic attenuation estimates for heterogeneous tissue. For accurate estimation of the attenuation coefficient, we also adopt a reference-phantombased diffraction-correction technique for both methods. The proposed attenuation estimation algorithm demonstrates better performance than other reported techniques in the tissue-mimicking phantom and the in vivo breast data analysis. PMID:25004473

Hasan, Md Kamrul; Hussain, Mohammad Arafat; Ara, Sharmin R; Lee, Soo Yeol; Alam, S Kaisar

2013-06-01

339

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

340

Tables of the coefficients A  

NASA Technical Reports Server (NTRS)

Numerical coefficients required to express the angular distribution for the rotationally elastic or inelastic scattering of electrons from a diatomic molecule were tabulated for the case of nitrogen and in the energy range from 0.20 eV to 10.0 eV. Five different rotational states are considered.

Chandra, N.

1974-01-01

341

Transport Coefficients of Quantum Plasma  

Microsoft Academic Search

The two time Green function method is applied to calculate the transport coefficients of an elecron gas. The sequence of equations for the Green functions is derived, and it is shown that the results corresponding to the random phase approximation (including the exchange effects) can be obtained by terminating this sequence at the first stage. Proceeding to the second stage,

Mitsuo Watabe

1962-01-01

342

Sublimation Coefficient of Water Ice  

NASA Astrophysics Data System (ADS)

In simulations of evolution of cometary nuclei it is commonly assumed that the coefficients of sublimation and condensation of the volatiles are both equal to one. However, the laboratory investigation of water ice samples under cometary-like conditions (Kossacki et al., 1997) suggests, that the sublimation flux calculated with the Hertz-Knudsen formula and the above assumption is nearly an order of magnitude too high. A similar conclusion can be drawn from the results of various experiments on growth from vapour phase and sublimation of ice crystals (Lamb and Scott, 1972; Beckmann and Lacmann, 1982; Sei and Gonda, 1989). These results imply that the sublimation coefficient can be as low as 0.1. The above coefficients depend on various parameters such as temperature, concentration of surface impurities as well as deviation of the vapour pressure from that of the phase equilibrium. In this work we discuss the temperature dependence of both of these coefficients. We also propose an empirical formula to fit the temperature dependence. This new formulation is also used to analyse the implications for the thermal conductivity of a porous cometary-like ice.

Kossacki, K. J.; Markiewicz, W. J.; Skorov, Y.; Koemle, N. I.

1999-09-01

343

The influence of porosity on ultrasound attenuation in carbon fiber reinforced plastic composites using the laser-ultrasound spectroscopy  

NASA Astrophysics Data System (ADS)

Wideband acoustic spectroscopy with a laser ultrasound source for quantitative analysis of the effect of porosity on the attenuation coefficient of longitudinal acoustic waves in carbon fiber reinforced plastic (CFRP) composite materials was experimentally implemented. The samples under study had different bulk-porosity levels (up to 10%), which were determined using X-ray computer tomography. A resonance ultrasound attenuation peak associated with the one-dimensional periodicity of the layered composite structure was observed for all samples. The absolute value of the resonance-peak maximum and its width depend on the local concentration of microscopic isolated pores and extended delaminations in the sample structure. The obtained empirical relationships between these parameters of the frequency dependence of the ultrasound attenuation coefficient and the type of inhomogeneities and their volume concentration can be used for rapid evaluation of the structural quality of CFRP composites.

Karabutov, A. A.; Podymova, N. B.; Belyaev, I. O.

2013-11-01

344

Effects of finite electron mean free path on the attenuation, electromagnetic generation, and detection of ultrasonic shear waves in superconductors  

Microsoft Academic Search

Use of the general many-body formalism allows us to derive a system of equations describing the propagation of electromagnetic shear waves coupled to ultrasonic shear waves in normal and superconducting metals with arbitrary electron mean free paths. From this system of equations we derive general expressions in terms of correlation functions for the attenuation coefficient as well as for the

Kurt Scharnberg

1978-01-01

345

An acoustic backscatter-based method for estimating attenuation towards monitoring lesion formation in high intensity focused ultrasound  

NASA Astrophysics Data System (ADS)

This work investigated the transient characteristics of tissue attenuation coefficient before, during and after HIFU treatment at different total acoustic powers (TAP) in ex vivo porcine muscle tissues. Dynamic changes of attenuation coefficient parameters were correlated with conventional B-mode ultrasound images over the whole HIFU treatment process. Two-dimensional pulse-echo radiofrequency (RF) data were acquired to estimate the changes of least squares attenuation coefficient slope (??) and attenuation coefficient intercept (??0) averaged in the region of interest, and to construct ??, ??0, and B-mode images simultaneously. During HIFU treatment, bubble activities were visible as strong hyperechoic regions in the B-mode images, causing fluctuations in ?? and ??0 estimations during treatment. ?? and ??0 increased with the appearance of bubble clouds in the B-mode images to values in the range of 1.5-2.5 [dB/(MHz.cm)] and 4-5 [dB/cm], respectively. After the treatment, ?? and ??0 gradually decreased, accompanied by fadeout of hyperechoic spot in the B-mode images, until they were stable at ranges of 0.75-1 [dB/(MHz.cm)] and 1-1.5 [dB/cm], respectively. In conclusion, ?? and ??0 images outperformed B-mode images in detecting HIFU thermal lesions by having significantly higher contrast to speckle ratios at all investigated TAP values.

Rahimian, Siavash; Tavakkoli, Jahan

2012-11-01

346

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

NASA Astrophysics Data System (ADS)

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

Rota Kops, Elena; Herzog, Hans

2013-02-01

347

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

NASA Astrophysics Data System (ADS)

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

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

2014-11-01

348

Apoptosis and necrosis-induced changes in light attenuation measured by optical coherence tomography  

Microsoft Academic Search

Optical coherence tomography (OCT) was used to determine optical properties of pelleted human fibroblasts in which necrosis\\u000a or apoptosis had been induced. We analysed the OCT data, including both the scattering properties of the medium and the axial\\u000a point spread function of the OCT system. The optical attenuation coefficient in necrotic cells decreased from 2.2?±?0.3 mm?1 to 1.3?±?0.6 mm?1, whereas, in the

Freek J. van der Meer; Dirk J. Faber; Maurice C. G. Aalders; Andre A. Poot; Istvan Vermes; Ton G. van Leeuwen

2010-01-01

349

Magnetic resonance imaging-guided attenuation and scatter corrections in three-dimensional brain positron emission tomography  

E-print Network

Reliable attenuation correction represents an essential component of the long chain of modules required for the reconstruction of artifact-free, quantitative brain positron emission tomography (PET) images. In this work we demonstrate the proof of principle of segmented magnetic resonance imaging (MRI)-guided attenuation and scatter corrections in 3D brain PET. We have developed a method for attenuation correction based on registered T1-weighted MRI, eliminating the need of an additional transmission (TX) scan. The MR images were realigned to preliminary reconstructions of PET data using an automatic algorithm and then segmented by means of a fuzzy clustering technique which identifies tissues of significantly different density and composition. The voxels belonging to different regions were classified into air, skull, brain tissue and nasal sinuses. These voxels were then assigned theoretical tissue-dependent attenuation coefficients as reported in the ICRU 44 report followed by Gaussian smoothing and additio...

Zaidi, H; Slosman, D O

2003-01-01

350

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

PubMed Central

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

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

2014-01-01

351

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

PubMed Central

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

2009-01-01

352

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

353

Coefficient systems and Jacquet modules.  

E-print Network

Let F be a locally compact non-archimedean field and G the group of F-rational points of an algebraic group assumed to be defined over F, semisimple, simply connected and of F-rank 1. Let pi be a complex irreducible supercuspidal representation of G. We prove that pi is "nearly" induced in the following sense. There exist a maximal compact subgroup K of G and an irreducible smooth representation lamba of K such that pi contains lambda by restriction to K and such that the representation compactly induced from lambda to G is a finite direct sum of irreducible supercuspidal representations. The proof relies on the Schneider and Stuhler theory of equivariant coefficient systems and on a lemma on coefficient systems and Jacquet modules.

Paul Broussous

354

Consistent transport coefficients in astrophysics  

NASA Technical Reports Server (NTRS)

A consistent theory for dealing with transport phenomena in stellar atmospheres starting with the kinetic equations and introducing three cases (LTE, partial LTE, and non-LTE) was developed. The consistent hydrodynamical equations were presented for partial-LTE, the transport coefficients defined, and a method shown to calculate them. The method is based on the numerical solution of kinetic equations considering Landau, Boltzmann, and Focker-Planck collision terms. Finally a set of results for the transport coefficients derived for a partially ionized hydrogen gas with radiation was shown, considering ionization and recombination as well as elastic collisions. The results obtained imply major changes is some types of theoretical model calculations and can resolve some important current problems concerning energy and mass balance in the solar atmosphere. It is shown that energy balance in the lower solar transition region can be fully explained by means of radiation losses and conductive flux.

Fontenla, Juan M.; Rovira, M.; Ferrofontan, C.

1986-01-01

355

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

356

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 propertymeasurement for evaluating the potential performance of novel thermoelectricmaterials. 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, thermoelectricmeasurements 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.; Tritt, T.; Uher, Ctirad

2010-01-01

357

Expression of optical diffusion coefficient in high-absorption turbid media  

NASA Astrophysics Data System (ADS)

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

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

1997-12-01

358

Seismic Rheological Model and Reflection Coefficients of the Brittle-Ductile Transition  

NASA Astrophysics Data System (ADS)

It is well established that the upper—cooler—part of the crust is brittle, while deeper zones present ductile behaviour. In some cases, this brittle-ductile transition is a single seismic reflector with an associated reflection coefficient. We first develop a stress-strain relation including the effects of crust anisotropy, seismic attenuation and ductility in which deformation takes place by shear plastic flow. Viscoelastic anisotropy is based on the eigenstrain model and the Zener and Burgers mechanical models are used to model the effects of seismic attenuation, velocity dispersion, and steady-state creep flow, respectively. The stiffness components of the brittle and ductile media depend on stress and temperature through the shear viscosity, which is obtained by the Arrhenius equation and the octahedral stress criterion. The P- and S-wave velocities decrease as depth and temperature increase due to the geothermal gradient, an effect which is more pronounced for shear waves. We then obtain the reflection and transmission coefficients of a single brittle-ductile interface and of a ductile thin layer. The PP scattering coefficient has a Brewster angle (a sign change) in both cases, and there is substantial PS conversion at intermediate angles. The PP coefficient is sensitive to the layer thickness, unlike the SS coefficient. Thick layers have a well-defined Brewster angle and show higher reflection amplitudes. Finally, we compute synthetic seismograms in a homogeneous medium as a function of temperature.

Carcione, José M.; Poletto, Flavio

2013-12-01

359

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

360

Computing Optical Variable Periods of BL Lac Object S5 0716+714 with Period04 Analysis Method  

NASA Astrophysics Data System (ADS)

From a large volume of literature, we have collected effective observation of BL Lac object S5 0716+714 in the optical band, and constructed its long-term light curve from 1994 to 2006 AD. The light curve shows that S5 0716+714 is very active and exhibits very complicated non-sinusoidal variations. We used Period04 to analyse the period of light curve variation. Our results show that for S5 0716+714, the long-term period of variation is 3.3 yr which is consistent with the result of Raiter et al. (2003).

Fu, Junping; Zhang, Xiong; Xiong, Dingrong

2014-11-01

361

Structural evidence for induced fit and a mechanism for sugar/H+ symport in LacY  

PubMed Central

Cation-coupled active transport is an essential cellular process found ubiquitously in all living organisms. Here, we present two novel ligand-free X-ray structures of the lactose permease (LacY) of Escherichia coli determined at acidic and neutral pH, and propose a model for the mechanism of coupling between lactose and H+ translocation. No sugar-binding site is observed in the absence of ligand, and deprotonation of the key residue Glu269 is associated with ligand binding. Thus, substrate induces formation of the sugar-binding site, as well as the initial step in H+ transduction. PMID:16525509

Mirza, Osman; Guan, Lan; Verner, Gill; Iwata, So; Kaback, H Ronald

2006-01-01

362

On the relation of mid-infrared emission with the gamma-ray properties of Fermi-detected BL Lac objects  

NASA Astrophysics Data System (ADS)

We present the Wide-field Infrared Survey Explorer (WISE) photometric data of 158 Fermi-detected BL Lacs and investigate the nature of their mid-infrared (MIR) continuum emission. In the [3.4]-[4.6]-[12] ?m color-color diagram, nearly all their colors lie within the WISE Blazar strip (WBS), which is an effective diagnostic tool to separate sources dominated by non-thermal radiation from those dominated by thermal radiation. This feature indicates that their MIR emission is predominantly non-thermal. This argument is further supported by the strong radio-MIR flux correlation. We derive their MIR spectral indices and compare them with the near-infrared (NIR) spectral indices. We find that there is a prevalent steepening from MIR spectrum to NIR spectrum. The low-frequency-peaked BL Lacs (LBLs) have on average a larger MIR spectral index and a higher MIR luminosity than the high-frequency-peaked BL Lacs (HBLs), and the intermediate-frequency-peaked BL Lacs (IBLs) appear to bridge them. The MIR- ?-ray flux correlation is highly significant. A strong positive correlation is also found between the MIR and ?-ray spectral indices. The ?-ray-MIR loudness is significantly correlated with the synchrotron peak frequency. Finally we propose that the ?-rays are highly associated with the MIR emission from the jet, and the ?-ray emission is likely from the synchrotron self-Compton process for the Fermi-detected BL Lacs in our sample.

Mao, Li-Sheng

2012-08-01

363

Databases and software for the analysis of mutations in the human p53 gene, human hprt gene and both the lacI and lacZ gene in transgenic rodents.  

PubMed

We have created databases and software applications for the analysis of DNA mutations at the human p53 gene, the human hprt gene and both the rodent transgenic lacI and lacZ loci. The databases themselves are stand-alone dBASE files and the software for analysis of the databases runs on IBM-compatible computers with Microsoft Windows. Each database has a separate software analysis program. The software created for these databases permit the filtering, ordering, report generation and display of information in the database. In addition, a significant number of routines have been developed for the analysis of single base substitutions. One method of obtaining the databases and software is via the World Wide Web. Open the following home page with a Web Browser: http://sunsite.unc.edu/dnam/mainpage. html . Alternatively, the databases and programs are available via public FTP from: anonymous@sunsite.unc.edu. There is no password required to enter the system. The databases and software are found beneath the subdirectory: pub/academic/biology/dna-mutations. Two other programs are available at the site, a program for comparison of mutational spectra and a program for entry of mutational data into a relational database. PMID:9399835

Cariello, N F; Douglas, G R; Gorelick, N J; Hart, D W; Wilson, J D; Soussi, T

1998-01-01

364

Calibration of an HPGe detector and self-attenuation correction for 210Pb: Verification by alpha spectrometry of 210Po in environmental samples  

NASA Astrophysics Data System (ADS)

In this work the calibration of an HPGe detector for 210Pb measurement is realised by a liquid standard source and the determination of this radionuclide in solid environmental samples by gamma spectrometry takes into account a correction factor for self-attenuation of its 46.5 keV line. Experimental, theoretical and Monte Carlo investigations are undertaken to evaluate self-attenuation for cylindrical sample geometry. To validate this correction factor, 210Po (at equilibrium with 210Pb) alpha spectrometry procedure using microwave acid digestion under pressure is developed and proposed. The different self-attenuation correction methods are in coherence, and corrected 210Pb activities are in good agreement with the results of 210Po. Finally, self-attenuation corrections are proposed for environmental solid samples whose density ranges between 0.8 and 1.4 g/cm 3 and whose mass attenuation coefficient is around 0.4 cm 2/g.

Saïdou; Bochud, François; Laedermann, Jean-Pascal; Buchillier, Thierry; Njock Moïse, Kwato; Froidevaux, Pascal

2007-08-01

365

Electrically tunable hot-silicon terahertz attenuator  

NASA Astrophysics Data System (ADS)

We have developed a continuously tunable, broadband terahertz attenuator with a transmission tuning range greater than 103. Attenuation tuning is achieved electrically, by simply changing the DC voltage applied to a heating wire attached to a bulk silicon wafer, which controls its temperature between room temperature and ˜550 K, with the corresponding free-carrier density adjusted between ˜1011 cm-3 and ˜1017 cm-3. This "hot-silicon"-based terahertz attenuator works most effectively at 450-550 K (corresponding to a DC voltage variation of only ˜7 V) and completely shields terahertz radiation above 550 K in a frequency range of 0.1-2.5 THz. Both intrinsic and doped silicon wafers were tested and demonstrated to work well as a continuously tunable attenuator. All behaviors can be understood quantitatively via the free-carrier Drude model taking into account thermally activated intrinsic carriers.

Wang, Minjie; Vajtai, Robert; Ajayan, Pulickel M.; Kono, Junichiro

2014-10-01

366

Regulation of mean and noise of the in vivo kinetics of transcription under the control of the lac/ara-1 promoter.  

PubMed

The kinetics of transcription initiation in Escherichia coli depend on the duration of two rate-limiting steps, the closed and the open complex formation. In a lac promoter variant, P(lac/ara-1), the kinetics of these steps is controlled by IPTG and arabinose. From in vivo single-RNA measurements, we find that induction affects the mean and normalized variance of the intervals between consecutive RNA productions. Transcript production is sub-Poissonian in all conditions tested. The kinetics of each step is independently controlled by a different inducer. We conclude that the regulatory mechanism of P(lac/ara-1) allows the stochasticity of gene expression to be environment-dependent. PMID:23017207

Kandhavelu, Meenakshisundaram; Lloyd-Price, Jason; Gupta, Abhishekh; Muthukrishnan, Anantha-Barathi; Yli-Harja, Olli; Ribeiro, Andre S

2012-11-01

367

Cyclic adenosine 3',5'-monophosphate-mediated hyperinduction of araBAD and lacZYA expression in a crp mutant of Escherichia coli K-12.  

PubMed Central

A spontaneous lac+ revertant of an adenylate cyclase deletion strain of Escherichia coli K-12 was isolated and characterized. This revertant, designated strain KC20, exhibited a pleiotropic suppression of the adenylate cyclase defect, with the crp locus being the site of the suppressor mutation. Cyclic adenosine 3',5'-monophosphate at an exogenous concentration of 1 mM severely inhibited the growth of strain KC20 in minimal media. Lower concentrations of the cyclic nucleotide elicited less pronounced effects. Studies on araBAD and lacZYA expression showed that cyclic adenosine 3',5'-monophosphate elicited an initial dose-dependent hyperinduction of these systems. Hyperinduction of araBAD, in L-arabinose grown cultures of strain KC20, resulted in accumulation of inhibitory concentrations of methylglyoxal. Hyperinduction of lacZYA in lactose-grown cultures of strain KC20 did not result in any such methylglyoxal production. Images PMID:6267010

Bankaitis, V A; Kline, E L

1981-01-01

368

The attenuation of strong shock waves  

E-print Network

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

Kirkpatrick, Ronald Crecelius

2012-06-07

369

Electron Effective-Attenuation-Length Database  

National Institute of Standards and Technology Data Gateway

SRD 82 NIST Electron Effective-Attenuation-Length Database (PC database, no charge)   This database provides values of electron effective attenuation lengths (EALs) in solid elements and compounds at selected electron energies between 50 eV and 2,000 eV. The database was designed mainly to provide EALs (to account for effects of elastic-eletron scattering) for applications in surface analysis by Auger-electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS).

370

The mtr locus is a two-gene operon required for transcription attenuation in the trp operon of Bacillus subtilis.  

PubMed Central

We have cloned and characterized the mtr operon of Bacillus subtilis. This operon encodes a presumed RNA-binding regulatory protein that is required for attenuation control of the trp operon. We have shown that the mtr operon consists of two structural genes, mtrA and mtrB, predicted to encode 22-kDa and 8-kDa polypeptides, respectively. MtrB shows homology with RegA, an RNA-binding regulatory protein of bacteriophage T4. The lesions in several mtr mutants were localized to mtrB or the putative mtr promoter. Several mtrB alleles were dominant to mtr+, suggesting that the regulatory factor is a multimeric protein. The in vivo action of the mtrA and mtrB gene products was analyzed in an E. coli strain containing a trpE-lacZ gene fusion under control of the B. subtilis trp promoter/attenuator region. Both MtrA and MtrB were necessary for regulation of beta-galactosidase production. Images PMID:2123343

Gollnick, P; Ishino, S; Kuroda, M I; Henner, D J; Yanofsky, C

1990-01-01

371

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

PubMed Central

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

Parente, Daniel J.; Swint-Kruse, Liskin

2013-01-01

372

The correlations between BL Lacs and ultra-high-energy cosmic rays deflected by using different GMF models  

E-print Network

Some studies suggested that a correlation between locations of BL Lacertae objects (BL Lacs) and the arrival directions of the ultrahigh energy cosmic rays (UHECRs) exists. Especially by assuming the primary particles charged +1 and using a galactic magnetic field (GMF) model to calculate the deflections of the UHECRs, the significance of correlation is improved. We construct a new GMF model by incorporating all progresses in the GMF measurements in recent years. Based on a thorough study of the deflections of the UHECRs measured by the AGASA experiment, we study the GFM model dependence of the correlation between the UHECRs and the selected BL Lacs using the new model together with others. It turns out that only specific one of those GMF models makes the correlation significant, even if neither GMF models themselves nor deflections of the UHECRs are not significantly different. It suggests that the significance of the correlation, calculated using a method suggested in those studies, is intensively depending on the GMF model. Great improvement in statistics may help to suppress the sensitivity to the GMF models.

Zhen Cao; Ben Zhong Dai; Jian Ping Yang; Li Zhang

2006-02-22

373

vanI: a novel D-Ala-D-Lac vancomycin resistance gene cluster found in Desulfitobacterium hafniense.  

PubMed

The glycopeptide vancomycin was until recently considered a drug of last resort against Gram-positive bacteria. Increasing numbers of bacteria, however, are found to carry genes that confer resistance to this antibiotic. So far, 10 different vancomycin resistance clusters have been described. A chromosomal vancomycin resistance gene cluster was previously described for the anaerobic Desulfitobacterium hafniense Y51. We demonstrate that this gene cluster, characterized by its d-Ala-d-Lac ligase-encoding vanI gene, is present in all strains of D.?hafniense, D. chlororespirans and some strains of Desulfosporosinus spp. This gene cluster was not found in vancomycin-sensitive Desulfitobacterium or Desulfosporosinus spp., and we show that this antibiotic resistance can be exploited as an intrinsic selection marker for Desulfitobacterium hafniense and D. chlororespirans. The gene cluster containing vanI is phylogenetically only distantly related with those described from soil and gut bacteria, but clusters instead with vancomycin resistance genes found within the phylum Actinobacteria that include several vancomycin-producing bacteria. It lacks a vanH homologue, encoding a D-lactate dehydrogenase, previously thought to always be present within vancomycin resistance gene clusters. The location of vanH outside the resistance gene cluster likely hinders horizontal gene transfer. Hence, the vancomycin resistance cluster in D.?hafniense should be regarded a novel one that we here designated vanI after its unique d-Ala-d-Lac ligase. PMID:25042042

Kruse, Thomas; Levisson, Mark; de Vos, Willem M; Smidt, Hauke

2014-09-01

374

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

PubMed

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

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

2014-09-15

375

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

NASA Technical Reports Server (NTRS)

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

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

2001-01-01

376

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

NASA Technical Reports Server (NTRS)

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

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

2001-01-01

377

Attenuation Estimation and Temperature Imaging Using Backscatter for Extracorporeal HIFU Treatment Planning  

NASA Astrophysics Data System (ADS)

For HIFU to be widely applicable in the clinic, problems relating to treatment planning, delivery and monitoring need to be resolved. The characterisation of the acoustic and thermal properties of specific tissues is an important pre-requisite to determining the optimal exposure parameters for individual treatments. We describe a preliminary evaluation of two methods that may be of use in deriving such planning information prior to HIFU. Both methods have been implemented on a diagnostic ultrasound scanner. One is backscatter attenuation estimation (BAE), which uses pulse-echo data and an axial beam translation substitution method to estimate the average attenuation coefficient of tissue overlying the region to be treated. The second method is backscatter temperature imaging (BTI) applied to a non-lesioning test exposure, which is normally used to determine the focal position but here the observed peak temperature rise is employed to provide an estimate of all case-specific losses involved in delivering a dose of thermal energy. HIFU lesioning experiments were performed in ex vivo bovine liver tissue, and used to test the ability of BAE and BTI to provide accurate information for adjusting the HIFU power so as to compensate for varying ultrasonic attenuation by overlying tissues (mimicked by gels with different attenuation properties). HIFU-induced lesions were made according to two types of exposure regime, (a) without regard for the differing attenuation coefficients of gels placed between the HIFU transducer and the tissue to be treated, and (b) after adjusting the HIFU drive power according to corrections derived from BAE and BTI measurements. Both correction methods were found to improve lesion size reproducibility, as measured from cut lesioned tissue specimens, although BTI performed better than BAE. The paper discusses likely reasons for this, as well as problems to be overcome if either method is to be clinically useful.

Civale, John; Bamber, Jeff; Miller, Naomi; Rivens, Ian; ter Haar, Gail

2007-05-01

378

p53 deficiency alters the yield and spectrum of radiation-induced lacZ mutants in the brain of transgenic mice.  

PubMed

Exposure to heavy particle radiation in the galacto-cosmic environment poses a significant risk in space exploration and the evaluation of radiation-induced genetic damage in tissues, especially in the central nervous system, is an important consideration in long-term manned space missions. We used a plasmid-based transgenic mouse model system, with the pUR288 lacZ transgene integrated in the genome of every cell of C57Bl/6(lacZ) mice, to evaluate the genetic damage induced by iron particle radiation. In order to examine the importance of genetic background on the radiation sensitivity of individuals, we cross-bred p53 wild-type lacZ transgenic mice with p53 nullizygous mice, producing lacZ transgenic mice that were either hemizygous or nullizygous for the p53 tumor suppressor gene. Animals were exposed to an acute dose of 1 Gy of iron particles and the lacZ mutation frequency (MF) in the brain was measured at time intervals from 1 to 16 weeks post-irradiation. Our results suggest that iron particles induced an increase in lacZ MF (2.4-fold increase in p53+/+ mice, 1.3-fold increase in p53+/- mice and 2.1-fold increase in p53-/- mice) and that this induction is both temporally regulated and p53 genotype dependent. Characterization of mutants based on their restriction patterns showed that the majority of the mutants arising spontaneously are derived from point mutations or small deletions in all three genotypes. Radiation induced alterations in the spectrum of deletion mutants and reorganization of the genome, as evidenced by the selection of mutants containing mouse genomic DNA. These observations are unique in that mutations in brain tissue after particle radiation exposure have never before been reported owing to technical limitations in most other mutation assays. PMID:11139594

Chang, P Y; Kanazawa, N; Lutze-Mann, L; Winegar, R A

2001-01-01

379

Ultrasonic velocity and attenuation during CO 2 injection into water-saturated porous sandstone: Measurements using difference seismic tomography  

NASA Astrophysics Data System (ADS)

We undertook laboratory-based seismic measurements with dense sensor array at ultrasonic frequencies during the injection of CO 2 into a water-saturated sandstone specimen. The resulting high-quality seismic data enabled detailed determination of the relative velocity and attenuation coefficient of the compressional wave using difference seismic tomography, which directly inverses time-lapse changes in rock properties from time-lapse changes in observed data. CO 2 migration and water displacement were clearly mapped using tomographic images of relative velocity and the attenuation coefficient. The final and largely stabilised volume fraction of CO 2 in the pore space of the sample is about 30-40%. On average, the P-velocity fell by 7.5, 12, and 14.5% and the attenuation coefficient Q-1 increased by factors of 3.3, 2.7, and 3.7 as a result of the replacement of water with CO 2 during the injection of gaseous, liquid, and supercritical CO 2, respectively. As a function of gas saturation, both the velocity and attenuation data are in good agreement with results obtained using the White and Dutta-Odé model for partial saturation, indicating that viscous losses due to fluid diffusion are of significant importance for compressional waves travelling at ultrasonic frequencies in porous rocks.

Lei, Xinglin; Xue, Ziqiu

2009-10-01

380

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

SciTech Connect

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

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

1994-09-10

381

Dual energy CT-based characterization of x-ray attenuation properties of breast equivalent material plates  

NASA Astrophysics Data System (ADS)

Breast density is more and more considered as an important risk factor for breast cancer and several quantitative breast density evaluation methods have been proposed. The reference material for simulation of the breast attenuation properties of glandular and adipose breast tissues is manufactured by a single provider. In order to characterize the attenuation properties of these materials, measurements in Hounsfield Units (HU) have been performed using a CT-scanner. Breastequivalent plates have been imaged in different configurations (plates in and orthogonal to image planes), providing consistent results (+/- 1.3 HU). Breast density equivalent plates of different nominal breast density equivalences and sizes were measured, demonstrating both a good homogeneity within the plates (+/- 1.8 HU) and a good consistency between plates of the same nominal breast density equivalence (+/- 1.5 HU). In addition, dual energy CT provided mono-energetic HU from which mono-energetic linear attenuation coefficients of water and glandular and adipose equivalent materials were computed. The values for these coefficients were found in good agreement with results from literature, respectively direct mono-energetic measurements of breast samples, and computation by combining published breast tissue atomic compositions and linear attenuation coefficient tables. In conclusion, CT was found effective for the verification of the breast equivalent material, and the homogeneity and consistency of the plates were found satisfactory. Furthermore, the most recent spectral CT technology allowed demonstrating a good agreement of the attenuation properties of breastequivalent material plates with state-of-the-art knowledge of real breast tissue attenuation.

Geeraert, N.; Klausz, R.; Giudici, P.; Muller, S.; Cockmartin, L.; Bosmans, H.

2012-03-01

382

Measurements of thermal accommodation coefficients.  

SciTech Connect

A previously-developed experimental facility has been used to determine gas-surface thermal accommodation coefficients from the pressure dependence of the heat flux between parallel plates of similar material but different surface finish. Heat flux between the plates is inferred from measurements of temperature drop between the plate surface and an adjacent temperature-controlled water bath. Thermal accommodation measurements were determined from the pressure dependence of the heat flux for a fixed plate separation. Measurements of argon and nitrogen in contact with standard machined (lathed) or polished 304 stainless steel plates are indistinguishable within experimental uncertainty. Thus, the accommodation coefficient of 304 stainless steel with nitrogen and argon is estimated to be 0.80 {+-} 0.02 and 0.87 {+-} 0.02, respectively, independent of the surface roughness within the range likely to be encountered in engineering practice. Measurements of the accommodation of helium showed a slight variation with 304 stainless steel surface roughness: 0.36 {+-} 0.02 for a standard machine finish and 0.40 {+-} 0.02 for a polished finish. Planned tests with carbon-nanotube-coated plates will be performed when 304 stainless-steel blanks have been successfully coated.

Rader, Daniel John; Castaneda, Jaime N.; Torczynski, John Robert; Grasser, Thomas W.; Trott, Wayne Merle

2005-10-01

383

Attenuation of ground-motion spectral amplitudes in southeastern Australia  

USGS Publications Warehouse

A dataset comprising some 1200 weak- and strong-motion records from 84 earthquakes is compiled to develop a regional ground-motion model for southeastern Australia (SEA). Events were recorded from 1993 to 2004 and range in size from moment magnitude 2.0 ??? M ??? 4.7. The decay of vertical-component Fourier spectral amplitudes is modeled by trilinear geometrical spreading. The decay of low-frequency spectral amplitudes can be approximated by the coefficient of R-1.3 (where R is hypocentral distance) within 90 km of the seismic source. From approximately 90 to 160 km, we observe a transition zone in which the seismic coda are affected by postcritical reflections from midcrustal and Moho discontinuities. In this hypocentral distance range, geometrical spreading is approximately R+0.1. Beyond 160 km, low-frequency seismic energy attenuates rapidly with source-receiver distance, having a geometrical spreading coefficient of R-1.6. The associated regional seismic-quality factor can be expressed by the polynomial: log Q(f) = 3.66 - 1.44 log f + 0.768 (log f)2 + 0.058 (log f)3 for frequencies 0.78 ??? f ??? 19.9 Hz. Fourier spectral amplitudes, corrected for geometrical spreading and anelastic attenuation, are regressed with M to obtain quadratic source scaling coefficients. Modeled vertical-component displacement spectra fit the observed data well. Amplitude residuals are, on average, relatively small and do not vary with hypocentral distance. Predicted source spectra (i.e., at R = 1 km) are consistent with eastern North American (ENA) Models at low frequencies (f less than approximately 2 Hz) indicating that moment magnitudes calculated for SEA earthquakes are consistent with moment magnitude scales used in ENA over the observed magnitude range. The models presented represent the first spectral ground-motion prediction equations develooed for the southeastern Australian region. This work provides a useful framework for the development of regional ground-motion relations for earthquake hazard and risk assessment in SEA.

Allen, T.I.; Cummins, P.R.; Dhu, T.; Schneider, J.F.

2007-01-01

384

Wave Attenuation in Mangrove Forests Numerical modelling of wave attenuation by implementation of a physical description of vegetation in SWAN  

E-print Network

Wave Attenuation in Mangrove Forests Numerical modelling of wave attenuation by implementation. H.J. Verhagen Drs. M. de Vries Dr. ir. M. Zijlema H.J. Opdam #12;Wave Attenuation in Mangrove of interest in this thesis is wave attenuation in vegetation and in particular in mangrove forests

Langendoen, Koen

385

Simultaneous estimation of SPECT activity and attenuation distributions from measured phantom data using a differential attenuation method  

Microsoft Academic Search

The Differential Attenuation Method (DAM) simultaneously estimates SPECT activity and attenuation distributions from emission data. In this work, we extend the investigation of DAM to measured data and compare the results obtained with FBP without compensating for attenuation, and Penalized Weighted Least Squares (PWLS) with uniform and no attenuation. An anthropomorphic torso phantom with a heart insert containing a myocardial

H. Vija; M. S. Kaplan; D. R. Haynor

1999-01-01

386

The emission coefficient of uranium plasmas  

NASA Technical Reports Server (NTRS)

The emission coefficient for uranium plasmas (Temperature: 8000 K) was measured for the wavelength range (200 A - 6000 A). The results are compared to theory and other measurements. The absorption coefficient for the same wavelength interval is also given.

Schneider, R. T.; Campbell, H. D.; Mack, J. M.

1973-01-01

387

Creating materials with a desired refraction coefficient  

E-print Network

A method is given for creating material with a desired refraction coefficient. The method consists of embedding into a material with known refraction coefficient many small particles of size $a$. The number of particles per unit volume around any point is prescribed, the distance between neighboring particles is $O(a^{\\frac{2-\\kappa}{3}})$ as $a\\to 0$, $0refraction coefficient is the coefficient $n^2(x)$ in the wave equation $[\

A. G. Ramm

2009-09-02

388

M-Bonomial Coefficients and Their Identities  

ERIC Educational Resources Information Center

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

Asiru, Muniru A.

2010-01-01

389

Soccer Ball Lift Coefficients via Trajectory Analysis  

ERIC Educational Resources Information Center

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

Goff, John Eric; Carre, Matt J.

2010-01-01

390

A search of CO emission lines in blazars: the low molecular gas content of BL Lac objects compared to quasars  

NASA Astrophysics Data System (ADS)

BL Lacertae (Lac) objects that are detected at very high energies (VHE) are of fundamental importance to study multiple astrophysical processes, including the physics of jets, the properties of the extragalactic background light and the strength of the intergalactic magnetic field. Unfortunately, since most blazars have featureless optical spectra that preclude a redshift determination, a substantial fraction of these VHE extragalactic sources cannot be used for cosmological studies. To assess whether molecular lines are a viable way to establish distances, we have undertaken a pilot programme at the Institut of Millimétrique (IRAM) 30 m telescope to search for CO lines in three BL Lac objects with known redshifts. We report a positive detection of 12 MH_2 ˜ 3 × 10>8 M? towards 1ES 1959+650, but due to the poor quality of the baseline, this value is affected by a large systematic uncertainty. For the remaining two sources, W Comae and RGB J0710+591, we derive 3? upper limits at, respectively, H2 < 8.0 × 108 and 1.6 × 109 M?, assuming a line width of 150 km s-1 and a standard conversion factor ? = 4 M? (K km s-1 pc2)-1. If these low molecular gas masses are typical for blazars, blind redshift searches in molecular lines are currently unfeasible. However, deep observations are still a promising way to obtain precise redshifts for sources whose approximate distances are known via indirect methods. Our observations further reveal a deficiency of molecular gas in BL Lac objects compared to quasars, suggesting that the host galaxies of these two types of active galactic nuclei (AGN) are not drawn from the same parent population. Future observations are needed to assess whether this discrepancy is statistically significant, but our pilot programme shows how studies of the interstellar medium in AGN can provide key information to explore the connection between the active nuclei and the host galaxies. Based on observations carried out with the IRAM 30 m telescope. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain).

Fumagalli, Michele; Dessauges-Zavadsky, Miroslava; Furniss, Amy; Prochaska, J. Xavier; Williams, David A.; Kaplan, Kyle; Hogan, Matthew

2012-08-01

391

Status of Two Species of Lac Insects in the Genus Kerria from China Based on Morphological, Cellular, and Molecular Evidence  

PubMed Central

The taxonomic status of the Chinese lac insects Kerria yunnanensis (Ou and Hong) (Hemiptera: Kerridae) and K. ruralis (Wang, Yao, Teiu and Liang) were analyzed in this paper by comparing morphological, cellular, and molecular data. Cladistic analysis showed K. yunnanensis and K. ruralis to be distinct from other Kerria species such as K. lacca and K. chinensis. The karyotype of K. yunnanensis was 3A and the chromosome structure was K = 6m + 2sm + 10T, while in K. ruralis the karyotype was 3B and the chromosome structure was K = 8m + 10T. Kerria ruralis and K. yunnanensis had the closest relationship among species in the genus as they had the most similar karyotype homology. Based on the karyotype analysis, K. sindica and K. lacca formed a sister group with K. ruralis and K. yunnanensis. Kerria pusana and K. nepalensis were clustered as a sister branch, indicating the close relationship of these taxa. The karyotype of K. chinensis was however, different from the other six species and formed a separate branch. RAPD analysis also showed that K. yunnanensis and K. ruralis had distinct differences from other species of Kerria, although they did not form sister taxa. Molecular analysis based on the EF1? gene using ML, MP, and Mr. Bayes' methods indicated that seven species of lac insects cluster in two major groups. In group 1, K. sindica and K. lacca formed a sister clade and were primitive members of the genus. In group 2, K. chinensis formed the earliest diverging branch followed by K. ruralis. Kerria yunnanensis was the next to diverge followed by the cluster containing K. pusana and K. nepalensis. Hybridization testing showed that crosses neither between K. yunnanensis and K. sindica, nor between K. yunnanensis and K. lacca could produce first generation larvae. This was indicative that K. yunnanensis had a distant genetic relationship from the other species. Morphological, cellular, molecular, and hybridization results confirmed the independent status of the Chinese endemic species K. yunnanensis and K. ruralis. Kerria ruralis was genetically closely related to K. yunnanensis, but relatively far from K. lacca. The main commercial species in China was K. yunnanensis, while in Thailand it was K. chinensis. The commercial species in Myanmar included K. nepalensis and K. pusana, the latter being most widely used in lac production. PMID:22221325

Chen, Xiaoming; Chen, Hang; Feng, Ying; He, Rui; Yang, Zixiang

2011-01-01

392

A comparison of mutation spectra detected by the Escherichia coli lac(+) reversion assay and the Salmonella typhimurium his(+) reversion assay.  

PubMed

Each of the Escherichia coli tester strains in the WP3101P-WP3106P series contains an F' plasmid with a different base substitution mutation within the lacZ gene. Each of the six possible base substitution mutations, therefore, can be assayed with these strains by Lac(+) reversion. We used the strains to characterize the mutational profiles of 21 chemical mutagens, including alkylating agents, base analogs and oxidative compounds. We also assayed the mutagens with Salmonella typhimurium tester strains TA7002, TA7004 and TA7005, which detect A.T-->T.A, G.C-->A.T and G.C-->T.A mutations, respectively, and we compared the sensitivity and specificity of the two systems. Escherichia coli strain WP3102P was more sensitive than the S.TYPHIMURIUM: strains to G.C-->A.T transitions induced by N(4)-aminocytidine, 5-azacytidine, cumene hydroperoxide (CHP), t-butyl hydroperoxide (BHP), N-ethyl-N'-nitro-N-nitrosoguanidine (ENNG), methyl methane sulfonate and N-ethyl-N-nitrosourea (ENU), while the reverse was true for G.C-->A.T transitions induced by 2-aminopurine and phosmet. Escherichia coli strain WP3104P, which detects G.C-->T.A transversions, was superior to the S.TYPHIMURIUM: strains in detecting transversions induced by N(4)-aminocytidine, 5-azacytidine, 5-diazouracil, CHP, BHP, ENNG, ENU, 4-nitroquinoline 1-oxide (4-NQO) and 3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX). Escherichia coli WP3105P was also more sensitive than S. TYPHIMURIUM: to A.T-->T.A transversions induced by N-methyl-N- nitrosourea (MNU), CHP and 4-NQO, but it was less sensitive to those induced by ENNG, ENU and 2-aminopurine. The present results indicate that the E.COLI: Lac(+) reversion system with tester strains WP3101P-WP3106P is as sensitive as the S.TYPHIMURIUM: His(+) reversion system for the detection of specific mutations induced by a variety of direct mutagens. PMID:10887210

Ohta, T; Watanabe-Akanuma, M; Yamagata, H

2000-07-01

393

Ultrasonic attenuation peak in steel and aluminum alloy during rotating bending fatigue  

SciTech Connect

Using electromagnetic acoustic resonance (EMAR), the authors studied the evolution of the surface shear wave attenuation and phase velocity in a 0.45 pct C steel and a 5052 aluminum alloy exposed to rotating bending fatigue. In the EMAR method, they used electromagnetic acoustic transducers (EMATs) for the contactless measurements of the axial shear wave, which is a surface shear wave that propagates along a cylindrical surface in the circumferential direction, with an axial polarization. There has been no precious report of continuous and contactless monitoring of the surface wave attenuation and velocity being performed without interrupting the fatigue. The attenuation coefficient always showed sharp peaks around 90 pct of the fatigue life, independent of the fatigue-stress amplitude. To interpret this phenomenon, the authors made crack-growth observations using replicas and measurements of recovery of attenuation and velocity by stopping the cyclic loading before and after the peak. From these results, they concluded that the evolution of the ultrasonic properties is caused by a drastic change in dislocation mobility being accompanied by the crack growth at the final stage of the fatigue life.

Ogi, Hirotsugu; Hamaguchi, Takayuki; Hirao, Masahiko

2000-04-01

394

Ultrasonic attenuation peak in steel and aluminum alloy during rotating bending fatigue  

NASA Astrophysics Data System (ADS)

Using electromagnetic acoustic resonance (EMAR), we studied the evolution of the surface shearwave attenuation and phase velocity in a 0.45 pct C steel and a 5052 aluminum alloy exposed to rotating bending fatigue. In the EMAR method, we used electromagnetic acoustic transducers (EMATs) for the contactless measurements of the axial shear wave, which is a surface shear wave that propagates along a cylindrical surface in the circumferential direction, with an axial polarization. There has been no previous report of continuous and contactless monitoring of the surface wave attenuation and velocity being performed without interrupting the fatigue. The attenuation coefficient always showed sharp peaks around 90 pct of the fatigue life, independent of the fatigue-stress amplitude. To interpret this phenomenon, we made crack-growth observations using replicas and measurements of recovery of attenuation and velocity by stopping the cyclic loading before and after the peak. From these results, we concluded that the evolution of the ultrasonic properties is caused by a drastic change in dislocation mobility being accompanied by the crack growth at the final stage of the fatigue life.

Ogi, Hirotsugu; Hamaguchi, Takayuki; Hirao, Masahiko

2000-04-01

395

Modeling Light Attenuation, Secchi Disk, and Effects of Tripton in Senaco River, New York, USA  

NASA Astrophysics Data System (ADS)

The development, testing, and application of a probabilistic model framework for the light attenuation coefficient for downwelling irradiance (Kd) and Secchi disc transparency (SD) that resolves the effects of several light attenuating constituents, including phytoplankton and nonliving particles (tripton), is documented. The model is consistent with optical theory, partitioning the magnitudes of the light attenuating processes of absorption and scattering according to the contributions of attenuating constituents as simple summations. The probabilistic framework accommodates variations in the character and concentrations of these constituents and ambient conditions during measurements, and recognizes a linear relationship between the magnitudes of absorption and scattering by tripton. The model is tested and applied for a 21 km reach of the Seneca River, New York, that features optical gradients caused by an intervening hypereutrophic lake and dam, and a severe infestation of the exotic zebra mussel. The model is applied to resolve the roles of phytoplankton and tripton in regulating measured longitudinal patterns of SD along the study reach of the river and increases in SD since the zebra mussel invasion, and to predict decreases in Kd since the invasion.

Effler, Steven W.; Gelda, Rakesh K.; Perkins, Mary Gail; O'Donnell, David M.

2005-08-01

396

Insulating epoxy/barite and polyester/barite composites for radiation attenuation.  

PubMed

A trial has been made to create insulating Epoxy/Barite (EP/Brt) (?=2.85 g cm(-3)) and Crosslinked Unsaturated Polyester/Barite (CUP/Brt) (?=3.25 g cm(-3)) composites with radiation attenuation and shielding capabilities. Experimental work regarding mechanical and physical properties was performed to study the composites integrity for practical applications. The properties were found to be reasonable. Radiation attenuation properties have been carried out using emitted collimated beam from a fission (252)Cf (100 µg) neutron source, and the neutron-gamma spectrometer with stilbene scintillator. The pulse shape discriminating (P.S.D) technique based on the zero cross-over method was used to discriminate between neutron and gamma-ray pulses. Thermal neutron fluxes, measured using the BF3 detector and thermal neutron detection system, were used to plot the attenuation relations. The fast neutron macroscopic effective removal cross-section ?R, gamma ray total attenuation coefficient µ and thermal neutron macroscopic cross-section ? have been evaluated. Theoretical calculations have been achieved using MCNP-4C2 code to calculate ?R, µ and ?. Also, MERCSF-N program was used to calculate macroscopic effective removal cross-section ?R. Measured and calculated results have been compared and were found to be in reasonable agreement. PMID:23722071

El-Sarraf, M A; El-Sayed Abdo, A

2013-09-01

397

A simple model for deep tissue attenuation correction and large organ analysis of Cerenkov luminescence imaging  

NASA Astrophysics Data System (ADS)

Cerenkov luminescence imaging (CLI) is an emerging cost effective modality that uses conventional small animal optical imaging systems and clinically available radionuclide probes for light emission. CLI has shown good correlation with PET for organs of high uptake such as kidney, spleen, thymus and subcutaneous tumors in mouse models. However, CLI has limitations for deep tissue quantitative imaging since the blue-weighted spectral characteristics of Cerenkov radiation attenuates highly by mammalian tissue. Large organs such as the liver have also shown higher signal due to the contribution of emission of light from a greater thickness of tissue. In this study, we developed a simple model that estimates the effective tissue attenuation coefficient in order to correct the CLI signal intensity with a priori estimated depth and thickness of specific organs. We used several thin slices of ham to build a phantom with realistic attenuation. We placed radionuclide sources inside the phantom at different tissue depths and imaged it using an IVIS Spectrum (Perkin-Elmer, Waltham, MA, USA) and Inveon microPET (Preclinical Solutions Siemens, Knoxville, TN). We also performed CLI and PET of mouse models and applied the proposed attenuation model to correct CLI measurements. Using calibration factors obtained from phantom study that converts the corrected CLI measurements to %ID/g, we obtained an average difference of less that 10% for spleen and less than 35% for liver compared to conventional PET measurements. Hence, the proposed model has a capability of correcting the CLI signal to provide comparable measurements with PET data.

Habte, Frezghi; Natarajan, Arutselvan; Paik, David S.; Gambhir, Sanjiv S.

2014-03-01

398

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

PubMed Central

LacI/GalR transcription regulators have extensive, non-conserved interfaces between their regulatory domains and the 18 amino acids that serve as ‘linkers’ to their DNA-binding domains. These non-conserved interfaces might contribute to functional differences between paralogs. Previously, two chimeras created by domain recombination displayed novel functional properties. Here, we present a synthetic protein family, which was created by joining the LacI DNA-binding domain/linker to seven additional regulatory domains. Despite ‘mismatched’ interfaces, chimeras maintained allosteric response to their cognate effectors. Therefore, allostery in many LacI/GalR proteins does not require interfaces with precisely matched interactions. Nevertheless, the chimeric interfaces were not silent to mutagenesis, and preliminary comparisons suggest that the chimeras provide an ideal context for systematically exploring functional contributions of non-conserved positions. DNA looping experiments revealed higher order (dimer–dimer) oligomerization in several chimeras, which might be possible for the natural paralogs. Finally, the biological significance of repression differences was determined by measuring bacterial growth rates on lactose minimal media. Unexpectedly, moderate and strong repressors showed an apparent induction phase, even though inducers were not provided; therefore, an unknown mechanism might contribute to regulation of the lac operon. Nevertheless, altered growth correlated with altered repression, which indicates that observed functional modifications are significant. PMID:22965134

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

2012-01-01

399

Characterization of Platelet-Derived Growth Factor-A Expression in Mouse Tissues Using a lacZ Knock-In Approach  

PubMed Central

Expression of the platelet-derived growth factor A-chain gene (Pdgfa) occurs widely in the developing mouse, where it is mainly localized to various epithelial and neuronal structures. Until now, in situ mRNA hybridization (ISH) has been the only reliable method to identify Pdgfa expression in tissue sections or whole mount preparations. Validated protocols for in situ detection of PDGF-A protein by immunohistochemistry is lacking. In particular, this has hampered understanding of Pdgfa expression pattern in adult tissues, where ISH is technically challenging. Here, we report a gene targeted mouse Pdgfa allele, Pdgfaex4COIN, which is a combined conditional knockout and reporter allele. Cre-mediated inversion of the COIN cassette inactivates Pdgfa coding while simultaneously activating a beta-galactosidase (lacZ) reporter under endogenous Pdgfa transcription control. The generated Pdgfaex4COIN-INV-lacZ allele can next be used to identify cells carrying a Pdgfa null allele, as well as to map endogenous Pdgfa expression. We evaluated the Pdgfaex4COIN-INV-lacZ allele as a reporter for endogenous Pdgfa expression patterns in mouse embryos and adults. We conclude that the expression pattern of Pdgfaex4COIN-INV-lacZ recapitulates known expression patterns of Pdgfa. We also report on novel embryonic and adult Pdgfa expression patterns in the mouse and discuss their implications for Pdgfa physiology. PMID:25166724

Andrae, Johanna; Gouveia, Leonor; He, Liqun; Betsholtz, Christer

2014-01-01

400

Lack of specialization in trophic morphology between genetically differentiated dwarf and normal forms of lake whitefish (Coregonus clupeaformis Mitchill) in Lac de IyEsty Quebec  

Microsoft Academic Search

We recently observed a bimodal distribution in size of sexually maturing lake whitefish (Coregonus clupeaformis Mitchill) in Lac de L'Est, Quebec. The objective of this study was to test the hypothesis that these two spawning size classes represent genetically distinct ecotypes, potentially adapted in morphology for occupying different trophic niches. This was accomplished by quantifying the extent of genetic (mitochondrial

Angelo Chouinard; Dany Pigeon; Louis Bernatchez

401

Spatial and temporal expression of an Antennapedia\\/lac Z gene construct integrated into the endogenous Antennapedia gene of Drosophila melanogaster  

Microsoft Academic Search

In order to study the regulation of spatial and temporal expression of the homeotic gene Antennapedia (Antp) in Drosophila melanogaster, we have constructed fusion genes which contain Antp sequences linked to the reporter gene lac Z of Escherichia coli. In one case of P-element transformation, a fusion gene construct integrated into the endogenous Antp gene close to one of the

Ylva Eugstriim; Stephan Schneuwly; Walter Jakob Gehring

1992-01-01

402

Attenuation correction of (111)In planar images by use of dual energy, fundamental study by Monte Carlo simulation.  

PubMed

In this study, we devised and evaluated a method for attenuation correction of the hot spot in (111)In planar images. By use of the difference in transmittance between two energies (171 and 245 keV), the depth of the hot spot was calculated. Planar images of point sources in a numerical phantom (water) with depths from 0 to 20 cm at 2 cm intervals were prepared by Monte Carlo simulation. From the linear attenuation coefficient of the two energies and the 171/245 keV count ratio-depth relationship, the depth of the point source was calculated, and an attenuation correction was performed. A simulation was made under conditions taking into account both attenuation and scatter (A(+)S(+)) and attenuation alone (A(+)S(-)). The attenuation correction was evaluated with use of corrected and true counts obtained from homogeneous phantoms mimicking attenuation in soft tissue, bone, and the lungs, and heterogeneous phantoms prepared by combining them. In the A(+)S(+) condition, images were affected markedly by scattered photons in all phantoms at depths of 4-8 cm. The errors at depths of 10 cm or greater were within ±10 % in water and within ±6 % in soft tissue. However, the errors were about -30 % in bone and about +70 % in lung, indicating that scatter distributions different from those in water increased the errors. In the A(+)S(-) condition, the errors were within ±5 % in all homogeneous and heterogeneous phantoms, and satisfactory results were obtained. Precise attenuation correction of scatter-corrected planar images was confirmed to be possible with this method. PMID:25149323

Shirakawa, Seiji; Tadokoro, Masanori; Hashimoto, Hiroshi; Ushiroda, Tomoya; Toyama, Hiroshi

2015-01-01

403

Is there seismic attenuation in the mantle?  

NASA Astrophysics Data System (ADS)

The small scale heterogeneity of the mantle is mostly due to the mixing of petrological heterogeneities by a smooth but chaotic convection and should consist in a laminated structure (marble cake) with a power spectrum S(k) varying as 1/k, where k is the wavenumber of the anomalies. This distribution of heterogeneities during convective stirring with negligible diffusion, called Batchelor regime is documented by fluid dynamic experiments and corresponds to what can be inferred from geochemistry and seismic tomography. This laminated structure imposes density, seismic velocity and potentially, anisotropic heterogeneities with similar 1/k spectra. A seismic wave of wavenumber k0 crossing such a medium is partly reflected by the heterogeneities and we show that the scattered energy is proportional to k0S(2k0). The reduction of energy for the propagating wave appears therefore equivalent to a quality factor 1/Q?k0S(2k0). With the specific 1/k spectrum of the mantle, the resulting apparent attenuation should therefore be frequency independent. We show that the total contribution of 6-9% RMS density, velocity and anisotropy would explain the observed S and P attenuation of the mantle. Although these values are large, they are not unreasonable and we discuss how they depend on the range of frequencies over which the attenuation is explained. If such a level of heterogeneity were present, most of the attenuation of the Earth would be due to small scale scattering by laminations, not by intrinsic dissipation. Intrinsic dissipation must certainly exist but might correspond to a larger, yet unobserved Q. This provocative result would explain the very weak frequency dependence of the attenuation, and the fact that bulk attenuation seems negligible, two observations that have been difficult to explain for 50 years.

Ricard, Y.; Durand, S.; Montagner, J.-P.; Chambat, F.

2014-02-01

404

A KPC-Scale X-Ray Jet in the BL Lac Source S5 2007+777  

NASA Technical Reports Server (NTRS)

X-ray jets in AGN are commonly observed in FRII and FRI radiogalaxies, but rarely in BL Lacs, most probably due to their orientation close to the line of sight and the ensuing foreshortening effects. Only three BL Lacs are known so far to contain a kpc-scale X-ray jet. In this paper, we present the evidence for the existence of a fourth extended X-ray jet in the classical radio-selected source S5 2007+777, which for its hybrid FRI/II radio morphology has been classified as a HYMOR (HYbrid MOrphology Radio source). Our Chandra ACISS observations of this source revealed an X-ray counterpart to the 19"-long radio jet. Interestingly, the X-ray properties of the kpc-scale jet in S5 2007+777 are very similar to those observed in FRII jets. First, the X-ray morphology closely mirrors the radio one, with the X-rays being concentrated in the discrete radio knots. Second, the X-ray continuum of the jet/brightest knot is described by a very hard power law, with photon index gamma(sub x) approximately 1. Third, the optical upper limit from archival HST data implies a concave radio-to-X-ray SED. If the X-ray emission is attributed to IC/CMB with equipartition, strong beaming (delta= 13) is required, implying a very large scale (Mpc) jet. The beaming requirement can be somewhat relaxed assuming a magnetic field lower than equipartition. Alternatively, synchrotron emission from a second population of very high-energy electrons is viable. Comparison to other HYMOR jets detected with Chandra is discussed, as well as general implications for the origin of the FRI/II division.

Sambruna, Rita M.; Donato, Davide; Cheung, C.C.; Tavecchio, F.; Maraschi, L.

2008-01-01

405

Prediction of aircraft sideline noise attenuation  

NASA Technical Reports Server (NTRS)

A computational study is made using the recommended ground effect theory by Pao, Wenzel, and Oncley. It is shown that this theory adequately predicts the measured ground attenuation data by Parkin and Scholes, which is the only available large data set. It is also shown, however, that the ground effect theory does not predict the measured lateral attenuations from actual aircraft flyovers. There remain one or more important lateral effects on aircraft noise, such as sideline shielding of sources, which must be incorporated in the prediction methods. Experiments at low elevation angles (0 deg to 10 deg) and low-to-intermediate frequencies are recommended to further validate the ground effect theory.

Zorumski, W. E.

1978-01-01

406

Spectral Attenuation of Sound in Dilute Suspensions with Nonlinear Particle Relaxation  

NASA Technical Reports Server (NTRS)

Theoretical studies on the dissipation and dispersion of sound in two-phase suspensions have been briefly reviewed. Previous studies on the sound attenuation in particle-laden flows under Stokesian drag and conduction-controlled heat transfer have been extended to accommodate the nonlinear drag and heat transfer. It has been shown that for large particle-to-fluid density ratio, the particle Reynolds number bears a cubic relationship with Omega Tau(sub d) (where Omega is the circular frequency and Tau(sub d) the Stokesian particle relaxation time). This dependence leads to the existence of a peak value in the linear absorption coefficient occurring at a finite value Omega Tau (sub d). Comparison of the predictions with the test data for the spectral attenuation of sound with water injection in a perfectly expanded supersonic air jet shows a satisfactory trend of the theory accounting for nonlinear particle relaxation processes.

Kandula, M.; Lonegran, M.

2008-01-01

407

Millimeter-wave attenuation and delay rates due to fog/cloud conditions  

NASA Astrophysics Data System (ADS)

Propagation properties of suspended water and ice particles which make up atmospheric haze, fog, and clouds were examined for microwave and millimeter-wave frequencies. Rates of attenuation alpha (dB/km) and delay tau (ps/km) are derived from a complex refractivity based on the Rayleigh absorption approximation of Mie's scattering theory. Key variables are particle mass content and permittivity, which depends on frequency and temperature both for liquid and ice states. Water droplet attenuation can be estimated within a restricted (10 + or - 10 C) temperature range using a simple two-coefficient approximation. Experimental data on signal loss and phase delay caused by fog at four frequencies (50, 82, 141, and 246 GHz) over a 0.81-km line-of-sight path were found to be consistent with the model.

Liebe, Hans J.; Hufford, George A.; Manabe, Takeshi

1989-12-01

408

Spectral Attenuation of Sound in Dilute Suspensions with Nonlinear Particle Relaxation  

NASA Technical Reports Server (NTRS)

Previous studies on the sound attenuation in particle-laden flows under Stokesian drag and conduction-controlled heat transfer have been extended to accommodate the nonlinear drag and heat transfer. It has been shown that for large particle-to-fluid density ratio, the particle Reynolds number bears a cubic relationship with (omega(tau))(sub d) (where omega is the circular frequency and (tau)(sub d) the Stokesian particle relaxation time). This dependence leads to the existence of a peak value in the linear absorption coefficient occurring at a finite value of(omega(tau))(sub d). Comparison of the predictions with the test data for the spectral attenuation of sound with water injection in a perfectly expanded supersonic air jet shows a satisfactory trend of the theory accounting for nonlinear particle relaxation processes.

Kandula, Max

2008-01-01

409

Instrument Package Manipulation Through the Generation and Use of an Attenuated-Fluent Gas Fold  

NASA Technical Reports Server (NTRS)

This document discusses a technique that provides a means for suspending large, awkward loads, instrument packages, components, and machinery in a stable, controlled, and precise manner. In the baseplate of the test machine, a pattern of grooves and ports is installed that when pressurized generates an attenuated- fluent gas fold providing a low-cost, near-zero-coefficient-of-friction lubrication boundary layer that supports the object evenly, and in a predictable manner. Package movement control requires minimal force. Aids to repeatable travel and positional accuracy can be added via the addition of simple guide bars and stops to the floor or object being moved. This allows easily regulated three-axis motions. Loads of extreme weight and size can be moved and guided by a single person, or by automated means, using minimal force. Upon removal of the attenuated fluent gas fold, the object returns to a stable resting position without impact forces affecting the object.

Breen, Daniel P.

2012-01-01

410

Measurements of the optical absorption coefficient of Ar8+ ion implanted silicon layers using the photothermal radiometry and the modulated free carrier absorption methods  

NASA Astrophysics Data System (ADS)

This paper presents a method of the measurement of the optical absorption coefficient of the Ar8+ ions implanted layers in the p-type silicon substrate. The absorption coefficient is calculated using a value of the attenuation of amplitudes of a photothermal radiometry (PTR) and/or a modulation free carrier absorption (MFCA) signals and the implanted layer thickness calculated by means of the TRIM program. The proposed method can be used to indicate the amorphization of the ions implanted layers.

Chrobak, ?.; Mali?ski, M.; Pawlak, M.

2014-11-01

411

Photoacoustic computed tomography correcting for heterogeneity and attenuation  

PubMed Central

Abstract. We report an investigation of image reconstruction in photoacoustic tomography for objects that possess heterogeneous material and acoustic attenuation distributions. When the object contains materials, such as bone and soft-tissue, that are modeled using power law attenuation models with distinct exponents, we demonstrate that the effects of acoustic attenuation due to the most strongly attenuating material can be compensated for if the attenuation of the other less attenuating material(s) are neglected. Experiments with phantom objects are presented to validated our findings. PMID:22734741

Huang, Chao; Nie, Liming; Schoonover, Robert W.; Anastasio, Mark A.

2012-01-01

412

Usable solar radiation and its attenuation in the upper water column  

NASA Astrophysics Data System (ADS)

new radiometric term named as usable solar radiation (USR) is defined to represent the spectrally integrated solar irradiance in the spectral window of 400-560 nm. Through numerical simulations of optically deep waters covering a wide range of optical properties, it is found that the diffuse attenuation coefficient of downwelling USR, Kd(USR), is nearly a constant vertically for almost all oceanic waters (chlorophyll concentration under ˜3 mg m-3). This feature is quite contrary to the diffuse attenuation coefficient of the photosynthetic available radiation, K(PAR), which varies significantly from surface to deeper depths for oceanic waters. It is also found that the ratio of the photosynthetic utilizable radiation (PUR) to the product of USR and phytoplankton absorption coefficient at 440 nm approximates a constant for most oceanic waters. These results support the use of a single Kd(USR) for each water and each sun angle for accurate estimation of USR propagation, and suggest an efficient approach to estimate PUR(z) in the upper water column. These results further indicate that it is necessary and valuable for the generation of USR and Kd(USR) products from satellite ocean color measurements, which can be used to facilitate the studies of heat transfer and photosynthesis in the global oceans.

Lee, Zhongping; Shang, Shaoling; Du, Keping; Wei, Jianwei; Arnone, Robert

2014-02-01

413

Touch Attenuates Infants' Physiological Reactivity to Stress  

ERIC Educational Resources Information Center

Animal studies demonstrate that maternal touch and contact regulate infant stress, and handling during periods of maternal deprivation attenuates the stress response. To measure the effects of touch on infant stress reactivity during simulated maternal deprivation, 53 dyads were tested in two paradigms: still-face (SF) and still-face with maternal…

Feldman, Ruth; Singer, Magi; Zagoory, Orna

2010-01-01

414

Brucellosis: The case for live, attenuated vaccines  

Microsoft Academic Search

The successful control of animal brucellosis and associated reduction in human exposure has limited the development of human brucellosis vaccines. However, the potential use of Brucella in bioterrorism or biowarfare suggests that direct intervention strategies are warranted. Although the dominant approach has explored the use of live attenuated vaccines, side effects associated with their use has prevented widespread use in

Thomas A. Ficht; Melissa M. Kahl-McDonagh; Angela M. Arenas-Gamboa; Allison C. Rice-Ficht

2009-01-01

415

UHF Radio Wave Attenuation Factor Database  

Microsoft Academic Search

As is known each sea-going vessel is equipped with navigation, communication and other radio engineering facilities that serve to secure the safety of navigation and are chiefly operated at UHF-wave band. In developing these systems and calculating the energy potential for a necessary coverage range one should be well aware of the radio signal attenuation processes on a propagation path.

S. I. Khomenko; V. L. Kostina; I. M. Mytsenko; A. N. Roenko

2007-01-01

416

Monitored Natural Attenuation Case Study Evaluations  

EPA Science Inventory

Monitored natural attenuation (MNA) has been selected as a component of groundwater remedies at several sites with metals and/or radionuclide contamination. An overview of the site characterization effort and remedy performance will be provided for several sites where MNA was se...

417

Theory of Ultrasonic Attenuation in Metals  

Microsoft Academic Search

A quantum mechanical theory of the attenuation of the longitudinal ultrasonic wave in metals due to the conduction electrons is developed according to the general theory of linear response given by Kubo. When the mean free path of electrons is longer than the wavelength of the ultrasonic wave, the result is reduced to that given by the ordinary perturbational treatment

Yosuke Nagaoka

1961-01-01

418

Traffic Noise Ground Attenuation Algorithm Evaluation  

Microsoft Academic Search

The Federal Highway Administration traffic noise prediction program, STAMINA 2.0, was evaluated for its accuracy. In addition, the ground attenuation algorithm used in the Ontario ORNAMENT method was evaluated to determine its potential to improve these predictions. Field measurements of sound levels were made at 41 sites on I-440 in Nashville, Tennessee in order to both study noise barrier effectiveness

Lloyd Allen Herman

1993-01-01