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1

Spectral induced polarization signatures of abiotic FeS precipitation  

Microsoft Academic Search

In recent years, geophysical methods have been shown to be sensitive to microbial induced mineralization processes. The spectral induced polarization (SIP) method appears to be very promising for monitoring mineralization and microbial processes. With this work, we study the links of mineralization and SIP signals, in the absence of microbial activity. We recorded the SIP response during abiotic FeS precipitation.

Dimitrios Ntarlagiannis; Rory Doherty; Kenneth H. Williams

2010-01-01

2

Determination of permeability from spectral induced polarization in granular media  

NASA Astrophysics Data System (ADS)

The surface conductivity of porous rocks has two contributions: the first is associated with the diffuse layer coating the grains and is frequency-independent as long as the diffuse layer is above a percolation threshold. The second contribution is associated with the Stern layer of weakly sorbed counterions on the mineral surface and is frequency-dependent if the Stern layer is discontinuous at the scale of the representative elementary volume. In the frequency range 1 mHz-100 Hz, this second contribution is also associated with the main polarization mechanism observed by the spectral induced polarization method in granular media (neglecting the contribution of other polarization processes like those associated with redox processes and membrane polarization). At the macroscale, we connect the Stern layer contribution to the complex conductivity and to the expectation of the probability distribution of the inverse of the grain size. This is done by performing a convolution between the probability distribution of the inverse of the grain size and the surface conductivity response obtained when all the grains have the same size. Surface conductivity at the macroscopic scale is also connected to an effective pore size used to characterize permeability. From these relationships, a new equation is derived connecting this effective pore size, the electrical formation factor, and the expected value of the probability distribution for the inverse of the grain size, which is in turn related to the distribution of the relaxation times. These new relationships are consistent with various formula derived in the literature in the limit where the grain size distribution is given by the delta function or a log normal distribution and agree fairly well with various experimental data showing also some limitations of the induced polarization method to infer permeability. One of these limitations is the difficulty to detect the relaxation, in the phase, associated with the smaller grains, as this polarization may be hidden by the Maxwell-Wagner polarization at relatively high frequencies (>100 Hz). Also, cemented aggregates of grains can behave as coarser grains.

Revil, A.; Florsch, N.

2010-06-01

3

Contribution of Stern layer and membrane polarization to spectral induced polarization of variably saturated sandy soils  

NASA Astrophysics Data System (ADS)

Spectral induced polarization is receiving increasing attention as a tool to map subsurface properties in a non-invasive manner. Although empirical correlations have been devised to link measurements to porous medium properties, such as the time constant of the Cole-Cole model to grain size distribution and hydraulic conductivity, a comprehensive process-based model is still missing. Two fundamentally different mechanisms have been proposed so far, (i) electrical double layer polarization, in particular of the Stern layer and (ii) membrane polarization. This latter mechanism is due to the accumulation of ions at the opposite sides of narrow pore-throats, which effectively act as ion-selective channels and lead to the formation of a membrane potential. Both mechanisms have so far shown the ability to explain to some degree experimental observations, although not in a completely convincing manner. The goal of this work was to test whether the two process concur to the observed polarization of the porous medium or rather are mutually exclusive. The Hashin-Shtrickman Average (HSA) model of Brovelli and Cassiani (2010, 2011) was extended to compute the complex bulk conductivity of variably saturated porous media. Complex surface conductance was computed from EDL polarization theory, whereas membrane polarization affects pore-water conductivity. The frequency-dependent HSA model was compared with the measured spectral induced polarization of variably-saturated sandy soils. A satisfactory comparison was found for most samples, in particular with water saturation above 0.8. It was observed that the two polarization mechanisms lead to separate phase peaks, which are related to the characteristic diffusion length and tortuosity of grains and pore-throats. When saturation is decreased, Stern layer polarization becomes the dominant mechanism, as the water phase is progressively less abundant and more disconnected. In addition, the measured polarization becomes more difficult to explain with the model, perhaps because additional mechanisms - such as the polarization of the air-water interface - come into play.

Brovelli, A.; Cassiani, G.

2012-04-01

4

Spectral induced polarization (SIP) response of mine tailings.  

PubMed

Mine tailings impoundments are a source of leachates known as acid mine drainage (AMD) which can pose a contamination risk for surrounding surface and groundwater. Methodologies which can help management of this environmental issue are needed. We carried out a laboratory study of the spectral induced polarization (SIP) response of tailings from the Haveri Au-Cu mine, SW Finland. The primary objectives were, (1) to determine possible correlations between SIP parameters and textural properties associated with oxidative-weathering mechanisms, mineralogical composition and metallic content, and (2) to evaluate the effects of the pore water chemistry on SIP parameters associated with redox-inactive and redox-active electrolytes varying in molar concentration, conductivity and pH. The Haveri tailings exhibit well defined relaxation spectra between 100 and 10,000Hz. The relaxation magnitudes are governed by the in-situ oxidative-weathering conditions on sulphide mineral surfaces contained in the tailings, and decrease with the oxidation degree. The oxidation-driven textural variation in the tailings results in changes to the frequency peak of the phase angle, the imaginary conductivity and chargeability, when plotted versus the pore water conductivity. In contrast, the real and the formation electrical conductivity components show a single linear dependence on the pore water conductivity. The increase of the pore water conductivity (dominated by the increase of ions concentration in solution) along with a transition to acidic conditions shifts the polarization peak towards higher frequencies. These findings show the unique sensitivity of the SIP method to potentially discriminate AMD discharges from reactive oxidation zones in tailings, suggesting a significant advantage for monitoring threatened aquifers. PMID:25528133

Placencia-Gómez, Edmundo; Parviainen, Annika; Slater, Lee; Leveinen, Jussi

2015-02-01

5

Spectral induced polarization (SIP) response of biodegraded oil in porous media  

NASA Astrophysics Data System (ADS)

Laboratory experiments were conducted to investigate the effect of different oil saturation (0.2-0.8), wetting conditions (water-wet and oil-wet), and the addition of asphaltene on the spectral induced polarization (SIP) response of biodegraded and fresh crude oil in sand columns. In the water-wet case, no significant differences were observed for both the fresh and biodegraded oil and both displayed an increase in the magnitude of the phase (?) and decrease in the magnitudes of the real (?') and imaginary (?'') conductivity components with increasing oil saturation. In this instance the SIP response is most likely controlled by the conduction and polarization of the electric double layer at the mineral-water interface. However, when oil is the wetting phase there were considerable differences in the magnitude of the SIP parameters between the fresh and biodegraded oil. The magnitude of ? and ?'' increased with increasing oil saturation, whereas ?' decreased. The magnitude of ?' and ?'' for the biodegraded oil-wetted sands were relatively higher compared to fresh oil-wetted sands. In experiments with fresh and biodegraded oil-wet sand, the addition of 1 per cent asphaltene increased ?' and ?'' with the biodegraded oil showing the highest magnitude. Asphaltenes are the most dipolar fraction of crude oil and increase in concentration with increasing biodegradation. Asphaltene creates a surface charge due to the ionization and complexation reactions of functional groups at interfaces. Therefore, the enhancement in the conduction and polarization observed with the biodegraded oil-wetted sands may be due to the increase in polar components (e.g. asphaltene) from the biodegradation process and the interactions of the polar components with the surfaces of water and mineral grains. Further studies are required to investigate the effect of other components in biodegraded oil such as resins, trace metals, biogenic metallic minerals (e.g. magnetite) and organic acids on the SIP response of porous media.

Abdel Aal, Gamal Z.; Atekwana, Estella A.

2014-02-01

6

Spectral induced polarization and electrodic potential monitoring of microbially mediated iron sulfide transformations  

SciTech Connect

Stimulated sulfate-reduction is a bioremediation technique utilized for the sequestration of heavy metals in the subsurface.We performed laboratory column experiments to investigate the geoelectrical response of iron sulfide transformations by Desulfo vibriovulgaris. Two geoelectrical methods, (1) spectral induced polarization (SIP), and (2) electrodic potential measurements, were investigated. Aqueous geochemistry (sulfate, lactate, sulfide, and acetate), observations of precipitates (identified from electron microscopy as iron sulfide), and electrodic potentials on bisulfide ion (HS) sensitive silver-silver chloride (Ag-AgCl) electrodes (630 mV) were diagnostic of induced transitions between an aerobic iron sulfide forming conditions and aerobic conditions promoting iron sulfide dissolution. The SIP data showed 10m rad anomalies during iron sulfide mineralization accompanying microbial activity under an anaerobic transition. These anomalies disappeared during iron sulfide dissolution under the subsequent aerobic transition. SIP model parameters based on a Cole-Cole relaxation model of the polarization at the mineral-fluid interface were converted to (1) estimated biomineral surface area to pore volume (Sp), and (2) an equivalent polarizable sphere diameter (d) controlling the relaxation time. The temporal variation in these model parameters is consistent with filling and emptying of pores by iron sulfide biofilms, as the system transitions between anaerobic (pore filling) and aerobic (pore emptying) conditions. The results suggest that combined SIP and electrodic potential measurements might be used to monitor spatiotemporal variability in microbial iron sulfide transformations in the field.

Hubbard, Susan; Personna, Y.R.; Ntarlagiannis, D.; Slater, L.; Yee, N.; O'Brien, M.; Hubbard, S.

2008-02-15

7

Delineation of subsurface hydrocarbon contamination at a former hydrogenation plant using spectral induced polarization imaging  

NASA Astrophysics Data System (ADS)

Broadband spectral induced polarization (SIP) measurements were conducted at a former hydrogenation plant in Zeitz (NE Germany) to investigate the potential of SIP imaging to delineate areas with different BTEX (benzene, toluene, ethylbenzene, and xylene) concentrations. Conductivity images reveal a poor correlation with the distribution of contaminants; whereas phase images exhibit two main anomalies: low phase shift values (< 5 mrad) for locations with high BTEX concentrations, including the occurrence of free-phase product (BTEX concentrations > 1.7 g/l), and higher phase values for lower BTEX concentrations. Moreover, the spectral response of the areas with high BTEX concentration and free-phase products reveals a flattened spectrum in the low frequencies (< 40 Hz), while areas with lower BTEX concentrations exhibit a response characterized by a frequency peak. The SIP response was modelled using a Debye decomposition to compute images of the median relaxation-time. Consistent with laboratory studies, we observed an increase in the relaxation-time associated with an increase in BTEX concentrations. Measurements were also collected in the time domain (TDIP), revealing imaging results consistent with those obtained for frequency domain (SIP) measurements. Results presented here demonstrate the potential of the SIP imaging method to discriminate source and plume of dissolved contaminants at BTEX contaminated sites.

Flores Orozco, Adrián; Kemna, Andreas; Oberdörster, Christoph; Zschornack, Ludwig; Leven, Carsten; Dietrich, Peter; Weiss, Holger

2012-08-01

8

Spectral induced polarization monitoring of CO2 injection in saturated sands: a laboratory experiment  

NASA Astrophysics Data System (ADS)

During the last decade, the interest of induced polarization methods for environmental studies has undoubtly grown. Here, we present a set of laboratory experiments aimed at assessing the ability of spectral induced polarisation (SIP) method to detect and monitor CO2 transfers in the subsurface. The objectives were the quantification of the influence of various parameters on the SIP response, such as the water conductivity, the chemical reactivity of the solid and of the gas phases, and the injection rate. SIP measurements in the frequency range 50 mHz - 20 kHz were thus performed during gas (N2 or CO2) injections in a metric-scaled, cylindrical tank filled with unconsolidated granular material (quartz or carbonate sands) and fully saturated with water. The system was most reactive to gas injection in the high frequency range (>1 kHz). In quartz sand, the presence of gas in the medium tends to decrease the measured values of the phase angle. This effect becomes more important when increasing the injection rate, and thus the amount of gas trapped in the medium. The magnitude of this effect decreases when the water conductivity increases. Dissolution processes (CO2 in water and also solid matrix in the case of carbonate sand) were evidenced from chemical measurements (pH, conductivity and anionic concentrations). The increased ionic strength resulted in a decrease of the bulk resistivity and in an increase of the phase values at high frequency. An interesting parameter is the ratio of the increase in phase to the decrease in resistivity. When dissolution processes are involved, this ratio increases strongly with the initial conductivity of the saturating fluid. Hence, in some cases the measured phase values still bring measurable information on the system evolution even if resistivity variations are very small.

Kremer, T.; Schmutz, M.; Agrinier, P.; Maineult, A. J.

2013-12-01

9

Monitoring of CO2-induced geochemical changes in a shallow aquifer by time domain spectral induced polarization  

NASA Astrophysics Data System (ADS)

Contamination of potable groundwater by leaking CO2 is a potential risk of carbon sequestration. With the help of a field experiment, we investigate if surface monitoring of electrical resistivity and induced polarization can detect geochemical changes induced by CO2 in a shallow aquifer. For this purpose, we injected CO2 at a depth of 5 and 10 m and monitored its migration using 320 electrodes on a 126 m × 25 m surface grid. A fully automated acquisition system continuously collected direct current (DC) resistivity and full-decay induced polarization (IP) data and uploaded it into an online database. CO2 was injected for a period of 72 days and DC/IP monitoring started 20 days before and continued until 120 days after the beginning of the injection. The DC/IP data were supplemented by chemical analysis of water samples collected in 29 wells at time intervals of approximately 10 days. DC/IP data are inverted using a 2-D algorithm (AarhusInv) that incorporates the full voltage decay of the IP response to resolve DC resistivity, intrinsic chargeability and spectral IP content parameterized using the Cole-Cole model. Borehole information and a baseline inversion reveals the geology at the site consisting of aeolian sands near the surface, glacial sands between 5 and 10 m depth and marine sands below 10 m depth. Following the injection, we use a time-lapse inversion where differences in the DC/IP data are inverted for changes to the Cole-Cole parameters. Two different geochemical signatures that occur due to the injected CO2 are evident both in the geophysical inversions and the water samples. The first and clearest subsurface signal is a decrease in DC resistivity that moves advectively with the groundwater. The area of resistivity decrease expands with time in the direction of the groundwater flow and there is good correlation between geophysical and geochemical results. A chargeability decrease after the injection has been also observed, but in contrast to the decrease in DC resistivity, the chargeability anomaly remains localized around and slightly downstream of the injection wells throughout the experiment. This chargeability decrease correlates in space and time with a decrease in pH, which is observed in the water samples. Consequently, we attribute this change in chargeability to pH-induced changes to the grains surfaces. These results highlight the potential for monitoring of field scale geochemical changes by means of surface DC/IP measurements. Especially the different development of the DC resistivity and chargeability anomalies and the different associated geochemical processes, highlight the added value of induced polarization to resistivity monitoring.

Doetsch, Joseph; Fiandaca, Gianluca; Auken, Esben; Christiansen, Anders V.; Cahill, Aaron G.; Jakobsen, Rasmus

2014-05-01

10

Application of a Spectral Induced Polarization Data Error Model for Field Scale Biogeophysical Monitoring  

NASA Astrophysics Data System (ADS)

The aim of this study was to find an appropriate model for the description of measurement errors in field spectral induced polarization (SIP) data and to show that its implementation within an inversion scheme offers significant improvements in the resulting images for use in bioremediation monitoring. Accompanying a biostimulation experiment near Rifle, Colorado, SIP data collected over the 0.25 to 1000Hz frequency range were obtained along profiles oriented perpendicular to groundwater flow and located downgradient from a region of acetate amendment. Data errors were evaluated in terms of discrepancy between normal and reciprocal measurements. In agreement with previous studies, the normal-reciprocal resistance error increases linearly with resistance. For the phase error, we found an exponentially decreasing behavior with increasing resistance (i.e. with increasing signal strength). The proposed error model for the phase is given parameters, and R is the resistance measured. The implementation of the error model for the phase in a complex resistivity inversion algorithm provides images free of artifacts, exhibiting anomalies well correlated with spatiotemporal changes in geochemical conditions resulting from stimulated microbial activity. Using this approach, inversion of SIP data delineated two distinct biogeochemical processes in the subsurface. At frequencies <1Hz, anomalies exceeding 10mrad were correlated with the presence of reduced sulfur species (e.g. dissolved sulfide and FeS) accompanying stimulated sulfate reduction. At frequencies >4Hz, anomalies of 4-6mrad were correlated with elevated concentrations of dissolved iron resulting from the activity of iron reducing bacteria. Additionally, SIP data were collected using two different acquisition systems. Resistance and phase values recorded by both systems were consistent; however, the parameters obtained for the error model are not the same even when the final images obtained for resistivity and phase are very similar.

Flores-Orozco, A.; Williams, K. H.; Kemna, A.

2008-12-01

11

Characterizing structural and textural subsurface patterns using spectral induced polarization: Effects of saturation  

NASA Astrophysics Data System (ADS)

Groundwater is a vulnerable resource that is endangered by pollutants and contaminants. Soil is an important protective buffer for groundwater and, therefore, the understanding of flow and transport processes in soils is very important. However, the prediction capabilities of unsaturated flow and transport models in the vadose zone are often limited due to an insufficient knowledge about the structural and textural heterogeneity of the soil. To obtain more information about soil structure, texture and heterogeneity, as well as hydraulic parameters, non-invasive electrical methods may be employed in field-scale studies. To investigate the potential of the approach, a laboratory measurement setup was developed which allows combined electrical and hydraulic measurements. The latter are conducted via a multi-step outflow device. Various pressure steps are applied to a saturated sample and the outflow is recorded. When equilibrium is reached, spectral induced polarization (SIP) measurements are conducted before the next pressure step is applied. The electrical measurements are carried out with a high-accuracy impedance spectrometer. Combined electrical and hydraulic measurements were conducted on packed sand-clay mixtures. The measured resistivity magnitude and phase spectra and their dependence on water content are clearly different for each mixture. For pure sand, the phase values increase with decreasing water content over the entire frequency range and a phase peak is present for low water content. The increasing phase is due to the increasing resistivity and an associated increasing chargeability of the sample. The phase spectrum of a sand-clay mixture with 5 % clay shows the same behaviour like the pure sand; however, the shift of the phase peak to higher frequencies is much stronger. This shift suggests that relaxation time and length become smaller with decreasing water content, which is related to the smaller pores that are active at lower water content. The sand-clay mixture with 20 % clay shows a significantly different behaviour. At full saturation, the phase spectrum exhibits a weak peak at about 0.2 Hz. With decreasing saturation, first a distinct phase peak is formed at about 0.02 Hz; then phase values decrease, and simultaneously a shift to higher frequencies occurs. The phase values are also much smaller than for the other mixtures. This unique dataset is used to investigate relationships between electrical and hydraulic properties.

Breede, K.; Esser, O.; Zimmermann, E.; Huisman, J. A.; Kemna, A.

2010-05-01

12

Investigating the effect of electro-active ion concentration on spectral induced polarization signatures arising from biomineralization pathways  

NASA Astrophysics Data System (ADS)

Spectral induced polarization (SIP) is a proven geophysical method for detecting biomineral formation with promising applications for monitoring biogeochemical products during microbial induced sequestration of heavy metals and radionuclides in soils. SIP has been used to monitor the evolution of bioremediation-induced end-products at the uranium-contaminated U.S. Department of Energy Rifle Integrated Field Research Challenge site in Colorado. Although a significant SIP response was detected, the quantitative interpretation is non-trivial as the polarization of metallic minerals depends both on the mineral surface properties and the electrolyte chemistry. In previous experiments SIP mechanisms were studied under complex environments and individual source mechanisms could not be evaluated. Here we examine the role of electrolyte chemistry by comparing the effect of redox active / inactive ions on metallic polarization. In these abiotic experiments magnetite was used as a proxy biomineral and dispersed within columns packed with sand. Parallel columns were saturated with solutions of different concentrations of active (Fe2+) and inactive (Ca2+) ions (0.01mM-10mM) and SIP measurements made (0.1-1000 Hz). Experimental results show small, but detectable, differences in the effect of active ion and inactive ion concentration on the SIP response. To better characterize the effect of electro-active ions on metallic minerals we used a Cole - Cole type relaxation model, to describe the SIP responses. In order to better resolve the relaxation model parameters, we followed a two-step approach whereby we started with a Bayesian based inversion to resolve for the initial parameter estimates, and subsequently used these estimates as a starting model for a deterministic solution. Our results suggest that changes in the active ion concentration, in the presence of magnetite, alone are unlikely to fully explain recent SIP monitoring data from the Rifle site.

Ntarlagiannis, D.; Slater, L. D.; Williams, K. H.; Hubbard, S. S.; Wu, Y.

2010-12-01

13

Investigating the Effect of Saturation and Wettability on Spectral Induced Polarization of Biodegraded Oil in Porous Media  

NASA Astrophysics Data System (ADS)

Spectral induced polarization (SIP) has been suggested as the technique most sensitive to the presence of contaminants as well as accompanying bio-physicochemical processes associated with hydrocarbon biodegradation. Previous laboratory investigations have suggested that wettability is an important factor to consider when investigating the SIP response of oil bearing sands. The results to date provide experimental data for mostly fresh oil. However, these results differ significantly from field investigations where the oil is mostly in the degraded form. In this study we extend the work of Schmutz and others and Revil and others by investigating the SIP response of biodegraded oil in porous media. Laboratory experiments were conducted to investigate the effect of different oil saturation (0.2-0.8) and wettability (water wet and oil wet) on SIP of biodegraded and fresh oil in sand columns. The laboratory experiments were performed using a sand column filled with a mix of oil, artificial ground water (AGW) with a conductivity of 0.01 S/m and fine sands. Each experiment was conducted with clean sands mixed with oil (oil wet case) or AGW (water wet case). The proportions of oil and water were calculated to obtain the desired oil and water saturations, and using the same amount of sand. SIP measurements were made using a National Instruments NI 4551 dynamic signal analyzer and four electrodes technique. Phase shift between current stimulus-voltage signal and conductivity magnitude were measured between 0.1 and 1000 Hz and the real and imaginary components of the complex surface conductivity were calculated. The same experimental procedure was repeated using fresh oil as background and for comparison with biodegraded oil results. The results show that when water is the wetting phase, there is no significant difference in the IP parameters measured for both the fresh and degraded oil. Furthermore, both the fresh and biodegraded oil showed an increase in the magnitude of the phase and a decrease in the magnitudes of the real and imaginary conductivity components with increasing oil saturation. However, when oil is the wetting phase there is a noticeable difference in the magnitude of the IP parameters between the fresh and biodegraded oil. The magnitude of the phase and imaginary conductivity component increased with increasing oil saturation whereas real conductivity decreased. At the same time, the magnitude of the real and imaginary conductivity components for the biodegraded oil wet sands were relatively higher compared to fresh oil wet sand. Our results suggest that the biodegraded oil enhances the polarization only for the case where oil is the wetting phase. The enhancement in the polarization (imaginary conductivity) observed with the biodegraded oil wet sands may be attributed to the increase in polar components and nanoparticulate metals (magnetite, vanadium, nickel, etc.) content resulting from the biodegradation process.

Abdel Aal, G. Z.; Atekwana, E. A.

2012-12-01

14

A Hierarchical Bayesian Model for Estimating Remediation-induced Biogeochemical Transformations Using Spectral Induced Polarization Data: Development and Application to the Contaminated DOE Rifle (CO) Site  

NASA Astrophysics Data System (ADS)

Although in-situ bioremediation is often considered as a key approach for subsurface environmental remediation, monitoring induced biogeochemical processes, needed to evaluate the efficacy of the treatments, is challenging over field relevant scales. In this study, we develop a hierarchical Bayesian model that builds on our previous framework for estimating biogeochemical transformations using geochemical and geophysical data obtained from laboratory column experiments. The new Bayesian model treats the induced biogeochemical transformations as both spatial and temporal (rather than just temporal) processes and combines time-lapse borehole ‘point’ geochemical measurements with inverted surface- or crosshole-based spectral induced polarization (SIP) data. This model consists of three levels of statistical sub-models: (1) data model (or likelihood function), which provides links between the biogeochemical end-products and geophysical attributes, (2) process model, which describes the spatial and temporal variability of biogeochemical properties in the disturbed subsurface systems, and (3) parameter model, which describes the prior distributions of various parameters and initial conditions. The joint posterior probability distribution is explored using Markov Chain Monte Carlo sampling methods to obtain the spatial and temporal distribution of the hidden parameters. We apply the developed Bayesian model to the datasets collected from the uranium-contaminated DOE Rifle site for estimating the spatial and temporal distribution of remediation-induced end products. The datasets consist of time-lapse wellbore aqueous geochemical parameters (including Fe(II), sulfate, sulfide, acetate, uranium, chloride, and bromide concentrations) and surface SIP data collected over 13 frequencies (ranging from 0.065Hz to 256Hz). We first perform statistical analysis on the multivariate data to identify possible patterns (or ‘diagnostic signatures’) of bioremediation, and then we invert the time-lapse SIP data for chargeability and time constant using Cole-Cole models. By combining the limited borehole time series data with spatially distributed time-lapse geophysical data, we can obtain the spatial and temporal distribution of the bioremediation end-products (such as volume fraction of FeS and calcite) and their associated uncertainty information. Our study results show how time-lapse SIP datasets, when incorporated into a Bayesian hierarchical model, can be useful for quantifying the spatiotemporal distribution of remediation-induced end-products. The study also documents how the diagnostic geophysical signatures can be useful for identifying when and where critical, remediation-induced system transitions occur, such as those accompanying a rebound in aquifer redox status and the associated impact on immobilized contaminant stability.

Chen, J.; Hubbard, S. S.; Williams, K. H.; Tuglus, C.; Flores-Orozco, A.; Kemna, A.

2010-12-01

15

Spectral and spectral-polarization characteristics of potato leaves  

NASA Astrophysics Data System (ADS)

The results of laboratory investigations of the spectral and spectral-polarization characteristics of radiation reflected from the leaves of potato (Solanum tuberosum) of different varieties are discussed. During the vegetation season of 1997, the angular dependence of the degree and azimuth of polarization of radiation reflected from potato leaves as well as the scattering indicatrices in the range 380 1080 nm were determined by a specially developed method with the use of a laboratory goniometric setup. The relationship between the spectral polarization characteristics of radiation and biological parameters of the potato has been obtained with the help of different methods of statistical analysis and explained on the basis of the known physical mechanisms.

Belyaev, B. I.; Belyaev, Yu. V.; Chumakov, A. V.; Nekrasov, V. P.; Shuplyak, V. I.

2000-07-01

16

Spectrally broadband channeled imaging polarimeter using polarization gratings  

E-print Network

Spectrally broadband channeled imaging polarimeter using polarization gratings Michael W. Kudenov1 linear imaging (CLI) polarimeter is demonstrated by incorporating two identical polarization gratings (PGs) into a shearing polarization interferometer. Placing the PGs in series causes the shear to become

Dereniak, Eustace L.

17

A comparison between Gauss-Newton and Markov chain Monte Carlo basedmethods for inverting spectral induced polarization data for Cole-Coleparameters  

SciTech Connect

We develop a Bayesian model to invert spectral induced polarization (SIP) data for Cole-Cole parameters using Markov chain Monte Carlo (MCMC) sampling methods. We compare the performance of the MCMC based stochastic method with an iterative Gauss-Newton based deterministic method for Cole-Cole parameter estimation through inversion of synthetic and laboratory SIP data. The Gauss-Newton based method can provide an optimal solution for given objective functions under constraints, but the obtained optimal solution generally depends on the choice of initial values and the estimated uncertainty information is often inaccurate or insufficient. In contrast, the MCMC based inversion method provides extensive global information on unknown parameters, such as the marginal probability distribution functions, from which we can obtain better estimates and tighter uncertainty bounds of the parameters than with the deterministic method. Additionally, the results obtained with the MCMC method are independent of the choice of initial values. Because the MCMC based method does not explicitly offer single optimal solution for given objective functions, the deterministic and stochastic methods can complement each other. For example, the stochastic method can first be used to obtain the means of the unknown parameters by starting from an arbitrary set of initial values and the deterministic method can then be initiated using the means as starting values to obtain the optimal estimates of the Cole-Cole parameters.

Chen, Jinsong; Kemna, Andreas; Hubbard, Susan S.

2008-05-15

18

Spectral polarization of clear and hazy coastal skies.  

PubMed

Linear polarization of the clear daytime sky has often been measured as a spectrally integrated or quasi-monochromatic variable, but seldom as a spectral one. So we use a hyperspectral imaging system to measure skylight polarization at high spectral and angular resolutions for clear and hazy skies at our coastal site. The resulting polarization maps and spectra exhibit both commonalities and differences that seem unexplained by an existing polarized radiative transfer model. Comparing the measured polarization spectra with those predicted by aerosol single scattering suggests some basic verisimilitude tests for improving such models. PMID:23128696

Lee, Raymond L; Samudio, Orlando R

2012-11-01

19

Wavelength-parallel techniques for efficient spectral polarimetry, polarization mode dispersion penalty monitoring, and differential group delay emulations  

Microsoft Academic Search

Polarization of light within an optical fiber constantly changes due to environmentally induced birefringence in the fiber, and the time scale of variation can be milliseconds or less. This phenomenon originates various fiber optic communication system impairments such as polarization mode dispersion (PMD) and polarization dependent loss. The first part of this thesis examines a purposefully designed spectral polarimeter for

Shawn X Wang

2006-01-01

20

THE EFFECT OF SYSTEMATICS ON POLARIZED SPECTRAL INDICES  

SciTech Connect

We study four particularly bright polarized compact objects (Tau A, Vir A, 3C 273, and For A) in the 7 year Wilkinson Microwave Anisotropy Probe (WMAP) sky maps, with the goal of understanding potential systematics involved in the estimation of foreground spectral indices. First, we estimate the spectral index, the polarization angle, the polarization fraction, and the apparent size and shape of these objects when smoothed to a nominal resolution of 1 Degree-Sign FWHM. Second, we compute the spectral index as a function of polarization orientation, {alpha}. Because these objects are approximately point sources with constant polarization angle, this function should be constant in the absence of systematics. However, for the K and Ka band WMAP data we find strong index variations for all four sources. For Tau A, we find a spectral index of {beta} = -2.59 {+-} 0.03 for {alpha} = 30 Degree-Sign , and {beta} = -2.03 {+-} 0.01 for {alpha} = 50 Degree-Sign . On the other hand, the spectral index between the Ka and Q bands is found to be stable. A simple elliptical Gaussian toy model with parameters matching those observed in Tau A reproduces the observed signal, and shows that the spectral index is particularly sensitive to the detector polarization angle. Based on these findings, we first conclude that estimation of spectral indices with the WMAP K band polarization data at 1 Degree-Sign scales is not robust. Second, we note that these issues may be of concern for ground-based and sub-orbital experiments that use the WMAP polarization measurements of Tau A for calibration of gain and polarization angles.

Wehus, I. K. [Oxford Astrophysics, University of Oxford, DWB, Keble Road, Oxford OX1 3RH (United Kingdom)] [Oxford Astrophysics, University of Oxford, DWB, Keble Road, Oxford OX1 3RH (United Kingdom); Fuskeland, U.; Eriksen, H. K., E-mail: i.k.wehus@fys.uio.no [Institute of Theoretical Astrophysics, University of Oslo, P.O. Box 1029, Blindern, N-0315 Oslo (Norway)

2013-02-15

21

Polarization diversity scheme on spectral polarization coding optical code-division multiple-access network  

NASA Astrophysics Data System (ADS)

We present an experiment demonstrating the spectral-polarization coding optical code-division multiple-access system introduced with a nonideal state of polarization (SOP) matching conditions. In the proposed system, the encoding and double balanced-detection processes are implemented using a polarization-diversity scheme. Because of the quasiorthogonality of Hadamard codes combining with array waveguide grating routers and a polarization beam splitter, the proposed codec pair can encode-decode multiple code words of Hadamard code while retaining the ability for multiple-access interference cancellation. The experimental results demonstrate that when the system is maintained with an orthogonal SOP for each user, an effective reduction in the phase-induced intensity noise is obtained. The analytical SNR values are found to overstate the experimental results by around 2 dB when the received effective power is large. This is mainly limited by insertion losses of components and a nonflattened optical light source. Furthermore, the matching conditions can be improved by decreasing nonideal influences.

Yen, Chih-Ta; Huang, Jen-Fa; Chang, Yao-Tang; Chen, Bo-Hau

2010-12-01

22

Spectral broadening of interacting pigments: polarized absorption by photosynthetic proteins.  

PubMed Central

Excitonic interaction between pigment molecules is largely responsible for the static and dynamic spectroscopic properties of photosynthetic pigment-proteins. This paper provides a new description of its effect on polarized absorption spectroscopy, in particular on circular dichroism (CD). We investigate excitonic spectra of finite width and use "spectral moments" to compare 1) inhomogeneously broadened excitonic spectra, 2) spectra that are (homogeneously broadened by vibrations or electron-phonon interaction, and 3) spectra that are simulated by applying convolution after the interaction has been evaluated. Two cases are distinguished. If the excitonic splitting is smaller than the width of the interacting absorption bands, the broadening of the excitonic spectrum can be approximated by a convolution approach, although a correction is necessary for CD spectra. If the excitonic splitting exceeds the bandwidth, the well-known exchange narrowing occurs. We demonstrate that this is accompanied by redistribution of dipole strength and spectral shifts. The magnitude of a CD spectrum is conveniently expressed by its first spectral moment. As will be shown, this is independent of spectral broadening as well as dispersive shifts induced by pigment-protein interactions. Consequently, it provides a simple tool to relate the experimental CD spectrum of a pigment complex to the excitonic interactions from which it originates. To illustrate the potential of the presented framework, the spectroscopy of the LH2 pigment-protein complex from purple bacteria is analyzed and compared for dimer-like and ring-like structures. Furthermore, it is demonstrated that the variability of the CD of chlorosomes from green bacteria can be explained by small changes in the structure of their cylindrical bacteriochlorophyll c subunits. Images FIGURE 3 FIGURE 4 PMID:8889168

Somsen, O J; van Grondelle, R; van Amerongen, H

1996-01-01

23

Current-induced spin polarization of holes in tellurium  

NASA Astrophysics Data System (ADS)

The current-induced optical activity in a tellurium single crystal has been experimentally investigated in the mid-infrared spectral region. The phenomenological theory of the current-induced optical activity has been considered and the microscopic mechanism of this phenomenon has been described. The dependence of the degree of spin polarization of holes in tellurium on the electric current density has been determined. An approximate analytical expression relating the current-induced optical activity to the degree of spin polarization of holes has been obtained.

Shalygin, V. A.; Sofronov, A. N.; Vorob'ev, L. E.; Farbshtein, I. I.

2012-12-01

24

Spectral and Polarization Sensitivity of the Dipteran Visual System  

Microsoft Academic Search

Spectral and polarization sensitivity measurements were made at several levels (retina, first and third optic ganglion, cervical connective, be- havior) of the dipteran visual nervous system. At all levels, it was possible to reveal contributions from the retinular cell subsystem cells 1 to 6 or the retinular cell subsystem cells 7 and 8 or both. Only retinular cells I to

GILBERT D. McCANN; DAVID W. ARNETT

2009-01-01

25

Relation between Radio Polarization and Spectral Index of Blazars  

NASA Astrophysics Data System (ADS)

University Michigan RAdio Observatory (UMRAO) supply many radio photometries and polarimetries. We select a sample of 81 blazars from UMRAO and analyse the correlations between their spectral index and polarizations. Out of 35 BL Lacs and 46 FSRQs in the sample, 8 and 15 show strong correlation.

Yuan, Yuhai

2014-11-01

26

NON-ZEEMAN CIRCULAR POLARIZATION OF MOLECULAR ROTATIONAL SPECTRAL LINES  

SciTech Connect

We present measurements of circular polarization from rotational spectral lines of molecular species in Orion KL, most notably {sup 12}CO (J = 2 {yields} 1), obtained at the Caltech Submillimeter Observatory with the Four-Stokes-Parameter Spectral Line Polarimeter. We find levels of polarization of up to 1%-2% in general; for {sup 12}CO (J = 2 {yields} 1) this level is comparable to that of linear polarization also measured for that line. We present a physical model based on resonant scattering in an attempt to explain our observations. We discuss how slight differences in scattering amplitudes for radiation polarized parallel and perpendicular to the ambient magnetic field, responsible for the alignment of the scattering molecules, can lead to the observed circular polarization. We also show that the effect is proportional to the square of the magnitude of the plane of the sky component of the magnetic field and therefore opens up the possibility of measuring this parameter from circular polarization measurements of Zeeman insensitive molecules.

Houde, Martin; Jones, Scott; Rajabi, Fereshte [Department of Physics and Astronomy, The University of Western Ontario, London, ON, N6A 3K7 (Canada)] [Department of Physics and Astronomy, The University of Western Ontario, London, ON, N6A 3K7 (Canada); Hezareh, Talayeh [Max-Planck-Institut fuer Radioastronomie, Auf dem Huegel 69, D-53121 Bonn (Germany)] [Max-Planck-Institut fuer Radioastronomie, Auf dem Huegel 69, D-53121 Bonn (Germany)

2013-02-10

27

Spectral polarization and spectral phase control of time-energy entangled photons  

NASA Astrophysics Data System (ADS)

We demonstrate a scheme to spectrally manipulate a collinear, continuous stream of time and energy entangled photons to generate beamlike, bandwidth-limited fluxes of polarization-entangled photons with nearly degenerate wavelengths. Utilizing an ultrashort-pulse shaper to control the spectral phase and polarization of the photon pairs, we tailor the shape of the Hong-Ou-Mandel interference pattern, demonstrating the rules that govern the dependence of this interference pattern on the spectral phases of the photons. We then use the pulse shaper to generate all four polarization Bell states. The singlet state generated by this scheme forms a very robust decoherence-free subspace, extremely suitable for long-distance fiber-optics-based quantum communication.

Dayan, Barak; Bromberg, Yaron; Afek, Itai; Silberberg, Yaron

2007-04-01

28

Interpretation of simulated polarization diversity radar spectral functions  

Microsoft Academic Search

Power spectra, cross spectrum and derived functions obtainable from a coherent polarization-diversity radar are simulated by means of a numerical model that is applicable to the investigation of the effects of air velocity variance, radar system noise, and differential propagation on spectral system functions. The results of 8.6-mm wavelength backscatter are compared with the functional forms obtained from theory and

James I. Metcalf

1984-01-01

29

Spectral signatures of polar stratospheric clouds and sulfate aerosol  

NASA Technical Reports Server (NTRS)

Multiwavelength observations of Antarctic and midlatitude aerosol by the Cryogenic Limb Array Etalon Spectrometer (CLAES) experiment on the Upper Atmosphere Research Satellite (UARS) are used to demonstrate a technique that identifies the location of polar stratospheric clouds. The technique discussed uses the normalized area of the triangle formed by the aerosol extinctions at 925, 1257, and 1605/cm (10.8, 8.0, and 6.2 micrometers) to derive a spectral aerosol measure M of the aerosol spectrum. Mie calculations for spherical particles and T-matrix calculations for spheriodal particles are used to generate theoretical spectral extinction curves for sulfate and polar stratospheric cloud particles. The values of the spectral aerosol measure M for the sulfate and polar stratospheric cloud particles are shown to be different. Aerosol extinction data, corresponding to temperatures between 180 and 220 K at a pressure of 46 hPa (near 21-km altitude) for 18 August 1992, are used to demonstrate the technique. Thermodynamic calculations, based upon frost-point calculations and laboratory phase-equilibrium studies of nitric acid trihydrate, are used to predict the location of nitric acid trihydrate cloud particles.

Massie, S. T.; Bailey, P. L.; Gille, J. C.; Lee, E. C.; Mergenthaler, J. L.; Roche, A. E.; Kumer, J. B.; Fishbein, E. F.; Waters, J. W.; Lahoz, W. A.

1994-01-01

30

Induced polarization response of microbial induced sulfideprecipitation  

SciTech Connect

A laboratory scale experiment was conducted to examine the use of induced polarization and electrical conductivity to monitor microbial induced sulfide precipitation under anaerobic conditions in sand filled columns. Three columns were fabricated; one for electrical measurements, one for geochemical sampling and a third non-inoculated column was used as a control. A continual upward flow of nutrients and metals in solution was established in each column. Desulfovibrio vulgaris microbes were injected into the middle of the geochemical and electrical columns. Iron and zinc sulfides precipitated along a microbial action front as a result of sulfate reduction due by Desulfovibrio vulgaris. The precipitation front initially developed near the microbial injection location, and subsequently migrated towards the nutrient inlet, as a result of chemotaxis by Desulfovibrio vulgaris. Sampling during and subsequent to the experiment revealed spatiotemporal changes in the biogeochemical measurements associated with microbial sulfate reduction. Conductivity measurements were insensitive to all biogeochemical changes occurred within the column. Changes in the IP response (of up to 14 mrad)were observed to coincide in place and in time with the active microbe respiration/sulfide precipitation front as determined from geochemical sampling. The IP response is correlated with the lactate concentration gradient, an indirect measurement of microbial metabolism, suggesting the potential of IP as a method for monitoring microbial respiration/activity. Post experimental destructive sample analysis and SEM imaging verified the geochemical results and supported our hypothesis that microbe induced sulfide precipitation is directly detectable using electrical methods. Although the processes not fully understood, the IP response appears to be sensitive to this anaerobic microbial precipitation, suggesting a possible novel application for the IP method.

Ntarlagiannis, Dimitrios; Williams, Kenneth Hurst; Slater, Lee; Hubbard, Susan

2004-06-04

31

Polarization maintaining fiber based ultra-high resolution spectral domain polarization sensitive optical coherence tomography  

PubMed Central

We present a new ultra high resolution spectral domain polarization sensitive optical coherence tomography (PS-OCT) system based on polarization maintaining (PM) fibers. The method transfers the principles of our previous bulk optic PS-OCT systems to a fiberized setup. The phase shift between the orthogonal polarization states travelling in the two orthogonal modes of the PM fiber is compensated by software in post processing. Thereby, the main advantage of our bulk optics setups, i.e. the use of only a single input polarization state to simultaneously acquire reflectivity, retardation, optic axis orientation, and Stokes vector, is maintained. The use of a broadband light source of 110 nm bandwidth provides improved depth resolution and smaller speckle size. The latter is important for improved resolution of depolarization imaging. We demonstrate our instrument for high-resolution PS-OCT imaging of the healthy human retina. PMID:20052196

2010-01-01

32

PMD Monitoring in Polarization-Multiplexed Transmission Systems by Spectral Polarimetric Analysis  

Microsoft Academic Search

A polarization-mode dispersion (PMD) monitoring technique tailored for polarization-multiplexed high capacity optical transmission systems is proposed and experimentally demonstrated. First-order PMD is evaluated calculating the vector product of the spectral components of the two state-of-polarization transmitted in the polarization-multiplexed system. The spectral components in each state-of-polarization are resolved by a real-time optical Fourier transformer. The technique is demonstrated measuring first-order

Roberto Llorente

2009-01-01

33

THE IMPACT OF QUANTUM INTERFERENCE BETWEEN DIFFERENT J-LEVELS ON SCATTERING POLARIZATION IN SPECTRAL LINES  

SciTech Connect

The spectral line polarization produced by optically pumped atoms contains a wealth of information on the thermal and magnetic structure of a variety of astrophysical plasmas, including that of the solar atmosphere. A correct decoding of such information from the observed Stokes profiles requires a clear understanding of the effects that radiatively induced quantum interference (or coherence) between pairs of magnetic sublevels produces on these observables, in the absence of and in the presence of magnetic fields of arbitrary strength. Here we present a detailed theoretical investigation of the role of coherence between pairs of sublevels pertaining to different fine-structure J-levels, clarifying when it can be neglected for facilitating the modeling of the linear polarization produced by scattering processes in spectral lines. To this end, we apply the quantum theory of spectral line polarization and calculate the linear polarization patterns of the radiation scattered at 90 Degree-Sign by a slab of stellar atmospheric plasma, both taking into account and neglecting the above-mentioned quantum interference. Particular attention is given to the {sup 2}S - {sup 2}P, {sup 5}S - {sup 5}P, and {sup 3}P - {sup 3}S multiplets. We point out the observational signatures of this kind of interference and analyze its sensitivity to the energy separation between the interfering levels, to the amount of emissivity in the background continuum radiation, to lower-level polarization, and to the presence of a magnetic field. Some interesting applications to the following spectral lines are also presented: Ca II H and K, Mg II h and k, Na I D{sub 1} and D{sub 2}, the Ba II 4554 #Angstrom# and 4934 #Angstrom# resonance lines, the Cr I triplet at 5207 #Angstrom#, the O I triplet at 7773 #Angstrom#, the Mg I b-lines, and the H{alpha} and Ly{alpha} lines of H I.

Belluzzi, Luca; Bueno, Javier Trujillo [Instituto de Astrofisica de Canarias, E-38205 La Laguna, Tenerife (Spain)

2011-12-10

34

Enhancement of spectral resolution and optical rejection ratio of Brillouin optical spectral analysis using polarization pulling.  

PubMed

High-resolution, wide-bandwidth optical spectrum analysis is essential to the measuring and monitoring of advanced optical, millimeter-wave, and terahertz communication systems, sensing applications and device characterization. One category of high-resolution spectrum analyzers reconstructs the power spectral density of a signal under test by scanning a Brillouin gain line across its spectral extent. In this work, we enhance both the resolution and the optical rejection ratio of such Brillouin-based spectrometers using a combination of two techniques. First, two Brillouin loss lines are superimposed upon a central Brillouin gain to reduce its bandwidth. Second, the vector attributes of stimulated Brillouin scattering amplification in standard, weakly birefringent fibers are used to change the signal state of polarization, and a judiciously aligned output polarizer discriminates between amplified and un-amplified spectral contents. A frequency resolution of 3 MHz, or eight orders of magnitude below the central optical frequency, is experimentally demonstrated. In addition, a weak spectral component is resolved in the presence of a strong adjacent signal, which is 30 dB stronger and detuned by only 60 MHz. The measurement method involves low-bandwidth direct detection, and does not require heterodyne beating. The measurement range of the proposed method is scalable to cover the C + L bands, depending on the tunable pump source. The accuracy of the measurements requires that the pump frequencies are well calibrated. PMID:22714534

Preussler, Stefan; Zadok, Avi; Wiatrek, Andrzej; Tur, Moshe; Schneider, Thomas

2012-06-18

35

Ellipsoidal Universe Induces Large Scale CMB Polarization  

E-print Network

We calculate the large scale polarization of the cosmic microwave background induced by the anisotropy of the spatial geometry of our universe. Assuming an eccentricity at decoupling of about $0.64 10^{-2}$, we find $\\Delta T_{pol}/ T_0 \\simeq 0.53 10^{-6}$ quite close to the average level of polarization detected by the Wilkinson Microwave Anisotropy Probe.

Paolo Cea

2007-02-11

36

Non-Zeeman Circular Polarization of Molecular Maser Spectral Lines  

E-print Network

We apply the anisotropic resonant scattering model developed to explain the presence of non-Zeeman circular polarization signals recently detected in the $^{12}\\mathrm{CO}\\;\\left(J=2\\rightarrow1\\right)$ and $\\left(J=1\\rightarrow0\\right)$ transitions in molecular clouds to Stokes $V$ spectra of SiO $v=1$ and $v=2$, $\\left(J=1\\rightarrow0\\right)$ masers commonly observed in evolved stars. It is found that the observed antisymmetric "S" and symmetric "$\\cup$" or "$\\cap$" shaped spectral profiles naturally arise when the maser radiation scatters off populations of foreground molecules located outside the velocity range covered by the background maser radiation. Using typical values for the relevant physical parameters, it is estimated that magnetic field strengths on the order of a few times 15 mG are sufficient to explain the observational results found in the literature.

Houde, Martin

2014-01-01

37

Optical Polarization and Spectral Variability in the M87 Jet  

NASA Technical Reports Server (NTRS)

During the last decade, M87's jet has been the site of an extraordinary variability event, with one knot (HST-1) increasing by over a factor 100 in brightness. Variability was also seen on timescales of months in the nuclear flux. Here we discuss the optical-UV polarization and spectral variability of these components, which show vastly different behavior. HST -1 shows a highly significant correlation between flux and polarization, with P increasing from approx 20% at minimum to > 40% at maximum, while the orientation of its electric vector stayed constant. HST-l's optical-UV spectrum is very hard (alpha(sub uv-0) approx. 0.5, F(sub v) varies as (v(exp -alpha)), and displays "hard lags" during epochs 2004.9-2005.5, including the peak of the flare, with soft lags at later epochs. We interpret the behavior of HST-1 as enhanced particle acceleration in a shock, with cooling from both particle aging and the relaxation of the compression. We set 2alpha upper limits of 0.5 delta parsecs and 1.02c on the size and advance speed of the flaring region. The slight deviation of the electric vector orientation from the jet PA, makes it likely that on smaller scales the flaring region has either a double or twisted structure. By contrast, the nucleus displays much more rapid variability, with a highly variable electric vector orientation and 'looping' in the (I, P) plane. The nucleus has a much steeper spectrum ((alpha(sub uv-0) approx. 1.5) but does not show UV-optical spectral variability. Its behavior can be interpreted as either a helical distortion to a steady jet or a shock propagating through a helical jet.

Perlman, Eric S.; Adams, Steven C.; Cara, Mihai; Bourque, Matthew; Harris, D. E.; Madrid, Juan P.; Simons, Raymond C.; Clausen-Brown, Eric; Cheung, C. C.; Stawarz, Lukasz; Georganopoulos, Markos; Sparks, William B.; Biretta, John A.

2011-01-01

38

OPTICAL POLARIZATION AND SPECTRAL VARIABILITY IN THE M87 JET  

SciTech Connect

During the last decade, M87's jet has been the site of an extraordinary variability event, with one knot (HST-1) increasing by over a factor 100 in brightness. Variability has also been seen on timescales of months in the nuclear flux. Here we discuss the optical-UV polarization and spectral variability of these components, which show vastly different behavior. HST-1 shows a highly significant correlation between flux and polarization, with P increasing from {approx}20% at minimum to >40% at maximum, while the orientation of its electric vector stayed constant. HST-1's optical-UV spectrum is very hard ({alpha}{sub UV-O} {approx} 0.5, F{sub {nu}}{proportional_to}{nu}{sup -{alpha}}), and displays 'hard lags' during epochs 2004.9-2005.5, including the peak of the flare, with soft lags at later epochs. We interpret the behavior of HST-1 as enhanced particle acceleration in a shock, with cooling from both particle aging and the relaxation of the compression. We set 2{sigma} upper limits of 0.5{delta} pc and 1.02c on the size and advance speed of the flaring region. The slight deviation of the electric vector orientation from the jet position angle (P.A.) makes it likely that on smaller scales the flaring region has either a double or twisted structure. By contrast, the nucleus displays much more rapid variability, with a highly variable electric vector orientation and 'looping' in the (I, P) plane. The nucleus has a much steeper spectrum ({alpha}{sub UV-O} {approx} 1.5) but does not show UV-optical spectral variability. Its behavior can be interpreted as either a helical distortion to a steady jet or a shock propagating through a helical jet.

Perlman, Eric S.; Cara, Mihai; Bourque, Matthew; Simons, Raymond C. [Department of Physics and Space Sciences, 150 W. University Blvd., Florida Institute of Technology, Melbourne, FL 32901 (United States); Adams, Steven C. [Department of Physics and Astronomy, University of Georgia, Athens, GA 30605 (United States); Harris, D. E. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Madrid, Juan P. [Center for Astrophysics and Supercomputing, Swinburne University of Technology, Hawthorn, VIC 3122 (Australia); Clausen-Brown, Eric [Department of Physics, Purdue University, West Lafayette, IN 47907 (United States); Cheung, C. C. [National Academy of Sciences, Washington, DC 20001 (United States); Stawarz, Lukasz [Institute of Space and Astronautical Science, JAXA, 3-1-1 Yoshinodai, Chuo-ku, Sagamihara, Kanagawa 252-5210 (Japan); Georganopoulos, Markos [Department of Physics, University of Maryland-Baltimore County, 1000 Hilltop Circle, Baltimore, MD 21250 (United States); Sparks, William B.; Biretta, John A., E-mail: eperlman@fit.edu [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)

2011-12-20

39

Design of hyper-spectral and full-polarization imager based on AOTF and LCVR  

NASA Astrophysics Data System (ADS)

With the development of spectral imaging technology and polarization imaging technology, capturing the spectral profile and polarization signatures simultaneously will provide a wealth of evidence which helps to recognize the objects. Thus it has become a new trend in the area of remote sensing technology. In this paper, the existing polarization spectral imaging technologies are introduced and compared a new designing scheme to realize the miniaturized hyper-spectral and full-polarization imager are proposed, which is based on the combination of Acousto-Optic Tunable Filter (AOTF) and Liquid Crystal Variable Retarder (LCVR). The designing scheme is mainly composed of three modules: the spectral splitting module based on AOTF, the polarization control module based on LCVR and the image acquisition module based on Charge Coupled Device (CCD). The use of AOTF assists in achieving a hyper-spectral resolution higher than 5nm, as well as the abundant spectral information. While the LCVR enables us to gain multiple sets of polarization images of the target, after that, the polarization state of the target can be extracted according to Stokes vector and Mueller matrix. This designing scheme ensures a wide spectral range from 400nm to 2400nm by means of electronic tuning, and also achieves the hyper-spectral and full-polarization images of the target in rapid succession without mechanical moving parts. Besides, the development, testing, calibration and test scheme of the system are also introduced in the rest of the paper.

Li, Feifei; Xu, Yingyu; Ma, Yanhua

2014-11-01

40

Polarization extinction ratio impact on spectral stability of Bragg grating stabilized laser diodes  

Microsoft Academic Search

We demonstrate that polarization extinction ratio (PER) affects the spectral instability of 980-nm band fiber Bragg grating stabilized pump lasers using a polarization-maintaining fiber pigtail. Enhanced spectral stability better than 0.01 nm is demonstrated in devices with superior PER.

Monica K. Davis; Alina Echavarria; David A. S. Loeber

2004-01-01

41

Exploration of polar lipid accumulation profiles in Euglena gracilis using LipidBlast, an MS/MS spectral library constructed in silico.  

PubMed

A rapid protocol for polar lipid profiling was applied to Euglena gracilis lipid metabolism by LipidBlast, an MS/MS spectral similarity search tool. The similarity search results suggested anoxia-induced polar lipid metabolism in Euglena characterized by the accumulation of differential lipid classes, carbon chain lengths, and unsaturated bond numbers. The informatics-supported MS spectral search provides an alternative option for global lipid profiling studies. PMID:25036478

Ogawa, Takumi; Furuhashi, Takeshi; Okazawa, Atsushi; Nakai, Rai; Nakazawa, Masami; Kind, Tobias; Fiehn, Oliver; Kanaya, Shigehiko; Arita, Masanori; Ohta, Daisaku

2014-01-01

42

Fiber-based single-channel polarization-sensitive spectral interferometry  

NASA Astrophysics Data System (ADS)

We present a novel, to our knowledge, fiber-based single-channel polarization-sensitive spectral interferometry system that provides depth-resolved measurement of polarization transformations of light reflected from a sample. Algebraic expressions for the Stokes parameters at the output of the interferometer are derived for light reflected from a birefringent sample by using the cross-spectral density function. By insertion of a fiber-optic spectral polarimetry instrument into the detection path of a common-path spectral interferometer, the full set of Stokes parameters of light reflected from a sample can be obtained with a single optical frequency scan. The methodology requires neither polarization-control components nor prior knowledge of the polarization state of light incident on the sample. The fiber-based single-channel polarization-sensitive spectral interferometer and analysis are demonstrated by measurement of phase retardation and fast-axis angle of a birefringent mica plate.

Kim, Eunha; Milner, Thomas E.

2006-06-01

43

Metamaterial polarization spectral filter: Isolated transmission line at any prescribed wavelength  

E-print Network

October 2011; published online 28 October 2011) We demonstrate that a narrowband spectral filter array of sub- wavelength resonators, which can be engineered to offer a narrow-band spectral filterMetamaterial polarization spectral filter: Isolated transmission line at any prescribed wavelength

Zheludev, Nikolay

44

Induced Polarization methodology: application to a hydrocarbon contaminated site  

NASA Astrophysics Data System (ADS)

Induced Polarization (IP) is a promising method for environmental studies (Vaudelet et al., 2011; Abdel Aal et al., 2006). This method has already been successful for the study of contaminations in the laboratory scale (Vanhala, 1997; Revil et al., 2011; Schmutz et al., 2012) but is still not trivial on the field. Temporal IP seems relatively common for field studies. When contamination implies a significative change of the polarization parameters, successful studies have been lead (Fiandaca et al. 2012; Dahlin et al., 2002 on landfills). Otherwise hydrocarbon contamination may induce small changes on IP parameters (Vaudelet et al., 2011). Spectral induced polarization has not been widely used for field application yet: this method is sensitive to coupling effects and time consuming. Moreover, all the phenomenon responsible of the signal is not completely understood yet (Kemna et al., 2012). The main aim of our presentation is about IP methodology, applied on site affected by a hydrocarbon contamination. In this case, precautions have to be taken to get explicit answers from the contamination. Field investigations have been made: chargeability measurements in order to delineate the free phase contamination extension and spectral induced polarization soundings in order to characterize more precisely the contamination. We would like to provide recommendations to improve induced polarization measurements especially on three aspects, (i) propose a different measurement sequence to make chargeability measurements and (ii) evaluate the influence of the current injection time on chargeability measurements (iii) give general precautions to achieve SIP measurements. A different new chargeability sequence is proposed integrating the use of separated injection and measure cables to avoid coupling phenomena in multicore cables. Indeed, this kind of coupling can significantly decrease the signal / noise ratio (Dahlin et al., 2012). Direct and reverse measurements have been made in order to evaluate if the data and data quality are comparable. Different times of injection have also been tested to evaluate their influence on chargeability measurements: long injection times (4 and 8 seconds) indicate the same high chargeability trend, to the contrary to small injection time (2 seconds). Long injection time generate (i) the polarization of more elements (ii) a stronger polarization of polarizable elements. For environmental purposes, long injection times are recommended. Spectral induced polarization soundings have been made using the SIP Fuchs device, with an amplifier in order to stabilize the injected current (Radic 2004). Unpolarizable measurement electrodes have been connected to the apparatus with optic fiber and metallic injection electrodes have been link with a specific cable arrangement, both to reduce coupling effect with the ground (Vaudelet et al., 2011; Ghorbani et al., 2007). These precautions give good quality result and allow the inversion of the data to obtain Cole Cole parameters (Ghorbani et al., 2007), useful for hydrogeological interpretations.

Blondel, Amelie; Schmutz, Myriam; Tichane, Frederic; Franceschi, Michel; Carles, Margaux

2013-04-01

45

Proton emission induced by polarized photons  

E-print Network

The proton emission induced by polarized photons is studied in the energy range above the giant resonance region and below the pion emission threshold. Results for the 12C, 16O and 40Ca nuclei are presented. The sensitivity of various observables to final state interaction, meson exchange currents and short range correlations is analyzed. We found relevant effects due to the virtual excitation of the $\\Delta$ resonance.

M. Anguiano; G. Co'; A. M. Lallena

2006-08-29

46

Selective absorption processes as the origin of puzzling spectral line polarization from the Sun.  

PubMed

Magnetic fields play a key role in most astrophysical systems, from the Sun to active galactic nuclei. They can be studied through their effects on atomic energy levels, which produce polarized spectral lines. In particular, anisotropic radiation 'pumping' processes (which send electrons to higher atomic levels) induce population imbalances that are modified by weak magnetic fields. Here we report peculiarly polarized light in the He I 10,830-A multiplet observed in a coronal filament located at the centre of the solar disk. We show that the polarized light arises from selective absorption from the ground level of the triplet system of helium, and that it implies the presence of magnetic fields of the order of a few gauss that are highly inclined with respect to the solar radius vector. This disproves the common belief that population imbalances in long-lived atomic levels are insignificant in the presence of inclined fields of the order of a few gauss, and opens up a new diagnostic window for the investigation of solar magnetic fields. PMID:11807547

Trujillo Bueno, J; Landi Degl'Innocenti, E; Collados, M; Merenda, L; Manso Sainz, R

2002-01-24

47

SPECTRAL MAPPING OF THE INTERMEDIATE POLAR DQ HERCULIS  

SciTech Connect

We report an eclipse-mapping study of the intermediate polar DQ Her based on time-resolved optical spectroscopy ({Delta}{lambda} {approx} 3800-5000 A) covering four eclipses. The spectra were sliced into 295 narrow passbands in the continuum and in the lines, and the corresponding light curves were analyzed to solve for a set of monochromatic maps of the disk brightness distribution and for the flux of an additional uneclipsed component in each band. Eclipse maps of the He II {lambda}4686 line indicate that an azimuthally and vertically extended bright spot at disk rim is an important source of the reprocessing of X-rays from the magnetic poles. The disk spectrum is flat with no Balmer or Helium lines in the inner regions, and shows double-peaked emission lines in the intermediate and outer disk regions, while the slope of the continuum becomes progressively redder with increasing radius. The inferred disk temperatures are in the range T {approx_equal} 13500-5000 K and can be reasonably well described by a steady-state disk with mass accretion rate of M-dot =(2.7{+-}1.0)x10{sup -9} M{sub sun} yr{sup -1}. A comparison of the radial intensity distribution for the Balmer lines reveals a linear correlation between the slope of the distribution and the transition energy. The spectrum of the uneclipsed light is dominated by Balmer and He I lines in emission (probably from the extended nova shell) with narrow absorption cores (likely from a collimated and optically thick wind from the accretion disk). The observed narrow and redshifted Ca II {lambda}3934 absorption line in the total light spectra plus the inverse P-Cygni profiles of the Balmer and He II {lambda}4686 emission lines in spectra of the asymmetric component indicate radial inflow of gas in the innermost disk regions and are best explained in terms of magnetically controlled accretion inside the white dwarf magnetosphere. We infer projected radial inflow velocities of {approx}200-500 km s{sup -1}, significantly lower than both the rotational and the free-fall velocities for the corresponding range of radii. A combined net emission He II plus H{beta} low-velocity eclipse map reveals a twisted dipole emitting pattern near disk center. This is interpreted as being the projection of accretion curtains onto the orbital plane at two specific spin phases, as a consequence of the selection in velocity provided by the spectral eclipse mapping.

Saito, R. K. [Departamento de AstronomIa y Astrofisica, Pontificia Universidad Catolica de Chile, Vicuna Mackenna 4860, Casilla 306, Santiago 22 (Chile); Baptista, R. [Departamento de Fisica, Universidade Federal de Santa Catarina, Trindade, 88040-900 Florianopolis, SC (Brazil); Horne, K. [School of Physics and Astronomy, University of St. Andrews, KY16 9SS, Scotland (United Kingdom); Martell, P., E-mail: rsaito@astro.puc.c [University of Wisconsin Center-Marinette, 750 W. Bay Shore Street, Marinette, WI 54143 (United States)

2010-06-15

48

Spectral Mapping of the Intermediate Polar DQ Herculis  

NASA Astrophysics Data System (ADS)

We report an eclipse-mapping study of the intermediate polar DQ Her based on time-resolved optical spectroscopy (?? ~ 3800-5000 Å) covering four eclipses. The spectra were sliced into 295 narrow passbands in the continuum and in the lines, and the corresponding light curves were analyzed to solve for a set of monochromatic maps of the disk brightness distribution and for the flux of an additional uneclipsed component in each band. Eclipse maps of the He II ?4686 line indicate that an azimuthally and vertically extended bright spot at disk rim is an important source of the reprocessing of X-rays from the magnetic poles. The disk spectrum is flat with no Balmer or Helium lines in the inner regions, and shows double-peaked emission lines in the intermediate and outer disk regions, while the slope of the continuum becomes progressively redder with increasing radius. The inferred disk temperatures are in the range T ~= 13500-5000 K and can be reasonably well described by a steady-state disk with mass accretion rate of \\dot{M}=(2.7± 1.0)× 10^{-9} M_{?} yr^{-1}. A comparison of the radial intensity distribution for the Balmer lines reveals a linear correlation between the slope of the distribution and the transition energy. The spectrum of the uneclipsed light is dominated by Balmer and He I lines in emission (probably from the extended nova shell) with narrow absorption cores (likely from a collimated and optically thick wind from the accretion disk). The observed narrow and redshifted Ca II ?3934 absorption line in the total light spectra plus the inverse P-Cygni profiles of the Balmer and He II ?4686 emission lines in spectra of the asymmetric component indicate radial inflow of gas in the innermost disk regions and are best explained in terms of magnetically controlled accretion inside the white dwarf magnetosphere. We infer projected radial inflow velocities of ~200-500 km s-1, significantly lower than both the rotational and the free-fall velocities for the corresponding range of radii. A combined net emission He II plus H? low-velocity eclipse map reveals a twisted dipole emitting pattern near disk center. This is interpreted as being the projection of accretion curtains onto the orbital plane at two specific spin phases, as a consequence of the selection in velocity provided by the spectral eclipse mapping.

Saito, R. K.; Baptista, R.; Horne, K.; Martell, P.

2010-06-01

49

Programmable polarization-independent spectral phase compensation and pulse shaping  

E-print Network

a Virtually Imaged Phased Array," presented at the Optical Fiber Communications Conference, Anaheim, CA, 17.S. Warren, "High Resolution, Ultrafast Laser Pulse Shaping and Its Applications," Adv. Magn. Opt. Reson. 20 shaping that operates independent of polarization. Such insensitivity to polarization is crucial for fiber

Purdue University

50

Polarization studies of Zeeman affected spectral lines using the MSFC magnetograph  

NASA Technical Reports Server (NTRS)

The Marshall Space Flight Center (MSFC) vector magnetograph records polarization images of absorption lines that are sensitive to magnetic fields. A method is presented for analyzing the Stokes spectral-line profiles of a photospheric Fe I absorption line (5250.2 A) which is influenced by the Zeeman effect. Using nonlinear least-square optimization, the observed Stokes profiles are compared with those generated from the theoretical solution of the polarized radiative transfer equations. The optimization process accounts for the spectral convolution of the source and the MSFC vector magnetograph. The resulting physical properties of the active region producing the polarized light are discussed.

Balasubramaniam, K. S.; West, E. A.

1990-01-01

51

Radio emission from RS CVn binaries. II - Polarization and spectral properties  

NASA Technical Reports Server (NTRS)

Multiepoch radio observations of circular polarization and spectral characteristics of several close, late-type stellar binaries are reported. The median luminosity of four well-studied systems ranged from 16.2 to 17.1 ergs/s/Hz. For individual systems, the fractional circular polarization decreases with increasing luminosity, particularly at frequencies above 5 GHz. Eclipsing binaries have significantly lower average circular polarization compared with noneclipsing systems. Helicity reversal is almost always observed between 1.4 and 4.9 GHz for systems with high orbital inclination. Comparison with ten years of previously published polarization observations for two RS CVn stellar systems show that the same helicity occurs at a given frequency for a given source, indicating a very stable, large-scale magnetic field geometry. These spectral and polarization characteristics strongly support a model of inhomogeneous gyrosynchrotron emission arising from electrons with power law energy spectra interacting with inhomogeneous magnetic fields.

Mutel, R. L.; Morris, D. H.; Doiron, D. J.; Lestrade, J. F.

1987-01-01

52

Recognition of camouflage targets with hyper-spectral polarization imaging system  

NASA Astrophysics Data System (ADS)

On the basis of the principle of polarization detection, a hyper-spectral polarization imaging system, which is based on linear polarizer and acousto-optic tunable filter (AOTF), was designed to detect and recognize camouflage target intelligently and rapidly in this paper. Our design has neither moving parts nor modulation, and has fast and electronically tuning property, so a quick scan of spectrum at 400 nm~1000 nm can be realized electronically. At the same time, it not only could obtain the intensity image, hyper-spectral information, but also could acquire polarization signatures of the scene. Then the spectral polarization experiment about aluminous plane which covered with the bottle green, shallow green and khaki camouflage pigments within meadow were conducted at specifically wavelength by the instrument. Finally, the polarization information of the man-made targets and natural background in the scene, and the fusion image based on HIS color space were deduced through processing the experiment data. The experimental result demonstrates that the polarization characteristics of camouflage pigments were different from that of natural background. As the contrast of target and background could be enhanced by polarization information, the camouflage target could be identified effectively from the image according to polarization information. On the other hand, the camouflage target is more obvious in the fused image. Therefore, the proposed method and the system in this paper are reasonable and effective. Consequently, the hyper-spectral polarization detection technique which relative to the classical intensity detection is of significance to improve the accuracy of recognition of camouflage targets in mixed background under proper detection condition.

Wang, Qi-chao; Wang, Jia-chun; Zhao, Da-peng; Ma, Li-fang; Chen, Zong-sheng; Li, Zhi-gang

2013-08-01

53

Scintillation-Induced Circular Polarization in Pulsars and Quasars  

E-print Network

We present a physical interpretation for the generation of circular polarization resulting from the propagation of radiation through a magnetized plasma in terms of a rotation measure gradient, or `Faraday wedges'. Criteria for the observability of scintillation-induced circular polarization are identified. Application of the theory to the circular polarization in pulsars and compact extragalactic sources is discussed.

J. -P. Macquart; D. B. Melrose

2000-07-28

54

Constraints on Inflation from Polarization and CMB Spectral Distortions  

NASA Astrophysics Data System (ADS)

This talk will summarize some things we can do with future CMB experiments to study the early Universe. An obvious first is to map the polarization from density perturbations to the cosmic-variance limit to improve upon the types of things (cosmological-parameter determination, lensing, etc.) that have been done so far with the temperature. Another direction, which already has considerable momentum, is the pursuit of the characteristic polarization signature of inflationary gravitational waves. But there is also a strong case, which I will review, now being assembled for a space mission to seek the tiny but nonzero departures from a blackbody spectrum that are expected in the standard cosmological model and that may arise from several interesting exotic mechanisms.

Kamionkowski, Marc

2014-01-01

55

Dual-polarization Raman spectral imaging to extract overlapping molecular fingerprints of living cells.  

PubMed

Raman spectral imaging is gaining more and more attention in biological studies because of its label-free characteristic. However, the discrimination of overlapping chemical contrasts has been a major challenge. In this study, we introduce an optical method to simultaneously obtain two orthogonally polarized Raman images from a single scan of the sample. We demonstrate how this technique can improve the quality and quantity of the hyperspectral Raman dataset and how the technique is expected to further extend the horizons of Raman spectral imaging in biological studies by providing more detailed chemical information. The dual-polarization Raman images of a HeLa cell. PMID:24733812

Chiu, Liang-da; Palonpon, Almar F; Smith, Nicholas I; Kawata, Satoshi; Sodeoka, Mikiko; Fujita, Katsumasa

2014-04-15

56

Polarization-sensitive spectral-domain optical coherence tomography using a single line scan camera  

Microsoft Academic Search

Polarization-sensitive optical coherence tomography can be used to measure the birefringence of biological tissue such as the human retina. Previous measurements with a time-domain polarization-sensitive optical coherence tomography system revealed that the birefringence of the human retinal nerve fiber layer is not constant, but varies as a function of location around the optic nerve head. Here we present a spectral-domain

Barry Cense; Mircea Mujat; Teresa C. Chen; B. H. Park; Johannes F. de Boer

2007-01-01

57

Polarization conversions of linearly and circularly polarized lights through a plasmon-induced transparent metasurface  

NASA Astrophysics Data System (ADS)

Polarization control of the light can be realized by ultrathin plasmonic structures, which is generally based on the effect of extraordinary optical transmission. In this paper, we designed a U-shaped plasmon-induced transparent metasurface to investigate the polarization state conversions of resonantly transmitted light through reducing the structural symmetry by rotation. A significant optical polarization conversion capability is found for impinging light with linear as well as circular polarization. In particular, the different polarization conversions between the left-handed and right-handed circular lights manifest the characteristic of circular dichroism. The results are useful for the potential applications such as a broadband quarter-wave plate.

Shao, Jian; Li, Jie; Wang, Ying-Hua; Li, Jia-Qi; Chen, Qian; Dong, Zheng-Gao

2014-06-01

58

Reflective and transmissive broadband coating polarizers in a spectral range centered at 121.6 nm  

NASA Astrophysics Data System (ADS)

Polarimetry is a powerful tool for the interpretation of the role of the coronal plasma in the energy transfer processes from the inner parts of the Sun to the outer space. One of the key lines for observations is H I Lyman ? (121.6 nm) among few spectral lines in the far ultraviolet (FUV), and hence efficient linear polarizers at this line are demanded. New designs based on (Al/MgF2)n multilayer coatings have been developed to obtain the smallest possible reflectance in the parallel plane of polarization (Rpar) with a simultaneous high reflectance in the perpendicular plane of polarization (Rper). Samples stored in nitrogen for ?8–17 months resulted in efficient polarizers at 121.6 nm, with Rpar ? 0.01–0.017 and Rper ? 0.69–0.725. The designs with a number n = 3–4 bilayers of Al/MgF2 result in a wider spectral range of efficient linear polarizers, compared to what can be obtained with n = 2. Coatings following various designs with good polarizing performance in a 7–8 nm wide FUV range were prepared. For the first time, a transmissive coating polarizer has been developed for this range, which has the benefit that it involves no deviation of the beam; it is based on another design of (Al/MgF2)3 multilayer coating. The transmissive polarizer has a good transmittance ratio between the two polarization components and, even though its figure of merit is not as high as that of the reflective polarizers, it incorporates filtering properties to reject wavelengths both below and above 121.6 nm; this property might enable a polarimeter for solar physics with an improved global figure of merit if a filter to isolate the H I Lyman ? line could be avoided.

Larruquert, Juan I.; Malvezzi, A. Marco; Giglia, Angelo; Aznárez, José A.; Rodríguez-de Marcos, Luis; Méndez, José A.; Miotti, Paolo; Frassetto, Fabio; Massone, Giuseppe; Nannarone, Stefano; Crescenzio, Giuseppe; Capobianco, Gerardo; Fineschi, Silvano

2014-12-01

59

Visualization of rat pial microcirculation using the novel orthogonal polarized spectral (OPS) imaging after brain injury  

Microsoft Academic Search

Recently, the novel optical system, orthogonal polarized spectral (OPS) imaging was developed to visualize microcirculation. Investigation of changes in microcirculation is essential for physiological, pathophysiological, and pharmacological studies. In the present study applicability of OPS imaging was assessed to study pial microcirculation in normal and traumatized rat brain. High quality images of rat pial microcirculation in normal and traumatized rats

Ulrich-Wilhelm Thomale; Klaus-Dieter Schaser; Andreas W. Unterberg; John F. Stover

2001-01-01

60

Lambda Polarization in Lepton Induced Reactions  

E-print Network

Different phenomenological approaches for Lambda and Lambda-bar polarization in polarized semi-inclusive deep inelastic scattering and electron-positron annihilation at Z^0 pole are considered. Current and future experiments will soon provide accurate enough data to study spin phenomena in these reactions and distinguish between various models.

A. M. Kotzinian

1997-09-05

61

Spin transfer and polarization of antihyperons in lepton induced reactions  

E-print Network

We study the polarization of antihyperon in lepton induced reactions such as $e^+e^-\\to\\bar H+X$ and $l+p\\to l'+\\bar H+X$ with polarized beams using different models for spin transfer in high energy fragmentation processes. We compare the results with the available data and those for hyperons. We make predictions for future experiments.

Hui Dong; Jian Zhou; Zuo-tang Liang

2005-06-22

62

Polarization dependent frequency shift induced BER penalty in DPSK demodulators  

Microsoft Academic Search

We experimentally analyzed the induced penalty due to polarization dependent frequency shift (PDf) for 10 GHz and 40 GHz DPSK demodulators, revealing a strong correlation with the PDf ratio and filtering effect of the delay interferometer.

Dragos Cotruta; Xian Xu; David V. Plant; Odile Liboiron-Ladouceur

2009-01-01

63

Estimating the spatiotemporal distribution of geochemical parameters associated with biostimulation using spectral  

E-print Network

using spectral induced polarization data and hierarchical Bayesian models Jinsong Chen,1 Susan S with in-situ bioremediation using surface spectral induced polarization (SIP) data and borehole with biostimulation using spectral induced polarization data and hierarchical Bayesian models, Water Resour. Res., 48

Hubbard, Susan

64

Plasmonic rainbow rings induced by white radial polarization.  

PubMed

This Letter presents a scheme to embed both angular/spectral surface plasmon resonance (SPR) in a unique far-field rainbow feature by tightly focusing (effective NA=1.45) a polychromatic radially polarized beam on an Au (20 nm)/SiO2 (500 nm)/Au (20 nm) sandwich structure. Without the need for angular or spectral scanning, the virtual spectral probe snapshots a wide operation range (n=1-1.42; ?=400-700 nm) of SPR excitation in a locally nanosized region. Combined with the high-speed spectral analysis, a proof-of-concept scenario was given by monitoring the NaCl liquid concentration change in real time. The proposed scheme will certainly has a promising impact on the development of objective-based SPR sensor and biometric studies due to its rapidity and versatility. PMID:22466196

Lan, Tzu-Hsiang; Chung, Yi-Kuan; Li, Jie-En; Tien, Chung-Hao

2012-04-01

65

Vacuum polarization induced by a uniformly accelerated charge  

E-print Network

We consider a point charge fixed in the Rindler coordinates which describe a uniformly accelerated frame. We determine an integral expression of the induced charge density due to the vacuum polarization at the first order in the fine structure constant. In the case where the acceleration is weak, we give explicitly the induced electrostatic potential.

B. Linet

1995-03-30

66

Polarization in Spectral Lines - Part Four - Resonance Polarization in the Hanle Effect Collisionless Regime  

NASA Astrophysics Data System (ADS)

The general formalism presented in a previous paper of this series (Landi Degl'Innocenti, 1983a) is particularized to deduce the radiative transfer equations for polarized radiation and the statistical equilibrium equations for a multi-level atom in the Hanle effect, collisionless regime. The formulae are developed both in the standard representation and in the representation of the statistical tensors. For resonance scattering in a two-level atom in the presence of a weak magnetic field, in the limiting case of complete depolarization of the ground level, we recover the classical results of the Hanle effect and we derive the expression of the phase matrix in terms of ordinary rotation matrices. A magnetic kernel is introduced in the formalism and its main properties are analyzed. In particular, an expression for the magnetic kernel is derived for a turbulent magnetic field and the corresponding phase matrix is evaluated. Firia~1y, the law of scattering is generalized to take properly into account the influence of the anisotropy of the radiation field on the atomic polarization of the ground level (depopulation pumping in the Hanle effect).

degl-Innocenti, E. Landi

1985-12-01

67

Polarization in spectral lines. IV - Resonance polarization in the Hanle effect, collisionless regime  

NASA Astrophysics Data System (ADS)

The general formalism presented in a previous paper of this series (Landi Degl'Innocenti, 1983) is particularized to deduce the radiative transfer equations for polarized radiation and the statistical equilibrium equations for a multilevel atom in the Hanle-effect collisionless regime. The formulae are developed both in the standard representation and in the representation of the statistical tensors. For resonance scattering in a two-level atom in the presence of a weak magnetic field, in the limiting case of complete depolarization of the ground level, the classical results of the Hanle effect are recovered and the expression of the phase matrix is derived in terms of ordinary rotation matrices. A magnetic kernel is introduced in the formalism, and its main properties are analyzed. In particular, an expression for the magnetic kernel is derived for a turbulent magnetic field and the corresponding phase matrix is evaluated. Finally, the law of scattering is generalized to properly take into account the influence of radiation field anisotropy on the atomic polarization of the ground level (depopulation pumping in the Hanle effect).

Landi Degl'Innocenti, E.

1985-12-01

68

Current-Induced Spin Polarizations in Surfaces of Topological Insulators  

NASA Astrophysics Data System (ADS)

Topological Insulators (TI) have gapless conducting states on their surfaces, which are largely spin-split. Former studies have showed that in spin-orbit coupled systems, current can induce a spin polarization. In this research, we calculate the response of the TI surface state to the dc electric field, that is, transverse conductivity and the induced in-plane spin polarization in the presence of delta-function impurities using Kubo formula. Additionally, in Bi2Te3, the shape of Fermi surface is warped to be 6-fold rotationally symmetric; thereby the transport properties are modified. In this warped Fermi surface, we predict that the current induces a component of spin polarization perpendicular to the surface as a nonlinear response. This out-of-plane polarization may be easier to detect than in-plane polarization. Using the 6-fold rotational symmetry, we discuss the nonlinear response of spin accumulation to the current and its implications on Bi2Te3. We also study another non-linear effect, the inverse Faraday effect, where the oscillating electric field induces the dc spin polarization.

Misawa, Tetsuro; Murakami, Shuichi

2011-03-01

69

Schistosoma japonicum infection induces macrophage polarization  

PubMed Central

Abstract The role of macrophages (M?) as the first line of host defense is well accepted. These cells play a central role in orchestrating crucial functions during schistosomal infection. Thus, understanding the functional diversity of these cells in the process of infection as well as the mechanisms underlying these events is crucial for developing disease control strategies. In this study, we adopted a M? polarization recognition system. M1 macrophage was characterized by expressing CD16/32, IL-12 and iNOS. M2 macrophage was characterized by expressing CD206, IL-10 and arg-1. In vivo (mouse peritoneal macrophages of different infection stages were obtained) and in vitro (different S. japonicum antigens were used to stimulate RAW264.7) were characterized by using the above mentioned system. NCA and ACA stimulated RAW264.7 express significantly higher levels of IL-12 while significantly higher levels of IL-10 were detected after soluble egg antigen (SEA) stimulation. The results showed that dramatic changes of antigen in the microenvironment before and after egg production led to macrophage polarization. Furthermore, through TLR blocking experiments, the TLR4 signaling pathway was found to play a role in the process of macrophage polarization toward M1. Our data suggest that macrophage polarization during S. japonicum infection had significant effects on host immune responses to S. japonicum. PMID:25050114

Xu, Jingwei; Zhang, Hao; Chen, Lin; Zhang, Donghui; Ji, Minjun; Wu, Haiwei; Wu, Guanling

2014-01-01

70

Antiproton polarization induced by lepton interactions  

E-print Network

We present expressions for electromagnetic helicity amplitudes and spin observables for any elastic spin 1/2 - spin 1/2 scattering to first order in QED. In particular all electromagnetic helicity amplitudes and spin observables for elastic antiproton-electron and antiproton-proton scattering via single t-channel photon exchange are presented. Spin observables are required to describe the rate of increase of polarization in spin filtering. The PAX collaboration at GSI Darmstadt is interested in the buildup of polarization of an antiproton beam by repeated interaction with a hydrogen gas target in a storage ring. In order for the beam particles to remain in the ring after scattering it is important to consider small angle scattering, hence small momentum transfer t. In the low momentum transfer region electromagnetic effects dominate the hadronic effects. Of immediate importance is whether the polarization of an antiproton beam can be built up by spin filtering off polarized electrons either in a target or in a beam. We present the theoretical background for this discussion.

D. S. O'Brien; N. H. Buttimore

2006-09-22

71

Global Spectral Energy Distribution of the Crab Nebula in the Prospect of the Planck Satellite Polarization Calibration  

NASA Astrophysics Data System (ADS)

Within the framework of the Planck satellite polarization calibration, we present a study of the Crab Nebula spectral energy distribution (SED) over more than six decades in frequency ranging from 1 to 106 GHz (from 299 to 2.99 × 10-4 mm). The Planck satellite mission observes the sky from 30 to 857 GHz (from 9.99 to 0.3498 mm) and therefore we focus on the millimeter region. We use radio and submillimeter data from the WMAP satellite between 23 and 94 GHz (from 13 to 3.18 mm), from the Archeops balloon experiment between 143 (2.1 mm) and 545 GHz (0.55 mm), and a compendium of other Crab Nebula observations. The Crab SED is compared to models including three main components: synchrotron that is responsible for the emission at low and high frequencies, dust that explains the excess of flux observed by the IRAS satellite, and an extra component on the millimeter regime. From this analysis, we conclude that the unpolarized emission of the Crab Nebula at microwave and millimeter wavelengths is the same synchrotron emission as the one observed in the radio domain. Therefore, we expect the millimeter emission of the Crab Nebula to be polarized with the same degree of polarization and orientation as the radio emission. We set upper limits on the possible errors induced by any millimeter extra component on the reconstruction of the degree and angle of polarization at the percent level as a maximum. This result strongly supports the choice by the Planck collaboration of the Crab Nebula emission for performing polarization cross-checks in the range 30 (299 mm) to 353 GHz (0.849 mm).

Macías-Pérez, J. F.; Mayet, F.; Aumont, J.; Désert, F.-X.

2010-03-01

72

Polarization Resolved Laser-Induced Breakdown Spectroscopy of Al  

NASA Astrophysics Data System (ADS)

It is shown that the continuous background of the laser-induced breakdown spectrum of Al produced by 800 nm femtosecond pulses is strongly polarized. Use of a polarizer to filter out the background significantly improves the signal/noise and signal/background ratios of the discrete line spectrum. The effects of the laser pulse energy, focal position, incidence and detection angles, and the polarization plane of the laser were investigated. Polarization resolved laser-induced breakdown spectroscopy (PRLIBS) is much less sensitive to these variables than conventional, ungated fs-LIBS, making this a much more versatile analytical tool. These measurements reveal qualitatively different mechanisms for the continuous and discrete parts of the spectrum.

Penczak, John S.; Liu, Yaoming; Gordon, Robert J.

2009-08-01

73

Electronic transport through nuclear-spin-polarization-induced quantum wire  

E-print Network

Electron transport in a new low-dimensional structure - the nuclear spin polarization induced quantum wire (NSPI QW) is theoretically studied. In the proposed system the local nuclear spin polarization creates the effective hyperfine field which confines the electrons with the spins opposite to the hyperfine field to the regions of maximal nuclear spin polarization. The influence of the nuclear spin relaxation and diffusion on the electron energy spectrum and on the conductance of the quantum wire is calculated and the experimental feasibility is discussed.

Yu. V. Pershin; S. N. Shevchenko; I. D. Vagner; P. Wyder

2001-09-25

74

Polar Lipids of Burkholderia pseudomallei Induce Different Host Immune Responses  

PubMed Central

Melioidosis is a disease in tropical and subtropical regions of the world that is caused by Burkholderia pseudomallei. In endemic regions the disease occurs primarily in humans and goats. In the present study, we used the goat as a model to dissect the polar lipids of B. pseudomallei to identify lipid molecules that could be used for adjuvants/vaccines or as diagnostic tools. We showed that the lipidome of B. pseudomallei and its fractions contain several polar lipids with the capacity to elicit different immune responses in goats, namely rhamnolipids and ornithine lipids which induced IFN-?, whereas phospholipids and an undefined polar lipid induced strong IL-10 secretion in CD4+ T cells. Autologous T cells co-cultured with caprine dendritic cells (cDCs) and polar lipids of B. pseudomallei proliferated and up-regulated the expression of CD25 (IL-2 receptor) molecules. Furthermore, we demonstrated that polar lipids were able to up-regulate CD1w2 antigen expression in cDCs derived from peripheral blood monocytes. Interestingly, the same polar lipids had only little effect on the expression of MHC class II DR antigens in the same caprine dendritic cells. Finally, antibody blocking of the CD1w2 molecules on cDCs resulted in decreased expression for IFN-? by CD4+ T cells. Altogether, these results showed that polar lipids of B. pseudomallei are recognized by the caprine immune system and that their recognition is primarily mediated by the CD1 antigen cluster. PMID:24260378

Gonzalez-Juarrero, Mercedes; Mima, Naoko; Trunck, Lily A.; Schweizer, Herbert P.; Bowen, Richard A.; Dascher, Kyle; Mwangi, Waithaka; Eckstein, Torsten M.

2013-01-01

75

Spectral selective radio frequency emissions from laser induced breakdown of target materials  

NASA Astrophysics Data System (ADS)

The radio frequency emissions scanned over broad spectral range (30 MHz-1 GHz) from single shot nanosecond (7 ns) and picosecond (30 ps) laser induced breakdown (LIB) of different target materials (atmospheric air, aluminum, and copper) are presented. The dominant emissions from ns-LIB, compared to those from the ps-LIB, indicate the presence and importance of atomic and molecular clusters in the plasma. The dynamics of laser pulse-matter interaction and the properties of the target materials were found to play an important role in determining the plasma parameters which subsequently determine the emissions. Thus, with a particular laser and target material, the emissions were observed to be spectral selective. The radiation detection capability was observed to be relatively higher, when the polarization of the input laser and the antenna is same.

Vinoth Kumar, L.; Manikanta, E.; Leela, Ch.; Prem Kiran, P.

2014-08-01

76

Three-dimensional induced polarization data inversion for complex resistivity  

SciTech Connect

The conductive and capacitive material properties of the subsurface can be quantified through the frequency-dependent complex resistivity. However, the routine three-dimensional (3D) interpretation of voluminous induced polarization (IP) data sets still poses a challenge due to large computational demands and solution nonuniqueness. We have developed a flexible methodology for 3D (spectral) IP data inversion. Our inversion algorithm is adapted from a frequency-domain electromagnetic (EM) inversion method primarily developed for large-scale hydrocarbon and geothermal energy exploration purposes. The method has proven to be efficient by implementing the nonlinear conjugate gradient method with hierarchical parallelism and by using an optimal finite-difference forward modeling mesh design scheme. The method allows for a large range of survey scales, providing a tool for both exploration and environmental applications. We experimented with an image focusing technique to improve the poor depth resolution of surface data sets with small survey spreads. The algorithm's underlying forward modeling operator properly accounts for EM coupling effects; thus, traditionally used EM coupling correction procedures are not needed. The methodology was applied to both synthetic and field data. We tested the benefit of directly inverting EM coupling contaminated data using a synthetic large-scale exploration data set. Afterward, we further tested the monitoring capability of our method by inverting time-lapse data from an environmental remediation experiment near Rifle, Colorado. Similar trends observed in both our solution and another 2D inversion were in accordance with previous findings about the IP effects due to subsurface microbial activity.

Commer, M.; Newman, G.A.; Williams, K.H.; Hubbard, S.S.

2011-03-15

77

High spectral and time resolution observations of the eclipsing polar RX J0719.2+6557  

E-print Network

We present phase-resolved spectral and multicolor CCD-photometric observations of the eclipsing polar RX J0719.2+6557 obtained with relatively high time (~600 sec/15 sec) and spectral (2.1 A) resolution when the system was in a high accretion state. The trailed spectrograms clearly reveal the presence of three different line components with different width and radial velocity variation. We were able to resolve all three components by line deblending, and by means of Doppler tomography were able to unambiguously identify the emission components with the secondary star, the ballistic part of the accretion stream and the magnetically funnelled part of the stream. The light curves and eclipse profiles provide additional information about the system geometry.

G. H. Tovmassian; P. Szkody; J. Greiner; S. Vrielmann; P. Kroll; S. Howell; R. Saxton; D. Ciardi; P. A. Mason; N. C. Hastings

1998-09-24

78

Bright source of spectrally pure polarization-entangled photon with nearly single-mode emission  

SciTech Connect

We present results of a bright entangled photon source operating at 1552 nm via type-II collinear degenerate spontaneous parametric down-conversion in periodically poled KTP crystal. We report a conservative inferred pair generation rate of 44,000/s/mW into collection modes. Minimization of spectral and spatial entanglement was achieved by group velocity matching the pump, signal and idler modes and through properly focusing the pump beam. By utilizing a pair of calcite beam displacers, we are able to overlap photons from adjacent collinear sources to obtain polarization-entanglement visibility of 94.7 +/- 1.1% with accidentals subtracted.

Evans, Philip G [ORNL; Schaake, Jason [ORNL; Bennink, Ryan S [ORNL; Grice, Warren P [ORNL; Humble, Travis S [ORNL

2010-01-01

79

Assessing Cd-induced stress from plant spectral response  

NASA Astrophysics Data System (ADS)

Remote sensing plays a significant role in local, regional and global monitoring of land covers. Ecological concerns worldwide determine the importance of remote sensing applications for the assessment of soil conditions, vegetation health and identification of stress-induced changes. The extensive industrial growth and intensive agricultural land-use arise the serious ecological problem of environmental pollution associated with the increasing anthropogenic pressure on the environment. Soil contamination is a reason for degradation processes and temporary or permanent decrease of the productive capacity of land. Heavy metals are among the most dangerous pollutants because of their toxicity, persistent nature, easy up-take by plants and long biological half-life. This paper takes as its focus the study of crop species spectral response to Cd pollution. Ground-based experiments were performed, using alfalfa, spring barley and pea grown in Cd contaminated soils and in different hydroponic systems under varying concentrations of the heavy metal. Cd toxicity manifested itself by inhibition of plant growth and synthesis of photosynthetic pigments. Multispectral reflectance, absorbance and transmittance, as well as red and far red fluorescence were measured and examined for their suitability to detect differences in plant condition. Statistical analysis was performed and empirical relationships were established between Cd concentration, plant growth variables and spectral response Various spectral properties proved to be indicators of plant performance and quantitative estimators of the degree of the Cd-induced stress.

Kancheva, Rumiana; Georgiev, Georgi

2014-10-01

80

A polarity-induced defect mechanism for conductivity and magnetism at polar–nonpolar oxide interfaces  

NASA Astrophysics Data System (ADS)

The discovery of conductivity and magnetism at the polar–nonpolar interfaces of insulating nonmagnetic oxides such as LaAlO3 and SrTiO3 has raised prospects for attaining interfacial functionalities absent in the component materials. Yet, the microscopic origin of such emergent phenomena remains unclear, posing obstacles to design of improved functionalities. Here we present first principles calculations of electronic and defect properties of LaAlO3/SrTiO3 interfaces and reveal a unifying mechanism for the origins of both conductivity and magnetism. We demonstrate that the polar discontinuity across the interface triggers thermodynamically the spontaneous formation of certain defects that in turn cancel the polar field induced by the polar discontinuity. The ionization of the spontaneously formed surface oxygen vacancy defects leads to interface conductivity, whereas the unionized Ti-on-Al antisite defects lead to interface magnetism. The proposed mechanism suggests practical design principles for inducing and controlling both conductivity and magnetism at general polar–nonpolar interfaces.

Yu, Liping; Zunger, Alex

2014-10-01

81

Induced polarization of Lambda(1116) in kaon electroproduction  

SciTech Connect

We have measured the induced polarization of the ?(1116) in the reaction ep?e?K+?, detecting the scattered e? and K+ in the final state along with the proton from the decay ??p??.The present study used the CEBAF Large Acceptance Spectrometer (CLAS), which allowed for a large kinematic acceptance in invariant energy W (1.6?W?2.7 GeV) and covered the full range of the kaon production angle at an average momentum transfer Q2=1.90 GeV2.In this experiment a 5.50 GeV electron beam was incident upon an unpolarized liquid-hydrogen target. We have mapped out the W and kaon production angle dependencies of the induced polarization and found striking differences from photoproduction data over most of the kinematic range studied. However, we also found that the induced polarization is essentially Q2 independent in our kinematic domain, suggesting that somewhere below the Q2 covered here there must be a strong Q2 dependence. Along with previously published photo- and electroproduction cross sections and polarization observables, these data are needed for the development of models, such as effective field theories, and as input to coupled-channel analyses that can provide evidence of previously unobserved s-channel resonances.

Gabrielyan, M.; Raue, B.A.; Carman, D.S.; Park, K.; Adhikari, K.P.; Adikaram, D.; Amaryan, M.J.; Anefalos Pereira, S.; Avakian, H.; Ball, J.; Baltzell, N.A.; Battaglieri, M.; Baturin, V.; Bedlinskiy, I.; Biselli, A.S.; Bono, J.; Boiarinov, S.; Briscoe, W.J.; Brooks, W.K.; Burkert, V.D.; Cao, T.; Celentano, A.; Chandavar, S.; Charles, G.; Cole, P.L.; Contalbrigo, M.; Cortes, O.; Crede, V.; D’Angelo, A.; Dashyan, N.; De Vita, R.; De Sanctis, E.; Deur, A.; Djalali, C.; Doughty, D.; Dupre, R.; ElFassi, L.; Eugenio, P.; Fedotov, G.; Fegan, S.; Fleming, J.A.; Forest, T.A.; Garillon, B.; Gevorgyan, N.; Ghandilyan, Y.; Gilfoyle, G.P.; Giovanetti, K.L.; Girod, F.X.; Goetz, J.T.; Golovatch, E.; Gothe, R.W.; Griffioen, K.A.; Guidal, M.; Guo, L.; Hafidi, K.; Hakobyan, H.; Hattawy, M.; Hicks, K.; Ho, D.; Holtrop, M.; Hughes, S.M.; Ilieva, Y.; Ireland, D.G.; Ishkhanov, B.S.; Jenkins, D.; Jiang, H.; Jo, H.S.; Joo, K.; Keller, D.; Khandaker, M.; Kim, W.; Klein, F.J.; Koirala, S.; Kubarovsky, V.; Kuhn, S.E.; Kuleshov, S.V.; Lenisa, P.; Levine, W.I.; Livingston, K.; MacGregor, I.J.D.; Mayer, M.; McKinnon, B.; Meyer, C.A.; Mestayer, M.D.; Mirazita, M.; Mokeev, V.; Moody, C.I.; Moutarde, H.; Movsisyan, A; Munevar, E.; Munoz Camacho, C.; Nadel-Turonski, P.; Niccolai, S.; Niculescu, G.; Osipenko, M.; Pappalardo, L.L.; Paremuzyan, R.; Pasyuk, E.; Peng, P.; Phelps, W.; Phillips, J.J.; Pisano, S.; Pogorelko, O.; Pozdniakov, S.; Price, J.W.; Procureur, S.; Protopopescu, D.; Rimal, D.; Ripani, M.; Rizzo, A.; Sabatie, F.; Salgado, C.; Schott, D.; Schumacher, R.A.; Simonyan, A.; Smith, G.D.; Sober, D.I.; Sokhan, D.; Stepanyan, S.S.; Stepanyan, S.; Strakovsky, I.I.; Strauch, S.; Sytnik, V.; Tang, W.; Ungaro, M.; Vlassov, A.V.; Voskanyan, H.; Voutier, E.; Walford, N.K.; Watts, D.P.; Wei, X.; Weinstein, L.B.; Zachariou, N.; Zana, L.; Zhang, J.

2014-09-01

82

Spectral-to-temporal amplitude mapping polarization spectroscopy of rotational transients.  

PubMed

A new implementation of pump-probe polarization spectroscopy is presented where the revivals of an impulsively excited rotational wavepacket are mapped onto a broad-band, chirped continuum pulse to measure a long temporal window without the need for delay scanning. Experimental measurements and a theoretical framework for spectral-temporal amplitude mapping polarization spectroscopy (STAMPS) as applied to impulsive rotational motion are presented. In this technique, a femtosecond laser pulse is used to prepare a rotational wavepacket in a gas-phase sample at room temperature. The rotational revivals of the wavepacket are then mapped onto a chirped continuum (400-800 nm) pulse created by laser filamentation in argon. Nearly single-shot time-resolved rotational spectra are recorded over a 65 ps time window. The transient birefringence spectra are simulated by including terms for polarization rotation of the probe as well as cross-phase modulation. Measurements and simulations are presented for the cylindrically symmetric N2, O2, and CO2 molecules. The long time window of the method allows measurement of rotational spectra for asymmetric top molecules, and here we present measurements for ethylene and methanol. PMID:23651318

McCole, Erin T; Odhner, Johanan H; Romanov, Dmitri A; Levis, Robert J

2013-07-25

83

Dependence of spectral width of polar cap HF echoes upon electric field  

NASA Astrophysics Data System (ADS)

The EISCAT Svalbard Radar (ESR) monitors plasma parameters in the ionospheric region that is frequently located near the polar cap boundary. The SuperDARN radar at Hankasalmi, Finland detects coherent echoes from this region and these echoes typically show increased spectral width. We consider data of joint ESR and SuperDARN observations to show that the spectral width of HF echoes tends to increase with the electric field. This relationship is explained in terms of non-linear evolution of the ExB gradient drift instability with energy cascade from hundred of meters wavelengths to meter wavelengths. We assume that non-linearly generated, relatively strong decameter waves (seen by the Hankasalmi radar) decay through three-wave interaction with shorter wavelengths and estimate that the decameter waves/irregularities decay time is determined by the parameters of the shorter wavelength structures. We associate the decameter wave decay time with the correlation time, and thus the spectral width, of HF echoes.

Koustov, A. V.; Shalimov, S.; Kozlovsky, A.

2010-12-01

84

Spectrally resolved laser-induced fluorescence for bioaerosols standoff detection  

NASA Astrophysics Data System (ADS)

An efficient standoff biological warfare detection capability could become an important asset for both defence and security communities based on the increasing biological threat and the limits of the presently existing protection systems. Defence R&D Canada (DRDC) has developed, by the end of the 90s, a standoff bioaerosol sensor prototype based on intensified range-gated spectrometric detection of Laser Induced Fluorescence (LIF). This LIDAR system named SINBAHD monitors the spectrally resolved LIF originating from inelastic interactions with bioaerosols present in atmospheric cells customizable in size and in range. SINBAHD has demonstrated the capability of near real-time detection and classification of bioaerosolized threats at multi-kilometre ranges. In spring 2005, DRDC has initiated the BioSense demonstration project, which combines the SINBAHD technology with a geo-referenced Near InfraRed (NIR) LIDAR cloud mapper. SINBAHD is now being used to acquire more signatures to add in the spectral library and also to optimize and test the new BioSense algorithm strategy. In September 2006, SINBAHD has participated in a two-week trial held at DRDC-Suffield where different open-air wet releases of live and killed bioagent simulants, growth media and obscurants were performed. An autoclave killing procedure was performed on two biological materials (Bacillus subtilis var globigii or BG, and Bacillus thuringiensis or Bt) before being aerosolized, disseminated and spectrally characterized with SINBAHD. The obtained results showed no significant impact of this killing process on their normalised spectral signature in comparison with their live counterparts. Correlation between the detection signals from SINBAHD, an array of slit samplers and a FLuorescent Aerosol Particle Sensor (C-FLAPS) was obtained and SINBAHD's sensitivity could then be estimated. At the 2006 trial, a detection limit of a few tens of Agent Containing Particles per Liter of Air (ACPLA) was obtained for a 15-m thick cloud of live BG located at a range of 400 m.

Buteau, Sylvie; Stadnyk, Laurie; Rowsell, Susan; Simard, Jean-Robert; Ho, Jim; Déry, Bernard; McFee, John

2007-09-01

85

Polarization-induced surface charges in hydroxyapatite ceramics  

NASA Astrophysics Data System (ADS)

Calcium hydroxyapatite (HAp; Ca10(PO4)6(OH)2) is a well-known biomaterial that is the main inorganic component of bones and teeth. Control over the surface charge on HAp would be a key advance in the development of the material for tissue engineering. We demonstrate here that surface charge can be induced by an electrical poling process using the Kelvin method. Positive and negative charges were induced on the HAp surface in response to the applied electric field in the poling process. The surface charging is attributed to dipole polarization that is homogeneously distributed in HAp. Additionally, the surface charging is considered to originate from the organization of OH- ions into a polar phase in the structure.

Horiuchi, N.; Nakaguki, S.; Wada, N.; Nozaki, K.; Nakamura, M.; Nagai, A.; Katayama, K.; Yamashita, K.

2014-07-01

86

Ion-induced nucleation in polar one-component fluids  

E-print Network

We present a Ginzburg-Landau theory of ion-induced nucleation in a gas phase of polar one-component fluids, where a liquid droplet grows with an ion at its center. By calculating the density profile around an ion, we show that the solvation free energy is larger in gas than in liquid at the same temperature on the coexistence curve. This difference much reduces the nucleation barrier in a metastable gas.

Hikaru Kitamura; Akira Onuki

2005-08-01

87

Induced energy polarization of the vacuum and the resulting cosmology  

E-print Network

The theory of an induced energy polarized vacuum provides an alternative to the standard cosmological model. The theory has previously been shown to lead to the Baryonic Tully-Fisher Relationship [1], to agree with the observed rotation curve of the Galaxy [2], to readily produce the observed features in the rotational curves of other spiral galaxies [3], and to agree with observations of the Coma cluster [4]. All without the need for any free parameters. The theory of an induced energy polarized vacuum is now applied to superclusters. From a model of the distribution of superclusters, the overall density parameter of universe as given by the theory of an induced energy polarized vacuum is Omega = 0.94 plus/minus 0.23. This is consistent with a geometrically flat universe. In addition, by treating the superclusters as unbound systems, the theory leads to an accelerating expansion of the universe in line with observations and without requiring the need for dark energy.

Albert Raymond Penner

2014-04-10

88

Ex vivo assessment of carbon tetrachloride (CCl(4))-induced chronic injury using polarized light spectroscopy.  

PubMed

The liver performs various functions, such as the production and detoxification of chemicals; therefore, it is susceptible to hepatotoxins such as carbon tetrachloride (CCl4), which causes chronic injury. Thus, assessment of injury and its status of severity are of prime importance. Current work reports an ex vivo study for probing the severance of hepatic injury induced by CCl4 with polarized light over the spectral range 400-800 nm. Different concentrations of CCl4 were used to induce varying severity of hepatic injury in a rat model. Linear retardance, depolarization rates, and diagonal Mueller matrix elements (m22, m33, and m44), were successfully used as the distinguishing criterion for normal and different liver injuries. Our results show that linear retardance for injured liver samples with lower doses of CCl4 tends to increase when compared with normal liver samples, while samples injured at higher doses of CCl4 offer almost no retardance. Total, linear, and circular depolarizations follow decreasing trends with increased liver injury severity over the entire investigated wavelength range. Linear polarization states were observed to be better maintained as compared to circular polarization states for all samples. Furthermore, numerical values of diagonal elements of the experimentally measured Mueller matrix also increase with increasing doses of CCl4. Liver fibroses, change in transport albedo, and the relative refractive index of the extracellular matrix caused by CCl4 are responsible for the observed differences. These results will provide a pathway to gauge the severity of injury caused by toxic chemicals. PMID:24359651

Ahmad, Manzoor; Ali, Safdar; Mehmood, Malik Sajjad; Ali, Hamid; Khurshid, Ahmat; Firdous, Shamaraz; Muhammad, Saleh; Ikram, Masroor

2013-12-01

89

Extracting structural features of rat sciatic nerve using polarization-sensitive spectral domain optical coherence tomography  

PubMed Central

Abstract. We present spectral domain polarization-sensitive optical coherence tomography (SD PS-OCT) imaging of peripheral nerves. Structural and polarization-sensitive OCT imaging of uninjured rat sciatic nerves was evaluated both qualitatively and quantitatively. OCT and its functional extension, PS-OCT, were used to image sciatic nerve structure with clear delineation of the nerve boundaries to muscle and adipose tissues. A long-known optical effect, bands of Fontana, was also observed. Postprocessing analysis of these images provided significant quantitative information, such as epineurium thickness, estimates of extinction coefficient and birefringence of nerve and muscle tissue, frequency of bands of Fontana at different stretch levels of nerve, and change in average birefringence of nerve under stretched condition. We demonstrate that PS-OCT combined with regular-intensity OCT (compared with OCT alone) allows for a clearer determination of the inner and outer boundaries of the epineurium and distinction of nerve and muscle based on their birefringence pattern. PS-OCT measurements on normal nerves show that the technique is promising for studies on peripheral nerve injury. PMID:22612135

Islam, M. Shahidul; Oliveira, Michael C.; Wang, Yan; Henry, Francis P.; Randolph, Mark A.; Park, B. Hyle; de Boer, Johannes F.

2012-01-01

90

Extracting structural features of rat sciatic nerve using polarization-sensitive spectral domain optical coherence tomography  

NASA Astrophysics Data System (ADS)

We present spectral domain polarization-sensitive optical coherence tomography (SD PS-OCT) imaging of peripheral nerves. Structural and polarization-sensitive OCT imaging of uninjured rat sciatic nerves was evaluated both qualitatively and quantitatively. OCT and its functional extension, PS-OCT, were used to image sciatic nerve structure with clear delineation of the nerve boundaries to muscle and adipose tissues. A long-known optical effect, bands of Fontana, was also observed. Postprocessing analysis of these images provided significant quantitative information, such as epineurium thickness, estimates of extinction coefficient and birefringence of nerve and muscle tissue, frequency of bands of Fontana at different stretch levels of nerve, and change in average birefringence of nerve under stretched condition. We demonstrate that PS-OCT combined with regular-intensity OCT (compared with OCT alone) allows for a clearer determination of the inner and outer boundaries of the epineurium and distinction of nerve and muscle based on their birefringence pattern. PS-OCT measurements on normal nerves show that the technique is promising for studies on peripheral nerve injury.

Islam, M. Shahidul; Oliveira, Michael C.; Wang, Yan; Henry, Francis P.; Randolph, Mark A.; Park, B. Hyle; de Boer, Johannes F.

2012-05-01

91

Building Better Electrodes for Electrical Resistivity and Induced Polarization Data  

NASA Astrophysics Data System (ADS)

In the third year of a project to understand and mitigate the systematic noise in resistivity and induced polarization measurements, we put a significant effort into understanding and developing better electrodes. The simple metal electrodes commonly used for both transmitting and receiving of electrical geophysical data are likely the Achilles" heal of the resistivity method. Even stainless steel, a commonly used electrode material because of its durability, showed only average results in laboratory tests for electrode noise. Better results have been found with non-polarizing metal-metal salt electrodes, which are widely used as surface electrodes and in IP surveys. But although they produce small measurement errors, they are not durable enough for in-situ borehole resistivity surveys, and often contain compounds that are toxic to the environment. They are also very seldom used as transmitters. In laboratory studies, we are exploring other materials and configurations for low-noise compound electrodes that will be nontoxic, inexpensive, and durable and can be used as both transmitters and receivers. Testing of the electrical noise levels of electrodes is an arduous task involving repeated measurements under varying conditions at field scales. Thus it is important to find methods of sorting out likely candidates from the mass of possible electrode configurations and construction methods. Testing of electrode impedance versus current density appears to provide simple criteria for predicting the suitability of electrodes. The best electrodes show relatively low overall contact impedance, relatively small changes in impedance with increased current density, and relatively small changes in impedance with time. Furthermore it can be shown that resistivity and induced polarization performance of electrodes is strongly correlated, so that methods of finding electrodes with low impedance and good direct current performance usually provide better quality induced polarization data and vice- versa.

Adkins, P. L.; La Brecque, D. J.

2007-12-01

92

Spatial Variations in the Spectral Index of Polarized Synchrotron Emission in the 9 yr WMAP Sky Maps  

NASA Astrophysics Data System (ADS)

We estimate the spectral index, ?, of polarized synchrotron emission as observed in the 9 yr Wilkinson Microwave Anisotropy Probe sky maps using two methods, linear regression ("T-T plot") and maximum likelihood. We partition the sky into 24 disjoint sky regions and evaluate the spectral index for all polarization angles between 0° and 85° in steps of 5°. Averaging over polarization angles, we derive a mean spectral index of ?all-sky = -2.99 ± 0.01 in the frequency range of 23-33 GHz. We find that the synchrotron spectral index steepens by 0.14 from low to high Galactic latitudes, in agreement with previous studies, with mean spectral indices of ?plane = -2.98 ± 0.01 and ?high-lat = -3.12 ± 0.04. In addition, we find a significant longitudinal variation along the Galactic plane with a steeper spectral index toward the Galactic center and anticenter than toward the Galactic spiral arms. This can be well modeled by an offset sinusoidal, ?(l) = -2.85 + 0.17sin (2l - 90°). Finally, we study synchrotron emission in the BICEP2 field, in an attempt to understand whether the claimed detection of large-scale B-mode polarization could be explained in terms of synchrotron contamination. Adopting a spectral index of ? = -3.12, typical for high Galactic latitudes, we find that the most likely bias corresponds to about 2% of the reported signal (r = 0.003). The flattest index allowed by the data in this region is ? = -2.5, and under the assumption of a straight power-law frequency spectrum, we find that synchrotron emission can account for at most 20% of the reported BICEP2 signal.

Fuskeland, U.; Wehus, I. K.; Eriksen, H. K.; Næss, S. K.

2014-08-01

93

Para-hydrogen induced polarization in heterogeneous hydrogenationreactions  

SciTech Connect

We demonstrate the creation and observation ofpara-hydrogen-induced polarization in heterogeneous hydrogenationreactions. Wilkinson's catalyst, RhCl(PPh3)3, supported on eithermodified silica gel or a polymer, is shown to hydrogenate styrene intoethylbenzene and to produce enhanced spin polarizations, observed throughNMR, when the reaction was performed with H2 gas enriched in the paraspinisomer. Furthermore, gaseous phase para-hydrogenation of propylene topropane with two catalysts, the Wilkinson's catalyst supported onmodified silica gel and Rh(cod)(sulfos) (cod = cycloocta-1,5-diene;sulfos) - O3S(C6H4)CH2C(CH2PPh2)3) supported on silica gel, demonstratesheterogeneous catalytic conversion resulting in large spin polarizations.These experiments serve as a direct verification of the mechanism ofheterogeneous hydrogenation reactions involving immobilized metalcomplexes and can be potentially developed into a practical tool forproducing catalyst-free fluids with highly polarized nuclear spins for abroad range of hyperpolarized NMR and MRI applications.

Koptyug, Igor V.; Kovtunov, Kirill; Burt, Scott R.; Anwar, M.Sabieh; Hilty, Christian; Han, Song-I; Pines, Alexander; Sagdeev, Renad Z.

2007-01-31

94

Current-induced spin polarization on metal surfaces probed by spin-polarized positron beam  

PubMed Central

Current-induced spin polarization (CISP) on the outermost surfaces of Au, Cu, Pt, Pd, Ta, and W nanoscaled films were studied using a spin-polarized positron beam. The Au and Cu surfaces showed no significant CISP. In contrast, the Pt, Pd, Ta, and W films exhibited large CISP (3~15% per input charge current of 105?A/cm2) and the CISP of Ta and W were opposite to those of Pt and Pd. The sign of the CISP obeys the same rule in spin Hall effect suggesting that the spin-orbit coupling is mainly responsible for the CISP. The magnitude of the CISP is explained by the Rashba-Edelstein mechanism rather than the diffusive spin Hall effect. This settles a controversy, that which of these two mechanisms dominates the large CISP on metal surfaces. PMID:24776781

Zhang, H. J.; Yamamoto, S.; Fukaya, Y.; Maekawa, M.; Li, H.; Kawasuso, A.; Seki, T.; Saitoh, E.; Takanashi, K.

2014-01-01

95

EXSAA: Environmentally-Induced X-ray Spectral Analysis Automation  

NASA Astrophysics Data System (ADS)

X-ray fluorescence (XRF) spectrometry is one of the principal means of compositional analysis in the lab and in the field: it will be a central tool in NASA's Exploration Initiative (EI) missions. No currently available XRF software has the generic functionality to provide the basis for XRF experiment design, instrument development, and data interpretation for the suite of prospective EI missions. In response to this need, we have developed EXSAA (Environmentally-induced X-ray Spectral Analysis Automation), a generic, fast, interactive spectral simulation tool which can be used in assessing broadband continuous spectra being generated and detected during reconnaissance missions and field campaigns involving planetary surfaces. The software produces model spectra of detectable environmentally-induced X-ray spectra from fundamental principles for target characteristics and conditions likely to be experienced in remote or in situ planetary missions. Fluorescence is modeled following Jenkins and DeVries (1967); coherent and Compton scattering following Hubbell (1969). The modeling provided is extensible, and a user interface provides for selection of source, detector characteristics, compositional components, and geometry for known targets. An immediate application of the tool is the prediction for mission planning purposes of X-ray flux to be expected for a range of targets and instrumentation. A longer-term application is the model basis for the recovery of surface composition from actual missions, where some parameters (e.g. source flux) will be known, and others obtained from a Bayesian analysis of the observations. Ultimately, EXSAA could function as part of the agent-based SAA Toolkit being developed by a group of physical scientists, systems engineers, and AI practitioners to automate portions of the spectral analysis process. EXSAA could be called on by human or machine agents to provide an understanding of XRF phenomena for tasks including specifically (1) instrument and mission design and planning, or (2) model-based data analysis. Thus EXSAA could support traditional design methods and enable a variety of experiments in automated design and operation. The far term objective is to develop a toolkit for use at the human/robotic interface during exploration of lunar or Martian surfaces.

Fallon, F. W.; Clark, P. E.; Rilee, M. L.; Truszkowski, W.

2005-05-01

96

Eustatic sea level fluctuations induced by polar wander  

NASA Technical Reports Server (NTRS)

It is shown here that polar wander of a viscoelastic, stratified earth can induce global sea level fluctuations comparable to the short-term component in eustatic sea-level curves. The sign of these fluctuations, which are very sensitive to the rheological stratification, depends on the geographical location of the observation point; rises and falls in sea level can thus be coeval in different parts of the world. This finding is a distinct contrast to the main assumption underlying the reconstruction of eustatic curves, namely that global sea-level events produce the same depositional sequence everywhere. It is proposed that polar wander should be added to the list of geophysical mechanisms that can control the third-order cycles in sea level.

Sabadini, Roberto; Doglioni, Carlo; Yuen, David A.

1990-01-01

97

Polarization-independent plasmon-induced transparency for plasmonic sensing  

NASA Astrophysics Data System (ADS)

We design a three-dimensional structure consisting of cross-slit metallic photonic crystals and dielectric photonic crystals embedded in a background material to achieve electromagnetically induced transparency for TE/TM polarization modes. Numerical simulation demonstrates that the mechanism of this phenomenon is based on the coupling effect between the excited surface plasmonic mode and waveguide mode supported by metallic and dielectric photonic crystals, respectively. In particular, one of the transmission dips of the system is very sensitive to the background material, where the sensitivity (nm/RIU) of the system is more than 700 nm/RIU. Meanwhile, polarization-independent transparency of the structure makes our system possess great potential for achieving high-performance sensors.

Chen, Zhihong; Dai, Lei; Jiang, Chun

2011-08-01

98

Design and fabrication of thin-film polarizer at wavelength of 1540 nm and investigation of its laser-induced damage threshold  

NASA Astrophysics Data System (ADS)

In this paper a thin-film polarizer at a wavelength of 1540 nm was designed and fabricated. These types of polarizer are usually used in laser systems to obtain linearly polarized light beams. Our design consists of a system of eighteen dielectric thin-film layers from repeated pairs of titanium dioxide and silicon dioxide layers that are deposited on a BK7 glass substrate. Design was carried out based on theoretical principles and computer calculations. Thin-film design software was used for designing the polarizer. The angle of incidence was supposed to be 56° that is the Browster angle for BK7 glass. Performance and laser-induced damage threshold of the polarizer were enhanced by a suitable selection of various parameters including thickness of each layer, their number and the electric field distribution of layers. After several designs, fabrications and refinement of parameters, the final polarizer was designed. Then the final sample of the polarizer was prepared using the electron beam evaporation (EBE) technique with Balzers BAK 760 coating machine. Spectral transmittance of the sample was measured by Shimadzu 3100 UV-VIS-NIR spectrophotometer. Investigation of spectral transmittance showed that at a wavelength of 1540nm, the transmission of P polarization is 87.82 and the transmission of S polarization is 0.43 which show a ratio ( T P / T S of 204. So, this ratio is an acceptable value for our desired polarizer.

Sahraee, Masoume; Fallah, Hamid Reza; Moradi, Badri; Zabolian, Hosein; Mahmoodzade, Morteza Haji

2014-12-01

99

Field-resolved measurement of reaction-induced spectral densities by polarizability response spectroscopy  

NASA Astrophysics Data System (ADS)

The experimental design and theoretical description of a novel five-pulse laser spectroscopy is presented with an application to a pyridinium charge transfer complex in acetonitrile and methanol. In field-resolved polarizability response spectroscopy (PORS), an electronically resonant laser pulse first excites a solvated chromophore (reactant) and off-resonant Raman spectra of the resulting nuclear motions are measured as a function of the reaction time. The present apparatus differs from our earlier design by performing the Raman probe measurement (with fixed pulse delays) in the frequency domain. In addition, the full electric fields of the signals are measured by spectral interferometry to separate nonresonant and Raman responses. Our theoretical model shows how the PORS signal arises from nuclear motions that are displaced/driven by the photoinduced reaction. The field-resolved off-resonant (of the solute's electronic transitions) probing favors detection of solvent (as opposed to solute) dynamics coupled to the reaction. The sign of the signal represents the relative strengths of polarization responses associated with the ground and photoexcited solutions. Signatures of nonresonant and PORS signal contributions to the experimental results are analyzed with numerical calculations based on a theoretical model we have developed for reaction-induced PORS. Our model identifies two mechanisms of PORS signal generation: (i) structural relaxation induced resonance; (ii) dephasing induced resonance. In the charge transfer reaction investigated, the solvent-dependent and time-evolving (solvent) polarizability spectral density (PSD) is readily obtained. The general trend of an initial broadband inertial nuclear response followed by a decrease in the linewidth of the PSD establishes that the measured PSD is inconsistent with the approximation of a linear response. Furthermore, the explicit time evolution of the PSD is important for properly describing solvent control of reactions that do not satisfy the time-scale separability inherent to nonadiabatic kinetic models.

Moran, Andrew M.; Nome, Rene A.; Scherer, Norbert F.

2007-11-01

100

Reorientation-induced spectral diffusion in vibrational sum-frequency-generation spectroscopy.  

PubMed

There is a growing appreciation that dynamic processes play an important role in determining the line shape in surface-selective, nonlinear spectroscopies such as vibrational sum-frequency-generation (VSFG). Here we analyze the influence that reorientation can have on VSFG spectra when the vibrational transition frequency is a function of orientation. Under these circumstances, reorientation-induced spectral diffusion (RISD) causes the underlying spectral line shape to become time dependent. Unlike previously reported mechanisms through which reorientation can contribute to the VSFG signal, RISD influences the line shape regardless of the degree of polarization of the Raman transition that is probed. We assess the impact of RISD on VSFG spectra using a model system of liquid acetonitrile at a silica interface. Comparison of delay-time-dependent VSFG spectra with simulations that employ static line shapes suggests that RISD contributes substantially to the spectra, particularly at delay times that are comparable to or greater than the probe pulse duration. The observed behavior is in qualitative agreement with a two-state RISD model that uses orientational distributions determined from previous molecular dynamics simulations. PMID:24088038

Rivera, Christopher A; Souna, Amanda J; Bender, John S; Manfred, Katherine; Fourkas, John T

2013-12-12

101

Black hole stereotyping: Induced gravito-static polarization  

E-print Network

We discuss the black hole effective action and define its static subsector. We determine the induced gravito-static polarization constants (electric Love numbers) of static black holes (Schwarzschild) in an arbitrary dimension, namely the induced mass multipole as a result of an external gravitational field. We demonstrate that in 4d these constants vanish thereby settling a disagreement in the literature. Yet in higher dimensions these constants are non-vanishing, thereby disproving (at least in d>4) speculations that black holes have no effective couplings beyond the point particle action. In particular, when l/(d-3) is half integral these constants demonstrate a (classical) renormalization flow consistent with the divergences of the effective field theory. In some other cases the constants are negative indicating a novel non-spherical instability. The theory of hypergeometric functions plays a central role.

Barak Kol; Michael Smolkin

2011-10-17

102

Induced polarization of clay-sand mixtures. Experiments and modelling.  

NASA Astrophysics Data System (ADS)

The complex conductivity of saturated unconsolidated sand-clay mixtures was experimentally investigated using two types of clay minerals, kaolinite and smectite (mainly Na-Montmorillonite) in the frequency range 1.4 mHz - 12 kHz. The experiments were performed with various clay contents (1, 5, 20, and 100 % in volume of the sand-clay mixture) and salinities (distilled water, 0.1 g/L, 1 g/L, and 10 g/L NaCl solution). Induced polarization measurements were performed with a cylindrical four-electrode sample-holder associated with a SIP-Fuchs II impedance meter and non-polarizing Cu/CuSO4 electrodes. The results illustrate the strong impact of the CEC of the clay minerals upon the complex conductivity. The quadrature conductivity increases steadily with the clay content. We observe that the dependence on frequency of the quadrature conductivity of sand-kaolinite mixtures is more important than for sand-bentonite mixtures. For both types of clay, the quadrature conductivity seems to be fairly independent on the pore fluid salinity except at very low clay contents. The experimental data show good agreement with predicted values given by our SIP model. This complex conductivity model considers the electrochemical polarization of the Stern layer coating the clay particles and the Maxwell-Wagner polarization. We use the differential effective medium theory to calculate the complex conductivity of the porous medium constituted of the grains and the electrolyte. The SIP model includes also the effect of the grain size distribution upon the complex conductivity spectra.

Okay, G.; Leroy, P.

2012-04-01

103

Relationships between induced polarization relaxation time and hydraulic properties of sandstone  

NASA Astrophysics Data System (ADS)

We investigated electrical and physical-chemical properties of six sandstone samples with contrasting mineralogical characteristics and with hydraulic conductivity varying in a wide range. The electrical data were obtained from time domain spectral induced polarization (IP) measurements. We inverted the IP decays to relaxation time distributions, and then compared the modal relaxation times with the dominant pore throat diameters obtained from the Mercury Injection Capillary Pressure (MICP) data. We found a positive logarithmic relationship between the relaxation time and the pore throat diameter. Also, we found the normalized chargeability (an integral IP parameter) to be positively correlated with the clay content. These two results suggest that the polarization of our sandstones is controlled by the pore throat distribution, and by the clay content. The logarithmic relationship contradicts previous theories, and is not universal. Adopting an approach of Kruschwitz and her co-workers, we calculated the effective diffusivity from IP and MICP data, and we found the effective diffusivity values ranging from 2.9 × 10-13 to 1.6 × 10-10 m2s-1. High diffusivity values, typical of surface diffusion, were obtained for clean sandstones. Low diffusivity values were obtained for clayey sandstones, and they were one to two orders of magnitude lower than those characteristic of the surface diffusion. We proposed two mechanisms to explain the `slow' diffusion: (1) the effect of surface tortuosity of pore throats filled with clay minerals and (2) the effect of pore geometry. These two effects represent an obstacle in assessing the pore throat diameter and hydraulic conductivity of sandstones with large specific surface and clay content on the basis of spectral IP measurements. However, we believe that the sandstones featuring `slow' diffusion can be discriminated based on the integral polarization parameters, and that the relaxation time remains a valuable parameter for assessing hydraulic properties of clean sandstones.

Titov, Konstantin; Tarasov, Andrey; Ilyin, Yuri; Seleznev, Nikita; Boyd, Austin

2010-03-01

104

Tomographic and spectral views on the lifecycle of polar mesospheric clouds from Odin/OSIRIS  

NASA Astrophysics Data System (ADS)

and horizontal structures of Polar Mesospheric Clouds (PMC) have been recovered by tomographic retrieval from the OSIRIS instrument aboard the Odin satellite. The tomographic algorithm has been used to return local scattering coefficients at seven wavelengths in the ultraviolet. This spectral information is used to retrieve PMC particle sizes, number density, and ice mass density. While substantial horizontal variations are found, local vertical structures are overall consistent with the idea of a growth-sedimentation process leading to a visible cloud. Large numbers of small particles are present near the top of the observed cloud layer. Toward lower altitudes, particle sizes increase while particle number densities decrease. A close relationship is found between the distribution of local PMC scattering coefficient and ice mass density. The bottom of the cloud often features large particles with mode radii exceeding 70 nm that rain out of the cloud before sublimating. The number density of these large particles is small, and they do not contribute significantly to the overall cloud brightness. As a consequence, the presence of these large particles can be difficult to identify for remote sensing techniques that integrate over the entire cloud column. When it comes to deriving absolute values of particle mode radius and number density, there is a strong sensitivity to assumptions on the mathematical form of the particle size distribution. We see a continued strong need to resolve this issue by co-analysis of various remote sensing techniques and observation geometries.

Hultgren, Kristoffer; Gumbel, Jörg

2014-12-01

105

N-polar III-nitride quantum well light-emitting diodes with polarization-induced doping  

SciTech Connect

Nitrogen-polar III-nitride heterostructures present unexplored advantages over Ga(metal)-polar crystals for optoelectronic devices. This work reports N-polar III-nitride quantum-well ultraviolet light-emitting diodes grown by plasma-assisted molecular beam epitaxy that integrate polarization-induced p-type doping by compositional grading from GaN to AlGaN along N-face. The graded AlGaN layer simultaneously acts as an electron blocking layer while facilitating smooth injection of holes into the active region, while the built-in electric field in the barriers improves carrier injection into quantum wells. The enhanced doping, carrier injection, and light extraction indicate that N-polar structures have the potential to exceed the performance of metal-polar ultraviolet light-emitting diodes.

Verma, Jai; Simon, John; Protasenko, Vladimir; Kosel, Thomas; Xing, Huili Grace; Jena, Debdeep [Department of Electrical Engineering, University of Notre Dame, Indiana 46556 (United States)

2011-10-24

106

Gravitational Wave Induced Large-scale Polarization of \\\\Cosmic Microwave Background Radiation  

E-print Network

We discuss the contribution of gravitational wave to the cosmic microwave background radiation (CMBR) anisotropy and polarization. It is found that the large-scale polarization of CMBR is less than 1\\% for a standard recombination universe. The effect of matter reionization will enhance the CMBR polarization to a 10\\% level. We have computed the CMBR polarization for two extreme cases (not absolutely ruled out) and found that further enhancement of the ratio is possible. We conclude that measuring the polarization of CMBR on large-angular scales can probe the ionization history of the early universe, set constraints on baryon density and the spectral index of the gravitational waves.

Ka Lok Ng; Kin-Wang Ng

1994-06-30

107

Spectral Broadening in a Polarization-Maintaining Photonic Crystal Fibre by Femtosecond Pulses from an Optical Parametric Amplifier  

NASA Astrophysics Data System (ADS)

The spectral broadening with the bandwidth of 83 nm (1.2486-1.3318 ?m) in the 1.3 ?m region is achieved in a 0.2-m-long, polarization-maintaining photonic crystal fibre (PCF) with an average core radius of 1.8 ?m, pumped by optical pulses at the wavelength 1.269 ?m, with the duration 250 fs and the repetition rate 250 kHz from an optical parametric amplifier. The polarization characteristics of the output spectra are also investigated.

Yu, Yong-Qin; Ruan, Shuang-Chen; Cheng, Chao; Du, Chen-Lin; Liu, Cheng-Xiang; Lin, Hao-Jia

2005-02-01

108

Polarization-sensitive spectral-domain optical coherence tomography using a multi-line single camera spectrometer.  

PubMed

We describe a polarization sensitive spectral domain optical coherence tomography technique based on a single camera spectrometer that includes a multiplexed custom grating, camera lenses, and a high-speed three-line CCD camera. Two orthogonally polarized beams could be separately taken by two lines of the camera as a result of vertically different incident angles. The system could provide the imaging capabilities of a full camera speed and increased measurable depth. The proposed optical coherence tomography system could make a distinction between the normal muscle and cancerous tissue from the chest of a DSred GFP mouse and the OCT images were compared with those of in vivo confocal microscopy. PMID:21164725

Song, Cheol; Ahn, MyoungKi; Gweon, DaeGab

2010-11-01

109

Polarization pulling induced by Raman amplification in telecommunication optical fibers  

Microsoft Academic Search

We exploit the polarization dependence of the Raman amplification to obtain a polarization pulling effect in telecommunication optical fibers. Experiments carried out with 1571 nm signal and copropagating high-power 1486 nm pump evidence the polarization pulling.

P. Martelli; M. Cirigliano; M. Ferrario; L. Marazzi; M. Martinelli

2009-01-01

110

Spectral binning for mitigation of polarization mode dispersion artifacts in catheter-based optical frequency domain imaging  

PubMed Central

Polarization mode dispersion (PMD) has been recognized as a significant barrier to sensitive and reproducible birefringence measurements with fiber-based, polarization-sensitive optical coherence tomography systems. Here, we present a signal processing strategy that reconstructs the local retardation robustly in the presence of system PMD. The algorithm uses a spectral binning approach to limit the detrimental impact of system PMD and benefits from the final averaging of the PMD-corrected retardation vectors of the spectral bins. The algorithm was validated with numerical simulations and experimental measurements of a rubber phantom. When applied to the imaging of human cadaveric coronary arteries, the algorithm was found to yield a substantial improvement in the reconstructed birefringence maps. PMID:23938487

Villiger, Martin; Zhang, Ellen Ziyi; Nadkarni, Seemantini K.; Oh, Wang-Yuhl; Vakoc, Benjamin J.; Bouma, Brett E.

2013-01-01

111

Geometrically induced electric polarization in conical topological insulators  

E-print Network

We study the topological magnetoelectric effect on a conical topological insulator when a point charge $q$ is near the cone apex. The Hall current induced on the cone surface and the image charge configuration are determined. We also study a kind of gravitational Aharonov-Bohm effect in this geometry and realize a phase diference betwen the components of the wavefunctions (spinors) upon closed parallel transport around the (singular) cone tip. Concretely, a net current flowing towards cone apex (or botton) shows up, yielding electric polarization of the conical topological insulator. Such an effect may be detected, for instance, by means of the net accumulated Hall charge near the apex. Once it depends only on the geometry of the material (essetially, the cone apperture angle) this may be faced as a microscopic scale realization of (2+1)-dimensional Einstein gravity.

Jakson M. Fonseca; Winder A. Moura-Melo; Afranio R. Pereira

2011-11-29

112

Induced spectral broadening of a weak picosecond pulse in glass produced by an intense picosecond pulse  

SciTech Connect

Spectral broadening of a weak 80-..mu..J picosecond 530-nm laser pulse in a BK-7 glass has been enhanced over the entire spectral band by the presence of an intense millijoule picosecond 1060-nm laser pulse. The spectral distributions of the self-phase modulation and the induced-phase modulation signals are similar. The dominant enhancement mechanism for the induced supercontinuum was determined to be caused by an induced-phase modulation process, not by stimulated four-photon scattering.

Alfano, R.R.; Li, Q.X.; Jimbo, T.; Manassah, J.T.; Ho, P.P.

1986-10-01

113

[The multi-angle polarization spectral character of water and its applications in water color remote sensing].  

PubMed

The reflectance of pure water is very low at visible and near infrared bands. Its spectral characteristics are not obvious. Water always shows dark hue in optical remote sensing images. This dark hue causes the difficulties in water remote sensing identification. There is an interesting phenomenon when the authors research the water polarization spectroscopy. The authors measured water's polarization spectra and reflectance spectra at different view zenith angles using the ASD spectrometer. When the view zenith angle was zero (measured vertically), as the spectrum people commonly measure, there was no polarization phenomenon at the water surface, and the reflectance was low at each band. Along with the increase in view zenith angle, the DOP spectra curves increased evidently, while the reflectance curves only changed a little. When the view zenith angle was over 30 degree, the values of DOP spectrum were much larger than the reflectance spectrum values at the entire visible and near infrared bands. At some bands, the DOP value was several dozen times than its reflectance value. This phenomenon shows that the water's brightness in DOP image is much higher than its brightness in intensity image under the same condition. This rule was verified by the PARASOL multiangle polarization satellite data. Comparing the average brightness of DOP images with the average brightness of intensity images at 490, 670 and 865 nm band, the former is higher than the latter apparently. The brighter DOP images are better for water remote sensing identification It is the first time that the authors found this special multiangle polarization spectral character of water. It revealed the advantage of water detection using the multiangle polarization remote sensing data. This method solved the low reflectivity problem of water color remote sensing. It will greatly improve the capability of water remote sensing identification and the retrieval accuracy of water quality parameters. PMID:20384143

Wu, Tai-Xia; Yan, Lei; Xiang, Yun; Zhao, Yun-Sheng; Chen, Wei

2010-02-01

114

A nanoparticle catalyst for heterogeneous phase para-hydrogen-induced polarization in water.  

PubMed

Para-hydrogen-induced polarization (PHIP) is a technique capable of producing spin polarization at a magnitude far greater than state-of-the-art magnets. A significant application of PHIP is to generate contrast agents for biomedical imaging. Clinically viable and effective contrast agents not only require high levels of polarization but heterogeneous catalysts that can be used in water to eliminate the toxicity impact. Herein, we demonstrate the use of Pt?nanoparticles capped with glutathione to induce heterogeneous PHIP in water. The ligand-inhibited surface diffusion on the nanoparticles resulted in a (1) H?polarization of P=0.25?% for hydroxyethyl propionate, a known contrast agent for magnetic resonance angiography. Transferring the (1) H?polarization to a (13) C?nucleus using a para-hydrogen polarizer yielded a polarization of 0.013?%. The nuclear-spin polarizations achieved in these experiments are the first reported to date involving heterogeneous reactions in water. PMID:25565403

Glöggler, Stefan; Grunfeld, Alexander M; Ertas, Yavuz N; McCormick, Jeffrey; Wagner, Shawn; Schleker, P Philipp M; Bouchard, Louis-S

2015-02-16

115

Phonon-induced spectral holes in the gain region of an inverted semiconductor  

NASA Astrophysics Data System (ADS)

Spectral-hole-burning experiments are performed in the gain region of an inverted semiconductor multiple quantum well. We find not only a spectral hole at the pump-pulse frequency but also replicas at higher frequencies. These replicas are qualitatively explained in terms of carrier-phonon interactions in which high-energy carriers relax into the optically induced spectral hole by LO-phonon emission.

Mohs, G.; Binder, R.; Fluegel, B.; Gießen, H.; Peyghambarian, N.

1996-06-01

116

Strain-induced Polarization Rotation in Epitaxial (001) BiFeO3 Thin Films  

SciTech Connect

Direct measurement of the remanent polarization of high quality (001)-oriented epitaxial BiFeO3 thin films shows a strong strain-dependence, even larger than conventional (001)-oriented PbTiO3 films. Thermodynamic analysis reveals that a strain-induced polarization rotation mechanism is responsible for the large change in the out-of-plane polarization of (001) BiFeO3 with biaxial strain while the spontaneous polarization itself remains almost constant.

Jang, J H [Univeristy of Wisconsson; Baek, S H [University of Wisconsin; Ortiz, D [University of Wisconsin; Das, R [University of Wisconsin; Folkman, C H [University of Wisconsin; Chu, Y H [University of Wisconsin; Shafer, Paul [University of Wisconsin; Zhang, J X [University of Wisconsin; S, Choudhury [Pennsylvania State University; Vaithyanathan, V [Pennsylvania State University; Chen, Y B [University of Michigan; Felker, D A [University of Wisconsin; Biegalski, Michael D [ORNL; Rzchowski, M [University of Wisconsin; Pan, X Q [University of Michigan; Chen, Long-Qing [Pennsylvania State University; Schlom, Darrell [Pennsylvania State University; Ramesh, R. [University of California, Berkeley; Eom, Chang-Beom [ORNL

2008-01-01

117

Ion-induced nucleation in polar one-component fluids Hikaru Kitamuraa  

E-print Network

Ion-induced nucleation in polar one-component fluids Hikaru Kitamuraa and Akira Onuki Department; published online 27 September 2005 We present a Ginzburg-Landau theory of ion-induced nucleation in a gas phase of polar one-component fluids, where a liquid droplet grows with an ion at its center

118

3D induced-polarization data inversion for complex resistivity Michael Commer1  

E-print Network

3D induced-polarization data inversion for complex resistivity Michael Commer1 , Gregory A. Newman1, the routine three-dimensional (3D) interpretation of voluminous induced polarization (IP) data sets still for both exploration and envi- ronmental applications. We experimented with an image focus- ing technique

Hubbard, Susan

119

Induced Nucleon Polarization and Meson-Exchange Currents in (e,e'p) Reactions  

E-print Network

Nucleon recoil polarization observables in $(e,e'\\vec{p})$ reactions are investigated using a semi-relativistic distorted-wave model which includes one- and two-body currents with relativistic corrections. Results for the induced polarization asymmetry are shown for closed-shell nuclei and a comparison with available experimental data for $^{12}$C is provided. A careful analysis of meson exchange currents shows that they may affect significantly the induced polarization for high missing momentum.

F. Kazemi Tabatabaei; J. E. Amaro; J. A. Caballero

2004-02-02

120

Polarization of the fluorescence excited in erbium-doped fibers in 1490-1570 nm spectral range  

NASA Astrophysics Data System (ADS)

We present data on the polarization degree of the fluorescence, excited in erbium-doped fibers (EDF) by linearly polarized light at three essentially different wavelengths in the spectral range of the fundamental absorption of Er3+ (1492, 1526, and 1568 nm). Experiments were performed in otherwise similar single-mode fibers with a broad range of erbium concentration (?640-5600 wt ppm). The polarization degree of the fluorescence demonstrated expected decay with the incident light power and proved to be significantly weaker for the central excitation wavelength of 1526 nm. The maximum value of the experimentally observed effect (?0.3%) is significantly lower than it is predicted by model of the randomly oriented non-interacting dipoles. This discrepancy is explained by the reduced anisotropy (to the value 0.7-0.8) of the erbium ions absorption/emission, the effect which was utilized to explain the experimentally observed weak polarization hole burning in EDF earlier. Additional reduction in the fluorescence polarization degree and accelerated depolarization relaxation which were experimentally observed in fibers with high erbium concentration are attributed to the spatial migration of the excited state.

Martínez-Martínez, Liliana O.; Hernández-Hernández, Eliseo; Stepanov, Serguei

2013-11-01

121

Flow induced vibration of a cantilever column jet: a spectral analysis  

E-print Network

FLON INDUCED VIBRATION OF A CANTILEVER COLUMN JET ? A SPECTRAL ANALYSIS A Thesis by ROY BRYANT SHILLING III Submitted to the Graduate College of Texas A8M University ir, partial fulfillment of the requirement for the degree of MASTER... OF SCIENCE May 1978 Major Subject: Ocean Engineering FLOW INDUCED VIBRATION OF A CANTILEVER COLUMN JET - A SPECTRAL ANALYSIS A Thesis by ROY BRYANT SHILLING III Approved as to style and content by: (Chairman of Committee) (Head of Department) ember...

Shilling, Roy Bryant

2012-06-07

122

LINE-INTERLOCKING EFFECTS ON POLARIZATION IN SPECTRAL LINES BY RAYLEIGH AND RAMAN SCATTERING  

SciTech Connect

The polarized spectrum of the Sun and stars is formed from the scattering of anisotropic radiation on atoms. Interpretation of this spectrum requires the solution of polarized line transfer in multilevel atomic systems. While sophisticated quantum theories of polarized line formation in multilevel atomic systems exist, they are limited by the approximation of complete frequency redistribution in scattering. The partial frequency redistribution (PRD) in line scattering is a necessary component in modeling the polarized spectra of strong lines. The polarized PRD line scattering theories developed so far confine themselves to a two-level or a two-term atom model. In this paper, we present a heuristic approach to the problem of polarized line formation in multilevel atoms taking into account the effects of PRD and a weak magnetic field. Starting from the unpolarized PRD multilevel atom approach of Hubeny et al., we incorporate the polarization state of the radiation field. However, the lower level polarization is neglected. Two iterative methods of solving the polarized PRD line transfer in multilevel atoms are also presented. Taking the example of a five-level Ca II atom model, we present illustrative results for an isothermal one-dimensional model atmosphere.

Sampoorna, M.; Nagendra, K. N. [Indian Institute of Astrophysics, Koramangala, Bangalore 560 034 (India); Stenflo, J. O., E-mail: sampoorna@iiap.res.in, E-mail: knn@iiap.res.in, E-mail: stenflo@astro.phys.ethz.ch [Institute of Astronomy, ETH Zurich, CH-8093 Zurich (Switzerland)

2013-06-20

123

Polarized Parton Distribution in Neutrino Induced Heavy Flavor Production  

E-print Network

In order to examine polarized strange quark distribution, semi-inclusive $D/\\Dbar$ production in neutrino deep inelastic scattering is studied including ${\\cal O}(\\alpha_s)$ corrections. Cross section and spin asymmetry are calculated by using various parametrizations of polarized parton distribution functions. It is found that $\\Dbar$ production is promising to directly extract the polarized strange sea.

Kazutaka Sudoh

2002-12-05

124

Polarization-dependent narrowband spectral filtering by chiral sculptured thin films  

Microsoft Academic Search

We analyse theoretically transmission through two layers of different thin-film helicoidal bianisotropic mediums (TFHBMs), wherein the pitch of each layer bears a precisely determined relation to the overall thickness of the bi-layer. A spectral hole emerges from the interaction of the circular Bragg regimes of both TFHBM layers. Our results generalize a recently discovered scheme for producing spectral holes in

Martin W. McCall; Akhlesh Lakhtakia

2000-01-01

125

Polarization manipulation based on electromagnetically induced transparency-like (EIT-like) effect.  

PubMed

We proposed, designed and fabricated a high transparency of metasurface-based polarization controller at microwave frequencies, which consists of orthogonal two pairs of cut wires. The high transmission and the strong dispersion properties governed by electromagnetically induced transparency-like (EIT-like) effects for both incident polarizations make our device efficiently manipulating the polarization of EM waves. In particular, the proposed polarization device is ultrathin (~0.017?), as opposed to bulky polarization devices. Microwave experiments are performed to successfully demonstrate our ideas, and measured results are in reasonable agreement with numerical simulations. PMID:24514804

Zhu, Lei; Meng, Fan-Yi; Dong, Liang; Fu, Jia-Hui; Zhang, Fang; Wu, Qun

2013-12-30

126

Modulation of TNF-induced macrophage polarization by synovial fibroblasts.  

PubMed

Mesenchymal stromal cells have emerged as powerful modulators of the immune system. In this study, we explored how the human macrophage response to TNF is regulated by human synovial fibroblasts, the representative stromal cell type in the synovial lining of joints that become activated during inflammatory arthritis. We found that synovial fibroblasts strongly suppressed TNF-mediated induction of an IFN-? autocrine loop and downstream expression of IFN-stimulated genes (ISGs), including chemokines CXCL9 and CXCL10 that are characteristic of classical macrophage activation. TNF induced the production of soluble synovial fibroblast factors that suppressed the macrophage production of IFN-?, and cooperated with TNF to limit the responsiveness of macrophages to IFN-? by suppressing activation of Jak-STAT signaling. Genome-wide transcriptome analysis showed that cocultured synovial fibroblasts modulate the expression of approximately one third of TNF-regulated genes in macrophages, including genes in pathways important for macrophage survival and polarization toward an alternatively activated phenotype. Pathway analysis revealed that gene expression programs regulated by synovial fibroblasts in our coculture system were also regulated in rheumatoid arthritis synovial macrophages, suggesting that these fibroblast-mediated changes may contribute to rheumatoid arthritis pathogenesis. This work furthers our understanding of the interplay between innate immune and stromal cells during an inflammatory response, one that is particularly relevant to inflammatory arthritis. Our findings also identify modulation of macrophage phenotype as a new function for synovial fibroblasts that may prove to be a contributing factor in arthritis pathogenesis. PMID:25057003

Donlin, Laura T; Jayatilleke, Arundathi; Giannopoulou, Eugenia G; Kalliolias, George D; Ivashkiv, Lionel B

2014-09-01

127

Parahydrogen-induced polarization in heterogeneous catalytic processes.  

PubMed

Parahydrogen-induced polarization of nuclear spins provides enhancements of NMR signals for various nuclei of up to four to five orders of magnitude in magnetic fields of modern NMR spectrometers and even higher enhancements in low and ultra-low magnetic fields. It is based on the use of parahydrogen in catalytic hydrogenation reactions which, upon pairwise addition of the two H atoms of parahydrogen, can strongly enhance the NMR signals of reaction intermediates and products in solution. A recent advance in this field is the demonstration that PHIP can be observed not only in homogeneous hydrogenations but also in heterogeneous catalytic reactions. The use of heterogeneous catalysts for generating PHIP provides a number of significant advantages over the homogeneous processes, including the possibility to produce hyperpolarized gases, better control over the hydrogenation process, and the ease of separation of hyperpolarized fluids from the catalyst. The latter advantage is of paramount importance in light of the recent tendency toward utilization of hyperpolarized substances in in vivo spectroscopic and imaging applications of NMR. In addition, PHIP demonstrates the potential to become a useful tool for studying mechanisms of heterogeneous catalytic processes and for in situ studies of operating catalytic reactors. Here, the known examples of PHIP observations in heterogeneous reactions over immobilized transition metal complexes, supported metals, and some other types of heterogeneous catalysts are discussed and the applications of the technique for hypersensitive NMR imaging studies are presented. PMID:23097028

Kovtunov, Kirill V; Zhivonitko, Vladimir V; Skovpin, Ivan V; Barskiy, Danila A; Koptyug, Igor V

2013-01-01

128

Parahydrogen Induced polarization by homogeneous catalysis: theory and applications.  

PubMed

The alignment of the nuclear spins in parahydrogen can be transferred to other molecules by a homogeneously catalyzed hydrogenation reaction resulting in dramatically enhanced NMR signals. In this chapter we introduce the involved theoretical concepts by two different approaches: the well known, intuitive population approach and the more complex but more complete density operator formalism. Furthermore, we present two interesting applications of PHIP employing homogeneous catalysis. The first demonstrates the feasibility of using PHIP hyperpolarized molecules as contrast agents in (1)H MRI. The contrast arises from the J-coupling induced rephasing of the NMR signal of molecules hyperpolarized via PHIP. It allows for the discrimination of a small amount of hyperpolarized molecules from a large background signal and may open up unprecedented opportunities to use the standard MRI nucleus (1)H for, e.g., metabolic imaging in the future. The second application shows the possibility of continuously producing hyperpolarization via PHIP by employing hollow fiber membranes. The continuous generation of hyperpolarization can overcome the problem of fast relaxation times inherent in all hyperpolarization techniques employed in liquid-state NMR. It allows, for instance, the recording of a reliable 2D spectrum much faster than performing the same experiment with thermally polarized protons. The membrane technique can be straightforwardly extended to produce a continuous flow of a hyperpolarized liquid for MRI enabling important applications in natural sciences and medicine. PMID:23536243

Buljubasich, Lisandro; Franzoni, María Belén; Münnemann, Kerstin

2013-01-01

129

Satellite observations of polar mesospheric clouds by the solar backscattered ultraviolet spectral radiometer - Evidence of a solar cycle dependence  

NASA Technical Reports Server (NTRS)

Results are presented on eight years of satellite observations of the polar mesospheric clouds (PMCs) by the SBUV spectral radiometer, showing that PMCs occur in the summertime polar cap regions of both hemispheres and that they exhibit year-to-year variability. It was also found that the increase in the PMC occurrence frequency was inversely correlated with solar activity. Two kinds of hemispherical asymmetries could be identified: (1) PMCs in the Northern Hemisphere were significantly brighter than in the Southern Hemisphere, in accordance with previous results derived from SME data; and (2) the solar cycle response in the south is more pronounced than in the north. The paper also describes the cloud detection algorithm.

Thomas, Gary E.; Mcpeters, Richard D.; Jensen, Eric J.

1991-01-01

130

Method And Apparatus For Examining A Tissue Using The Spectral Wing Emission Therefrom Induced By Visible To Infrared Photoexcitation.  

DOEpatents

Method and an apparatus for examining a tissue using the spectral wing emission therefrom induced by visible to infrared photoexcitation. In one aspect, the method is used to characterize the condition of a tissue sample and comprises the steps of (a) photoexciting the tissue sample with substantially monochromatic light having a wavelength of at least 600 nm; and (b) using the resultant far red and near infrared spectral wing emission (SW) emitted from the tissue sample to characterize the condition of the tissue sample. In one embodiment, the substantially monochromatic photoexciting light is a continuous beam of light, and the resultant steady-state far red and near infrared SW emission from the tissue sample is used to characterize the condition of the tissue sample. In another embodiment, the substantially monochromatic photoexciting light is a light pulse, and the resultant time-resolved far red and near infrared SW emission emitted from the tissue sample is used to characterize the condition of the tissue sample. In still another embodiment, the substantially monochromatic photoexciting light is a polarized light pulse, and the parallel and perpendicular components of the resultant polarized time-resolved SW emission emitted from the tissue sample are used to characterize the condition of the tissue sample.

Alfano, Robert R. (3777 Independence Ave., Bronx, NY 10463); Demos, Stavros G. (3550 Pacific Ave., Apt. 304, Livermore, CA 94550); Zhang, Gang (3 Rieder Rd., Edison, NJ 08817)

2003-12-16

131

Retrieval of aerosol optical properties over a vegetation surface using multi-angular, multi-spectral, and polarized data  

NASA Astrophysics Data System (ADS)

An algorithm to retrieve aerosol optical properties using multi-angular, multi-spectral, and polarized data without a priori knowledge of the land surface was developed. In the algorithm, the surface polarized reflectance was estimated by eliminating the atmospheric scattering from measured polarized reflectance at 1640 nm. A lookup table (LUT) and an iterative method were adopted in the algorithm to retrieve the aerosol optical thickness (AOT, at 665 nm) and the Ångström exponent (computed between the AOTs at 665 and 865 nm). Experiments were performed in Tianjin to verify the algorithm. Data were provided by a newly developed airborne instrument, the Advanced Atmosphere Multi-angle Polarization Radiometer (AMPR). The AMPR measurements over the target field agreed well with the nearby ground-based sun photometer. An algorithm based on Research Scanning Polarimeter (RSP) measurements was introduced to validate the observational measurements along a flight path over Tianjin. The retrievals were consistent between the two algorithms. The AMPR algorithm shows potential in retrieving aerosol optical properties over a vegetation surface.

Wang, Han; Sun, Xiaobing; Sun, Bin; Liang, Tianquan; Li, Cuili; Hong, Jin

2014-07-01

132

Metallic nano-structures for polarization-independent multi-spectral filters  

PubMed Central

Cross-shaped-hole arrays (CSHAs) are selected for diminishing the polarization-dependent transmission differences of incident plane waves. We investigate the light transmission spectrum of the CSHAs in a thin gold film over a wide range of features. It is observed that two well-separated and high transmission efficiency peaks could be obtained by designing the parameters in the CSHAs for both p-polarized and s-polarized waves; and a nice transmission band-pass is also observed by specific parameters of a CSHA too. It implicates the possibility to obtain a desired polarization-independent transmission spectrum from the CSHAs by designing their parameters. These findings provide potential applications of the metallic nano-structures in optical filters, optical band-pass, optical imaging, optical sensing, and biosensors. PMID:21711927

2011-01-01

133

Sudden Death of Entanglement induced by Polarization Mode Dispersion  

E-print Network

We study the decoherence of polarization-entangled photon pairs subject to the effects of polarization mode dispersion, the chief polarization decoherence mechanism in optical fibers. We show that fiber propagation reveals an intriguing interplay between the concepts of entanglement sudden death, decoherence-free sub-spaces and non-locality. We define the boundaries in which entanglement-based quantum communications protocols relying on fiber propagation can be applied.

Cristian Antonelli; Mark Shtaif; Misha Brodsky

2011-01-27

134

Lambda and Lambda-bar Polarization in Lepton Induced Processes  

E-print Network

The study of the longitudinal polarization of Lambda and Lambda-bar hyperons produced in polarized deep inelastic scattering, neutrino scattering, and in Z0 decays allows to access the spin dynamics of the quark fragmentation process. Different phenomenological spin transfer mechanisms are considered and predictions for the Lambda and Lambda-bar longitudinal polarization in various processes using unpolarized and polarized targets are made. Current and future semi-inclusive deep inelastic scattering experiments will provide soon accurate enough data to study these phenomena and distinguish between various models for the spin transfer mechanisms.

A. Kotzinian; A. Bravar; D. von Harrach

1997-01-27

135

Spectral-Content Readout Of Stress-Induced Birefringence  

NASA Technical Reports Server (NTRS)

Spectrum of transmitted light indicates stress in sensor or specimen. Photoelastic apparatus demonstrates feasibility of analysis of spectrum of transmitted light to quantify birefringence in transparent specimen. By augmenting conventional photoelastic analysis with spectral sensors and automating it with computer control and processing of data, technique made more versatile and useful. Potential uses include measurement of stresses in optical fibers and transparent materials in general.

Redner, Alex S.; Voloshin, Arkady S.

1992-01-01

136

A Signaling Network Induced by ?2 Integrin Controls the Polarization of Lytic Granulesin Cytotoxic Cells  

PubMed Central

Cytotoxic lymphocyte skill target cells by polarized release of the content of perforin-containing granules. In natural killer cells, the binding of ?2 integrin to its ligand ICAM-1 is sufficient to promote not only adhesion but also lytic granule polarization. This provided a unique opportunity to study polarization in the absence of degranulation, and ?2 integrin signaling independently of inside-out signals from other receptors. Using an unbiased proteomics approach we identified a signaling network centered on an integrin-linked kinase (ILK)–Pyk2–Paxillin core that was required for granule polarization. Downstream of ILK, the highly conserved Cdc42–Par6 signaling pathway that controls cell polarity was activated and required for granule polarization. These results delineate two connected signaling networks induced upon ?2 integrin engagement alone, which are integrated to control polarization of the microtubule organizing center and associated lytic granules toward the site of contact with target cells during cellular cytotoxicity. PMID:25292215

Zhang, Minggang; March, Michael E.; Lane, William S.; Long, Eric O.

2014-01-01

137

Rotational effect of fissile nucleus in binary fission of 235U induced by cold polarized neutrons  

Microsoft Academic Search

We have found a small inclination of the symmetry axis of the prompt fission gamma-quanta angular distribution relative to the “fission axis” in binary fission of 235U induced by cold polarized neutrons using the neutron beam line V13 at Berlin Neutron Scattering Center (BENSC). The sign of the shift depends on the direction of the cold neutron beam polarization and

G. V. Danilyan; P. Granz; V. A. Krakhotin; F. Mezei; V. V. Novitsky; V. S. Pavlov; M. Russina; P. B. Shatalov; T. Wilpert

2009-01-01

138

Spectral-Polarization Properties and Light Resistance of Polyvinyl-Alcohol Films Colored With Disazo Dyes  

NASA Astrophysics Data System (ADS)

Polarizers containing disazo dyes from the group of azobenzene-azonaphthalene have been developed. It has been established that their polarizing ability is determined by the mutual disposition of the azo group and electron-donor substituents in the naphthalene ring. On diazo coupling of ? acid into the ? position relative to the oxy group, the M1 and M3 dyes are formed, the polarizing ability of which in uniaxially oriented polyvinyl-alcohol films is higher than in the M2 dye produced as a result of diazo coupling into the ? position relative to the amino group. On irradiation by UV light, the dyes are subjected to photodestruction, which, in the case of M2, proceeds through trans-cis-isomerization. The rate of photodestruction depends on the aggregation of the dye molecules, and it increases in the presence of a free-radical initiator. The UV absorber (substituted benzotriazole) and the uniaxial orientation of the film retard this process.

Fillipovich, L. N.; Ariko, N. G.; Agabekov, V. E.; Malashko, P. M.

2005-09-01

139

Polar Solvent-induced Changes in Membrane Lipid Lateral Diffusion in Human Colon Cancer Cells  

Microsoft Academic Search

Polar organic solvents, such as A\\/-methylformamide (NMF), A\\/,A\\/-dimethylformamide, and dimethyl sulfoxide, have been dem onstrated to induce differentiation in a number of neoplastic cell lines, including human colon cancer cells. Although the mecha nism of action of these agents is yet unknown, one possibility is that polar solvents induce a change in lateral mobility of mem brane lipids, important to

Mark D. Dibner; Kathleen A. Ireland; Louise A. Koerner; Daniel L. Dexter

140

Multiple-view spectrally resolved x-ray imaging observations of polar-direct-drive implosions on OMEGA  

NASA Astrophysics Data System (ADS)

We present spatially, temporally, and spectrally resolved narrow- and broad-band x-ray images of polar-direct-drive (PDD) implosions on OMEGA. These self-emission images were obtained during the deceleration phase and bang time using several multiple monochromatic x-ray imaging instruments fielded along two or three quasi-orthogonal lines-of-sight, including equatorial and polar views. The instruments recorded images based on K-shell lines from a titanium tracer located in the shell as well as continuum emission. These observations constitute the first such data obtained for PDD implosions. The image data show features attributed to laser imprinting and zero-order hydrodynamics. Equatorial-view images show a "double bun" structure that is consistent with synthetic images obtained from post-processing 2D and 3D radiation-hydrodynamic simulations of the experiment. Polar-view images show a pentagonal, petal pattern that correlates with the PDD laser illumination used on OMEGA, thus revealing a 3D aspect of PDD OMEGA implosions not previously observed. Differences are noted with respect to a PDD experiment performed at National Ignition Facility.

Mancini, R. C.; Johns, H. M.; Joshi, T.; Mayes, D.; Nagayama, T.; Hsu, S. C.; Baumgaertel, J. A.; Cobble, J.; Krasheninnikova, N. S.; Bradley, P. A.; Hakel, P.; Murphy, T. J.; Schmitt, M. J.; Shah, R. C.; Tregillis, I. L.; Wysocki, F. J.

2014-12-01

141

Optimized Spectral Editing of 13C MAS NMR Spectra of Rigid Solids Using Cross-Polarization Methods  

NASA Astrophysics Data System (ADS)

Combinations of 13C magic-angle spinning (MAS) NMR experiments employing cross polarization (CP), cross polarization-depolarization (CPD), and cross polarization-depolarization-repolarization are analyzed quantitatively to derive simple and general procedures for optimized spectral editing of 13C CP/MAS NMR spectra of rigid solids by separation of the 13C resonances into CH n subspectra ( n = 0, 1, 2, and 3). Special attention is devoted to a differentiation by CPD/MAS of CH and CH 2 resonances since these groups behave quite similarly during spin lock under Hartmann-Hahn match and are therefore generally difficult to distinguish unambiguously. A general procedure for the design of subexperiments and linear combinations of their spectra to provide optimized signal-to-noise ratios for the edited subspectra is described. The technique is illustrated by a series of edited 13C CP/MAS spectra for a number of rigid solids ranging from simple organic compounds (sucrose and l-menthol) to complex pharmaceutical products (calcipotriol monohydrate and vitamin D 3) and polymers (polypropylene, polyvinyl alcohol, polyvinyl chloride, and polystyrene).

Sangill, R.; Rastrupandersen, N.; Bildsoe, H.; Jakobsen, H. J.; Nielsen, N. C.

142

Effect of PDL-induced coherent crosstalk on polarization-division-multiplexed direct-detection systems.  

PubMed

We analyze the effect of polarization-dependent loss (PDL) on the performance of the polarization-division-multiplexed (PDM) signals in direct-detection systems. We present the theoretical analysis of the sensitivity penalty caused by PDL-induced coherent crosstalk and compare the results with experimental data obtained by using a simple variable PDL emulator based on a LiNbO3 Mach-Zehnder modulator. Also presented is the performance degradation caused by the polarization misalignment between the received signals and the polarization beam splitter at the receiver in the presence of PDL. PMID:19188943

Ji, Ho-Chul; Lee, J H; Kim, Hoon; Park, Paul K J; Chung, Y C

2009-02-01

143

Interaction induced deformation in momentum distribution of spin polarized nuclear matter  

E-print Network

Effects of spin polarization on the structure of symmetric nuclear matter and pure neutron matter are investigated. We show that the spin polarization induces a deformation of the Fermi spheres for nucleons with spin parallel and opposite to the polarization axes. This feature can be related to the structure of the one pion exchange contribution to a realistic nucleon-nucleon interaction. While the anisotropies in the momentum distribution lower the energy of the system by small amount, the associated variations of the single particle energies with the angle between the polarization axis and the particle momentum are significant.

T. Frick; H. Müther; A. Sedrakian

2002-03-19

144

Circular Polarization Induced by Scintillation in a Magnetized Medium  

E-print Network

A new theory is presented for the development of circular polarization as radio waves propagate through the turbulent, birefringent interstellar medium. The fourth order moments of the wavefield are calculated and it is shown that unpolarized incident radiation develops a nonzero variance in circular polarization. A magnetized turbulent medium causes the Stokes parameters to scintillate in a non-identical manner. A specific model for this effect is developed for the case of density fluctuations in a uniform magnetic field.

J. -P. Macquart; D. B. Melrose

2000-06-30

145

Nonvolatile data storage using mechanical force-induced polarization switching in ferroelectric polymer  

NASA Astrophysics Data System (ADS)

Ferroelectric polymers offer the promise of low-cost and flexible electronic products. They are attractive for information storage due to their spontaneous polarization which is usually switched by electric field. Here, we demonstrate that electrical signals can be readily written on ultra-thin ferroelectric polymer films by strain gradient-induced polarization switching (flexoelectric effect). A force with magnitude as small as 64nN is enough to induce highly localized (40 nm feature size) change in the polarization states. The methodology is capable of realizing nonvolatile memory devices with miniaturized cell size and storage density of tens to hundreds Gbit per square inch.

Chen, Xin; Tang, Xin; Chen, Xiang-Zhong; Chen, Yu-Lei; Guo, Xu; Ge, Hai-Xiong; Shen, Qun-Dong

2015-01-01

146

Current-Induced Spin Polarization in Anisotropic Spin-Orbit Fields  

NASA Astrophysics Data System (ADS)

The magnitude and direction of current-induced spin polarization and spin-orbit splitting are measured in In0.04Ga0.96 As epilayers as a function of in-plane electric and magnetic fields. We show that, contrary to expectation, the magnitude of the current-induced spin polarization is smaller for crystal directions corresponding to larger spin-orbit fields. Furthermore, we find that the steady-state in-plane spin polarization does not align along the spin-orbit field, an effect due to anisotropy in the spin relaxation rate.

Norman, B. M.; Trowbridge, C. J.; Awschalom, D. D.; Sih, V.

2014-02-01

147

Interfacial polarization and pyroelectricity in antiferrodistortive structures induced by a flexoelectric effect and rotostriction  

NASA Astrophysics Data System (ADS)

Theoretical analysis based on the Landau-Ginzburg-Devonshire theory is used to show that the combined effect of flexoelectricity and rotostriction can lead to a spontaneous polarization and pyroelectricity in the vicinity of antiphase boundaries, structural twin walls, surfaces, and interfaces in the octahedrally tilted phase of otherwise nonferroelectric perovskites such as CaTiO3, SrTiO3, and EuTiO3. As an example, we numerically demonstrate a spontaneous polarization and pyroelectric response at the SrTiO3 antiphase and twin boundaries at temperatures lower than the antiferrodistortive structural phase transition temperature of TS˜105 K in agreement with previously unexplained experimental results. At temperatures lower than effective Curie temperature TC* (˜25 K for twins and ˜50 K for antiphase boundaries) biquadratic coupling between oxygen octahedron tilt and polarization vectors essentially enhances the polarization induced by the combined flexoelectric and rotostriction effects near the hard domain wall. Biquadratic coupling cannot induce polarization inside easy twins and antiphase boundaries; their polarization and pyroelectricity originates below TS from the built-in flexoelectric field. The spontaneous polarization reaches the values ˜0.1-5 ?C/cm2 at the SrTiO3 antiphase boundaries and twins without free charges. A principal difference between the influence of biquadratic and flexoelectric couplings on the interfacial polarization is the following: the biquadratic coupling induces bistable ferroelectric polarization inside hard antiphase boundaries and hard twins below TC*, while the flexoelectric coupling induces improper spontaneous polarization via the flexoelectric field below TS.

Morozovska, Anna N.; Eliseev, Eugene A.; Glinchuk, Maya D.; Chen, Long-Qing; Gopalan, Venkatraman

2012-03-01

148

Phase-resolved X-ray spectroscopy and spectral energy distribution of the X-ray soft polar RS Caeli  

NASA Astrophysics Data System (ADS)

Context. RS Cae is the third target in our series of XMM-Newton observations of soft X-ray-dominated polars. Aims: Our observational campaign aims to better understand and describe the multiwavelength data, the physical properties of the system components, and the short- and long-term behavior of the component fluxes in RS Cae. Methods: We employ stellar atmosphere, stratified accretion-column, and widely used X-ray spectral models. We fit the XMM-Newton spectra, model the multiband light curves, and opt for a mostly consistent description of the spectral energy distribution. Results: Our XMM-Newton data of RS Cae are clearly dominated by soft X-ray emission. The X-ray light curves are shaped by emission from the main accretion region, which is visible over the whole orbital cycle, interrupted only by a stream eclipse. The optical light curves are formed by cyclotron and stream emission. The XMM-Newton X-ray spectra comprise a black-body-like and a plasma component at mean temperatures of 36 eV and 7 keV. The spectral fits give evidence of a partially absorbing and a reflection component. Multitemperature models, covering a broader temperature range in the X-ray emitting accretion regions, reproduce the spectra appropriately well. Including archival data, we describe the spectral energy distribution with a combination of models based on a consistent set of parameters and derive a lower limit estimate of the distance d ? 750 pc. Conclusions: The high bolometric soft-to-hard flux ratios and short-term variability of the (X-ray) light curves are characteristic of inhomogeneous accretion. RS Cae clearly belongs in the group of polars that show a very strong soft X-ray flux compared to their hard X-ray flux. The different black-body fluxes and similar hard X-ray and optical fluxes during the XMM-Newton and ROSAT observations show that soft and hard X-ray emission are not directly correlated. Based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA.

Traulsen, I.; Reinsch, K.; Schwope, A. D.; Schwarz, R.; Walter, F. M.; Burwitz, V.

2014-02-01

149

Detection and calculation of reflected spectral shifts in fiber-Bragg gratings (FBG) in polarization maintaining optical fiber  

NASA Astrophysics Data System (ADS)

Fiber-Bragg Gratings (FBG) for Structural Health Monitoring (SHM) have been studied extensively as they offer electrically passive operation, EMI immunity, high sensitivity, and multiple multiplexing schemes, as compared to conventional electricity based strain sensors. FBG sensors written in Polarization Maintaining (PM) optical fiber offer an additional dimension of strain measurement simplifying sensor implementation within a structure. This simplification however, adds complexity to the detection of the sensor's optical response to its corresponding applied strain. We propose a method that calculates spectral shifts caused by axial and traversal strains for PM FBG sensors. The system isolates the orthogonal propagating optical waves incident to the optical interrogators. The post-processing algorithm determines the wavelength shifts, and compares to a predetermined baseline then correlates the shift magnitudes to a respective strain. This exercise validates the method of optical detection and shift calculation of multi-axis sensors as an automated, integrated system.

Quintana, Joel; Gonzalez, Virgilio

2014-04-01

150

CMB-induced Cluster Polarization as a Cosmological Probe  

E-print Network

Scattering of the temperature anisotropy quadrupole by free electrons in galaxy clusters leads to a secondary polarization signal in the cosmic microwave background (CMB) fluctuations. At low redshifts, the temperature quadrupole contains a significant contribution from the integrated Sachs-Wolfe (ISW) effect associated with the growth of density fluctuations. Using polarization data from a sample of clusters over a wide range in redshift, one can statistically establish the presence of the ISW effect and determine its redshift evolution. Given the strong dependence of the ISW effect on the background cosmology, cluster polarization can eventually be used as a powerful probe of dark energy. As a further application, we also discuss how it might be used to understand the potential lack of power on large scales.

Daniel Baumann; Asantha Cooray

2003-04-23

151

Valley polarization induced second harmonic generation in graphene  

NASA Astrophysics Data System (ADS)

The valley degeneracy of electron states in graphene stimulates intensive research of valley-related optical and transport phenomena. While many proposals on how to manipulate valley states have been put forward, experimental access to the valley polarization in graphene is still a challenge. Here, we develop a theory of the second optical harmonic generation in graphene and show that this effect can be used to measure the degree and sign of the valley polarization. We show that, at the normal incidence of radiation, the second harmonic generation stems from an imbalance of carrier populations in the valleys. The effect has a specific polarization dependence reflecting the trigonal symmetry of the electron valley and is resonantly enhanced if the energy of the incident photons is close to the Fermi energy.

Golub, L. E.; Tarasenko, S. A.

2014-11-01

152

Raman-induced rotational coherence in gaseous molecules observed by the ultrafast polarization spectroscopy  

Microsoft Academic Search

Raman-induced rotational coherence in the ground vibronic state of gaseous molecules, air, nitrogen, and oxygen, was studied by using the femtosecond polarization spectroscopy. Coherence-burst signals due to the rotational coherences were observed in picosecond region. Their Fourier spectra give the frequencies of the induced coherences between the rotational levels.

T. Kohmoto; Y. Fukuda; M. Kunitomo

2000-01-01

153

Spectral analysis of induced color change on periodically nanopatterned silk films  

E-print Network

Spectral analysis of induced color change on periodically nanopatterned silk films Jason J. Amsden1 on periodic nanopatterned 2D lattices in pure protein films of silk fibroin. We show here periodic lattices in silk fibroin films with feature sizes of hundreds of nanometers that exhibit different colors

154

Spectral analysis of seismic noise induced by rivers: A new tool to monitor spatiotemporal changes in  

E-print Network

Spectral analysis of seismic noise induced by rivers: A new tool to monitor spatiotemporal changes and deeply incised channel of the Trisuli River, a major trans-Himalayan river. The early summer increase the Trisuli River. Seasonal increase in ambient noise coincides with the strong monsoon rainfall and a period

Demouchy, Sylvie

155

The inference of vector magnetic fields from polarization measurements with limited spectral resolution  

NASA Technical Reports Server (NTRS)

A method is presented for recovery of the vector magnetic field and thermodynamic parameters from polarization measurement of photospheric line profiles measured with filtergraphs. The method includes magneto-optic effects and may be utilized on data sampled at arbitrary wavelengths within the line profile. The accuracy of this method is explored through inversion of synthetic Stokes profiles subjected to varying levels of random noise, instrumental wave-length resolution, and line profile sampling. The level of error introduced by the systematic effect of profile sampling over a finite fraction of the 5 minute oscillation cycle is also investigated. The results presented here are intended to guide instrumental design and observational procedure.

Lites, B. W.; Skumanich, A.

1985-01-01

156

Broadening, shift and polarization of spectral line emitted from hollow cathode discharge  

NASA Astrophysics Data System (ADS)

The radial behavior of hollow cathode discharge (HCD) proper emission function has been studied by using a double Fabri-Perot interferogram, i.e., simultaneous recording of spectral line shapes, emitted from two different regions. Radial inhomogeneity and shift of the line shape center are established at buffer gas pressure lower than 0.3 Torr. At these pressures electric field in cathode dark space is concluded/found to penetrate into the negative glow and keeping the fast electron radial vector. It is a precondition for self-alignment of the atoms in HCD. The optical manifestation of this coherence is observed.

Zhechev, D.; Parvanova, N.

2002-11-01

157

HIGH-FREQUENCY RADIO SPECTRAL ENERGY DISTRIBUTIONS AND POLARIZATION FRACTIONS OF SOURCES IN AN ATACAMA COSMOLOGY TELESCOPE SURVEY FIELD  

SciTech Connect

We present flux densities and polarization percentages of 159 radio galaxies based on nearly simultaneous Very Large Array observations at four frequencies, 4.86, 8.46, 22.46, and 43.34 GHz. This sample is selected from the high-frequency Australia Telescope 20 GHz (AT20G) survey and consists of all sources with flux density S{sub 20GHz} > 40 mJy in an equatorial field of the Atacama Cosmology Telescope (ACT) survey. For a subset of 25 of these sources, we used the Green Bank Telescope (GBT) to obtain 90 GHz data. The goals of this program are: (1) a characterization of the spectra, polarization, and variability of high-frequency-selected radio sources, (2) extrapolating from the few GHz regime to the {approx}150 GHz regime of the ACT survey, allowing for more accurate removal of the radio source signal in our particular field, and (3) providing a data set that will allow more accurate modeling of the high-frequency radio source contamination in current and future Sunyaev-Zeldovich and cosmic microwave background experiments. We find that, as expected, this sample consists of flatter spectrum and more compact or point-like sources than low-frequency-selected samples. In the K band, variability is typically {approx}<20%, although there are exceptions. The higher frequency data are well suited to the detection of extreme gigahertz peak spectrum sources. The inclusion of the 43 GHz data causes the relative fraction of inverted spectrum sources to go down and of peaked spectrum sources to go up when compared with the AT20G survey results. The trend largely continues with the inclusion of the 90 GHz data, although {approx}10% of the sources with GBT data show a spectral upturn from 43 GHz to 90 GHz. The measured polarization fractions are typically <5%, although in some cases they are measured to be up to {approx}20%. For sources with detected polarized flux in all four bands, about 40% of the sample, the polarization fractions typically increase with frequency. This trend is stronger for steeper spectrum sources as well as for the lower flux density sources.

Sajina, Anna [Department of Physics and Astronomy, Tufts University, Medford, MA 02155 (United States); Partridge, Bruce; Evans, Tyler; Vechik, Nicholas [Department of Physics and Astronomy, Haverford College, Haverford, PA 19041 (United States); Stefl, Shannon [Kent State University, Kent, OH 44242 (United States); Myers, Steve [National Radio Astronomy Observatory, Socorro, NM 87801 (United States); Dicker, Simon; Korngut, Phillip [Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, PA 19104 (United States)

2011-05-01

158

Possible methane-induced polar warming in the early Eocene.  

PubMed

Reconstructions of early Eocene climate depict a world in which the polar environments support mammals and reptiles, deciduous forests, warm oceans and rare frost conditions. At the same time, tropical sea surface temperatures are interpreted to have been the same as or slightly cooler than present values. The question of how to warm polar regions of Earth without noticeably warming the tropics remains unresolved; increased amounts of greenhouse gases would be expected to warm all latitudes equally. Oceanic heat transport has been postulated as a mechanism for heating high latitudes, but it is difficult to explain the dynamics that would achieve this. Here we consider estimates of Eocene wetland areas and suggest that the flux of methane, an important greenhouse gas, may have been substantially greater during the Eocene than at present. Elevated methane concentrations would have enhanced early Eocene global warming, and also might specifically have prevented severe winter cooling of polar regions because of the potential of atmospheric methane to promote the formation of optically thick, polar stratospheric ice clouds. PMID:11536496

Sloan, L C; Walker, J C; Moore, T C; Rea, D K; Zachos, J C

1992-05-28

159

X-ray polarization fluctuations induced by cloud eclipses in active galactic nuclei  

NASA Astrophysics Data System (ADS)

Context. A fraction of active galactic nuclei (AGN) show dramatic X-ray spectral changes on the day-to-week time scales associated with variation in the line of sight of the cold absorber. Aims: We intend to model the polarization fluctuations arising from an obscuration event, thereby offering a method of determining whether flux variations are due to occultation or extreme intrinsic emission variability. Methods: Undertaking 1-100 keV polarimetric simulations with the Monte Carlo code Stokes, we simulated the journey of a variety of cold gas clouds in front of an extended primary source. We varied the hydrogen column density nH and size of the absorber, as well as the initial polarization state of the emitting source, to cover a wide range of scenarios. Results: Simulations indicate that different results are expected according to the initial polarization of the extended continuum source. For unpolarized primary fluxes, large (~50°) variations of the polarization position angle ? are expected before and after an occultation event, which is associated with very low residual polarization degrees (P ? 1%). In the case of an emitting disk with intrinsic, position-independent polarization, and for a given range of parameters, X-ray eclipses significantly alter the observed polarization spectra, with most of the variations seen in ?. Finally, non-uniformly polarized emitting regions produce very distinctive polarization variations due to the successive covering and uncovering of different portions of the disk. Plotted against time, variations in P and ? form detectable P Cygni type profiles that are distinctive signatures of non-axisymmetric emission. Conclusions: We find that X-ray polarimetry is particularly adapted to probing X-ray eclipses due to Compton-thin and Compton-thick gas clouds. Polarization measurements would distinguish between intrinsic intensity fluctuations and external eclipsing events, constrain the geometry of the covering medium, and test the hypothesis of non-uniformly emitting disks predicted by general relativity.

Marin, F.; Dov?iak, M.

2015-01-01

160

Sensing and compensation of femtosecond waveform distortion induced by all-order  

E-print Network

Sensing and compensation of femtosecond waveform distortion induced by all-order polarization mode of femtosecond pulse distortion induced by all-order polarization mode dispersion (PMD) at selected polarization of spectral phase distortions induced by all-order PMD. Since our FROG setup is polarization sensitive

Purdue University

161

Theoretical study of polarization insensitivity of carrier-induced refractive index change of multiple quantum well.  

PubMed

Characteristics of polarization insensitivity of carrier-induced refractive index change of 1.55 ?m tensile-strained multiple quantum well (MQW) are theoretically investigated. A comprehensive MQW model is proposed to effectively extend the application range of previous models. The model considers the temperature variation as well as the nonuniform distribution of injected carrier in MQW. Tensile-strained MQW is expected to achieve polarization insensitivity of carrier-induced refractive index change over a wide wavelength range as temperature varies from 0°C to 40°C, while the magnitude of refractive index change keeps a large value (more than 3 × 10-3). And that the polarization insensitivity of refractive index change can maintain for a wide range of carrier concentration. Multiple quantum well with different material and structure parameters is anticipated to have the similar polarization insensitivity of refractive index change, which shows the design flexibility. PMID:25607157

Miao, Qingyuan; Zhou, Qunjie; Cui, Jun; He, Ping-An; Huang, Dexiu

2014-12-29

162

Passive polarization agile antenna based on the electromagnetically induced transparency-like effect  

NASA Astrophysics Data System (ADS)

We propose a design method for a passive polarization agile antenna based on the electromagnetically induced transparency-like (EIT-like) effect. Benefiting from strong dispersion properties governed by EIT-like effects, the proposed structure can endow electromagnetic waves transmitted through it with quite different polarization states at very close frequencies. The experimental measurement was conducted to demonstrate agile polarization controls by placing a designed EIT-like waveplate in front of a standard microwave horn antenna. Results show that the polarization state of radiated waves by the horn antenna with a waveplate can be easily transformed among linear, circular and elliptical polarizations through fine-tuning the operating frequency, which is extremely important for certain special applications, e.g. electronic countermeasures. Our scheme could also be utilized at higher operating frequencies by the simply scaling principle.

Zhu, Lei; Meng, Fan-Yi; Wu, Qun; Dong, Liang; Chen, Wan; Fu, Jia-Hui

2014-10-01

163

Fluorescent probing of protein bovine serum albumin stability and denaturation using polarity sensitive spectral response of a charge transfer probe.  

PubMed

The polarity sensitive photo-induced intra-molecular charge transfer (ICT) fluorescence probe (E)-3-(4-methylamino-phenyl)-acrylic acid ethyl ester (MAPAEE) has been used to study the model protein Bovine Serum Albumin (BSA) in its native and thermal and urea induced denatured states. The interaction between BSA and the regular surfactant Sodium Dodecyl Sulphate (SDS) as well as the biologically relevant steroid-based amphiphile Sodium Deoxycholate (NaDC) has also been very keenly followed using this ICT probe. The variation of micellar properties of both SDS and NaDC with increasing ionic strengths and in presence of the chaotrope urea has also been well documemted by the same probe. Steady-state spectroscopy, FRET, and fluorescence anisotropy measurements have been used to gain better insight into these processes and the molecule MAPAEE to be a full-bodied fluorescent probe for studying such intricate biological systems, their properties and interactions. PMID:20922468

Ghosh, Shalini; Jana, Sankar; Nath, Debnarayan; Guchhait, Nikhil

2011-01-01

164

Spectral Modifications and Polarization Dependent Coupling in Tailored Assemblies of Quantum Dots and Plasmonic Nanowires  

PubMed Central

The coupling of optical emitters with a nanostructured environment is at the heart of nano- and quantum optics. We control this coupling by the lithographic positioning of a few (1–3) quantum dots (QDs) along plasmonic silver nanowires with nanoscale resolution. The fluorescence emission from the QD-nanowire systems is probed spectroscopically, by microscopic imaging and decay time measurements. We find that the plasmonic modes can strongly modulate the fluorescence emission. For a given QD position, the local plasmon field dictates the coupling efficiency, and thus the relative weight of free space radiation and emission into plasmon modes. Simulations performed with a generic few-level model give very good agreement with experiment. Our data imply that the 2D degenerate emission dipole orientation of the QD can be forced to predominantly emit to one polarization component dictated by the nanowire modes. PMID:23968490

2013-01-01

165

Adaptation of the University of Wisconsin High Spectral Resolution Lidar for Polarization and Multiple Scattering Measurements  

NASA Technical Reports Server (NTRS)

Quantitative lidar measurements of aerosol scattering are hampered by the need for calibrations and the problem of correcting observed backscatter profiles for the effects of attenuation. The University of Wisconsin High Spectral Resolution Lidar (HSRL) addresses these problems by separating molecular scattering contributions from the aerosol scattering; the molecular scattering is then used as a calibration target that is available at each point in the observed profiles. While the HSRl approach has intrinsic advantages over competing techniques, realization of these advantages requires implementation of a technically demanding system which is potentially very sensitive to changes in temperature and mechanical alignments. This paper describes a new implementation of the HSRL in an instrumented van which allows measurements during field experiments. The HSRL was modified to measure depolarization. In addition, both the signal amplitude and depolarization variations with receiver field of view are simultaneously measured. This allows for discrimination of ice clouds from water clouds and observation of multiple scattering contributions to the lidar return.

Eloranta, E. W.; Piironen, P. K.

1996-01-01

166

Femtosecond Raman induced polarization spectroscopy studies of coherent rotational dynamics in molecular fluids  

SciTech Connect

We develop a polarization-sensitive femtosecond pump probe technique, Raman induced polarization spectroscopy (RIPS), to study coherent rotation in molecular fluids. By observing the collisional dephasing of the coherently prepared rotational states, we are able to extract information concerning the effects of molecular interactions on the rotational motion. The technique is quite sensitive because of the zero background detection method, and is also versatile due to its nonresonant nature.

Morgen, M.M. [Univ. of California, Berkeley, CA (United States). Dept. of Chemistry; [Lawrence Berkeley National Lab., CA (United States)

1997-05-01

167

Polarization-dependent single-beam laser-induced grating-like effects on titanium films  

Microsoft Academic Search

In this paper we present results on polarization-dependent laser-induced effects on titanium (Ti) thin films. We irradiated the titanium films, in ambient air, using a nanosecond Nd:YAG laser (532nm, 9ns pulse duration, 10Hz). Using a series of pulses of fluence well below the ablation threshold, it was possible to form grating-like structures, whose grooves run parallel to the linear polarization

Santiago Camacho-López; Rodger Evans; Luis Escobar-Alarcón; Miguel A. Camacho-López; Marco A. Camacho-López

2008-01-01

168

The effects of XPM-induced fast polarization-state fluctuations on PMD compensated WDM systems  

Microsoft Academic Search

We show numerically and experimentally the system degradation caused by cross-phase modulation-induced fast polarization fluctuations in wavelength-division-multiplexing systems that use polarization-mode dispersion compensation. A simple pump-probe model is used to investigate this effect and a technique is proposed to mitigate this problem. For a 10-Gb\\/s system with a 40-ps differential group delay compensator, the significant improvement is achieved over standard

Z. Pan; Q. Yu; Y. Arieli; A. E. Willner

2004-01-01

169

Observation of linear-polarization-sensitivity in the microwave-radiation-induced magnetoresistance oscillations  

SciTech Connect

We examine the linear polarization sensitivity of the radiation- induced magneto-resistance oscillations by investigating the effect of rotating in-situ the electric field of linearly polarized microwaves relative to the current, in the GaAs/AlGaAs system. We find that the frequency and the phase of the photo-excited magneto-resistance oscillations are insensitive to the polarization. On the other hand, the amplitude of the resistance oscillations are strongly sensitive to the relative orientation between the microwave antenna and the current-axis in the specimen.

Mani, R. G.; Ramanayaka, A. N. [Department of Physics and Astronomy, Georgia State University, Atlanta, Georgia 30303 (United States); Wegscheider, W. [Laboratorium für Festkörperphysik, ETH Zürich, CH-8093 Zürich (Switzerland)

2013-12-04

170

Magnetic Flux Effect on a Kondo-Induced Electric Polarization in a Triangular Triple Quantum Dot  

NASA Astrophysics Data System (ADS)

A magnetic flux effect is studied theoretically on an electric polarization induced by the Kondo effect in a triangular triple-quantum-dot system, where one of the three dots is connected to a metallic lead. This electric polarization exhibits an Aharonov–Bohm oscillation as a function of the magnetic flux penetrating through the triangular loop. The numerical renormalization group analysis reveals how the oscillation pattern depends on the Kondo coupling of a local spin with lead electrons, which is sensitive to the point contact with the lead. It provides an experimental implication that the Kondo effect is the origin of the emergent electric polarization.

Koga, Mikito; Matsumoto, Masashige; Kusunose, Hiroaki

2014-08-01

171

Direct experimental measurement of SRS-induced spectral tilt in multichannel multispan communication systems  

SciTech Connect

Nonlinear SRS-induced tilt of the spectrum of a multichannel DWDM signal is studied experimentally in standard singlemode fibreoptic communication lines. It is found that at a fixed spectral bandwidth and total power the nonlinear SRS tilt is independent of the number of channels, radiation source type, and the initial tilt (positive or negative). In a multispan line consisting of identical spans the total nonlinear tilt of the spectrum (in dB) is proportional to the number of spans, spectral width and total power. (optical fibres, lasers and amplifiers. properties and applications)

Kapin, Yu A; Nanii, Oleg E; Novikov, A G; Pavlov, V N; Plotskii, A Yu; Treshchikov, V N

2012-09-30

172

Laser-induced hole filling and spectral diffusion of aluminum phthalocyanine tetrasulfonate in hyperquenched glassy films  

NASA Astrophysics Data System (ADS)

Laser-induced hole filling and spectral diffusion for the dye aluminum phthalocyanine tetrasulfonate in hyperquenched glassy films of water, ethanol, and methanol are investigated. Burning multiple holes into these films reveals a dependence on the burn direction, which is explained by the asymmetry of the antihole produced in the burning process. Spectral diffusion rates are shown to be dependent on sample annealing at temperatures well below the glass transition temperature, Tg. This is interpreted in terms of a ?-relaxation process of the glass and is identified with transport of free volume.

Reinot, T.; Hayes, J. M.; Small, G. J.

1999-03-01

173

Elemental analysis of laser induced breakdown spectroscopy aided by an empirical spectral database.  

PubMed

Laser induced breakdown spectroscopy (LIBS) is commonly used to identify elemental compositions of various samples. To facilitate this task, we propose the use of an elemental spectral library for single-pulsed, nanosecond LIBS in the spectral range 198-968 nm. This spectroscopic library is generated by measuring optical emissions from plasmas of 40 pure elements. To demonstrate the usefulness of the proposed database, we measure and analyze the LIBS spectra of pure iron and of ethanol and show that we identify these samples with a high degree of certainty. PMID:19122709

Rock, Steven; Marcano, Aristides; Markushin, Yuri; Sabanayagam, Chandran; Melikechi, Noureddine

2008-11-01

174

A holistic view of a black hole binary: bringing together spectral, timing, and polarization analysis of Cygnus X-1  

NASA Astrophysics Data System (ADS)

The microquasar Cygnus X-1 is a persistent high mass X-ray binary, consisting of an O-type supergiant and a stellar mass black hole, and therefore one of those systems which are often considered downscaled versions of AGN, an analogy supported in Cyg X-1 by observations of radio jets. The size and proximity of such systems allow us to observe phenomena on time-scales which are not accessible in their supermassive siblings. Cyg X-1 shows distinct X-ray states, characterized by X-ray spectral and timing properties. Radio behavior is strongly correlated with the X-ray states and a jet-break exists in the mid-IR range in the hard state. The source state is therefore essential for the interpretation of data at all wavelengths. For most observations lacking broadband X-ray coverage, however, the exact state determination proves challenging. In this work, I will present a recently developed novel approach that uses data from all sky monitors such as RXTE-ASM, MAXI, Swift-BAT, and Fermi-GBM to define states and state transitions on a timescales of a few hours over a period of more than 17 years. This approach can be used to investigate the context of high resolution observations of Cyg X-1 with Chandra and XMM, and to conduct state-resolved polarization analysis with INTEGRAL. I then combine spectral and model-independent X-ray timing analysis of over 1900 RXTE orbits over 14 years and investigate the evolution of Fourier-dependent timing parameters such as power spectra, coherence, and time lag at different photon energies over all spectral states. Results include a correlation between the shape of the power and time lag spectra in all hard and intermediate states, a photon-energy dependent increase of the fractional rms in the soft state, and a strong energy-dependency of the power spectra shapes during state transitions. The findings are crucial for constraining physical models for accretion and ejection in compact objects and for comparisons with other accreting objects, especially AGN, since timescales and energies in accreting black holes scale with mass so that observations at the same energies may probe different physical processes therefore show different spectral and timing behavior.

Grinberg, Victoria

2014-01-01

175

Magnetic field induced nutation of exciton-polariton polarization in (Cd,Zn)Te crystals  

NASA Astrophysics Data System (ADS)

We study the polarization dynamics of exciton-polaritons propagating in sub-mm-thick (Cd,Zn)Te bulk crystals using polarimetric time-of-flight techniques. The application of a magnetic field in Faraday geometry leads to synchronous temporal oscillations of all Stokes parameters of an initially linearly or circularly polarized, spectrally broad optical pulse of 150-fs duration propagating through the crystal. Strong dispersion for photon energies close to the exciton resonance leads to stretching of the optical pulse to a duration of 200-300 ps and enhancement of magneto-optical effects such as the Faraday rotation and the nonreciprocal birefringence. The oscillation frequency of the exciton-polariton polarization increases with magnetic field B, reaching 10 GHz at B˜5 T. Surprisingly, the relative contributions of Faraday rotation and nonreciprocal birefringence undergo strong changes with photon energy, which is attributed to a nontrivial spectral dependence of Faraday rotation in the vicinity of the exciton resonance. This leads to polarization nutation of the transmitted optical pulse in the time domain. The results are well explained by a model that accounts for Faraday rotation and magnetospatial dispersion in zinc-blende crystals. We evaluate the exciton g factor |gexc|=0.2 and the magnetospatial constant |V|=5×10-12 eV cm T-1.

Godde, T.; Glazov, M. M.; Akimov, I. A.; Yakovlev, D. R.; Mariette, H.; Bayer, M.

2013-10-01

176

All-optically induced currents resulting from frequency modulated coherent polarization  

E-print Network

We employ polarization-shaped ultrafast optical pulses to generate photocurrents which only arise if the optically induced coherent polarization is frequency modulated. This frequency modulation is obtained via detuned excitation of light-hole excitons in (110)-oriented GaAs quantum wells. The observed photocurrents vanish for resonant excitation of excitons and reverse their direction with a change of the sign of detuning. Moreover, the currents do not exist for continuous-wave excitation. Our work reveals the existence of a new class of photocurrents and visualizes the complexity of current response tensors. This is helpful for the better understanding of optically induced microscopic transport in semiconductors.

Priyadarshi, Shekhar; Bieler, Mark

2013-01-01

177

Contact-induced spin polarization in BNNT(CNT)/TM (TM=Co, Ni) nanocomposites  

NASA Astrophysics Data System (ADS)

The interaction between carbon and BN nanotubes (NT) and transition metal Co and Ni supports was studied using electronic structure calculations. Several configurations of interfaces were considered, and the most stable ones were used for electronic structure analysis. All NT/Co interfaces were found to be more energetically favorable than NT/Ni, and conductive carbon nanotubes demonstrate slightly stronger bonding than semiconducting ones. The presence of contact-induced spin polarization was established for all nanocomposites. It was found that the contact-induced polarization of BNNT leads to the appearance of local conductivity in the vicinity of the interface while the rest of the nanotube lattice remains to be insulating.

Kuzubov, Alexander A.; Kovaleva, Evgenia A.; Avramov, Paul; Kuklin, Artem V.; Mikhaleva, Natalya S.; Tomilin, Felix N.; Sakai, Seiji; Entani, Shiro; Matsumoto, Yoshihiro; Naramoto, Hiroshi

2014-08-01

178

All-optically induced currents resulting from frequency-modulated coherent polarization  

NASA Astrophysics Data System (ADS)

We employ polarization-shaped ultrafast optical pulses to generate photocurrents, which only arise if the optically induced coherent polarization is frequency modulated. This frequency modulation is obtained via detuned excitation of light-hole excitons in (110)-oriented GaAs quantum wells. The observed photocurrents vanish for resonant excitation of excitons and reverse their direction with a change of the sign of detuning. Moreover, the currents do not exist for continuous-wave excitation. Our work reveals the existence of a new class of photocurrents and visualizes the complexity of current response tensors. This is helpful for the better understanding of optically induced microscopic transport in semiconductors.

Priyadarshi, Shekhar; Pierz, Klaus; Bieler, Mark

2013-03-01

179

Geometrically induced polarization and alignment of cells on nanopillar arrays  

NASA Astrophysics Data System (ADS)

Topological features at the nano and microscale can trigger mammalian cell growth and differentiation. In this work, we describe geometrical tuning of ordered arrays of nanopillars and micropillars that elicit specialized morphologies in adherent cells. Systematic analysis of the effects of the pillar radius, height, and spacing reveals that stem cells assume either flattened, polarized, or stellate morphologies in direct response to interpillar spacing. Notably, on patterns of pitch near a critical spacing (dcrit = 2 ?m for C3H10T1/2 cells), cells exhibit rounding of the cell body, pronounced polarization, and extension of narrow axon-like cell projections aligned with the square or hexagonal lattice of the NP array. This morphology persists for various stem cell lines and primary mesenchymal stem cells. The neuron-like morphological characteristics suggest that NP arrays can be utilized in tissue engineering applications that require directed axon growth. The ability of nano and micropillars to support various morphogenetic trends will allow rational design of scaffolds that may be useful for stem cell lineage specification, formation of patterned neural networks, and enhancement of implant integration with adjoining tissue.

Vasquez, Yolanda; Bucaro, Michael; Hatton, Benjamin; Aizenberg, Joanna

2012-02-01

180

Momentum and polarization dependence of single-magnon spectral weight for CuL3 -edge resonant inelastic x-ray scattering from layered cuprates  

NASA Astrophysics Data System (ADS)

Recently it was predicted theoretically and confirmed experimentally that in cuprates single-magnon dispersions can be mapped out with resonant inelastic x-ray scattering (RIXS) at the copper L3 edge. To further establish RIXS as a viable technique we investigate the momentum and incident photon polarization dependence of the single-magnon spectral weight in a variety of layered undoped antiferromagnetic compounds. The agreement of experimental and theoretical results bolsters the assignment of RIXS spectral features to single magnons. This detailed analysis allows to disentangle single-magnon scattering from other spectral contributions. Moreover, it is a necessary premise for future research aimed at investigating processes that modulate spectral weights beyond the predictions of linear spin-wave theory.

Braicovich, L.; Moretti Sala, M.; Ament, L. J. P.; Bisogni, V.; Minola, M.; Balestrino, G.; di Castro, D.; de Luca, G. M.; Salluzzo, M.; Ghiringhelli, G.; van den Brink, J.

2010-05-01

181

Measurement of the Induced Polarization of ? (1116) in Kaon Electroproduction with CLAS  

NASA Astrophysics Data System (ADS)

The CLAS Collaboration is using the p(e, e'K+p)?- reaction to measure the induced polarization of the electroproduced ?(1116). In this experiment a 5.499-GeV electron beam was incident upon an unpolarized liquid-hydrogen target. The CEBAF Large Acceptance Spectrometer (CLAS) was used to detect the scattered electron, the kaon, and the decay proton from the ? hyperon. CLAS allowed for a large kinematic acceptance in Q2(0.75?Q2?3.5 GeV2) and W(1.6?W?3.0 GeV), as well as the kaon center-of-mass scattering angle. The goal is to map out the kinematic dependencies for the induced polarization in order to provide new constraints on models of K-hyperon production. Along with previously published photo- and electroproduction cross sections and polarization observables from CLAS, LEPS, SAPHIR, and GRAAL, these new induced polarization data are needed in coupled-channel analyses to search for previously unobserved s-channel resonances. Preliminary polarization results are presented.

Gabrielyan, Marianna; Raue, Brian; Dhamija, Seema; Carman, Daniel S.

2010-08-01

182

Polarization peculiarities of femtosecond laser induced harmonic generation from solid surface plasma  

NASA Astrophysics Data System (ADS)

Polarization characteristics of harmonic generation from solid surface plasma were studied using a femtosecond CPA Ti:S-Nd:glass laser. The ratios between the harmonics intensities produced by p-polarized and s-polarized pump were 25 and 6 for the second and fifth harmonics, respectively, at pump intensities ( I) below 10 17 W cm -2. The same ratios decreased to 2.4 and 1.5 for I>2×10 17 W cm -2. This decrease was explained by the rippling caused by Rayleigh-Taylor-like instability at the critical density surface, and Faraday rotation effect due to the influence of the spontaneous magnetic fields generated in plasma. Theoretical analysis of s- and p-polarization-induced harmonic generation was presented using LPIC code. The blueshift of the harmonics has been also observed. It was found that the blueshift increases with the harmonic order.

Ganeev, R. A.; Ishizawa, A.; Kanai, T.; Ozaki, T.; Kuroda, H.

2003-11-01

183

Magnetic-field-induced ferroelectric polarization reversal in magnetoelectric composites revealed by piezoresponse force microscopy.  

PubMed

Controlling electric polarization (or magnetization) in multiferroic materials with external magnetic fields (or electric fields) is very important for fundamental physics and spintronic devices. Although there has been some progress on magnetic-field-induced polarization reversal in single-phase multiferroics, such behavior has so far never been realized in composites. Here we show that it is possible to reverse ferroelectric polarization using magnetic fields in a bilayer Terfenol-D/PMN-33%PT composite. We realized this by ferroelectric domain imaging using piezoresponse force microscopy (PFM) under applied magnetic field loading. The internal electric field caused by the magnetoelectric (ME) effect in the PMN-PT crystal is considered as the driving force for the 180° polarization switching, and its existence is verified by switching spectroscopy PFM testing under a series of external magnetic fields. A quantitative method is further suggested to estimate the local ME coefficient based on the switching spectroscopy PFM testing results. PMID:24953042

Miao, Hongchen; Zhou, Xilong; Dong, Shuxiang; Luo, Haosu; Li, Faxin

2014-08-01

184

Different temporal patterns of vector soliton bunching induced by polarization-dependent saturable absorber  

NASA Astrophysics Data System (ADS)

A fiber laser with either a polarization-independent semiconductor saturable absorption mirror (PID-SESAM) or a polarization-dependent SESAM (PD-SESAM) as a passive mode-locker is constructed for obtaining the vector soliton bunching. The temporal patterns of the soliton bunching generated from the fiber laser with a PD-SESAM are much more abundant than that in fiber laser with a PID-SESAM. Only the vibrating soliton bunching is generated from the fiber laser with a PID-SESAM. However, there are another three interesting temporal patterns of the soliton bunching generated from the fiber laser with a PD-SESAM except for the vibrating soliton bunching. They are variable length soliton bunching, breathing soliton bunching and stable soliton bunching along the slow axis induced by polarization instability. It is found that the polarization property of the saturable absorber plays a pivotal role for achieving different temporal patterns of the soliton bunching.

Chen, Wei-Cheng; Chen, Guo-Jie; Han, Ding-An; Li, Bin

2014-06-01

185

Spin-transfer torque and current-induced switching in metallic spin valves with perpendicular polarizers  

NASA Astrophysics Data System (ADS)

We present a theoretical description of spin-transfer torque in a spin valve with perpendicularly magnetized polarizer. The polarizer consisting of several ultrathin layers is considered as a single interfacial magnetic scatterer between two nonmagnetic layers, and is included in the theory based on diffusive transport via appropriate boundary conditions. The model has been used to study systematically the spin-transfer torque and current-induced switching in a spin valve with both perpendicular and in-plane polarizers and with in-plane magnetized free layer. The wave-function matching ab initio calculations have been used to determine transport parameters of the perpendicular polarizer. Additionally, the effect of disorder on the spin-transfer torque has been examined.

Baláž, Pavel; Zwierzycki, Maciej; Barna?, Józef

2013-09-01

186

Microwave polarization in the direction of galaxy clusters induced by the CMB quadrupole anisotropy  

E-print Network

Electron scattering induces a polarization in the cosmic microwave background (CMB) signal measured in the direction of a galaxy cluster due to the presence of a quadrupole component in the CMB temperature distribution. Measuring the polarization towards distant clusters provides the unique opportunity to observe the evolution of the CMB quadrupole at moderate redshifts, z~0.5-3. We demonstrate that for the local cluster population the polarization degree will depend on the cluster celestial position. There are two extended regions in the sky, which are opposite to each other, where the polarization is maximal, 0.1(tau/0.02) microK in the Rayleigh-Jeans part of the CMB spectrum (tau being the Thomson optical depth across the cluster) exceeding the contribution from the cluster transverse peculiar motion if v_tpolarization components produced in clusters. These polarization effects, which are of the order of (v_t/c)^2 tau, (v_t/c) tau^2 and (kT_e/m_ec^2) tau^2, as well as the polarization due to the CMB quadrupole, were previously calculated by Sunyaev and Zel'dovich for the Rayleigh-Jeans region. We fully confirm their earlier results and present exact frequency dependencies for all these effects. The polarization is considerably higher in the Wien region of the CMB spectrum.

S. Y. Sazonov; R. A. Sunyaev

1999-03-18

187

Gut dysbiosis promotes M2 macrophage polarization and allergic airway inflammation via fungi-induced PGE?.  

PubMed

Although imbalances in gut microbiota composition, or "dysbiosis," are associated with many diseases, the effects of gut dysbiosis on host systemic physiology are less well characterized. We report that gut dysbiosis induced by antibiotic (Abx) treatment promotes allergic airway inflammation by shifting macrophage polarization in the lung toward the alternatively activated M2 phenotype. Adoptive transfer of alveolar macrophages derived from Abx-treated mice was sufficient to increase allergic airway inflammation. Abx treatment resulted in the overgrowth of a commensal fungal Candida species in the gut and increased plasma concentrations of prostaglandin E? (PGE?), which induced M2 macrophage polarization in the lung. Suppression of PGE? synthesis by the cyclooxygenase inhibitors aspirin and celecoxib suppressed M2 macrophage polarization and decreased allergic airway inflammatory cell infiltration in Abx-treated mice. Thus, Abx treatment can cause overgrowth of particular fungal species in the gut and promote M2 macrophage activation at distant sites to influence systemic responses including allergic inflammation. PMID:24439901

Kim, Yun-Gi; Udayanga, Kankanam Gamage Sanath; Totsuka, Naoya; Weinberg, Jason B; Núñez, Gabriel; Shibuya, Akira

2014-01-15

188

The effects of tidally induced disc structure on white dwarf accretion in intermediate polars  

E-print Network

We investigate the effects of tidally induced asymmetric disc structure on accretion onto the white dwarf in intermediate polars. Using numerical simulation, we show that it is possible for tidally induced spiral waves to propagate sufficiently far into the disc of an intermediate polar that accretion onto the central white dwarf could be modulated as a result. We suggest that accretion from the resulting asymmetric inner disc may contribute to the observed X-ray and optical periodicities in the light curves of these systems. In contrast to the stream-fed accretion model for these periodicities, the tidal picture predicts that modulation can exist even for systems with weaker magnetic fields where the magnetospheric radius is smaller than the radius of periastron of the mass transfer stream. We also predict that additional periodic components should exist in the emission from low mass ratio intermediate polars displaying superhumps.

J. R. Murray; P. J. Armitage; L. Ferrario; D. T Wickramasinghe

1998-09-10

189

Left-handed electromagnetic waves in materials with induced polarization and magnetization  

NASA Astrophysics Data System (ADS)

We analyze the properties of electromagnetic waves inside materials with induced polarization and magnetization. We show that if the polarization and magnetization of the material are sufficiently large and appropriately phased, then the system supports the formation of left-handed waves. In some respects, such a system behaves similarly to materials with a negative index of refraction, yet there is one important advantage: Left-handed waves in materials with induced polarization and magnetization do not require as stringent material properties (such as the strength of resonances and the density of radiators). We numerically investigate the formation and propagation of such left-handed waves using finite-difference approximation to Maxwell's equations. We also discuss possible experimental observation of these ideas in a rare-earth-doped crystal.

Yavuz, D. D.; Brewer, N. R.

2014-12-01

190

Investigation of the electronic transport in polarization-induced nanowires using conductive atomic force microscopy (AFM)  

NASA Astrophysics Data System (ADS)

In the search to improve short wavelength light emitting diodes (LED's), where the dislocations limit their performance and hole doping (Mg) is a fundamental challenge, the III-Nitride polarization-induced nanowire LED provides a promising system to address these problems. The new type of pn diode, polarization-induced nanowire LED (PINLED), was developed by linearly grading AlGaN composition of the nanowires (from GaN to AlN and back to GaN) from 0% to 100% and back to 0% Al (Carnevale et al, Nano Lett., 12, 915 (2012)). In III-Nitrides (Ga,Al/N), the effects of polarization are commonly observed at the surfaces and interfaces. Thus, in the case of the polarization-induced nanowire LEDs, taking advantage of the bound polarization charge, due to the grading of the AlGaN, the pn diodes are formed. The polarity of the nanowires determines the carrier type in each graded region, and therefore the diode orientation (n/p vs p/n). We used conductive AFM to investigate polarity of the PINLED's as well as hole conductivity in PINLED's made of AlGaN with and without acceptor doping. The results reveal that most of the wires are n-top/p-bottom (N-face), but some are p-top/n-bottom (Ga-face). Also, we found that the current density is 3 orders of magnitude larger in the case of the doped nanowires than the nanowires with no impurity doping.

Selcu, Camelia; Carnevale, Santino C.; Kent, Thomas F.; Akyol, Fatih; Phillips, Patrick J.; Mills, Michael J.; Rajan, Siddharth; Pelz, Jonathan P.; Myers, Roberto C.

2013-03-01

191

The Infrared Spectral Energy Distribution And Polarization Of Comet C/1995 O1 (Hale Bopp) During 1997  

NASA Astrophysics Data System (ADS)

Comets, such as C/1995 O1 (Hale-Bopp), are important to studies of the origins of the solar system because they are believed to be frozen reservoirs of the most primitive pre-solar dust grains and ices. Here, we report 1.2 18.5 ?m infrared (IR) spectrophotometric and polarimetric observations of comet Hale-Bopp. Our measurements of the spectral energy distribution (SED) and IR polarization near perhelion passage suggest that emission from the coma was dominated by scattering and thermal emission from sub-micron sized dust grains. Hale-Bopp's surprising brightness may have been largely a result of the properties of its coma grains rather than the size of its nucleus. The thermal emission continuum from the grains had a superheat of S = Tcolor/TBB ? 1.7, the peak of the 10 ?m silicate emission feature was 1.7 mags above the carbon grain continuum, and the albedo (reflectivity) of the grains was ? 0.4 at a scattering angles, ? ? 135°

Woodward, Charles E.; Gehrz, R. D.; Mason, C. G.; Jones, T. J.; Williams, D. M.

1998-10-01

192

Measurements of submillimeter polarization induced by oblique reflection from aluminum alloy  

E-print Network

Measurements of submillimeter polarization induced by oblique reflection from aluminum alloy Tom of submillimeter radiation when it is obliquely reflected by a flat mirror made of aluminum alloy. For angles by oblique reflection from aluminum alloy at a wavelength of 1 cm agrees with the prediction of the ordinary

Novak, Giles

193

Tensor-Induced CMB Temperature-Polarization Correlation in Reionized Universes  

E-print Network

We reexamine the temperature-polarization correlation function of the cosmic microwave background induced by tensor mode with a scale-invariant spectrum in reionized standard cold dark matter models. It is found that the sign of the correlation function is positive on all angular scales even in a model with substantial reionization.

Kin-Wang Ng

1999-05-04

194

Neuropeptide Y induces potent migration of human immature dendritic cells and promotes a Th2 polarization.  

PubMed

Neuropeptide Y (NPY), a major autonomic nervous system and stress mediator, is emerging as an important regulator of inflammation, implicated in autoimmunity, asthma, atherosclerosis, and cancer. Yet the role of NPY in regulating phenotype and functions of dendritic cells (DCs), the professional antigen-presenting cells, remains undefined. Here we investigated whether NPY could induce DCs to migrate, mature, and polarize naive T lymphocytes. We found that NPY induced a dose-dependent migration of human monocyte-derived immature DCs through the engagement of NPY Y1 receptor and the activation of ERK and p38 mitogen-activated protein kinases. NPY promoted DC adhesion to endothelial cells and transendothelial migration. It failed to induce phenotypic DC maturation, whereas it conferred a T helper 2 (Th2) polarizing profile to DCs through the up-regulation of interleukin (IL)-6 and IL-10 production. Thus, during an immune/inflammatory response NPY may exert proinflammatory effects through the recruitment of immature DCs, but it may exert antiinflammatory effects by promoting a Th2 polarization. Locally, at inflammatory sites, cell recruitment could be amplified in conditions of intense acute, chronic, or cold stress. Thus, altered or amplified signaling through the NPY-NPY-Y1 receptor-DC axis may have implications for the development of inflammatory conditions.-Buttari, B., Profumo, E., Domenici, G., Tagliani, A., Ippoliti, F., Bonini, S., Businaro, R., Elenkov, I., Riganò, R. Neuropeptide Y induces potent migration of human immature dendritic cells and promotes a Th2 polarization. PMID:24699455

Buttari, Brigitta; Profumo, Elisabetta; Domenici, Giacomo; Tagliani, Angela; Ippoliti, Flora; Bonini, Sergio; Businaro, Rita; Elenkov, Ilia; Riganò, Rachele

2014-07-01

195

Relativistic Calculations of Induced Polarization in $^{12}C$(e, e' \\vec{p})$ Reactions  

E-print Network

Relativistic calculations of the induced proton polarization in quasifree electron scattering on $^{12}C$ are presented. Good agreement with the experimental data of Woo et al. is obtained. The relativistic calculations yield a somewhat better description of the data than the non-relativistic ones. Differences between the two approaches are more pronounced at larger missing momenta suggesting further experimental work in this region.

J. I. Johansson; H. S. Sherif

1999-05-06

196

Optical Sensing of Ecosystem Carbon Fluxes Combining Spectral Reflectance Indices with Solar Induced Fluorescence  

NASA Astrophysics Data System (ADS)

Optical sampling of spectral reflectance and solar induced fluorescence provide information on the physiological status of vegetation that can be used to infer stress responses and estimates of production. Multiple repeated observations can observe the effects of changing environmental conditions on vegetation. This study examines the use of optical signals to determine inputs to a light use efficiency (LUE) model describing productivity of a cornfield where repeated observations of carbon flux, spectral reflectance and fluorescence were collected. Data were collected at the Optimizing Production Inputs for Economic and Environmental Enhancement (OPE3) fields (39.03°N, 76.85°W) at USDA Beltsville Agricultural Research Center. Agricultural Research Service researchers measured CO2 fluxes using eddy covariance methods throughout the growing season. Optical measurements were made from the nearby tower supporting the NASA FUSION sensors. This sensor system consists of two dual channel, upward and downward looking, spectrometers used to simultaneously collect high spectral resolution measurements of reflected and fluoresced light from vegetation canopies. Estimates of chlorophyll fluorescence, combined with measures of vegetation pigment content and the Photosynthetic Reflectance Index (PRI) derived from the spectral reflectance are compared with CO2 fluxes over diurnal periods for multiple days. PRI detects changes in Xanthophyll cycle pigments using reflectance at 531 nm compared to a reference band at 570 nm. The relationships among the different optical measurements indicate that they are providing different types of information on the vegetation and that combinations of these measurements provide improved retrievals of CO2 fluxes than any index alone.

Huemmrich, K. F.; Corp, L.; Campbell, P. K.; Cook, B. D.; Middleton, E.; Cheng, Y.; Zhang, Q.; Russ, A.; Kustas, W. P.

2013-12-01

197

Dual-band wavelength tunable nonlinear polarization rotation mode-locked Erbium-doped fiber lasers induced by birefringence variation and gain curvature alteration.  

PubMed

With the combining effects of the fiber birefringence induced round-trip phase variation and the gain profile reshaping induced spectral filtering in the Erbium-doped fiber laser (EDFL) cavity, the mechanism corresponding to the central wavelength tunability of the EDFL passively mode-locked by nonlinear polarization rotation is explored. Bending the intracavity fiber induces the refractive index difference between orthogonal axes, which enables the dual-band central wavelength shift of 2.9 nm at 1570 nm region and up to 10.2 nm at 1600 nm region. The difference between the wavelength shifts at two bands is attributed to the gain dispersion decided by the gain spectral curvature of the EDFA, and the spacing between two switchable bands is provided by the birefringence induced variation on phase delay which causes transmittance variation. In addition, the central wavelength shift can also be controlled by varying the pumping geometry. At 1570 nm regime, an offset of up to 5.9 nm between the central wavelengths obtained under solely forward or backward pumping condition is observed, whereas the bidirectional pumping scheme effectively compensates the gain spectral reshaping effects to minimize the central wavelength shift. In contrast, the wavelength offset shrinks to only 1.1 nm when mode-locking at 1600 nm under single-sided pumping, as the gain profile strongly depends on the spatial distribution of the excited erbium ions under different pumping schemes. Except the birefringence variation and the gain spectral filtering phenomena, the gain-saturation mechanism induced refractive index change and its influence to the dual-band central wavelength tunability are also observed and analyzed. PMID:25321587

Lin, Sheng-Fong; Lin, Gong-Ru

2014-09-01

198

Polarized and unpolarized $?$-pair meson-induced Drell--Yan production and the pion distribution amplitude  

E-print Network

We present a detailed analysis of meson-induced massive lepton (muon) Drell--Yan production for the process $\\pi^{-}N\\to\\mu^{+}\\mu^{-}X$, considering both an unpolarized nucleon target and longitudinally polarized protons. Using a QCD framework, we focus on the angular distribution of $\\mu^+$, which is sensitive to the shape of the pion distribution amplitude, the goal being to test corresponding results against available experimental data. Predictions are made, employing various pion distribution amplitudes, for the azimuthal angle dependence of the $\\mu^{+}$ distribution in the polarized case, relevant for the planned COMPASS experiment. QCD evolution is given particular attention in both considered cases.

A. P. Bakulev; N. G. Stefanis; O. V. Teryaev

2007-06-28

199

Surface-induced heating of cold polar molecules  

E-print Network

We study the rotational and vibrational heating of diatomic molecules placed near a surface at finite temperature on the basis of macroscopic quantum electrodynamics. The internal molecular evolution is governed by transition rates that depend on both temperature and position. Analytical and numerical methods are used to investigate the heating of several relevant molecules near various surfaces. We determine the critical distances at which the surface itself becomes the dominant source of heating and we investigate the transition between the long-range and short-range behaviour of the heating rates. A simple formula is presented that can be used to estimate the surface-induced heating rates of other molecules of interest. We also consider how the heating depends on the thickness and composition of the surface.

Stefan Yoshi Buhmann; M. R. Tarbutt; Stefan Scheel; E. A. Hinds

2008-06-18

200

December 1, 2004 / Vol. 29, No. 23 / OPTICS LETTERS 2785 Polarization conversion in ring resonator phase shifters  

E-print Network

The effect of the polarization rotation induced by curved waveguides on the spectral behavior of phase waveguide with an index contrast of a few percent can induce considerable polarization coupling betweenDecember 1, 2004 / Vol. 29, No. 23 / OPTICS LETTERS 2785 Polarization conversion in ring resonator

Melloni, Andrea

201

Polarization effects induced by a two-mirror laser beam scanner  

NASA Astrophysics Data System (ADS)

The polarization lidar technique requires that the transmitted laser beam in the atmosphere is linearly polarized so that a depolarization ratio from hydrometeors and aerosol particles can be detected. This is easily achieved in vertically pointing lidars used to study clouds. However, in scanning lidars, which are of interest for wind and pollution studies, stand-off detection and biodefense, the state of polarization of the laser beam is modified upon reflection by the mirrors of the scanner. We study experimentally the effect of a two-mirror scanner, or beam steering unit (BSU), on the polarization state of a linearly polarized beam at 1.54 micron wavelength. We built a miniature BSU in the lab and used a polarimeter to map the state of polarization (SOP) for all combinations of azimuth-elevation angles. We found that the linear polarization is preserved for a horizontal scan (elevation angle is 0°) but it rotates as a function of azimuth angle. There are a few more pointing directions in which the SOP is linear. Overall, the transmit beam is elliptically polarized for a non-zero elevation angle. The ellipticity and orientation of the ellipses is not constant. However, we found a period of repeatability of 180° in both azimuth and elevation angles. When comparing two different coatings, we note that the ellipticity is a function of the type of coating. We propose a method to eliminate the induced ellipticity by the BSU mirrors for all scan directions by means of altering the incident SOP on the BSU.

Gimbal, Scott; Li, Qiaochu; Petrova-Mayor, Anna

2012-10-01

202

Modeling and inversion Matlab algorithms for resistivity, induced polarization and seismic data  

NASA Astrophysics Data System (ADS)

M. Karaoulis (1), D.D. Werkema (3), A. Revil (1,2), A., B. Minsley (4), (1) Colorado School of Mines, Dept. of Geophysics, Golden, CO, USA. (2) ISTerre, CNRS, UMR 5559, Université de Savoie, Equipe Volcan, Le Bourget du Lac, France. (3) U.S. EPA, ORD, NERL, ESD, CMB, Las Vegas, Nevada, USA . (4) USGS, Federal Center, Lakewood, 10, 80225-0046, CO. Abstract We propose 2D and 3D forward modeling and inversion package for DC resistivity, time domain induced polarization (IP), frequency-domain IP, and seismic refraction data. For the resistivity and IP case, discretization is based on rectangular cells, where each cell has as unknown resistivity in the case of DC modelling, resistivity and chargeability in the time domain IP modelling, and complex resistivity in the spectral IP modelling. The governing partial-differential equations are solved with the finite element method, which can be applied to both real and complex variables that are solved for. For the seismic case, forward modeling is based on solving the eikonal equation using a second-order fast marching method. The wavepaths are materialized by Fresnel volumes rather than by conventional rays. This approach accounts for complicated velocity models and is advantageous because it considers frequency effects on the velocity resolution. The inversion can accommodate data at a single time step, or as a time-lapse dataset if the geophysical data are gathered for monitoring purposes. The aim of time-lapse inversion is to find the change in the velocities or resistivities of each model cell as a function of time. Different time-lapse algorithms can be applied such as independent inversion, difference inversion, 4D inversion, and 4D active time constraint inversion. The forward algorithms are benchmarked against analytical solutions and inversion results are compared with existing ones. The algorithms are packaged as Matlab codes with a simple Graphical User Interface. Although the code is parallelized for multi-core cpus, it is not as fast as machine code. In the case of large datasets, someone should consider transferring parts of the code to C or Fortran through mex files. This code is available through EPA's website on the following link http://www.epa.gov/esd/cmb/GeophysicsWebsite/index.html Although this work was reviewed by EPA and approved for publication, it may not necessarily reflect official Agency policy.

Karaoulis, M.; Revil, A.; Minsley, B. J.; Werkema, D. D.

2011-12-01

203

Surface polar states and pyroelectricity in ferroelastics induced by flexo-roto field  

NASA Astrophysics Data System (ADS)

Theoretical analysis based on the Landau-Ginzburg-Devonshire theory is used to show that the joint action of flexoelectric effect and rotostriction leads to a large spontaneous in-plane polarization (˜1-5 ?C/cm2) and pyroelectric coefficient (˜10-3 C/m2K) in the vicinity of surfaces of otherwise non-ferroelectric ferroelastics, such as SrTiO3, with static octahedral rotations. The origin of the improper polarization and pyroelectricity is an electric field we name flexo-roto field whose strength is proportional to the convolution of the flexoelectric and rotostriction tensors with octahedral tilts and their gradients. Flexo-roto field should exist at surfaces and interfaces in all structures with static octahedral rotations, and thus, it can induce surface polar states and pyroelectricity in a large class of otherwise nonpolar materials.

Morozovska, A. N.; Eliseev, E. A.; Kalinin, S. V.; Qing Chen, Long; Gopalan, Venkatraman

2012-04-01

204

Polarization and collision-induced coherence in the beam-foil light source  

NASA Technical Reports Server (NTRS)

Monatomic systems were excited by the beam-foil method in order to re-examine the possibility that a particular magnetic substate was preferentially populated. O II, Ar II and He I levels were used. The results reveal that: (1) with a tilted foil substantial polarization (up to 15%) may be achieved, (2) the polarization is due to the foil, (3) the foil induces coherence among Zeeman substates with the appearance of quantum beats among these substates and that their coherence is due to the externally applied magnetic field perpendicular to the beam direction, and (4) the angular momentum of the emitted photon is perpendicular to the ion velocity. The possibility for detecting separate effects of alignment and polarization is noted.

Liu, C. H.; Bashkin, S.; Church, D. A.

1974-01-01

205

Measurement of sub-pulse-width temporal delays via spectral interference induced by weak value amplification  

NASA Astrophysics Data System (ADS)

We demonstrate experimentally a scheme to measure small temporal delays, much smaller than the pulse width, between optical pulses. Specifically, we observe an interference effect, based on the concepts of quantum weak measurements and weak value amplification, through which a sub-pulse-width temporal delay between two femtosecond pulses induces a measurable shift of the central frequency of the pulse. The amount of frequency shift, and the accompanying losses of the measurement, can be tailored by postselecting different states of polarization. Our scheme requires only spectrum measurements and linear optics elements, hence greatly facilitating its implementation. Thus it appears to be a promising technique for measuring small and rapidly varying temporal delays.

Salazar-Serrano, Luis José; Janner, Davide; Brunner, Nicolas; Pruneri, Valerio; Torres, Juan P.

2014-01-01

206

B-mode polarization induced by gravitational waves from kinks on infinite cosmic strings  

E-print Network

We investigate the effect of the stochastic gravitational wave (GW) background produced by kinks on infinite cosmic strings, whose spectrum was derived in our previous work, on the B-mode power spectrum of the cosmic microwave background (CMB) anisotropy. We find that the B-mode polarization due to kinks is comparable to that induced by the motion of the string network and hence the contribution of GWs from kinks is important for estimating the B-mode power spectrum originating from cosmic strings. If the tension of cosmic strings \\mu is large enough i.e., G\\mu >~ 10^{-8}, B-mode polarization induced by cosmic strings can be detected by future CMB experiments.

Masahiro Kawasaki; Koichi Miyamoto; Kazunori Nakayama

2010-03-19

207

Induced Polarization in the $^2$H($?,\\vec n$)$^1$H Reaction at Low Energy  

E-print Network

The induced polarization, $P^\\prime_y$, of the neutron in the deuteron photo-disintegration from threshold up to 30 MeV is calculated using a variety of different, latest-generation potentials--Argonne $v_{18}$, Bonn 2000, and Nijmegen I-- and a realistic model for the nuclear electromagnetic current operator, including one- and two-body terms. The model dependence of the theoretical predictions is found to be very small. These predictions are systematically larger in magnitude than the measured $P^\\prime_y$ values, and corroborate the conclusions of an earlier, and much older, study. There is considerable scatter in the available experimental data. New and more accurate measurements of the induced polarization in the $^2$H($\\gamma,\\vec n$)$^1$H reaction are needed in order to establish unequivocally whether there is a discrepancy between theory and experiment.

R. Schiavilla

2005-05-25

208

Doping-induced spectral shifts in two-dimensional metal oxides  

NASA Astrophysics Data System (ADS)

Doping of strongly layered ionic oxides is an established paradigm for creating novel electronic behavior. This is nowhere more apparent than in superconductivity, where doping gives rise to high-temperature superconductivity in cuprates (hole doped) and to surprisingly high Tc in HfNCl (Tc = 25.5 K, electron doped). First-principles calculations of hole doping of the layered delafossite CuAlO2 reveal unexpectedly large doping-induced shifts in spectral density, strongly in opposition to the rigid-band picture that is widely used as an accepted guideline. These spectral shifts, of similar origin as the charge transfer used to produce negative electron affinity surfaces and adjust Schottky barrier heights, drastically alter the character of the Fermi level carriers, leading in this material to an O-Cu-O molecule-based carrier (or polaron, at low doping) rather than a nearly pure-Cu hole as in a rigid-band picture. First-principles linear response electron-phonon coupling (EPC) calculations reveal, as a consequence, net weak EPC and no superconductivity rather than the high Tc obtained previously using rigid-band expectations. These specifically two-dimensional dipole-layer-driven spectral shifts provide new insights into materials design in layered materials for functionalities besides superconductivity.

Ylvisaker, E. R.; Pickett, W. E.

2013-03-01

209

PORTA: A three-dimensional multilevel radiative transfer code for modeling the intensity and polarization of spectral lines with massively parallel computers  

NASA Astrophysics Data System (ADS)

The interpretation of the intensity and polarization of the spectral line radiation produced in the atmosphere of the Sun and of other stars requires solving a radiative transfer problem that can be very complex, especially when the main interest lies in modeling the spectral line polarization produced by scattering processes and the Hanle and Zeeman effects. One of the difficulties is that the plasma of a stellar atmosphere can be highly inhomogeneous and dynamic, which implies the need to solve the non-equilibrium problem of the generation and transfer of polarized radiation in realistic three-dimensional (3D) stellar atmospheric models. Here we present PORTA, an efficient multilevel radiative transfer code we have developed for the simulation of the spectral line polarization caused by scattering processes and the Hanle and Zeeman effects in 3D models of stellar atmospheres. The numerical method of solution is based on the non-linear multigrid iterative method and on a novel short-characteristics formal solver of the Stokes-vector transfer equation which uses monotonic Bézier interpolation. Therefore, with PORTA the computing time needed to obtain at each spatial grid point the self-consistent values of the atomic density matrix (which quantifies the excitation state of the atomic system) scales linearly with the total number of grid points. Another crucial feature of PORTA is its parallelization strategy, which allows us to speed up the numerical solution of complicated 3D problems by several orders of magnitude with respect to sequential radiative transfer approaches, given its excellent linear scaling with the number of available processors. The PORTA code can also be conveniently applied to solve the simpler 3D radiative transfer problem of unpolarized radiation in multilevel systems.

Št?pán, Ji?í; Trujillo Bueno, Javier

2013-09-01

210

The Spectral Signature of Dust Scattering and Polarization in the Near IR to Far UV. I. Optical Depth and Geometry Effects  

E-print Network

Spectropolarimetry from the near IR to the far UV of light scattered by dust provides a valuable diagnostic of the dust composition, grain size distribution and spatial distribution. To facilitate the use of this diagnostic, we present detailed calculations of the intensity and polarization spectral signature of light scattered by optically thin and optically thick dust in various geometries. The polarized light radiative transfer calculations are carried out using the adding-doubling method for a plane-parallel slab, and are extended to an optically thick sphere by integrating over its surface. The calculations are for the Mathis, Rumple & Nordsieck Galactic dust model, and cover the range from 1 $\\mu m$ to 500 \\AA. We find that the wavelength dependence of the scattered light intensity provides a sensitive probe of the optical depth of the scattering medium, while the polarization wavelength dependence provides a probe of the grain scattering properties, which is practically independent of optical depth. We provide a detailed set of predictions, including polarization maps, which can be used to probe the properties of dust through imaging spectropolarimetry in the near IR to far UV of various Galactic and extragalactic objects. In a following paper we use the codes developed here to provide predictions for the dependence of the intensity and polarization on grain size distribution and composition.

Victor G. Zubko; Ari Laor

1999-05-23

211

Polar Motion Analysis  

NASA Astrophysics Data System (ADS)

A deconvolution has been performed using seven years BIH polar motion data from 1977 - 1984. Frequency-domain as well as time-domain deconvolution procedures are applied. The spectral representation of the excitation process reveals peaks at frequencies which are similar to those obtained by evaluating atmospheric data and length of day fluctuations. Additional peaks can be found close to tidally-induced nutation frequencies.

Lenhardt, H.; Groten, E.

212

Analysis and spectral assignments of mixed actinide oxide samples using laser-induced breakdown spectroscopy (LIBS).  

PubMed

In this paper, we report for the first time the identification and assignments of complex atomic emission spectra of mixed actinide oxides using laser-induced plasma spectroscopy or laser-induced breakdown spectroscopy (LIBS). Preliminary results of LIBS measurements on samples of uranium dioxide (UO2)/plutonium dioxide (PuO2) and UO2/PuO2/americium dioxide (AmO2)/neptunium dioxide (NpO2) simulated fuel pellets (or mixed actinide oxide samples) are reported and discussed. We have identified and assigned >800 atomic emission lines for a UO2/PuO2/AmO2/NpO2 fuel pellet thus far. The identification and assignments of spectral emission lines for U, Pu, and Am are consistent with wavelength data from the literature. However, only a few emission lines have been assigned with a high degree of confidence for Np compared with atomic emission data from the literature. We also indicate where atomic emission lines for Cm would most likely appear in the spectral regions shown. Finally, we demonstrate that a LIBS system with a resolving power of approximately 20,000 is adequate for analyzing complex mixtures of actinide elements within the same sample. PMID:23601543

Barefield, James E; Judge, Elizabeth J; Berg, John M; Willson, Stephen P; Le, Loan A; Lopez, Leon N

2013-04-01

213

Large anisotropy of spin polarization in Heusler alloy Ni2MnGa induced by martensitic transformation  

E-print Network

Large anisotropy of spin polarization in Heusler alloy Ni2MnGa induced by martensitic as to extend the family of the GMR materials? The Heusler alloy Ni2MnGa is one of the well-known ferromagnetic polarization both in the cubic austenitic and tetragonal martensitic phases of the Ni2MnGa alloy has been

Zexian, Cao

214

Polar solvent-induced changes in membrane lipid lateral diffusion in human colon cancer cells.  

PubMed

Polar organic solvents, such as N-methylformamide (NMF), N,N-dimethylformamide, and dimethyl sulfoxide, have been demonstrated to induce differentiation in a number of neoplastic cell lines, including human colon cancer cells. Although the mechanism of action of these agents is yet unknown, one possibility is that polar solvents induce a change in lateral mobility of membrane lipids, important to the maturational process. To determine the relationship between polar solvent treatment and changes in membranes, we examined the effects of exposure to NMF on membrane fluidity in human colon cancer cells (DLD-1; clone A). Membrane viscosity was assessed by determining lipid lateral diffusion following photobleaching of a fluorescent lipid probe in individual intact cells. Exposure of cells to NMF led to a significant increase in membrane viscosity following 2 days of treatment, with maximal changes occurring after 11 days. NMF induced these effects over a limited concentration range with 1.0% NMF in the medium having the maximal effect, and 0.5% or 1.5% having less or no effect. Growth of cells with N,N-dimethylformamide (0.8%) also led to increases in membrane viscosity. The observed membrane changes correlated well with the effect of NMF on differentiation in these cells as previously reported, as well as with cell growth rate and morphology in the present study. The increase in viscosity caused by prolonged NMF treatment was reversible, with a return to untreated levels by 9-11 days after removal of NMF. Thus, there is a strong correlation between the attainment of more benign, better differentiated phenotype in polar solvent-treated clone A cells and increases in membrane viscosity. PMID:4027982

Dibner, M D; Ireland, K A; Koerner, L A; Dexter, D L

1985-10-01

215

Reduction of polarization-induced performance degradation in WDM PON utilizing MQW-SLD-based broadband source.  

PubMed

We report on the reduction of polarization-induced performance degradation in WDM PON utilizing MQW-SLD-based ASE source for injection locking to FPLD. The results show that, to suppress the polarization-induced Q penalty sufficiently less than 0.5 dB, the MQW-SLD output should be depolarized within the locking range of the wavelength-locked FPLD. PMID:19550697

Park, Paul K J; Jun, S B; Kim, Hoon; Jung, D K; Lee, W R; Chung, Y C

2007-10-17

216

Linear correlation for identification of materials by laser induced breakdown spectroscopy: Improvement via spectral filtering and masking  

NASA Astrophysics Data System (ADS)

The purpose of this work is to improve the performance of a linear correlation method used for material identification in laser induced breakdown spectroscopy. The improved correlation procedure is proposed based on the selection and use of only essential spectral information and ignoring empty spectral fragments. The method is tested on glass samples of forensic interest. The 100% identification capability of the new method is demonstrated in contrast to the traditional approach where the identification rate falls below 100% for many samples.

Gornushkin, I. B.; Panne, U.; Winefordner, J. D.

2009-10-01

217

Induced polarized state in intentionally grown oxygen deficient KTaO{sub 3} thin films  

SciTech Connect

Deliberately oxygen deficient potassium tantalate thin films were grown by RF magnetron sputtering on Si/SiO{sub 2}/Ti/Pt substrates. Once they were structurally characterized, the effect of oxygen vacancies on their electric properties was addressed by measuring leakage currents, dielectric constant, electric polarization, and thermally stimulated depolarization currents. By using K{sub 2}O rich KTaO{sub 3} targets and specific deposition conditions, KTaO{sub 3-{delta}} oxygen deficient thin films with a K/Ta = 1 ratio were obtained. Room temperature X-ray diffraction patterns show that KTaO{sub 3-{delta}} thin films are under a compressive strain of 2.3% relative to KTaO{sub 3} crystals. Leakage current results reveal the presence of a conductive mechanism, following the Poole-Frenkel formalism. Furthermore, dielectric, polarization, and depolarization current measurements yield the existence of a polarized state below T{sub pol} {approx} 367 Degree-Sign C. A Cole-Cole dipolar relaxation was also ascertained apparently due to oxygen vacancies induced dipoles. After thermal annealing the films in an oxygen atmosphere at a temperature above T{sub pol}, the aforementioned polarized state is suppressed, associated with a drastic oxygen vacancies reduction emerging from annealing process.

Mota, D. A.; Romaguera-Barcelay, Y.; Tkach, A.; Agostinho Moreira, J.; Almeida, A. [IFIMUP and IN-Institute of Nanoscience and Nanotechnology, Department of Physics and Astronomy, Faculty of Science of University of Porto, Rua do Campo Alegre, 687, 4169-007 Porto (Portugal); Perez de la Cruz, J. [INESC TEC, Rua do Campo Alegre, 687, 4169-007 Porto (Portugal); Vilarinho, P. M. [Department of Ceramics and Glass Engineering, CICECO, University of Aveiro, 3810-193 Aveiro (Portugal); Tavares, P. B. [Centro de Quimica, Universidade de Tras-os-Montes e Alto Douro, Apartado 1013, 5001-801 Vila Real (Portugal)

2013-07-21

218

ParaHydrogen Induced Polarization of (13)C carboxylate resonance in acetate and pyruvate.  

PubMed

The advent of nuclear spins hyperpolarization techniques represents a breakthrough in the field of medical diagnoses by magnetic resonance imaging. Dynamic nuclear polarization (DNP) is the most widely used method, and hyperpolarized metabolites such as [1-(13)C]-pyruvate are shown to report on status of tumours. Parahydrogen-induced polarization (PHIP) is a chemistry-based technique, easier to handle and much less expensive in respect to DNP, with significantly shorter polarization times. Its main limitation is the availability of unsaturated precursors for the target substrates; for instance, acetate and pyruvate cannot be obtained by direct incorporation of the parahydrogen molecule. Herein we report a method that allows us to achieve hyperpolarization in this kind of molecule by means of a tailored precursor containing a hydrogenable functionality that, after polarization transfer to the target (13)C moiety, is cleaved to obtain the metabolite of interest. The reported procedure can be extended to a number of other biologically relevant substrates. PMID:25556844

Reineri, Francesca; Boi, Tommaso; Aime, Silvio

2015-01-01

219

Spectral Induced Polarization Response of Unconsolidated Saturated Sand and Surfactant Solutions  

EPA Science Inventory

Dense non-aqueous phase liquids (DNAPL), such as chlorinated solvents, are common groundwater contaminants. Traditional pump-and-treat methods are often not effective at removing residual DNAPL from the subsurface. Surfactant-enhanced aquifer remediation is a promising remediatio...

220

Polarization of macrophages induced by Toxoplasma gondii and its impact on abnormal pregnancy in rats.  

PubMed

Toxoplasma gondii infection is the leading cause of fetal intrauterine growth retardation among the five kinds of pathogens termed as TORCH, including Toxoplasma, Rubella virus, Cytomegalo virus, herpes virus and others during pregnancy. Pathogens infect the fetus through the placenta. T. gondii infection may result in congenital toxoplasmosis, miscarriage, stillbirth, and preemie, and increase pregnancy complications. Adaptive immune response induced by T. gondii infection stimulates T cells and macrophages to produce high levels of cytokines. Physiologically, the microenvironment of pregnancy was Th2-dominant. Here we set up a pregnant Sprague-Dawley rat model, and reported the polarization of macrophages induced by genotype Chinese 1 strain (Wh6) of Toxoplasma, and its adverse impact on pregnancy. The results showed that Wh6 infection pre- or in-gestation both led to abnormal pregnancy outcomes. Peritoneal macrophages in pre-gestation infection were polarized toward classically activated macrophages (M1), while in-gestation infection drove macrophages to polarize toward M2 activation. The Th2-dominant immune response in pregnant rat somewhat inhibits the excessive bias of the macrophages toward M1, and partially, toward M2. Infection of pre- and in-gestation may alter the physiological immune microenvironment in pregnant rats, giving rise to abnormal pregnancy outcomes. PMID:25496968

Kong, Lanting; Zhang, Qian; Chao, Jing; Wen, Huiqin; Zhang, Yihua; Chen, He; Pappoe, Faustina; Zhang, Aimei; Xu, Xiucai; Cai, Yihong; Li, Min; Luo, Qingli; Zhang, Linjie; Shen, Jilong

2015-03-01

221

Phase instability induced by polar nanoregions in a relaxor ferroelectric system  

NASA Astrophysics Data System (ADS)

Relaxor ferroelectrics are a special class of material that exhibit an enormous electromechanical response and are easily polarized with an external field. These properties make them attractive for applications as sensors and actuators. Local clusters of randomly oriented polarization, known as polar nanoregions (PNRs), are specific to relaxor ferroelectrics and play a key role in governing their dielectric properties. Here, we show through neutron inelastic scattering experiments that the PNRs can also significantly affect the structural properties of the relaxor ferroelectric Pb(Zn1/3Nb2/3)O3-4.5%PbTiO3 (PZN-4.5%PT). A strong interaction is found between the PNRs and the propagation of acoustic phonons. A comparison between acoustic phonons propagating along different directions reveals a large asymmetry in the lattice dynamics that is induced by the PNRs. We suggest that a phase instability induced by this PNR-phonon interaction may contribute to the ultrahigh piezoelectric response of this and related relaxor ferroelectric materials. Our results naturally explain the emergence of the various observed monoclinic phases in these systems.

Xu, Guangyong; Wen, Jinsheng; Stock, C.; Gehring, P. M.

2008-07-01

222

Contact-Induced Mitochondrial Polarization Supports HIV-1 Virological Synapse Formation  

PubMed Central

ABSTRACT Rapid HIV-1 spread between CD4 T lymphocytes occurs at retrovirus-induced immune cell contacts called virological synapses (VS). VS are associated with striking T cell polarization and localized virus budding at the site of contact that facilitates cell-cell spread. In addition to this, spatial clustering of organelles, including mitochondria, to the contact zone has been previously shown. However, whether cell-cell contact specifically induces dynamic T cell remodeling during VS formation and what regulates this process remain unclear. Here, we report that contact between an HIV-1-infected T cell and an uninfected target T cell specifically triggers polarization of mitochondria concomitant with recruitment of the major HIV-1 structural protein Gag to the site of cell-cell contact. Using fixed and live-cell imaging, we show that mitochondrial and Gag polarization in HIV-1-infected T cells occurs within minutes of contact with target T cells, requires the formation of stable cell-cell contacts, and is an active, calcium-dependent process. We also find that perturbation of mitochondrial polarization impairs cell-cell spread of HIV-1 at the VS. Taken together, these data suggest that HIV-1-infected T cells are able to sense and respond to contact with susceptible target cells and undergo dynamic cytoplasmic remodeling to create a synaptic environment that supports efficient HIV-1 VS formation between CD4 T lymphocytes. IMPORTANCE HIV-1 remains one of the major global health challenges of modern times. The capacity of HIV-1 to cause disease depends on the virus's ability to spread between immune cells, most notably CD4 T lymphocytes. Cell-cell transmission is the most efficient way of HIV-1 spread and occurs at the virological synapse (VS). The VS forms at the site of contact between an infected cell and an uninfected cell and is characterized by polarized assembly and budding of virions and clustering of cellular organelles, including mitochondria. Here, we show that cell-cell contact induces rapid recruitment of mitochondria to the contact site and that this supports efficient VS formation and consequently cell-cell spread. Additionally, we observed that cell-cell contact induces a mitochondrion-dependent increase in intracellular calcium, indicative of cellular signaling. Taken together, our data suggest that VS formation is a regulated process and thus a potential target to block HIV-1 cell-cell spread. PMID:25320323

Groppelli, Elisabetta; Starling, Shimona

2014-01-01

223

Induced orbital polarization of Ga ligand atoms in UTGa5 ( T=Ni , Pd, and Pt)  

NASA Astrophysics Data System (ADS)

We report a resonant x-ray scattering study of antiferromagnetic uranium compounds UTGa5 ( T=Ni , Pd, and Pt) at the Ga K edge. A large resonant signal is observed below the Néel temperatures. The azimuth dependence in both ?-?' and ?-?' polarization channels establishes that the resonant signal has the symmetry of the magnetic dipole. This resonance with the band electrons is interpreted within a semilocalized model as an orbital polarization of the Ga 4p states induced through strong hybridization with U 5f valence level. These results demonstrate that resonant magnetic x-ray scattering at the anions, taken in combination with symmetry arguments, can be used to determine the configuration of the U 5f moments and provide information about the hybridization.

Kuzushita, K.; Ishii, K.; Wilkins, S. B.; Janousova, B.; Inami, T.; Ohwada, K.; Tsubota, M.; Murakami, Y.; Kaneko, K.; Metoki, N.; Ikeda, S.; Haga, Y.; ?nuki, Y.; Bernhoeft, N.; Lander, G. H.

2006-03-01

224

Strain-induced phase transition and electron spin-polarization in graphene spirals  

NASA Astrophysics Data System (ADS)

Spin-polarized triangular graphene nanoflakes (t-GNFs) serve as ideal building blocks for the long-desired ferromagnetic graphene superlattices, but they are always assembled to planar structures which reduce its mechanical properties. Here, by joining t-GNFs in a spiral way, we propose one-dimensional graphene spirals (GSs) with superior mechanical properties and tunable electronic structures. We demonstrate theoretically the unique features of electron motion in the spiral lattice by means of first-principles calculations combined with a simple Hubbard model. Within a linear elastic deformation range, the GSs are nonmagnetic metals. When the axial tensile strain exceeds an ultimate strain, however, they convert to magnetic semiconductors with stable ferromagnetic ordering along the edges. Such strain-induced phase transition and tunable electron spin-polarization revealed in the GSs open a new avenue for spintronics devices.

Zhang, Xiaoming; Zhao, Mingwen

2014-07-01

225

Polarization dependent formation of femtosecond laser-induced periodic surface structures near stepped features  

SciTech Connect

Laser-induced periodic surface structures (LIPSS) are formed near 110?nm-tall Au microstructured edges on Si substrates after single-pulse femtosecond irradiation with a 150 fs pulse centered near a 780 nm wavelength. We investigate the contributions of Fresnel diffraction from step-edges and surface plasmon polariton (SPP) excitation to LIPSS formation on Au and Si surfaces. For certain laser polarization vector orientations, LIPSS formation is dominated by SPP excitation; however, when SPP excitation is minimized, Fresnel diffraction dominates. The LIPSS orientation and period distributions are shown to depend on which mechanism is activated. These results support previous observations of the laser polarization vector influencing LIPSS formation on bulk surfaces.

Murphy, Ryan D. [Applied Physics Program, University of Michigan, Ann Arbor, Michigan 48109 (United States); Torralva, Ben [Department of Atmospheric, Oceanic and Space Sciences, University of Michigan, Ann Arbor, Michigan 48109 (United States); Adams, David P. [Sandia National Laboratories, Albuquerque, New Mexico 87123 (United States); Yalisove, Steven M. [Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109 (United States)

2014-06-09

226

Statistics of polarization mode dispersion-induced gain fluctuations in Raman amplified optical transmissions.  

PubMed

A systematic experimental evaluation of polarization mode dispersion (PMD) -induced polarization-dependent gain (PDG) in forward pumped Raman amplification in dispersion-shifted and in dispersion-compensating fiber was performed. Good agreement was obtained between the measured statistical parameters and the current analytical model for PDG fluctuation statistics. The probability distribution of the PDG was approximately Maxwellian within the range PMD >0.05 ps/km(1/2). The interplay between PMD and gain fluctuations is discussed; random birefringence strongly reduces PDG fluctuations. However, the trade-off between reduction of the power penalties for PDG and increase of the penalties for PMD distortion precludes the use of PMD instead of source depolarization techniques for reduction of PDG. PMID:15233423

Bessa dos Santos, Alexandre; von der Weid, Jean Pierre

2004-06-15

227

Vector magnetometry based on electromagnetically induced transparency in linearly polarized light  

SciTech Connect

We develop a generalized principle of electromagnetically induced transparency (EIT) vector magnetometry based on high-contrast EIT resonances and the symmetry of atom-light interaction in the linearly polarized bichromatic fields. Operation of such vector magnetometer on the D{sub 1} line of {sup 87}Rb has been demonstrated. The proposed compass-magnetometer has an increased immunity to shifts produced by quadratic Zeeman and ac-Stark effects, as well as by atom-buffer gas and atom-atom collisions. In our proof-of-principle experiment the detected angular sensitivity to magnetic field orientation is 10{sup -3} deg/Hz{sup 1/2}, which is limited by laser intensity fluctuations, light polarization quality, and magnitude of the magnetic field.

Yudin, V. I. [Institute of Laser Physics, Siberian Branch of RAS, Novosibirsk 630090 (Russian Federation); Novosibirsk State University, Novosibirsk 630090 (Russian Federation); Novosibirsk State Technical University, Novosibirsk 630092 (Russian Federation); Taichenachev, A. V. [Institute of Laser Physics, Siberian Branch of RAS, Novosibirsk 630090 (Russian Federation); Novosibirsk State University, Novosibirsk 630090 (Russian Federation); Dudin, Y. O. [School of Physics, Georgia Institute of Technology, Atlanta, Georgia 30332-0430 (United States); Velichansky, V. L. [Moscow State Engineering and Physics Institute, Moscow 115409 (Russian Federation); Lebedev Physical Institute, RAS, Moscow 117924 (Russian Federation); Zibrov, A. S. [Physics Department, Harvard University, Cambridge, Massachusetts 02138 (United States); Zibrov, S. A. [Lebedev Physical Institute, RAS, Moscow 117924 (Russian Federation)

2010-09-15

228

ANALYSIS OF SEEING-INDUCED POLARIZATION CROSS-TALK AND MODULATION SCHEME PERFORMANCE  

SciTech Connect

We analyze the generation of polarization cross-talk in Stokes polarimeters by atmospheric seeing, and its effects on the noise statistics of spectropolarimetric measurements for both single-beam and dual-beam instruments. We investigate the time evolution of seeing-induced correlations between different states of one modulation cycle and compare the response to these correlations of two popular polarization modulation schemes in a dual-beam system. Extension of the formalism to encompass an arbitrary number of modulation cycles enables us to compare our results with earlier work. Even though we discuss examples pertinent to solar physics, the general treatment of the subject and its fundamental results might be useful to a wider community.

Casini, R.; De Wijn, A. G.; Judge, P. G. [High Altitude Observatory, National Center for Atmospheric Research, P.O. Box 3000, Boulder, CO 80307-3000 (United States)

2012-09-20

229

First principles calculation of polarization induced interfacial charges in GaN/AlN heterostructures  

E-print Network

We propose a new method to calculate polarization induced interfacial charges in semiconductor heterostructures using classical electrostatics applied to real-space band diagrams from first principles calculations and apply it to GaN/AlN heterostructures with ultrathin AlN layers (4-6 monolayers). We show that the calculated electric fields and interfacial charges are independent of the exchange-correlation functionals used (local-density approximation and hybrid functionals). We also find the calculated interfacial charge of (6.8 +/- 0.4) x 10^13 cm-2 to be in excellent agreement with experiments and the value of 6.58 x 10^13 cm-2 calculated from bulk polarization constants, validating the use of bulk constants even for very thin films.

Rohan Mishra; Oscar D. Restrepo; Siddharth Rajan; Wolfgang Windl

2011-05-17

230

Strain-induced phase transition and electron spin-polarization in graphene spirals  

PubMed Central

Spin-polarized triangular graphene nanoflakes (t-GNFs) serve as ideal building blocks for the long-desired ferromagnetic graphene superlattices, but they are always assembled to planar structures which reduce its mechanical properties. Here, by joining t-GNFs in a spiral way, we propose one-dimensional graphene spirals (GSs) with superior mechanical properties and tunable electronic structures. We demonstrate theoretically the unique features of electron motion in the spiral lattice by means of first-principles calculations combined with a simple Hubbard model. Within a linear elastic deformation range, the GSs are nonmagnetic metals. When the axial tensile strain exceeds an ultimate strain, however, they convert to magnetic semiconductors with stable ferromagnetic ordering along the edges. Such strain-induced phase transition and tunable electron spin-polarization revealed in the GSs open a new avenue for spintronics devices. PMID:25027550

Zhang, Xiaoming; Zhao, Mingwen

2014-01-01

231

Flexoelectric polarization changes induced by light in a nematic liquid crystal  

NASA Astrophysics Data System (ADS)

In a nematic liquid crystal where the director field has a splay-bend deformation mediated by the boundary conditions there is a certain intrinsic polarization density distribution characteristic of the flexoelectric properties of the medium. By application of an electric field perpendicular to the director, a twist is induced which is a measure of the flexoelectric anisotropy [I. Dozov, Ph. Martinot-Lagarde, and G. Durand, J. Phys. (Paris) Lett. 43, L-365 (1982)]. We show that in molecules susceptible to a photoinduced configurational change we may change the volume polarization by UV illumination and relate the change in flexoelectric coefficients to the configurational change in the molecule. In the experiment we use the British Drug House (Merck) nematic mixture E7 doped with 5 wt % of the dye 4-hexyloxy-(4'-hexyl)azobenzene. The photoinduced trans-cis configurational change leads to an increase by 40% in the flexoelectric anisotropy (es-eb)/K.

Hermann, D. S.; Rudquist, P.; Ichimura, K.; Kudo, K.; Komitov, L.; Lagerwall, S. T.

1997-03-01

232

Spectral analysis of bilateral or alternate-site kindling-induced afterdischarges in the rabbit hippocampi.  

PubMed

Kindling is one of the popular animal models of temporal lobe epilepsy. In the present study following the previous results obtained using unilateral hippocampal kindling (UK), we performed spectral analysis of bilateral or alternate-site kindling-induced afterdischarges (ADs) in the rabbit hippocampi. Eight and ten adult rabbits were used for bilateral kindling (BK) and alternate-site kindling (AK), respectively. Kindling stimuli consisted of a train of biphasic pulses (1ms duration each) of 50Hz for 1s, with suprathreshold intensity for AD. The stimulations were applied simultaneously to the bilateral hippocampi in the BK and were delivered to the right and left hippocampus once every 24h in the AK. Motor responses were classified into five stages according to the conventional criteria. All animals in BK as well as AK developed stage 5 convulsions. This contrasts to the result of UK (kindled: 50%; incomplete: 50%). We normalized power spectral density (PSD) and monitored the changes in the proportion of lower frequency band component (LFB: 0-9Hz) and the higher frequency band (HFB: 12-30Hz). BK animals showed a significantly large decrement (0.5 times, p<0.01) in LFB component at the final stage compared to the initial stage, but a very large increment (4.7 times) in HFB component. Likewise, AK animals exhibited a significantly large decrement (0.6 times, p<0.01) in LFB component at the final stage, but a very large increment (3.6 times) in HFB component. Correlation analyses were performed between the HFB component and AD duration, interictal discharge frequency, and behavioral stages during kindling progression. Very strong positive correlations were found in both kindling animals. Chronological spectral analysis of seizure discharges, resulting in a pattern of LFB decrement accompanied by HFB increment, is a convenient tool to investigate epileptic disorders and diagnose epileptic states. PMID:22578702

Tsuchiya, Komei; Kogure, Shinichi

2012-09-01

233

Unexpected temporal evolution of atomic spectral lines of aluminum in a laser induced breakdown spectroscopy experiment  

NASA Astrophysics Data System (ADS)

The temporal evolution of the laser induced breakdown (LIBS) signal of a pure aluminum sample was studied under nitrogen and air atmospheres. In addition to the usual decrease of signal due to plasma cooling, unexpected temporal evolutions were observed for a spectral lines of aluminum, which revealed the existence of collisional energy transfer effects. Furthermore, molecular bands of AlN and AlO were observed in the LIBS spectra, indicating recombination of aluminum with the ambient gas. Within the experimental conditions reported in this study, both collisional energy transfer and recombination processes occurred around 1.5 ?s after the laser shot. This highlights the possible influence of collisional and chemical effects inside the plasma that can play a role on LIBS signals.

Saad, Rawad; L'Hermite, Daniel; Bousquet, Bruno

2014-11-01

234

Vacuum polarization induced by a cosmic string in anti-de Sitter spacetime  

E-print Network

In this paper we investigate the vacuum expectation values (VEVs) of the field squared and the energy-momentum tensor associated with a massive scalar quantum field induced by a generalized cosmic string in D-dimensional anti-de Sitter (AdS) spacetime. In order to develop this analysis we evaluate the corresponding Wightman function. As we shall observe, this function is expressed as the sum of two terms: the first one corresponds to the Wightman function in pure AdS bulk and the second one is induced by the presence of the string. The second contribution is finite at coincidence limit and is used to provide closed expressions for the parts in the VEVs of the field squared and the energy-momentum tensor induced by the presence of the string. Because the analysis of vacuum polarizations effects in pure AdS spacetime have been developed in the literature, here we are mainly interested in the investigation of string-induced effects. We show that the curvature of the background spacetime has an essential influence on the VEVs at distances larger than the curvature radius. In particular, at large distances the decay of the string-induced VEVs is power-law for both massless and massive fields. The string-induced parts vanish on the AdS boundary and they dominate the pure AdS part for points near the AdS horizon.

E. R. Bezerra de Mello; A. A. Saharian

2011-10-10

235

Self-screening of the quantum confined Stark effect by the polarization induced bulk charges in the quantum barriers  

NASA Astrophysics Data System (ADS)

InGaN/GaN light-emitting diodes (LEDs) grown along the polar orientations significantly suffer from the quantum confined Stark effect (QCSE) caused by the strong polarization induced electric field in the quantum wells, which is a fundamental problem intrinsic to the III-nitrides. Here, we show that the QCSE is self-screened by the polarization induced bulk charges enabled by designing quantum barriers. The InN composition of the InGaN quantum barrier graded along the growth orientation opportunely generates the polarization induced bulk charges in the quantum barrier, which well compensate the polarization induced interface charges, thus avoiding the electric field in the quantum wells. Consequently, the optical output power and the external quantum efficiency are substantially improved for the LEDs. The ability to self-screen the QCSE using polarization induced bulk charges opens up new possibilities for device engineering of III-nitrides not only in LEDs but also in other optoelectronic devices.

Zhang, Zi-Hui; Liu, Wei; Ju, Zhengang; Tiam Tan, Swee; Ji, Yun; Kyaw, Zabu; Zhang, Xueliang; Wang, Liancheng; Wei Sun, Xiao; Volkan Demir, Hilmi

2014-06-01

236

Self-screening of the quantum confined Stark effect by the polarization induced bulk charges in the quantum barriers  

SciTech Connect

InGaN/GaN light-emitting diodes (LEDs) grown along the polar orientations significantly suffer from the quantum confined Stark effect (QCSE) caused by the strong polarization induced electric field in the quantum wells, which is a fundamental problem intrinsic to the III-nitrides. Here, we show that the QCSE is self-screened by the polarization induced bulk charges enabled by designing quantum barriers. The InN composition of the InGaN quantum barrier graded along the growth orientation opportunely generates the polarization induced bulk charges in the quantum barrier, which well compensate the polarization induced interface charges, thus avoiding the electric field in the quantum wells. Consequently, the optical output power and the external quantum efficiency are substantially improved for the LEDs. The ability to self-screen the QCSE using polarization induced bulk charges opens up new possibilities for device engineering of III-nitrides not only in LEDs but also in other optoelectronic devices.

Zhang, Zi-Hui; Liu, Wei; Ju, Zhengang; Tiam Tan, Swee; Ji, Yun; Kyaw, Zabu; Zhang, Xueliang; Wang, Liancheng; Wei Sun, Xiao, E-mail: exwsun@ntu.edu.sg, E-mail: volkan@stanfordalumni.org [LUMINOUS Centre of Excellence for Semiconductor Lighting and Displays, School of Electrical and Electronic Engineering, School of Physical and Mathematical Sciences, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798 (Singapore); Volkan Demir, Hilmi, E-mail: exwsun@ntu.edu.sg, E-mail: volkan@stanfordalumni.org [LUMINOUS Centre of Excellence for Semiconductor Lighting and Displays, School of Electrical and Electronic Engineering, School of Physical and Mathematical Sciences, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798 (Singapore); Department of Electrical and Electronics, Department of Physics, and UNAM-Institute of Material Science and Nanotechnology, Bilkent University, TR-06800 Ankara (Turkey)

2014-06-16

237

Mycobacterium tuberculosislpdC, Rv0462, induces dendritic cell maturation and Th1 polarization  

SciTech Connect

Highlights: {yields} Treatment with Rv0462 induces the expression of surface molecules and the production of cytokines in DCs. {yields} Rv0462 induces the activation of MAPKs. {yields} Rv0462-treated DCs enhances the proliferation of CD4{sup +} T cells. -- Abstract: Mycobacterium tuberculosis, the etiological factor of pulmonary tuberculosis, causes significant morbidity and mortality worldwide. Activation of host immune responses for containment of mycobacterial infections involves participation of innate immune cells, such as dendritic cells (DCs). In this study, we demonstrated that the gene encoding lipoamide dehydrogenase C (lpdC) from M. tuberculosis, Rv0462, induce maturation and activation of DCs involved in the MAPKs signaling pathway. Moreover, Rv0462-treated DCs activated naive T cells, polarized CD4{sup +} and CD8{sup +} T cells to secrete IFN-{gamma} in syngeneic mixed lymphocyte reactions, which would be expected to contribute to Th1 polarization of the immune response. Our results suggest that Rv0462 can contribute to the innate and adaptive immune responses during tuberculosis infection, and thus modulate the clinical course of tuberculosis.

Heo, Deok Rim [Department of Microbiology and Immunology, School of Medicine, Pusan National University, Beom-eo Ri, Mulgum Eop, Yangsan, Gyeongsangnam-do 626-770 (Korea, Republic of)] [Department of Microbiology and Immunology, School of Medicine, Pusan National University, Beom-eo Ri, Mulgum Eop, Yangsan, Gyeongsangnam-do 626-770 (Korea, Republic of); Shin, Sung Jae; Kim, Woo Sik [Department of Microbiology, College of Medicine, Chungnam National University, Munwha-Dong, Jung-Ku, Daejeon 301-747 (Korea, Republic of)] [Department of Microbiology, College of Medicine, Chungnam National University, Munwha-Dong, Jung-Ku, Daejeon 301-747 (Korea, Republic of); Noh, Kyung Tae; Park, Jin Wook; Son, Kwang Hee [Department of Microbiology and Immunology, School of Medicine, Pusan National University, Beom-eo Ri, Mulgum Eop, Yangsan, Gyeongsangnam-do 626-770 (Korea, Republic of)] [Department of Microbiology and Immunology, School of Medicine, Pusan National University, Beom-eo Ri, Mulgum Eop, Yangsan, Gyeongsangnam-do 626-770 (Korea, Republic of); Park, Won Sun [Department of Physiology, Kangwon National University, School of Medicine, Chuncheon 200-701 (Korea, Republic of)] [Department of Physiology, Kangwon National University, School of Medicine, Chuncheon 200-701 (Korea, Republic of); Lee, Min-Goo [Department of Physiology, Korea University, College of Medicine, Anam-dong, Sungbuk-Gu, Seoul 136-705 (Korea, Republic of)] [Department of Physiology, Korea University, College of Medicine, Anam-dong, Sungbuk-Gu, Seoul 136-705 (Korea, Republic of); Kim, Daejin [Department of Anatomy, Chung-Ang University, College of Medicine, 221 Heuksuk-Dong, Dongjak-Ku, Seoul 156-756 (Korea, Republic of)] [Department of Anatomy, Chung-Ang University, College of Medicine, 221 Heuksuk-Dong, Dongjak-Ku, Seoul 156-756 (Korea, Republic of); Shin, Yong Kyoo [Department of Pharmacology, Chung-Ang University, College of Medicine, 221 Heuksuk-Dong, Dongjak-Ku, Seoul 156-756 (Korea, Republic of)] [Department of Pharmacology, Chung-Ang University, College of Medicine, 221 Heuksuk-Dong, Dongjak-Ku, Seoul 156-756 (Korea, Republic of); Jung, In Duk, E-mail: jungid@pusan.ac.kr [Department of Microbiology and Immunology, School of Medicine, Pusan National University, Beom-eo Ri, Mulgum Eop, Yangsan, Gyeongsangnam-do 626-770 (Korea, Republic of); Research Institute of Convergence of Biomedical Science and Technology, Pusan National University Yangsan Hospital, Beom-eo Ri, Mulgum Eop, Yangsan, Gyeongsangnam-do 626-770 (Korea, Republic of); Park, Yeong-Min, E-mail: immunpym@pusan.ac.kr [Department of Microbiology and Immunology, School of Medicine, Pusan National University, Beom-eo Ri, Mulgum Eop, Yangsan, Gyeongsangnam-do 626-770 (Korea, Republic of) [Department of Microbiology and Immunology, School of Medicine, Pusan National University, Beom-eo Ri, Mulgum Eop, Yangsan, Gyeongsangnam-do 626-770 (Korea, Republic of); Research Institute of Convergence of Biomedical Science and Technology, Pusan National University Yangsan Hospital, Beom-eo Ri, Mulgum Eop, Yangsan, Gyeongsangnam-do 626-770 (Korea, Republic of)

2011-08-05

238

Polyunsaturated fatty acids induce polarized submembranous F-actin aggregates and kill Entamoeba histolytica.  

PubMed

We have recently identified a novel galacto-glycerolipid (GGL) from the plant Oxalis corniculata that killed the human pathogen Entamoeba histolytica. In this study, we show that the anti-amoebic activity of GGL was due to the polyunsaturated fatty acid ?-linolenic acid (C18:3 ) side chain. Treatment of ?-linolenic acid to E. histolytica trophozoites disrupted the cytoskeletal network and led to polarization of F-actin at one end of the cells with prominent filopodial extensions. In addition, clustering of surface receptors and signaling molecules was also observed adjacent to the polarized actin similar to concanavalin-A-(Con-A) induced capping. But, in contrast to Con-A-induced capping, ?-linolenic acid induced caps were not shed and showed accumulation of long and numerous filopodia at the cap site. We found that ?-linolenic acid disrupts the actin cytoskeletal network, which led to the detachment of plasma membrane from the underlying cytoskeleton. A similar effect was observed with other dietary fatty acids such as linoleic acid (C18:2 ), arachidonic acid (C20:4 ), eicosapentaenoic acid (C20:5 ), and docosahexaenoic acid (C22:6 ). Our findings showed that dietary polyunsaturated fatty acids are powerful anti-amoebic agents that lead to disruption of the actin cytoskeleton. PMID:23568815

Manna, Dipak; Grewal, Jaspreet Singh; Sarkar, Bidyut; Maiti, Sudipta; Lohia, Anuradha

2013-05-01

239

Cytochalasin-induced actin disruption of polarized enterocytes can augment internalization of bacteria.  

PubMed

Cytochalasin-induced actin disruption has often been associated with decreased bacterial internalization by cultured epithelial cells, although polarized enterocytes have not been systematically studied. In assays using confluent polarized HT-29 enterocytes, cytochalasin D appeared to increase internalization of wild-type Salmonella typhimurium, Proteus mirabilis, and Escherichia coli. HeLa and HEp-2 epithelial cells, as well as HT-29 and Caco-2 enterocytes, were used to clarify this unexpected observation. Resulting data showed that cytochalasin D was associated with increased internalization of S. typhimurium and P. mirabilis by both HT-29 and Caco-2 enterocytes and with increased internalization of E. coli by HT-29 enterocytes; with either HeLa or HEp-2 cells, cytochalasin was associated with no change or a decrease in internalization of these same bacterial strains. Cytochalasin caused decreased internalization of Listeria monocytogenes by HT-29, Caco-2, HeLa, and HEp-2 cells, indicating that cytochalasin did not consistently augment bacterial internalization by polarized enterocytes. Fluorescein-labeled phalloidin confirmed marked disruption of filamentous actin in cytochalasin-treated HT-29, Caco-2, HeLa, and HEp-2 cells. Cytochalasin had no noticeable effect on epithelial viability but caused distorted apical microvilli, cell rounding, and separation of adjacent enterocytes in confluent cultures (with a corresponding decrease in transepithelial electrical resistance). Scanning electron microscopy showed that cytochalasin-induced enhanced bacterial internalization was associated with preferential bacterial adherence on the exposed enterocyte lateral surface. Colchicine, used to disrupt microtubules, had no noticeable effect on bacterial internalization by HT-29 or Caco-2 enterocytes. These data indicated that for HT-29 and Caco-2 enterocytes, cytochalasin-induced disruption of filamentous actin might augment internalization of some bacterial species by a mechanism that appeared to involve exposure of the enterocyte lateral surface. PMID:9596696

Wells, C L; van de Westerlo, E M; Jechorek, R P; Haines, H M; Erlandsen, S L

1998-06-01

240

Shear wave induced resonance elastography of spherical masses with polarized torsional waves  

PubMed Central

Shear Wave Induced Resonance (SWIR) is a technique for dynamic ultrasound elastography of confined mechanical inclusions. It was developed for breast tumor imaging and tissue characterization. This method relies on the polarization of torsional shear waves modeled with the Helmholtz equation in spherical coordinates. To validate modeling, an in vitro set-up was used to measure and image the first three eigenfrequencies and eigenmodes of a soft sphere. A preliminary in vivo SWIR measurement on a breast fibroadenoma is also reported. Results revealed the potential of SWIR elastography to detect and mechanically characterize breast lesions for early cancer detection. PMID:23687384

Henni, Anis Hadj; Schmitt, Cédric; Trop, Isabelle; Cloutier, Guy

2013-01-01

241

Gravitational Wave Induced Rotation of the Plane of Polarization of Pulsar Signals  

E-print Network

We derive in this an expression for the rotation of plane of polarization, of an electromagnetic wave, induced by the field of a gravitational wave propagating along the same direction $\\approx \\f{G\\mu d^2\\Omega^4}{3\\o}$, $\\o$ and $\\Omega$ being their respective frequencies using the geometrical optics limit of the wave equation for fields. Estimating the effect for the case of pulses from binary pulsars, one finds it too small to be observable, there could be other sources like inspiralling binary or an asymmetric neutron star where the effect could be in the observable region.

A. R. Prasanna; S. Mohanty

2001-10-29

242

Spin polarized electric currents in semiconductor heterostructures induced by microwave radiation  

NASA Astrophysics Data System (ADS)

We report on microwave (mw) radiation induced electric currents in (Cd,Mn)Te/(Cd,Mg)Te and InAs/(In,Ga)As quantum wells subjected to an external in-plane magnetic field. The current generation is attributed to the spin-dependent energy relaxation of electrons heated by mw radiation. The relaxation produces equal and oppositely directed electron flows in the spin-up and spin-down subbands yielding a pure spin current. The Zeeman splitting of the subbands in the magnetic field leads to the conversion of the spin flow into a spin-polarized electric current.

Drexler, C.; Bel'kov, V. V.; Ashkinadze, B.; Olbrich, P.; Zoth, C.; Lechner, V.; Terent'ev, Ya. V.; Yakovlev, D. R.; Karczewski, G.; Wojtowicz, T.; Schuh, D.; Wegscheider, W.; Ganichev, S. D.

2010-11-01

243

Optically induced angular alignment of birefringent micro-objects by linear polarization  

NASA Astrophysics Data System (ADS)

Fluorinated polyimide micro-objects having large birefringence of ?n=-0.13 (refractive index n1=1.62, n2=1.49 for the wavelength ?=1.06 ?m), which were fabricated by reactive ion etching and suspended in water (n=1.33), were trapped and angularly aligned in a single Gaussian laser beam (?=1.06 ?m, power P>3 ?W). The optically induced angular alignment effect is caused by the transfer of spin angular momentum due to the interaction between their birefringence and the linearly polarized light.

Higurashi, E.; Sawada, R.; Ito, T.

1998-11-01

244

Degeneracy doubling and sublattice polarization in strain-induced pseudo-Landau levels  

NASA Astrophysics Data System (ADS)

The degeneracy and spatial support of pseudo-Landau levels (pLLs) in strained honeycomb lattices systematically depends on the geometry; for instance, in hexagonal and rectangular flakes the zeroth pLL displays a twofold increased degeneracy, while the characteristic sublattice polarization of the zeroth pLL is only fully realized in a zigzag-terminated triangle. These features are dictated by algebraic constraints in the atomistic theory and signify a departure from the standard picture in which all qualitative differences between pLLs and Landau levels induced by a magnetic field trace back to the valley antisymmetry of the pseudomagnetic field.

Poli, Charles; Arkinstall, Jake; Schomerus, Henning

2014-10-01

245

Parahydrogen-induced polarization of carboxylic acids: a pilot study of valproic acid and related structures.  

PubMed

Parahydrogen-induced polarization (PHIP) is a promising new tool for medical applications of MR, including MRI. The PHIP technique can be used to transfer high non-Boltzmann polarization, derived from parahydrogen, to isotopes with a low natural abundance or low gyromagnetic ratio (e.g. (13)C), thus improving the signal-to-noise ratio by several orders of magnitude. A few molecules acting as metabolic sensors have already been hyperpolarized with PHIP, but the direct hyperpolarization of drugs used to treat neurological disorders has not been accomplished until now. Here, we report on the first successful hyperpolarization of valproate (valproic acid, VPA), an important and commonly used antiepileptic drug. Hyperpolarization was confirmed by detecting the corresponding signal patterns in the (1)H NMR spectrum. To identify the optimal experimental conditions for the conversion of an appropriate VPA precursor, structurally related molecules with different side chains were analyzed in different solvents using various catalytic systems. The presented results include hyperpolarized (13)C NMR spectra and proton images of related systems, confirming their applicability for MR studies. PHIP-based polarization enhancement may provide a new MR technique to monitor the spatial distribution of valproate in brain tissue and to analyze metabolic pathways after valproate administration. PMID:24812006

Lego, Denise; Plaumann, Markus; Trantzschel, Thomas; Bargon, Joachim; Scheich, Henning; Buntkowsky, Gerd; Gutmann, Torsten; Sauer, Grit; Bernarding, Johannes; Bommerich, Ute

2014-07-01

246

An Internal Polarity Landmark Is Important for Externally Induced Hyphal Behaviors in Candida albicans?  

PubMed Central

Directional growth is a function of polarized cells such as neurites, pollen tubes, and fungal hyphae. Correct orientation of the extending cell tip depends on signaling pathways and effectors that mediate asymmetric responses to specific environmental cues. In the hyphal form of the eukaryotic fungal pathogen Candida albicans, these responses include thigmotropism and galvanotropism (hyphal turning in response to changes in substrate topography and imposed electrical fields, respectively) and penetration into semisolid substrates. During vegetative growth in C. albicans, as in the model yeast Saccharomyces cerevisiae, the Ras-like GTPase Rsr1 mediates internal cellular cues to position new buds in a prespecified pattern on the mother cell cortex. Here, we demonstrate that Rsr1 is also important for hyphal tip orientation in response to the external environmental cues that induce thigmotropic and galvanotropic growth. In addition, Rsr1 is involved in hyphal interactions with epithelial cells in vitro and its deletion diminishes the hyphal invasion of kidney tissue during systemic infection. Thus, Rsr1, an internal polarity landmark in yeast, is also involved in polarized growth responses to asymmetric environmental signals, a paradigm that is different from that described for the homologous protein in S. cerevisiae. Rsr1 may thereby contribute to the pathogenesis of C. albicans infections by influencing hyphal tip responses triggered by interaction with host tissues. PMID:18281602

Brand, Alexandra; Vacharaksa, Anjalee; Bendel, Catherine; Norton, Jennifer; Haynes, Paula; Henry-Stanley, Michelle; Wells, Carol; Ross, Karen; Gow, Neil A. R.; Gale, Cheryl A.

2008-01-01

247

Qubit-induced high-order nonlinear interaction of the polar molecules in a stripline cavity  

SciTech Connect

By the exchange of virtual microwave photon induced by a stripline cavity, we present a collective spin-qubit model for the indirect interaction between a superconducting charge-phase qubit and an ensemble of the polar molecules. More importantly, the high-order nonlinear interaction among the polar molecules is generated successfully by using the SU(2) commutation relations of the qubit. Numerical simulation shows that this high-order nonlinear interaction can lead to a strong macroscopic quantum coherent effect, even if the parameters including the molecular number are small. For a large molecular number, the Kerr nonlinear interaction is also obtained. Moreover, it is found that this Kerr nonlinear parameter depends linearly on the molecular number, and as a result, has a giant value, which is 2 to 3 orders of magnitude larger than that in the other proposal schemes of the solid-state systems. Our results present a way to investigate the quantum nonlinear dynamics of the polar molecules.

Chen Gang [State Key Laboratory of Quantum Optics and Quantum Optics Devices, Shanxi University, Taiyuan 030006 (China); Department of Physics, Shaoxing University, Shaoxing 312000 (China); Zhang Hao; Yang Yonggang; Xiao Liantuan; Jia Suotang [State Key Laboratory of Quantum Optics and Quantum Optics Devices, Shanxi University, Taiyuan 030006 (China); Wang Rui [Department of Physics, Zhejiang Ocean University, ZhouShan 316000 (China)

2010-07-15

248

Detection of gravity-induced polarity of cytoplasmic streaming in Chara  

NASA Technical Reports Server (NTRS)

Gravity induces a polarity of cytoplasmic streaming in vertically-oriented internodal cells of characean algae. The motive force that powers cytoplasmic streaming is generated at the ectoplasmic/endoplasmic interface. The velocity of streaming, which is about 100 micrometers/s at this interface, decreases with distance from the interface on either side of the cell to 0 micrometers/s near the middle. Therefore, when discussing streaming velocity it is necessary to specify the tangential plane through the cell in which streaming is being measured. This is easily done with a moderate resolution light microscope (which has a lateral resolution of 0.6 micrometers and a depth of field of 1.4 micrometers), but is obscured when using any low resolution technique, such as low magnification light microscopy or laser Doppler spectroscopy. In addition, the effect of gravity on the polarity of cytoplasmic streaming declines with increasing physiological age of isolated cells. Using a classical mechanical analysis, we show that the effect of gravity on the polarity of cytoplasmic streaming cannot result from the effect of gravity acting directly on individual cytoplasmic particles. We suggest that gravity may best be perceived by the entire cell at the plasma membrane-extracellular matrix junction.

Staves, M. P.; Wayne, R.; Leopold, A. C.

1995-01-01

249

Proteomic Analysis of Acetaminophen-Induced Changes in Mitochondrial Protein Expression Using Spectral Counting  

PubMed Central

Comparative proteomic analysis following treatment with acetaminophen (APAP) was performed on two different models of APAP-mediated hepatocellular injury in order to both identify common targets for adduct formation and track drug-induced changes in protein expression. Male C57BL/6 mice were used as a model for APAP-mediated liver injury in vivo and TAMH cells were used as a model for APAP-mediated cytotoxicity in vitro. SEQUEST was unable to identify the precise location of sites of adduction following treatment with APAP in either system. However, semiquantitative analysis of the proteomic datasets using spectral counting revealed a downregulation of P450 isoforms associated with APAP bioactivation, and an upregulation of proteins related to the electron transport chain by APAP compared to control. Both mechanisms are likely compensatory in nature as decreased P450 expression is likely to attenuate toxicity associated with N-acetyl-p-quinoneimine (NAPQI) formation, whereas APAP-induced electron transport chain component upregulation may be an attempt to promote cellular bioenergetics. PMID:21329376

Stamper, Brendan D.; Mohar, Isaac; Kavanagh, Terrance J.; Nelson, Sidney D.

2011-01-01

250

Accommodation-induced variations in retinal thickness measured by spectral domain optical coherence tomography  

NASA Astrophysics Data System (ADS)

To research retinal stretching or distortion with accommodation, accommodation-induced changes in retinal thickness (RT) in the macular area were investigated in a population of young adults (n=23) by using a dual-channel spectral domain optical coherence tomography (SD-OCT) system manufactured in-house for this study. This dual-channel SD-OCT is capable of imaging the cornea and retina simultaneously with an imaging speed of 24 kHz A-line scan rate, which can provide the anatomical dimensions of the eye, including the RT and axial length. Thus, the modification of the RT with accommodation can be calculated. A significant decrease in the RT (13.50±1.25 ?m) was observed during maximum accommodation. In the 4 mm×4 mm macular area centered at the fovea, we did not find a significant quadrant-dependent difference in retinal volume change, which indicates that neither retinal stretching nor distortion was quadrant-dependent during accommodation. We speculate that the changes in RT with maximum accommodation resulted from accommodation-induced ciliary muscle contractions.

Fan, Shanhui; Sun, Yong; Dai, Cuixia; Zheng, Haihua; Ren, Qiushi; Jiao, Shuliang; Zhou, Chuanqing

2014-09-01

251

Humidity effects on tip-induced polarization switching in lithium niobate  

SciTech Connect

In the last several decades, ferroelectrics have attracted much attention as perspective materials for nonlinear optics and data storage devices. Scanning probe microscopy (SPM) has emerged as a powerful tool both for studies of domain structures with nanoscale spatial resolution and for writing the isolated nanodomains by local application of the electric field. Quantitative analysis of the observed behavior requires understanding the role of environmental factors on imaging and switching process. Here, we study the influence of the relative humidity in the SPM chamber on tip-induced polarization switching. The observed effects are attributed to existence of a water meniscus between the tip and the sample surface in humid atmosphere. These results are important for a deeper understanding of complex investigations of ferroelectric materials and their applications and suggest the necessity for fundamental studies of electrocapillary phenomena at the tip-surface junction and their interplay with bias-induced materials responses.

Ievlev, A. V. [The Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37922 (United States); Ferroelectric Laboratory, Institute of Natural Sciences, Ural Federal University, 51 Lenin Ave., 620000 Ekaterinburg (Russian Federation); Morozovska, A. N. [Institute of Physics, National Academy of Sciences of Ukraine, 46 pr. Nauki, 03028 Kiev (Ukraine); Shur, V. Ya. [Ferroelectric Laboratory, Institute of Natural Sciences, Ural Federal University, 51 Lenin Ave., 620000 Ekaterinburg (Russian Federation); Kalinin, S. V. [The Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37922 (United States)

2014-03-03

252

Time lapse electrical resistivity and induced polarization monitoring of near-surface CO2 injection  

NASA Astrophysics Data System (ADS)

Field experiments were carried out to investigate the efficiency and the reliability of electrical geophysical methods to detect and monitor CO2 leakages at field scale. Each test consisted of injecting CO2 for approximately four hours at five meters depth, corresponding to a cumulative mass of gas of around six kilograms. Electrical resistivity tomography and temporal induced polarization were acquired at the surface before, during and after injections along profiles centered to the injection well. Time lapse measurements were compared to a reference acquisition performed before the injection. We observe that both methods are sensitive to variations in terms of gas saturation, the chargeability measurements being more sensitive to the presence of CO2 than electrical resistivity. During the injection, an increase of chargeability and a decrease of the measured resistivity are observed at depth in the vinicity of the injection well. Afterwards, the medium equilibrates and retrieves its original state, corresponding to the reference acquisition. The temporal variations of electrical resistivity and induced polarization responses are interpreted in terms of gas dissolution and water/gas saturation.

Allègre, V.; Kremer, T.; Williard, E.; Schmutz, M.; Maineult, A. J.

2013-12-01

253

Combined straightforward inversion of resistivity and induced polarization (time-domain) sounding data  

NASA Astrophysics Data System (ADS)

It is proposed that the Straightforward Inversion Scheme (SIS) developed by the authors for 1D inversion of resistivity sounding and magneto-telluric sounding data can also be used in similar fashion for time-domain induced polarization sounding data. The necessary formulations based on dynamic dipole theory are presented. It is shown that by using induced polarization potential, measured at the instant when steady state current is switched off, an equation can be developed for apparent 'chargeability-resistivity' which is similar to the one for apparent resistivity. The two data sets of apparent resistivity and apparent chargeability-resistivity can be inverted in a combined manner, using SIS for a common uniform thickness layer earth model to estimate the respective subsurface distributions of resistivity and chargeability-resistivity. The quotient of the two profiles will give the sought after chargeability profile. A brief outline of SIS is provided for completeness. Three theoretical models are included to confirm the efficacy of SIS software by inverting only the synthetic resistivity sounding data. Then one synthetic data set based on a geological model and three field data sets (combination of resistivity and IP soundings) from diverse geological and geographical regions are included as validation of the proposal. It is hoped that the proposed scheme would complement the resistivity interpretation with special reference to shaly sand formations.

Sri Niwas; Gupta, Pravin K.

2011-10-01

254

Polarization rotation and piezoelectricity of electric field-induced monoclinic and triclinic structures in strained PbTiO3  

NASA Astrophysics Data System (ADS)

Electric field-induced polarization rotation, phase changes, and piezoelectric effect of strained PbTiO3 films have been investigated using a phenomenological approach. Low-symmetry monoclinic and triclinic structures have been induced, and the type of intermediate phases during polarization rotation is closely related to both the initial state at zero electric field and anisotropy of the in-plane strain. The monoclinic MC and triclinic structures in general may exhibit high shear piezoelectric coefficient d35 and sometimes also remarkable enhancement of longitudinal piezoelectric coefficient d33 around the transition point. High piezoelectric activity and low critical field have been found in epitaxial PbTiO3 with equal but opposite in-plane strain where monoclinic MC is the only intermediate phase on the polarization path. The present results suggest that anisotropy of epitaxial strain may have significant impact on polarization rotation behavior and electromechanical coupling of ferroelectric thin films.

Ma, Wenhui; Hao, Aize

2014-12-01

255

Thermal and kinematic corrections to the microwave background polarization induced by galaxy clusters along the line of sight  

E-print Network

We derive analytic expressions for the leading-order corrections to the polarization induced in the cosmic microwave background (CMB) due to scattering off hot electrons in galaxy clusters along the line of sight. For a thermal distribution of electrons with a kinetic temperature of 10 keV and a bulk peculiar velocity of 1000 km/s, the dominant corrections to the polarization induced by the primordial CMB quadrupole and the cluster peculiar velocity arise from electron thermal motion and are at the level of 10 per cent in each case, near the peak of the polarization signal. When more sensitive measurements become feasible, these effects will be significant for the determination of transverse peculiar velocities, and the value of the CMB quadrupole at the cluster redshift, via the cluster polarization route.

Anthony Challinor; Matthew Ford; Anthony Lasenby

1999-05-18

256

High-resolution polarization observations inside spectral lines of magnetic Ap stars. I. Instrumentation and observations of. beta. Coronae Borealis  

Microsoft Academic Search

We have constructed a coude photon-counting polarimeter capable of attaining (with a Fabry-Perot interferometer) a high resolution. A description of the instrument is given, with a discussion of various sources of systematic error in the polarimetry. Observations of linear and circular polarization in the spectrum of the Ap star ..beta.. Coronae Borealis, throughout the magnetic cycle, are obtained across an

E. F. Borra; A. H. Vaughan

1977-01-01

257

Symmetry Breaking and Electrical Frustration during Tip-Induced Polarization Switching in the Nonpolar Cut of Lithium Niobate Single Crystals.  

PubMed

Polarization switching in ferroelectric materials is governed by a delicate interplay between bulk polarization dynamics and screening processes at surfaces and domain walls. Here we explore the mechanism of tip-induced polarization switching at nonpolar cuts of uniaxial ferroelectrics. In this case, the in-plane component of the polarization vector switches, allowing for detailed observations of the resultant domain morphologies. We observe a surprising variability of resultant domain morphologies stemming from a fundamental instability of the formed charged domain wall and associated electric frustration. In particular, we demonstrate that controlling the vertical tip position allows the polarity of the switching to be controlled. This represents a very unusual form of symmetry breaking where mechanical motion in the vertical direction controls the lateral domain growth. The implication of these studies for ferroelectric devices and domain wall electronics are discussed. PMID:25506745

Ievlev, Anton V; Alikin, Denis O; Morozovska, Anna N; Varenyk, Olexander V; Eliseev, Eugene A; Kholkin, Andrei L; Shur, Vladimir Ya; Kalinin, Sergei V

2015-01-27

258

Inhibition of cyclophosphamide-induced oxidative stress in rat brain by polar and non-polar extracts of Annatto (Bixa orellana) seeds.  

PubMed

Annatto (Bixa orellana) seeds are widely distributed throughout the Tropics and have been used to provide both colour and flavour to food. This study sought to assess the ability of dietary inclusion of polar (water) and non-polar (chloroform) extracts of Annatto (B. orellana) seeds on cyclophosphamide-induced oxidative stress in rat brain. The total phenol content and antioxidant activities of polar (water) and non-polar (chloroform) extracts of Annatto seeds were determined in vitro and in vivo. The results of the study showed that intraperitoneal administration of cyclophosphamide (75 mg/kg of body weight) caused a significant increase (P<0.05) in the malondialdehyde (MDA) content of the brain; however, dietary inclusion of Annatto seed extracts (0.1% and 0.2%) caused dose-dependent significant decrease (P<0.05) in the MDA content of the brain. Likewise, the extracts also caused dose-dependent inhibition of the elevated serum glutamate oxaloacetate transaminase (SGOT), glutamate pyruvate transaminase (SGPT), alkaline phosphatase and total bilirubin. However, the non-polar extract had significantly higher inhibitory effects on the elevated MDA production in brain and serum liver function markers. This higher protective effect of the non-polar extract could be attributed to its higher antioxidant properties as typified by its significantly higher (P<0.05) reducing power, free-radical scavenging and Fe (II) chelating ability. Therefore, dietary inclusion of Annato seed extracts as food colourant could prevent oxidative stress occasioned by cyclophosphamide administration, but the non-polar extract is a better protectant. PMID:20137904

Oboh, Ganiyu; Akomolafe, Toyin L; Adefegha, Stephen A; Adetuyi, Abayomi O

2011-03-01

259

Spectral observation of the soft X-ray background and of the North Polar Spur with solid state spectrometers  

NASA Technical Reports Server (NTRS)

Soft X-ray diffuse background observations in the 0.3-1.5 keV interval of two sky regions, near the north galactic pole and the North Polar Spur (NPS) are reported. Data were taken with a solid-state spectrometer carried by a rocket. The near-polar region exhibited O VII ion emissions at 530 eV. A second component was not identified but was attributed to the Galactic Halo. Fe XVIII, Ne IX, and O VIII contributions were detected in the NPS, along with an enhancement at 1.35 keV from Mg XI lines. A two-temperature contour was fit to the spectra and chi-square confidence levels of 90 and 68 percent were obtained.

Rocchia, R.; Arnaud, M.; Blondel, C.; Cheron, C.; Christy, J. C.; Koch, L.; Rothenflug, R.; Schnopper, H. W.; Delvaille, J. P.

1983-01-01

260

Spectral lineshapes of collision-induced absorption (CIA) and collision-induced light scattering (CILS) for molecular nitrogen using isotropic intermolecular potential. New insights and perspectives  

NASA Astrophysics Data System (ADS)

The rototranslational collision-induced absorption (CIA) at different temperatures and collision-induced light scattering (CILS) at room temperature of nitrogen gas are analyzed in terms of new isotropic intermolecular potential, multipole-induced dipole functions and interaction-induced pair polarizability models, using quantum spectral lineshape computations. The irreducible spherical form for the induced operator of light scattering mechanisms was determined. The high frequency wings are discussed in terms of the collision-induced rotational Rayleigh effect and estimates for the dipole-octopole polarizability E4, is obtained and checked with the ab initio theoretical value. The quality of the present potential has been checked by comparing between calculated and experimental thermo-physical and transport properties over a wide temperature range, which are found to be in good agreement.

El-Kader, M. S. A.; Mostafa, S. I.; Bancewicz, T.; Maroulis, G.

2014-08-01

261

Ligand Induced Circular Dichroism and Circularly Polarized Luminescence in CdSe Quantum Dots  

PubMed Central

Chiral thiol capping ligands L- and D-cysteines induced modular chiroptical properties in achiral cadmium selenide quantum dots (CdSe QDs). Cys-CdSe prepared from achiral oleic acid capped CdSe by post-synthetic ligand exchange displayed size-dependent electronic circular dichroism (CD) and circularly polarized luminescence (CPL). Opposite CPL signals were measured for the CdSe QDs capped with D- and L-cysteine. The CD profile and CD anisotropy varied with size of CdSe nanocrystals with largest anisotropy observed for CdSe nanoparticles of 4.4 nm. Magic angle spinning solid state NMR (MAS ssNMR) experiments suggested bidentate interaction between cysteine and the surface of CdSe. Density functional theory (DFT) calculations verified that attachment of L- and D-cysteine to the surface of model (CdSe)13 nanoclusters induces measurable opposite CD signals for the exitonic band of the nanocluster. The chirality was induced by the hybridization of highest occupied CdSe molecular orbitals with those of the chiral ligand. PMID:24200288

Tohgha, Urice; Deol, Kirandeep K.; Porter, Ashlin G.; Bartko, Samuel G.; Choi, Jung Kyu; Leonard, Brian M.; Varga, Krisztina; Kubelka, Jan; Muller, Gilles; Balaz, Milan

2014-01-01

262

[A spectral-correlational analysis of the electrical activity of the sensorimotor cortex and the internal geniculate body during a motor-polarization dominant].  

PubMed

By spectral-correlative analysis the dynamics was studied of structural changes of coherent relations of the electrical activity of the sensorimotor cortex and medial geniculate body (MGB) of the rabbit under motor polarization dominant created by the action of DC anode on the sensorimotor cortex area. It was shown, that in the power spectra of the MGB, besides the increase of the delta-region components in interstimulus intervals at the dominant, during the action of the sound stimulus a distinct maximum appeared in the alpha-rhythm range of the electrical activity of MGB of the "dominant" hemisphere. The coherence increase of the delta-range of the MGB and the sensorimotor cortex electrical activity in the "dominant" part of the brain was manifested exclusively in the period of sound stimulus action. PMID:1329385

Rusinova, E V

1992-01-01

263

Morphologies of laser-induced damage in hafnia-silica multilayer mirror and polarizer coatings  

SciTech Connect

Hafnium-silica multilayer mirrors and polarizers were deposited by e-beam evaporation onto BK7 glass substrates. The mirrors and polarizers were coated for operation at 1053 nm at 45{degree} and at Brewster`s angle (56{degree}), respectively. They were tested with a single 3-ns laser pulse. Morphology of the laser-induced damage was characterized by optical and scanning electron microscopy. Four distinct damage morphologies were found: pits, flatbottom pits, scalds, and delaminates. The pits and flat bottom pits (<30{mu}m dia) were detected at lower fluences (as low as 5 J/cm{sup 2}). The pits seemed to result from ejection of nodular defects by causing local enhancement of the electric field. Scalds and delaminates could be observed at higher fluences (above 13 J/cm{sup 2}) and seemed to result from the formation of plasmas on the surface. These damage types often originated at pits and were less than 300 {mu}m diameter; their size increased almost linearly with fluence. Finally, effects of the damage on the beam (reflectivity degradation and phase modulations) were measured.

Genin, F.Y.; Stolz, C.J.

1996-08-01

264

Intramolecular electron transfer in lysozyme studied by time-resolved chemically induced dynamic nuclear polarization.  

PubMed

The kinetics of the chemically induced dynamic nuclear polarization (CIDNP) produced in reactions of hen lysozyme with photosensitizers have been studied for the native state of the protein at pH 3.8 and for two denatured states. The latter were generated by raising the temperature to 80 degrees C or by combining a temperature rise (to 50 degrees C) with the addition of chemical denaturant (10 M urea). Detailed analysis of the CIDNP time dependence on a microsecond time scale revealed that, in both denatured states, intramolecular electron transfer (IET) from a tyrosine residue to the cation radical of a tryptophan residue (rate constant k(f)) is highly efficient and plays a decisive role in the evolution of the nuclear polarization. To describe the observed CIDNP kinetics with a self-consistent set of parameters, IET in the reverse direction, from a tryptophan residue to a tyrosine residue radical (rate constant k(r)), has also to be taken into account. The IET rate constants determined by analysis of the CIDNP kinetics are, at 80 degrees C: k(f) = 1 x 10(5) s(-1) and k(r) = 1 x 10(4) s(-1); at 50 degrees C in the presence of 10 M urea: k(f) = 7 x 10(4) s(-1), k(r) = 1 x 10(4) s(-1). IET does not appear to influence the CIDNP kinetics of the native state. PMID:16853855

Morozova, Olga B; Hore, P J; Sagdeev, Renad Z; Yurkovskaya, Alexandra V

2005-11-24

265

Mapping polarization induced surface band bending on the Rashba semiconductor BiTeI.  

PubMed

Surfaces of semiconductors with strong spin-orbit coupling are of great interest for use in spintronic devices exploiting the Rashba effect. BiTeI features large Rashba-type spin splitting in both valence and conduction bands. Either can be shifted towards the Fermi level by surface band bending induced by the two possible polar terminations, making Rashba spin-split electron or hole bands electronically accessible. Here we demonstrate the first real-space microscopic identification of each termination with a multi-technique experimental approach. Using spatially resolved tunnelling spectroscopy across the lateral boundary between the two terminations, a previously speculated on p-n junction-like discontinuity in electronic structure at the lateral boundary is confirmed experimentally. These findings realize an important step towards the exploitation of the unique behaviour of the Rashba semiconductor BiTeI for new device concepts in spintronics. PMID:24898943

Butler, Christopher John; Yang, Hung-Hsiang; Hong, Jhen-Yong; Hsu, Shih-Hao; Sankar, Raman; Lu, Chun-I; Lu, Hsin-Yu; Yang, Kui-Hon Ou; Shiu, Hung-Wei; Chen, Chia-Hao; Kaun, Chao-Cheng; Shu, Guo-Jiun; Chou, Fang-Cheng; Lin, Minn-Tsong

2014-01-01

266

Laser-induced damage in nonlinear crystals on irradiation direction and polarization  

NASA Astrophysics Data System (ADS)

Nonlinear-optical crystals are attractive materials for the high-power frequency converter with high damage threshold, phase matching characteristics, wide transparency range, and large effective nonlinear coefficients. Especially as to the power laser applications, its laser-induced damage threshold determines the limit of performance in the optical system. The threshold depends not only on the intrinsic material parameters but also on the laser beam parameters is use. We have investigated the bulk damage threshold of several crystals at a single-shot operation for frequency converter depending on the laser irradiation direction and its polarization. For KDP and CLBO crystals, the damage threshold in the direction of c-axis is about tow times higher than that in the a- or b-axis at 1.064 micrometers of wavelength. This result is consistent with the molecular bonding structure in different directions of the crystal. The relation between the bulk damage pattern and the crystal structure is also discussed.

Yoshida, Hidetsugu; Jitsuno, Takahisa; Fujita, Hisanori; Nakatsuka, Masahiro; Kamimura, Tomosumi; Yoshimura, Masashi; Sasaki, Takatomo; Miyamoto, Akio; Yoshida, Kunio

2000-03-01

267

Focusing Sources on Induced Polarization and Electrical Resistivity Method Applied to Soil Pollution Problems  

NASA Astrophysics Data System (ADS)

In recent years the problems of soil contamination have been increasing and geophysical methods, particularly electrical resistivity tomography (ERT) have struggled to find and monitor cases of contamination. Moreover, Induced Polarization (IP) has shown promise in mapping contaminant plumes, although both techniques (ERT and IP) have problems like noise, inductive coupling, effects of electrodes, etc. limiting the precision and accuracy of the data. To overcome these problems, this paper introduces a novel technique of focusing sources. This technique reduces the effects of adjacent vertical formations and contacts due to the flowing of current in a vertical way at the zone where the electrode potentials have been deployed. This fact allows obtaining cleaner data of ERT and IP. In order to introduce the proposed technique a vertical contact synthetic model is studied and after to a cultivar area in Hidalgo State, México which presents different types of

Tejero, A.; Lopez, A.; Induced Polarization Team

2013-05-01

268

COMPLEX RESISTIVITY OF FAULT GOUGE AND ITS SIGNIFICANCE FOR EARTHQUAKE LIGHTS AND INDUCED POLARIZATION.  

USGS Publications Warehouse

The authors measured complex resistivity of 2 water-saturated San Andreas fault gouges from 10** minus **3 to 10**6 Hz and confining pressures of 0. 2 to 200 MPa. Consistent with earlier observations of clays and common rocks, large low-frequency permittivities were observed in all cases. Comparisons were made to induced polarization (IP) measurements by inversion of the data into the time domain, where it was found that principal features of the IP response curves were due to these large low-frequency permittivities. The results also suggest that following large earthquakes, significant electrical charge could remain for many seconds and could result in a variety of reported electromagnetic effects. Refs.

Lockner, David A.; Byerlee, James D.

1985-01-01

269

Ferroelectric polarization induces electric double layer bistability in electrolyte-gated field-effect transistors.  

PubMed

The dense surface charges expressed by a ferroelectric polymeric thin film induce ion displacement within a polyelectrolyte layer and vice versa. This is because the density of dipoles along the surface of the ferroelectric thin film and its polarization switching time matches that of the (Helmholtz) electric double layers formed at the ferroelectric/polyelectrolyte and polyelectrolyte/semiconductor interfaces. This combination of materials allows for introducing hysteresis effects in the capacitance of an electric double layer capacitor. The latter is advantageously used to control the charge accumulation in the semiconductor channel of an organic field-effect transistor. The resulting memory transistors can be written at a gate voltage of around 7 V and read out at a drain voltage as low as 50 mV. The technological implication of this large difference between write and read-out voltages lies in the non-destructive reading of this ferroelectric memory. PMID:24251907

Fabiano, Simone; Crispin, Xavier; Berggren, Magnus

2014-01-01

270

Angular distribution of products of ternary nuclear fission induced by cold polarized neutrons  

NASA Astrophysics Data System (ADS)

Within quantum fission theory, angular distributions of products originating from the ternary fission of nuclei that is induced by polarized cold and thermal neutrons are investigated on the basis of a nonevaporative mechanism of third-particle emission and a consistent description of fission-channel coupling. It is shown that the inclusion of Coriolis interaction both in the region of the discrete and in the region of the continuous spectrum of states of the system undergoing fission leads to T-odd correlations in the aforementioned angular distributions. The properties of the TRI and ROT effects discovered recently, which are due to the interference between the fission amplitudes of neutron resonances, are explored. The results obtained here are compared with their counterparts from classic calculations based on the trajectory method.

Bunakov, V. E.; Kadmensky, S. G.; Kadmensky, S. S.

2008-11-01

271

Holding beam injection for improving self-induced polarization rotation in a semiconductor optical amplifier  

NASA Astrophysics Data System (ADS)

A scheme for improving the self-induced polarization rotation (SPR) in a semiconductor optical amplifier (SOA) based on holding beam injection is proposed. Gain recovery of TE and TM modes can be largely accelerated through an appropriate holding beam injection, with which the response of SPR in the SOA for ultrafast signal can be speeded up. Holding beam injection is employed in SPR-based optical power equalization as an example of validation, in which the distortion of RZ (return-to-zero)and the overshoot of NRZ (non-return-to-zero) signal are largely suppressed, and the extension ratio are improved by 10 dB and 7 dB, respectively.

Zhang, S. J.; Zhang, Y. L.; Liu, S.; Liu, Y.

2012-11-01

272

Circularly polarized luminescence from individual microstructures of conjugated polymer aggregates with solvent-induced chirality.  

PubMed

We report a microscopic study of circularly polarized luminescence (CPL) from R and S isomers of aggregates of the conjugated polymer F8BT, a copolymer containing fluorene and thiophene monomer units. Chirality in the aggregates is induced by addition of either (R)- or (S)-limonene during aggregation in solution. Solid-state samples are prepared either by drop-casting or spin-coating of the aggregate solution. CPL dissymmetry parameter g measured for individual aggregate microstructures shows a broad distribution of values ranging from positive to negative even for the same isomer. The difference in the centers of the g distribution between the R and S isomers reflects the intrinsic CPL from the chiral aggregates, and is found to depend on the size of the aggregate structures. On the other hand, the large widths of the distributions are ascribed to an optical effect arising from phase retardation along the optical path of the CPL inside the sample. PMID:25050630

Katayama, Kenta; Hirata, Shuzo; Vacha, Martin

2014-09-01

273

Reduction of polarization-induced artifacts in grating-based spectrometers  

Microsoft Academic Search

An optical device that converts unpolarized light into a single polarization state is described. The device is based on a polarizing beam splitter that separates the two polarization directions. The beam splitter is combined with two pairs of equilateral prisms that are used to collimate the two beams in terms of both propagation and polarization directions. When it is used

Kiang Wei Kho; Paul R. Stoddart; Gavan Rosman; Martin Harris; Alex Mazzolini

2005-01-01

274

Field Trials of the Multi-Source Approach for Resistivity and Induced Polarization Data Acquisition  

NASA Astrophysics Data System (ADS)

Implementing systems of distributed receivers and transmitters for resistivity and induced polarization data is an almost inevitable result of the availability of wireless data communication modules and GPS modules offering precise timing and instrument locations. Such systems have a number of advantages; for example, they can be deployed around obstacles such as rivers, canyons, or mountains which would be difficult with traditional 'hard-wired' systems. However, deploying a system of identical, small, battery powered, transceivers, each capable of injecting a known current and measuring the induced potential has an additional and less obvious advantage in that multiple units can inject current simultaneously. The original purpose for using multiple simultaneous current sources (multi-source) was to increase signal levels. In traditional systems, to double the received signal you inject twice the current which requires you to apply twice the voltage and thus four times the power. Alternatively, one approach to increasing signal levels for large-scale surveys collected using small, battery powered transceivers is it to allow multiple units to transmit in parallel. In theory, using four 400 watt transmitters on separate, parallel dipoles yields roughly the same signal as a single 6400 watt transmitter. Furthermore, implementing the multi-source approach creates the opportunity to apply more complex current flow patterns than simple, parallel dipoles. For a perfect, noise-free system, multi-sources adds no new information to a data set that contains a comprehensive set of data collected using single sources. However, for realistic, noisy systems, it appears that multi-source data can substantially impact survey results. In preliminary model studies, the multi-source data produced such startling improvements in subsurface images that even the authors questioned their veracity. Between December of 2012 and July of 2013, we completed multi-source surveys at five sites with depths of exploration ranging from 150 to 450 m. The sites included shallow geothermal sites near Reno Nevada, Pomarance Italy, and Volterra Italy; a mineral exploration site near Timmins Quebec; and a landslide investigation near Vajont Dam in northern Italy. These sites provided a series of challenges in survey design and deployment including some extremely difficult terrain and a broad range of background resistivity and induced values. Despite these challenges, comparison of multi-source results to resistivity and induced polarization data collection with more traditional methods support the thesis that the multi-source approach is capable of providing substantial improvements in both depth of penetration and resolution over conventional approaches.

LaBrecque, D. J.; Morelli, G.; Fischanger, F.; Lamoureux, P.; Brigham, R.

2013-12-01

275

Observation of spectral composition and polarization of sub-terahertz emission from dense plasma during relativistic electron beam–plasma interaction  

SciTech Connect

The paper presents results of measurements of sub-terahertz electromagnetic emission from magnetized plasma during injection of a powerful relativistic electron beam of microsecond duration in plasma with the density of 3?×?10{sup 14?}cm{sup ?3}. It was found that the spectrum of the radiation concentrated in three distinct regions with high level of spectral power density. The first region is located near f{sub 1}?=?100?GHz; the second one is in the vicinity of 190?GHz, and the third region is in the frequency interval f{sub 3}?=?280–340?GHz. Polarization vectors of the emission in the first and third regions (f{sub 1} and f{sub 3}) are directed mainly perpendicular to the magnetic field in the plasma. At the same time, the polarization of the radiation in the vicinity of f{sub 2}?=?190?GHz is parallel to the magnetic field. The most likely mechanism of electromagnetic wave generation in the frequency regions f{sub 1} and f{sub 2} is the linear conversion of the plasma oscillations into the electromagnetic waves on strong gradients of the plasma density. The third region is situated in the vicinity of second harmonic of electron plasma frequency, and we explain this emission by the coalescence of the upper-hybrid oscillations at high level turbulence in plasma.

Arzhannikov, A. V.; Burmasov, V. S.; Ivanov, I. A.; Kuznetsov, S. A.; Postupaev, V. V.; Sinitsky, S. L.; Vyacheslavov, L. N. [Budker Institute of Nuclear Physics, 11 Lavrentiev Ave., Novosibirsk 630090 (Russian Federation); Novosibirsk State University, 2 Pirogova St., Novosibirsk 630090 (Russian Federation); Burdakov, A. V. [Budker Institute of Nuclear Physics, 11 Lavrentiev Ave., Novosibirsk 630090 (Russian Federation); Novosibirsk State Technical University, 20 Karl Marks Ave., Novosibirsk 630092 (Russian Federation); Gavrilenko, D. E.; Kasatov, A. A.; Mekler, K. I.; Rovenskikh, A. F. [Budker Institute of Nuclear Physics, 11 Lavrentiev Ave., Novosibirsk 630090 (Russian Federation); Polosatkin, S. V.; Sklyarov, V. F. [Budker Institute of Nuclear Physics, 11 Lavrentiev Ave., Novosibirsk 630090 (Russian Federation); Novosibirsk State University, 2 Pirogova St., Novosibirsk 630090 (Russian Federation); Novosibirsk State Technical University, 20 Karl Marks Ave., Novosibirsk 630092 (Russian Federation)

2014-08-15

276

Polarization phase-shifting interferometer by rotating azo-polymer film with photo-induced optical anisotropy  

NASA Astrophysics Data System (ADS)

A new type of phase-shifting interferometer was presented by rotating an azo-polymer film with photo-induced optical anisotropy in the light path of orthogonal polarization interferometry. By changing the angle of the optical axis of the azo-polymer film, four phase-shifted fringe patterns were obtained, from which phase difference between orthogonal polarized light could be calculated. The polarization states and the formation of the interferograms were analyzed theoretically using Jones matrix calculations and the experimental verification of the proposed method was also given. This method has a simple optical configuration which utilizes commercially available polarization devices and anisotropic azo-polymer film of low cost. The phase-shifting interferometer also demonstrates a new application of azo-polymer film.

Yan, Peizheng; Wang, Keyi; Gao, Jiangang

2015-01-01

277

Red/blue spectral shifts of laser-induced fluorescence emission due to different nanoparticle suspensions in various dye solutions.  

PubMed

Red/blue shifts of laser-induced fluorescence (LIF) are investigated using several guest dielectric nanoscatterers, such as TiO2, ZnO, Al2O3, and SiO2, in the host Rd6G, RdB, Coumarin 4, and Coumarin 7 ethanolic solutions. A couple of inflection points are identified varying nanoparticle (NP) density into dye solutions based on LIF spectroscopy. The inflection of the spectral shift exhibits that the suspension of NPs in dye solutions significantly involves a couple of competitive chemical and optical mechanisms during photon traveling in scattering media regarding ballistic and diffusive transport. It is shown that the low, medium, and high NP additives in fluorescent suspension induce blue, red, and blue spectral shifts, respectively. PMID:25321111

Bavali, A; Parvin, P; Mortazavi, S Z; Mohammadian, M; Mousavi Pour, M R

2014-08-20

278

Orientational and interaction induced dynamics in the isotropic phase of a liquid crystal: Polarization resolved ultrafast optical Kerr effect spectroscopy  

Microsoft Academic Search

The ultrafast dynamics of the isotropic phase of a liquid crystal 4'-pentyl-4-p-biphenylcarbonitrile (5CB) have been investigated using polarization resolved optical Kerr effect spectroscopy. Measurements were made as a function of both temperature and dilution in nonpolar solvents. To separate single molecule and interaction induced components to the relaxation of the induced birefringence, measurements of both the anisotropic and isotropic response

Neil T. Hunt; Stephen R. Meech

2004-01-01

279

Orientational and interaction induced dynamics in the isotropic phase of a liquid crystal: Polarization resolved ultrafast optical Kerr effect spectroscopy  

Microsoft Academic Search

The ultrafast dynamics of the isotropic phase of a liquid crystal 4?-pentyl-4-p-biphenylcarbonitrile (5CB) have been investigated using polarization resolved optical Kerr effect spectroscopy. Measurements were made as a function of both temperature and dilution in nonpolar solvents. To separate single molecule and interaction induced components to the relaxation of the induced birefringence, measurements of both the anisotropic and isotropic response

Neil T. Hunt; Stephen R. Meech

2004-01-01

280

Strain-induced polarity switching of magnetic vortex in Fe1-xGax alloys with different compositions  

NASA Astrophysics Data System (ADS)

The strain-induced polarity switching of magnetic vortex in the Fe1-xGax nanodots with different compositions is demonstrated by a real-space phase-field model, which explicitly includes the cross-coupling between magnetization and mechanical strain. The composition of Fe1-xGax nanodots has significant influence on the critical shear strain that induces the polarity switching of magnetization vortex. The critical shear strain in the Fe71Ga29 nanodot is one order of magnitude smaller than that of the Fe19Ga81 nanodot, which makes the polarity switching much easier under a mechanical shear strain. In addition, we elucidate that both the magnetostrictive coefficient and exchange stiffness that changes with compositions play the decisive role in the critical behavior; the higher magnetostrictive coefficient (or lower exchange stiffness) decreases critical shear strain.

Li, Gui-ping; Wang, Jie; Shimada, Takahiro; Fang, Hui; Kitamura, Takayuki

2014-05-01

281

Switchable Induced Polarization in LaAlO3/SrTiO3 Heterostructures C. W. Bark,  

E-print Network

-based heterostructures as viable electronic devices. These control mechanisms include field effect from a back or frontSwitchable Induced Polarization in LaAlO3/SrTiO3 Heterostructures C. W. Bark, P. Sharma, Y. Wang, S that this effect is a result of electrical modification of the LaAlO3 surface (either due to electrochemical

Eom, Chang Beom

282

PHYSICAL REVIEW B 84, 155319 (2011) Nonequilibrium nuclear polarization and induced hyperfine and dipolar magnetic fields in  

E-print Network

PHYSICAL REVIEW B 84, 155319 (2011) Nonequilibrium nuclear polarization and induced hyperfine Department of Physics and Astronomy, California State University, Fullerton, California 92835, USA 2 Department of Physics and Astronomy and Optical Science and Technology Center, University of Iowa, Iowa City

Flatte, Michael E.

283

changes of L and K. Further, to estimate the MAE due to the induced polarization of the Pt  

E-print Network

changes of L and K. Further, to estimate the MAE due to the induced polarization of the Pt substrate, K can be decomposed in partial con- tributions arising from Co and Pt sites (28). For a single Co adatom, Pt sites contribute to about 15% of the total MAE. Because of the strong decrease of the Co MAE

Boyce, C. Kevin

284

Interferon Tau Alleviates Obesity-Induced Adipose Tissue Inflammation and Insulin Resistance by Regulating Macrophage Polarization  

PubMed Central

Chronic adipose tissue inflammation is a hallmark of obesity-induced insulin resistance and anti-inflammatory agents can benefit patients with obesity-associated syndromes. Currently available type I interferons for therapeutic immunomodulation are accompanied by high cytotoxicity and therefore in this study we have examined anti-inflammatory effects of interferon tau (IFNT), a member of the type I interferon family with low cellular toxicity even at high doses. Using a diet-induced obesity mouse model, we observed enhanced insulin sensitivity in obese mice administered IFNT compared to control mice, which was accompanied by a significant decrease in secretion of proinflammatory cytokines and elevated anti-inflammatory macrophages (M2) in adipose tissue. Further investigations revealed that IFNT is a potent regulator of macrophage activation that favors anti-inflammatory responses as evidenced by activation of associated surface antigens, production of anti-inflammatory cytokines, and activation of selective cell signaling pathways. Thus, our study demonstrates, for the first time, that IFNT can significantly mitigate obesity-associated systemic insulin resistance and tissue inflammation by controlling macrophage polarization, and thus IFNT can be a novel bio-therapeutic agent for treating obesity-associated syndromes and type 2 diabetes. PMID:24905566

Ying, Wei; Kanameni, Srikanth; Chang, Cheng-An; Nair, Vijayalekshmi; Safe, Stephen; Bazer, Fuller W.; Zhou, Beiyan

2014-01-01

285

Pressure-induced polar phases in multiferroic delafossite CuFeO2  

NASA Astrophysics Data System (ADS)

The pressure effect on the frustrated magnetic system CuFeO2 exhibiting multiferroic behavior has been studied by means of time-of-flight single crystal neutron diffraction combined with a hybrid-anvil-type pressure cell. The nonpolar collinear magnetic ground state (CM1 phase) with propagation vector k =(0,1/2,1/2) turns into a proper screw magnetic ordering with incommensurate modulation k =(0,q,1/2;q?0.4) and a polar 21' magnetic point group (ICM2 phase), between 3 and 4 GPa. This spin structure is similar to the ferroelectric phase induced by magnetic field or chemical doping under ambient pressure. Above, 4 GPa, a magnetic phase (ICM3) appears, with an incommensurate propagation vector that is unique for the CuFeO2 system, k =(qa,qb,qc;qa?0,qb?0.34,qc?0.43). This propagation vector at the general point results in triclinic magnetic symmetry which implies an admixture of both cycloidal and proper screw spin configurations. The ICM3 phase is stable in a narrow pressure range, and above 6 GPa, the spin-density collinear structure (ICM1 phase), similar to the first ordered state at ambient pressure, takes place. Comparing the degree of lattice distortions among the magnetic phases observed at ambient pressure, we discuss the origin of the pressure-induced magnetic phase transitions in CuFeO2.

Terada, Noriki; Khalyavin, Dmitry D.; Manuel, Pascal; Osakabe, Toyotaka; Radaelli, Paolo G.; Kitazawa, Hideaki

2014-06-01

286

The mechanism for continuum polarization in laser induced breakdown spectroscopy of Si(111)  

NASA Astrophysics Data System (ADS)

Polarization of the plasma luminescence produced by both nanosecond and femtosecond laser ablation of Si(111) was analyzed under different conditions of fluence and detection geometry. It is shown that the luminescence is partially polarized and is directed in the plane of the crystal. The time evolution of the plasma emission signal was also investigated with the use of a streak camera. The mechanism for polarization is proposed to be preferential reflection of s-polarized light (i.e., light polarized normal to the plane of laser incidence) by the melted surface, in agreement with the Fresnel equations. Earlier reports of much stronger polarization are shown to be erroneous.

Penczak, John S., Jr.; Liu, Yaoming; Schaller, Richard D.; Rich, Daniel H.; Gordon, Robert J.

2012-08-01

287

Resistivity and induced polarization monitoring of salt transport under natural hydraulic gradients  

SciTech Connect

The authors demonstrate the use of resistivity/induced polarization (IP) monitoring of salt transport under natural hydraulic loads. Electrical monitoring of saline tracer transport during forced injection has been demonstrated previously. Detection of tracer transport under natural hydraulic loading is difficult because neither the hydraulic load nor the tracer resistivity can be controlled. In one study, the authors identify the electrical response to salt transport in a dynamic beach environment. Resistivity/IP imagine resolved the structure of the saltwater-freshwater interface and evidence for tide-induced groundwater transport. Resistivity increases in the near surface and at depth, upbeach of the high-tide mark, accompanied by tidal transgression. They attribute this to desaturation and decreasing salinity in the near surface and to decreasing salinity at depth, despite tidal transgression. Monitoring of groundwater levels indicates a phase lag between the tide level and groundwater level, supporting the electrical data. IP was insensitive to groundwater salinity variation. In a second study, the authors identify the electrical response to recharge-induced salt transport from a road-sale storage facility. Conductivity and IP models for monitoring lines, located on the basis of an EM31 survey, resolved the subsurface salt distribution, IP modeling resolved the sediment-bedrock interface. Modeling of monthly conductivity differences revealed conductivity increases and decreases at the locations of salt contamination, which correlate with the recharge pattern. They attribute near-surface conductivity increases after heavy rainfall to increasing saturation and ion dissolution. Corresponding conductivity decreases at depth are attributed to flushing of the bedrock with freshwater. Essentially, the opposite response was observed during a quiet monitoring period following heavy recharge. Near-surface IP changes are consistent with this interpretation. Salt transport occurring under natural hydraulic conditions was monitored with resistivity imaging. IP improved characterization of the hydrogeologic framework but was of limited value in monitoring salt transport in these environments.

Slater, L.D.; Sandberg, S.K.

2000-04-01

288

Modulated spin structure responsible for the magnetic-field-induced polarization switching in multiferroic TbMn2O5  

NASA Astrophysics Data System (ADS)

Orthorhombic TbMn2O5 (o -TMO ) is a well-known multiferroic manganite with the remarkable property of polarization switching at 3 K under a bias magnetic (H) field along the a axis of P b 21m . To theoretically account for this outstanding observation, we have proposed a modulated spin structure under the saturated bias H field by considering the relative strength of the three relevant exchange parameters in o -TMO . The proposed modulated structure based on density-functional theory (DFT) calculations is described in terms of the spin angle ? between the neighboring M n4 +-Mn3 + spin moments on the a-b plane. We have shown that the computed DFT polarization plotted as a function of ? satisfactorily accounts for the observed H -field-induced polarization switching. We have further theoretically shown that the square of the critical field strength (Hc) needed for the polarization switching is inversely proportional to the degree of the extrinsic magnetoelectric coupling. The computed partial charge density demonstrates that the H -field-induced polarization switching also accompanies with the switching in the sign of the excess valence-electron density.

Lee, Jung-Hoon; Jang, Hyun Myung

2015-01-01

289

Over-limiting currents and deionization "shocks" in current-induced polarization: local-equilibrium analysis.  

PubMed

The problem is considered theoretically of dynamics of current-induced concentration polarization of interfaces between ideally perm-selective and non-ideally perm-selective ("leaky") ion-exchange media in binary electrolyte solutions under galvanostatic conditions and at negligible volume flow. In contrast to the previous studies, the analysis is systematically carried out in terms of local thermodynamic equilibrium in the approximation of local electric neutrality in virtual solution. For macroscopically homogeneous media, this enables one to obtain model-independent results in quadratures for the stationary state as well as an approximate scaling-form solution for the transient response to the step-wise increase in electric-current density. These results are formulated in terms of such phenomenological properties of the "leaky" medium as ion transport numbers, diffusion permeability to salt and specific chemical capacity. An easy-to-solve numerically 1D PDE is also formulated in the same terms. A systematic parametric study is carried out within the scope of fine-pore model of "leaky" medium in terms of such properties as volumetric concentration of fixed electric charges and diffusivities of ions of symmetrical electrolyte. While previous studies paid principal attention to the shape and propagation rate of the so-called deionization "shocks", we also consider in detail the time evolution of voltage drop and interface salt concentration. Our analysis confirms the previously predicted pattern of propagating deionization "shocks" within the "leaky" medium but also reveals several novel features. In particular, we demonstrate that the deionization-shock pattern is really pronounced only at intermediate ratios of fixed-charge concentration to the initial salt concentration and at quite high steady-state voltages where the model used in this and previous studies is applicable only at relatively early stages of concentration-polarization process. PMID:22947188

Yaroshchuk, Andriy

2012-11-15

290

Laser induced infrared spectral shift of the MgB2:Cr superconductor films  

NASA Astrophysics Data System (ADS)

During illumination of the MgB2:Cr2O3 films it was established substantial spectral shift of the infrared spectra in the vicinity of 20-50 cm-1. The excitations were performed by nanosecond Er:glass laser operating at 1.54 ?m and by microsecond 10.6 ?m CO2 laser. The spectral shifts of the IR maxima were in opposite spectral directions for the two types of lasers. This one observed difference correlates well with spectral shift of their critical temperatures. The possible explanation is given by performance of DFT calculations of the charge density redistribution and the time kinetics of the photovoltaic response. To understand the kinetics of the photoinduced processes the time kinetics of photoresponse was done for the particular laser wavelengths.

AlZayed, N. S.; Kityk, I. V.; Soltan, S.; El-Naggar, A. M.; Shahabuddin, M.

2015-02-01

291

Laser induced infrared spectral shift of the MgB2:Cr superconductor films.  

PubMed

During illumination of the MgB2:Cr2O3 films it was established substantial spectral shift of the infrared spectra in the vicinity of 20-50cm(-1). The excitations were performed by nanosecond Er:glass laser operating at 1.54?m and by microsecond 10.6?m CO2 laser. The spectral shifts of the IR maxima were in opposite spectral directions for the two types of lasers. This one observed difference correlates well with spectral shift of their critical temperatures. The possible explanation is given by performance of DFT calculations of the charge density redistribution and the time kinetics of the photovoltaic response. To understand the kinetics of the photoinduced processes the time kinetics of photoresponse was done for the particular laser wavelengths. PMID:25467659

AlZayed, N S; Kityk, I V; Soltan, S; El-Naggar, A M; Shahabuddin, M

2014-10-28

292

Investigation of the field-induced ferromagnetic phase transition in spin polarized neutron matter: a lowest order constrained variational approach  

E-print Network

In this paper, the lowest order constrained variational (LOCV) method has been used to investigate the magnetic properties of spin polarized neutron matter in the presence of strong magnetic field at zero temperature employing $AV_{18}$ potential. Our results indicate that a ferromagnetic phase transition is induced by a strong magnetic field with strength greater than $10^{18}\\ G$, leading to a partial spin polarization of the neutron matter. It is also shown that the equation of state of neutron matter in the presence of magnetic field is stiffer than the case in absence of magnetic field.

G. H. Bordbar; Z. Rezaei; Afshin Montakhab

2011-03-18

293

Magnetic-field-induced ferroelectric polarization reversal in the multiferroic Ge(1-x)Mn(x)Te semiconductor.  

PubMed

Ge(1-x)Mn(x)Te is shown to be a multiferroic semiconductor, exhibiting both ferromagnetic and ferroelectric properties. By ferromagnetic resonance we demonstrate that both types of order are coupled to each other. As a result, magnetic-field-induced ferroelectric polarization reversal is achieved. Switching of the spontaneous electric dipole moment is monitored by changes in the magnetocrystalline anisotropy. This also reveals that the ferroelectric polarization reversal is accompanied by a reorientation of the hard and easy magnetization axes. By tuning the GeMnTe composition, the interplay between ferromagnetism and ferroelectricity can be controlled. PMID:24580486

Przybyli?ska, H; Springholz, G; Lechner, R T; Hassan, M; Wegscheider, M; Jantsch, W; Bauer, G

2014-01-31

294

Magnetic-Field-Induced Ferroelectric Polarization Reversal in the Multiferroic Ge1-xMnxTe Semiconductor  

NASA Astrophysics Data System (ADS)

Ge1-xMnxTe is shown to be a multiferroic semiconductor, exhibiting both ferromagnetic and ferroelectric properties. By ferromagnetic resonance we demonstrate that both types of order are coupled to each other. As a result, magnetic-field-induced ferroelectric polarization reversal is achieved. Switching of the spontaneous electric dipole moment is monitored by changes in the magnetocrystalline anisotropy. This also reveals that the ferroelectric polarization reversal is accompanied by a reorientation of the hard and easy magnetization axes. By tuning the GeMnTe composition, the interplay between ferromagnetism and ferroelectricity can be controlled.

Przybyli?ska, H.; Springholz, G.; Lechner, R. T.; Hassan, M.; Wegscheider, M.; Jantsch, W.; Bauer, G.

2014-01-01

295

Spectral Integration Plasticity in Cat Auditory Cortex Induced by Perceptual Training  

PubMed Central

We investigated the ability of cats to discriminate differences between vowel-like spectra, assessed their discrimination ability over time, and compared spectral receptive fields in primary auditory cortex (AI) of trained and untrained cats. Animals were trained to discriminate changes in the spectral envelope of a broad-band harmonic complex in a 2-alternative forced choice procedure. The standard stimulus was an acoustic grating consisting of a harmonic complex with a sinusoidally modulated spectral envelope ('ripple spectrum'). The spacing of spectral peaks was conserved at 1, 2, or 2.66 peaks/octave. Animals were trained to detect differences in the frequency location of energy peaks, corresponding to changes in the spectral envelope phase. Average discrimination thresholds improved continuously during the course of the testing from phase-shifts of 96° at the beginning to 44° after 4–6 months of training. Responses of AI single units and small groups of neurons to pure tones and ripple spectra were modified during perceptual discrimination training with vowel-like ripple stimuli. The transfer function for spectral envelope frequencies narrowed and the tuning for pure tones sharpened significantly in discriminant versus naive animals. By contrast, control animals that used the ripple spectra only in a lateralization task showed broader ripple transfer functions and narrower pure-tone tuning than naïve animals. PMID:17896103

Keeling, M. Diane; Calhoun, Barbara M.; Krüger, Katharina; Polley, Daniel B.; Schreiner, Christoph E.

2008-01-01

296

Relationships between Hydrological Parameters obtained from Multi-Step Outflow Experiments and Induced Polarization Spectra of Soil Samples  

NASA Astrophysics Data System (ADS)

The investigation of relationships between complex electrical parameters and hydrological properties of soil samples is necessary to allow an interpretation of spectral induced polarization (SIP) data in terms of soil hydrological properties. Therefore, laboratory SIP measurements in a frequency range between 0.01 Hz and 100 Hz and hydrological multi-step outflow (MSO) experiments are performed on different samples of unconsolidated sediments. The investigated material includes a fine sand sample with a narrow grain size distribution between 0.1 and 0.3 mm and soil samples from different locations in the vicinity of Braunschweig. The SIP measurements were performed on samples fully saturated with a sodium chloride solution and a calcium chloride solution, respectively. Both solutions had a salt concentration of 0.001 mol/l. From the measured SIP spectra the mean relaxation time, the normalized total chargeability and a parameter describing the spreading of the relaxation time distribution were derived with the Debye decomposition approach. After finishing all SIP measurements, the MSO experiments were carried out to obtain the retention curves and hydraulic conductivity functions. The parameters of these functions, obtained by fitting the van Genuchten-Mualem model to the MSO data, were then compared with the parameters resulting from the Debye decomposition of the SIP spectra to find relationships between the electrical and hydrological properties. Evaluation of the first measurements indicates a correlation between the mean relaxation time and the van Genuchten-Mualem parameter ?. In literature, the mean relaxation time or equivalent parameters of models fitted to SIP spectra are often related to a characteristic pore size of the investigated material. The van Genuchten-Mualem parameter ? correlates with the inverse of the air entry pressure head of soils and thus can also be related to a pore size. The evidence for a relationship will be further studied by extending the number of investigated soil samples. A second pair of electrical and hydrological parameters promising a correlation is the so called non-uniformity parameter U? resulting from the Debye decomposition of SIP spectra and the van Genuchten-Mualem parameter n. Both parameters are related to the distribution of relaxation times and pore sizes, respectively.

Nordsiek, S.; Hördt, A.; Durner, W.; Diamantopoulos, E.

2012-04-01

297

LabVIEW-based control software for para-hydrogen induced polarization instrumentation  

NASA Astrophysics Data System (ADS)

The elucidation of cell metabolic mechanisms is the modern underpinning of the diagnosis, treatment, and in some cases the prevention of disease. Para-Hydrogen induced polarization (PHIP) enhances magnetic resonance imaging (MRI) signals over 10 000 fold, allowing for the MRI of cell metabolic mechanisms. This signal enhancement is the result of hyperpolarizing endogenous substances used as contrast agents during imaging. PHIP instrumentation hyperpolarizes Carbon-13 (13C) based substances using a process requiring control of a number of factors: chemical reaction timing, gas flow, monitoring of a static magnetic field (Bo), radio frequency (RF) irradiation timing, reaction temperature, and gas pressures. Current PHIP instruments manually control the hyperpolarization process resulting in the lack of the precise control of factors listed above, resulting in non-reproducible results. We discuss the design and implementation of a LabVIEW based computer program that automatically and precisely controls the delivery and manipulation of gases and samples, monitoring gas pressures, environmental temperature, and RF sample irradiation. We show that the automated control over the hyperpolarization process results in the hyperpolarization of hydroxyethylpropionate. The implementation of this software provides the fast prototyping of PHIP instrumentation for the evaluation of a myriad of 13C based endogenous contrast agents used in molecular imaging.

Agraz, Jose; Grunfeld, Alexander; Li, Debiao; Cunningham, Karl; Willey, Cindy; Pozos, Robert; Wagner, Shawn

2014-04-01

298

LabVIEW-based control software for para-hydrogen induced polarization instrumentation  

SciTech Connect

The elucidation of cell metabolic mechanisms is the modern underpinning of the diagnosis, treatment, and in some cases the prevention of disease. Para-Hydrogen induced polarization (PHIP) enhances magnetic resonance imaging (MRI) signals over 10 000 fold, allowing for the MRI of cell metabolic mechanisms. This signal enhancement is the result of hyperpolarizing endogenous substances used as contrast agents during imaging. PHIP instrumentation hyperpolarizes Carbon-13 ({sup 13}C) based substances using a process requiring control of a number of factors: chemical reaction timing, gas flow, monitoring of a static magnetic field (B{sub o}), radio frequency (RF) irradiation timing, reaction temperature, and gas pressures. Current PHIP instruments manually control the hyperpolarization process resulting in the lack of the precise control of factors listed above, resulting in non-reproducible results. We discuss the design and implementation of a LabVIEW based computer program that automatically and precisely controls the delivery and manipulation of gases and samples, monitoring gas pressures, environmental temperature, and RF sample irradiation. We show that the automated control over the hyperpolarization process results in the hyperpolarization of hydroxyethylpropionate. The implementation of this software provides the fast prototyping of PHIP instrumentation for the evaluation of a myriad of {sup 13}C based endogenous contrast agents used in molecular imaging.

Agraz, Jose, E-mail: joseagraz@ucla.edu; Grunfeld, Alexander; Li, Debiao [Department of Bioengineering, University of California, Los Angeles, California 91791 (United States) [Department of Bioengineering, University of California, Los Angeles, California 91791 (United States); BIRI, Cedars Sinai Medical Center, West Hollywood, California 90048 (United States); Cunningham, Karl [Ectron Corp, San Diego, California 92111 (United States)] [Ectron Corp, San Diego, California 92111 (United States); Willey, Cindy [Harris Corp, San Diego, California 92154 (United States)] [Harris Corp, San Diego, California 92154 (United States); Pozos, Robert [Department of Biology, San Diego State University, San Diego, California 92182 (United States)] [Department of Biology, San Diego State University, San Diego, California 92182 (United States); Wagner, Shawn [BIRI, Cedars Sinai Medical Center, West Hollywood, California 90048 (United States)] [BIRI, Cedars Sinai Medical Center, West Hollywood, California 90048 (United States)

2014-04-15

299

LabVIEW-based control software for para-hydrogen induced polarization instrumentation.  

PubMed

The elucidation of cell metabolic mechanisms is the modern underpinning of the diagnosis, treatment, and in some cases the prevention of disease. Para-Hydrogen induced polarization (PHIP) enhances magnetic resonance imaging (MRI) signals over 10,000 fold, allowing for the MRI of cell metabolic mechanisms. This signal enhancement is the result of hyperpolarizing endogenous substances used as contrast agents during imaging. PHIP instrumentation hyperpolarizes Carbon-13 ((13)C) based substances using a process requiring control of a number of factors: chemical reaction timing, gas flow, monitoring of a static magnetic field (Bo), radio frequency (RF) irradiation timing, reaction temperature, and gas pressures. Current PHIP instruments manually control the hyperpolarization process resulting in the lack of the precise control of factors listed above, resulting in non-reproducible results. We discuss the design and implementation of a LabVIEW based computer program that automatically and precisely controls the delivery and manipulation of gases and samples, monitoring gas pressures, environmental temperature, and RF sample irradiation. We show that the automated control over the hyperpolarization process results in the hyperpolarization of hydroxyethylpropionate. The implementation of this software provides the fast prototyping of PHIP instrumentation for the evaluation of a myriad of (13)C based endogenous contrast agents used in molecular imaging. PMID:24784636

Agraz, Jose; Grunfeld, Alexander; Li, Debiao; Cunningham, Karl; Willey, Cindy; Pozos, Robert; Wagner, Shawn

2014-04-01

300

Inducible IL10(+) suppressor B cells inhibit CNS inflammation and T helper 17 polarization.  

PubMed

Granulocyte-macrophage colony-stimulating factor (GMCSF) and MCP3 (aka CCL7) exert complementary, nonoverlapping, proimmune effects on responsive lymphoid and myeloid cells. We hypothesized that a synthetic cytokine linking GMCSF to MCP3 (hereafter GMME3) as part of a single polypeptide would acquire novel, therapeutically desirable immunomodulatory properties. We demonstrate that GMME3 has enhanced CC-chemokine receptor (CCR)-mediated intracellular Ca(++) mobilization with selective effects on the CD21(hi)CD24(hi) CD1.d(hi) subset of splenic B cells inducing substantial interleukin 10 (IL10) production. We demonstrate that B(GMME3) exert their suppressive effect through an IL10-mediated inhibition of antigen presentation. More importantly, B(GMME3) inhibit the reactivation of encephalomyelitis (EAE)-derived or TGF?/IL6 differentiated Th17 cells by altering their polarization toward a Th1 or Th2 phenotype. The secretion of interferon-? (IFN?) and IL4 in turn inhibits IL17 production. The adoptive transfer of B(GMME3), but not IL10(-/-) B(GMME3) cells, to mice symptomatic with experimental autoimmune encephalitis significantly improves their disease score and inhibits lymphoid infiltration into the central nervous system (CNS). We propose that designed CCR modulators such as GMME3, allows for conversion of naive B-cells to a novel suppressor phenotype allowing for the personalized cell therapy of autoimmune ailments. PMID:22760541

Hsieh, Jeremy; Williams, Patrick; Rafei, Moutih; Birman, Elena; Cuerquis, Jessica; Yuan, Shala; Wu, JianHui; Galipeau, Jacques

2012-09-01

301

Inducible IL10+ Suppressor B Cells Inhibit CNS Inflammation and T Helper 17 Polarization  

PubMed Central

Granulocyte–macrophage colony-stimulating factor (GMCSF) and MCP3 (aka CCL7) exert complementary, nonoverlapping, proimmune effects on responsive lymphoid and myeloid cells. We hypothesized that a synthetic cytokine linking GMCSF to MCP3 (hereafter GMME3) as part of a single polypeptide would acquire novel, therapeutically desirable immunomodulatory properties. We demonstrate that GMME3 has enhanced CC-chemokine receptor (CCR)–mediated intracellular Ca++ mobilization with selective effects on the CD21hiCD24hi CD1.dhi subset of splenic B cells inducing substantial interleukin 10 (IL10) production. We demonstrate that BGMME3 exert their suppressive effect through an IL10-mediated inhibition of antigen presentation. More importantly, BGMME3 inhibit the reactivation of encephalomyelitis (EAE)-derived or TGF?/IL6 differentiated Th17 cells by altering their polarization toward a Th1 or Th2 phenotype. The secretion of interferon-? (IFN?) and IL4 in turn inhibits IL17 production. The adoptive transfer of BGMME3, but not IL10–/– BGMME3 cells, to mice symptomatic with experimental autoimmune encephalitis significantly improves their disease score and inhibits lymphoid infiltration into the central nervous system (CNS). We propose that designed CCR modulators such as GMME3, allows for conversion of naive B-cells to a novel suppressor phenotype allowing for the personalized cell therapy of autoimmune ailments. PMID:22760541

Hsieh, Jeremy; Williams, Patrick; Rafei, Moutih; Birman, Elena; Cuerquis, Jessica; Yuan, Shala; Wu, JianHui; Galipeau, Jacques

2012-01-01

302

Concentration polarization effects in nanochannel induced-charge electro-osmosis  

NASA Astrophysics Data System (ADS)

Concentration polarization (CP) has been observed in a variety of configurations: nanochannels, nanopores, ion-permselective membranes, and embedded conductors. It is believed, but not conclusively proven, that electric double-layer (EDL) overlap plays a significant role in CP. Consequently, further studies of fundamental electrokinetic effects related to CP are needed. We present theoretical and numerical studies of CP effects near an un-biased conductor placed in a straight nanoslit. In our model we combine the full Poisson-Nernst-Planck equations with Helmholtz-Smoluchowski slip, whereby we can construct large computational domains and at the same time resolve the EDL in the vicinity of the conductor. Based on our results we try to identify the basic physical mechanisms that lead to the CP. We show that when subjected to an external bias the axial symmetry is broken by the electro-osmotic flow. This leads to nonlinear interactions between flow, electric potential, and charged chemical species in the induced EDL on the conductor.

Andersen, Mathias; Bruus, Henrik

2009-11-01

303

Subsidence-induced methane clouds in Titan's winter polar stratosphere and upper troposphere  

NASA Astrophysics Data System (ADS)

Titan's atmospheric methane most likely originates from lakes at the surface and subsurface reservoirs. Accordingly, it has been commonly assumed that Titan's tropopause region, where the vertical temperature profile is a minimum, acts as a cold trap for convecting methane, leading to the expectation that the formation of methane clouds in Titan's stratosphere would be rare. The additional assumption that Titan's tropopause temperatures are independent of latitude is also required. However, Cassini Composite InfraRed Spectrometer (CIRS) and Radio Science Subsystem (RSS) data sets reveal colder temperatures in Titan's tropopause region near the winter pole than those at low latitudes and in the summer hemisphere. This, combined with the presence of a cross-equatorial meridional circulation with winter polar subsidence, as suggested by current general circulation models, implies the inevitable formation of Subsidence-Induced Methane Clouds (SIMCs) over Titan's winter pole. We verified this by retrieving the stratospheric methane mole fraction at 70°N from the strength of the far infrared methane pure rotation lines observed by CIRS and by assuming the RSS-derived thermal profile at 74.1°N. Our retrieved methane mole fraction of 1.50 ± 0.15% allows for methane to condense and form SIMCs at altitudes between ?48 and ?20 km. Radiative transfer analyses of a color composite image obtained by the Cassini Visible and Infrared Mapping Spectrometer (VIMS) during northern winter appear to corroborate the existence of these clouds.

Anderson, C. M.; Samuelson, R. E.; Achterberg, R. K.; Barnes, J. W.; Flasar, F. M.

2014-11-01

304

Chloroplasts do not have a polarity for light-induced accumulation movement.  

PubMed

Chloroplast photorelocation movement in green plants is generally mediated by blue light. However, in cryptogam plants, including ferns, mosses, and algae, both red light and blue light are effective. Although the photoreceptors required for this phenomenon have been identified, the mechanisms underlying this movement response are not yet known. In order to analyze this response in more detail, chloroplast movement was induced in dark-adapted Adiantum capillus-veneris gametophyte cells by partial cell irradiation with a microbeam of red and/or blue light. In each case, chloroplasts were found to move toward the microbeam-irradiated area. A second microbeam was also applied to the cell at a separate location before the chloroplasts had reached the destination of the first microbeam. Under these conditions, chloroplasts were found to change their direction of movement without turning and move toward the second microbeam-irradiated area after a lag time of a few minutes. These findings indicate that chloroplasts can move in any direction and do not exhibit a polarity for chloroplast accumulation movement. This phenomenon was analyzed in detail in Adiantum and subsequently confirmed in Arabidopsis thaliana palisade cells. Interestingly, the lag time for direction change toward the second microbeam in Adiantum was longer in the red light than in the blue light. However, the reason for this discrepancy is not yet understood. PMID:19037581

Tsuboi, Hidenori; Yamashita, Hiroko; Wada, Masamitsu

2009-01-01

305

Polarized linewidth-controllable double-trapping electromagnetically induced transparency spectra in a resonant plasmon nanocavity  

PubMed Central

Surface plasmons with ultrasmall optical mode volume and strong near field enhancement can be used to realize nanoscale light-matter interaction. Combining surface plasmons with the quantum system provides the possibility of nanoscale realization of important quantum optical phenomena, including the electromagnetically induced transparency (EIT), which has many applications in nonlinear quantum optics and quantum information processing. Here, using a custom-designed resonant plasmon nanocavity, we demonstrate polarized position-dependent linewidth-controllable EIT spectra at the nanoscale. We analytically obtain the double coherent population trapping conditions in a double-? quantum system with crossing damping, which give two transparent points in the EIT spectra. The linewidths of the three peaks are extremely sensitive to the level spacing of the excited states, the Rabi frequencies and detunings of pump fields, and the Purcell factors. In particular the linewidth of the central peak is exceptionally narrow. The hybrid system may have potential applications in ultra-compact plasmon-quantum devices. PMID:24096943

Wang, Luojia; Gu, Ying; Chen, Hongyi; Zhang, Jia-Yu; Cui, Yiping; Gerardot, Brian D.; Gong, Qihuang

2013-01-01

306

CTLA-4Ig immunotherapy of obesity-induced insulin resistance by manipulation of macrophage polarization in adipose tissues  

SciTech Connect

Highlights: •CTLA-4Ig completely alleviates HFD-induced insulin resistance. •CTLA-4Ig reduces epididymal and subcutaneous fat tissue weight and adipocyte size. •CTLA-4Ig alters ATM polarization from inflammatory M1 to anti-inflammatory M2. •CTLA-4Ig may lead to a novel anti-obesity/inflammation/insulin resistance agent. •We identified the mechanism of the novel favorable effects of CTLA-4lg. -- Abstract: It has been established that obesity alters the metabolic and endocrine function of adipose tissue and, together with accumulation of adipose tissue macrophages, contributes to insulin resistance. Although numerous studies have reported that shifting the polarization of macrophages from M1 to M2 can alleviate adipose tissue inflammation, manipulation of macrophage polarization has not been considered as a specific therapy. Here, we determined whether cytotoxic T-lymphocyte-associated antigen-4IgG1 (CTLA-4Ig) can ameliorate insulin resistance by induction of macrophages from proinflammatory M1 to anti-inflammatory M2 polarization in the adipose tissues of high fat diet-induced insulin-resistant mice. CTLA4-Ig treatment prevented insulin resistance by changing gene expression to M2 polarization, which increased the levels of arginase 1. Furthermore, flow cytometric analysis confirmed the alteration of polarization from CD11c (M1)- to CD206 (M2)-positive cells. Concomitantly, CTLA-4Ig treatment resulted in weight reductions of epididymal and subcutaneous adipose tissues, which may be closely related to overexpression of apoptosis inhibitors in macrophages. Moreover, proinflammatory cytokine and chemokine levels decreased significantly. In contrast, CCAAT enhancer binding protein ?, peroxisome proliferator-activated receptor ?, and adiponectin expression increased significantly in subcutaneous adipose tissue. This novel mechanism of CTLA-4lg immunotherapy may lead to an ideal anti-obesity/inflammation/insulin resistance agent.

Fujii, Masakazu, E-mail: masakazu731079@yahoo.co.jp [Department of Internal Medicine and Bioregulatory Science, Graduate School of Medical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582 (Japan)] [Department of Internal Medicine and Bioregulatory Science, Graduate School of Medical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582 (Japan); Inoguchi, Toyoshi, E-mail: toyoshi@intmed3.med.kyushu-u.ac.jp [Department of Internal Medicine and Bioregulatory Science, Graduate School of Medical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582 (Japan) [Department of Internal Medicine and Bioregulatory Science, Graduate School of Medical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582 (Japan); Innovation Center for Medical Redox Navigation, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582 (Japan); Batchuluun, Battsetseg, E-mail: battsetseg.batchuluun@gmail.com [Department of Internal Medicine and Bioregulatory Science, Graduate School of Medical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582 (Japan)] [Department of Internal Medicine and Bioregulatory Science, Graduate School of Medical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582 (Japan); Sugiyama, Naonobu, E-mail: nao1@intmed1.med.kyushu-u.ac.jp [Department of Medicine and Biosystemic Science, Graduate School of Medical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582 (Japan)] [Department of Medicine and Biosystemic Science, Graduate School of Medical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582 (Japan); Kobayashi, Kunihisa, E-mail: nihisak@fukuoka-u.ac.jp [Department of Endocrinology and Diabetes Mellitus, Fukuoka University Chikushi Hospital, 1-1-1 Zokumyoin, Chikushino, Fukuoka 818-8502 (Japan)] [Department of Endocrinology and Diabetes Mellitus, Fukuoka University Chikushi Hospital, 1-1-1 Zokumyoin, Chikushino, Fukuoka 818-8502 (Japan); Sonoda, Noriyuki, E-mail: noriyuki@intmed3.med.kyushu-u.ac.jp [Department of Internal Medicine and Bioregulatory Science, Graduate School of Medical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582 (Japan) [Department of Internal Medicine and Bioregulatory Science, Graduate School of Medical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582 (Japan); Innovation Center for Medical Redox Navigation, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582 (Japan); Takayanagi, Ryoichi, E-mail: takayana@intmed3.med.kyushu-u.ac.jp [Department of Internal Medicine and Bioregulatory Science, Graduate School of Medical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582 (Japan)] [Department of Internal Medicine and Bioregulatory Science, Graduate School of Medical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582 (Japan)

2013-08-16

307

Spectral bluing induced by small particles under the Mie and Rayleigh regimes  

NASA Astrophysics Data System (ADS)

Scattering by particles significantly smaller than the wavelength is an important physical process in the icy and rocky bodies in our Solar System and beyond. A number of observations of spectral bluing (referred to in those papers as ‘Rayleigh scattering’) on planetary surfaces and cometary comas have been recently reported, however, the necessary mathematical modeling of this phenomenon has not yet achieved maturity. This paper is a first step to this effect, by examining the effect of grain size and optical index on the albedo of small conservative and absorbing particles as a function of wavelength. The conditions necessary for maximization of spectral bluing effects in real-world situations are identified. We find that any sufficiently narrow size distribution of scattering particles will cause spectral bluing in some part of the EM spectrum regardless of its optical index. We also investigate the effect of including a distribution of particle sizes.

Brown, Adrian J.

2014-09-01

308

Ferroelectric Polarization Flop in a Frustrated Magnet MnWO4 Induced by a Magnetic Field  

Microsoft Academic Search

The relationship between magnetic order and ferroelectric properties has been investigated for MnWO4 with a long-wavelength magnetic structure. Spontaneous electric polarization is observed in an elliptical spiral spin phase. The magnetic-field dependence of electric polarization indicates that the noncollinear spin configuration plays a key role for the appearance of the ferroelectric phase. An electric polarization flop from the b direction

K. Taniguchi; N. Abe; T. Takenobu; Y. Iwasa; T. Arima

2006-01-01

309

Interface-induced chiral domain walls, spin spirals and skyrmions revealed by spin-polarized scanning tunneling microscopy.  

PubMed

The spin textures of ultra-thin magnetic layers exhibit surprising variety. The loss of inversion symmetry at the interface of the magnetic layer and substrate gives rise to the so-called Dzyaloshinskii-Moriya interaction which favors non-collinear spin arrangements with unique rotational sense. Here we review the application of spin-polarized scanning tunneling microscopy to such systems, which has led to the discovery of interface-induced chiral domain walls and spin spirals. Recently, different interface-driven skyrmion lattices have been found, and the writing as well as the deleting of individual skyrmions based on local spin-polarized current injection has been demonstrated. These interface-induced non-collinear magnetic states offer new exciting possibilities to study fundamental magnetic interactions and to tailor material properties for spintronic applications. PMID:25214495

von Bergmann, Kirsten; Kubetzka, André; Pietzsch, Oswald; Wiesendanger, Roland

2014-10-01

310

Interface-induced chiral domain walls, spin spirals and skyrmions revealed by spin-polarized scanning tunneling microscopy  

NASA Astrophysics Data System (ADS)

The spin textures of ultra-thin magnetic layers exhibit surprising variety. The loss of inversion symmetry at the interface of the magnetic layer and substrate gives rise to the so-called Dzyaloshinskii-Moriya interaction which favors non-collinear spin arrangements with unique rotational sense. Here we review the application of spin-polarized scanning tunneling microscopy to such systems, which has led to the discovery of interface-induced chiral domain walls and spin spirals. Recently, different interface-driven skyrmion lattices have been found, and the writing as well as the deleting of individual skyrmions based on local spin-polarized current injection has been demonstrated. These interface-induced non-collinear magnetic states offer new exciting possibilities to study fundamental magnetic interactions and to tailor material properties for spintronic applications.

von Bergmann, Kirsten; Kubetzka, André; Pietzsch, Oswald; Wiesendanger, Roland

2014-10-01

311

Investigations of Polarization-Induced Hole Accumulations and Vertical Hole Conductions in GaN/AlGaN Heterostructures  

NASA Astrophysics Data System (ADS)

We investigated hole concentrations induced by spontaneous and piezoelectric polarization charges in GaN/AlGaN/GaN heterostructures. An AlN mole fraction dependence reveals that the induced hole concentrations were accurately controlled by the AlN mole fractions up to 0.34 in the GaN/AlGaN/GaN structures. We then demonstrated vertical hole conduction across an undoped graded AlGaN layer and hole injection to an active region in a LED structure to some extent. These results suggest that the controlled polarization charges by AlN mole fractions have potential as an alternative doping method for high hole concentrations in nitride semiconductors.

Yasuda, Toshiki; Yagi, Kouta; Suzuki, Tomoyuki; Nakashima, Tsubasa; Watanabe, Masahiro; Takeuchi, Tetsuya; Iwaya, Motoaki; Kamiyama, Satoshi; Akasaki, Isamu

2013-08-01

312

Polarization and angular effects of femtosecond laser-induced nanostructure-covered large scale waves on metals  

NASA Astrophysics Data System (ADS)

In this paper, we find that nanostructure-covered large scale waves (NC-LSWs) can be produced on metals using both s- and p-polarized femtosecond laser pulses. We show that the period of NC-LSWs can be controlled by laser fluence, the number of irradiating pulses, and the incident beam angle. By modeling angular dependence of NC-LSW period induced by s-polarized light, we reveal that inhomogeneous energy deposition plays an important role in the formation of NC-LSWs. This allows us to establish a three-step model for NC-LSW formation, the formation of laser-induced surface unevenness, inhomogeneous energy deposition due to the interference of the incident light with the scattered light, and nonuniform energy deposition due to shielding by LSWs.

Hwang, Taek Yong; Guo, Chunlei

2011-10-01

313

Self-induced spin-polarized carrier source in active photonic device with artificial optical chirality  

NASA Astrophysics Data System (ADS)

We demonstrate a scheme of active photonic devices which can spontaneously polarize the carrier spin in active regions. Rather than externally breaking the time-reversal symmetry of carrier spin states such as applying magnetic fields, only the optical chirality is required in this setup. Spin-polarized carriers are generated by interactions between carriers and self-initiated circularly polarized photons without the spin-selective optical pumping/electrical injection and breaking of the reciprocity. The device requires a cavity which supports modes with only one circular polarization and can be implemented with the vertical-cavity type of arrangements for distributed Bragg reflectors and artificial chiral photonic structures.

Ye, Yuqian; Chang, Shu-Wei

2012-10-01

314

J. Non-Newtonian Fluid Mech. 134 (2006) 3343 Flow-induced anisotropy in polar ice and related  

E-print Network

. To construct ice-sheet flow models aimed at obtaining ac- curate information on the origin and the age of iceJ. Non-Newtonian Fluid Mech. 134 (2006) 33­43 Flow-induced anisotropy in polar ice and related ice of ice can be orientated by using only one single vector, i.e. its c-axis. Such a characteristic allows

Gagliardini, Olivier

315

Electric polarization induced by a proper helical magnetic ordering in a delafossite multiferroic CuFe1-xAlxO2  

Microsoft Academic Search

We have established the relationship between the electric polarization vector and the local spin arrangement including vector spin chirality in delafossite multiferroic CuFe1-xAlxO2 . The results of polarized neutron diffraction and pyroelectric measurements demonstrate that proper helical magnetic ordering in CuFe1-xAlxO2 induces a spontaneous electric polarization parallel to the vector spin chirality. This result cannot be explained by the Katsura-Nagaosa-Balatsky

T. Nakajima; S. Mitsuda; S. Kanetsuki; K. Tanaka; K. Fujii; N. Terada; M. Soda; M. Matsuura; K. Hirota

2008-01-01

316

Experimental and theoretical investigation of a self-absorbed spectral line emitted from laser-induced plasmas.  

PubMed

Using well-known expressions describing radiative transfer, we have established an expression predicting the spectral profile of a self-absorbed Ca(++)393.4?nm emission line as emitted by a transient laser-induced plasma. In this approach, the plasma was approximated as comprising five distinct layers, each of thickness 0.5?mm, and each characterized by a unique uniform electron density, electron temperature, and optical depth. The validity of the theoretical model was confirmed by successful comparison with experimental data. Inhomogeneous laser-induced plasmas were produced on the surface of an aqueous CaCl(2) (0.01?mol/l) solution using a frequency-doubled Nd:YAG laser. Optical emission spectra were collected in such a way as to allow for temporal and spatial diagnostics of the plasma plumes. PMID:20563216

Ben Ahmed, Jalloul; Cowpe, John

2010-06-20

317

Birefringence-induced wavelength mismatch between the polarization rotation and resonant modes in magnetophotonic structures containing nematic layers  

NASA Astrophysics Data System (ADS)

The present work is devoted to the study of spectral characteristics of normal incident light transmitted by a multilayered structure composed of an alternated sequence of nematic and magnetic layers presenting a central magneto-optical defect. Using the Berreman 4 × 4 matrix formalism, we numerically obtain the transmission spectrum and the polarization rotation angle of the system as a function of the nematic optical axis direction. Our results reveal the emergence of a shift between the wavelengths of the resonant mode and polarization rotation angle, which strongly depends on the birefringence of the nematic layers. In particular, we show the existence of distinct regimes for the wavelength mismatch between the transmission of resonant modes and the maximum polarization rotation angle, which are governed by the ordinary and extraordinary refractive indices of nematic layers. The mechanism behind such shift is discussed under the light of propagation eigenmodes for a medium presenting circular and linear birefringence. The effects associated with the defect thickness are also analyzed.

da Silva, R. R.; Zanetti, F. M.; de Oliveira, I. N.

2014-01-01

318

Characterization of ice Content in Permafrost Soils on the Seward Peninsula, Alaska Using Induced Polarization  

NASA Astrophysics Data System (ADS)

Zones of high ice content are imaged using direct current (DC) and induced polarization (IP) electrical measurements in Permafrost soils on the Northern Seward Peninsula. Variable ice content in near surface permafrost as a result of ice wedge development is a major control on thermokarst erosion rates, making the characterization of distribution important to process modeling. A set of IP and DC resistivity measurements were collected at five locations, four in varying generations of thermokarst lake basins and one where there is no evidence of thermokarst lake basin development. GPR data was also collected using 100 and 200 mHz unsheilded antenna at each line, as well as high precision DGPS measurements, vegetation mapping, active layer thickness measurements, and soil characterization using test pits and nearby outcrops. DC resistivity and GPR results correspond well to the active layer probe and test pits dug to the bottom of the active layer. IP imaging shows the location of elevated ice content as strongly nonpolarizable anomolies which correlate to ice wedge ridges measured with GPS and observed from vegetation patterning. Non-polarizable targets found deeper in the permefrost at the site not yet effected by thermokarst erosion indicates that Pleistocene aged ice wedges are below the Holocene ice wedges expressed at the surface as distinct patterning, confirming that ice content distribution may not be easily estimated from surface patterning alone. These observations are confirmed by nearby exposures of ice wedges. The results show that the IP measurements are useful for characterizing ice content distribution in permafrost soils may be used to link ground based observations with larger scale estimates that are needed for process and carbon balance modeling of permafrost soils.

Nolan, J.; Parsekian, A.; Slater, L.; Plug, L.; Grosse, G.; Walter, K.

2008-12-01

319

Simultaneous electromagnetically induced transparency for two circularly polarized lasers coupled to the same linearly polarized laser in a four-level atomic system in the W scheme  

SciTech Connect

Electromagnetic induced transparency (EIT) can be produced in a four-level atomic system in the W scheme using a linearly polarized optical field for simultaneously slowing down two {sigma}{sup +} and {sigma}{sup -} circularly polarized optical fields. This four-level atomic system can be set up with a |{sup 1}S{sub 0}> ground state and three Zeeman levels of the |{sup 1}P{sub 1}> excited state of any alkali-metal atom placed in a weak magnetic field. We apply our W scheme to ultracold magnesium atoms for neglecting the collisional dephasing. Atomic coherences are reported after solving a density matrix master equation including radiative relaxations from Zeeman states of the |{sup 1}P{sub 1}> multiplet to the |{sup 1}S{sub 0}> ground state. The EIT feature is analyzed using the transit time between the normal dispersive region and the EIT region. The evolution of the EIT feature with the variation of the coupling field is discussed using an intuitive dressed-state representation. We analyze the sensitivity of an EIT feature to pressure broadening of the excited Zeeman states.

Bahrim, Cristian; Nelson, Chris [Department of Physics, Lamar University, P.O. Box 10046, Beaumont, Texas 77710 (United States)

2011-03-15

320

Magnetically induced electric polarization in an organometallic magnet V. S. Zapf,1 M. Kenzelmann,2 F. Wolff-Fabris,1,* F. Balakirev,1  

E-print Network

an electric polarization.5­13 These materials are ei- ther low-dimensional or frustrated magnets in whichMagnetically induced electric polarization in an organometallic magnet V. S. Zapf,1 M. Kenzelmann,2 F. Wolff-Fabris,1,* F. Balakirev,1 and Y. Chen3,4,5 1 National High Magnetic Field Laboratory (NHMFL

McQuade, D. Tyler

321

The Spectral Dependence for UVA-Induced Cumulative Damage in Human Skin  

Microsoft Academic Search

The wavelength dependence for UVA-induced cumulative damage was investigated in human skin. Epidermal changes (stratum corneum thickening, viable epidermal thickening sunburn cell production), as well as dermal alterations (lysozyme deposition, inflammation), were used as indices of cumulative photoperturbation. UVA wavelengths between 320 lint and 345 nm were more effective than longer wavelengths (360-400 nm) in inducing viable epidermal thickening. Similarly,

Robert Lavker; Kays Kaidbey

1997-01-01

322

Tuning the polarization-induced free hole density in nanowires graded from GaN to AlN  

NASA Astrophysics Data System (ADS)

We report a systematic study of p-type polarization-induced doping in graded AlGaN nanowire light emitting diodes grown on silicon wafers by plasma-assisted molecular beam epitaxy. The composition gradient in the p-type base is varied in a set of samples from 0.7%Al/nm to 4.95%Al/nm corresponding to negative bound polarization charge densities of 2.2 × 1018 cm-3 to 1.6 × 1019 cm-3. Capacitance measurements and energy band modeling reveal that for gradients greater than or equal to 1.30%Al/nm, the deep donor concentration is negligible and free hole concentrations roughly equal to the bound polarization charge density are achieved up to 1.6 × 1019 cm-3 at a gradient of 4.95%Al/nm. Accurate grading lengths in the p- and n-side of the pn-junction are extracted from scanning transmission electron microscopy images and are used to support energy band calculation and capacitance modeling. These results demonstrate the robust nature of p-type polarization doping in nanowires and put an upper bound on the magnitude of deep donor compensation.

Golam Sarwar, A. T. M.; Carnevale, Santino D.; Kent, Thomas F.; Yang, Fan; McComb, David W.; Myers, Roberto C.

2015-01-01

323

Polarization effects in the photon-induced process of electron-positron pair creation in a magnetic field, studied in the ultra-quantum-mechanical approximation  

E-print Network

The photon-induced process of electron-positron pair creation in a strong homogeneous magnetic field, provided that the polarization of particles is arbitrary, has been considered. The polarization of a photon is described in terms of the well-known Stokes parameters, and the relevant probabilities of the process turn out to have simple analytical expressions, which allows us to analyze the polarization and spin effects. A substantial influence of the linear polarization of a photon on the spin orientations of electrons and positrons has been demonstrated.

O. P. Novak; R. I. Kholodov

2010-02-05

324

Tunnel-injection quantum dot deep-ultraviolet light-emitting diodes with polarization-induced doping in III-nitride heterostructures  

SciTech Connect

Efficient semiconductor optical emitters in the deep-ultraviolet spectral window are encountering some of the most deep rooted problems of semiconductor physics. In III-Nitride heterostructures, obtaining short-wavelength photon emission requires the use of wide bandgap high Al composition AlGaN active regions. High conductivity electron (n-) and hole (p-) injection layers of even higher bandgaps are necessary for electrical carrier injection. This approach requires the activation of very deep dopants in very wide bandgap semiconductors, which is a difficult task. In this work, an approach is proposed and experimentally demonstrated to counter the challenges. The active region of the heterostructure light emitting diode uses ultrasmall epitaxially grown GaN quantum dots. Remarkably, the optical emission energy from GaN is pushed from 365?nm (3.4?eV, the bulk bandgap) to below 240?nm (>5.2?eV) because of extreme quantum confinement in the dots. This is possible because of the peculiar bandstructure and band alignments in the GaN/AlN system. This active region design crucially enables two further innovations for efficient carrier injection: Tunnel injection of carriers and polarization-induced p-type doping. The combination of these three advances results in major boosts in electroluminescence in deep-ultraviolet light emitting diodes and lays the groundwork for electrically pumped short-wavelength lasers.

Verma, Jai, E-mail: jverma@nd.edu; Islam, S. M.; Protasenko, Vladimir; Kumar Kandaswamy, Prem; Xing, Huili; Jena, Debdeep [Department of Electrical Engineering, University of Notre Dame, Notre Dame, Indiana 46556 (United States)

2014-01-13

325

Space charge polarization induced memory in SmNiO3/Si transistors  

NASA Astrophysics Data System (ADS)

The correlated oxide, SmNiO3 (SNO), is characterized and explored as a phase transition material in silicon capacitors and transistors with SNO as a floating gate sandwiched between silicon dioxide gate insulators. The structures show hysteresis at low bias voltages. The capacitance and its voltage hysteresis window increase as the frequency of the applied field decreases with a response time of polarization of above a microsecond. This suggests a space charge polarization dominated by low frequency permittivity response. Instability of 3+ oxidation state of Ni and presence of oxygen vacancies are believed to lead to a polarization effect through Poole-Frenkel charge trapping/de-trapping. Metal-oxide-semiconductor transistors show counterclockwise voltage hysteresis consistent with polarization switching effect. The stored information decays gradually due to the depolarization field with retention times of the order of 10 s at room temperature.

Hyeon Lee, Sang; Kim, Moonkyung; Ha, Sieu D.; Lee, Jo-Won; Ramanathan, Shriram; Tiwari, Sandip

2013-02-01

326

microRNA-223 Regulates Macrophage Polarization and Diet-induced Insulin Resistance  

E-print Network

-mediated regulation of adipose tissue inflammation and insulin resistance were then confirmed by transplantation analysis. Moreover, using bone marrow-derived macrophages, we demonstrated that miR-223 is a novel regulator of macrophage polarization, which suppresses...

Meng, Cong

2013-05-01

327

Effective all-optical polarization control induced by Raman nonlinear amplification  

Microsoft Academic Search

An effective all-optical Raman-based stabilization of any input polarization into a single state is experimentally proved exploiting an optimal combination of pump power, fibre PMD and fibre length, identified through systematic numerical simulations.

Maddalena Ferrario; Valentina Gilardone; Paolo Martelli; Lucia Marazzi; Mario Martinelli

2010-01-01

328

Adsorbate-induced spin-polarization enhancement of Fe3O4(0 0 1)  

Microsoft Academic Search

Using a spin-polarized metastable helium beam, we have investigated the remanent spin polarization at the surface of clean, hydrogen-terminated and benzene-adsorbed Fe3O4(0 0 1) thin films prepared on MgO(0 0 1) substrates. For the clean surface, a small negative asymmetry is detected in the ejected electron yields for helium-electron spins aligned parallel and anti-parallel to the sample magnetization direction. This

A. Pratt; M. Kurahashi; X. Sun; Y. Yamauchi

2011-01-01

329

Broadband polarizing films by photopolymerization-induced phase separation and in situ Swelling  

SciTech Connect

This letter describes the spectral broadening of cholesteric liquid crystal films prepared from a blend comprising a cross-linkable liquid crystal polymer and a noncross-linkable low-molecular-weight liquid crystal. The bandwidth of the broadened reflection band can be increased by several times upon photopolymerization. The spectral broadening arises from the formation of gradient pitch across the film thickness. It is shown that both phase separation and in situ swelling are important mechanisms for the resulting film structure.

Fan, B.; Vartak, S.; Eakin, J. N.; Faris, S. M. [Reveo Inc., 6 Skyline Drive, Hawthorne, New York 10532 (United States)

2008-02-11

330

Tunneling-induced spectral broadening of a single atom in a three-dimensional optical lattice.  

PubMed

We have investigated the spectral broadening in the near-resonance fluorescence spectrum of a single rubidium atom trapped in a three-dimensional (3D) optical lattice in a strong Lamb-Dicke regime. Besides the strong Rayleigh peak, the spectrum exhibited weak Stokes and anti-Stokes Raman sidebands. The line width of the Rayleigh peak for low potential depths was well explained by matter-wave tunneling between the first-two lowest vibrational states of 3D anisotropic harmonic potentials of adjacent local minima of the optical lattice. PMID:21194201

Kim, Wookrae; Park, Changwon; Kim, Jung-Ryul; Choi, Youngwoon; Kang, Sungsam; Lim, Sooin; Lee, Yea-Lee; Ihm, Jisoon; An, Kyungwon

2011-02-01

331

Laser ablation-induced spectral plasma characteristics in optical far- and near fields  

SciTech Connect

The aim of this work is to elucidate the ablation-induced plasma physics for chemical species analysis by laser-induced breakdown spectroscopy at higher spatial resolution. To accomplish this, the effect of the laser spot size on the laser ablation-induced plasma characteristics is experimentally investigated, both in optical far-field and near-field ablation configurations, utilizing a Cr thin film of {approx}200 nm thickness on quartz substrate as a target. The far-field ablation is affected under tight focusing conditions, wherein nanosecond laser pulses of 532 nm wavelength are focused to laser focal spot diameters of {approx}7 and 1.5 {mu}m. The measured results show that the ablation-induced plasma from sub-10 {mu}m ablation craters exhibits complex three-dimensional behavior, leading to greatly reduced laser-plasma interaction and an order of magnitude shorter plasma lifetime. Nanosecond laser pulses of 532 nm wavelength are also coupled to a pulled fiber based near-field scanning optical microscopy probe. Due to the sharp tip presence in close proximity of the ablation craters, entirely different plasma evolution behavior is observed, highlighted by orders of magnitude shorter plasma lifetime and strongly directional material ejection. The ablation-induced plasma from reduced lateral crater dimensions both in far- and near-field shows improved contrast of atomic transition signals with respect to the wide-spectrum background, hence confirming the potential for laser-induced breakdown spectroscopy with high spatial resolution.

Hwang, David J.; Jeon, Hojeong; Grigoropoulos, Costas P. [Laser Thermal Laboratory, Department of Mechanical Engineering, University of California, Berkeley, California 94720-1740 (United States); Yoo, Jong; Russo, Richard E

2008-07-01

332

Model for optically-induced nuclear spin polarization in gallium arsenide  

NASA Astrophysics Data System (ADS)

New technologies and corresponding research fields have recently emerged that aim to develop solid-state devices based on large polarizations of electron and/or nuclear spins. These include spin-based strategies for parallel information processing through quantum entanglement ("quantum computing") and semi-classical electronic devices controlled via the spin degree of freedom ("spintronics"). A new rule of thumb - polarization has application - makes the optically pumped semiconductor an interesting system, as it exhibits both large electron and nuclear polarizations. However, several aspects of the process by which nuclear polarization is generated through optical pumping were not understood prior to this thesis, even for the most well studied semiconductor, GaAs. These include the dependence of the nuclear polarization on laser power, irradiation time, and especially on photon energy, which exhibits a dramatic peak near 1.5 eV. This thesis presents a quantitative model for optical nuclear polarization in GaAs. The model makes predictions for all quantities observable in a hulk optically pumped NMR (OPNMR) spectrum: the OPNMR signal magnitude, the hyperfine shift of the NMR frequency, and the nuclear spin temperature. The model may help researchers to optimize experimental conditions for maximizing nuclear polarization in spintronics or quantum computing architectures. A clear correlation is shown between the OPNMR signal and the photoconductivity. A photoconductivity model is developed herein that accounts for the varying penetration depth of the light with photon energy and for the presence of band-to-band and band-to-defect recombination of charge carriers. The model's predictions agree well with the photoconductivity data. The photoconductivity model is then combined with a nuclear polarization model. The resulting picture for near-band-gap (1.495 eV ? by ? 1.6 eV) optical nuclear polarization is as follows. Optical absorption generates free, non-equilibrium electron spins, whose polarization depends on the light polarization. During their excited-state lifetime, these electrons may relax into shallow-donor-bound states, where they experience a strong hyperfine interaction and can cross-relax with nuclear spins. The nuclear polarization near shallow donor defects then evolves over space and time according to a diffusion equation that accounts for localized generation and loss. This model predicts the photon-energy dependence and laser-power dependence of the OPNMR signal very well. The peak at 1.5 eV is predicted to arise from an optimal balance between a high nuclear polarization and a large irradiation volume. Both theory and experiment exhibit a deviation from linear growth of OPNMR signal with laser power at high powers and an earlier onset of non-linear growth for higher photon energy. Finally, the model predicts a time-dependent hyperfine shift of the NMR frequency that fits the data with quantitative agreement. All free parameters within the model are constrained through the fitting of these various data sets. With this model, analytical expressions are derived for helicity asymmetries in OPNMR spectra. These asymmetries are related simply enough to electron spin parameters that they provide a methodology for extracting the initially-excited and steady-state electron spin polarizations from OPNMR spectra, allowing the dependence of these polarizations on temperature and photon-energy to be investigated herein. The OPNMR asymmetry is furthermore used as a local thermometer of the irradiated volume, which provides experimental verification of a quantitative model for laser heating. Several unusual effects in optically pumped GaAs are characterized. Perhaps the most dramatic is a bi-exponential decay of the photoconductivity with irradiation time, observed at all near-band-gap photon energies. This serves as clear evidence of photoquenching of the deep defect known as EL2 under the conditions typical of OPNMR measurements. Further experiments are suggested to complete the studies in this

Coles, Patrick Joseph

333

Spectral features of lightning-induced ion cyclotron waves at low latitudes: DEMETER observations and simulation  

NASA Astrophysics Data System (ADS)

We use a comprehensive analysis of 6-component ELF wave data from the DEMETER satellite to study proton whistlers, placing emphasis on low-latitude events originating from lightning strokes in the hemisphere opposite to the hemisphere of observation. In this case, the formation of proton whistlers does not involve mode conversion caused by a strong mode coupling at a crossover frequency, although a polarization reversal remains an important element in formation of the phenomenon. DEMETER measurements of the six electromagnetic field components in the frequency band below 1000 Hz make it possible to determine not only the dynamic spectrum, but also the wave polarization, the wave normal angle, and the normalized parallel component of the Poynting vector. This permits us to address fine features of proton whistlers, in particular, we show that the deviation of the upper cutoff frequency from the equatorial cyclotron frequency is related to the Doppler shift. Experimental study of proton whistlers is supplemented by an investigation of ion cyclotron wave propagation in a multicomponent magnetoplasma and by numerical modeling of spectrograms, both in the frame of geometrical optics.

Shklyar, D. R.; Storey, L. R. O.; Chum, J.; Ji?í?Ek, F.; N?Mec, F.; Parrot, M.; Santolik, O.; Titova, E. E.

2012-12-01

334

Experimental study of the spectral characteristics of laser-induced air plasma  

SciTech Connect

The characteristics of laser-induced air, N2, and O2 plasma spectra are investigated spectroscopically. The study concentrates mainly on the temporal behavior of laser-induced plasma after breakdown. We used delayed spectra and spectra evolution for this study. Except for the general one-beam laser-induced breakdown experiment, a second laser beam was added to further probe the behavior of plasma during its decay. We report the experimental results of spectra composition, spectra time evolution, and spectra affected by a second laser beam. We determined that all the laser-induced air plasma spectra are from a continuous spectrum and some line spectra superposed on the continuous spectrum. The stronger short wavelength continuous spectrum is caused by bremsstrahlung radiation of electrons in the plasma, and the weaker long wavelength continuous spectrum is caused by electron and ion recombination. Line spectra originate from excited molecules, atoms, and their first-order ions, but no line spectra form higher-order ions. The results show that the temporal behavior of some spectra is a decay-rise-redecay pattern. With the two laser beam experiment we found that all the spectra intensities are enhanced by the second laser beam, but the response of various spectra to the delay of the second laser beam is quite different, in particular, the intensity increments of some spectra increase with the delay of the second laser beam. Some microscopic processes of laser-induced plasma obtained from the experimental results are discussed. These results are useful for a better understanding of some laser-induced air plasma related applications, such as laser-guided lightning and laser-induced breakdown spectroscopy.

Lin Zhaoxiang; Wu Jinquan; Sun Fenglou; Gong Shunsheng

2010-05-01

335

Preferential macrophage recruitment and polarization in LPS-induced animal model for COPD: noninvasive tracking using MRI.  

PubMed

Noninvasive imaging of macrophages activity has raised increasing interest for diagnosis of chronic obstructive respiratory diseases (COPD), which make them attractive vehicles to deliver contrast agents for diagnostic or drugs for therapeutic purposes. This study was designed to monitor and evaluate the migration of differently polarized M1 and M2 iron labeled macrophage subsets to the lung of a LPS-induced COPD animal model and to assess their polarization state once they have reached the inflammatory sites in the lung after intravenous injection. Ex vivo polarized bone marrow derived M1 or M2 macrophages were first efficiently and safely labeled with amine-modified PEGylated dextran-coated SPIO nanoparticles and without altering their polarization profile. Their biodistribution in abdominal organs and their homing to the site of inflammation in the lung was tracked for the first time using a free-breathing non-invasive MR imaging protocol on a 4.7T magnet after their intravenous administration. This imaging protocol was optimized to allow both detection of iron labeled macrophages and visualization of inflammation in the lung. M1 and M2 macrophages were successfully detected in the lung starting from 2 hours post injection with no variation in their migration profile. Quantification of cytokines release, analysis of surface membrane expression using flow cytometry and immunohistochemistry investigations confirmed the successful recruitment of injected iron labeled macrophages in the lung of COPD mice and revealed that even with a continuum switch in the polarization profile of M1 and M2 macrophages during the time course of inflammation a balanced number of macrophage subsets predominate. PMID:24598763

Al Faraj, Achraf; Sultana Shaik, Asma; Pureza, Mary Angeline; Alnafea, Mohammad; Halwani, Rabih

2014-01-01

336

Preferential Macrophage Recruitment and Polarization in LPS-Induced Animal Model for COPD: Noninvasive Tracking Using MRI  

PubMed Central

Noninvasive imaging of macrophages activity has raised increasing interest for diagnosis of chronic obstructive respiratory diseases (COPD), which make them attractive vehicles to deliver contrast agents for diagnostic or drugs for therapeutic purposes. This study was designed to monitor and evaluate the migration of differently polarized M1 and M2 iron labeled macrophage subsets to the lung of a LPS-induced COPD animal model and to assess their polarization state once they have reached the inflammatory sites in the lung after intravenous injection. Ex vivo polarized bone marrow derived M1 or M2 macrophages were first efficiently and safely labeled with amine-modified PEGylated dextran-coated SPIO nanoparticles and without altering their polarization profile. Their biodistribution in abdominal organs and their homing to the site of inflammation in the lung was tracked for the first time using a free-breathing non-invasive MR imaging protocol on a 4.7T magnet after their intravenous administration. This imaging protocol was optimized to allow both detection of iron labeled macrophages and visualization of inflammation in the lung. M1 and M2 macrophages were successfully detected in the lung starting from 2 hours post injection with no variation in their migration profile. Quantification of cytokines release, analysis of surface membrane expression using flow cytometry and immunohistochemistry investigations confirmed the successful recruitment of injected iron labeled macrophages in the lung of COPD mice and revealed that even with a continuum switch in the polarization profile of M1 and M2 macrophages during the time course of inflammation a balanced number of macrophage subsets predominate. PMID:24598763

Al Faraj, Achraf; Sultana Shaik, Asma; Pureza, Mary Angeline; Alnafea, Mohammad; Halwani, Rabih

2014-01-01

337

Spectral analysis of paramagnetic centers induced in human tooth enamel by x-rays and gamma radiation  

NASA Astrophysics Data System (ADS)

Based on study of spectral and relaxation characteristics, we have established that paramagnetic centers induced in tooth enamel by x-rays and gamma radiation are identical in nature. We show that for the same exposure dose, the intensity of the electron paramagnetic resonance (EPR) signal induced by x-radiation with effective energy 34 keV is about an order of magnitude higher than the amplitude of the signal induced by gamma radiation. We have identified a three-fold attenuation of the EPR signal along the path of the x-radiation from the buccal to the lingual side of a tooth, which is evidence that the individual had undergone diagnostic x-ray examination of the dentition or skull. We have shown that the x-ray exposure doses reconstructed from the EPR spectra are an order of magnitude higher than the applied doses, while the dose loads due to gamma radiation are equal to the applied doses. The data obtained indicate that for adequate reconstruction of individual absorbed doses from EPR spectra of tooth enamel in the population subjected to the combined effect of x-radiation and accidental external gamma radiation as a result of the disaster at the Chernobyl nuclear power plant, we need to take into account the contribution to the dose load from diagnostic x-rays in examination of the teeth, jaw, or skull.

Kirillov, V. A.; Kuchuro, I. I.

2010-03-01

338

Probing of spontaneous polarization screened by defect-induced free carriers in gallium ferrite thin films  

NASA Astrophysics Data System (ADS)

Gallium ferrite, GaFeO3 (GFO), is known as a potential multiferroic material with spontaneous polarization and magnetization [1,2]. However, it was difficult to measure the polarization reversal of GFO thin films because conduction electrons screen the polarization switching responsible for ferroelectricity. Therefore, controlling charge conduction of a multiferroic material is key issue. In this study, we investigated the carrier transport behavior and the charge conduction mechanism in epitaxial GFO thin films deposited on metallic oxide-coated single crystal SrTiO3 substrates by pulsed laser deposition. Macroscopic carrier transports result showed that the interface limited model was the dominant conduction mechanism of the large leakage current and the nature of carrier transport at interface between GFO thin films and substrates was demonstrated by band profiles. Local charge conduction of GFO thin films was studied by conducting atomic force microscope. The polarization switching behavior of GFO thin films was showed by polarization-electric field curve and the positive-up-negative-down method. [1] A. Roy et al., J. Phys.: Condens. Matter 23 (2011) 325902. [2] D. Stoeffler, J. Phys.: Condens. Matter 24 (2012) 185502.

Oh, S. H.; Shin, R. H.; Jo, W.; Lefevre, C.; Roulland, F.; Thomassn, A.; Meny, C.; Viart, N.

2013-03-01

339

A polar barrier to transcription can be circumvented by remodeler-induced nucleosome translocation.  

PubMed

Many eukaryotic genes are regulated at the level of transcript elongation. Nucleosomes are likely targets for this regulation. Previously, we have shown that nucleosomes formed on very strong positioning sequences (601 and 603), present a high, orientation-dependent barrier to transcription by RNA polymerase II in vitro. The existence of this polar barrier correlates with the interaction of a 16-bp polar barrier signal (PBS) with the promoter-distal histone H3-H4 dimer. Here, we show that the polar barrier is relieved by ISW2, an ATP-dependent chromatin remodeler, which translocates the nucleosome over a short distance, such that the PBS no longer interacts with the distal H3-H4 dimer, although it remains within the nucleosome. In vivo, insertion of the 603 positioning sequence into the yeast CUP1 gene results in a modest reduction in transcription, but this reduction is orientation-independent, indicating that the polar barrier can be circumvented. However, the 603-nucleosome is present at the expected position in only a small fraction of cells. Thus, the polar barrier is probably non-functional in vivo because the nucleosome is not positioned appropriately, presumably due to nucleosome sliding activities. We suggest that interactions between PBSs and chromatin remodelers might have significant regulatory potential. PMID:21245049

Gaykalova, Daria A; Nagarajavel, V; Bondarenko, Vladimir A; Bartholomew, Blaine; Clark, David J; Studitsky, Vasily M

2011-05-01

340

A polar barrier to transcription can be circumvented by remodeler-induced nucleosome translocation  

PubMed Central

Many eukaryotic genes are regulated at the level of transcript elongation. Nucleosomes are likely targets for this regulation. Previously, we have shown that nucleosomes formed on very strong positioning sequences (601 and 603), present a high, orientation-dependent barrier to transcription by RNA polymerase II in vitro. The existence of this polar barrier correlates with the interaction of a 16-bp polar barrier signal (PBS) with the promoter-distal histone H3–H4 dimer. Here, we show that the polar barrier is relieved by ISW2, an ATP-dependent chromatin remodeler, which translocates the nucleosome over a short distance, such that the PBS no longer interacts with the distal H3–H4 dimer, although it remains within the nucleosome. In vivo, insertion of the 603 positioning sequence into the yeast CUP1 gene results in a modest reduction in transcription, but this reduction is orientation-independent, indicating that the polar barrier can be circumvented. However, the 603-nucleosome is present at the expected position in only a small fraction of cells. Thus, the polar barrier is probably non-functional in vivo because the nucleosome is not positioned appropriately, presumably due to nucleosome sliding activities. We suggest that interactions between PBSs and chromatin remodelers might have significant regulatory potential. PMID:21245049

Gaykalova, Daria A.; Nagarajavel, V.; Bondarenko, Vladimir A.; Bartholomew, Blaine; Clark, David J.; Studitsky, Vasily M.

2011-01-01

341

Endoscopic autofluorescence micro-spectroimaging of alveoli: comparative spectral analysis of amiodarone-induced pneumonitis patients and healthy smokers  

NASA Astrophysics Data System (ADS)

Fibered confocal fluorescence microscopy (FCFM) with spectroscopic analysis capability was used during bronchoscopy, at 488nm excitation, to record autofluorescence images and associated emission spectra of the alveoli of 5 healthy smoking volunteers and 7 non-smoking amiodarone-induced pneumonitis (AIP) patients. Alveolar fluorescent cellular infiltration was observed in both groups. Our objective was to assess the potential of spectroscopy in differentiating these two groups. Methods: We previously demonstrated that in healthy smokers alveolar elastin backbone and tobacco tar contained in macrophages contribute to the observed signal. Each normalized spectrum was modeled as a linear combination of 3 components: Sexp(?) = Ce.Se(?)+Ct.St(?)+CG.SG(?), Ce, Ct and CG are amplitude coefficients. Se(?) and St(?) are respectively the normalized elastin and tobacco tar emission spectra measured experimentally and SG(?) a gaussian spectrum with tunable width and central wavelength. Levenbergt-Marquardt algorithm determined the optimal set of coefficients. Results: AIP patient autofluorescence spectra can be uniquely modelized by the linear combination of the elastin spectrum (Ce = 0.61) and of a gaussian spectrum (center wavelength 550nm, width 40nm); the tobacco tar spectrum coefficient Ct is found to be zero. For healthy smoking volunteers, only two spectral components were considered: the tobacco tar component (Ct = 1,03) and the elastin component (Ce = 0). Conclusion: Spectral analysis is able to distinguish cellular infiltrated images from AIP patients and healthy smoking volunteers. It appears as a powerful complementary tool for FCFM.

Bourg-Heckly, G.; Vever-Bizet, C.; Blondel, W.; Salaün, M.; Thiberville, L.

2011-03-01

342

MASS SPECTRAL FRAGMENTATION PATHWAYS IN NITRAMINES. A COLLISION-INDUCED DISSOCIATION STUDY  

EPA Science Inventory

A collision-induced dissociation (CID) study of five synthesized nitramines was carried out using a hybrid EBQQ mass spectrometer. ID spectra were obtained in two modes: /E linked-scan mode and MS/MS mode using the EB sector combination as the first mass spectrometer and the QQ a...

343

Field-free molecular alignment induced by elliptically polarized laser pulses: non invasive 3 dimensional characterization  

E-print Network

An investigation of field-free molecular alignment produced by elliptically polarized laser pulses is reported. Experiments are conducted in CO$_2$ at room temperature. A non invasive all-optical technique, based on the cross defocusing of a probe pulse, is used to measure the alignment along two orthogonal directions that is sufficient to provide a 3 dimensional characterization. The field-free molecular alignment produced by a laser of elliptical polarization is in good agreement in terms of amplitude and shape with theoretical predictions. It turns out to be almost equivalent to the superposition of the effects that one would obtain with two individual cross-polarized pulses. The investigation highlights notably the occurrence of field-free two-direction alignment alternation for a suitably chosen degree of ellipticity. The analogy between this specific ellipticity and the well known "magic angle" used in time resolved spectroscopy to prevent rotational contributions is discussed.

E. Hertz; D. Daems; S. Guérin; H. R. Jauslin; B. Lavorel; O. Faucher

2008-12-17

344

Spin-transfer force acting on vortex induced by current gradient in a planar polarizer geometry  

NASA Astrophysics Data System (ADS)

We discuss a new mechanism of changing the magnetic vortex gyrotropic motion in a permalloy/nonmagnet bi-layers system. In this system, a spin current characterized by an in-plane polarizer is injected from the nonmagnetic layer to the permalloy disk. We introduce current density gradient to the spin current, and find that the interplay between the planar polarizer and current gradient can change the damping of the vortex motion. This change originates from a spin-transfer force acting on the vortex. The influence of the spin-transfer force on the vortex motion is dependent on the direction of the planar polarizer, the orientation of the current density gradient, and the vortex state.

Liu, Yan; Li, Huanan; Hu, Yong; Du, An

2013-09-01

345

Contact-induced spin polarization of monolayer hexagonal boron nitride on Ni(111)  

SciTech Connect

Hexagonal boron nitride (h-BN) is a promising barrier material for graphene spintronics. In this Letter, spin-polarized metastable de-excitation spectroscopy (SPMDS) is employed to study the spin-dependent electronic structure of monolayer h-BN/Ni(111). The extreme surface sensitivity of SPMDS enables us to elucidate a partial filling of the in-gap states of h-BN without any superposition of Ni 3d signals. The in-gap states are shown to have a considerable spin polarization parallel to the majority spin of Ni. The positive spin polarization is attributed to the ?-d hybridization and the effective spin transfer to the nitrogen atoms at the h-BN/Ni(111) interface.

Ohtomo, Manabu; Entani, Shiro; Matsumoto, Yoshihiro; Naramoto, Hiroshi; Sakai, Seiji [Advanced Science Research Center, Japan Atomic Energy, Agency 2-4 Shirakata-Shirane, Tokai, Naka, Ibaraki 319-1195 (Japan); Yamauchi, Yasushi [National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047 (Japan); Kuzubov, Alex A.; Eliseeva, Natalya S. [L.V. Kirensky Institute of Physics SB RAS, Academgorodok, Krasnoyarsk 660036 (Russian Federation); Siberian Federal University, 79 Svobodniy av., Krasnoyarsk 660041 (Russian Federation); Avramov, Pavel V. [Advanced Science Research Center, Japan Atomic Energy, Agency 2-4 Shirakata-Shirane, Tokai, Naka, Ibaraki 319-1195 (Japan); L.V. Kirensky Institute of Physics SB RAS, Academgorodok, Krasnoyarsk 660036 (Russian Federation); Siberian Federal University, 79 Svobodniy av., Krasnoyarsk 660041 (Russian Federation)

2014-02-03

346

Rectified elongational streaming due to asymmetric electro-osmosis induced by ac polarization  

NASA Astrophysics Data System (ADS)

We demonstrate a microelongational streaming generated by nonlinear electro-osmosis with high-frequency ac polarization. The phenomenon is attributed to the unique rectification mechanism that coordinates three-dimensional flow interactions between adjacent microvortices in an asymmetric quadrupole electric field. This streaming exhibits a stagnation-point structure with velocity of 300?m/s at 100Hz due to Faradaic polarization, but is reversed with slower velocity at 1kHz by Ohmic charging. The measured extensional rate shows a quadratic dependence on the field in line with nonlinear Smoluchowski scale. The flow can be ready to control fluid transport and manipulate particles in microdevices.

Wu, Jie-Tang; Du, Jiong-Rong; Juang, Yi-Je; Wei, Hsien-Hung

2007-03-01

347

Resistivity, induced polarization, and self-potential methods in geothermal exploration  

SciTech Connect

An overview of the literature is presented. This is followed by a statement of some elementary electromagnetic theory necessary to establish the MKS system of units and the fundamental physics governing electrical methods of exploration. Next there is presented a reasonably detailed discussion of the electrical properties of earth materials including normal mode of conduction, surface conduction, electrode polarization, membrane polarization, semiconduction, melt conduction, real and complex resistivity, and the origin of self-potentials in geothermal systems. To illustrate how electrical methods are used within the framework of integrated geological, geochemical, and geophysical exploration, the case history of the Monroe-Red Hill hot springs system is presented.

Ward, S.H.; Sill, W.R.

1982-01-01

348

Investigating the fracture non-linear dynamics through multi-spectral time series analysis of fracture-induced electromagnetic emissions  

NASA Astrophysics Data System (ADS)

Electromagnetic (EM) emissions (EME) in a wide frequency spectrum ranging from kHz to MHz are produced by cracks' opening, considered as fracture precursors. Thus, their study constitutes a nondestructive method for the monitoring of the evolution of damage process at the laboratory scale. Earthquakes (EQs) are large-scale fracture phenomena in the Earth's heterogeneous crust. Accordingly, it has been suggested that fracture induced MHz-kHz EME, emerging from a few days up to a few hours before the main seismic shock permit a monitoring of the damage process during the last stages of EQ preparation. The use of spectral decomposition techniques, namely Singular Spectral Analysis (SSA), Wavelets Analysis (WA) and their Monte Carlo counterparts (MC SSA and MC WA), as well as the revised Multi-Taper Method (MTM) for a reliable discrimination of fracto-EM emissions from the natural geo-EM field is proposed here; the well documented fracture-induced kHz EME time-series associated with the Athens' EQ (M=5.9, 7 September 1999) is employed as a test case. An adequately long time period (> month) prior to the occurrence of the EQ is considered in order to include all different phases of a large-scale fracture, from the "quite" period where only the geo-EM field and its modulation by the ionospheric variations is observed, to the final stages of the EQ preparation process where fracto-EM emissions occur. The examined time series, recorded at the 10 kHz band and at a high temporal resolution (sampling frequency 1 Hz), is first split into three characteristic excerpts (a) the quiet period well (35 to 25 days) before the event, (b) the first epoch of the candidate pre-seismically active time period (8 to 4 days before the event), and (c) the final epoch of the candidate pre-seismically active time period (~3 days before the event until short after the event). The Maximum Entropy and Blackman-Tukey FFT methods are initially used for the preliminary evaluation of the time-series excerpts. Then, each of them is studied through the aforementioned spectral decomposition methods. Following standard methodology we attempt to decompose each of the partial time-series into statistically significant non-linear trends, oscillatory modes and noise, by testing each spectral component against red noise and alternatively against locally white noise background. Monte Carlo simulations of AR(1)-process red noise simulations are also utilized in this analysis phase and finally the significant temporal empirical orthogonal functions (T-EOFs) and the associated temporal principal components (T-PCs) are specified. In this way, a non-parametric (and non-empirical) signal to noise resolution is achieved and the reconstruction of the statistically significant signal can be realized by adding the associated Reconstructed Components (RCs). By applying the aforementioned technique we reveal the significant signal characteristics for each period and try to interpret the underlying dynamics. Given the statistically significant reconstructed signal for each partial time-series we further attempt a comparison between their morphology (also using a spectral cross-correlation study) in order to detect similarities and differences mostly between the quiet and the active periods that could be signify the pre-seismic activity.

Kalimeris, Anastasios; Potirakis, Stelios M.; Eftaxias, Konstantinos; Antonopoulos, George; Kopanas, John; Nomicos, Constantinos

2013-04-01

349

The effect of the external medium on the gravity-induced polarity of cytoplasmic streaming in Chara corallina (Characeae)  

NASA Technical Reports Server (NTRS)

Gravity induces a polarity of cytoplasmic streaming in vertical internodal cells of Chara such that the downwardly directed stream moves faster than the upwardly directed stream. In order to determine whether the statolith theory (in which intracellular sedimenting particles are responsible for gravity sensing) or the gravitational pressure theory (in which the entire protoplast acts as the gravity sensor) best explain the gravity response in Chara internodal cells, we controlled the physical properties of the external medium, including density and osmolarity, with impermeant solutes and examined the effect on the polarity of cytoplasmic streaming. As the density of the external medium is increased, the polarity of cytoplasmic streaming decreases and finally disappears when the density of the external medium is equal to that of the cell (1015 kg/m3). A further increase in the density of the external medium causes a reversal of the gravity response. These results are consistent with the gravitational pressure theory of gravity sensing since the buoyancy of the protoplast is dependent on the difference between the density of the protoplast and the external medium, and are inconsistent with the statolith theory since the buoyancy of intracellular particles are unaffected by changes in the external medium.

Staves, M. P.; Wayne, R.; Leopold, A. C.

1997-01-01

350

A model for the spectral dependence of optically induced absorption in amorphous silicon  

NASA Technical Reports Server (NTRS)

A model based on transitions from localized band tail states to states above the mobility edge is used to explain the broad band induced absorptions observed in recent pump-probe experiments. The model gives the observed decrease of absorption with frequency at subband gap photo energies and high carrier densities (of about 10 to the 20th/cu cm). At lower carrier densities, the absorption has a maximun which is sensitive to the spatial extent of the band tail states.

Lawandy, N. M.

1990-01-01

351

Electric Field-Induced Polarization of Charged Cell Surface Proteins Does Not  

E-print Network

germ agglutinin. We treated cells with neuraminidase to remove sialic acids; as expected, by conjugating cationic avidin to the surface of live cells. Neuraminidase inhib- ited the electric field the directional polarization of sialic acids. Neuraminidase treatment inhibited directionality but did not alter

Tong, Liang

352

Mechanically induced long-period gratings in polarization maintaining photonic crystal fiber with a supercontinuum generation source  

NASA Astrophysics Data System (ADS)

We present the results from the fabrication and characterization of mechanically induced long period fiber gratings in polarization maintaining photonic crystal fiber (PM-PCF). A supercontinuum source in the range of 600nm - 1700nm is used. This source is generated using a micro-chip laser at 1064nm and a single mode fiber. A long-period grating is induced over 40mm long unjacketed PCF using a V-grooved aluminum plate. External pressure is gradually applied with a metal screw and a torque meter and a loss dip with resonance wavelength is observed. Low insertion losses are depicted from (1-3) dBm with a bandwidth of about 30nm and a loss dip around 15dBm. Sensitivity for this preliminary work is found at 27 dB/Lb. Several applications are potentially possible with the optimization of the transmission spectrum controlled by applied pressure.

Huerta-Mascotte, E.; Mata-Chávez, R. I.; Estudillo-Ayala, J. M.; Guzman-Chavez, A. D.; Cano-Contreras, M.; Trejo-Durán, M.; Rojas-Laguna, R.; Vargas-Rodriguez, E.; Guryev, I. V.

2014-09-01

353

Spectral line polarization with angle-dependent partial frequency redistribution. II. Accelerated lambda iteration and scattering expansion methods for the Rayleigh scattering  

Microsoft Academic Search

Context. The linear polarization of strong resonance lines observed in the solar spectrum is created by the scattering of the photospheric radiation field. This polarization is sensitive to the form of the partial frequency redistribution (PRD) function used in the line radiative transfer equation. Observations have been analyzed until now with angle-averaged PRD functions. With an increase in the polarimetric

M. Sampoorna; K. N. Nagendra; H. Frisch

2011-01-01

354

Stress-induced alteration of chlorophyll fluorescence polarization and spectrum in leaves of Alocasia macrorrhiza L. Schott.  

PubMed

The value of intrinsic chlorophyll fluorescence polarization, and the intensity in emission spectrum were investigated in leaf segments of Alocasia macrorrhiza under several stress conditions including different temperatures (25-50 degrees C), various concentrations of NaCl (0-250 mM), methyl viologen (MV, 0-25 microM), SDS (0-1.0%) and NaHSO(3) (0-80 microM). Fluorescence emission spectrum of leaves at wavelength regions of 500-800 nm was monitored by excitation at 436 nm. The value of fluorescence polarization (P value), as result of energy transfer and mutual orientation between chlorophyll molecules, was determined by excitation at 436 nm and emission at 685 nm. The results showed that elevated temperature and concentrations of salt (NaCl), photooxidant (MV), surfactant (SDS) and simulated SO(2) (NaHSO(3)) treatments all induced a reduction of fluorescence polarization to various degrees. However, alteration of the fluorescence spectrum and emission intensity of F(685) and F(731) depended on the individual treatment. Increase in temperature and concentration of NaHSO(3) enhanced fluorescence intensity mainly at F(685), while an increase in MV concentration led to a decrease at both F(685) and F(731). On the contrary, NaCl and SDS did not cause remarkable change in fluorescence spectrum. Among different treatments, the negative correlation between polarization and fluorescence intensity was found with NaHSO(3) treatments only. We concluded that P value being measured with intrinsic chlorophyll fluorescence as probe in leaves is a susceptible indicator responding to changes in environmental conditions. The alteration of P value and fluorescence intensity might not always be shown a functional relation pattern. The possible reasons of differed response to various treatments were discussed. PMID:17665291

Lin, Zhi-Fang; Liu, Nan; Lin, Gui-Zhu; Pan, Xiao-Ping; Peng, Chang-Lian

2007-11-01

355

Assessment of laser photobiomodulation and polarized light on the healing of cutaneous wounds on euthyroid and hypothyroid induced rats  

NASA Astrophysics Data System (ADS)

The aim of this study was to assess the influence of low-level laser therapy (LLLT) or polarized light (PL) in cutaneous wound healing of hypothyroid rats at dosages of 20 or 40J/cm2. Bioestimulatory effects of Laser radiation and Polarized light are recognized alternative therapies to improve healing on systemic disease patients, but their usefulness in the improvement of hypothyroidism healing impairment is uncertain till date. Forty Wistar rats were used in this study. Hypothyroidism was propylthiouracil- induced. Standard excisional cutaneous wounds were created without suturing and LLLT (?660nm, 30mW, ? 3mm) or PL (? 400-2000nm, 40mW, ? 10mm) was applied every 48 hours up to seven days on experimental groups. The rats were killed on the eighth day when wound contraction was assessed. The healing features were evaluated by light microscopy (H/E and Sirius Red). The cutaneous wounds of hypothyroid rats showed delayed healing process characterized by reduced thickness of epithelial layers, incipient formation of disorganized collagen fibers and wound contraction to a lesser extent (FISHER, p=0.0276), when compared to the euthyroid group. The use of both the Laser and Polarized Light on hypothyroid rats increased the amount of fibroblasts and the thickness of collagen fibers, especially on the L 20J/cm2 group. Euthyroid rats have still demonstrated more regular collagen fibers pattern than hypothyroid rats. It was therefore concluded that hypothyroidism delays wound healing and both Laser photobiomodulation and Polarized Light at 20j/cm2 dosages had improved the healing process in hypothyroid rats.

Ramalho, Luciana Maria Pedreira; Weyll, Barbara Mayoral Pedroso; da Costa Lino, Maíra Dória M.; Ramalho, Maria Jose Pedreira; Barbosa Pinheiro, Antonio Luis

2010-02-01

356

Plant abiotic stress diagnostic by laser induced chlorophyll fluorescence spectral analysis of in vivo leaf tissue of biofuel species  

NASA Astrophysics Data System (ADS)

Laser induced fluorescence is exploited to evaluate the effect of abiotic stresses upon the evolution and characteristics of in vivo chlorophyll emission spectra of leaves tissues of brazilian biofuel plants species(Saccharum officinarum and Jatropha curcas). The chlorophyll fluorescence spectra of 20 min predarkened intact leaves were studied employing several excitation wavelengths in the UV-VIS spectral region. Red(Fr) and far-red (FFr) chlorophyll fluorescence emission signals around 685 nm and 735 nm, respectively, were analyzed as a function of the stress intensity and the time of illumination(Kautsky effect). The Chl fluorescence ratio Fr/FFr which is a valuable nondestructive indicator of the chlorophyll content of leaves was investigated during a period of time of 30 days. The dependence of the Chl fluorescence ratio Fr/FFr upon the intensity of the abiotic stress(salinity) was examined. The results indicated that the salinity plays a major hole in the chlorophyll concentration of leaves in both plants spieces, with a significant reduction in the chlorophyll content for NaCl concentrations in the 25 - 200 mM range. The laser induced chlorophyll fluorescence analysis allowed detection of damage caused by salinity in the early stages of the plants growing process, and can be used as an early-warning indicator of salinity stress

Gouveia-Neto, Artur S.; Silva, Elias A., Jr.; Costa, Ernande B.; Bueno, Luciano A.; Silva, Luciana M. H.; Granja, Manuela M. C.; Medeiros, Maria J. L.; Câmara, Terezinha J. R.; Willadino, Lilia G.

2010-02-01

357

IP4DI: A software for time-lapse 2D/3D DC-resistivity and induced polarization tomography  

NASA Astrophysics Data System (ADS)

We propose a 2D/3D forward modelling and inversion package to invert direct current (DC)-resistivity, time-domain induced polarization (TDIP), and frequency-domain induced polarization (FDIP) data. Each cell used for the discretization of the 2D/3D problems is characterized by a DC-resistivity value and a chargeability or complex conductivity for TDIP/FDIP problems, respectively. The governing elliptic partial differential equations are solved with the finite element method, which can be applied for both real and complex numbers. The inversion can be performed either for a single snapshot of data or for a sequence of snapshots in order to monitor a dynamic process such as a salt tracer test. For the time-lapse inversion, we have developed an active time constrained (ATC) approach that is very efficient in filtering out noise in the data that is not correlated over time. The forward algorithm is benchmarked with simple analytical solutions. The inversion package IP4DI is benchmarked with three tests, two including simple geometries. The last one corresponds to a time-lapse resistivity problem for cross-well tomography during enhanced oil recovery. The algorithms are based on MATLAB® code package and a graphical user interface (GUI).

Karaoulis, M.; Revil, A.; Tsourlos, P.; Werkema, D. D.; Minsley, B. J.

2013-04-01

358

Tuning of polarization sensitivity in closely stacked trilayer InAs/GaAs quantum dots induced by overgrowth dynamics  

NASA Astrophysics Data System (ADS)

Tailoring of electronic and optical properties of self-assembled InAs quantum dots (QDs) is a critical limit for the design of several QD-based optoelectronic devices operating in the telecom frequency range. We describe how fine control of the strain-induced surface kinetics during the growth of vertically stacked multiple layers of QDs allows for the engineering of their self-organization process. Most noticeably, this study shows that the underlying strain field induced along a QD stack can be modulated and controlled by time-dependent intermixing and segregation effects occurring after capping with a GaAs spacer. This leads to a drastic increase of the TM/TE polarization ratio of emitted light, not accessible from conventional growth parameters. Our detailed experimental measurements, supported by comprehensive multi-million atom simulations of strain, electronic and optical properties, provide in-depth analysis of the grown QD samples allowing us to give a clear picture of the atomic scale phenomena affecting the proposed growth dynamics and consequent QD polarization response.

Tasco, Vittorianna; Usman, Muhammad; De Giorgi, Milena; Passaseo, Adriana

2014-02-01

359

Observation of field-induced polarization of valleys in p-type Sb2Te3 single crystals  

NASA Astrophysics Data System (ADS)

A flow of carriers along the c axis is extremely sensitive to the orientation of an in-plane magnetic field due to in-plane mass anisotropy in layered compounds. Based on this mechanism, a rotatable in-plane magnetic field has been applied as a valley valve to tune the contribution of each valley in p-type Sb2Te3 bulk single crystals to the total conductivity and interlayer magnetoresistance (MR). A valley-polarized current is generated, and the angular-dependent interlayer MR of up to 160% represents strong anisotropy. There are six inequivalent peaks over all temperature and magnetic field ranges. The giant MR results from the intravalley and intervalley hole Coulomb scattering in upper valence bands. The interlayer MR anisotropy originates from field-induced polarization of valleys, and Coulomb interaction-induced valley distortion. The strong anisotropy of the angular-dependent interlayer MR reflects strong anisotropies of carrier scattering time and effective mass in the six valleys and their inequivalent contributions to total magnetoconductivity and interlayer MR in p-type Sb2Te3 bulk.

Yue, Z. J.; Zhu, C. B.; Dou, S. X.; Wang, X. L.

2012-11-01

360

The M2 polarization of macrophage induced by fractalkine in the endometriotic milieu enhances invasiveness of endometrial stromal cells  

PubMed Central

Fractalkine (FKN) is involved in the immunopathogenesis of inflammatory diseases, including endometriosis. Our objective was to investigate the role of FKN in the cross-talking between endometrial stromal cells (ESCs) and U937 (macrophage line) in the endometriotic milieu. We have found that FKN levels in peritoneal fluid and ESCs positively correlate with the progress of endometriosis. The expression of CX3CR1 in the normal ESCs were significantly lower than that in eutopic and ectopic ESCs from women with endometriosis. CX3CR1 expression in U937 was higher than that in ectopic ESCs. FKN secreted by eutopic ESCs could change the balance between the release of IL10 and IL12 of macrophages with the upregulation of IL10 production and downregulation of IL12 production. Moreover, FKN could induce M2 polarization of macrophage with decreased expression of CD86. FKN could increase the expression of matrix metalloproteinase 9 and decrease the expression of tissue inhibitor of metalloproteinase1 and 2, and promote the invasiveness of ESCs by activating p38MAPK and integrin?1 signal pathway. In conclusion, the higher levels of FKN secreted by eutopic ESCs facilitate the onset and progression of endometriosis by inducing M2 polarization of macrophage which in turn enhances invasiveness of ESCs. PMID:24427339

Wang, Yun; Fu, Yonglun; Xue, Songguo; Ai, Ai; Chen, Hong; Lyu, Qifeng; Kuang, Yanping

2014-01-01

361

Spectral Response of the Pulsationally-Induced Shocks in the Atmosphere of BW Vulpeculae  

E-print Network

The star BW Vul excites an extremely strong radial pulsation that grows in its envelope and is responsible for visible shock features in the continuum flux and spectral line profiles emerging in the atmosphere At two phases separated by 0.8 cycles. Material propelled upwards in the atmosphere from the shock returns to the lower photosphere where it creates a second shock just before the start of the next cycle. We have obtained three nights of echelle data for this star over about 5 pulsation cycles (P = 0.201 days) in order to evaluate the effects of on a number of important lines in the spectrum, including the HeI 5875A and 6678A lines. These data were supplemented by archival high-dispersion IUE (UV) data from 1994. A comparison of profiles of the two HeI lines during the peak of the infall activity suggests that differences in the development of the blue wing at this time are due to heating and short-lived formations of an optically thin layer above the atmospheric region compressed by the infall. This discovery and the well-known decreases in equivalent widths of the CII 6578-83A doublet at the two shock phases, suggests that shock flattens the temperature gradient and produces heating in heating the upper atmosphere. Except for absorptions in the blue wings of the UV resonance lines, we find no evidence for sequential shock delays arriving at various regions of line formation of the photosphere (a "Van Hoof effect"). Phase lags cited by some former observers may be false indicators arising from varying degrees of desaturation of multiple lines, such as for the red HeI lines. In addition, an apparent lag in the equivalent width curve of lines arising from less excited atomic levels could instead be caused by post-shock cooling, followed by a rebound shock.

Myron A. Smith; C. Simon Jeffery

2002-10-08

362

Two dimensional electron gases induced by spontaneous and piezoelectric polarization in undoped and doped AlGaN\\/GaN heterostructures  

Microsoft Academic Search

Two dimensional electron gases in AlxGa1-xN\\/GaN based heterostructures, suitable for high electron mobility transistors, are induced by strong polarization effects. The sheet carrier concentration and the confinement of the two dimensional electron gases located close to the AlGaN\\/GaN interface are sensitive to a large number of different physical properties such as polarity, alloy composition, strain, thickness, and doping of the

O. Ambacher; B. Foutz; J. Smart; J. R. Shealy; N. G. Weimann; K. Chu; M. Murphy; A. J. Sierakowski; W. J. Schaff; L. F. Eastman; R. Dimitrov; A. Mitchell; M. Stutzmann

2000-01-01

363

Polarization control of ultrabroadband supercontinuum generation from midinfrared laser-induced harmonic emission  

NASA Astrophysics Data System (ADS)

We present an efficient scheme for generation of an isolated attosecond (as) pulse based on the combination of two well-known methods: polarization gating method plus a method based on using two colors (? +?/2). The first uses a pulse whose ellipticity is small within a very short time interval (called a polarization gating). By adding a second pulse whose frequency is a half-frequency (midinfrared) of the first pulse, we extend significantly the cutoff frequency, as well as the width of the supercontinuum harmonic spectrum. The high-order harmonic generation is calculated using the strong-field approximation theory. As a result, an isolated 42-as pulse is generated directly by superposing the hundreds of harmonics. To explain the mechanism of the ultrashort attosecond generation, we perform the semiclassical three-step model simulation and wavelet time-frequency transform of the harmonic spectra.

Jiao, Zhi-Hong; Wang, Guo-Li; Li, Peng-Cheng; Zhou, Xiao-Xin

2014-08-01

364

Instanton-induced charm contribution to polarized deep-inelastic scattering  

E-print Network

Recent data on B decays involving $\\eta'$ may be explained if the singlet axial current of charmed quarks has large matrix element to $\\eta'$, and instantons were shown to be able to generate this effect. We study the magnitude of charm contributions to nucleon polarized structure functions generated in a similar way. Comparing the charm contribution, which is related to a dim(6) gluonic operator, to that of light quarks, which are related by the anomaly equation to $G\\tilde G$, we found that $\\Delta c/\\Delta\\Sigma$ = -(0.2-0.08). Future experiments like COMPASS at CERN identifying charm production in DIS can measure this ``intrinsic polarized charm'' component of the nucleon.

Andree Blotz; Edward Shuryak

1997-10-30

365

Birefringence-induced polarization-independent and nearly all-angle transparency through a metallic film  

NASA Astrophysics Data System (ADS)

We propose a birefringence route to perfect electromagnetic (EM) wave tunneling through a metallic film which relies on homogeneous birefringent coatings with moderate and positive parameters only. EM transparency is achieved in such a birefringent-metal-birefringent (BMB) structure for both polarizations and over nearly all incident angles. The stringent restrictions in conventional dielectric-metal-dielectric media, i.e., dielectrics with extremely negative permittivity, high magnetic field and polarization dependence (only for TE waves), are not required in our method. The criterion for perfect transmission is obtained by analyzing the effective medium theory and the EM fields of such a birefringent structure. The solutions hold for lossless and lossy cases in a quite large frequency range.

Gao, D. L.; Gao, L.; Qiu, C. W.

2011-08-01

366

Induced polarization and electronic properties of carbon-doped boron nitride nanoribbons  

NASA Astrophysics Data System (ADS)

The electronic properties of boron nitride nanoribbons (BNNRs) doped with a line of carbon atoms are investigated using density functional calculations. By replacing a line of alternating B and N atoms with carbons, three different configurations are possible depending on the type of the atoms which bond to the carbons. We found very different electronic properties for these configurations: (i) the NCB arrangement is strongly polarized with a large dipole moment having an unexpected direction, (ii) the BCB and NCN arrangements are nonpolar with zero dipole moment, (iii) the doping by a carbon line reduces the band gap regardless of the local arrangement of the borons and the nitrogens around the carbon line, and (iv) the polarization and energy gap of the carbon-doped BNNRs can be tuned by an electric field applied parallel to the carbon line. Similar effects were found when either an armchair or zigzag line of carbon was introduced.

Beheshtian, J.; Sadeghi, A.; Neek-Amal, M.; Michel, K. H.; Peeters, F. M.

2012-11-01

367

Photon polarization entanglement induced by biexciton: experimental evidence for violation of Bell's inequality  

E-print Network

We have investigated the polarization entanglement between photon pairs generated from a biexciton in a CuCl single crystal via resonant hyper parametric scattering. The pulses of a high repetition pump are seen to provide improved statistical accuracy and the ability to test Bell's inequality. Our results clearly violate the inequality and thus manifest the quantum entanglement and nonlocality of the photon pairs. We also analyzed the quantum state of our photon pairs using quantum state tomography.

Goro Oohata; Ryosuke Shimizu; Keiichi Edamatsu

2006-07-20

368

Nuclear Lamin A\\/C Deficiency Induces Defects in Cell Mechanics, Polarization, and Migration  

Microsoft Academic Search

Lamin A\\/C is a major constituent of the nuclear lamina, a thin filamentous protein layer that lies beneath the nuclear envelope. Here we show that lamin A\\/C deficiency in mouse embryonic fibroblasts (Lmna?\\/? MEFs) diminishes the ability of these cells to polarize at the edge of a wound and significantly reduces cell migration speed into the wound. Moreover, lamin A\\/C

Jerry S. H. Lee; Christopher M. Hale; Porntula Panorchan; Shyam B. Khatau; Jerry P. George; Yiider Tseng; Colin L. Stewart; Didier Hodzic; Denis Wirtz

2007-01-01

369

Laser-Induced, Polarization Dependent Shape Transformation of Au/Ag Nanoparticles in Glass  

PubMed Central

Bimetallic, initially spherical Ag/Au nanoparticles in glass prepared by ion implantation have been irradiated with intense femtosecond laser pulses at intensities still below the damage threshold of the material surface. This high-intensity laser processing produces dichroism in the irradiated region, which can be assigned to the observed anisotropic nanoparticle shapes with preferential orientation of the longer particle axis along the direction of laser polarization. In addition, the particle sizes have considerably been increased upon processing. PMID:20628450

2009-01-01

370

Weak measurement of photon polarization by back-action induced path interference  

E-print Network

The essential feature of weak measurements on quantum systems is the reduction of measurement back-action to negligible levels. To observe the non-classical features of weak measurements, it is therefore more important to avoid additional back-action errors than it is to avoid errors in the actual measurement outcome. In this paper, it is shown how an optical weak measurement of diagonal (PM) polarization can be realized by path interference between the horizontal (H) and vertical (V) polarization components of the input beam. The measurement strength can then be controlled by rotating the H and V polarizations towards each other. This well-controlled operation effectively generates the back-action without additional decoherence, while the visibility of the interference between the two beams only limits the measurement resolution. As the experimental results confirm, we can obtain extremely high weak values, even at rather low visibilities. Our method therefore provides a realization of weak measurements that is extremely robust against experimental imperfections.

Masataka Iinuma; Yutaro Suzuki; Gen Taguchi; Yutaka Kadoya; Holger F. Hofmann

2010-12-04

371

Rapid and robust analysis of cellular and molecular polarization induced by chemokine signaling.  

PubMed

Cells respond to chemokine stimulation by losing their round shape in a process called polarization, and by altering the subcellular localization of many proteins. Classic imaging techniques have been used to study these phenomena. However, they required the manual acquisition of many cells followed by time consuming quantification of the morphology and the co-localization of the staining of tens of cells. Here, a rapid and powerful method is described to study these phenomena on samples consisting of several thousands of cells using an imaging flow cytometry technology that combines the advantages of a microscope with those of a cytometer. Using T lymphocytes stimulated with CCL19 and staining for MHC Class I molecules and filamentous actin, a gating strategy is presented to measure simultaneously the degree of shape alterations and the extent of co-localization of markers that are affected by CCL19 signaling. Moreover, this gating strategy allowed us to observe the segregation of filamentous actin (at the front) and phosphorylated Ezrin-Radixin-Moesin (phospho-ERM) proteins (at the rear) in polarized T cells after CXCL12 stimulation. This technique was also useful to observe the blocking effect on polarization of two different elements: inhibition of actin polymerization by a pharmacological inhibitor and expression of mutants of the Par6/atypical PKC signaling pathway. Thus, evidence is shown that this technique is useful to analyze both morphological alterations and protein redistributions. PMID:25548867

Megrelis, Laura; Delon, Jérôme

2014-01-01

372

GEOPHYSICS, ASTRONOMY AND ASTROPHYSICS: Turbulence-induced changes in degree of polarization, degree of coherence and spectrum of partially coherent electromagnetic beams  

NASA Astrophysics Data System (ADS)

Based on a recently formulated unified theory of coherence and polarization, a method is described to study turbulence-induced changes in the polarization, the coherence and the spectrum of partially coherent electromagnetic beams on propagation. The electromagnetic Gaussian Schell-model beam is taken as a typical example of partially coherent electromagnetic beams, and the closed-form expressions for the degree of polarization, the degree of coherence and the spectrum of electromagnetic Gaussian Schell-model beams propagating through atmospheric turbulence are derived in the quadratic approximation of Rytov's phase structure function. Some interesting results are obtained, which are illustrated by numerical examples and are explained in physics.

Ji, Xiao-Ling; Pu, Zheng-Cai

2010-02-01

373

Influence of polarization-induced electric fields on coherent electron tunneling in AlN/GaN coupled double quantum wells  

NASA Astrophysics Data System (ADS)

The influence of polarization-induced electric fields on the coherent electron tunneling probability in AlN/GaN coupled double quantum wells (CDQWs) has been performed by solving Schrödinger and Poisson equations self-consistently. It is found that when the first excited state (E2) and the second excited state (E3) resonate in AlN/GaN CDQWs, the coherent electron tunneling probability is 16 times higher than that in AlN/GaN single quantum well, which is attributed to the Fabry-Perot quantum interference mechanism in AlN/GaN CDQWs. However, the coherent electron tunneling probability decreases rapidly with the polarization-induced electric fields increasing, which is attributed to the resonance between the E2 and E3 subbands weakening with the polarization-induced electric fields increasing in AlN/GaN CDQWs.

Cen, L. B.; Shen, B.; Huang, C. C.; Xu, F. J.; Qin, Z. X.; Zhang, G. Y.; Chen, X. S.; Lu, W.

2010-12-01

374

Using elaborative interrogation to induce characteristics of polar and nonpolar solvents from animations of their molecular structures  

NASA Astrophysics Data System (ADS)

This study concerned (a) how general chemistry students learn to classify solvent polarity from animated molecules, (b) whether peer interaction increases the number of correct classifications, and (c) whether language, academic ability, logical thinking ability, or prior knowledge interact with rate of learning or posttest performance. Two types of interaction were compared, group discussion and elaborative interrogation. The study rested on three assumptions: (a) animated molecules are appropriate for learning the concept of solvent polarity, (b) question stems and a guided interrogation enhance learning of a visual concept, (c) general chemistry students can induce the concept of solvent polarity from animated molecules when no guiding cues, either visual or verbal, are given. After a review of molecular geometry and bonding theories, students were presented with four trials of ten animated molecular structures. Ten three-to-five minute discussions were distributed among the four trials. Prior to the trials the experimental group received a 45-minute training session on elaborative interrogation; the topic was what happens on the molecular level when a carbonated beverage is opened. The control group received a 45-minute expository lecture on the same carbonated beverage topic. Participants were given a four-part posttest immediately following the trials. Results of the study suggest that most students tend to classify the solvent polarity of animated molecules based on certain structural features using a prototype or feature-frequency categorization strategy. Elaborative interrogation did not show a significant effect on the rate of learning or on the performance of learners on posttest measures of recall and comprehension. The experimental group noted a significantly greater number and range of types of features, and offered higher quality generalizations and explanations of their polarity classification procedure. Finally, the results implied that learning from animations depends more on prior knowledge of relevant concepts than on academic ability, logical thinking ability, or preferred language. Although some benefits may arise from accompanying computer animation with an interactive discussion, additional visual and verbal, cueing may be necessary for optimal outcomes.

Ems-Wilson, Janice

375

Laser-induced fluorescence of green plants. III - LIF spectral signatures of five major plant types  

NASA Technical Reports Server (NTRS)

A technique amenable to remote sensing use which utilizes laser-induced fluorescence (LIF) properties of plants has been successfully used in the laboratory to identify five major plant types. These included herbaceous dicots, herbaceous monocots, conifers, hardwoods, and algae. Each of these plant types exhibited a characteristic LIF spectra when excited by a pulsed N2 laser emitting at 337 nm. Although monocots and dicots possess common fluorescence maxima at 440, 685, and 740 nm, they could be differentiated from one another by using the ratio of the square of the fluorescence intensity at 440 nm to the nonsquared intensity at 685 nm, i.e., (440)-squared/685. In all cases, monocots yielded a significantly higher ratio. Conifers have fluorescence maxima at 440, 525, and 740 nm but none at 685 nm. Hardwoods exhibited fluorescence at 440, 525, 685, and 740 nm. Algae had very low fluorescence at 440 nm, no fluorescence at 525 nm, and fluorescence maxima at 685 and 740 nm. For algae, the ratio of the fluorescence intensity at 685 nm to that at 740 nm was much greater than that for monocots, dicots, and hardwoods. The potential use of the LIF technique for individual species identification is suggested.

Chappelle, E. W.; Wood, F. M., Jr.; Newcomb, W. W.; Mcmurtrey, J. E., III

1985-01-01

376

Coupling of Pressure-Induced Structural Shifts to Spectral Changes in a Yellow Fluorescent Protein  

PubMed Central

X-ray diffraction analysis of pressure-induced structural changes in the Aequorea yellow fluorescent protein Citrine reveals the structural basis for the continuous fluorescence peak shift from yellow to green that is observed on pressurization. This fluorescence peak shift is caused by a reorientation of the two elements of the Citrine chromophore. This study describes the structural linkages in Citrine that are responsible for the local reorientation of the chromophore. The deformation of the Citrine chromophore is actuated by the differential motion of two clusters of atoms that compose the ?-barrel scaffold of the molecule, resulting in a slight bending of the ?-barrel. The high-pressure structures also show a perturbation of the hydrogen bonding network that stabilizes the excited state of the Citrine chromophore. The perturbation of this network is implicated in the reduction of fluorescence intensity of Citrine. The blue-shift of the Citrine fluorescence spectrum resulting from the bending of the ?-barrel provides structural insight into the transient blue-shifting of isolated yellow fluorescent protein molecules under ambient conditions and suggests mechanisms to alter the time-dependent behavior of Citrine under ambient conditions. PMID:19751677

Barstow, Buz; Ando, Nozomi; Kim, Chae Un; Gruner, Sol M.

2009-01-01

377

Precise Extraction of the Induced Polarization in the {sup 4}He(e,e{sup '}p-vector){sup 3}H Reaction  

SciTech Connect

We measured with unprecedented precision the induced polarization P{sub y} in {sup 4}He(e,e{sup '}p-vector){sup 3}H at Q{sup 2}=0.8 and 1.3 (GeV/c){sup 2}. The induced polarization is indicative of reaction-mechanism effects beyond the impulse approximation. Our results are in agreement with a relativistic distorted-wave impulse approximation calculation but are overestimated by a calculation with strong charge-exchange effects. Our data are used to constrain the strength of the spin-independent charge-exchange term in the latter calculation.

Malace, S. P.; Paolone, M.; Strauch, S.; Ilieva, Y.; Tedeschi, D. [University of South Carolina, Columbia, South Carolina 29208 (United States); Albayrak, I.; Christy, M. E.; Keppel, C. E.; Tang, L.; Tvaskis, V. [Hampton University, Hampton, Virginia 23668 (United States); Arrington, J.; Solvignon, P. [Argonne National Laboratory, Argonne, Illinois 60439 (United States); Berman, B. L.; Briscoe, B. [George Washington University, Washington, D.C. 20052 (United States); Brash, E. J. [Christopher Newport University, Newport News, Virginia 23606 (United States); Camsonne, A.; Chen, J.-P.; Chudakov, E.; Ent, R.; Higinbotham, D. W. [Thomas Jefferson National Accelerator Facility, Newport News, Virginia 23606 (United States)

2011-02-04

378

Mechanism of Lattice-Distortion-Induced Electric-Polarization Flop in the Multiferroic Perovskite Manganites  

Microsoft Academic Search

Magnetoelectric phase diagrams of the perovskite manganites, Eu1-xYxMnO3 and\\u000aGd1-xTbxMnO3, are theoretically studied. We first construct a microscopic\\u000amodel, and then analyze the model using the Monte-Carlo method. We reproduce\\u000athe diagrams, which contain two different multiferroic states, i.e., the\\u000aab-plane spin cycloid with electric polarization P\\/\\/a and the bc-plane spin\\u000acycloid with P\\/\\/c. We reveal that their competition originates

Masahito Mochizuki; Nobuo Furukawa

2008-01-01

379

Cavity-induced coherence effects in spontaneous emission from pre-Selection of polarization  

E-print Network

Spontaneous emission can create coherences in a multilevel atom having close lying levels, subject to the condition that the atomic dipole matrix elements are non-orthogonal. This condition is rarely met in atomic systems. We report the possibility of bypassing this condition and thereby creating coherences by letting the atom with orthogonal dipoles to interact with the vacuum of a pre-selected polarized cavity mode rather than the free space vacuum. We derive a master equation for the reduced density operator of a model four level atomic system, and obtain its analytical solution to describe the interference effects. We report the quantum beat structure in the populations.

Anil K. Patnaik; G. S. Agarwal

1998-10-16

380

Thermally or Magnetically Induced Polarization Reversal in the Multiferroic CoCr2O4  

NASA Astrophysics Data System (ADS)

We report the unexpected evolution, with thermal and magnetic-field (H) variations, of the interrelation between the polarization P, magnetization M, and spiral wave vector Q in CoCr2O4, which has a ferrimagnetic conical-spiral magnetic order. For example, P suddenly jumps and changes its sign at the magnetic lock-in transition (TL) with thermal variation, or with isothermal variation of H (without changing its direction) at TL, which surprisingly occurs without change in spiral handedness (i.e., the sign of Q). The presence of multiple spiral sublattices may be behind this unusual behavior.

Choi, Y. J.; Okamoto, J.; Huang, D. J.; Chao, K. S.; Lin, H. J.; Chen, C. T.; van Veenendaal, M.; Kaplan, T. A.; Cheong, S.-W.

2009-02-01

381

Thermally or magnetically induced polarization reversal in the Multiferroic CoCr2O4.  

PubMed

We report the unexpected evolution, with thermal and magnetic-field (H) variations, of the interrelation between the polarization P, magnetization M, and spiral wave vector Q in CoCr2O4, which has a ferrimagnetic conical-spiral magnetic order. For example, P suddenly jumps and changes its sign at the magnetic lock-in transition (T_{L}) with thermal variation, or with isothermal variation of H (without changing its direction) at T_{L}, which surprisingly occurs without change in spiral handedness (i.e., the sign of Q). The presence of multiple spiral sublattices may be behind this unusual behavior. PMID:19257633

Choi, Y J; Okamoto, J; Huang, D J; Chao, K S; Lin, H J; Chen, C T; van Veenendaal, M; Kaplan, T A; Cheong, S-W

2009-02-13

382

Faster motion of double 360° domain walls system induced by spin-polarized current  

SciTech Connect

By micromagnetic simulation, we investigated a double 360° domain walls system in two parallel nanowires. Two domain walls are coupled to each other via magnetostatic interaction. When a spin-polarized current is applied to only one nanowire or both nanowires with the same direction, the two domain walls propagate along nanowires together. The critical velocity of such system is obviously higher than that of a single 360° domain wall. The interaction between the two domain walls can be modeled as two bodies that connected by a spring, and we analyzed the coupling characteritics of the double 360° domain walls at last.

Zhang, S. F.; Zhu, Q. Y.; Mu, C. P.; Zheng, Q.; Liu, X. Y.; Liu, Q. F.; Wang, J. B., E-mail: wangjb@lzu.edu.cn [Institute of Applied Magnetics, Key Laboratory for Magnetism and Magnetic Materials of Ministry of Education, Lanzhou University, Lanzhou 730000 (China)

2014-05-07

383

Measurements of the broadening and shift parameters of methane spectral lines in the 5550-6140 cm-1 region induced by pressure of carbon dioxide  

NASA Astrophysics Data System (ADS)

The absorption spectra of a mixture of CH4 with CO2 at different partial pressures of both gases have been recorded at room temperature in the 5390-6200 cm-1 region using a Bruker IFS 125 HR FTIR spectrometer. The multispectrum fitting procedure has been applied to these spectra to recover the broadening and shift parameters of the methane spectral lines. The CO2 broadening and pressure induced shift coefficients, respectively, for 533 and 386 CH4 spectral lines with good values of the signal to noise ratio have been derived. The rotational dependence of the values of these coefficients is discussed.

Lyulin, O. M.; Petrova, T. M.; Solodov, A. M.; Solodov, A. A.; Perevalov, V. I.

2014-11-01

384

Glucagon-like peptide-1 (GLP-1) induces M2 polarization of human macrophages via STAT3 activation.  

PubMed

It is known that glucagon-like peptide-1 (GLP-1) is a hormone secreted postprandially from the L-cells of the small intestine and regulates glucose homeostasis. GLP-1 is now used for the treatment of diabetes because of its beneficial role against insulin resistance. The GLP-1 receptor (GLP-1R) is expressed on many cell types, including macrophages, and GLP-1 suppresses the development of atherosclerosis by inhibiting macrophage function. However, there have so far been few studies that have investigated the significance of GLP-1/GLP-1R signaling in macrophage activation. In the present study, we examined the effect of GLP-1 and exenatide, a GLP-1R agonist, on human monocyte-derived macrophage (HMDM) activation. We found that GLP-1 induced signal transducer and activator of transcription 3 (STAT3) activation. Silencing of GLP-1R suppressed the GLP-1-induced STAT3 activation. In addition, alternatively activated (M2) macrophage-related molecules, such as IL-10, CD163, and CD204 in HMDM, were significantly upregulated by GLP-1. Furthermore, the co-culture of 3T3-L1 adipocytes with GLP-1-treated RAW 264.7 macrophages increased the secretion of adiponectin compared to co-culture of the 3T3-L1 adipocytes with untreated RAW 264.7 macrophages. Our results demonstrate that GLP-1 induces macrophage polarization toward the M2 phenotype, which may contribute to the protective effects of GLP-1 against diabetes and cardiovascular diseases. PMID:22842565

Shiraishi, Daisuke; Fujiwara, Yukio; Komohara, Yoshihiro; Mizuta, Hiroshi; Takeya, Motohiro

2012-08-24

385

Nitrogen Limitation and Slow Drying Induce Desiccation Tolerance in Conjugating Green Algae (Zygnematophyceae, Streptophyta) from Polar Habitats  

PubMed Central

Background Filamentous Zygnematophyceae are typical components of algal mats in the polar hydro-terrestrial environment. Under field conditions, they form senescent vegetative cells, designated as pre-akinetes, which are tolerant to desiccation and osmotic stress. Key Findings Pre-akinete formation and desiccation tolerance was investigated experimentally under monitored laboratory conditions in four strains of Arctic and Antarctic isolates with vegetative Zygnema sp. morphology. Phylogenetic analyses of rbcL sequences revealed one Arctic strain as genus Zygnemopsis, phylogenetically distant from the closely related Zygnema strains. Algae were cultivated in liquid or on solidified medium (9 weeks), supplemented with or lacking nitrogen. Nitrogen-free cultures (liquid as well as solidified) consisted of well-developed pre-akinetes after this period. Desiccation experiments were performed at three different drying rates (rapid: 10% relative humidity, slow: 86% rh and very slow); viability, effective quantum yield of PS II, visual and ultrastructural changes were monitored. Recovery and viability of pre-akinetes were clearly dependent on the drying rate: slower desiccation led to higher levels of survival. Pre-akinetes survived rapid drying after acclimation by very slow desiccation. Conclusions The formation of pre-akinetes in polar Zygnema spp. and Zygnemopsis sp. is induced by nitrogen limitation. Pre-akinetes, modified vegetative cells, rather than specialized stages of the life cycle, can be hardened by mild desiccation stress to survive rapid drying. Naturally hardened pre-akinetes play a key role in stress tolerance and dispersal under the extreme conditions of polar regions, where sexual reproduction and production of dormant stages is largely suppressed. PMID:25398135

Pichrtová, Martina; Kulichová, Jana; Holzinger, Andreas

2014-01-01

386

Electrostatic interaction in the presence of dielectric interfaces and polarization-induced like-charge attraction  

E-print Network

Electrostatic polarization is important in many nano-/micro-scale physical systems such as colloidal suspensions, biopolymers, and nanomaterials assembly. The calculation of polarization potential requires an efficient algorithm for solving 3D Poisson's equation. We have developed a useful image charge method to rapid evaluation of the Green's function of the Poisson's equation in the presence of spherical dielectric discontinuities. This paper presents an extensive study of this method by giving an convergence analysis and developing a coarse-graining algorithm. The use of the coarse graining could reduce the number of image charges to around a dozen, by 1-2 orders of magnitude. We use the algorithm to investigate the interaction force between likely charged spheres in different dielectric environments. We find the size and charge asymmetry leads to an attraction between like charges, in agreement with existing results. Furthermore, we study three-body interaction and find in the presence of an external interface, the interaction force depends on the curvature of the interface, and behavior a non-monotonic electrostatic force.

Zhenli Xu

2012-10-23

387

Spin-polarized electric currents in diluted magnetic semiconductor heterostructures induced by terahertz and microwave radiation  

NASA Astrophysics Data System (ADS)

We report on the study of spin-polarized electric currents in diluted magnetic semiconductor (DMS) quantum wells subjected to an in-plane external magnetic field and illuminated by microwave or terahertz radiation. The effect is studied in (Cd,Mn)Te/(Cd,Mg)Te quantum-wells (QWs) and (In,Ga)As/InAlAs:Mn QWs belonging to the well-known II-VI and III-V DMS material systems, as well as in heterovalent AlSb/InAs/(Zn,Mn)Te QWs, which represent a promising combination of II-VI and III-V semiconductors. Experimental data and developed theory demonstrate that the photocurrent originates from a spin-dependent scattering of free carriers by static defects or phonons in the Drude absorption of radiation and subsequent relaxation of carriers. We show that in DMS structures, the efficiency of the current generation is drastically enhanced compared to nonmagnetic semiconductors. The enhancement is caused by the exchange interaction of carrier spins with localized spins of magnetic ions resulting, on the one hand, in the giant Zeeman spin splitting, and, on the other hand, in the spin-dependent carrier scattering by localized Mn2+ ions polarized by an external magnetic field.

Olbrich, P.; Zoth, C.; Lutz, P.; Drexler, C.; Bel'kov, V. V.; Terent'ev, Ya. V.; Tarasenko, S. A.; Semenov, A. N.; Ivanov, S. V.; Yakovlev, D. R.; Wojtowicz, T.; Wurstbauer, U.; Schuh, D.; Ganichev, S. D.

2012-08-01

388

Soliton-induced nonlocal resonances observed through high-intensity tunable spectrally compressed second-harmonic peaks  

NASA Astrophysics Data System (ADS)

Experimental data of femtosecond thick-crystal second-harmonic generation show that when tuning away from phase matching, a dominating narrow spectral peak appears in the second harmonic that can be tuned over hundreds of nanometers by changing the phase-mismatch parameter. Traditional theory explains this as phase matching between a sideband in the broadband pump to its second harmonic. However, our experiment is conducted under high input intensities and instead shows excellent quantitative agreement with a nonlocal theory describing cascaded quadratic nonlinearities. This theory explains the detuned peak as a nonlocal resonance that arises due to phase matching between the pump and a detuned second-harmonic frequency, but where in contrast to the traditional theory the pump is assumed dispersion free. As a soliton is inherently dispersion free, the agreement between our experiment and the nonlocal theory indirectly proves that we have observed a soliton-induced nonlocal resonance. The soliton exists in the self-defocusing regime of the cascaded nonlinear interaction and in the normal dispersion regime of the crystal, and needs high input intensities to become excited.

Zhou, Binbin; Guo, Hairun; Bache, Morten

2014-07-01

389

Polarization of protective immunity induced by replication-incompetent adenovirus expressing glycoproteins of pseudorabies virus  

PubMed Central

Replication-incompetent adenoviruses expressing three major glycoproteins (gB, gC, and gD) of pseudorabies virus (PrV) were constructed and used to examine the ability of these glycoproteins to induce protective immunity against a lethal challenge. Among three constructs, recombinant adenovirus expressing gB (rAd-gB) was found to induce the most potent immunity biased to Th1-type, as determined by the IgG isotype ratio and the profile of the Th1/Th2 cytokine production. Conversely, the gC-expressing adenovirus (rAd-gC) revealed Th2-type immunity and the gD-expressing adenovirus (rAd-gD) induced lower levels of IFN-? and IL-4 production than other constructs, except IL-2 production. Mucosal delivery of rAd-gB induced mucosal IgA and serum IgG responses and biased toward Th2-type immune responses. However, these effects were not observed in response to systemic delivery of rAd-gB. In addition, rAd-gB appeared to induce effective protective immunity against a virulent viral infection, regardless of whether it was administered via the muscular or systemic route. These results suggest that administration of replication-incompetent adenoviruses can induce different types of immunity depending on the expressed antigen and that recombinant adenoviruses expressing gB induced the most potent Th1-biased humoral and cellular immunity and provided effective protection against PrV infection. PMID:19116444

Han, Young Woo; Aleyas, Abi G.; George, Junu A.; Kim, Seon Ju; Kim, Hye Kyung; Yoon, Hyun A; Yoo, Dong Jin; Kang, Seong Ho; Kim, Koanhoi

2008-01-01

390

T invariance and T-odd asymmetries for the cold-polarized-neutron-induced fission of nonoriented nuclei  

NASA Astrophysics Data System (ADS)

It is shown that the coefficients D exp for all T-odd asymmetries observed experimentally in the cross sections for the reactions of cold-polarized-neutron-induced fission of nonoriented target nuclei (which involves the emission of prescission and evaporated particles) comply in shape and scale with the coefficients D theor calculated for the analogous asymmetries on the basis of quantum-mechanical nuclear-fission theory for T-invariant Hamiltonians of fissile systems. It is also shown that the asymmetries in question arise upon taking into account the effect of (i) the interference between the fission amplitudes of s- and p-wave resonances of a polarized fissile compound nucleus formed in the aforementioned reactions; (ii) the collective rotation of the compound nucleus in question (this rotation entails a change in the angular distributions of fission fragments and third particles); and (iii) the wriggling vibrations of this compound nucleus in the vicinity of its scission point, which lead to the appearance of high aligned spins of fission fragments, with the result that the emission of neutrons and photons evaporated from these fragments becomes anisotropic. The possible contribution of T-noninvariant interactions to the formation of the T-odd asymmetries under analysis is estimated by using the results obtained in experimentally testing the detailed-balance principle, ( P-A) theorem, and T invariance of cross sections for elastic proton-proton and proton-neutron scattering.

Kadmensky, S. G.; Bunakov, V. E.; Titova, L. V.

2014-12-01

391

Current-induced spin polarization at the surface of metallic films: A theorem and an ab initio calculation  

NASA Astrophysics Data System (ADS)

The broken inversion symmetry at the surface of a metallic film (or, more generally, at the interface between a metallic film and a different metallic or insulating material) greatly amplifies the influence of the spin-orbit interaction on the surface properties. The best known manifestation of this effect is the momentum-dependent splitting of the surface-state energies (Rashba effect). Here we show that the same interaction also generates a spin polarization of the bulk states when an electric current is driven through the bulk of the film. For a semi-infinite jellium model, which is representative of metals with a closed Fermi surface, we prove as a theorem that regardless of the shape of the confinement potential, the induced surface spin density at each surface is given by S =-? ? z ?×j , where j is the particle current density in the bulk, z ? the unit vector normal to the surface, and ? =?/4 m c2 contains only fundamental constants. For a general metallic solid, ? becomes a material-specific parameter that controls the strength of the interfacial spin-orbit coupling. Our theorem, combined with an ab initio calculation of the spin polarization of the current-carrying film, enables a determination of ? , which should be useful in modeling the spin-dependent scattering of quasiparticles at the interface.

Tokatly, I. V.; Krasovskii, E. E.; Vignale, Giovanni

2015-01-01

392

Application of Dipole-dipole, Induced Polarization, and CSAMT Electrical Methods to Detect Evidence of an Underground Nuclear Explosion  

NASA Astrophysics Data System (ADS)

There is little experience with application of electrical methods that can be applied during the continuation period of an on-site inspection (OSI), one of the verification methods of the Comprehensive Nuclear-Test-Ban Treaty (CTBT). In order add to such experience, we conducted controlled source audiomagnetotelluric (CSAMT), dipole-dipole resistivity, and induced polarization electrical measurements along three survey lines over and near to ground zero of an historic nuclear explosion. The presentation will provide details and results of the surveys, an assessment of application of the method toward the purposes of an OSI, and an assessment of the manpower and time requirements for data collection and processing that will impact OSI inspection team operations. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Sweeney, J. J.; Felske, D.

2013-12-01

393

Generating long-lasting 1H and 13C hyperpolarization in small molecules with parahydrogen-induced polarization  

NASA Astrophysics Data System (ADS)

Recently, Levitt and co-workers demonstrated that conserving the population of long-lasting nuclear singlet states in weak magnetic fields can lead to a preservation of nuclear spin information over times substantially longer than governed by the (high-field) spin-lattice relaxation time T1. Potential benefits of the prolonged spin information for magnetic resonance imaging and spectroscopy were pointed out, particularly when combined with the parahydrogen induced polarization (PHIP) methodology. In this contribution, we demonstrate that an increase of the effective relaxation time by a factor up to three is achieved experimentally, when molecules hyperpolarized by PHIP are kept in a weak magnetic field instead of the strong field of a typical NMR magnet. This increased lifetime of spin information makes the known PHIP phenomena more compatible with the time scales of biological processes and, thus, more attractive for future investigations.

Jonischkeit, Thorsten; Bommerich, Ute; Stadler, Jörg; Woelk, Klaus; Niessen, Heiko G.; Bargon, Joachim

2006-05-01

394

Deep ultraviolet emitting polarization induced nanowire light emitting diodes with AlxGa1?xN active regions  

NASA Astrophysics Data System (ADS)

In this report, we demonstrate band gap tuning of the active region emission wavelength from 365 nm to 250 nm in light emitting diodes fashioned from catalyst-free III-nitride nanowires. Optical characteristics of the nanowire heterostructures and fabricated devices are studied via electroluminescence (EL) and photoluminescence spectroscopy over a wide range of active region compositions. It is observed that for typical nanowire plasma assisted molecular beam epitaxy growth conditions, tuning of emission to wavelengths shorter than 300 nm is hampered by the presence of an optically active defect level. We show that by increasing the AlGaN nanowire growth temperatures this defect emission can be suppressed. These findings are applied to growth of the active region of a nanowire light emitting diode, resulting in a polarization-induced nanowire light emitting diode with peak EL at 250 nm.

Kent, Thomas F.; Carnevale, Santino D.; Sarwar, A. T. M.; Phillips, Patrick J.; Klie, Robert F.; Myers, Roberto C.

2014-11-01

395

Three-dimension Cole-Cole model inversion of induced polarization data based on regularized conjugate gradient method  

NASA Astrophysics Data System (ADS)

Modeling of induced polarization (IP) phenomena is important for developing effective methods for remote sensing of subsurface geology and is widely used in mineral exploration. However, the quantitative interpretation of IP data in a complex 3D environment is still a challenging problem of applied geophysics. In this dissertation I use the regularized conjugate gradient method to determine the 3D distribution of the four parameters of the Cole-Cole model based on surface induced polarization (IP) data. This method takes into account the nonlinear nature of both electromagnetic induction (EMI) and IP phenomena. The solution of the 3D IP inverse problem is based on the regularized smooth inversion only. The method was tested on synthetic models with DC conductivity, intrinsic chargeability, time constant, and relaxation parameters, and it was also applied to the practical 3D IP survey data. I demonstrate that the four parameters of the Cole-Cole model, DC electrical resistivity, rho 0 , chargeability, eta time constant, tau and the relaxation parameter, C, can be recovered from the observed IP data simultaneously. There are four Cole-Cole parameters involved in the inversion, in other words, within each cell, there are DC conductivity (sigma0 ), chargeability (eta), time parameters (tau), and relaxation parameters (C) compared to conductivity only, used in EM only inversion. In addition to more inversion parameters used in IP survey, dipole-dipole configuration which requires more sources and receivers. One the other hand, calculating Green tensor and Frechet matrix time consuming and storing them requires a lot of memory. So, I develop parallel computation using MATLAB parallel tool to speed up the calculation.

Xu, Zhengwei

396

Modeling of nonlinear polarization rotation in tensile-strained semiconductor optical amplifiers using Mueller matrices and carrier density induced refractive index change calculations  

NASA Astrophysics Data System (ADS)

A model of nonlinear polarization rotation in a tensile-strained bulk SOA is presented. The model uses a wideband steady-state SOA model to determine the SOA carrier density and the polarization dependent gain. The carrier density distribution is used to determine the phase difference between the TE and TM components of an amplified CW probe signal in the presence of a counter-propagating pump. The active waveguide polarization dependent effective index difference is determined using the Marcatili method and the carrier induced refractive index changes are calculated using a detailed material band structure model. The SOA Mueller matrix, which is modeled as the product of an diattenuator and phase shifter, is used to predict the Stokes vector of the amplified signal. This allows a simple comparison with experiment as the Stokes vector can be easily measured using a polarization analyzer. The model is used to predict the polarization rotation of a probe signal induced by a counter-propagating pump. The model can be used to aid in the design of all-optical signal processing functions such as wavelength conversion and optical logic that use SOA polarization rotation effects.

Connelly, Michael J.

2013-11-01

397

Conversion of Helicobacter pylori CagA from senescence inducer to oncogenic driver through polarity-dependent regulation of p21  

PubMed Central

The Helicobacter pylori CagA bacterial oncoprotein plays a critical role in gastric carcinogenesis. Upon delivery into epithelial cells, CagA causes loss of polarity and activates aberrant Erk signaling. We show that CagA-induced Erk activation results in senescence and mitogenesis in nonpolarized and polarized epithelial cells, respectively. In nonpolarized epithelial cells, Erk activation results in oncogenic stress, up-regulation of the p21Waf1/Cip1 cyclin-dependent kinase inhibitor, and induction of senescence. In polarized epithelial cells, CagA-driven Erk signals prevent p21Waf1/Cip1 expression by activating a guanine nucleotide exchange factor–H1–RhoA–RhoA-associated kinase–c-Myc pathway. The microRNAs miR-17 and miR-20a, induced by c-Myc, are needed to suppress p21Waf1/Cip1 expression. CagA also drives an epithelial-mesenchymal transition in polarized epithelial cells. These findings suggest that CagA exploits a polarity-signaling pathway to induce oncogenesis. PMID:20855497

Saito, Yasuhiro; Murata-Kamiya, Naoko; Hirayama, Toshiya; Ohba, Yusuke

2010-01-01

398

Anomalous spectral dependence of optical polarization and its impact on spin detection in InGaAs/GaAs quantum dots  

NASA Astrophysics Data System (ADS)

We show that circularly polarized emission light from InGaAs/GaAs quantum dot (QD) ensembles under optical spin injection from an adjacent GaAs layer can switch its helicity depending on emission wavelengths and optical excitation density. We attribute this anomalous behavior to simultaneous contributions from both positive and negative trions and a lower number of photo-excited holes than electrons being injected into the QDs due to trapping of holes at ionized acceptors and a lower hole mobility. Our results call for caution in reading out electron spin polarization by optical polarization of the QD ensembles and also provide a guideline in improving efficiency of spin light emitting devices that utilize QDs.

Puttisong, Y.; Huang, Y. Q.; Buyanova, I. A.; Yang, X. J.; Subagyo, A.; Sueoka, K.; Murayama, A.; Chen, W. M.

2014-09-01

399

Spectral line polarization with angle-dependent partial frequency redistribution. II. Accelerated lambda iteration and scattering expansion methods for the Rayleigh scattering  

NASA Astrophysics Data System (ADS)

Context. The linear polarization of strong resonance lines observed in the solar spectrum is created by the scattering of the photospheric radiation field. This polarization is sensitive to the form of the partial frequency redistribution (PRD) function used in the line radiative transfer equation. Observations have been analyzed until now with angle-averaged PRD functions. With an increase in the polarimetric sensitivity and resolving power of the present-day telescopes, it will become possible to detect finer effects caused by the angle dependence of the PRD functions. Aims: We devise new efficient numerical methods to solve the polarized line transfer equation with angle-dependent PRD, in plane-parallel cylindrically symmetrical media. We try to bring out the essential differences between the polarized spectra formed under angle-averaged and the more realistic case of angle-dependent PRD functions. Methods: We use a recently developed Stokes vector decomposition technique to formulate three different iterative methods tailored for angle-dependent PRD functions. Two of them are of the accelerated lambda iteration type, one is based on the core-wing approach, and the other one on the frequency by frequency approach suitably generalized to handle angle-dependent PRD. The third one is based on a series expansion in the mean number of scattering events (Neumann series expansion). Results: We show that all these methods work well on this difficult problem of polarized line formation with angle-dependent PRD. We present several benchmark solutions with isothermal atmospheres to show the performance of the three numerical methods and to analyze the role of the angle-dependent PRD effects. For weak lines, we find no significant effects when the angle-dependence of the PRD functions is taken into account. For strong lines, we find a significant decrease in the polarization, the largest effect occurring in the near wing maxima.

Sampoorna, M.; Nagendra, K. N.; Frisch, H.

2011-03-01

400

Superlattices PhotoPolarization  

E-print Network

are polarization steady­state light­induced the of fall the and rise the both that show a as operated be can­­ ­­ Superlattices Asymmetric in Effect Photo­Polarization Internal Luryi Serge Liu Chun the provided effect, tangible a is superlattice the of polarization resultant field­ a of gate the control

Luryi, Serge

401

Induced formation of dominating polar phases of poly(vinylidene fluoride): positive ion-CF2 dipole or negative ion-CH2 dipole interaction.  

PubMed

The "ion-dipole" interaction has been the most widely accepted mechanism for the direct formation of polar phases (?, ?) of poly(vinylidene fluoride) (PVDF), which have been widely used as transducers, actuators, and sensors. However, the type of charged ions is still controversial. In order to throw light upon this issue, two types of charged small organic molecules that are in different physical states (melt or solid) during the crystallization of PVDF were melt-blended with PVDF resin. Results revealed that only the incorporation of positive charged molecules can lead to the formation of polar phases. Additionally, it is interesting to find that during the crystallization of PVDF, molten positively charged molecules resulted in ?-phase dominating, while solid positively charged molecules exclusively induced ?-phase. These results lead to the understanding that the induced formation of polar phases of PVDF is due to the "positive ion-CF2 dipole" interaction. PMID:25010928

Liang, Cheng-Lu; Mai, Zhong-Hai; Xie, Qi; Bao, Rui-Ying; Yang, Wei; Xie, Bang-Hu; Yang, Ming-Bo

2014-07-31

402

A Model of Polar Solar Magnetic Field Line-of-Sight Component Slow Temporal Variations Induced by Rossby Waves in the Coronal Base  

Microsoft Academic Search

Based on asymmetries (Trellis,1960) and on other observational features of the red line corona a linear model of Rossby waves in the red line emanating coronal layer is proposed. Long-term evolution of the solar polar magnetic field induced by the first Rossby mode is simulated with the help of a magnetic rotator image. The model demonstrates the reversal of the

Yu. V. Pisanko

1999-01-01

403

Adenoviruses Activate Human Dendritic Cells without Polarization toward a T-Helper Type 1-Inducing Subset  

Microsoft Academic Search

Human monocyte-derived dendritic cells (DC) infected with recombinant adenoviruses (rAd) are promising candidate vaccines for inducing protective immunity against pathogens and tumors. However, since some viruses are known to negatively affect DC function, it is important to investigate the interactions between rAd and DC. We now show that infection by rAd enhances the immunostimulatory capacity of immature human monocyte-derived DC

DELPHINE REA; FREDERIK H. E. SCHAGEN; ROB C. HOEBEN; MAJID MEHTALI; MENZO J. E. HAVENGA; RENE E. M. TOES; CORNELIS J. M. MELIEF; RIENK OFFRINGA

1999-01-01

404

Femtosecond Raman-induced Kerr effect study of polar solvent dynamics: Amides  

Microsoft Academic Search

We have measured the ultrafast pure solvent dynamics of highly power liquids, formamide (FA), N-methylformamide (NMF), N-methylacetamide (NMA), N-methylpropioamide (NMP) and N,Nâ²-dimethylformamide (DMF) using femtosecond optical-heterodyne-detected Raman-induced Kerr effect spectroscopy (OHD-RIKES). The effects of deuteration and temperature-dependence were studied to characterize in detail both the inertial (or non-diffusive) and diffusive intermolecular motions in these liquids.

Yong Joon Chang; E. W. Jr. Castner

1993-01-01

405

Femtosecond Raman-induced Kerr effect study of polar solvent dynamics: Amides  

SciTech Connect

We have measured the ultrafast pure solvent dynamics of highly power liquids, formamide (FA), N-methylformamide (NMF), N-methylacetamide (NMA), N-methylpropioamide (NMP) and N,N{prime}-dimethylformamide (DMF) using femtosecond optical-heterodyne-detected Raman-induced Kerr effect spectroscopy (OHD-RIKES). The effects of deuteration and temperature-dependence were studied to characterize in detail both the inertial (or non-diffusive) and diffusive intermolecular motions in these liquids.

Chang, Yong Joon; Castner, E.W. Jr.

1993-07-01

406

CCR2 Antagonism Alters Brain Macrophage Polarization and Ameliorates Cognitive Dysfunction Induced by Traumatic Brain Injury.  

PubMed

Traumatic brain injury (TBI) is a major risk factor for the development of multiple neurodegenerative diseases. With respect to the increasing prevalence of TBI, new therapeutic strategies are urgently needed that will prevent secondary damage to primarily unaffected tissue. Consistently, neuroinflammation has been implicated as a key mediator of secondary damage following the initial mechanical insult. Following injury, there is uncertainty regarding the role that accumulating CCR2(+) macrophages play in the injury-induced neuroinflammatory sequelae and cognitive dysfunction. Using CX3CR1(GFP/+)CCR2(RFP/+) reporter mice, we show that TBI initiated a temporally restricted accumulation of peripherally derived CCR2(+) macrophages, which were concentrated in the hippocampal formation, a region necessary for learning and memory. Multivariate analysis delineated CCR2(+) macrophages' neuroinflammatory response while identifying a novel therapeutic treatment window. As a proof of concept, targeting CCR2(+) macrophages with CCX872, a novel Phase I CCR2 selective antagonist, significantly reduced TBI-induced inflammatory macrophage accumulation. Concomitantly, there was a significant reduction in multiple proinflammatory and neurotoxic mediators with this treatment paradigm. Importantly, CCR2 antagonism resulted in a sparing of TBI-induced hippocampal-dependent cognitive dysfunction and reduced proinflammatory activation profile 1 month after injury. Thus, therapeutically targeting the CCR2(+) subset of monocytes/macrophages may provide a new avenue of clinical intervention following TBI. PMID:25589768

Morganti, Josh M; Jopson, Timothy D; Liu, Sharon; Riparip, Lara-Kirstie; Guandique, Cristian K; Gupta, Nalin; Ferguson, Adam R; Rosi, Susanna

2015-01-14

407

Dual Polarized Versus Single Polarized MIMO: A Study Over NLOS Propagation with Polarization  

E-print Network

transmit antennas and two receive antennas when comparing the capacity of the dual polarized MIMO system to the capacity of MIMO system with single polarized antennas. The effect of the antenna depolarization as well such as dual antennas polarization have been shown to improve the channel spectral efficiency of multiple

Paris-Sud XI, Université de

408

Spectral range of operation of coupled-mode optical filters  

NASA Astrophysics Data System (ADS)

The spectral range of operation of optical coupled-mode filters (CMF) is investigated. The CMF principle is based upon the stress-induced energy transfer between orthogonally polarized optical modes, which occurs in birefringent materials at the isotropic wavelength where phase matching is ensured. A nonexhaustive list of birefringent materials which exhibit an isotropic wavelength is drawn up. The whole visible spectral range is covered continuously by using mixed graded-band-gap hexagonal crystals such as CdS-CdSe and ZnS-CdS. This range is extended up to 2.1 microns by using piezobirefringent cubic compounds. Materials with other crystalline structures enable the extension of this spectral range down to 1200 A. The optical activity of chalcopyrite-structure semiconductors can advantageously replace stress-induced mode coupling.

Laurenti, J. P.

1984-11-01

409

Sheath-induced distortions in particle distributions near enhanced polar outflow probe particle sensors  

SciTech Connect

We discuss sheath and kinetic effects on ion and electron distribution functions at the aperture of enhanced Polar Outflow Probe particle sensors. For this purpose, the interaction between the CASSIOPE spacecraft and space environment is simulated fully kinetically using the electrostatic Particle In Cell code PTetra. The simulations account for the geometry of the main features of the spacecraft body, the booms, and the sensors. In addition to the background plasma, the model also accounts for Earth magnetic field. The plasma parameters assumed in the simulations are obtained from the latest version of the International Reference Ionosphere (IRI) model and the value of magnetic field is obtained from the International Geophysical Reference Field model. Our analysis shows significant distortions in the ion distribution function in the plane of the sensor aperture, as well as in the direction along the boom holding the sensor. We argue that significant distortions and asymmetries should also occur at the aperture of the suprathermal electron imager when suprathermal electrons are detected, with energies of 5?eV or more.

Hussain, S. [Department of Physics, University of Alberta, Edmonton, Alberta, T6G 2E1 (Canada); Theoretical Physics Division, PINSTECH, Nilore, Islamabad (Pakistan); Department of Physics and Applied Mathematics, PIEAS, Nilore, Islamabad (Pakistan); Marchand, R. [Department of Physics, University of Alberta, Edmonton, T6G 2E1 Alberta (Canada)

2014-07-15

410

Pressure-induced Polarization Reversal in Z-type Hexaferrite Single Crystal  

NASA Astrophysics Data System (ADS)

Multiferroic materials with a gigantic magnetoelectric (ME) coupling at room temperature have been searched for applications to novel devices. Recently, large direct and converse ME effects were realized at room temperature in the so-called Z-type hexaferrite (Ba,Sr)3Co2Fe24O41 single crystals [1,2]. To obtain a new control parameter for realizing a sensitive ME tuning, we studied ME properties of the crystals under uniaxial pressure. Upon applying a tiny uniaxial pressure of about 0.6 GPa, magnetic field-driven electric polarization reversal and anomaly in a M-H loop start to appear at 10 K and gradually disappear at higher temperature above 130 K. By comparing those results with longitudinal magnetostriction at ambient pressure, we propose the pressure-dependent variations of transverse conical spin configuration as well as its domain structure under small magnetic field bias, and point out the possibility of having two different physical origins of the ME coupling in this system. [1] Y. Kitagawa et al., Nat. Mater. 9, 797 (2010) [2] S. H. Chun et al., submitted.

Jeon, Byung-Gu; Chun, Sae Hwan; Kim, Kee Hoon

2012-02-01