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1

Spectral induced polarization signature of contaminated soil  

NASA Astrophysics Data System (ADS)

Spectral induced polarization (SIP) signatures of porous media contaminated with non aqueous phase liquids (NAPL) were measured using an accurate impedance meter. The samples were prepared by mixing air-dried sand with 15% by weight of bentonite clay, tap water and either diesel fuel or motor oil. Next, the soil was packed in a column and left for 24 hr before electrical measurements were performed. For all the samples, water saturation was constant (Sw = 0.47) and the NAPL saturation was 0 (control), 5, or 15 percent. Counter-intuitively, the results show that addition of NAPL to the porous media resulted in an increase of the real part of the complex conductivity. Evidently, for each type of contaminant, an increase in the contaminant saturation resulted in an increase in the real part of the conductivity. The imaginary part of the complex conductivity showed a reversed behavior: higher NAPL saturation resulted in a reduction of the imaginary part of the complex conductivity. For both the real and the imaginary part of the complex conductivity, the effect of NAPL on the complex electrical conductivity was more significant for motor oil than for diesel fuel. In addition to the electrical measurements, we also performed an extraction experiment to examine the effect of the presence of NAPL on the electrical conductivity (EC) of the pore water. The results from the extraction experiment showed that addition of NAPL to the porous media resulted in an increase of the pore water EC. We argue that this increase in the real part of the complex conductivity is related to adsorption of organic polar compounds from the NAPL onto the mineral surface and the associated release of inorganic ions from the mineral surface to the pore water. These exchange processes affect both the surface and the pore water conductivity. In addition, we suggest that the decrease in polarization (associated with the imaginary part of the complex conductivity) of the NAPL contaminated porous media is related to stronger binding of the adsorbed NAPL polar compounds to the mineral surface. Ongoing experiments are targeted at further elucidating these phenomena.

Schwartz, N.; Huisman, J. A.; Shefer, I.; Furman, A.

2012-04-01

2

Salinity dependence of spectral induced polarization in sands and sandstones  

NASA Astrophysics Data System (ADS)

In electrolyte-saturated sands, the reversible storage of electrical charges is responsible for a phase lag between the current (injected and retrieved by two current electrodes) and the electrical field recorded by two voltage electrodes. This phenomenon is called 'spectral induced polarization' in geophysics and can potentially be used to monitor salt tracer tests in shallow aquifers to infer their permeability and dispersivity tensors. We demonstrate analytically that the polarization of the inner part of the electrical triple layer coating the surface of the grains (named the Stern layer in electrochemistry) is consistent with available data. We also perform new experiments using silica sands saturated by NaCl and CaCl2 pore water solutions. The salinity dependence of quadrature conductivity can be modelled using an analytical solution of the triple layer model, which offers a simple way to interpret laboratory and field data. This analytical solution depends on the total site density of the mineral surface, the pH value and the sorption coefficient of the cation in the Stern layer. This model shows that both the specific surface conductivity of the Stern layer and the quadrature conductivity of the porous material depend on the conductivity of the pore water. The quadrature conductivity is becoming independent of the salinity above 1 S m-1. The parameters entering the analytical model are consistent with independent estimates from titration data and zeta potential measurements, which are two classical methods to characterize the electrical triple layer at the pore water mineral interface.

Revil, A.; Skold, M.

2011-11-01

3

Spectral Induced Polarization In Clean Water- Saturated Sand  

NASA Astrophysics Data System (ADS)

A theoretical model of Spectral Induced Polarization (IP) of sand is proposed. In this model, contacts of sand grains and inter-grain solution-filled space are considered as electrical current passages of varying thickness, which differ in values of ion transport numbers. Ion-selective narrow passages are considered active zones, large passages - passive ones. The proposed model, called SShort Narrow PoreT(SNP) model, de- & cedil; scribes spectral IP characteristics for the medium where the length of passive zones is much greater than that of the active zones. Both time domain and frequency domain parameters were described. The SNP model predicts a growth of IP time constant with increase of length of the ion-selective zone. The parameters of Cole-Cole model cor- responding to the SNP model were found. The behaviour of the model parameters was compared with experimental data obtained on natural and sieved sands using the time domain technique. The spectra of natural sands correspond neither to the simple SNP model nor to the simple Cole-Cole model with single time constant. The constant phase angle model also cannot be applied. As long as the lengths of the ion-selective zones vary according to the grain size distribution, different values of time constant are produced, which explain the spectra behaviour. A comparison of the sieved sand spectra and the SNP model theoretical spectra reveals close correspondence between the experimental data and theoretical parameters. For four sieved sands, both the the- oretical and experimental data show that the time constant of IP is proportional to the square of the average grain size. This work was supported by INTAS, project No 32046.

Titov, K.; Komarov, V.; Tarasov, V.; Levitski, A.

4

Spectral induced polarization (SIP) measurement of NAPL contaminated soils  

NASA Astrophysics Data System (ADS)

The potential applicability of spectral induce polarization (SIP) as a tool to map NAPLs (non aqueous phase liquids) contaminants at the subsurface lead researchers to investigate the electric signature of those contaminant on the spectral response. However, and despite the cumulative efforts, the effect of NAPL on the electrical properties of soil, and the mechanisms that control this effect are largely unknown. In this work a novel experiment is designed to further examine the effect of NAPL on the electrical properties of partially saturated soil. The measurement system that used is the ZEL-SIP04 impedance meter developed at the Forschungszentrum Julich, Germany. The system accurately (nominal phase precision of 0.1 mrad below 1 kHz) measures the phase and the amplitude of a material possessing a very low polarization (such as soil). The sample holder has a dimension of 60 cm long and 4.6 cm in diameter. Current and potential electrodes were made of brass, and while the current electrodes were inserted in full into the soil, the contact between the potential electrode and the soil was made through an Agarose bridge. Two types of soils were used: clean quartz sand, and a mixture of sand with clean Bentonite. Each soil (sandy or clayey) was mixed with water to get saturation degree of 30%. Following the mixture with water, NAPL was added and the composite were mixed again. Packing was done by adding and compressing small portions of the soil to the column. A triplicate of each mixture was made with a good reproducible bulk density. Both for the sandy and clayey soils, the results indicate that additions of NAPL decrease the real part of the complex resistivity. Additionally, for the sandy soil this process is time depended, and that a further decrease in resistivity develops over time. The results are analyzed considering geometrical factors: while the NAPL is electrically insulator, addition of NAPL to the soil is expected to increase the connectivity of the water phase, and therefore a decrease in the real part of the complex resistivity occurs.

Schwartz, N.; Huisman, J. A.; Furman, A.

2010-12-01

5

Spectral induced polarization signatures of hydroxyl adsorption in porous media  

NASA Astrophysics Data System (ADS)

There is a growing interest in applying geophysical methods to monitor microbial enhanced mineral precipitation through urea hydrolysis. Sensing changes in mineral surface properties as well as changes in fluid chemistry could be used to track geochemical reactions fronts in subsurface environments. Frequency-dependent complex conductivity measured with the spectral induced polarization (SIP) technique is sensitive to both fluid chemistry and mineral surface properties. We had previously observed phase shifts (?) between current and voltage waveforms associated with hydroxyl concentration changes in a silica gel column during a urea hydrolysis experiment. In a study using less complex conditions we applied both SIP and geochemical measurements on a saturated column composed of sequential zones with Ottawa sand and silica gel in order to: 1) understand whether adsorption of hydroxyl contributes to the changes in complex conductivity, and 2) to determine whether changes in solution chemistry follow changes in surface chemistry in porous media (or vice versa). Silica gel is a highly porous form of silica (surface area is ~500 m2/g vs. <0.1 m2/g for Ottawa sand) and has a high sorption capacity for hydroxide ions. A column (48 cm) was packed with Ottawa sand at both the bottom and top sections, and with silica gel beads in the middle part of the column. The experiment started with a pH 7 sodium chloride solution (50 mM) flowing through the column at 10 ml/min, then sodium chloride solutions at higher pH (pH 8 and pH 10) replaced this solution and continued flow at the same rate for 49 hours. SIP measurements were made along the column as a function of time, and effluent samples along the column were taken for pH and conductivity measurements. The results show phase angle shifts (~4.5 mrad) in the silica gel, while no significant phase changes occurred in the Ottawa sands. Although changes in complex conductivity were only observed on synthetic high surface area material, the experiment opens the door to further investigate the correlation between complex conductivity and surface chemistry.

Zhang, C.; Johnson, T. C.; Slater, L. D.; Redden, G. D.

2010-12-01

6

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

Microsoft Academic Search

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 Desulfovibrio vulgaris. 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

Yves Robert Personna; Dimitrios Ntarlagiannis; Lee Slater; Nathan Yee; Michael O'Brien; Susan Hubbard

2008-01-01

7

Spectral Induced Polarization Signatures of Hydroxide Adsorption and Mineral Precipitation in Porous Media  

SciTech Connect

The spectral induced polarization (SIP) technique is a promising approach for delineating subsurface physical and chemical property changes in a minimally invasive manner. To facilitate the understanding of position and chemical properties of reaction fronts that involve mineral precipitation in porous media, we investigated spatiotemporal variations in complex conductivity during evolution of urea hydrolysis and calcite precipitation reaction fronts within a silica gel column. The real and imaginary parts of complex conductivity were shown to be sensitive to changes in both solution chemistry and calcium carbonate precipitation. Distinct changes in imaginary conductivity coincided with increased hydroxide ion concentration during urea hydrolysis. In a separate experiment focused on the effect of hydroxide concentration on interfacial polarization of silica gel and well-sorted sand, we found a significant dependence of the polarization response on pH changes of the solution. We propose a conceptual model describing hydroxide ion adsorption behavior in silica gel and its control on interfacial polarizability. Our results demonstrate the utility of SIP for noninvasive monitoring of reaction fronts, and indicate its potential for quantifying geochemical processes that control the polarization responses of porous media at larger spatial scales in the natural environment.

Zhang, Chi; Slater, Lee; Redden, George D.; Fujita, Yoshiko; Johnson, Timothy C.; Fox, Don

2012-04-17

8

Spectral induced polarization signatures of hydroxide adsorption and mineral precipitation in porous media  

SciTech Connect

The spectral induced polarization (SIP) technique is a promising approach for delineating subsurface physical and chemical property changes in a minimally invasive manner. We investigated spatiotemporal variations in complex conductivity during evolution of urea hydrolysis and calcite precipitation reaction fronts within a silica gel column. The real and imaginary parts of complex conductivity were shown to be sensitive to changes in both solution chemistry and calcium carbonate precipitation. Distinct changes in imaginary conductivity coincided with increased hydroxide ion concentration during urea hydrolysis. In a separate experiment focused on the effect of hydroxide concentration on interfacial polarization of silica gel and well-sorted sand, we found a strong dependence of the polarization response on pH changes of the solution. We propose a conceptual model describing hydroxide ion adsorption behavior in silica gel and its control on interfacial polarizability. Our results demonstrate the utility of SIP for non-invasive monitoring of reaction fronts, and indicate its potential for quantifying geochemical processes that control the polarization responses of porous media at larger spatial scales in the natural environment.

Chi Zhang; Lee Slater; George Redden; Yoshiko Fujita; Timothy Johnson; Don Fox

2012-04-01

9

Resolving spectral information from time domain induced polarization data through 2-D inversion  

NASA Astrophysics Data System (ADS)

Field-based time domain (TD) induced polarization (IP) surveys are usually modelled by taking into account only the integral chargeability, thus disregarding spectral content. Furthermore, the effect of the transmitted waveform is commonly neglected, biasing inversion results. Given these limitations of conventional approaches, a new 2-D inversion algorithm has been developed using the full voltage decay of the IP response, together with an accurate description of the transmitter waveform and receiver transfer function. This allows reconstruction of the spectral information contained in the TD decay series. The inversion algorithm is based around a 2-D complex conductivity kernel that is computed over a range of frequencies and converted to the TD through a fast Hankel transform. Two key points in the implementation ensure that computation times are minimized. First, the speed of the Jacobian computation, time transformed from frequency domain through the same transformation adopted for the forward response is optimized. Secondly, the reduction of the number of frequencies where the forward response and Jacobian are calculated: cubic splines are used to interpolate the responses to the frequency sampling necessary in the fast Hankel transform. These features, together with parallel computation, ensure inversion times comparable with those of direct current algorithms. The algorithm has been developed in a laterally constrained inversion scheme, and handles both smooth and layered inversions; the latter being helpful in sedimentary environments, where quasi-layered models often represent the actual geology more accurately than smooth minimum-structure models. In the layered inversion approach, a general method to derive the thickness derivative from the complex conductivity Jacobian is also proposed. One synthetic example of layered inversion and one field example of smooth inversion show the capability of the algorithm and illustrates a complete uncertainty analysis of the model parameters. With this new algorithm, in situ TD IP measurements give access to the spectral content of the polarization processes, opening up new applications in environmental and hydrogeophysical investigations.

Fiandaca, Gianluca; Ramm, James; Binley, Andrew; Gazoty, Aurélie; Christiansen, Anders Vest; Auken, Esben

2013-02-01

10

Spectral induced polarization signatures from a crude-oil contaminated site undergoing biodegradation, Bemidji, MN  

NASA Astrophysics Data System (ADS)

The spectral induced polarization (SIP) technique is a promising biogeophysical technique for sensing microbially-induced changes in the petrophysical properties of porous media. Recent studies by Schmutz et al. for samples freshly contaminated with oil show a well defined relaxation peak in the 0.001-0.1 Hz frequency rangewith the magnitude of the phase and resistivity increasing with increase in the relative saturation of the oil. In this study, we extend work of Abdel Aal et al. by acquiring SIP measurements in the frequency range between 0.001 and 1000 Hz on sediment cores retrieved from a hydrocarbon contaminated site where intrinsic bioremediation is occurring. Our results show the following: (1) in general for both the saturated and unsaturated zone samples, the real and imaginary conductivity for samples from within the plume are higher than those for background samples; (2) the imaginary conductivity results show a well defined peak in the frequency range between 0.001 - 0.01 Hz for contaminated samples with the magnitude higher for samples from the smear zone (contaminated with residual-phase hydrocarbon), exceeding values obtained for samples contaminated with dissolved-phase hydrocarbons; (3) a secondary peak not observed in uncontaminated samples is also observed around 100 Hz for the contaminated samples. Our results are consistent with the Abel Aal et al. study suggesting that biodegradation increases the magnitude of the imaginary conductivity response. The peak at the lower frequency may be due to the polarization of the Stern layer as suggested by Schmutz et al. Our laboratory SIP measurements from core samples are consistent with downhole time domain induced polarization measurements that also how that the contaminated borehole is more chargeable than the background borehole.

Mewafy, F.; Atekwana, E. A.; Ntarlagiannis, D.; Slater, L. D.; Revil, A.; Skold, M.; Gorby, Y.; Werkema, D.

2010-12-01

11

On the use of the Cole-Cole equations in spectral induced polarization  

NASA Astrophysics Data System (ADS)

Two different equations, both of which are often called `the Cole-Cole equation', are widely used to fit experimental Spectral Induced Polarization data. The data are compared on the basis of fitting model parameters: the chargeability, the time constant and the exponent. The difference between the above two equations (the Cole-Cole equation proposed by the Cole brothers and Pelton's equation) is manifested in one of the fitting parameters, the time constant. The Cole-Cole time constant is an inverse of the peak angular frequency of the imaginary conductivity, while Pelton's time constant depends on the chargeability and exponent values. The difference between the time constant values corresponding to the above two equations grows with the increase of the chargeability value, and with the decrease of the Cole-Cole exponent value. This issue must be taken into consideration when comparing the experimental data sets for high polarizability media presented in terms of the Cole-Cole parameters.

Tarasov, Andrey; Titov, Konstantin

2013-10-01

12

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

13

Induced Polarization with Electromagnetic Coupling: 3D Spectral Imaging Theory, EMSP Project No. 73836  

SciTech Connect

This project was designed as a broad foundational study of spectral induced polarization (SIP) for characterization of contaminated sites. It encompassed laboratory studies of the effects of chemistry on induced polarization, development of 3D forward modeling and inversion codes, and investigations of inductive and capacitive coupling problems. In the laboratory part of the project a physico-chemical model developed in this project was used to invert laboratory IP spectra for the grain size and the effective grain size distribution of the sedimentary rocks as well as the formation factor, porosity, specific surface area, and the apparent fractal dimension. Furthermore, it was established that the IP response changed with the solution chemistry, the concentration of a given solution chemistry, valence of the constituent ions, and ionic radius. In the field part of the project, a 3D complex forward and inverse model was developed. It was used to process data acquired at two frequencies (1/16 Hz and 1/ 4Hz) in a cross-borehole configuration at the A-14 outfall area of the Savannah River Site (SRS) during March 2003 and June 2004. The chosen SRS site was contaminated with Tetrachloroethylene (TCE) and Trichloroethylene (PCE) that were disposed in this area for several decades till the 1980s. The imaginary conductivity produced from the inverted 2003 data correlated very well with the log10 (PCE) concentration derived from point sampling at 1 ft spacing in five ground-truth boreholes drilled after the data acquisition. The equivalent result for the 2004 data revealed that there were significant contaminant movements during the period March 2003 and June 2004, probably related to ground-truth activities and nearby remediation activities. Therefore SIP was successfully used to develop conceptual models of volume distributions of PCE/TCE contamination. In addition, the project developed non-polarizing electrodes that can be deployed in boreholes for years. A total of 28 of these electrodes were deployed at the SRS site in September of 2002. The project found that (1) currently available field instrumentation need to be faster by an order of magnitude for full SIP to be engaged for broadband characterization in the field, (2) some aspects of the capacitive coupling problem in borehole geometries can be solved by use of a high impedance receiver, (3) a careful investigation of ways to adequately compare inversion results to ground-truth data is warranted, (4) more laboratory studies should be directed to understand the influence of micro-organisms and long residence time of contaminants (aging) on spectral IP properties.

Morgan, F. Dale; Sogade, John

2004-12-14

14

Spectral induced polarization measurements for predicting the hydraulic conductivity in sandy aquifers  

NASA Astrophysics Data System (ADS)

Field and laboratory spectral induced polarization (SIP) measurements are integrated to characterize the hydrogeological conditions at the Schillerslage test site in Germany. The phase images are capable of monitoring thin peat layers within the sandy aquifers. However, the field results show limitations of decreasing resolution with depth. In comparison with the field inversion results, the SIP laboratory measurements show a certain shift in SIP response due to different compaction and sorting of the samples. The SIP data are analyzed to derive an empirical relationship for predicting the hydraulic conductivity (K). In particular, two significant but weak correlations between individual real resistivities (?') and relaxation times (?), based on a Debye decomposition (DD) model, with measured K are found for the upper groundwater aquifer. The maximum relaxation time (?max) and logarithmically weighted average relaxation time (?lw) show a better relation with K values than the median value ?50. A combined power law relation between individual ?' and ? with K is developed with an expression of A · (?')B · (?lw)C, where A, B and C are determined using a least-squares fit between the measured and predicted K. The suggested approach with the calculated coefficients of the first aquifer is applied for the second. Results show good correlation with the measured K indicating that the derived relationship is superior to single phase angle models as Börner or Slater models.

Attwa, M.; Günther, T.

2013-10-01

15

A new model for the spectral induced polarization signature of bacterial growth in porous media  

NASA Astrophysics Data System (ADS)

The complex conductivity of porous materials and colloidal suspensions comprises two components: an in-phase conductivity associated with electromigration of the charge carriers and a quadrature conductivity associated with the reversible storage of the charges at some polarization length scales. We developed a quantitative model to investigate the frequency domain induced polarization response of suspensions of bacteria and bacteria growth in porous media. Induced polarization of bacteria (? polarization) is related to the properties of the electrical double layer of the bacteria. Surface conductivity and ? polarization are due to the Stern layer of counterions occurring in a brush of polymers coating the surface of the bacteria. These phenomena can be related to their cation exchange capacity. The mobility of the counterions in this Stern layer is found to be very small (4.7 × 10-10 m2 s-1 V-1 at 25°C). This implies a very low relaxation frequency for the ?polarization of the bacteria cells (typically around 0.1-5 Hz), in agreement with experimental observations. This new model can be coupled to reactive transport modeling codes in which the evolution of bacterial populations are usually described by Monod kinetics. We show that the growth rate and endogenous decay coefficients of bacteria in a porous sand can be inferred nonintrusively from time-lapse frequency domain induced polarization data.

Revil, A.; Atekwana, E.; Zhang, C.; Jardani, A.; Smith, S.

2012-09-01

16

The pH dependence of spectral induced polarization of silica sands: Experiment and modeling  

NASA Astrophysics Data System (ADS)

In electrolyte-saturated sands, the storage of electrical charges under an alternating electrical field (called “induced polarization”) is responsible for a phase lag between the applied current and the resulting electrical field. Because a variety of polarization mechanisms exists in porous materials, the underlying physics of induced polarization is somehow unclear and the field data difficult to interpret quantitatively. Measurements at various pHs and salinities can be used to discriminate between different competing mechanisms at low frequencies (1 mHz-1 kHz) in porous media in the absence of electronic conductors. New experimental data point out that, in addition to the polarization of the Stern layer (the inner part of the electrical double layer coating the surface of the silica grains), there is another polarization mechanism possibly associated with a hopping process of the protons on the silica surface. We propose that such a process could follow a Grotthuss cooperation mechanism (as in ice) involving the bound water of the silica surface. Our data also rule out a mechanism based on the diffuse layer. The new polarization mechanism may be applied to quantifying induced-polarization data collected over acidic contaminant plumes.

Skold, M.; Revil, A.; Vaudelet, P.

2011-06-01

17

Spectral Induced Polarization (SIP) monitoring during Microbial Enhanced Oil Recovery (MEOR)  

NASA Astrophysics Data System (ADS)

Jeffrey Heenan, Dimitrios Ntarlagiannis, Lee Slater Department of Earth and Environmental Sciences, Rutgers University, Newark NJ Microbial Enhanced Oil Recovery (MEOR) is an established, cost effective, method for enhancing tertiary oil recovery. Although not commonly used for shallow heavy oils, it could be a viable alternative since it can offer sustainable economic recovery and minimal environmental impact. A critical component of successful MEOR treatments is accurate, real time monitoring of the biodegradation processes resulting from the injection of microbial communities into the formation; results of recent biogeophysical research suggest that minimally-invasive geophysical methods could significantly contribute to such monitoring efforts. Here we present results of laboratory experiments, to assess the sensitivity of the spectral induced polarization method (SIP) to MEOR treatments. We used heavy oil, obtained from a shallow oilfield in SW Missouri, to saturate three sand columns. We then followed common industry procedures,and used a commercially available microbial consortia, to treat the oil columns. The active MEOR experiments were performed in duplicate while a control column maintained similar conditions, without promoting microbial activity and oil degradation. We monitored the SIP signatures, between 0.001 Hz and 1000 Hz, for a period of six months. To support the geophysical measurements we also monitored common geochemical parameters, including pH, Eh and fluid conductivity, and collected weekly fluid samples from the outflow and inflow for further analysis; fluid samples were analyzed to confirm that microbes actively degraded the heavy oils in the column while destructive analysis of the solid materials was performed upon termination of the experiment. Preliminary analysis of the results suggests that SIP is sensitive to MEOR processes. In both inoculated columns we recorded an increase in the low frequency polarization with time; measureable changes up to 3.5 mrads in the phase shift were recorded for both active columns, and for all electrode pairs. On the contrary, no change was observed in the control column for the duration of the experiment. These results may indicate that remote geophysical methods could successfully complement current MEOR monitoring schemes for promoting sustainable oil recovery.

Heenan, J. W.; Ntarlagiannis, D.; Slater, L. D.

2010-12-01

18

Influence of oil saturation upon spectral induced polarization of oil-bearing sands  

Microsoft Academic Search

The induced polarization model developed recently by Revil and Florsch to understand the complex conductivity of fully saturated granular materials has been extended to partial saturation conditions. It is an improvement over previous models like the Vinegar and Waxman model, which do not account explicitly for the effect of frequency. The Vinegar and Waxman model can be considered as a

M. Schmutz; A. Revil; P. Vaudelet; M. Batzle; P. Femenía Viñao; D. D. Werkema

2010-01-01

19

Induced Polarization with Electromagnetic Coupling: 3D Spectral Imaging Theory EMSP Project No. 73836  

SciTech Connect

This report summarizes the research work completed on the project between December 2001 and September 2002. (1) A model of all Spectral IP capacitive couplings revealed that potential bearing electrodes should be carefully chosen to obviate some of the capacitive coupling problems. This need becomes more important for borehole sampling. Thus, work had been done to design a porous pot electrode hat has all the desired characteristics (low input impedance = 100{Omega}, low noise = 1 {micro}V/{radical} z, low temperature sensitivity = 10{micro}V/{sup o}C) and that can be implanted in a borehole for up to two ears. Further constructional/fabrication details will be given in the final report. The attached pictures are rom a sample of the prototype electrode. Four strings, each consisting of 14 electrodes (7 potential electrodes alternated with 7 metallic-copper current electrodes, each electrode 6ft apart), were constructed and are to be employed into the four boreholes. (They were eventually deployed in Dec. 2002 and measurements acquired in March 2003). (2) The MIT's Earth Resources Laboratory (ERL) performed Spectral Induced Polarization SIP and Time Domain Induced Polarization (TDIP) measurements at the A-14 Outfall during the summer of Y01 as a participant in a DOE-sponsored exercise to assess the state-of-the-art in cross-borehole IP technology for delineating subsurface contaminants. To demonstrate the utility of SIP to map DNAPL contaminants, we inverted cross-borehole SIP data, taken within a very narrow frequency bandwidth of 1/32 o 9/32 Hz. The narrow bandwidth was selected after carefully studying when effects of emc, electrode polarization, etc. begin to set in. The upper frequency is limited by electromagnetic couplings (emc) and strong capacitive behavior observed for the electrodes and the low-frequency limit is set by the time to take measurements. Because below 9/32 Hz, the IP response seems to be greater than emc in all our measurements, the data was considered invertible by our existing 2D/3D complex resistivity codes. The results of this exercise were inconclusive because the ground-truthing phase of the operation failed to detect ny concentration of NAPL above a requisite threshold of 40-50{micro}g/g. It is our understanding that this threshold level is based upon analytic chemical partition analysis, which is dependent upon the physicochemical properties of the soil, its pore-fluid, and organic constituents [Cohen and Mercer, 1993], and thus represents a necessary and sufficient condition to confirm the presence of NAPL. Therefore, since the round-truthing phase never found PCE concentrations in excess of {approx}3mg/g, there is no irrefutable evidence of NAPL; hence, the objective of the FY01 exercise could not be completed. Nonetheless, ERL's conversion results agree well with the ground truth considering the sparseness of the CRS boreholes, low concentrations of ''PCE'' (< 3{micro}g/g), and despite poor electrodes. Note that the displacement of the enter of the SIP phase anomaly from that of the ground truth data might be due to inaccuracies in the SIP conversion (which we are still working on improving) or sampling depth errors during the ground-truthing phase which could cumulatively amount to a meter or more. (3) As a continuation of the FY01 efforts, another et of surface and borehole SIP measurements were planned at another SRS site during FY02, which unlike he FY01 site,had been verified to have substantial DNAPL presence by SRS engineers. The plan to use phoenix Geophysics SIP equipment could not materialize because Phoenix discontinued its SIP line and planned to introduce a new line in the Spring/Summer of 2003, which will be too late for us. So our planned second fieldwork of FY02 defaults again to Zonge Engineering and Research Organization equipment. (4) developments on the modeling and inversion of the new complex resistivity code, that will incorporate conductive coupling, stalled to give way to the electrode design, fabrication and testing(s), which were not anticipated earlier.

Morgan, F. Dale

2003-06-01

20

Spectral shifts with polarization control  

NASA Astrophysics Data System (ADS)

The spectral behavior of a limited bandwidth light with different polarization states reflected from an air-water interface near the absorption band of water is theoretically investigated. The results indicate that, at oblique incidence, the reflected wave’s spectral change is blue- or red-shifted for different polarizations and the shift is most obvious when the angle is close to the Brewster angle. This phenomenon can be used as a polarization spectrum selector, and a data transmission scheme utilizing this effect is also proposed.

Han, Pin

2013-10-01

21

Influence of oil saturation upon spectral induced polarization of oil-bearing sands  

NASA Astrophysics Data System (ADS)

The induced polarization model developed recently by Revil and Florsch to understand the complex conductivity of fully saturated granular materials has been extended to partial saturation conditions. It is an improvement over previous models like the Vinegar and Waxman model, which do not account explicitly for the effect of frequency. The Vinegar and Waxman model can be considered as a limiting case of the Revil and Florsch model in the limit where the distribution of relaxation times is very broad. The extended model is applied to the case of unconsolidated sands partially saturated with oil and water. Laboratory experiments were performed to investigate the influence of oil saturation, frequency, grain size, and conductivity of the pore water upon the complex resistivity response of oil-bearing sands. The low-frequency polarization (below 100 Hz) is dominated by the polarization of the Stern layer (the inner part of the electrical double layer coating the surface of the grains in contact with water). The phase exhibits a well-defined relaxation peak with a peak frequency that is dependent on the mean grain diameter as predicted by the model. Both the resistivity and the magnitude of the phase increase with the relative saturation of the oil. The imaginary (quadrature) component of the complex conductivity is observed to decrease with the oil saturation. All these observations are reproduced by the new model.

Schmutz, M.; Revil, A.; Vaudelet, P.; Batzle, M.; Viñao, P. Femenía; Werkema, D. D.

2010-10-01

22

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

23

The effect of pH and redox active ions on the spectral induced polarization signatures of magnetite  

NASA Astrophysics Data System (ADS)

Spectral induced polarization (SIP) is a promising technique for monitoring biogeochemically induced changes in porous subsurface media, such as biomineral formation during the remediation of contaminated sites. A primary mechanism responsible for low-frequency SIP signatures is the frequency-dependent polarization of the electrical double layer (EDL) at the mineral-water interface. pH exerts a fundamental control on mineral-water interface properties, controlling the nature and number of charged surface functional groups. This in turn controls the surface complexation of ions sorbed to the mineral surface and, together with ionic strength, the thickness of the EDL and the distribution of ions in the diffuse and Stern layers of the EDL. Despite this, there are relatively few datasets on the effect of pH on SIP signatures. For electrically conductive minerals, such as magnetite, it has been further postulated that redox-active ions, such as Fe2+, enable charge-transfer from electrolytic to electronic conduction mechanisms. This process is often represented as a charge-transfer resistance and Warburg impedance and is thought to be an additional contribution to the SIP response. Here we report initial experimental results investigating the effect of pH and redox active ions on the SIP signature of magnetite grains (5 wt%) dispersed in Ottawa sand. Increasing the pH of a 2.5 mM FeCl2 solution from pH 4.5 to 8.0 made little difference to the resistivity or maximum phase angle magnitude of the magnetite-sand mixture but decreased the peak frequency from ~50 Hz to ~1 Hz. This has important implications for interpreting SIP data at contaminated sites where pH can vary across groundwater plumes and during/following remediation processes. We postulate that the shift in peak frequency reflects changes in the structure of the EDL as pH increases; this pH range overlaps with the published positions of both the point of zero charge (pzc) and the sorption edge of Fe2+ onto Fe-(oxyhydr)oxides. Ongoing experiments are being conducted to compare and contrast the observed pH dependent behaviour of Fe2+ with redox inactive ions and thereby help determine the importance of the charge-transfer mechanism for magnetite.

Hubbard, C. G.; West, L. J.; Rodriguez-Blanco, J. D.; Ntarlagiannis, D.; Slater, L. D.; Shaw, S.

2011-12-01

24

Coded aperture snapshot spectral polarization imaging.  

PubMed

We describe a single-shot polarization spectral imager that combines two birefringent crystals with a binary coded aperture to encode the spatial, spectral and polarization data cube for compressive sampling on a two-dimensional (2D) detector array. We use a total variation prior to reconstruct the four-dimensional (4D) data cube from the single 2D measurement. The 4D data cube includes 1500×1240 pixels in the spatial domain, 19 wavelength channels between 400 and 680 nm and two Stokes parameters. PMID:23545971

Tsai, Tsung-Han; Brady, David J

2013-04-01

25

Prostate Cancer Detection Using Near Infrared Spectral Polarization Imaging.  

National Technical Information Service (NTIS)

Specific aims: The objective of this grant is to develop a near infrared (NIR) spectral polarization imaging technique for prostate cancer detection. The technique is based on the spectral and polarization properties of light scattered, absorbed and emitt...

R. Alfano W. B. Wang

2005-01-01

26

Spectral fine-structure in the polarization of skylight  

Microsoft Academic Search

High-spectral resolution polarization measurements of the clear daylight sky reveal an unexpected rich spectral fine-structure in the polarization superimposed on the more familiar broad-band continuum. This polarization spectrum shows the spectral fingerprints of scattering and absorption processes which is illustrated with radiative transfer calculations. In particular, radiative transfer calculations suggest the potential of high-spectral resolution polarimetry within absorption bands for

I. Aben; F. Helderman; D. M. Stam; P. Stammes

1999-01-01

27

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

28

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

29

Spectral analysis of the device operators in polarization dynamics  

NASA Astrophysics Data System (ADS)

The spectral analysis of the device (instrument) operators, as an alternative approach to the dynamical polarization phenomena, is presented by means of two examples of classical time-varying optical device: the electro-optical modulator with longitudinal effect in crystals of KDP and the rotating birefringent plate. The polarization-spectral structure of the modulated light is analyzed on this basis, in terms of spectral Jones vectors.

Tudor, Tiberiu S.

2002-02-01

30

The Effect of Systematics on Polarized Spectral Indices  

NASA Astrophysics Data System (ADS)

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° FWHM. Second, we compute the spectral index as a function of polarization orientation, ?. 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 ? = -2.59 ± 0.03 for ? = 30°, and ? = -2.03 ± 0.01 for ? = 50°. 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° 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.; Fuskeland, U.; Eriksen, H. K.

2013-02-01

31

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

32

Inductive source induced polarization  

NASA Astrophysics Data System (ADS)

Induced polarization (IP) surveys are commonly performed to map the distribution of electrical chargeability that is a diagnostic physical property in mineral exploration and in many environmental problems. Although these surveys have been successful in the past, the galvanic sources required for traditional IP and magnetic IP (MIP) surveys prevent them from being applied in some geological settings. We develop a new methodology for processing frequency domain EM data to identify the presence of IP effects in observations of the magnetic fields arising from an inductive source. The method makes use of the asymptotic behaviour of the secondary magnetic fields at low frequency. A new quantity, referred to as the ISIP datum, is defined so that it equals zero at low frequencies for any frequency-independent (non-chargeable) conductivity distribution. Thus, any non-zero response in the ISIP data indicates the presence of chargeable material. Numerical simulations demonstrate that the method can be applied even in complicated geological situations. A 3-D inversion algorithm is developed to recover the chargeability from the ISIP data and the inversion is demonstrated on synthetic examples.

Marchant, David; Haber, Eldad; Oldenburg, Douglas W.

2013-02-01

33

A comparison between non-linear optimization methods of Bayesian inversion and genetic algorithm for inverting spectral induced polarization data for Cole-Cole parameters  

NASA Astrophysics Data System (ADS)

The induced polarization (IP) method has been used in mining prospecting and increasingly in environmental investigations because IP measurements are very sensitive to the low frequency capacitive properties of rocks and soils. Cole-Cole model parameters widely use to interpret both of time and frequency domain induced polarization data. Among many studies in which Cole-Cole parameters are estimated from SIP measurements on soils and rocks, the majority use least squares methods. In this work, we developed a Bayesian method with simulated annealing sampling algorithm to invert for double Cole-Cole parameters from SIP data. We also reproduced the genetic algorithm developed by Cao et al. and compared performance of simulated annealing method with genetic algorithm method through inversion of synthetic data. Both of two methods are provides a global approach for inverting SIP data for Cole-Cole parameters; the obtained estimates are independent of initial values. Our results show that for the SIP synthetic data with random noises up to 10%, the inversed parameters obtained from simulated annealing method in comparison with genetic algorithm method are more close to the real parameters.

Ghorbani, Ahmad; Okay, Gonca; Cosenza, Philippe

2010-05-01

34

Spectral manifestations of polarization action of narrow slit  

NASA Astrophysics Data System (ADS)

Experimental study of quasimonochromatic and polychromatic ("white-light") radiation, that diffracts on very narrow (in order of several wavelength) slit in metallic screen is represented. It is shown that for monochromatic light slit acts similarly to linear analyzer. And for polychromatic light polarization action of a slit is accompanied with a spectral effect, viz. considerable predomination of blue component in total radiation. The chromascopic technique is applied for analyzing this spectral effect.

Felde, Ch. V.; Oleksyuk, M. V.; Polyanskii, P. V.

2013-06-01

35

The anomalous spectral dependence of polarization in comets  

Microsoft Academic Search

We have found an anomalous (negative) spectral dependence of polarization for split comet 73P\\/Schwassmann–Wachmann 3, i.e. polarization degree in the I filter is systematically less (?4%) than that in the R filter for both B and C subnuclei of the comet. Earlier we revealed a similar effect for comets 21P\\/Giacobini–Zinner, C\\/1999 S4 (LINEAR), and 9P\\/Tempel 1. Together with comet C\\/1989

Nikolai Kiselev; Vera Rosenbush; Ludmilla Kolokolova; Kirill Antonyuk

2008-01-01

36

Simultaneous Teleportation of the Spectral and Polarization States of a Photon  

SciTech Connect

We describe how spectrally multimode, polarization-entangled photons simultaneously teleport quantum information encoded into the spectral and polarization degrees of freedom of a single photon using sum frequency generation to implement a Bell-state measurement.

Humble, Travis S [ORNL; Bennink, Ryan S [ORNL; Grice, Warren P [ORNL

2008-01-01

37

Efficient and spectrally bright source of polarization-entangled photons  

SciTech Connect

We demonstrate an efficient fiber-coupled source of nondegenerate polarization-entangled photons at 795 and 1609 nm using bidirectionally pumped parametric down-conversion in bulk periodically poled lithium niobate. The single-mode source has an inferred bandwidth of 50 GHz and a spectral brightness of 300 pairs/(s GHz mW) of pump power that is suitable for narrowband applications such as entanglement transfer from photonic to atomic qubits.

Koenig, Friedrich; Mason, Elliott J.; Wong, Franco N. C.; Albota, Marius A. [Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States)

2005-03-01

38

Filament-induced breakdown remote spectroscopy in a polar environment  

NASA Astrophysics Data System (ADS)

We demonstrate the feasibility of filament-induced breakdown spectroscopy (FIBS) for remote sensing of solid samples in a polar environment. FIBS spectra from an aluminum target induced by 800-nm laser pulses propagating in air were probed. The air visibility in an open winter field was as low as 3.2 km fluctuating with precipitation, pressure and relative humidity. Under such polar condition, clean spectral Al I lines from an aluminum target located at a distance of 60 m were obtained. This shows the technique FIBS could be potentially useful for sensing remote targets in a variety of polar environments.

Xu, H. L.; Simard, P. T.; Kamali, Y.; Daigle, J.-F.; Marceau, C.; Bernhardt, J.; Dubois, J.; Châteauneuf, M.; Théberge, F.; Roy, G.; Chin, S. L.

2012-12-01

39

Multilayer thin film design for far ultraviolet polarizers using an induced transmission and absorption technique  

Microsoft Academic Search

An explanation of induced transmission for spectral regions excluding the far ultraviolet (FUV) is given to better understand how induced transmission and absorption can be used to design effective polarizers in the FUV spectral region. We achieve high s-polarization reflectance and a high degree of polarization (P equals (Rs-Rp)\\/(Rs+Rp)) by means of a MgF2\\/Al\\/MgF2 three layer structure on an opaque

Jongmin Kim; Muamer Zukic; Douglas G. Torr

1993-01-01

40

Complex variation of spectral line widths observed in polar corona  

NASA Astrophysics Data System (ADS)

Spectroscopic observations of the solar corona, using high spatial and spectral resolution 25cm coronagraph, at Norikura observatory, were made on large number of days during 2004 at the mid latitude and polar coronal regions. We have analyzed several raster scans that cover mid and high latitude regions on the off-limb corona in four bright emission lines of iron, namely, [Fe X] 6374 Å, [Fe XI]~7892~Å, [Fe XIII] 10747~Å, and [Fe XIV]~5303~Å. We find that the FWHM of red line increases with height and that of green line decreases with height as observed earlier, at equatorial regions. The comparison of line widths and their gradients with the results from equatorial regions indicate that these are higher for polar regions for the observed emission lines except for the green line. FWHM values show an increase towards poles in all the lines except for the green line which shows little or no change. Higher values of FWHM at polar regions may imply higher non-thermal velocities which could be linked to the solar wind, but the behavior of green emission line with almost same values of FWHM at equatorial and polar regions is surprising. This may also give some indications on the existence of preferential heating.

Prasad Samayamanthula, Krishna; Banerjee, Dipankar; Singh, Jagdev

2012-07-01

41

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

42

Radiative interactions with micromachined surfaces: Spectral polarized emittance  

SciTech Connect

The spectral, angular, polarized emittance (SAPE) is a simple means for observing the allowed electromagnetic energy states associated with periodic structures whose dimensions are comparable to the wavelength of the observed light. Other methods for measuring absorption are far more time consuming when a broad survey is of interest. An extensive body of SAPE data was obtained on 350-- 400{degrees}C intrinsic silicon lamellar gratings. Current approximations to the vector wave equation such as guided wave, modal and Bloch wave methods provided insight into our experiments. A qualitative picture of the stationary electromagnetic states (SES) of lamellar gratings has been developed which agrees with experiment for a number of polarizations, and angular orientations of the emission k vector relative to the gratings. However, one type of emission does not fit any simple model we have examined and raises intriguing questions about emission from grating structures. A new, higher angular resolution emissometer (0.8{degrees} instead of 5{degrees}) has been completed. This system significantly increases the wavelength range from the current 3--14 {mu}m range to 2-25{mu}m, a doubling of the spectral regime. The system is currently in a shakedown'' mode. Preliminary data indicates that the new emissometer meets the design goals. 24 refs., 10 figs.

Zemel, J.N.

1991-01-01

43

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

44

Induced-polarization effects from grounded structures  

Microsoft Academic Search

Fences, power lines, pipelines, and other extensive man-made structures with earthed grounds produce spurious induced polarization anomalies by acting as secondary sources and sinks of current. This problem is especially difficult to detect because the redistributed current wave forms are similar to the desired induced-polarization signal. If the structure grounds were purely resistive, there would be no problem; but, because

P. H. Nelson

1977-01-01

45

Biological Response to the Dynamic Spectral-Polarized Underwater Light Field.  

National Technical Information Service (NTIS)

Camouflage in marine environments requires matching all of the background optical properties: spectral, intensity and polarization components - all of which can change dynamically in space and time. Some of the most sophisticated examples of camouflage oc...

A. Gilerson H. M. Dierssen M. E. Cummings S. A. Ahmed W. F. Gilly

2009-01-01

46

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

47

Variance of a generalized polarity-coincidence spectral-centroid estimator for Gaussian processes  

Microsoft Academic Search

The polarity coincidence estimator of the spectral centroid counts the net number of times the phasor of a stationary Gaussian process crosses a chosen phase-reference straight line through the origin during a time T. By following Pawula's (1968) approach, the covariance of two different simultaneous polarity-coincidence estimates having distinct phase reference lines is derived. This basic result is applied to

Alberto Laurenti; Gaetano Scarano

1994-01-01

48

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

Microsoft Academic Search

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

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

1987-01-01

49

A study of spectral-polarization characteristics of plant canopies using land-based remote sensing  

NASA Astrophysics Data System (ADS)

The study addresses reflection and spectral-polarization characteristics of forest stands and farm crops obtained under field conditions. The study of the reflection properties of farm crops shows that during the summer plant growing season, the major factors influencing the plant canopy reflectance are morpho-physiological parameters, plant architectonics, solar elevation h0, and viewing angle. The crop reflectance minimum was recorded at viewing angles 25-30° with respect to the nadir. Coniferous and broadleaf forest stands had similar reflectance spectra of polarized light. The polarized component was smaller for all coniferous stands than for broadleaf ones. For broad-leaved farm crops (wheat and corn), the polarized component of the spectral brightness coefficients had a greater influence on the plant reflectance in the red and near-infrared spectral regions, ?>720 nm.

Sid`ko, A. F.; Botvich, I. Yu.; Pisman, T. I.; Shevyrnogov, A. P.

2013-11-01

50

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

SciTech Connect

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. 35 references.

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

1987-05-01

51

Modal, spectral, and polarization entanglement in guided-wave parametric down-conversion  

SciTech Connect

We examine the modal, spectral, and polarization entanglement properties of photon pairs generated in a nonlinear periodically poled two-mode waveguide (one-dimensional planar or two-dimensional circular) via nondegenerate spontaneous parametric down-conversion. Any of the possible degrees of freedom - mode number, frequency, or polarization - can be used to distinguish the down-converted photons while the others serve as attributes of entanglement. Distinguishing the down-converted photons based on their mode numbers enables us to efficiently generate spectral or polarization entanglement that is either narrowband or broadband. On the other hand, when the generated photons are distinguished by their frequencies in a type-0 process, modal entanglement turns out to be an efficient alternative to polarization entanglement. Moreover, modal entanglement in type-II down-conversion may be used to generate a doubly entangled state in frequency and polarization.

Saleh, Mohammed F.; Saleh, Bahaa E. A.; Teich, Malvin Carl [Department of Electrical and Computer Engineering, Quantum Photonics Laboratory, Boston University, Boston, Massachusetts 02215 (United States); Department of Electrical and Computer Engineering, Quantum Photonics Laboratory, Boston University, Boston, Massachusetts 02215, USA and Quantum Photonics Laboratory, College of Optics and Photonics (CREOL), University of Central Florida, Orlando, Florida 32816 (United States); Department of Electrical and Computer Engineering, Quantum Photonics Laboratory, Boston University, Boston, Massachusetts 02215 (United States) and Department of Physics, Boston University, Boston, Massachusetts 02215 (United States)

2009-05-15

52

[Polarization characteristic of LiF polarizer at UV-VUV spectral range].  

PubMed

A method of determinating the degree of polarization of grating, polarizer and analyzer at some wavelength is introduced. The degrees of polarization of LiF polarizers were determined with 1 m Seya-Namioka monochromator by this way. The source is hollow cathode source. The degrees of polarization of two, four and eight LiF plates were measured at 120, 149.2, 174.2, 214.2, 235.0, 300 and 340 nm. The theoretical and experimental reults were consistent within the error. The angular extinction dependence of the LiF polarizer and analyzer was measured at VUV wavelengths. The results showed the expected cosine square dependence, so a high degree of polarization was indeed produced. Also, the LiF polarizer was used to measure the polarization characters of the Al + MgF2 reflectance and the absolute grating efficiency at both parallel and perpendicular to their incident plane. PMID:12938362

Liu, Ying; Li, Fu-tian

2002-08-01

53

Spectral analyses of the dual polarization Doppler weather radar data  

NASA Astrophysics Data System (ADS)

Echoes in clear air from biological scatterers mixed within the resolution volumes over a large region are presented. These echoes were observed with the polarimetric prototype of the forthcoming WSR-88D weather radar. The study case occurred in the evening of September 7, 2004, at the beginning of the bird migrating season. Novel polarimetric spectral analyses are used for distinguishing signatures of birds and insects in multimodal spectra. These biological scatterers were present at the same time in the radar resolution volumes over a large area. Spectral techniques for (1) data censoring, (2) wind retrieval and (3) estimation of intrinsic values/functions of polarimetric variables for different types of scatterers are presented. The technique for data censoring in the frequency domain allows detection of weak signals. Censoring is performed on the level of spectral densities, allowing exposure of contributions to the spectrum from multiple types of scatterers. The spectral techniques for wind retrieval allow simultaneous estimation of wind from the data that are severely contaminated by migrating birds, and assessment of bird migration parameters. The intrinsic polarimetric signatures associated with the variety of scatterers can be evaluated using presented methodology. Algorithms for echo classification can be built on these. The possibilities of spectral processing using parametric estimation techniques are explored for resolving contributions to the Doppler spectrum from the three types of scatterers: passive wind tracers, actively flying insects and birds. A combination of parametric and non-parametric polarimetric spectral analyses is used to estimate the small bias introduced to the wind velocity by actively flying insects.

Bachmann, Svetlana Monakhova

54

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

55

Spectral Mapping of the Intermediate Polar DQ Herculis  

Microsoft Academic Search

We report an eclipse-mapping study of the intermediate polar DQ Her based on time-resolved optical spectroscopy (Deltalambda ~ 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

R. K. Saito; Raymundo Baptista; Keith Horne; Phillip Martell

2010-01-01

56

Operatorial form of the theory of polarization optical devices: I. Spectral theory of the basic devices  

NASA Astrophysics Data System (ADS)

While the theory of operators in quantum mechanics is expressed nowadays in a pure operatorial form (wrapped mostly in Dirac's symbolic language), in optics the polarization device operators and their action are analyzed yet in the old matrix (Jones or Muller) formalism. The theory of polarization device operators has not taken systematically advantage of the very general, fundamental and deep results of the spectral theory of operators, on the basis of which it can be structured in an elegant deductive and physically expressive form. In this paper we apply the spectral theorem to the polarization device operators, we calculate their expansions in a pure operatorial Dirac-dyadic form and give some examples which illustrate the advantages from the physical insight viewpoint of such an approach. We are concerning here only with the basic polarization devices, to which correspond normal operators.

Tudor, T.

57

Spectral Interferometric Implementation with Passive Polarization Optics of Coherent Anti-Stokes Raman Scattering  

NASA Astrophysics Data System (ADS)

We have developed an interferometric implementation of coherent anti-Stokes Raman scattering which enables broadband coherent Raman spectroscopy free from the nonresonant background, with a signal strength proportional to concentration. Spectra encode mode symmetry information into the amplitude response, which can be directly compared to polarized spontaneous Raman spectra. The method requires only passive polarization optics and is suitable for a wide range of laser linewidths and pulse durations. The method’s application to Raman spectral imaging is demonstrated.

Littleton, Brad; Kavanagh, Thomas; Festy, Frederic; Richards, David

2013-09-01

58

Are high polarization quasars and BL Lacertae objects really different? A study of the optical spectral properties.  

NASA Astrophysics Data System (ADS)

The continuum and emission lines properties of a sample of 73 blazars is studied, investigating differences and similarities among normal low-polarization quasars (LPQ), radio-loud high polarized quasars (HPQ), and BL Lacertae objects (BLL). We found that at variance with LPQ, most HPQ have power law optical continua (fnu_{prop.to}?alpha^ ) with no indication of blue bumps or strong FeII and Balmer emission. Comparison of LPQ with blazars, considered as a class including both HPQ and BLL, confirms and put on firm statistical bases that the optical continuum of blazars (?_O_=-1.00 +/-0.09) is significantly steeper than that of LPQ (?_O_~-0.5). On the other hand the average spectral index for the HPQ and BLL subsamples is rather similar (=-1.01+/-0.17 and =-0.99+/-0.11). In the ?_O_-?_RX_ plane HPQ do not split in two distinct groups as do BLL, which spilt in Radio (RBL) and X-ray selected (XBL) objects. All HPQ cluster together in the same region occupied by RBL, while XBL are clearly distinguished. A significant correlation is found between the maximum percentage of optical polarization and both ?_O_ and ?_RX_ , the less polarized object having the steeper spectral index. The comparison of emission line luminosities shows that LPQ have on average stronger lines (~ a factor of 6) with respect to blazars. Comparing HPQ and RBL we show they exhibit similar range of line luminosity, BL Lacs being just the objects with lines of smaller equivalent width as directly induced by the e.w.<5Å definition criteria. This leads us to conclude that from the point of view of optical spectral properties HPQ and RBL are quite similar objects while XBL may be different.

Scarpa, R.; Falomo, R.

1997-09-01

59

Excitation transfer induced spectral diffusion and the influence of structural spectral diffusion  

NASA Astrophysics Data System (ADS)

The theory of vibrational excitation transfer, which causes spectral diffusion and is also influenced by structural spectral diffusion, is developed and applied to systems consisting of vibrational chromophores. Excitation transfer induced spectral diffusion is the time-dependent change in vibrational frequency induced by an excitation on an initially excited molecule jumping to other molecules that have different vibrational frequencies within the inhomogeneously broadened vibrational absorption line. The excitation transfer process is modeled as Förster resonant transfer, which depends on the overlap of the homogeneous spectra of the donating and accepting vibrational chromophores. Because the absorption line is inhomogeneously broadened, two molecules in close proximity can have overlaps of their homogeneous lines that range from substantial to very little. In the absence of structural dynamics, the overlap of the homogeneous lines of the donating and accepting vibrational chromophores would be fixed. However, dynamics of the medium that contains the vibrational chromophores, e.g., a liquid solvent or a surrounding protein, produce spectral diffusion. Spectral diffusion causes the position of a molecule's homogeneous line within the inhomogeneous spectrum to change with time. Therefore, the overlap of donating and accepting molecules' homogeneous lines is time dependent, which must be taken into account in the excitation transfer theory. The excitation transfer problem is solved for inhomogeneous lines with fluctuating homogeneous line frequencies. The method allows the simultaneous treatment of both excitation transfer induced spectral diffusion and structural fluctuation induced spectral diffusion. It is found that the excitation transfer process is enhanced by the stochastic fluctuations in frequencies. It is shown how a measurement of spectral diffusion can be separated into the two types of spectral diffusion, which permits the structural spectral diffusion to be determined in the presence of excitation transfer spectral diffusion. Various approximations and computational methodologies are explored.

Rosenfeld, Daniel E.; Fayer, Michael D.

2012-08-01

60

Spectral characteristics of polar mesosphere winter echoes (PMWE) observed with the EISCAT VHF-Radar  

NASA Astrophysics Data System (ADS)

Polar mesosphere winter echoes (PMWE) are strong coherent radar echoes observed with VHF-Radars and primarily occur during the winter months at altitudes between 60-80 km. In recent years, the morphology of these echoes has been well documented, however, the physical mechanism leading to these radar echoes is yet to be established. In the current study we consider PMWE-observations with the EISCAT VHF-radar (224 MHz, Bragg wavelength = 0.67 m) in Tromsø, Northern Norway. Doppler spectra obtained inside and outside PMWE-regions are analyzed in terms of spectral shape, spectral width, and Doppler shift. For the analysis of spectral shape we employ a simple generalized fit to the autocorrelation function (ACF; note that the ACF is the Fourier transform of the Doppler power spectrum) which yields a spectral parameter that attains a value of 1 in case the spectra reveal a Lorentzian shape and a value of 2 if the spectra are Gaussian. Spectral widths and Doppler shifts are analyzed with respect to gravity wave signatures where we will also scrutinize to which extent the possible effect of high frequency gravity waves affects the spectral width and the spectral shape. Finally, these results will be discussed in the framework of current PMWE-theories.

Rapp, Markus; Engler, Norbert; Strelnikova, Irina

61

Ternary Fission Induced by Polarized Neutrons  

SciTech Connect

P-odd and T-odd asymmetries in the emission of fragments and light particles have been investigated in ternary fission induced by polarized neutrons. P-odd asymmetries unambiguously point to a violation of parity in the fission process. By contrast, T-odd asymmetries do not necessarily imply a violation of time reversal invariance. The asymmetries observed are rather due to a final state interaction between the light ternary particle and the nucleus from which they are ejected. New results with interesting information on the ternary fission process are presented.

Goennenwein, F.; Jesinger, P. [Physikalisches Institut, Universitaet Tuebingen, 72076 Tuebingen (Germany); Gagarski, A.; Petrov, G.; Bunakov, V. [Petersburg Nuclear Physics Institute, 188300 Gatchina (Russian Federation); Mutterer, M. [Institut fuer Kernphysik, Technische Universitaet, 64289 Darmstadt (Germany); Trzaska, W. [Department of Physics, Jyvaeskylae University, 40351 Jyvaeskylae (Finland); Nesvizhevsky, V.; Lelievre-Berna, E. [Institut Laue Langevin, 38042 Grenoble (France)

2005-05-24

62

Confocal fluorescence polarization microscopy for linear unmixing of spectrally similar labels.  

PubMed

Studies of biological samples often call for simultaneous identification of multiple molecular or structural components. Multiple labelling fluorescence techniques are a powerful way of achieving this. However, the ability to distinguish a number of fluorescent probes unambiguously can be restricted by the fact that fluorescence spectra are generally broad and overlapping. Recently a technique known as linear unmixing has been combined with spectral imaging to discriminate between multiple fluorophores. In this study a scheme is proposed whereby fluorescence polarization information is used to expand the capability of the linear unmixing technique to accommodate additional fluorescent probes. As a proof-of-concept, it is shown that this polarization-based technique can be used to divide the signals generated by two spectrally similar fluorescent probes into their separate components. PMID:18996704

Kho, Kiang Wei; Stoddart, Paul R; Harris, Martin; Mazzolini, Alex P

2008-09-26

63

Chromosome identification in human oocytes and polar bodies by spectral karyotyping  

Microsoft Academic Search

Sixty unfertilized human oocytes and two fresh polar bodies were karyotyped by spectral karyotyping (SKY). The oocytes were provided by 29 women ranging from 30 to 42 yr of age. The mean hybridization efficiency for oocytes was 95.2% (60\\/63). Nondisjunction of bivalent chromosomes (13.3%) and predivision of sister chromatids at meiosis I (3.3%) were unequivocally determined by analysis first with

C. Márquez; J. Cohen; S. Munné

1998-01-01

64

Development of the ZJU polarized near-infrared high spectral resolution lidar  

NASA Astrophysics Data System (ADS)

Quantitative measurements of atmospheric aerosol optical properties are required for studies of the Earth's radiation budget and climate change. Taking advantage of the broad spectrum of the Cabannes-Brillouin scattering from atmospheric molecules, the high spectral resolution lidar (HSRL) technique employs a narrow spectral filter to reject the aerosol Mie scattering component in the lidar return signals. Therefore, an HSRL can directly measure the extinction and backscatter coefficient as well as the lidar ratio. Since the backscattering signal is proportional to 1/?4, it presents high requirements for the spectral filter to build a near-infrared HSRL. The atomic/molecular absorption filters are limited by the wavelength and it is also challenging for Fabry-Perot interferometers (FPI) due to their small field of view(FOV). The field-widened Michelson interferometer, which has a large FOV, is considered to be a good candidate for the spectral filter of near-infrared HSRL. A polarized near-infrared HSRL instrument, which employs a field-widened Michelson interferometer as the spectral filter, is under development at the Zhejiang University (ZJU), China. In this paper, the methodology and design process of the instrument will be described in detail. The capability of the HSRL in determining the properties of the atmosphere will be addressed. The retrieval of the aerosol optical properties, such as extinction-to-backscatter ratio and aerosol depolarization ratio, will be presented. Sensitivity of the aerosol retrieval to errors in characterizing the spectral filter will also be investigated.

Liu, Dong; Yang, Yongying; Cheng, Zhongtao; Huang, Hanlu; Zhang, Bo; Shen, Yibing

2013-09-01

65

A Comparison of Multi-angle, Hyper-spectral Polarization Measurements and Radiative Transfer Model Calculations  

NASA Astrophysics Data System (ADS)

In the quest for a more detailed understanding of the Earth-atmosphere system, remote sensing techniques that go beyond those currently in practice are being explored. One such set of measurements is multi-angle, hyper-spectral polarization in the solar reflective range (wavelengths less than 4 um), where the polarization state of the continuous spectrum of back-scattered sun-light is recorded over a selected wavelength range and angular range. One application of these measurements is the estimation of atmospheric aerosol properties, i.e. moments of the size distribution, refractive index, and another is the estimation of tropospheric ozone amount. We present a method for calculating, and the resultant calculations, the back-scattered full-Stokes parameters covering the visible to near-IR spectral region. Conditions of the calculations are representative of that observed during the Megacity Initiative: Local and Global Research Observations (MILAGRO) field campaign that took place during March 2006. Corresponding measurements taken by the HyperSpectral Polarimeter for Aerosol Retrievals (HySPAR) instrument (collected from an aircraft at a nominal altitude of 9 km) are also presented. The HySPAR simultaneously records the full-Stokes vector over the 600-900 nm spectral range and 120 degrees of field angle, in a continuous fashion with a single two-dimensional CCD and specially designed and built fore-optics. The emphasis is upon the examination of cloud-free scenes over ocean and land.

Flittner, D. E.; Hu, Y.; Hostetler, C. A.; Jones, S. H.; Iannarilli, F. J.; Cairns, B.; Hair, J. W.; Ferrare, R. A.

2006-12-01

66

High-resolution measurement and spectral overlap of cross-phase modulation induced spectral broadening  

Microsoft Academic Search

Cross-phase modulation induced spectral broadening in WDM systems is measured using a high-resolution optical spectrum analyzer. The measured spectra are consistent with recently developed theoretical models. Using the theoretical models, the spectral overlap between two adjacent WDM channels is estimated for a typical 10-Gb\\/s system having 50 GHz of channel spacing. For -20 dB overlap, the product of number of

Frank Tong; Lian-Kuan Chen; Haito Yu; Keang-Po Ho

2000-01-01

67

Integrated optical spectral polarimeter for signal monitoring and feedback to a polarization-mode dispersion compensator  

NASA Astrophysics Data System (ADS)

An integrated, high-resolution spectral polarimeter is demonstrated in 4%-index-contrast Ge-doped silica waveguides. A ring resonator achieves a wavelength selectivity of less than 2 GHz FWHM, and tunability is realized via thermo-optic phase shifters with scanning speeds on the millisecond time scale. Real-time, in-service polarization-mode dispersion monitoring is thus possible for studying dynamic channel behavior and for feedback to adaptive compensators. Measurements of the differential group delay, output state of polarization, and principal states of polarization of 10- and 40-Gbit/s modulated signals are presented. Measurements of time-varying PMD and higher-order PMD are also presented to demonstrate the device's capability.

Madsen, C. K.; Oswald, P.; Cappuzzo, M.; Chen, E.; Gomez, L.; Griffin, A.; Laskowski, E. J.; Wong-Foy, A.; Chandrasekhar, S.; Buhl, L.

2004-07-01

68

Speckle noise reduction in high speed polarization sensitive spectral domain optical coherence tomography.  

PubMed

We present a high speed polarization sensitive spectral domain optical coherence tomography system based on polarization maintaining fibers and two high speed CMOS line scan cameras capable of retinal imaging with up to 128 k A-lines/s. This high imaging speed strongly reduces motion artifacts and therefore averaging of several B-scans is possible, which strongly reduces speckle noise and improves image quality. We present several methods for averaging retardation and optic axis orientation, the best one providing a 5 fold noise reduction. Furthermore, a novel scheme of calculating images of degree of polarization uniformity is presented. We quantitatively compare the noise reduction depending on the number of averaged frames and discuss the limits of frame numbers that can usefully be averaged. PMID:21934820

Götzinger, Erich; Pircher, Michael; Baumann, Bernhard; Schmoll, Tilman; Sattmann, Harald; Leitgeb, Rainer A; Hitzenberger, Christoph K

2011-07-18

69

Negative induced-polarization effects from layered media  

Microsoft Academic Search

Negative induced-polarization responses from lateral resistivity distributions such as near-surface vertical contacts and dikes, three-dimensional buried bodies, etc., have been well known for years. Recent comprehensive computations of resistivity and induced-polarization response functions over a three horizontally layered earth have revealed that negative induced-polarization effects can also occur whenever the geoelectric section is of K type (p⁠< pâ >

M. N. Nabighian; C. L. Elliot

1976-01-01

70

High Proton Polarization by Microwave-Induced Optical Nuclear Polarization at 77 K  

Microsoft Academic Search

Protons in naphthalene and p-terphenyl doped with pentacene have been polarized up to 32% and 18%, respectively, at liquid nitrogen temperature in a magnetic field of 0.3 T by means of microwave-induced optical nuclear polarization. The polarization was measured by nuclear magnetic resonance as well as by the neutron transmission method. The relaxation time of the proton polarization at 0.0007

M. Iinuma; Y. Takahashi; I. Shaké; M. Oda; A. Masaike; T. Yabuzaki; H. M. Shimizu

2000-01-01

71

Magnetic-Field-Induced Electric Polarization in Multiferroic Nanostructures  

NASA Astrophysics Data System (ADS)

Magnetic-field-induced electric polarization in nanostructured multiferroic composite films was studied by using the Green’s function approach. The calculations showed that large magnetic-field-induced polarization could be produced in multiferroic nanostructures due to enhanced elastic coupling interaction. Especially, the 1-3 type films with ferromagnetic nanopillars embedded in a ferroelectric matrix exhibited large magnetic-field-induced polarization responses, while the 2-2 type films with ferroelectric and ferromagnetic nanolaminates showed much weaker magnetoelectric coupling and lower magnetic induced polarization due to large in-plane constraint effect, which was in agreement with the recent observations.

Nan, Ce-Wen; Liu, Gang; Lin, Yuanhua; Chen, Haydn

2005-05-01

72

Detection of a new spectral unit on the South Polar Region of Mars  

NASA Astrophysics Data System (ADS)

In this work we report on the detection of a new spectral unit on the Martian southern polar region. Data used in this study have been acquired by the OMEGA (Observatoire pour la Minéralogie, l'Eau, les Glaces et l'Activité) imaging spectrometer on board the ESA mission Mars Express (MEX). Spectrally, the unit is characterized by a 1 ?m band depth ~60% higher than the average value of surrounding terrain (LAT<-60°S), a distinctive shape of the reflectance peak at about 0.685 ?m and a steeper negative slope between ~0.8-1 ?m. The spectral parameters used to map the unit have been defined according to [1] and they show values similar to the one observed on the cratered Noachian terrain of the southern hemisphere (- 60 °S < LAT < 0°) characterized by a mineralogical composition rich in pyroxene. Morphologically, the considered area falls inside one of the flattest regions of Mars. In Figure 1 we show the spectral unit location and its typical spectrum (red curve), in comparison with other spectra. In Fig. 2 we show the spectral ratios between the spectra of the sites of Fig. 1. The spectrum 1 has bands near 1.05 and 2.3 ?m. The best match of this spectrum is the diopside, while the spectrum 2 has absorptions near 1.04 and 2.1 ?m consistent with a basalt, probably LCP.

Carrozzo, F. G.; Altieri, F.; Bellucci, G.; Poulet, F.; D'Aversa, E.; Bibring, J.-P.

2012-09-01

73

Time-Resolved Measurements of Polarized X-Ray Spectral Lines Emitted from Discharges of the Plasma-Focus Type  

SciTech Connect

The paper presents results of experimental studies of the polarization of the X-ray spectral lines observed during high-current Plasma-Focus (PF) discharges. Time-resolved measurements of the highly-ionized argon lines were performed within the MAJA-PF facility operated at 44 kJ. The detailed studies confirmed considerable differences in relative intensities of the investigated spectral lines, what could be treated as an evidence of their different polarization.

Jakubowski, L.; Sadowski, M. J.; Stanislawski, J. [Andrzej Soltan Institute for Nuclear Studies, 05-400 Swierk (Poland); Baronova, E. O. [Nuclear Fusion Institute, NRC Kurchatov Institute, 123182 Moscow (Russian Federation)

2006-01-15

74

Ultrafast dynamics of orbital-order-induced polarization  

NASA Astrophysics Data System (ADS)

Ultrafast photoinduced modulation is demonstrated in the orbital-order-induced polarization in manganite thin films. The evolution of the polarization modulation and the lattice temperature rise after photoexcitation are tracked separately by monitoring the relevant nonlinear optical susceptibility tensor elements. Substantial portion of the polarization disappears within the excitation pulse width (~120 fs), indicating the purely electronic origin triggered by an interband excitation. We propose oxide heterostructure devices incorporating polar gating layers capable of ultrafast optical control of electronic phases.

Ogawa, Naoki; Ogimoto, Yasushi; Miyano, Kenjiro

2013-06-01

75

Compensation for the spectral dispersion of light polarization states in electro-optic modulators based on chiral liquid crystals  

NASA Astrophysics Data System (ADS)

The effect of compensation for the spectral dispersion of light polarization states at the output of a single-domain layer of a chiral liquid crystal (CLC) is experimentally studied. It is shown that such dispersion can be decreased significantly with the aid of phase plates of two types that have different signs of the spectral dispersion of birefringence. The dispersion compensation allows one to significantly increase the operating spectral range of fast light modulators based on chiral nematic liquid crystals (NLCs).

Barnik, M. I.; Geivandov, A. R.; Palto, S. P.; Palto, V. S.; Umanskii, B. A.; Shtykov, N. M.

2013-01-01

76

High Proton Polarization by Microwave-Induced Optical Nuclear Polarization at 77 K  

NASA Astrophysics Data System (ADS)

Protons in naphthalene and p-terphenyl doped with pentacene have been polarized up to 32% and 18%, respectively, at liquid nitrogen temperature in a magnetic field of 0.3 T by means of microwave-induced optical nuclear polarization. The polarization was measured by nuclear magnetic resonance as well as by the neutron transmission method. The relaxation time of the proton polarization at 0.0007 T and 77 K was found to be almost 3 h and the polarization enhancement reached a record value of 8×104. The usefulness of the method in many areas of physics and chemistry is discussed.

Iinuma, M.; Takahashi, Y.; Shaké, I.; Oda, M.; Masaike, A.; Yabuzaki, T.; Shimizu, H. M.

2000-01-01

77

High proton polarization by microwave-induced optical nuclear polarization at 77 K  

PubMed

Protons in naphthalene and p-terphenyl doped with pentacene have been polarized up to 32% and 18%, respectively, at liquid nitrogen temperature in a magnetic field of 0.3 T by means of microwave-induced optical nuclear polarization. The polarization was measured by nuclear magnetic resonance as well as by the neutron transmission method. The relaxation time of the proton polarization at 0.0007 T and 77 K was found to be almost 3 h and the polarization enhancement reached a record value of 8x10(4). The usefulness of the method in many areas of physics and chemistry is discussed. PMID:11015862

Iinuma; Takahashi; Shake; Oda; Masaike; Yabuzaki; Shimizu

2000-01-01

78

Temporal and spectral studies of high-order harmonics generated by polarization-modulated infrared fields  

SciTech Connect

The temporal confinement of high harmonic generation (HHG) via modulation of the polarization of the fundamental pulse is studied in both temporal and spectral domains. In the temporal domain, a collinear cross-correlation setup using a 40 fs IR pump for the HHG and a 9 fs IR pulse to probe the generated emission is used to measure the XUV pulse duration. The observed temporal confinement is found to be consistent with theoretical predictions. An increased confinement is observed when a 9 fs pulse is used to generate the harmonics. An important spectral broadening, including a continuum background, is also measured. Theoretical calculations show that with 10 fs driving pulses, either one or two main attosecond pulses are created depending on the value of the carrier envelope phase.

Sola, I. J.; Zaier, A.; Cormier, E.; Mevel, E.; Constant, E. [Centre Lasers Intenses et Applications (CELIA), Domaine du Haut-Carre, Universite Bordeaux 1, 351 Cours de la Liberation, 33405 Talence (France); Lopez-Martens, R.; Johnsson, P.; Varju, K.; Mauritsson, J.; L'Huillier, A. [Department of Physics, Lund Institute of Technology, P.O. Box 118, S-221 00 Lund (Sweden); Strelkov, V. [General Physics Institute of Russian Academy of Sciences, 38, Vavilova st., Moscow 119991 (Russian Federation)

2006-07-15

79

Possible creation of net circular polarization and not only depolarization of spectral lines by isotropic collisions  

NASA Astrophysics Data System (ADS)

We will show that isotropic collisions of electrons and protons with neutral hydrogen can lead to creation of net orientation of the atomic levels in the presence of a magnetic field. Consequently, the emitted Stokes-V profile of the spectral lines can be almost symmetric in contrast to the typical antisymmetric signature of the Zeeman effect. Moreover, the amplitude of the symmetric lobe can be significantly higher than the amplitude of the antisymmetric components. This mechanism is caused by a ±{M} symmetry breaking of the collisional transitions between different Zeeman sublevels. We will show an example of our first results for the H? line. This new mechanism could perhaps explain the net circular polarization of spectral lines observed in some solar limb observations and which are currently not understood. However, our results are very preliminary and more developments are needed for going further on.

Št?pán, J.; Sahal-Bréchot, S.

2008-11-01

80

Propagation of beams with any spectral, coherence, and polarization properties in turbulent atmosphere  

NASA Astrophysics Data System (ADS)

The combination of the angular spectrum representation (in space-frequency domain) and of the Rytov perturbation theory is applied for description of the second-order statistical properties of arbitrary (coherent and partially coherent) stochastic fields (whether scalar or electromagnetic) which propagate in turbulent atmosphere. The analysis is restricted to weak regime of atmospheric fluctuations. We first introduce the new method for scalar fields and derive expressions for the cross-spectral density function, from which the spectral and the coherence properties of the propagating fields can be determined. Next we extend the new technique to electromagnetic domain, i.e. we derive expressions for the elements of the 2x2 cross-spectral density matrix of the electric field from which its spectral, coherence and polarization properties can then be found. We illustrate the new method by applying it to propagation of several model beams through the atmosphere. In particular, we consider Gaussian beam, Bessel beam, Gaussian Schell-model beam in their scalar or electromagnetic versions. We find that the results obtained on the basis of the new theory are in good agreement with those obtained earlier by standard techniques.

Korotkova, Olga; Gbur, Greg

2007-03-01

81

Nonadiabatic molecular high-order harmonic generation from polar molecules: Spectral redshift  

SciTech Connect

Molecular high-order harmonic generation (MHOHG) from the polar diatomic molecule HeH{sup 2+} in short intense laser fields is studied numerically. Due to the nonadiabatic response of the molecular dipole to the rapid change of laser intensity, a spectral redshift is predicted in high-intensity and ultrashort laser pulses, contrary to the blueshift observed in the harmonics generated from atoms in long laser pulses. The MHOHG temporal structures are investigated by a wavelet time-frequency analysis, which shows that the enhanced excitation of localized long lifetime excited states shifts the harmonic generation spectrum in the falling part of short laser pulses, due to the presence of a permanent dipole moment, and thus is unique to polar molecules.

Bian Xuebin; Bandrauk, Andre D. [Departement de Chimie, Universite de Sherbrooke, Sherbrooke, Quebec, J1K 2R1 (Canada)

2011-04-15

82

A new soft X-ray spectral model for polars with an application to AM Herculis  

NASA Astrophysics Data System (ADS)

We present a simple heuristic model for the time-averaged soft X-ray temperature distribution in the accretion spot on the white dwarf in polars. The model is based on the analysis of the Chandra LETG spectrum of the prototype polar AM Her and involves an exponential distribution of the emitting area vs. blackbody temperature a(T) = a0 exp( - T/T0). With one free parameter besides the normalization, it is mathematically as simple as the single blackbody, but is physically more plausible and fits the soft X-ray and far-ultraviolet spectral fluxes much better. The model yields more reliable values of the wavelength-integrated flux of the soft X-ray component and the implied accretion rate than reported previously. Based on observations with the Chandra and ROSAT satellites.

Beuermann, K.; Burwitz, V.; Reinsch, K.

2012-07-01

83

Polarized spectral properties of Er3+ ions in NaGd(WO4)2 crystal  

NASA Astrophysics Data System (ADS)

Polarized spectral properties of Er3+:NaGd(WO4)2 single crystal are reported. The crystal was grown by the Czochralski method. The Judd Ofelt theory was applied to analyze the polarized absorption spectra and then calculate the spontaneous emission probabilities, radiative lifetimes, and branching ratios. Fluorescence decay curves of the 4 I 13/2, 4 I 11/2, and 4 S 3/2 multiplets for the Er3+ ions were measured. Stimulated emission cross-sections of the 4 I 13/2?4 I 15/2 transition obtained by the Fuchtbauer Ladenberg formula and the reciprocity method were compared. Multi-phonon relaxation rates of the crystal were estimated. Green up-conversion fluorescence around 531 and 552 nm was observed, and the possible up-conversion mechanisms were proposed.

Huang, J. H.; Gong, X. H.; Chen, Y. J.; Lin, Y. F.; Liao, J. S.; Chen, X. Y.; Luo, Z. D.; Huang, Y. D.

2007-10-01

84

High-spectral resolution simulation of polarization of skylight: Sensitivity to aerosol vertical profile  

NASA Astrophysics Data System (ADS)

A vector radiative transfer model was used in conjunction with the line-by-line radiative transfer model and the database of high-resolution transmission (HITRAN) molecular absorption to simulate the degree of linear polarization of skylight in cloud-free conditions. Differences between simulated and measured polarization data in high-spectral resolution are found to be within 1% after aerosol scattering and gas absorptions are carefully considered. Limiting experiments are conducted at wavelengths around 0.760-0.765 ?m O2-A absorption band for the same columnar aerosol optical thickness but different aerosol profiles. Results showed that the degree of linear polarization of skylight at surface varies strongly and is sensitive to the vertical change of tropospheric aerosol mass (or extinction) as the wavelengths approach to the edge of O2-A absorption band. However, such sensitivity is minimal at all wavelengths when the aerosol composition or single scattering properties are vertically homogeneous. This study suggests that the polarization data can be used together with radiance data to constrain the simulation of vertical distribution of aerosol composition in chemistry transport models.

Zeng, Jing; Han, Qingyuan; Wang, Jun

2008-10-01

85

Influence of pore fluid chemistry on the complex conductivity and induced polarization responses of Berea sandstone  

Microsoft Academic Search

The spectral induced-polarization (IP) response of rocks and soils is a complex function of pore solution chemistry, sample microgeometry, and surface chemical properties. We measure the complex conductivity and the time domain IP responses of Berea sandstone as a function of pore fluid ionic strength and pH. Complex conductivity is measured over the frequency range 10-3 to 106Hz, and chargeability

David P. Lesmes; Kevin M. Frye

2001-01-01

86

The dependence of induced polarization on natural iron concentration in wetland soils  

Microsoft Academic Search

Spectral Induced polarization (SIP) measurements in the frequency range 0.1-1000 Hz were conducted on clay and peat marsh soils, obtained from a contaminated freshwater weltand in New Jersey, that were subsequently analyzed for heavy metal concentrations, moisture content, organic matter, porosity, specific surface area, and pore fluid conductivity. A Cole-Cole relaxation model was fit to each of the samples and

L. D. Slater; N. Mansoor

2006-01-01

87

Induced and Form Birefringence in High-Frequency Polarization Gratings  

NASA Astrophysics Data System (ADS)

High-frequency phase polarization gratings are fabricated holographically in dichromated gelatin dyed with malachite green. It is observed that the intensity of the -1 diffracted beam is a sinusoidal function of the incident polarization angle. In addition, we analyze the dependence of the diffracted order polarization on grating frequency. It is evident from our results that form birefringence becomes significant when the grating period is smaller than the illumination wavelength, thus modifying the optically induced birefringence. Then, in polarization hologram reconstruction, it is not possible to obtain the polarization distribution at the recording step for high-frequency objects.

Martinez-Ponce, Geminiano; Solano, Cristina

2001-08-01

88

Polarization and depolarization currents resulting from the temperature or pressure induced volume changes in polarized dielectrics  

NASA Astrophysics Data System (ADS)

We investigate the emission of electric current from a polarized dielectric whenever the matrix dilates. The thermal volume expansivity, the isothermal bulk modulus, its temperature and pressure derivatives and the rate of temperature or pressure variation would determine the shape and the magnitude of the electric signal. We emphasize the permanent dipole polarization and the ionic (induced) polarization. Numerical estimates of the current density, which would be recorded in polarization or depolarization experiments in a model system with cubic symmetry, such as sodium chloride doped with a small amount of divalent cation impurities, are obtained.

Papathanassiou, A. N.

2000-12-01

89

Nuclear reactivity control using laser induced polarization  

DOEpatents

A control element for reactivity control of a fission source provides an atomic density of {sup 3}He in a control volume which is effective to control criticality as the {sup 3}He is spin-polarized. Spin-polarization of the {sup 3}He affects the cross section of the control volume for fission neutrons and hence, the reactivity. An irradiation source is directed within the {sup 3}He for spin-polarizing the {sup 3}He. An alkali-metal vapor may be included with the {sup 3}He where a laser spin-polarizes the alkali-metal atoms which in turn, spin-couple with {sup 3}He to spin-polarize the {sup 3}He atoms. 5 figs.

Bowman, C.D.

1989-05-26

90

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

2013-05-16

91

Analysis of random induced cross polarization  

NASA Astrophysics Data System (ADS)

Streamlined radomes will always introduce depolarization because of the fact that any material surface viewed at an oblique angle has different transmission coefficients for fields polarized parallel and perpendicular to the plane of incidence, a phenomenon known as divorce. The cross polarized fields are similar in nature to those responsible for Condon lobes of parabolic reflectors, and which are known to make those antennas susceptible to cross polarization jamming. The relative strength of those lobes is directly related to the amount of divorce, and is quite sensitive to the phase difference of parallel and perpendicular transmission coefficients. A mere 20 deg of phase divorce has a comparable effect to 3 dB of amplitude divorce. This paper presents a detailed analysis for general radome shapes, based on geometrical optics (ray tracing). Example results are presented for conical and tangent ogive radome geometries used in conjunction with a circular-aperture antenna that is mechanically scanned. The results show that when the antenna is scanned off axis, the cross polarized pattern changes from a Condon lobe structure to a difference pattern in the direction orthogonal to the axis of scan, e.g.: under azimuth scanning the cross polarized sum pattern resembles an elevation difference pattern, while the cross polarized elevation difference resembles a sum beam. Hence, interference in the cross polarization will introduce a tracking error in the direction orthogonal to the scan plane.

McGrath, Daniel T.

1992-03-01

92

Spectral albedo and emissivity of CO sub 2 in Martian polar caps: Model results  

SciTech Connect

A model originally developed to explain the spectral albedo and emissivity of terrestrial snow is extended to the case of carbon dioxide snow on Mars. The variation of albedo and emissivity with wavelength is caused by the spectral variation of the absorption coefficient of solid CO{sub 2}. The most important variables controlling the radiative properties are grain size and contamination by dust or water. Solar zenith angle and snowpack thickness are of less importance. The observation that red albedo is higher than blue albedo in the Martian south polar cap indicates that the snow is contaminated with red dust. The interband absorption coefficient of CO{sub 2} ice in the thermal infrared is 2-3 orders of magnitude smaller than that of H{sub 2}O ice, due to the absence of hydrogen bonding in CO{sub 2}. This allows CO{sub 2} snow emissivity to be sensitive to grain size, emission angle, and impurities, in contrast to water snow which is nearly a blackbody under all conditions. The emissivity of CO{sub 2} snow varies substantially with wavelength, so energy budget modeling should be done in spectral detail. The addition of a thin layer of water frost over CO{sub 2} snow dramatically raises the thermal emissivity but causes little change to the spectrally averaged albedo unless the underlying CO{sub 2} snow is dirty. Remote sensing of CO{sub 2} grain size, H{sub 2}O content, and dust content may be possible. However, the design of a remote-sensing strategy awaits more accurate laboratory determination of the optical constants of CO{sub 2} ice.

Warren, S.G. (Univ. of Melbourne (Australia)); Wiscombe, W.J. (NASA Goddard Space Flight Center, Greenbelt, MD (USA)); Firestone, J.F. (Univ. of Washington, Seattle (USA))

1990-08-30

93

Model estimates soil permeability using induced polarization  

NASA Astrophysics Data System (ADS)

The speed at which water flows through the ground depends on a number of physical parameters, including the density of the soil and the number and sizes of open pores, with the cumulative effect of these parameters dictating the soil's permeability. When exposed to an electric field, sediment grains within the soil get polarized because of an extremely thin structure that surrounds each grain known as the electrical double layer. The electrical double layer consists of a thin layer of adsorbed ions and a diffuse layer of ions that encircle each soil particle. Researchers are able to measure the polarization of the soil to nonintrusively estimate the soil's textural properties, and hence its permeability, with the polarization of the soil being controlled by the polarization of the electrical double layer.

Schultz, Colin

2012-04-01

94

Polarization-induced astigmatism caused by topographic masks  

NASA Astrophysics Data System (ADS)

With the continuous shrink of feature sizes the pitch of the mask comes closer to the wave length of light. It has been recognized that in this case polarization effects of the mask become much more pronounced and deviations in the diffraction efficiencies from the well-known Kirchhoff approach can no longer be neglected. It is not only the diffraction efficiencies that become polarization-dependent, also the phases of the diffracted orders tend to deviate from Kirchhoff theory when calculated rigorously. This also happens for large structures, where these phase deviations can mimic polarization dependent wave front aberrations, which in the case of polarized illumination can lead to non-negligible focus shifts that depend on the orientation and the features size themselves. This orientation dependence results in a polarization induced astigmatism offset, which can be of the same order of magnitude or even larger as polarization effects stemming from the lens itself. Hence, for correctly predicting polarization induced astigmatism offsets, one has to both consider lens and mask effects at the same time. In this paper we present a comprehensive study of polarized induced phase effects of topographic masks and develop a simple theoretical model that accurately describes the observed effects.

Ruoff, Johannes; Neumann, Jens Timo; Schmitt-Weaver, Emil; van Setten, Eelco; le Masson, Nicolas; Progler, Chris; Geh, Bernd

2007-10-01

95

Spectral characteristics of polar mesosphere winter echoes measured with the EISCAT VHF and ESRAD MST radars  

NASA Astrophysics Data System (ADS)

Polar mesosphere winter echoes (PMWE), between 55-80 km altitude, are seen by high latitude radars when excess ionization is produced by energetic particle precipitation. The mechanism of PMWE generation is still unclear though both turbulent and non-turbulent (highly damped ion-acoustic waves) hypotheses have been suggested. The EISCAT VHF radar (224 MHz) in Tromso, Norway and the ESRAD MST (52 MHz) radar at Esrange, Sweden detected strong backscatter from narrow layers at 65-75 km altitude during the solar proton event on 10-12 November 2004. Spectral characteristics of the echoes have been derived for both radars and compared to each other and to the models for an incoherent scatter (ion line) and coherent isotropic turbulent scatter. Widths and shapes of the spectra are discussed in a context of possible mechanism of PMWE generation.

Belova, E.; Kirkwood, S.; Sergienko, T.

2012-04-01

96

Stratified media theory interpretation of measurements of the spectral polarized directional emissivity of some oxidized metals  

NASA Astrophysics Data System (ADS)

The emissivities of metals are strongly affected by the growth of oxide films. For small film thicknesses, perturbations are limited to the visible range. As thicknesses increase, they spread to the infrared range. Various samples of optically polished metals (Fe, Ni, Cr) and stainless steels (ELI.T 1803 MoT and AISI 304 or 316) have been oxidized at temperatures ranging from 400 to 800‡C. Their spectral polarized directional emissivities, ?'?? and ?'??, have been measured with two experimental techniques. The spectral range studied extends from 0.4 to 14 ?m; the measurement directions vary between 0 and 80‡ from the normal to the sample. After measurement, each sample was analyzed by glowdischarge optical spectroscopy (GDOS). From the results of the analysis and from the survey of bibliographical data, we characterized the structure of the oxide films, i.e., their approximate thicknesses and compositions. If the complex optical indices of the metals and oxides are known, the stratified media theory enables the computation of the emissivities ?'?? and ?'??. Computed and measured values have been compared. It appears that the theory accounts well for experimental data when the thicknesses of the oxides are small as in stainless steels. But for thicker oxide films, discrepancies are ascribed to several reasons.

Ane, J. M.; Huetz-Aubert, M.

1986-11-01

97

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

98

Two dimensional spectral analyses of wave structures in polar mesospheric clouds  

NASA Astrophysics Data System (ADS)

The primary goal of the Aeronomy of Ice in the Mesosphere (stocktickerAIM) satellite is to investigate the nature, formation and evolution of Polar Mesospheric Clouds (stocktickerPMC) near the high-latitude summer mesopause region. The Cloud Imaging and Particle Size experi-ment (CIPS) on stocktickerAIM is a four camera, wide-field (120° x 80° ) UV imager capable of measuring stocktickerPMC morphology and imaging extensive gravity wave events within the PMCs over a broad range of scale sizes with high spatial resolution (˜5 km). In this study, we present new results of a 2-D spectral analysis of wave structures imaged in the stocktickerPMC field during the northern hemisphere summer 2007 season. The data have been analyzed to investigate the occurrence of gravity waves with horizontal scales in the range of 20-600 km. The results reveal strong anisotropy in the wave alignments that varied during the course of the 2007 season as well as longitudinal variability in the averaged wave power of up to ˜15%. These measurements set the scene for an investigation of gravity waves and their potential sources in the summer polar mesosphere (in both hemispheres) using the extensive stocktickerAIM data set (2007-ongoing).

Zhao, Yucheng; Taylor, Michael J.; Pautet, Pierre-Dominique; Randall, Cora; Bailey, Scott; Russell, J. M., III

99

Spectral characteristics of carbonyl substituted 2,2'-bithiophenes in polymer matrices and low polar solvents.  

PubMed

The spectral characteristics of monosubstituted derivatives of 2,2'-bithiophene (1-BT) with simple carbonyl substituents, including -COCF3 (trifluoroacetyl, 2-BTCF), -COCH2CN (oxopropanenitrile, 3-BTCN) and -COCH3 (acetyl, 4-BTCE), and the more complex 5'-((9H-fluoren-9-ylidene)methyl)-3-methyl, 5-methyl carboxylate (5-BTFL) were investigated. Absorption and fluorescence spectra and fluorescence lifetimes were measured in solvents with various polarities and compared with those in polymer matrices (polystyrene, PS; polymethyl methacrylate, PMMA; and polyvinyl chloride, PVC). Although the parent, 1-BT, absorbed near 300 nm and exhibited no or weak fluorescence, the substitution of 1-BTwith simple substituents at position 5 resulted in a bathochromic shift of approximately 50 nm or more in absorption and distinct fluorescence above 400 nm. The largest shift in absorption and fluorescence was observed for the complex 5-BTFL with fluorene as a substituent for 1-BT. The most intense fluorescence was observed for the derivative 2-BTCF with trifluoroacetyl as a substituent in the polar PVC matrix. The lifetimes of fluorescence of all substituted 2,2'-bithiophenes were in the range from 0.3 to 3 ns. The polymer matrices increased the intensity of fluorescence to some extent and prolonged the lifetime of the 2,2'-bithiophene derivatives. The reasons for the variation in the fluorescence intensity resulting from the substitution of the parent dimer are discussed. PMID:23644743

Danko, Martin; Andicsová, Anita; Hrdlovi?, Pavol; Ra?ko, Dušan; Végh, Daniel

2013-07-01

100

Characterization of two-dimensional finite-aperture wire grid polarizers by a spectral-domain technique.  

PubMed

We investigate the transmission characteristics of perfectly conducting two-dimensional wire grid polarizers fabricated in finite and infinite apertures using a rigorous spectral-domain mode-matching method. Specifically, the transmission coefficient for both transverse-electric and transverse-magnetic polarizations, extinction ratio, and diffraction pattern are characterized for a wide variety of geometric and material parameters including aperture dimension, conducting wire fill factor, wire spacing, polarizer thickness, material dielectric constants, and incident wave arrival angle. The results indicate that the transmission behavior is largely insensitive to aperture dimension. PMID:18360516

Jensen, M A; Nordin, G P

2001-09-10

101

Remote sensing of aerosols by using polarized, directional and spectral measurements within the A-Train: the PARASOL mission  

NASA Astrophysics Data System (ADS)

Instruments dedicated to aerosol monitoring are recently available and the POLDER (POLarization and Directionality of the Earth's Reflectances) instrument on board the PARASOL (Polarization & Anisotropy of Reflectances for Atmospheric Sciences coupled with Observations from a Lidar) mission is one of them. By measuring the spectral, angular and polarization properties of the radiance at the top of the atmosphere, in coordination with the other A-Train instruments, PARASOL provides the aerosol optical depths (AOD) as well as several optical and microphysical aerosol properties. The instrument, the inversion schemes and the list of aerosol parameters are described. Examples of retrieved aerosol parameters are provided as well as innovative approaches and further inversion techniques.

Tanré, D.; Bréon, F. M.; Deuzé, J. L.; Dubovik, O.; Ducos, F.; François, P.; Goloub, P.; Herman, M.; Lifermann, A.; Waquet, F.

2011-07-01

102

Soft X-Ray Spectral Analysis of the North Polar Spur  

NASA Astrophysics Data System (ADS)

I present a soft X-ray spectral observation of the North Polar Spur (NPS), an enhanced feature in the Soft X-ray Background. The observation was made with a Charge Coupled Device (CCD) aboard a sounding rocket on May 2, 1997. CCD temperature during flight was -72°C, approximately 15° higher than optimal. A total of 330 seconds of data was collected. The spectrum, in the 0.22-10 keV energy range, was analyzed using the XSPEC data package. The data were fit by a three component model: an absorbed power law representing the extragalactic emission, a thermal plasma model representing the foreground emission from the Local Hot Bubble and a thermal plasma model representing emission from the North Polar Spur. The extragalactic component was fit with an absorbed power law, using a column density of 2 × 1020cm -2. The best fit gave a spectral index of 1.391 and a normalization of 11.11. The local component was fit with a Raymond and Smith thermal plasma model. The best fit resulted in a temperature of 1.5 × 106 K and an emission measure of 6.76 × 103cm-6 pc. The NPS component was fit with an absorbed Raymond and Smith thermal plasma model with a temperature of 3.5 × 106 K and an emission measures of 3.53 × 103cm-6 pc. The fit was significantly improved with the addition of Gaussians at energies of known astrophysical lines corresponding to N VII, Ne IX, Mg XI and Si Ly?. It was also significantly improved when the abundances of N, O, Ne, Ar, Fe, and Ni were allowed to vary using a variable Raymond and Smith thermal plasma model for the NPS component. Both fits are evidence of abundance variations in the North Polar Spur. An NEI (nonequilibrium ionization) model for the NPS component did not result in a significant improvement of the fit, suggesting that the NPS plasma is already in collisional ionization equilibrium.

Cawley, Laura Joan

103

Polarization and fluence dependence of the polarized emission in nanosecond laser-induced breakdown spectroscopy  

NASA Astrophysics Data System (ADS)

Several studies have appeared in the past two years reporting that the continuum emission produced by the laser ablation of solid materials is strongly polarized. In a paper that appears to conflict with these findings, Asgill et al. report that they did not observe a significant amount of polarization produced by nanosecond laser excitation of nitrogen gas and laser ablation of copper and steel ( M.E. Asgill, H.Y. Moon, N. Omenetto, D.W. Hahn, Investigation of polarization effects for nanosecond laser-induced breakdown spectroscopy, Spectrochim. Acta Part B (2010) xxx-xxx [7]). Here we show that the apparent discrepancy is resolved when laser fluence and polarization are taken into account. Using a 532 nm Nd:YAG laser to ablate Al samples in air, we find that the degree of polarization, P, of the continuum is greater for s- vs. p-polarized excitation and that P decreases with increasing fluence. We show that P would be < 10% under the conditions of Asgill et al., whereas P > 60% is obtained at low fluences with s-polarized excitation. We also confirm that at high fluence the polarization of the discrete emission is much smaller than that of the continuum.

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

2011-02-01

104

Polarization-induced ?-holes and hydrogen bonding.  

PubMed

The strong collinear polarizability of the A-H bond in A-H···B hydrogen bonds is shown to lead to an enhanced ?-hole on the donor hydrogen atom and hence to stronger hydrogen bonding. This effect helps to explain the directionality of hydrogen bonds, the well known cooperative effect in hydrogen bonding, and the occurrence of blue-shifting. The latter results when significant additional electron density is shifted into the A-H bonding region by the polarization effect. The shift in the A-H stretching frequency is shown to depend essentially linearly on the calculated atomic charge on the donor hydrogen for all donors in which A belongs to the same row of the periodic table. A further result of the polarization effect, which is also expected for other ?-hole bonds, is that the strength of the non-covalent interaction depends strongly on external electric fields. PMID:22015592

Hennemann, Matthias; Murray, Jane S; Politzer, Peter; Riley, Kevin E; Clark, Timothy

2011-10-21

105

Polarization-induced torque in optical traps  

SciTech Connect

In the field of optical trapping and micromanipulation it is well known that linearly polarized Gaussian beams, which possess no inherent angular momentum, can exert an orienting torque on optically or geometrically anisotropic particles. Conservation of angular momentum requires that the application of such a torque be compensated for by an equivalent, and opposite, angular momentum flux in the beam. In the following paper we analyze this effect in terms of both the scattered field, and the mechanical torque experienced by the particle. It is demonstrated that, in general, the scattered field has a complicated form, carrying both spin and orbital angular momentum. However, we show that the variation of torque with rotation angle is identically equal to A+B sin(2{alpha}+{beta}) for arbitrarily shaped particles, where A, B, and {beta} are constants and {alpha} is the angular displacement of the major axis of the particle from the polarization direction. The scattered field, and the mechanical torque, are seen to reduce to qualitatively distinct forms that depend on the symmetry group of the scattering particle. Our findings are verified and illustrated by a series of numerical calculations of the forces and torques experienced by arbitrarily shaped particles trapped in linearly polarized Gaussian beams.

Simpson, Stephen H.; Benito, David C.; Hanna, Simon [H. H. Wills Physics Laboratory, University of Bristol, Tyndall Avenue, Bristol BS8 1TL (United Kingdom)

2007-10-15

106

X-Ray Induced Electrical Polarization in Glass  

Microsoft Academic Search

Electrical polarization in a lead silicate glass induced by the action of x-rays on the material is found to exist. This phenomenon is surveyed experimentally as a function of total dose (incident and absorbed), dose rate, x-ray tube potential, radiation temperature, and temperature at which the polarization is released and measured. Net surface charges of the order of 10-9 coulomb\\/cm2

T. M. Proctor

1959-01-01

107

Spin-Polarized Electron Induced Asymmetric Reactions in Chiral Molecules  

NASA Astrophysics Data System (ADS)

Understanding the origin of chirality in nature has been an active area of research since the time of Pasteur. In this chapter we examine one possible route by which this asymmetry could have arisen, namely chiral-specific chemistry induced by spin-polarized electrons. The various sources of spin-polarized electrons (parity violation, photoemission, and secondary processes) are discussed. Experiments aimed at exploring these interactions are reviewed starting with those based on the Vester-Ulbricht hypothesis through recent studies of spin polarized secondary electrons from a magnetic substrate. We will conclude with a discussion of possible new avenues of research that could impact this area.

Rosenberg, Richard A.

108

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

109

[Wavelength conversion and spectral analysis in periodically polarized lithium niobate waveguide].  

PubMed

Wavelength conversion exploiting cascaded second harmonic and difference frequency generation (c(SHG/DFG)) in periodically polarized LiNbO3 (PPLN) waveguides was experimentally researched. While wavelength converter was pumped with a pulsed wave, the pump pulse can be used to carry the information and wavelength conversion occurs between the pump wave and converted wave, thus wavelength conversion transferring the information from the pump wave to the converted waves includes two processes of second order nonlinear reaction: the first wavelength conversion from pump wave to SH wave occurs with SHG process, and the second wavelength conversion from SH wave to converted wave occurs with DFG process. In the first process the group velocities mismatching (GVM) for pulses at different wavelengths due to material property load the temporal walk-off between pump pulse and SH pulse located in the 1.5 microm band and in the 0.8 microm band, respectively, so that SH pulse slowly propagates compared with pump pulse, and SH pulse width is broadened along propagation length. As a result, in the second process the converted DF pulse generates waveform distortion owing to the broadening of SH pulse in the first process. Both the waveform and the spectrum of converted pulse in our experimental results testify to the fact that SH pulse possesses a narrow spectral width, which is consistent with a long SH pulse, and the spectral width of converted DF pulse is compressed but its temporal width is broadened correspondingly. Therefore the influence of walk-off between pulses demonstrates that the pulsed pumping wavelength conversion is disadvantageous to the transparence of the data format. However, pulsed pumping wavelength conversion also presents great potential that can be applied in future optical networks. Tunable wavelength conversion can be easily implemented by changing the wavelength of control CW, and single-to-multiple channel wavelength conversion can be realized by increasing the number of the CW lasing pump channels. This is very important and it enhances the flexibility in the management of the multi-channel WDM network. Finally, a tunable and single-to-dual channel wavelength converter based on the scheme of pulsed pumping wavelength conversion achieved by our experiment setup, and two channel converted pulses simultaneously replicate the bit rate carried on pump pulses. It is pointed out that the quality such the signal-to-noise ratio of converted pulse is affected by spectral width of control CW. PMID:18800689

Luo, Chuan-hong; Sun, Jun-qiang; Zhu, Yuan-xiang; Wang, Jian

2008-06-01

110

Polarization-induced pairing in high-temperature superconductivity  

SciTech Connect

We propose a mechanism for the pairing of electrons at the copper sites on the spin of quasi-one-dimensional Cu-O chains induced by the electronic polarization of the oxygen atoms in the side chains. We use a model Hamiltonian for a cluster of Cu-O chains and calculate the various correlation functions for a wide range of parameters. We examine the conditions for the onset of polarization-induced pairing states. Our results may be relevant to high-T/sub c/ superconductor YBa/sub 2/Cu/sub 3/O/sub 7-//sub x/. .AE

Callaway, J.; Kanhere, D.G.; Misra, P.K.

1987-11-01

111

Spatial, spectral, and polarization properties of radio emission of the 3 February, 1983 proton flare  

NASA Astrophysics Data System (ADS)

The spatial, spectral, and polarization evolutionary features of a proton flare of 2B importance observed on February 3, 1983, are analyzed comprehensively via optical and radio observations obtained by various techniques. The flare was a long-duration process (about 1.5 hr) of energy release and particle acceleration, which consecutively covered still greater regions of the active-region magnetosphere extending in both area and altitude. The cm-range showed flare precursors, i.e., quasi-periodic fluctuations of the radio flux density. As a new magnetic flux was emerging, there was restructuring of the magnetic field, resulting in a long-duration formation of coronal or postflare loops which gradually embraced the area outside the sunspots, penetrating into still greater heights of up to hundreds of thousands of kilometers above the photosphere. The magnetic field strength inside the coronal transient inferred from the zebra-structure and fiber bursts at about 110 MHz was found to be higher (1-2 G) as compared with the stationary source at the end of the flare at about 230 MHz (0.5-1 G).

Bakunin, L. M.; Ledenev, V. G.; Nefed'Ev, V. P.; Potapov, N. N.; Smolkov, G. Ia.; Uralov, A. M.; Chernov, G. P.; Fomichev, V. V.; Mel'Nikov, V. P.; Podstrigach, T. S.

1991-09-01

112

Tip-induced spectral dynamics of single molecules  

NASA Astrophysics Data System (ADS)

Manipulation of spectral dynamics of single molecules (SM) by a metallized scanning probe tip is demonstrated. The Stark effect of the zero-phonon lines of single pentacene molecules in a p-terphenyl host at 1.8 K is investigated by applying a voltage to the tip in contact with the sample. The measured Stark shifts exhibit a plateau and the line widths depend on the electric field. These anomalies are explained by a model based on two-level systems with field-dependent double-well potentials. The experimental data show that the two-level systems are induced by the tip.

Segura, J.-M.; Zumofen, G.; Renn, A.; Hecht, B.; Wild, U. P.

2001-05-01

113

Spectral properties of identified polarized-light sensitive interneurons in the brain of the desert locust Schistocerca gregaria.  

PubMed

Many migrating animals employ a celestial compass mechanism for spatial navigation. Behavioral experiments in bees and ants have shown that sun compass navigation may rely on the spectral gradient in the sky as well as on the pattern of sky polarization. While polarized-light sensitive interneurons (POL neurons) have been identified in the brain of several insect species, there are at present no data on the neural basis of coding the spectral gradient of the sky. In the present study we have analyzed the chromatic properties of two identified POL neurons in the brain of the desert locust. Both neurons, termed TuTu1 and LoTu1, arborize in the anterior optic tubercle and respond to unpolarized light as well as to polarized light. We show here that the polarized-light response of both types of neuron relies on blue-sensitive photoreceptors. Responses to unpolarized light depended on stimulus position and wavelength. Dorsal unpolarized blue light inhibited the neurons, while stimulation from the ipsilateral side resulted in opponent responses to UV light and green light. While LoTu1 was inhibited by UV light and was excited by green light, one subtype of TuTu1 was excited by UV and inhibited by green light. In LoTu1 the sensitivity to polarized light was at least 2 log units higher than the response to unpolarized light stimuli. Taken together, the spatial and chromatic properties of the neurons may be suited to signal azimuthal directions based on a combination of the spectral gradient and the polarization pattern of the sky. PMID:17401118

Kinoshita, Michiyo; Pfeiffer, Keram; Homberg, Uwe

2007-04-01

114

Rapid methods for interpretation of induced polarization anomalies  

Microsoft Academic Search

The induced polarization (IP) method is used at various stages of prospecting in poorly accessible regions that have complex structure. For such conditions we suggest approximate procedures for acquiring information about the location of the structures in question. Correlation between the observed fields and the heights of observation points is used for reducing the effect of terrain relief. Simultaneously, the

B. Khesin; V. Alexeyev; L. Eppelbaum

1997-01-01

115

Polar Cap Spectral Emission Intensities and Their Relationship to Selected Geomagnetic Parameters.  

National Technical Information Service (NTIS)

Selected spectral emission data from the One Meter Fastie-Ebert Scanning Spectrometer located at the AFCRL Geopole Station, Thule, Greenland have been scaled and analyzed. The autocorrelation power spectral density and diurnal variation of the emission ha...

D. L. Miller J. H. Frey W. L. Fischer

1972-01-01

116

Polarization-induced noise in resonator fiber optic gyro.  

PubMed

An optical fiber ring resonator (OFRR) is the key rotation-sensing element in the resonator fiber optic gyro (R-FOG). In comparing between different OFRR types, a simulation model that can apply to all cases is set up. Both the polarization crosstalk and polarization-dependent loss in the coupler are fully investigated for the first time to our knowledge. Three different splicing schemes, including a single 0°, a single 90°, and twin 90° polarization axis rotated spices, are compared. Two general configurations of the OFRR are considered. One is a reflector OFRR, the other is a transmitter OFRR. This leads to six different OFRR types. The output stability of the R-FOG with six OFRR types is fully investigated theoretically and experimentally. Additional Kerr noise due to the polarization fluctuation is discovered. The OFRR with twin 90° polarization axis rotated splices is of lower additional Kerr noise and hence has better temperature stability. As the coupler is polarization dependent, we notice that in a reflector OFRR, the straight-through component of the output lightwave, which can be isolated by a transmitter configuration, would produce large polarization fluctuation-induced noise. The experimental results show that the bias stability of the transmitter OFRR is 8 times improved over that of the reflector OFRR, which is in accord with the theoretical analysis. By the analysis and experiments above, it is reasonable to make a conclusion that an R-FOG based on a transmitter OFRR with twin 90° polarization axis rotated splices is of better temperature stability and smaller additional Kerr effect noise. PMID:23033085

Ma, Huilian; Chen, Zhen; Yang, Zhihuai; Yu, Xuhui; Jin, Zhonghe

2012-10-01

117

Spectral and polarization effects in deterministically non-periodic multilayers containing optically anisotropic and gyrotropic materials  

Microsoft Academic Search

The influence of material anisotropy and gyrotropy on optical properties of fractal multilayer nanostructures is theoretically investigated. Gyrotropy is found to uniformly rotate the output polarization for bi-isotropic multilayers of arbitrary geometrical structure without any changes in transmission spectra. When introduced in a polarization splitter based on a birefringent fractal multilayer, isotropic gyrotropy is found to resonantly alter output polarizations

S. V. Zhukovsky; V. M. Galynsky

2006-01-01

118

Induced Polarization Responses of the Specimen with Sulfide Ore Minerals  

NASA Astrophysics Data System (ADS)

Basic data of the physical properties of the rocks is required to effectively interpret geologic structures and mineralized zones in study areas from the geophysical data in the field of subsurface investigations and mineral resources explorations. In this study, the spectral induced polarization (SIP) measurement system in the laboratory was constructed to obtain the IP characteristics of the specimen with sulfide ore minerals. The SIP measurement system consists of lab transmitter for electrical current transmission, and GDP-32 for current receiver. The SIP system employs 14 steps of frequencies from 0.123 to 1,024 Hz, and uses copper sulfate solution as an electrolyte. The SIP data for system verification was acquired using a measurement system of parallel circuit with fixed resistance and condenser. This measured data was in good agreement with Cole-Cole model data. First of all, the experiment on the SIP response was conducted in the laboratory with the mixture of glass beads and pyrite powders for ore grade assessment using characteristics of IP response of the rocks. The results show that the phase difference of IP response to the frequency is nearly proportional to the weight content of pyrite, and that the dominant frequency of the IP response varies with the size of the pyrite powder. Subsequently, the specimens used for SIP measurement are slate and limestone which were taken from drilling cores and outcrops of skarn ore deposits. All specimens are cylindrical in shape, with a diameter of 5 cm and a length of 10 cm. When measuring SIP of water-saturated specimens, the specimen surface is kept dry, tap water is put into the bottom of sample holder and a lid is closed. It is drawn that the SIP characteristics of the rocks show the phase difference depends on the amount of the sulfide minerals. The phase difference did not occur with frequencies applied in the absence of sulfide minerals in the rock specimens. On the contrary, the rock specimens containing sulfide minerals such as galena, sphalerite, pyrrhotite, chalcopyrite, pyrite show large phase differences with frequencies applied. In particular, the slate specimens with skarn Pb-Zn show high IP responses to the frequencies applied since the specimens contain high amount of the sulfide minerals. The specimens of other rocks in the skarn ore deposits, on the other hand, do not provide the detectable IP responses since the rocks consist mostly of silicate minerals. The phase difference derived from the frequency applied was converted to the data for ore grade since the phase of SIP response shows high relationship with the ore grade.

Park, S.; Sung, N. H.

2012-04-01

119

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

120

Intensity-Induced Changes in Optical Polarizations in Glasses  

Microsoft Academic Search

Using a single-mode ruby laser we have made the first measurements of intensity-induced changes of the optical polarization (ellipse rotation) in solids, viz., fused quartz and Schott BK-7 and SF-7 glasses for which we have obtained the nonlinear susceptibility values c1221(-omega, omega, omega, - omega)=1.5, 2.3, and 9.9×10-15 esu, respectively. These values are accurate to within 10% relative to the

Adelbert Owyoung; R. W. Hellwarth; Nicholas George

1972-01-01

121

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

SciTech Connect

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. [Department of Chemistry and the James Franck Institute, University of Chicago, 929 East 57th St., Chicago, Illinois 60637 (United States)

2007-11-14

122

Properties of induced polarization evanescent reflection with a solid immersion lens (SIL).  

PubMed

Properties of the induced polarization signal with a solid immersion lens (SIL) are investigated by experiments and simulations. A LaSFN9 SIL (NA=1.5) is used in the experiment. Physics of the induced polarization signal are described for several configurations of optical systems and substrates. Induced polarization signals from evanescent-wave coupling to dielectric, semiconductor and metal substrates are studied in detail. It is shown that surface plasmon waves are excited with Au substrates and the induced polarization signal is affected by the surface plasmon waves. Simulation results of the induced polarization signal for a gallium phosphide SIL (NA=2.64) are discussed. PMID:19532348

Chen, Tao; Milster, Tom D

2007-02-01

123

Effects of Buflomedil and Pentoxifylline on Hamster Skin-Flap Microcirculation: Prediction of Flap Viability Using Orthogonal Polarization Spectral Imaging  

PubMed Central

OBJECTIVE This study investigated the effects of buflomedil and pentoxifylline, both of which are used in reconstructive surgery of hamster skin flap microcirculation, and evaluated the skin flap survival rate by orthogonal polarization spectral imaging. METHOD Twenty-four adult male Syrian golden hamsters were divided into three groups: a control (C, 0.1 ml 0.9% saline), buflomedil (B, 3 mg/kg/day), and pentoxifylline group (P, 14.5 mg/kg/day). Treatments administered intraperitoneally were initiated 1 hour before skin flap preparation and continued for 7 days post-operatively at 12-hour intervals. Preparations (skin flaps) were divided into 12 fields, which were organized into six bands. Functional capillary density (FCD, in mm/mm2), distance from the skin flap base to blood flow cessation (Distwith flow, in cm), percentage of viable skin (VA, in%), and qualitative analysis of blood flow by orthogonal polarization spectral imaging were performed at 1 and 24 hours and on the seventh post-operative day. RESULT Bands IV, V, and VI presented no flow independent of time. The functional capillary density group B was higher than that of groups C and P, primarily after 24 hours. All groups showed an increase in D with time but reached similar final distances (C = 2.73, B = 2.78 and P = 2.70 cm). Moreover, the percentage of viable areas remained at approximately 50%. The orthogonal polarization spectral imaging was useful to assess viability by counting fields with and without blood flow. CONCLUSIONS Functional capillary density values were higher in the buflomedil group compared to the control and pentoxifylline groups in this model. Functional capillary density did not influence D or the percentage of VA, and the technique showed favorable potential to assess/predict the viability of skin flaps within 1 h after surgery.

Coelho da Mota, Denise Salles; Furtado, Eliane; Bottino, Daniel Alexandre; Bouskela, Eliete

2009-01-01

124

Development of a field-widened Michelson spectroscopic filter for a polarized near-infrared high spectral resolution lidar  

NASA Astrophysics Data System (ADS)

Standard backscatter lidars encounter problems when solving the two unknowns (aerosol backscatter coefficient and extinction coefficient) from the only one recorded lidar equation. With the help of the high-spectral-resolution filter, high spectral resolution lidars (HSRLs) can provide unambiguous retrieval without critical assumptions. Spectral discrimination between scattering from molecules and aerosols or cloud particles is the basis of the HSRL technique, and several lidar approaches have been developed to obtain this discrimination. Iodine cell filter, which is a kind of atomic/molecular absorption filter, is robust, stable, and can achieve very good separation of aerosol Mie scattering from atmosphere molecular Cabannes scattering. However, absorption filters are lossy and gaseous absorption lines do not exist at many convenient laser wavelengths. Fabry-Perot interferometers are simple and can be tuned to any wavelength, but are limited by acceptance angle. Field-widened Michelson interferometer (FWMI) is considered to have the ability to overcome the deficiencies of the aforementioned filters as it can perform well at relatively large off-axis angles, is nearly lossless, and can be built to any wavelength. In this paper, the development process of an FWMI that is introduced to be the spectroscopic filter for a polarized near-infrared HSRL instrument will be present. The retrieval process of the aerosol optical properties, the design requirements with special focus on the selection of the free spectral range (FSR) of the FWMI, as well as the design result will be described in detail.

Liu, Dong; Yang, Yongying; Cheng, Zhongtao; Ling, Tong; Huang, Hanlu; Zhou, Yudi; Zhang, Qiaoshuang; Zhang, Bo; Shen, Yibing

2013-09-01

125

Polarized spectral analysis and laser demonstration of Nd3+:Bi2(MoO4)3 biaxial crystal  

NASA Astrophysics Data System (ADS)

Nd3+:Bi2(MoO4)3 single crystal grown by the Czochralski technique was oriented and the orientation relationship between the principal axes of the optical indicatrix (X, Y, Z) and the crystallographic axes (a, b, c) was determined. The polarized absorption spectra, polarized fluorescence spectra, and fluorescence decay curve of the crystal were measured at room temperature. The Judd-Ofelt theory and the Fuchtbauer-Landenburg formula were applied to analyze the spectroscopic parameters. The relation between the spectral properties and the crystal structure was discussed. A primary laser output of about 235 mW at 1064 nm with the slope efficiency of 25% has been obtained under a Ti:sapphire laser pumping.

Gong, Xinghong; Chen, Yujin; Lin, Yanfu; Tan, Qiguang; Luo, Zundu; Huang, Yidong

2008-01-01

126

Characterization of aerosol scattering and spectral absorption by unique methods: a polar/imaging nephelometer and spectral reflectance measurements of aerosol samples collected on filters  

NASA Astrophysics Data System (ADS)

Characterization of aerosol scattering and absorption properties is essential to accurate radiative transfer calculations in the atmosphere. Applications of this work include remote sensing of aerosols, corrections for aerosol distortions in satellite imagery of the surface, global climate models, and atmospheric beam propagation. Here we demonstrate successful instrument development at the Laboratory for Aerosols, Clouds and Optics at UMBC that better characterizes aerosol scattering phase matrix using an imaging polar nephelometer (LACO-I-Neph) and enables measurement of spectral aerosol absorption from 200 nm to 2500 nm. The LACO-I-Neph measures the scattering phase function from 1.5° to 178.5° scattering angle with sufficient sensitivity to match theoretical expectations of Rayleigh scattering of various gases. Previous measurements either lack a sufficiently wide range of measured scattering angles or their sensitivity is too low and therefore the required sample amount is prohibitively high for in situ measurements. The LACO-I-Neph also returns expected characterization of the linear polarization signal of Rayleigh scattering. Previous work demonstrated the ability of measuring spectral absorption of aerosol particles using a reflectance technique characterization of aerosol samples collected on Nuclepore filters. This first generation methodology yielded absorption measurements from 350 nm to 2500 nm. Here we demonstrate the possibility of extending this wavelength range into the deep UV, to 200 nm. This extended UV region holds much promise in identifying and characterizing aerosol types and species. The second generation, deep UV, procedure requires careful choice of filter substrates. Here the choice of substrates is explored and preliminary results are provided.

Dolgos, Gergely; Martins, J. Vanderlei; Remer, Lorraine A.; Correia, Alexandre L.; Tabacniks, Manfredo; Lima, Adriana R.

2010-02-01

127

Hole-induced Dynamic Nuclear Polarization in Quantum Dots  

NASA Astrophysics Data System (ADS)

We present a microscopic theory showing that through the non- collinear hole-nuclear dipolar hyperfine interaction, an optically excited heavy hole in a quantum dot can induce a steady-state nuclear polarization. The preferential direction of the nuclear spin flip is set by the energy mismatch of relevant transitions instead of thermal relaxation. The induced nuclear polarization shows a sign dependence on the product of the nuclear Zeeman splitting and the frequency detuning of the pumping laser, leading to bidirectional hysteretic locking of the optical absorption peak onto resonance or bidirectional hysteretic shift of the peak away from zero detuning. This sheds light on a puzzling observation of bidirectional hysteretic locking of the neutral exciton absorption peak in Faraday geometry [C. Latta et al., Nature Phys. 5, 758 (2009)]. By solving the Fokker-Planck equation for the nuclear polarization distribution, we found a 10-fold suppression of the steady- state nuclear fluctuation, in reasonable agreement with the single pump experiment in Voigt geometry [X. Xu et al., Nature 459, 1105 (2009)].

Yang, Wen; Sham, L. J.

2011-03-01

128

Very-large-mode-area photonic bandgap Bragg fiber polarizing in a wide spectral range.  

PubMed

A design of a polarizing all-glass Bragg fiber with a microstructure core has been proposed for the first time. This design provides suppression of high-order modes and of one of the polarization states of the fundamental mode. The polarizing fiber was fabricated by a new, simple method based on a combination of the modified chemical vapor deposition (MCVD) process and the rod-in-tube technique. The mode field area has been found to be about 870 ?m² near ?=1064 nm. The polarization extinction ratio better than 13 dB has been observed over a 33% wavelength range (from 1 to 1.4 ?m) after propagation in a 1.7 m fiber piece bent to a radius of 70 cm. PMID:21931392

Aleshkina, Svetlana S; Likhachev, Mikhail E; Pryamikov, Andrey D; Gaponov, Dmitry A; Denisov, Alexandr N; Bubnov, Mikhail M; Salganskii, Mikhail Yu; Laptev, Alexandr Yu; Guryanov, Aleksei N; Uspenskii, Yurii A; Popov, Nikolay L; Février, Sébastien

2011-09-15

129

MAPPING THE LINEARLY POLARIZED SPECTRAL LINE EMISSION AROUND THE EVOLVED STAR IRC+10216  

SciTech Connect

We present spectro-polarimetric observations of several molecular lines obtained with the Submillimeter Array toward the carbon-rich asymptotic giant branch star IRC+10216. We have detected and mapped the linear polarization of the CO 3-2, SiS 19-18, and CS 7-6 lines. The polarization arises at a distance of {approx_equal} 450 AU from the star and is blueshifted with respect to the Stokes I. The SiS 19-18 polarization pattern appears to be consistent with a locally radial magnetic field configuration. However, the CO 3-2 and CS 7-6 line polarization suggests an overall complex magnetic field morphology within the envelope. This work demonstrates the feasibility of using spectro-polarimetric observations to carry out tomographic imaging of the magnetic field in circumstellar envelopes.

Girart, J. M. [Institut de Ciencies de l'Espai, (CSIC-IEEC), Campus UAB, Facultat de Ciencies, C5p 2, 08193 Bellaterra, Catalunya (Spain); Patel, N. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Vlemmings, W. H. T. [Department of Earth and Space Sciences, Chalmers University of Technology, Onsala Space Observatory, SE-439 92 Onsala (Sweden); Rao, Ramprasad, E-mail: girart@ice.cat [Submillimeter Array, Academia Sinica Institute of Astronomy and Astrophysics, 645 N. Aohoku Place, Hilo, HI 96720 (United States)

2012-05-20

130

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

NASA Astrophysics Data System (ADS)

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.

Tang, Yongan; Vlahovic, Branislav; Brady, David Jones

2011-05-01

131

Mapping the Linearly Polarized Spectral Line Emission around the Evolved Star IRC+10216  

NASA Astrophysics Data System (ADS)

We present spectro-polarimetric observations of several molecular lines obtained with the Submillimeter Array toward the carbon-rich asymptotic giant branch star IRC+10216. We have detected and mapped the linear polarization of the CO 3-2, SiS 19-18, and CS 7-6 lines. The polarization arises at a distance of ~= 450 AU from the star and is blueshifted with respect to the Stokes I. The SiS 19-18 polarization pattern appears to be consistent with a locally radial magnetic field configuration. However, the CO 3-2 and CS 7-6 line polarization suggests an overall complex magnetic field morphology within the envelope. This work demonstrates the feasibility of using spectro-polarimetric observations to carry out tomographic imaging of the magnetic field in circumstellar envelopes.

Girart, J. M.; Patel, N.; Vlemmings, W. H. T.; Rao, Ramprasad

2012-05-01

132

Dual-Polarization Spectral Analysis for Retrieval of Effective Raindrop Shapes  

Microsoft Academic Search

Dual-polarization radar observations of precipitation depend on size-shape relations of raindrops. There are several studies presented in literature dedicated to the investigation of this relation. In this work a new approach of investigating raindrop size-shape relation on short time and spatial scales from radar obser- vations is presented. The presented method is based on the use of dual-polarization Doppler power

D. N. Moisseev; V. Chandrasekar; C. M. H. Unal; H. W. J. Russchenberg

2006-01-01

133

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

134

Reduction of polarization-fluctuation induced drift in resonator fiber optic gyro by a resonator integrating in-line polarizers.  

PubMed

A method to decrease the polarization-fluctuation induced drift in a resonator fiber optic gyro (R-FOG) is demonstrated by inserting two in-line polarizers in a polarization-maintaining fiber resonator with twin 90° polarization-axis rotated splices. The in-line polarizers attenuate the unwanted resonance by introducing high loss for the unwanted eigenstates of polarization in the resonator. Compared to the resonator without in-line polarizers, the polarization-fluctuation induced drift is reduced by 6×10(3) times. The desired resonance in the resonator can keep excellent stability in a wide temperature range; thus the temperature-dependent polarization-fluctuation drift in the R-FOG is sufficiently suppressed. A typical bias stability of 4.7°/h over 6500 s with an integration time of 10 s has been carried out. To the best of our knowledge, the long-term bias stability and high temperature stability are the best ever demonstrated in an R-FOG. PMID:23381251

Ma, Huilian; Yu, Xuhui; Jin, Zhonghe

2012-08-15

135

High-resolution ultraviolet spectral irradiance monitoring program in polar regions - nearly a decade of data available to polar researchers in ozone and ultraviolet-related studies  

SciTech Connect

The Antarctic Ultraviolet Spectroradiometer Monitoring Network was established by the U.S. National Science Foundation (NSF) in 1988 in response to predictions of increased ultraviolet (UV) radiation in the polar regions. It is the first automated, high-resolution UV scanning spectroradiometer network installed in the world. The network consists of five automated, high-resolution spectroradiometers, placed in strategic locations in Antarctica and the Arctic, and one established in San Diego to collect data and serve as a training and testing facility. The network, which makes essential measurements of UV spectral irradiance, has been successfully operated in the harshest environments of Antarctica and the Arctic. It is currently returning data to researchers studying the effects of ozone depletion on terrestrial and marine biological systems, as well as being used to develop and verify models of atmospheric light transmission. 24 refs., 1 fig., 2 tabs.

Booth, C.R.; Lucas, T.B.; Mestechkina, T.; Tusson, J. IV [Biospherical Instruments Inc., San Diego, CA (United States)

1994-12-31

136

Polarization and incidence insensitive dielectric electromagnetically induced transparency metamaterial.  

PubMed

In this manuscript, we demonstrate numerically classical analogy of electromagnetically induced transparency (EIT) with a windmill type metamaterial consisting of two dumbbell dielectric resonator. With proper external excitation, dielectric resonators serve as EIT bright and dark elements via electric and magnetic Mie resonances, respectively. Rigorous numerical analyses reveal that dielectric metamaterial exhibits sharp transparency peak characterized by large group index due to the destructive interference between EIT bright and dark resonators. Furthermore, such EIT transmission behavior keeps stable property with respect to polarization and incidence angles. PMID:24105514

Zhang, Fuli; Zhao, Qian; Zhou, Ji; Wang, Shengxiang

2013-08-26

137

Polarization switching induced by phase change in extremely short external cavity vertical-cavity surface-emitting lasers  

Microsoft Academic Search

We experimentally investigate the spectral and polarization properties of vertical-cavity surface-emitting lasers (VCSELs) subject to polarization insensitive optical feedback from an extremely short external cavity (few microns) and find that the wavelength and the current at which the light polarization switches between the two linearly polarized fundamental modes of the VCSEL are periodically modulated with the length of the external

Krassimir Panajotov; Mikel Arizaleta; Miren Camarena; Hugo Thienpont; Heiko J. Unold; Johannes Michael Ostermann; Rainer Michalzik

2004-01-01

138

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

139

Black hole stereotyping: induced gravito-static polarization  

NASA Astrophysics Data System (ADS)

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.

Kol, Barak; Smolkin, Michael

2012-02-01

140

Fly Photoreceptors. II. Spectral and Polarized Light Sensitivity in the Drone Fly Eristalis  

Microsoft Academic Search

Eristalis tenax, the honeybee mimic, has photoreceptors mainly with double peaks as in typical flies, but the peaks are near 350 and 450 nm. Other cell types with peaks at 350 or 450 or 520 nm were encountered but not commonly. Measurements of the polarization sensitivity lead to the conclusion, as in Calliphora, that where there are two visual pigments

G. A. Horridge; K. Mimura; Y. Tsukahara

1975-01-01

141

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

142

Role of methyl-induced polarization in ion binding.  

PubMed

The chemical property of methyl groups that renders them indispensable to biomolecules is their hydrophobicity. Quantum mechanical studies undertaken here to understand the effect of point substitutions on potassium (K-) channels illustrate quantitatively how methyl-induced polarization also contributes to biomolecular function. K- channels regulate transmembrane salt concentration gradients by transporting K(+) ions selectively. One of the K(+) binding sites in the channel's selectivity filter, the S4 site, also binds Ba(2+) ions, which blocks K(+) transport. This inhibitory property of Ba(2+) ions has been vital in understanding K-channel mechanism. In most K-channels, the S4 site is composed of four threonine amino acids. The K channels that carry serine instead of threonine are significantly less susceptible to Ba(2+) block and have reduced stabilities. We find that these differences can be explained by the lower polarizability of serine compared with threonine, because serine carries one less branched methyl group than threonine. A T?S substitution in the S4 site reduces its polarizability, which, in turn, reduces ion binding by several kilocalories per mole. Although the loss in binding affinity is high for Ba(2+), the loss in K(+) binding affinity is also significant thermodynamically, which reduces channel stability. These results highlight, in general, how biomolecular function can rely on the polarization induced by methyl groups, especially those that are proximal to charged moieties, including ions, titratable amino acids, sulfates, phosphates, and nucleotides. PMID:23878238

Rossi, Mariana; Tkatchenko, Alexandre; Rempe, Susan B; Varma, Sameer

2013-07-22

143

Self-phase-modulation induced spectral broadening in silicon waveguides  

NASA Astrophysics Data System (ADS)

The prospect for generating supercontinuum pulses on a silicon chip is studied. Using ~4ps optical pulses with 2.2GW/cm2 peak power, a 2 fold spectral broadening is obtained. Theoretical calculations, that include the effect of two-photon-absorption, indicate up to 5 times spectral broadening is achievable at 10x higher peak powers. Representing a nonlinear loss mechanism at high intensities, TPA limits the maximum optical bandwidth that can be generated.

Boyraz, Ozdal; Indukuri, Tejaswi; Jalali, Bahram

2004-03-01

144

Spectral-mismatch-induced resolution limit of interferometric fiber Fabry–Perot sensor system  

Microsoft Academic Search

The mismatch of fiber Bragg gratings (FBGs) in spectral profiles can lead to a severe degraded resolution of the constructed fiber Fabry–Perot (FFP) sensor system through its effect on the fringe visibility. The variation of visibility induced by spectral mismatch and the corresponding phase resolution limit are analyzed theoretically and experimentally. Theoretical analyses are based on the approximation of Gaussian

Siliang Niu; Lina Ma; Shuidong Xiong; Yongming Hu

2011-01-01

145

Polarized spectral properties of Nd3+ ions in CaYAlO4 crystal  

NASA Astrophysics Data System (ADS)

Nd:CaYAlO4 single crystal has been grown by the Czochralski technique. The cell parameters were analyzed with X-ray diffraction (XRD). The polarized absorption spectra, the polarized fluorescence spectra, and the fluorescence decay curve of the crystal were measured at room temperature. The spectroscopic parameters were determined by Judd-Ofelt theory and Fuchtbauer-Ladenburg formula. The effective intensity parameters ? 2, ? 4, and ? 6 were obtained to be 2.19, 8.16, and 8.57×10-20 cm2, respectively. The calculated radiative probabilities, branching ratios, and radiative lifetime were also evaluated for the 4F3/2 excited state using the calculated intensity parameters. The results indicate Nd:CaYAlO4 has potential as a laser gain medium for ultrashort laser system.

Li, D. Z.; Xu, X. D.; Cheng, S. S.; Zhou, D. H.; Wu, F.; Zhao, Z. W.; Xia, C. T.; Xu, J.; Zhang, J.; Zhu, H. M.; Chen, X. Y.

2010-10-01

146

Orthogonal polarization spectral (OPS) imaging: a new technique for the visualization and study of microcirculation  

NASA Astrophysics Data System (ADS)

OPS-imaging is a novel technique which can be used to obtain images of the microcirculation using reflected light. High contrast transillumination quality images can be collected not only from thin tissues, but from the surface of solid organs as well. In OPS-imaging the tissue is illuminated with light that has been linearly polarized in one plane. The light is then both scattered and reflected by the tissue. In front of the camera there is a second polarizer which is oriented in a plane precisely orthogonal to that of the illuminating light. This means that light which is directly reflected by the tissue, which maintains its polarization, is rejected by the polarizer in front of the camera. The only light which enters the camera and forms the image is light which has become depolarized, which typically requires at least 10 scattering events. Thus, the light which forms the image comes from deep (0.5 mm) within the tissue and effectively back-illuminates the absorbing material in the foreground. When the light has a wavelength within the hemoglobin absorption spectrum (548 nm), the scattered light is absorbed by the hemoglobin in the red cells, making it possible to visualize the blood vessels as in transillumination intravital microscopy. Thus, images of the microcirculation of solid organs can be obtained without the use of fluorescent dyes. OPS-imaging has been incorporated into a small, hand held device which is easily transportable (CYTOSCAN). Because of these two advantages, it is possible to not only use OPS-imaging in the laboratory, but also in the clinic on patients.

Harris, A. G.; Sinitsina, I.; Pahernik, S.; Langer, S.; von Dobschuetz, E.; Biberthaler, P.; Uhl, E.; Genzel, O.; Messmer, K.

2001-05-01

147

Digital dispersion compensation for ultrabroad-bandwidth single-camera spectral-domain polarization-sensitive OCT  

NASA Astrophysics Data System (ADS)

Polarization-sensitive OCT is used to examine tissue microstructure by providing imaging of birefringent properties. Single-camera spectral-domain polarization-sensitive OCT has been of recent interest, whereby a custom spectrometer is employed to simultaneously measure orthogonal polarization states scattered from the sample. This avoids synchronization and triggering issues associated with multiple-camera setups. It also has the advantage that the optic axis can be extracted without polarization modulating the incident light. However, the disadvantage is that the line camera pixel-to-wavenumber nonlinearity requires either careful spectrometer alignment, or digital compensation. In fact, this problem is further exacerbated in high resolution PSOCT systems as they require compensation over larger bandwidths. Here we report the construction of an ultrabroad-bandwidth PSOCT system using a single camera spectrometer similar to Baumann et al. In order to enjoy the benefits of this instrument, we outline a method for digital dispersion compensation that removes the necessity for special camera alignment. We find that there are three non-negligible types of dispersion to consider: 1) the aforementioned camera pixel-to-wavenumber nonlinearity, 2) the refractive index dispersion in the sample itself, and 3) the dispersion imbalance between the arms of the OCT interferometer. The latter two were previously recognized for time-domain high-resolution OCT, where a digital dispersion compensation method was successfully employed to treat them both. For our SDOCT application, we find that dispersion types 1 and 2 have the same functional effect and can be combined into one compensation step, and as such, much of the previous compensation method can be used. However, we find that it is necessary to add two steps to the analysis technique whereby the relative scaling and positioning of the two polarization images is adjusted to align the scatterers. We also find that better results are achieved by fitting to larger polynomial orders. We show how our technique provides high-resolution PSOCT with precise alignment between the orthogonal polarization images.

Oldenburg, Amy L.; Chhetri, Raghav K.

2011-02-01

148

Darkfield orthogonal polarized spectral imaging for studying endovascular laser-tissue interactions in vivo a preliminary study  

NASA Astrophysics Data System (ADS)

Due to the limited number of suitable intravital microscopy techniques, relatively little is known about the opto-thermal (endo)vascular responses to selective photothermolysis, used as a default treatment modality for superficial vascular anomalies such as port wine stains, telangiectasias, and hemangiomas. In this preliminary study we present a novel microscopy technique for studying (endo)vascular laser-tissue interactions in vivo, in which conventional orthogonal polarized spectral (OPS) imaging is combined with darkfield (DF) illumination. DFOPS imaging of rat mesenteric vasculature irradiated at increasing powers revealed the following (tissular) responses: formation of translucent aggregates, retrograde flow, gradual and immediate hemostasis, reinstatement of flow, vessel disappearance, and perivascular collagen damage. DFOPS imaging therefore constitutes a useful tool for examining (endo)vascular events following selective photothermolysis.

Heger, Michal; Beek, Johan F.; Stenback, Karin; Faber, Dirk J.; van Gemert, Martin J. C.; Ince, Can

2005-02-01

149

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

150

Polar behaviour induced by lithium in potassium tantalate ceramics  

NASA Astrophysics Data System (ADS)

Polar behaviour in K1-xLixTaO3 ceramics with x = 0.02, 0.05 and 0.10, processed by the conventional solid state method, is studied by Raman spectroscopy and thermally stimulated depolarization current (TSDC) techniques between 10 and 290 K. The TO1 mode of KTaO3 is revealed to harden in the whole temperature range and to split in the low-temperature range by Li doping. One splitting is observed for x = 0.02 and two consequent splittings are detected for x = 0.05 and 0.10. The temperatures, where TO1 mode splitting occurs, are found to correspond to those of the peaks of TSDC, and hence to the onset of the electric polarization. Such behaviour provides evidence for the order-disorder ferroelectric phase transition induced in KTaO3 by lithium doping, which emerges from deformations of the cubic phase developed on cooling either in one (for x = 0.02) or two steps (for x = 0.05 and 0.10).

Tkach, A.; Almeida, A.; Agostinho Moreira, J.; Chaves, M. R.; Espinha, A.; Vilarinho, P. M.

2012-02-01

151

Polar behaviour induced by lithium in potassium tantalate ceramics.  

PubMed

Polar behaviour in K(1-x)Li(x)TaO(3) ceramics with x = 0:02, 0.05 and 0.10, processed by the conventional solid state method, is studied by Raman spectroscopy and thermally stimulated depolarization current (TSDC) techniques between 10 and 290 K. The TO1 mode of KTaO(3) is revealed to harden in the whole temperature range and to split in the low-temperature range by Li doping. One splitting is observed for x = 0:02 and two consequent splittings are detected for x = 0:05 and 0.10. The temperatures, where TO1 mode splitting occurs, are found to correspond to those of the peaks of TSDC, and hence to the onset of the electric polarization. Such behaviour provides evidence for the order-disorder ferroelectric phase transition induced in KTaO(3) by lithium doping, which emerges from deformations of the cubic phase developed on cooling either in one (for x = 0:02) or two steps (for x = 0:05 and 0.10). PMID:22223586

Tkach, A; Almeida, A; Moreira, J Agostinho; Chaves, M R; Espinha, A; Vilarinho, P M

2012-02-01

152

Fluorescence in situ hybridization and spectral imaging analysisof human oocytes and first polar bodies  

SciTech Connect

We investigated the frequencies of abnormalities involving either chromosome 1, 16, 18 or 21 in failed-fertilized human oocytes.While abnormalities involving chromosome 16 showed an age-dependant increase, results for the other chromosomes did not show statistically significant differences between the three age groups <35 yrs, 35-39 yrs, and >39 yrs. The scoring of four chromosomes is likely to underestimate the true rate of aneuploid cells. Thus, for a pilot study investigating a more comprehensive analysis of oocytes and their corresponding first polar bodies (1PBs), we developed a novel 8-probe chromosome enumeration scheme using FISH and SIm.

Weier, Heinz-Ulli G.; Weier, Jingly F.; Oter Renom, Maria; Zheng,Xuezhong; Colls, Pere; Nureddin, Aida; Pham, Chau D.; Chu, Lisa W.; Racowsky, Catherine; Munne, Santiago

2004-10-06

153

Obesity induces a phenotypic switch in adipose tissue macrophage polarization.  

PubMed

Adipose tissue macrophages (ATMs) infiltrate adipose tissue during obesity and contribute to insulin resistance. We hypothesized that macrophages migrating to adipose tissue upon high-fat feeding may differ from those that reside there under normal diet conditions. To this end, we found a novel F4/80(+)CD11c(+) population of ATMs in adipose tissue of obese mice that was not seen in lean mice. ATMs from lean mice expressed many genes characteristic of M2 or "alternatively activated" macrophages, including Ym1, arginase 1, and Il10. Diet-induced obesity decreased expression of these genes in ATMs while increasing expression of genes such as those encoding TNF-alpha and iNOS that are characteristic of M1 or "classically activated" macrophages. Interestingly, ATMs from obese C-C motif chemokine receptor 2-KO (Ccr2-KO) mice express M2 markers at levels similar to those from lean mice. The antiinflammatory cytokine IL-10, which was overexpressed in ATMs from lean mice, protected adipocytes from TNF-alpha-induced insulin resistance. Thus, diet-induced obesity leads to a shift in the activation state of ATMs from an M2-polarized state in lean animals that may protect adipocytes from inflammation to an M1 proinflammatory state that contributes to insulin resistance. PMID:17200717

Lumeng, Carey N; Bodzin, Jennifer L; Saltiel, Alan R

2007-01-01

154

Interaction-induced spin polarization in quantum dots.  

PubMed

The electronic states of lateral many-electron quantum dots in high magnetic fields are analyzed in terms of energy and spin. In a regime with two Landau levels in the dot, several Coulomb-blockade peaks are measured. A zigzag pattern is found as it is known from the Fock-Darwin spectrum. However, only data from Landau level 0 show the typical spin-induced bimodality, whereas features from Landau level 1 cannot be explained with the Fock-Darwin picture. Instead, by including the interaction effects within spin-density-functional theory a good agreement between experiment and theory is obtained. The absence of bimodality on Landau level 1 is found to be due to strong spin polarization. PMID:20867873

Rogge, M C; Räsänen, E; Haug, R J

2010-07-20

155

Interaction-Induced Spin Polarization in Quantum Dots  

NASA Astrophysics Data System (ADS)

The electronic states of lateral many-electron quantum dots in high magnetic fields are analyzed in terms of energy and spin. In a regime with two Landau levels in the dot, several Coulomb-blockade peaks are measured. A zigzag pattern is found as it is known from the Fock-Darwin spectrum. However, only data from Landau level 0 show the typical spin-induced bimodality, whereas features from Landau level 1 cannot be explained with the Fock-Darwin picture. Instead, by including the interaction effects within spin-density-functional theory a good agreement between experiment and theory is obtained. The absence of bimodality on Landau level 1 is found to be due to strong spin polarization.

Rogge, M. C.; Räsänen, E.; Haug, R. J.

2010-07-01

156

Polarization rotation and field induced phase transition in PZN-4.5%PT single crystal  

NASA Astrophysics Data System (ADS)

We have investigated both the polarization rotations and the field induced phase transitions in [100], [110], and [111]-oriented PZN-4.5%PT single crystals on the basis of the single domain polarization rotation model. The dependence of the polarization, the electrostrictive response, and the lattice parameters in ferroelectric crystals on the field has been numerically obtained. The numerical results, in agreement with the experimental data, have shown that the polarization rotation is strongly dependent on the initial polarization state and polarization history in the single crystals, and the rhombohedral-monoclinic-tetragonal phase transitions occur for E//[100].

Zhang, Hui

2013-08-01

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

Growth-induced polarity formation in two-component crystals of organic molecules: A statistical analysis  

Microsoft Academic Search

On the basis of a layer-by-layer growth model, growth-induced polarity formation is investigated in two-component crystals (solid solutions) of polar H (host) and non-polar G (guest) or polar H and G molecules, with native H and G crystals being assumed centrosymmetric. These two types of chemical systems are compared with one another in terms of a statistical analysis being comprised

Thomas Wüst; Jürg Hulliger

2006-01-01

159

Spectral modifications and polarization dependent coupling in tailored assemblies of quantum dots and plasmonic nanowires.  

PubMed

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

Gruber, Christian; Trügler, Andreas; Hohenau, Andreas; Hohenester, Ulrich; Krenn, Joachim R

2013-08-26

160

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.

2013-01-01

161

Self-induced spectral splits in supernova neutrino fluxes  

Microsoft Academic Search

In the dense-neutrino region above the neutrino sphere of a supernova (r≲400km), neutrino-neutrino refraction causes collective flavor transformations. They can lead to ``spectral splits'' where an energy Esplit splits the transformed spectrum sharply into parts of almost pure but different flavors. Unless there is an ordinary MSW resonance in the dense-neutrino region, Esplit is determined by flavor-lepton number conservation alone.

Georg G. Raffelt; Alexei Yu. Smirnov

2007-01-01

162

Spectral evolution and polarization of variable structures in the pulsar wind nebula of PSR B0540-69.3  

NASA Astrophysics Data System (ADS)

We present high spatial resolution optical imaging and polarization observations of the PSR B0540-69.3 and its highly dynamical pulsar wind nebula (PWN) performed with Hubble Space Telescope, and compare them with X-ray data obtained with the Chandra X-ray Observatory. In particular, we have studied the bright region south-west of the pulsar where a bright 'blob' is seen in 1999. In a recent paper by De Luca et al. it was argued that the 'blob' moves away from the pulsar at high speed. We show that it may instead be a result of local energy deposition around 1999, and that the emission from this then faded away rather than moved outward. Polarization data from 2007 show that the polarization properties show dramatic spatial variations at the 1999 blob position arguing for a local process. Several other positions along the pulsar-'blob' orientation show similar changes in polarization, indicating previous recent local energy depositions. In X-rays, the spectrum steepens away from the 'blob' position, faster orthogonal to the pulsar-'blob' direction than along this axis of orientation. This could indicate that the pulsar-'blob' orientation is an axis along where energy in the PWN is mainly injected, and that this is then mediated to the filaments in the PWN by shocks. We highlight this by constructing an [S II]-to-[O III]-ratio map, and comparing this to optical continuum and X-ray emission maps. We argue, through modelling, that the high [S II]/[O III] ratio is not due to time-dependent photoionization caused by possible rapid X-ray emission variations in the 'blob' region. We have also created a multiwavelength energy spectrum for the 'blob' position showing that one can, to within 2?, connect the optical and X-ray emission by a single power law. The slope of that power law (defined from ?) would be ??= 0.74 ± 0.03, which is marginally different from the X-ray spectral slope alone with ??= 0.65 ± 0.03. A single power law for most of the PWN is, however, not be possible. We obtain best power-law fits for the X-ray spectrum if we include 'extra' oxygen, in addition to the oxygen column density in the interstellar gas of the Large Magellanic Cloud and the Milky Way. This oxygen is most naturally explained by the oxygen-rich ejecta of the supernova remnant. The oxygen needed likely places the progenitor mass in the 20-25 M? range, i.e. in the upper mass range for progenitors of Type IIP supernovae.

Lundqvist, N.; Lundqvist, P.; Björnsson, C.-I.; Olofsson, G.; Pires, S.; Shibanov, Yu. A.; Zyuzin, D. A.

2011-05-01

163

Reduction of polarization-fluctuation induced drift in resonator fiber optic gyro by a resonator with twin 90 degrees polarization-axis rotated splices.  

PubMed

A method to suppress polarization-fluctuation induced drift in resonator fiber optic gyro (R-FOG) is demonstrated by a polarization-maintaining fiber (PMF) resonator with twin 90 degrees polarization-axis rotated splices. By setting the length difference of the fiber segments between two 90 degrees polarization-axis rotated splicing points to a half of the beat-length of the fiber, a single eigen-state of polarization (ESOP) is excited with incident lightwave linearly polarized along the polarization-axis of the fiber. Compared to the previously reported resonator employing single 90 degrees polarization-axis rotated splice [1], in which two ESOPs are excited, our new scheme avoids the effect from the unwanted ESOP and thus suppresses the polarization-fluctuation induced drift in R-FOG output significantly. PMID:20173995

Wang, Xijing; He, Zuyuan; Hotate, Kazuo

2010-01-18

164

Thermally induced spin polarization of a two-dimensional electron gas  

NASA Astrophysics Data System (ADS)

Spin polarization of a two-dimensional electron gas with Rashba spin-orbit interaction, induced by a thermo-current, is considered theoretically. It is shown that a temperature gradient gives rise to an in-plane spin polarization of the electron gas, which is normal to the temperature gradient. The low-temperature spin polarization changes sign when the Fermi level crosses the bottom edge of the upper electronic subband. We also compare the results with spin polarization induced by an external electric field (current).

Dyrda?, A.; Inglot, M.; Dugaev, V. K.; Barna?, J.

2013-06-01

165

Integrin-Induced PIP5K1C Kinase Polarization Regulates Neutrophil Polarization, Directionality, and in vivo Infiltration  

PubMed Central

Neutrophils are important in innate immunity and acute inflammatory responses. However, the regulation of their recruitment to sites of inflammation has not been well characterized. Here, we investigated the kinase PIP5K1C and showed that PIP5K1C-deficiency impaired neutrophil recruitment due to an adhesion defect. PIP5K1C regulated the adhesion through facilitating RhoA GTPase and integrin activation by chemoattractants. Integrins could induce an isoform of PIP5K1C, PIP5K1C-90, polarization in neutrophils through intracellular vesicle transport independently of exogenous chemoattractant. PIP5K1C-90 polarization was required for polarized RhoA activation at uropods and provided an initial directional cue for neutrophil polarization on the endothelium. Importantly, the polarization was also required for circumventing the inhibition of lamellipodium formation by RhoA so that neutrophils could form leading edges required for transendothelial migration. Because integrins are not known to regulate neutrophil polarization, our study revealed a previously underappreciated role of integrin signaling in neutrophil regulation.

Xu, Wenwen; Wang, Ping; Petri, Bjorn; Zhang, Yong; Tang, Wenwen; Sun, Le; Kress, Holger; Mann, Tom; Shi, Yan; Kubes, Paul; Wu, Dianqing

2010-01-01

166

Solvent polarity-induced conformational unlocking of asparagine.  

PubMed

Classical and Car-Parrinello molecular dynamics simulations are performed to study the solvent effect on the conformational distribution of asparagine. Conformational populations obtained from the simulations in gas phase and in nonpolar chloroform solvent are in agreement with the most probable single conformation of asparagine in the gas phase measured in recent laser ablation with molecular beam Fourier transform microwave spectroscopy experiments. We rationalize that intramolecular hydrogen bonding and dipole-dipole interactions between carbonyl groups dictate such a conformational locking to a single asparagine conformer. The solvent polarity induced interlocking or intermolecular hydrogen bonding with water solvent molecules destabilizes the (NH···O?C) bonding between side chain and terminal groups of asparagine, while not essentially affecting the (NH···O?C) intramolecular hydrogen bondings within the side chain nor within the terminal groups. Such a conformational unlocking or cage effect is observed in asparagine within aqueous solution. We observed a spontaneous conversion of neutral to zwitterionic isomer of asparagine in aqueous solution, which is in agreement with interpretation of Raman spectroscopy results. Using Møller-Plesset second order perturbation theory, we show that a tautomeric shift from neutral to zwitterionic occurs on asparagine in between DMSO and water solvents. The ramification of these findings for the conformational character of asparagine is briefly discussed. PMID:23110399

Selvaraj, Ananda Rama Krishnan; Murugan, N Arul; Ågren, Hans

2012-11-13

167

High-speed spectral domain polarization-sensitive OCT using a single InGaAs line-scan camera and an optical switch  

NASA Astrophysics Data System (ADS)

We demonstrated high-speed spectral domain polarization-sensitive optical coherence tomography (SD-PSOCT) using a single InGaAs line-scan camera and an optical switch at 1.3-?m region. The polarization-sensitive low coherence interferometer in the system was based on the original free-space PS-OCT system published by Hee et al. The horizontal and vertical polarization light rays split by polarization beam splitter were delivered and detected via an optical switch to a single spectrometer by turns instead of dual spectrometers. The SD-PSOCT system had an axial resolution of 8.2 ?m, a sensitivity of 101.5 dB, and an acquisition speed of 23,496 Alines/s. We obtained the intensity, phase retardation, and fast axis orientation images of a biological tissue. In addition, we calculated the averaged axial profiles of the phase retardation in human skin.

Lee, Sang-Won; Jeong, Hyun-Woo; Kim, Beop-Min

2010-02-01

168

A new strategy for in vivo spectral editing. Application to GABA editing using selective homonuclear polarization transfer spectroscopy  

NASA Astrophysics Data System (ADS)

A novel single-shot in vivo spectral editing method is proposed in which the signal to be detected, is regenerated anew from the thermal equilibrium magnetization of a source to which it is J-coupled. The thermal equilibrium magnetization of the signal to be detected together with those of overlapping signals are suppressed by single-shot gradient dephasing prior to the signal regeneration process. Application of this new strategy to in vivo GABA editing using selective homonuclear polarization transfer allows complete suppression of overlapping creatine and glutathione while detecting the GABA-4 methylene resonance at 3.02 ppm with an editing yield similar to that of conventional editing methods. The NAA methyl group at 2.02 ppm was simultaneously detected and can be used as an internal navigator echo for correcting the zero order phase and frequency shifts and as an internal reference for concentration. This new method has been demonstrated for robust in vivo GABA editing in the rat brain and for study of GABA synthesis after acute vigabatrin administration.

Shen, Jun; Yang, Jehoon; Choi, In-Young; Li, Shizhe Steve; Chen, Zhengguang

2004-10-01

169

Polarization in Perovskite Manganites induced by Shear Stress  

NASA Astrophysics Data System (ADS)

We found static polarization in perovskite manganite films when they are under shear stress. The phenomenon is omnipresent in films deformed in (at least) monoclinic fashion due to the substrate-imposed strain, whereas it is absent in bulk crystals even though they are distorted in a similar manner in thermal equilibrium. The substrate stress of low symmetry is clearly the driving force for the appearance of the polarization. Optical second-harmonic generation (SHG) confirms the loss of inversion symmetry in strained films and pyroelectricity was detected in insulating films confirming the presence of the static polarization. DFT calculations show that the stable atomic positions in the experimentally observed structure is polar with the shift of the center of gravity of anions relative to that of cations as much as 10-2 å. The calculated polar structure is consistent with the symmetry obtained from the SHG polarimetry.

Miyano, K.; Ogawa, N.; Ida, Y.; Tamaki, R.; Shimizu, K.; Nomura, Y.; Arita, R.; Ogimoto, Y.

2012-02-01

170

Spectral-mismatch-induced resolution limit of interferometric fiber Fabry-Perot sensor system  

NASA Astrophysics Data System (ADS)

The mismatch of fiber Bragg gratings (FBGs) in spectral profiles can lead to a severe degraded resolution of the constructed fiber Fabry-Perot (FFP) sensor system through its effect on the fringe visibility. The variation of visibility induced by spectral mismatch and the corresponding phase resolution limit are analyzed theoretically and experimentally. Theoretical analyses are based on the approximation of Gaussian profiles to the reflection spectra of weak FBGs, especially with consideration of side lobes. The investigation provides an insight into the evolution of the fringe visibility caused by spectral mismatch, and shows good agreement with experimental results. An optimum phase resolution of about 55 ?rad/Hz1/2 above 100 Hz is achieved for a nearly 4 m-long FFP sensor by matching spectral profiles of the gratings and balancing path length differences of the tandem interferometers.

Niu, Siliang; Ma, Lina; Xiong, Shuidong; Hu, Yongming

2011-12-01

171

Large ferroelectric polarization in the new double perovskite NaLaMnWO6 induced by non-polar instabilities.  

PubMed

Based on density functional theory calculations and group theoretical analysis, we have studied NaLaMnWO(6) compound which has been recently synthesized [G. King, A. Wills and P. M. Woodward, Phys. Rev. B: Condens. Matter, 2009, 79, 224428] and belongs to the AA'BB'O(6) family of double perovskites. At low temperature, the structure has monoclinic P2(1) symmetry, with layered ordering of the Na and La ions and rocksalt ordering of Mn and W ions. The Mn atoms show an antiferromagnetic collinear spin ordering, and the compound has been reported as a potential multiferroic. By comparing the low symmetry structure with a parent phase of P4/nmm symmetry, two distortion modes are found dominant. They correspond to MnO(6) and WO(6) octahedron tilt modes, often found in many simple perovskites. While in the latter these common tilting instabilities yield non-polar phases, in NaLaMnWO(6) the additional presence of the A-A' cation ordering is sufficient to make these rigid unit modes a source of the ferroelectricity. Through a trilinear coupling with the two unstable tilting modes, a polar distortion is induced, although the system has no intrinsic polar instability. The calculated electric polarization resulting from this polar distortion is as large as ?16 ?C cm(-2). Despite its secondary character, this polarization is coupled with the dominant tilting modes and its switching is bound to produce the switching of one of two tilts, enhancing in this way a possible interaction with the magnetic ordering. The transformation of common non-polar purely steric instabilities into sources of ferroelectricity through a controlled modification of the parent structure, as done here by the cation ordering, is a phenomenon to be further explored. PMID:21647478

Fukushima, T; Stroppa, A; Picozzi, S; Perez-Mato, J M

2011-06-06

172

Large ferroelectric polarization in the new double perovskite NaLaMnWO6 induced by non-polar instabilities  

NASA Astrophysics Data System (ADS)

Based on density functional theory and group theoretical analysis, we have studied NaLaMnWO6 compound. At low temperature, the structure has monoclinic P21 symmetry, with layered ordering of the Na and La ions and rocksalt ordering of Mn and W ions. By comparing the low symmetry structure with a parent phase of P4/nmm symmetry, two distortion modes are found dominant. They correspond to MnO6 and WO6 octahedron tilt modes, often found in many simple perovskites. While in the latter these common tilting instabilities yield non-polar phases, in NaLaMnWO6 the additional presence of the Na-La cation ordering is sufficient to make these rigid unit modes a source of the ferroelectricity. Through a trilinear coupling with the two unstable tilting modes, a polar distortion is induced, although the system has no intrinsic polar instability. The calculated electric polarization is as large as 16 ?C/cm^2. Despite its secondary character, this polarization is coupled with the dominant tilting modes and its switching is bound to produce the switching of one of two tilts, enhancing in this way a possible interaction with the magnetic ordering.

Fukushima, Tetsuya; Stroppa, Alessandro; Picozzi, Silvia; Perez-Mato, J. Manuel

2012-02-01

173

Polar auxin transport and auxin-induced elongation in the absence of cytoplasmic streaming  

Microsoft Academic Search

When cytoplasmie streaming in oat and maize coleoptile cells is completely inhibited by cytochalasin B (CB), polar transport of auxin (indole-3-acetic acid) continues at a slightly reduced rate. Therefore, cytoplasmic streaming is not required for polar transport. Auxin induces elongation in CB-inhibited coleoptile and pea stem segments, but elongation rate is reduced about 40% by CB. Therefore, stimulation of cytoplasmic

W. Z. Cande; Mary Helen M. Goldsmith; P. M. Ray

1973-01-01

174

Spectrally resolved laser-induced fluorescence for bioaerosols standoff detection  

Microsoft Academic Search

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

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

2007-01-01

175

The dependence of induced polarization on natural iron concentration in wetland soils  

NASA Astrophysics Data System (ADS)

Spectral Induced polarization (SIP) measurements in the frequency range 0.1-1000 Hz were conducted on clay and peat marsh soils, obtained from a contaminated freshwater weltand in New Jersey, that were subsequently analyzed for heavy metal concentrations, moisture content, organic matter, porosity, specific surface area, and pore fluid conductivity. A Cole-Cole relaxation model was fit to each of the samples and the model parameters analyzed in terms of the measured physiochemical properties. A linear relationship between the normalized chargeability (mn) and the estimated surface area to pore volume (Sp) is found when the iron content (ranging from 0.25 to 1.63 percent by volume between samples) is accounted for as a polarizable element of the soil. In fact, the dependence of mn on volumetric Fe concentration per unit volume of the bulk soil is described by a linear relationship with a correlation coefficient of 0.94. As the Fe concentration of soils is a critical biogeochemical parameter, these results suggest that SIP measurements may provide a hitherto unrecognized approach to probing soil geochemistry, iron cycling and anaerobic microbial activity. Furthermore, our results yield new insight into the physiochemical controls on SIP in natural, unconsolidated soils.

Slater, L. D.; Mansoor, N.

2006-12-01

176

Energy Conservation with Partially Coherent Sources Which Induce Spectral Changes in Emitted Radiation  

Microsoft Academic Search

Some questions are examined that have been raised in connection with the recently discovered phenomenon of spectral changes induced by the state of coherence of sources. It is shown that even though the spectrum of light changes on propagation in free space, there is no violation of the law of conservation of energy throughout the space outside the source region

Emil Wolf; Avshalom Gamliel

1992-01-01

177

Light-Induced Polar pH Changes in Leaves of Elodea canadensis1  

PubMed Central

The effect of an extracellular electron acceptor, ferricyanide, on the light-induced polar leaf pH changes of the submerged angiosperm Elodea canadensis in light and in darkness was determined. The rate of transmembrane ferricyanide reduction was stimulated by increased light intensity and was inhibited by inorganic carbon, indicating that changes in the redox state of the chloroplast were reflected at the plasma membrane. The addition of ferricyanide inhibited the light-induced polar leaf pH reaction. This effect could be balanced by increasing the light intensity. In the dark, the acidification induced by ferricyanide was not influenced by diethylstilbestrol at concentrations that completely inhibited the polar leaf pH changes. This indicates that the ferricyanide-induced H+ extrusion and the H+ transport during the polar reaction were mediated by different mechanisms.

Elzenga, J. Theo M.; Prins, Hidde B. A.

1989-01-01

178

Spin-Exchange-Induced Circularly-Polarized Molecular Fluorescence  

NASA Astrophysics Data System (ADS)

We have measured the circular polarization of light emitted from both atomic H and molecular H2 after bombarding H2 with longitudinally polarized electrons [1]. For both atomic and molecular fluorescence near threshold we observe a circular polarization as great as 10electron polarization. Such polarization is comparable to that observed with alkali targets [2], and represents the first direct observation of spin transfer in electron-molecule collisions. Earlier experiments involving the scattering of polarized electrons by heavier (NO, O_2, N_2) molecules failed to observe significant exchange effects [2-4]. Possible explanations for the observation of such effects in H2 will be reviewed. [1] A.S.Green, G.A.Gallup, M.A.Rosenberry, and T.J.Gay, Phys. Rev. Lett. in press. [2] C P. Na?, M. Eller, N. Ludwig, E. Reichert, and M. Webersinke, Z. Phys. D 11,71 (1989). [3] T. Hegemann, M. Oberste-Vorth, R. Vogts, and G.F. Hanne, Phys. Rev. Lett.66,2968 (1991). [4] J.M. Ratliff, G.H. Rutherford, F.B. Dunning, G.K. Walters, Phys. Rev. A39,5584 (1989).

Gay, T. J.

2004-05-01

179

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

NASA Astrophysics Data System (ADS)

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 to the a direction has been observed when a magnetic field above 10 T is applied along the b axis. This result demonstrates that an electric polarization flop can be induced by a magnetic field in a simple system without rare-earth 4f moments.

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

2006-09-01

180

Acoustical phonon induced and polaron induced modulational amplification in polar semiconductors: a comparative study  

NASA Astrophysics Data System (ADS)

The paper aims to comparatively study the amplification and excitation characteristics of polaron induced and acoustical phonon induced modulators. Based on the hydrodynamic model, an analytical investigation of frequency modulational interaction is made. An explicit expression for the growth rate and threshold electric field for the onset of the acoustic phonon driven and polaron driven instability is presented and analyzed analytically. We have numerically investigated the dependence of the threshold electric field for different values of the external parameters of a typical polar semiconductor (InSb) and have given a numerical estimation of the growth rate. We also found that the amplification coefficient in polaron induced modulation enhances by a factor of 10 as compared to acoustical phonon induced modulation; though polaron induced modulational instability occurs at a lower threshold than acoustical phonon induced modulational instability. The cyclotron frequency can be used as a control parameter to reduce thresholds and improve growth rates. These results could be important for understanding and improving the performance of modulators. It is hoped that a low cost modulator using the n-InSb–CO2 system can be fabricated as the outcome of this work.

Agrawal, R.; Dubey, S.; Ghosh, S.

2013-10-01

181

Microtubule-Induced Pins\\/G?i Cortical Polarity in Drosophila Neuroblasts  

Microsoft Academic Search

SUMMARY Cortical polarity regulates cell division, mi- gration, and differentiation. Microtubules induce cortical polarity in yeast, but few ex- amples are known in metazoans. We show that astral microtubules, kinesin Khc-73, and Discs large (Dlg) induce cortical polari- zation of Pins\\/Ga ii nDrosophila neuro- blasts; this cortical domain is functional for generating spindle asymmetry, daughter- cell-size asymmetry, and distinct sibling

Sarah E. Siegrist; Chris Q. Doe

2005-01-01

182

Polarization, temporal, and spectral parameters of solar flare hard X-rays as measured by the SPR-N instrument onboard the CORONAS-F satellite  

NASA Astrophysics Data System (ADS)

The SPR-N polarimeter onboard the CORONAS-F satellite allows the X-ray polarization degree to be measured in energy ranges of 20 40, 40 60, and 60 100 keV. To measure the polarization, the method based on the Thompson scattering of solar X-ray photons in beryllium plates was used; the scattered photons were detected with a system of six CsI(Na) scintillation sensors. During the observation period from August 2001 to January 2005, the SPR-N instrument detected the hard X-rays of more than 90 solar flares. The October 29, 2003, event showed a significant polarization degree exceeding 70% in channels of E = 40 60 and 60 100 keV and about 50% in the 20-to 40-keV channel. The time profile of the polarization degree and the projection of the polarization plane onto the solar disk were determined. For 25 events, the upper limits of the part of polarized X-rays were estimated at 8 to 40%. For all the flares detected, time profiles (with a resolution of up to 4 s), hard X-ray radiation fluxes, and spectral index estimates were obtained.

Zhitnik, I. A.; Logachev, Yu. I.; Bogomolov, A. V.; Denisov, Yu. I.; Kavanosyan, S. S.; Kuznetsov, S. N.; Morozov, O. V.; Myagkova, I. N.; Svertilov, S. I.; Ignat'ev, A. P.; Oparin, S. N.; Pertsov, A. A.; Tindo, I. P.

2006-03-01

183

Microwave polarization study of radiation-induced magneto-resistance oscillations  

NASA Astrophysics Data System (ADS)

Under microwave irradiation, high mobility GaAs/AlGaAs samples display radiation-induced magnetoresistance oscillations and zero resistance states. These novel phenomena have attracted significant theoretical and experimental efforts over the last few years. Here, we experimentally investigate the effect of polarization direction for linearly polarized microwaves on the radiation induced magnetoresistance oscillations. Previous investigations suggest the independence of the oscillations on the polarization direction in consistency with theoretical predictions (Jes'us Iñarrea and Gloria Platero, PRB 76, 073311 (2007)). Here, we present the results of our study and discuss the implications of the results for existing theoretical models.

Ghanem, Tarek; Mani, R. G.; Wegscheider, W.

2010-03-01

184

Field-induced strain associated with polarization reversal in a rhombohedral ferroelectric ceramic.  

SciTech Connect

The polarization reversal process in a rhombohedral ferroelectric ceramic material was investigated using field-induced strain measurements and texture development. Special attention was focused on the difference in the field-induced strains between the first quarter cycle and subsequent loading conditions. Results show that the initial field-induced strain is about twelve times greater than the subsequent strain, which immediately suggests that mechanisms involved in these conditions during the polarization reversal process are different. The difference in the magnitude of field-induced strain is discussed in terms of 180 degree and non-180 degree domain reorientation processes.

Rodriguez, Mark Andrew; Yang, Pin; Burns, George Robert

2003-03-01

185

Shock-induced polarized hydrogen emission lines in omicron Ceti  

NASA Astrophysics Data System (ADS)

Hydrogen emission lines in Mira variable stars are a well-known phenomenon whose origin has been established as related to the propagation of radiative hypersonic shock waves throughout the stellar atmosphere. A polarimetric observation by McLean and Coyne [1] made on omicron Ceti (the prototype of Mira variable stars) has revealed the existence of linear polarization signatures associated with Balmer emission lines. However, the polarizing mechanism has never been properly explained so far. The study presented here is the first of its kind since it displays the results of a spectropolarimetric survey of omicron Ceti in the Balmer lines. The survey was made with the NARVAL spectropolarimeter (Telescope Bernard Lyot, France) in full Stokes mode. We did not just confirm the appearance of this polarization but we also and above all showed the temporal variation of the linear polarization in the lines. We conclude that the polarizing mechanism is definitely intrinsic to the shock wave propagation throughout the stellar atmosphere of Mira and give some leads about the nature of this mechanism.

Fabas, N.; Lèbre, A.; Gillet, D.

2012-05-01

186

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

SciTech Connect

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, T{sub g}. This is interpreted in terms of a {beta}-relaxation process of the glass and is identified with transport of free volume. {copyright} {ital 1999 American Institute of Physics.}

Reinot, T.; Hayes, J.M.; Small, G.J. [Ames Laboratory and Department of Chemistry, Iowa State University, Ames, Iowa 50011 (United States)

1999-03-01

187

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

SciTech Connect

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.

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

2008-11-01

188

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

189

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

190

Spontaneous polarization induced by natural thermalization of incoherent light.  

PubMed

We analyze theoretically the polarization properties of a partially coherent optical field that propagates in a nonlinear Kerr medium. We consider the standard model of two resonantly coupled nonlinear Schrödinger equations, which account for a wave-vector mismatch between the orthogonal polarization components. We show that such a phase-mismatch is responsible for the existence of a spontaneous repolarization process of the partially incoherent optical field during its nonlinear propagation. The repolarization process is characterized by an irreversible evolution of the unpolarized beam towards a highly polarized state, without any loss of energy. This unexpected result contrasts with the commonly accepted idea that an optical field undergoes a depolarization process under nonlinear evolution. The repolarization effect can be described in details by simple thermodynamic arguments based on the kinetic wave theory: It is shown to result from the natural tendency of the optical field to approach its thermal equilibrium state. The theory then reveals that it is thermodynamically advantageous for the optical field to evolve towards a highly polarized state, because this permits the optical field to reach the ???most disordered state???, i.e., the state of maximum (nonequilibrium) entropy. The theory is in quantitative agreement with the numerical simulations, without adjustable parameters. The physics underlying the reversible property of the repolarization process is briefly discussed in analogy with the celebrated Joule???s experiment of free expansion of a gas. Besides its fundamental interest, the repolarization effect may be exploited to achieve complete polarization of unpolarized incoherent light without loss of energy. PMID:18957998

Picozzi, Antonio

2008-10-27

191

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

192

Interference of spin states in resonant photoemission induced by circularly polarized light from magnetized Gd  

SciTech Connect

We have observed the spin-state interference by measuring the photoelectron spin polarization in the resonant preedge 4d{yields}4f photoemission from magnetized Gd. The photoemission is induced by circularly polarized light which determines one preferential direction of electron spin orientation due to polarization transfer and spin-orbit interaction. Another direction perpendicular to the first one is determined by the target electron spin orientation connected with the target magnetization. We have measured the component of spin polarization perpendicular to those two directions which can only appear due to spin-state interference which implies coherence of the spin states produced by the two mechanisms of the photoelectron spin polarization.

Mueller, N.; Khalil, T.; Pohl, M.; Uphues, T.; Heinzmann, U. [Fakultaet fuer Physik, Universitaet Bielefeld, D-33615 Bielefeld (Germany); Polcik, M. [Fritz-Haber-Institut der MPG, D-14195 Berlin (Germany); Rader, O. [BESSY, D-12489 Berlin (Germany); Heigl, F.; Starke, K. [Freie Universitaet Berlin, Fachbereich Physik, D-14195 Berlin (Germany); Fritzsche, S. [Institut fuer Physik, Universitaet Kassel, D-34132 Kassel (Germany); Kabachnik, N. M. [Fakultaet fuer Physik, Universitaet Bielefeld, D-33615 Bielefeld (Germany); Institute of Nuclear Physics, Moscow State University, Moscow 119992 (Russian Federation)

2006-10-15

193

Spin-polarized current induced by a local exchange field in a silicene nanoribbon  

NASA Astrophysics Data System (ADS)

A mechanism to generate a spin-polarized current in a two-terminal zigzag silicene nanoribbon is predicted. When a weak local exchange field that is parallel to the surface of silicene is applied on one of edges of the silicene nanoribbon, a gap is opened in the corresponding edge states but another pair of gapless edge states with opposite spin are still protected by the time-reversal symmetry. Hence, a spin-polarized current can be induced in the gap opened by the local exchange field in this two-terminal system. What is important is that the spin-polarized current can be obtained even in the absence of Rashba spin-orbit coupling and in the case of the very weak exchange field. That is to say, the mechanism to generate the spin-polarized currents can be easily realized experimentally. We also find that the spin-polarized current is insensitive to weak disorder.

An, Xing-Tao; Zhang, Yan-Yang; Liu, Jian-Jun; Li, Shu-Shen

2012-08-01

194

Discrimination of corn, grasses and dicot weeds by their UV-induced fluorescence spectral signature  

Microsoft Academic Search

Real-time spot spraying of weed patches requires the development of sensors for the automatic detection of weeds within a\\u000a crop. In this context, the potential of UV-induced fluorescence of green plants for corn-weed discrimination was evaluated.\\u000a A total of 1 440 spectral signatures of fluorescence were recorded in a greenhouse from three plant groups (four corn hybrids,\\u000a four dicotyledonous weed species

Louis Longchamps; Bernard Panneton; Guy Samson; Gilles D. Leroux; Roger Thériault

2010-01-01

195

Spectral dependence of light-induced microwave reflection coefficient from optoelectronic waveguide gratings  

Microsoft Academic Search

After a short description of the method of operation of optoelectronic microwave filters, a detailed analysis of the spectral dependence of light-induced microwave reflection coefficient from an optoelectronically generated distributed Bragg reflection waveguide grating is reported. The theory is based on an improved stepped-impedance model utilizing a diffusion-controlled abrupt-profile approach of photoconductivity along with a conformal mapping technique for the

Walter Platte

1995-01-01

196

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

197

Light-Induced Polar pH Changes in Leaves of Elodea canadensis1  

PubMed Central

Leaves of the submerged aquatic Elodea canadensis Michx. exhibit a light induced polar pH reaction. In this study, the effects of light intensity and dissolved inorganic carbon concentration on this polar reaction were examined. At a light intensity of 100 watts per square meter the leaf showed a polar pH response when the dissolved inorganic carbon concentration was less than about 1 millimolar. The polar reaction was suppressed at a higher dissolved inorganic carbon concentration. This suppression was not due to the buffering capacity of bicarbonate. Because another weak acid, acetate, did not inhibit the polarity, but even had a small stimulatory effect, the effect of bicarbonate is also not due to acidification of the cytoplasm. The suppression of the polar reaction by CO2/HCO3? was relieved when the light intensity was increased. Apparently there is competition for product(s) of the photosynthetic light reactions between processes generating the polar reaction and the carbon fixation reactions. The possibility that the redox state of the cell regulates the generation of the polar reaction is discussed.

Elzenga, J. Theo M.; Prins, Hidde B. A.

1989-01-01

198

Shock-Induced Polarized Hydrogen Emission Lines in Omicron Ceti  

NASA Astrophysics Data System (ADS)

We have performed a spectropolarimetric survey of the variable Mira star omicron Ceti along three pulsation cycles. We present those new data collected with the Narval instrument mounted on the Telescope Bernard Lyot (TBL) in Pic du Midi, France. We have detected time variable polarimetric signatures (on QUV Stokes spectra) associated with Balmer hydrogen emission lines supposed to be formed behind the front of a shock wave propagating throughout the stellar atmosphere. We associate the linear polarization of Balmer emission lines in Mira stars to the presence and the structure of the radiative shock wave.

Fabas, N.; Lèbre, A.; Gillet, D.

2011-04-01

199

Shock-Induced Polarized Hydrogen Emission Lines in omicron Ceti  

NASA Astrophysics Data System (ADS)

We have performed a spectropolarimetric survey of the variable Mira star omicron Ceti along three pulsation cycles. We present those new data collected with the Narval instrument mounted on the Telescope Bernard Lyot (TBL) in Pic du Midi, France. We have detected time variable polarimetric signatures (on QUV Stokes spectra) associated with Balmer hydrogen emission lines supposed to be formed behind the front of a shock wave propagating throughout the stellar atmosphere. We associate the linear polarization of Balmer emission lines in Mira stars to the presence and the structure of the radiative shock wave.

Lèbre, A.; Fabas, N.; Gillet, D.

2011-12-01

200

High-speed spectral domain polarization- sensitive optical coherence tomography using a single camera and an optical switch at 1.3 ?m  

NASA Astrophysics Data System (ADS)

We propose high-speed spectral domain polarization-sensitive optical coherence tomography (SD-PS-OCT) using a single camera and a 1×2 optical switch at the 1.3-?m region. The PS-low coherence interferometer used in the system is constructed using free-space optics. The reflected horizontal and vertical polarization light rays are delivered via an optical switch to a single spectrometer by turns. Therefore, our system costs less to build than those that use dual spectrometers, and the processes of timing and triggering are simpler from the viewpoints of both hardware and software. Our SD-PS-OCT has a sensitivity of 101.5 dB, an axial resolution of 8.2 ?m, and an acquisition speed of 23,496 A-scans per second. We obtain the intensity, phase retardation, and fast axis orientation images of a rat tail tendon ex vivo.

Lee, Sang-Won; Jeong, Hyun-Woo; Kim, Beop-Min

2010-01-01

201

Oxidized LDL/CD36 interaction induces loss of cell polarity and inhibits macrophage locomotion  

PubMed Central

Cell polarization is essential for migration and the exploratory function of leukocytes. However, the mechanism by which cells maintain polarity or how cells revert to the immobilized state by gaining cellular symmetry is not clear. Previously we showed that interaction between oxidized low-density lipoprotein (oxLDL) and CD36 inhibits macrophage migration; in the current study we tested the hypothesis that oxLDL/CD36-induced inhibition of migration is the result of intracellular signals that regulate cell polarity. Live cell imaging of macrophages showed that oxLDL actuated retraction of macrophage front end lamellipodia and induced loss of cell polarity. Cd36 null and macrophages null for Vav, a guanine nucleotide exchange factor (GEF), did not show this effect. These findings were caused by Rac-mediated inhibition of nonmuscle myosin II, a cell polarity determinant. OxLDL induced dephosphorylation of myosin regulatory light chain (MRLC) by increasing the activity of Rac. Six-thioguanine triphosphate (6-thio-GTP), which inhibits Vav-mediated activation of Rac, abrogated the effect of oxLDL. Activation of the Vav-Rac-myosin II pathway by oxidant stress may induce trapping of macrophages at sites of chronic inflammation such as atherosclerotic plaque.

Park, Young Mi; Drazba, Judith A.; Vasanji, Amit; Egelhoff, Thomas; Febbraio, Maria; Silverstein, Roy L.

2012-01-01

202

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

203

Chiral-Selective Chemistry Induced by Spin-Polarized Secondary Electrons from a Magnetic Substrate  

NASA Astrophysics Data System (ADS)

We demonstrate for the first time that low-energy spin-polarized secondary electrons, produced by irradiation of a magnetic substrate, can induce chiral-selective chemistry. Our approach was to perform detailed measurements of the reaction rate for x-ray induced, secondary electron photolysis of a model chiral compound, (R)- or (S)-2-butanol, adsorbed on a magnetized Permalloy substrate. The results showed that there is an enhancement of ˜10% in the rate of CO bond cleavage that depends on the chirality of the molecule and the spin polarization of the substrate secondary electrons.

Rosenberg, R. A.; Abu Haija, M.; Ryan, P. J.

2008-10-01

204

Early detection of oil-induced stress in crops using spectral and thermal responses  

NASA Astrophysics Data System (ADS)

Oil pollution is a major source of environmental degradation, and requires accurate monitoring and timely detection for an effective control of its occurrence. This paper examines the potential of a remote sensing approach using the spectral and thermal responses of crops for the early detection of stress caused by oil pollution. In a glasshouse, pot-grown maize was treated with oil at sublethal and lethal applications. Thereafter, leaf thermal, spectral and physiological measurements were taken every two to three days to monitor the development of stress responses. Our results indicate that absolute leaf temperature was a poor indicator of developing stress. However, a derived thermal index (IG) responded consistently in the early stages of physiological damage. Various spectral reflectance features were highly sensitive to oil-induced stress. A narrow-band index using wavelengths in the near-infrared and red-edge region, (R755-R716)/(R755+R716), was optimal for previsual detection of oil-induced stress. This index had a strong linear relationship with photosynthetic rate. This indicates that by detecting vegetation stress, thermal and hyperspectral remote sensing has considerable potential for the timely detection of oil pollution in the environment.

Emengini, Ebele Josephine; Blackburn, George Alan; Theobald, Julian Charles

2013-01-01

205

[Study on the automatic extraction method of spectral data features in laser induced breakdown spectroscopy].  

PubMed

According to that the spectral line broadening of laser induced breakdown spectroscopy (LIBS) was lorentz nonlinear function model, using Levenberg-Marquardt (L-M) agorithm to optimally estimate the undetermined parameter in the function, the continuum background radiation and peak position and peak intensity were corrected, and the method of data points automatic extraction for fitting was analysed. Automatic fitting and feature parameter extraction for spectral data of LIBS based on L-M algorithm that was hybrid programming with matrixVB and VB were accomplished,and the result was compared with the origin 7.5 data analysis software which was manual and commonly used and verified its stability and reliability. PMID:22295778

Liu, Li-tuo; Liu, Jian-guo; Zhao, Nan-jing; Lu, Cui-ping; Chen, Dong; Shi, Huan; Wang, Chun-long; Zhang, Yu-jun; Liu, Wen-qing

2011-12-01

206

The Origin of the Ultra-Violet Spectral Components in the Polar-Like Intermediate Polar, RE075 Cycle 4 High  

NASA Astrophysics Data System (ADS)

RE0751+14, is arguably the most important magnetic cataclysmic variable (CV) to be discovered for many years. Although it is undoubtedly an intermediate polar, it also exhibits highly unusual properties (e.g. a strong EUV component, modulated optical/IR polarization, X-ray, optical and IR dips in its rotational light curve and a very red rotational pulsation) which strongly suggest that its white dwarf possesses a powerful magnetic field, similar to that associated with the strongly magnetic (B>10MG) polars. Thus RE0751+14 is apparently an interloper, occupying a new, uncharted domain in the field distribution of the magnetic CVs which was previously thought to be bimodal. The study of RE0751+14 is therefore of fundamental importance to our knowledge of the field distribution in magnetic CVs and consequently of their evolutionary relationship. The UV waveband is crucial to this study because magnetic disruption and control of the accretion flow occurs at radii where the hot UV emitting material exists. We are proposing to use the HST FOS to secure the first highly time-resolved UV spectroscopy of RE0751+14. These will enable us, for the first time, to a) segregate the different UV continuum components (via their different temporal behaviour) and characterize their sources and b) measure the emission line flux variations to probe physical structure within the system. These observations will be complemented by a parallel HRS proposal to study the CIV line in detail.

Rosen, Simon

1994-07-01

207

Ferroelectric polarization flop in a frustrated magnet MnWO4 induced by a magnetic field.  

PubMed

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 to the a direction has been observed when a magnetic field above 10 T is applied along the b axis. This result demonstrates that an electric polarization flop can be induced by a magnetic field in a simple system without rare-earth 4f moments. PMID:17026396

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

2006-08-30

208

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

209

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

210

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

211

Anisotropy of induced polarization in the context of the generalized effective-medium theory.  

NASA Astrophysics Data System (ADS)

The rock samples are examples of heterogeneous complex structure material. Modeling of electromagnetic response of this medium makes it possible to study the anisotropy of induced polarization (IP) effect. The IP effect is studied it in the context of the developed generalized effective-medium theory of induced polarization (GEMTIP). The effective-medium conductivity defined by the GEMTIP model, in a general case, is represented by a tensor function. This tensorial property of the effective-medium conductivity provides a new insight in the anisotropy phenomenon in the IP effect. As an example, we consider a multiphase composite polarized model of a rock formation with ellipsoidal inclusions. We demonstrate that the effective conductivity of this formation may be anisotropic, even if the host rock and all the grains are electrically isotropic.

Burtman, Vladimir; Zhdanov, Michael S.; Gribenko, Alexander

2009-03-01

212

Enhancement of induced V polarization due to rough interfaces in polycrystalline V/Fe/V trilayers  

SciTech Connect

The effect of interface roughness on the induced polarization of V in polycrystalline V/Fe/V trilayers was investigated with x-ray magnetic circular dichroism, x-ray resonant magnetic scattering, and polarized neutron reflectometry. Trilayer samples were sputter deposited onto Si substrates at room temperature to minimize interdiffusion. The films were polycrystalline and exhibited an average 0.5 nm root-mean-square interfacial roughness at the Fe/V interfaces. The induced polarization found in V was constrained to the Fe/V interface extending approximately up to 2-3 monolayers into the V and exhibited antiferromagnetic alignment to the Fe layer. A magnetic moment for V ranging between -0.46 and -0.86 {micro}{sub B}/V atom is consistent with the neutron and resonant x-ray data. Notably, this value for structurally rough interfaces is significantly larger than that reported for samples with atomically flat Fe/V interfaces.

Clavero, C.; Sanchez-Hanke, C.; Skuza, R.; Choi,Y.; Loloee,R.; Zhernenkov, M.; Fitzsimmons, M.R.; Lukaszew, R.A

2009-07-20

213

Enhancement of induced V polarization due to rough interfaces in polycrystalline V/Fe/V trilayers  

NASA Astrophysics Data System (ADS)

The effect of interface roughness on the induced polarization of V in polycrystalline V/Fe/V trilayers was investigated with x-ray magnetic circular dichroism, x-ray resonant magnetic scattering, and polarized neutron reflectometry. Trilayer samples were sputter deposited onto Si substrates at room temperature to minimize interdiffusion. The films were polycrystalline and exhibited an average 0.5 nm root-mean-square interfacial roughness at the Fe/V interfaces. The induced polarization found in V was constrained to the Fe/V interface extending approximately up to 2-3 monolayers into the V and exhibited antiferromagnetic alignment to the Fe layer. A magnetic moment for V ranging between -0.46 and -0.86?B/V atom is consistent with the neutron and resonant x-ray data. Notably, this value for structurally rough interfaces is significantly larger than that reported for samples with atomically flat Fe/V interfaces.

Clavero, C.; Skuza, J. R.; Choi, Y.; Haskel, D.; Sánchez-Hanke, C.; Loloee, R.; Zhernenkov, M.; Fitzsimmons, M. R.; Lukaszew, R. A.

2009-07-01

214

Bastille Day Flare Multi-Spectral Characterization of Radio Emission Polarization from Milliseconds to Minutes Time Scale  

NASA Astrophysics Data System (ADS)

In this work we pay attention to the characteristics of millisecond spikes in relation to the general activity in which they are included, processes with very different time scales. Observations were provided by the Trieste Astronomical Observatory (OAT) radio polarimeters in 237, 327, 408, 610, 1420 and 2695 MHz, with 100 Hz temporal resolution. Some complementary data were obtained from open sources in Internet (Goes X-R, SOHO images, etc.) The waiting time distribution between individual maxima (flux >10 sfu) was calculated searching for self-organized criticality. Left and right polarization components were analyzed separately. The analyzed temporal interval presents two activity periods. The first related to HXR and gamma emission with both polarization millisecond events, and the following activity period is dominated by the right polarized component events. This behavior is considered evidence of two different dominant generation mechanisms for millisecond events.

Rodríguez Taboada, R. E.; Méndez Berhondo, A. L.

2006-12-01

215

Field-induced polarization of Dirac valleys in bismuth  

NASA Astrophysics Data System (ADS)

The principal challenge in the field of ``valleytronics'' is to lift the valley degeneracy of electrons in a controlled way. In graphene, a number of methods to generate a valley-polarized flow of electrons have been proposed, which are yet to be experimentally realized. In bulk semi-metallic bismuth, the Fermi surface includes three cigar-shaped electron valleys lying almost perpendicular to the high-symmetry axis known as the trigonal axis. The in-plane mass anisotropy of each valley exceeds 200 as a consequence of Dirac dispersion, which drastically reduces the effective mass along two out of the three orientations. We present a study of angle-dependent magnetoresistance in bismuth which shows that a flow of Dirac electrons along the trigonal axis is extremely sensitive to the orientation of in-plane magnetic field. The effect is visible even at room temperature. Thus, a rotatable magnetic field can be used as a valley valve to tune the contribution of each valley to the total conductivity. At high temperature and low magnetic field, the three valleys are interchangeable and the three-fold symmetry of the underlying lattice is respected. As the temperature is decreased or the magnetic field increased, this symmetry is spontaneously lost. This loss may be an experimental manifestation of the recently proposed valley-nematic Fermi liquid state.

Behnia, Kamran; Zhu, Zengwei; Callaudin, Aurelie; Fauque, Benoit; Kang, Woun

2012-02-01

216

Multi-array borehole resistivity and induced polarization method with mathematical inversion of redundant data  

DOEpatents

Multiple arrays of electric or magnetic transmitters and receivers are used in a borehole geophysical procedure to obtain a multiplicity of redundant data suitable for processing into a resistivity or induced polarization model of a subsurface region of the earth. 30 figs.

Ward, S.H.

1989-10-17

217

Helicobacter pylori CagA induces a transition from polarized to invasive phenotypes in MDCK cells  

PubMed Central

CagA is a bacterial effector protein of Helicobacter pylori that is translocated via a type IV secretion system into gastric epithelial cells. We previously described that H. pylori require CagA to disrupt the organization and assembly of apical junctions in polarized epithelial cells. In this study, we provide evidence that CagA expression is not only sufficient to disrupt the apical junctions but also perturbs epithelial differentiation. CagA-expressing cells lose apicobasal polarity and cell–cell adhesion, extend migratory pseudopodia, and degrade basement membranes, acquiring an invasive phenotype. Expression of the CagA C-terminal domain, which contains the tyrosine phosphorylated EPIYA motifs, induces pseudopodial activity but is not sufficient to induce cell migration. Conversely, the N terminus targets CagA to the cell–cell junctions. Neither domain is sufficient to disrupt cell adhesion or cell polarity, but coexpressed in trans, the N terminus determines the localization of both polypeptides. We show that CagA induces a morphogenetic program in polarized Madin–Darby canine kidney cells resembling an epithelial-to-mesenchymal transition. We propose that altered cell–cell and cell matrix interactions may serve as an early event in H. pylori-induced carcinogenesis.

Bagnoli, Fabio; Buti, Ludovico; Tompkins, Lucy; Covacci, Antonello; Amieva, Manuel R.

2005-01-01

218

Spin-orbit coupling induced electron spin polarization in photoinduced electron transfer reactions  

Microsoft Academic Search

The observation of net-absorptive chemically induced dynamic electron polarization (CIDEP) spectra induced by spin-orbit coupling (SOC) interactions due to heavy atoms gives proof of the generation of a contact radical pair (RP) or triplet exciplex as the intermediate. Recent time-resolved EPR and pulsed EPR studies on the spin dynamics are reviewed. The SOC interaction causes simultaneous changes in the orbital

Shozo Tero-Kubota; Akio Katsuki; Yasuhiro Kobori

2001-01-01

219

Dual-spectral plasmon electromagnetically induced transparency in planar metamaterials based on bright-dark coupling  

NASA Astrophysics Data System (ADS)

The optical properties of a planar metamaterials, composed of asymmetric two gold wire pairs located at the two sides of the gold bar, have been investigated theoretically in this paper. The calculated results show that this structure can exhibit dual-spectral plasmonic electromagnetically-induced transparency analogous to the quantum optical phenomenon. The electric field distributions demonstrate that the double transparency windows originate from dual bright-dark coupling modes. Moreover, in accompany with the double tunable transparency windows modulated by the symmetry-reduced displacement, two large group indexes for multi-band slow light applications are also found.

He, Xun-jun; Wang, Jian-min; Tian, Xiao-hua; Jiang, Jiu-xing; Geng, Zhao-xin

2013-03-01

220

Sperm Chromatin-Induced Ectopic Polar Body Extrusion in Mouse Eggs after ICSI and Delayed Egg Activation  

Microsoft Academic Search

Meiotic chromosomes in an oocyte are not only a maternal genome carrier but also provide a positional signal to induce cortical polarization and define asymmetric meiotic division of the oocyte, resulting in polar body extrusion and haploidization of the maternal genome. The meiotic chromosomes play dual function in determination of meiosis: 1) organizing a bipolar spindle formation and 2) inducing

Manqi Deng; Rong Li

2009-01-01

221

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

222

Exposure and compositional factors that influence polarization induced birefringence in silica glass  

NASA Astrophysics Data System (ADS)

Silica glass exhibits a permanent anisotropic response, referred to as polarization induced birefringence (PIB), when exposed to short wavelength, polarized light. The magnitude of the PIB has been empirically correlated with the OH content of the glass. Our recent studies pertaining to PIB have focused on careful characterization of PIB, with particular emphasis on understanding all of the contributions to the measured birefringence signal and finally extracting only that signal associated with birefringence arising from exposure to a polarized light beam. We will demonstrate that a critical contributor to the total birefringence signal is birefringence that comes from exposure beam inhomogeneities. After subtracting beam profile effects we are able to show that PIB is proportional to the OH content of the glass. Polarized infrared (IR) measurements were performed on glasses that developed PIB as a consequence of exposure to polarized 157-nm light. These studies reveal that there is preferential bleaching of a specific hydroxyl (OH) species in the glass with OH aligned parallel to the incident polarization undergoing more bleaching than those perpendicular. Further, we observe a very strong correlation between the measured PIB of these samples and the anisotropic bleaching. From these studies we propose a mechanism that can explain the role of hydroxyl in PIB.

Allan, Douglas C.; Mlejnek, Michal; Neukirch, Ulrich; Smith, Charlene M.; Smith, Frances M.

2007-03-01

223

Spectral Induced Polarization (SIP) monitoring during Microbial Enhanced Oil Recovery (MEOR)  

Microsoft Academic Search

Jeffrey Heenan, Dimitrios Ntarlagiannis, Lee Slater Department of Earth and Environmental Sciences, Rutgers University, Newark NJ Microbial Enhanced Oil Recovery (MEOR) is an established, cost effective, method for enhancing tertiary oil recovery. Although not commonly used for shallow heavy oils, it could be a viable alternative since it can offer sustainable economic recovery and minimal environmental impact. A critical component

J. W. Heenan; D. Ntarlagiannis; L. D. Slater

2010-01-01

224

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

225

Polarization induced instabilities in external four-mirror Fabry-Perot cavities.  

PubMed

Various four-mirror optical resonators are studied from the perspective of realizing passive stacking cavities. A comparative study of the mechanical stability is provided. The polarization properties of the cavity eigenmodes are described, and it is shown that the effect of mirror misalignments (or motions) induces polarization and stacking power instabilities. These instabilities increase with the finesse of the Fabry-Perot cavity. A tetrahedral configuration of the four mirrors is found to minimize the consequences of the mirrors' motion and misalignment by reducing the instability parameter by at least 2 orders of magnitude. PMID:20011005

Zomer, Fabian; Fedala, Yasmina; Pavloff, Nicolas; Soskov, Viktor; Variola, Alessandro

2009-12-10

226

Current-Induced Magnetization Switching with a Spin-Polarized Scanning Tunneling Microscope  

NASA Astrophysics Data System (ADS)

The understanding of current-induced magnetization switching is in the focus of many ongoing investigations since switching the magnetization by the injection of a spin-polarized current rather than by magnetic fields may open the gateway for new data storage technologies at much higher bit densities. We show how individual superparamagnetic Fe nanoislands with typical sizes of 100 atoms can be addressed and locally switched using a magnetic scanning probe tip. We demonstrate current-induced magnetization reversal across a vacuum barrier and combine it with the ultimate resolution of spin-polarized scanning tunneling microscopy. This technique allows us to clearly separate and quantify three fundamental contributions that are involved in magnetization switching, i.e. current-induced spin torque, heating the island by the tunneling current, and Oersted field effects.

Bode, Matthias; Krause, Stefan; Berbil-Bautista, Luis; Herzog, Gabriela; Wiesendanger, Roland

2008-03-01

227

A new strategy for in vivo spectral editing. Application to GABA editing using selective homonuclear polarization transfer spectroscopy  

Microsoft Academic Search

A novel single-shot in vivo spectral editing method is proposed in which the signal to be detected, is regenerated anew from the thermal equilibrium magnetization of a source to which it is J-coupled. The thermal equilibrium magnetization of the signal to be detected together with those of overlapping signals are suppressed by single-shot gradient dephasing prior to the signal regeneration

Jun Shen; Jehoon Yang; In-Young Choi; Shizhe Steve Li; Zhengguang Chen

2004-01-01

228

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

229

Relationship between Hydrological Parameters and Induced Polarization Spectra of Soil Samples  

NASA Astrophysics Data System (ADS)

Problems concerning groundwater renewal, surface runoff, and agricultural questions are examples where soil hydraulic properties are relevant. Soil hydraulic properties describe the relationships between the state properties water content, capillary pressure, and hydraulic conductivity in partially water saturated soils. To obtain these properties for an area by soil hydrologic measurement techniques is time-consuming. Furthermore, the information gained is valid only for the vicinity of the investigated location. Geophysical methods offer a relatively quick way to get areal information. Geoelectrical measurements are most suitable for this purpose due to the correlation between electrical resistivity and properties like pore fluid conductivity and water saturation. Measuring complex resistivity instead of direct current resistivity yields the additional information of the quadrature component of resistivity, which is expected to correlate with properties of the interface between the pore fluid and the solid matrix. The spectral induced polarization (SIP) is a common geoelectrical method to investigate complex resistivity for a defined frequency range. The amplitude of the complex resistivity and the phase angle between real and imaginary part of resistivity are recorded for frequencies from 0.01 Hz to 100 Hz. The understanding of the correlation between complex electrical and hydraulic properties is essential for a successful application of the SIP method to hydrological problems. Therefore, laboratory SIP measurements and hydrologic Multi-Step-Outflow (MSO) experiments were performed on different soil samples. The investigated material include sand with a narrow grain size distribution as well as real soil samples from different locations in the vicinity of Braunschweig. The SIP measurements were performed at first on samples fully saturated with a sodium-chloride solution. The fluid conductivity is approximately 20 mS/m. Later, additional SIP spectra were recorded at different desaturation states. From the measured SIP spectra the mean relaxation time and the total chargeability were derived by application of the Deybe decomposition approach. After finishing all SIP measurements, the samples were re-saturated completely to perform the MSO experiments to obtain the retention curves and hydraulic conductivity functions. The parameters of the functions were then compared with the mean relaxation time and the total chargeability, respectively, to find correlations between the electrical and hydrological properties.

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

2011-12-01

230

Dynamical heating of the polar summer mesopause induced by solar proton events  

NASA Astrophysics Data System (ADS)

A solar proton event (SPE) causes enhanced ionization of water vapor and nitrogen in the lower mesosphere, leading to production of odd hydrogen and odd nitrogen and hence a temporary depletion of ozone. Therefore, the main direct effect on the large circulation in the summer mesosophere/lower thermosphere (MLT) is a diabatic cooling perturbation centered around the pole in the lower mesosphere. Satellite observations made with the MLS/Aura showed a maximum increase of ¿ 10 K in zonally averaged temperatures around the southern polar summer mesopause during the SPE in January 2005 (v. Savigny et al., 2007, GRL). We propose a mechanism that explains this warming as a dynamical consequence of the cooling below (Becker and v. Savigny, 2009, JGR). We employ the Kuehlungsborn Mechanistic general Circulation Model (KMCM), which is a spectral model with high spatial resolution and a sophisticated parameterization of turbulence, giving rise to explicit simulation of gravity-wave effects in the MLT (Becker, 2009, JAS). An SPE is mimicked in the following way: We start with a control simulation for permanent Jan-uary conditions, extract an arbitrary snapshot, and integrate the model with an additional lower mesospheric cooling. This cooling is switched off after 5 days and the model is integrated for another 10 days. The resulting 15 day time series constitutes an SPE-related perturbation simulation when compared to the corresponding 15-day time series of the control simulation. To improve the statistics, the procedure is repeated six times and composite time series are con-structed. The model response in the SPE case reproduces the warming around the mesopause, which can be explained as follows. The diabatic cooling in the lower summer mesosphere induces an anomalous eastward zonal wind component. As a result, eastward propagating gravity waves are Doppler-shifted to smaller intrinsic frequencies and hence are subject to turbulent damping at lower altitudes. Hence, the maximum gravity-wave drag and the residual circulation also shift downward, causing reduced adiabatic cooling or higher temperatures around the mesopause. A detailed inspection of the momentum and sensible heat budgets shows that also the changes of westward propagating planetary waves and of the direct thermal effects due to gravity waves (dissipation and diffusion) must be considered.

Becker, Erich; von Savigny, Christian

231

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

232

Polarized spectral analysis of Nd3+ ions in Li6Gd(BO3)3 biaxial crystals  

NASA Astrophysics Data System (ADS)

The orientation relationship between the crystallographic axes and the principal axes of the optical indicatrix for a Li6Gd(BO3)3 single crystal grown by the Czochralski method was determined. The polarized absorption spectra, polarized fluorescence spectra, and fluorescence decay curve of Nd3+:Li6Gd(BO3)3 were measured at room temperature. On the basis of the Judd-Ofelt theory and the Fuchtbauer-Landenburg formula, the spectroscopic parameters of Nd3+:Li6Gd(BO3)3 relevant to laser properties were obtained and compared with other borate laser crystals. A primary laser output of about 130 mW at 1056 nm with the slope efficiency of 13% was obtained under a Ti:sapphire laser pumping.

Gong, Xinghong; Lin, Yanfu; Chen, Yujin; Luo, Zundu; Tan, Qiguang; Huang, Yidong

2006-10-01

233

Parahydrogen-induced polarization at zero magnetic field  

NASA Astrophysics Data System (ADS)

We use symmetry arguments and simple model systems to describe the conversion of the singlet state of parahydrogen into an oscillating sample magnetization at zero magnetic field. During an initial period of free evolution governed by the scalar-coupling Hamiltonian HJ, the singlet state is converted into scalar spin order involving spins throughout the molecule. A short dc pulse along the z axis rotates the transverse spin components of nuclear species I and S through different angles, converting a portion of the scalar order into vector order. The development of vector order can be described analytically by means of single-transition operators, and it is found to be maximal when the transverse components of I are rotated by an angle of +/-?/2 relative to those of S. A period of free evolution follows the pulse, during which the vector order evolves as a set of oscillating coherences. The imaginary parts of the coherences represent spin order that is not directly detectable, while the real parts can be identified with oscillations in the z component of the molecular spin dipole. The dipole oscillations are due to a periodic exchange between Iz and Sz, which have different gyromagnetic ratios. The frequency components of the resulting spectrum are imaginary, since the pulse cannot directly induce magnetization in the sample; it is only during the evolution under HJ that the vector order present at the end of the pulse evolves into detectable magnetization.

Butler, Mark C.; Kervern, Gwendal; Theis, Thomas; Ledbetter, Micah P.; Ganssle, Paul J.; Blanchard, John W.; Budker, Dmitry; Pines, Alexander

2013-06-01

234

Disorder-induced reversal of spin polarization in the Heusler alloy Co2FeSi  

NASA Astrophysics Data System (ADS)

We study the spin polarization in the conduction band of Co2FeSi layers with a different degree of structural order. The injected spin polarization in Co2FeSi/(Al,Ga)As spin light-emitting diodes as well as the planar Hall effect measured for the Co2FeSi injectors exhibit a sign reversal between injectors crystallized in the ordered L21 phase and the Fe-Si disordered B2 phase. These results are explained by a disorder-induced change in the spin polarization at the Fermi energy of Co2FeSi. Support for the occurrence of such a striking change in the electronic band structure is obtained by first principles calculations.

Bruski, P.; Erwin, S. C.; Ramsteiner, M.; Brandt, O.; Friedland, K.-J.; Farshchi, R.; Herfort, J.; Riechert, H.

2011-04-01

235

Use of the vacuum ultraviolet spectral region for laser-induced breakdown spectroscopy-based Martian geology and exploration  

Microsoft Academic Search

Several elements important to planetary geology (e.g. Br, C, Cl, P, S) and the human exploration of Mars (e.g. toxic elements such as As) have strong emission lines in the purge and vacuum ultraviolet (VUV) spectral region (100–200 nm). This spectral region has not been extensively studied for space applications using geological samples. We studied emissions from the laser-induced breakdown

Leon Radziemski; David A. Cremers; Katharine Benelli; Cynthia Khoo; Ronny D. Harris

2005-01-01

236

Sensitivity of force-detected NMR spectroscopy with resonator-induced polarization  

NASA Astrophysics Data System (ADS)

In the low-temperature regime where the thermal polarization P is of order unity and spin-lattice relaxation is “frozen out,” resonator-induced relaxation can be used to polarize a nuclear-spin sample for optimal detection sensitivity. We characterize the potential of resonator-induced polarization for enhancing the sensitivity of nuclear-magnetic-resonance spectroscopy. The sensitivities of two detection schemes are compared, one involving detection of a polarized sample dipole and the other involving detection of spin-noise correlations in an unpolarized sample. In the case where the dominant noise source is instrument noise associated with resonator fluctuations and with detection of the mechanical motion, a simple criterion can be used to compare the two schemes. Polarizing the sample improves sensitivity when P is larger than the signal-to-noise ratio for detection of a fully-polarized spin during a single transient. Even if the instrument noise is decreased to a level near the quantum-mechanical limit, it is larger than spin noise for unpolarized samples containing up to a few tens of nuclei. Under these conditions, spin polarization of order unity would enhance spectroscopic detection sensitivity by an order of magnitude or more. In the limiting case where signal decay is due to resonator-induced dissipation during ideal spin locking, and where resonator fluctuations are the noise source, the only parameter of the spin-resonator system that affects the sensitivity per spin is the ratio of frequency to temperature. A balance between the coupling strength, the noise power, and the signal lifetime causes the cancellation of other parameters from the sensitivity formula. Partial cancellation of parameters, associated with a balance between the same three quantities, occurs more generally when the resonator is both the dominant noise source and the dominant source of signal decay. An intrinsic sensitivity limit exists for resonant detection of coherent spin evolution, due to the fact that the detector causes signal decay by enhancing the spins' spontaneous emission. For a single-spin sample, the quantum-limited signal-to-noise ratio for resonant detection is 1/3. In contrast to the sensitivity, the time required for sample polarization between transients depends strongly on resonator parameters. We discuss resonator design and show that for a torsional resonator, the coupling is optimal when the resonator's magnetization remains aligned with the applied field during the mechanical oscillations.

Butler, Mark C.; Weitekamp, Daniel P.

2013-02-01

237

Polarized spectral properties and 1.5-1.6 ?m laser operation of Er:Sr3Yb2(BO3)4 crystal  

NASA Astrophysics Data System (ADS)

Undoped and Er3+-doped Sr3Yb2(BO3)4 crystals were grown by the Czochralski method. Room temperature polarized spectral properties of the Er:Sr3Yb2(BO3)4 crystal were investigated. The efficiency of the energy transfer from Yb3+ to Er3+ ions in this crystal was calculated to be about 95%. End-pumped by a diode laser at 970 nm in a hemispherical cavity, a 0.75 W quasi-CW laser at 1.5-1.6 ?m with a slope efficiency of 7% and an absorbed pump threshold of 3.8 W was achieved in a 0.5-mm-thick Z-cut crystal glued on a 5-mm-thick pure YAG crystal with UV-curable adhesive.

Lin, F. L.; Huang, J. H.; Chen, Y. J.; Gong, X. H.; Lin, Y. F.; Luo, Z. D.; Huang, Y. D.

2013-10-01

238

Remote sensing of aerosols by using polarized, directional and spectral measurements within the A-Train: the PARASOL mission  

NASA Astrophysics Data System (ADS)

The aerosol remote sensing from space has started in the 1980's using observations provided by geostationary satellites or by polar orbiting platforms not specifically designed for observing aerosols. As a result, the number of retrieved parameters was limited and retrievals in the visible restricted over ocean. Over land, because of the important surface contribution, the aerosol detection was performed in the UV (or in the dark blue) where most of the earth surfaces are dark enough but with overlap of multiple aerosols parameters, content, altitude and absorption. Instruments dedicated to aerosol monitoring are recently available and the POLDER instrument on board the PARASOL mission is one of them. By measuring the wavelength, angular and polarization properties of the radiance at the top of the atmosphere, in coordination with the other A-Train instruments, PARASOL can better quantify aerosol optical depths (AOD) and improve the derivation of the radiative and physical properties. The instrument, the inversion schemes and the list of aerosol parameters are described. Examples of retrieved aerosol parameters are provided as well as innovative approaches and further inversion techniques.

Tanré, D.; Bréon, F. M.; Deuzé, J. L.; Dubovik, O.; Ducos, F.; François, P.; Goloub, P.; Herman, M.; Lifermann, A.; Waquet, F.

2011-04-01

239

Light Induced Polarity of Redox Reactions in Leaves of Elodea canadensis Michx 1  

PubMed Central

This paper reports that extracellular reductase activity in leaves of Elodea canadensis, hitherto never associated with polar processes thought to be involved in bicarbonate utilization, also shows a very marked polarity in light. The effect of ferricyanide, applied to the lower side of illuminated leaves, was a depolarization of the membrane electrical potential of up to 110 millivolts, while no depolarization was induced when ferricyanide was applied to the upper side. In the dark ferricyanide induced a depolarization when applied to either the upper or to the lower side of the leaf. Staining with tetrazolium salts, specific indicators for reductase activity, resulted in the formation of a precipitate on the lower side of the leaf when illuminated and on both sides in the dark. The precipitate was only located along the plasmalemma. Images Fig. 1 Fig. 2

Elzenga, J. Theo M.; Prins, Hidde B. A.

1987-01-01

240

Measurement of the Induced Proton Polarization Pn in the 12C(e, e', p) reaction  

SciTech Connect

The first measurements of the induced proton polarization Pn for the 12C(e,e',p) reaction are reported. The experiment was performed at quasifree kinematics for energy and momentum transfer (w,q) = (294 MeV, 765 MeV/c) and sampled a missing momentum range of 0-250 MeV/c. The induced polarization arises from final-state interactions and for these kinematics is dominated by the real part of the spin-orbit optical potential. The distorted-wave impulse approximation provides good agreement with data for the 1 p3/2 shell. The data for the continuum suggest that both the 1s1/2 shell and underlying l > 1 configurations contribute.

R.J. Woo; David Barkhuff; William Bertozzi; Jian-ping Chen; Dan Dale; G. Dodson; K.A. Dow; Marty Epstein; Manouchehr Farkhondeh; Mike Finn; Shalev Gilad; Mark K. Jones; Kyungseon Joo; James Kelly; Stanley Kowalski; Bob Lourie; Richard Madey; Dimitri Margaziotis; Pete Markowitz; Justin McIntyre; Christoph Mertz; Brian Milbrath; Joseph Mitchell; Charles F. Perdrisat; Vina Punjabi; Paul Rutt; Adam Sarty; D. Tieger; C. Tschalaer; William Turchinetz; Paul E. Ulmer; S.P. Van Verst; C. Vellidis; Glen Warren; Lawrence Weinstein

1998-01-19

241

Calculation of optical thicknesses of magnesium emission spectral lines for diagnostics of laser-induced plasmas.  

PubMed

In this work, plasma characterization by laser-induced breakdown spectroscopy (LIBS) has been investigated. We propose a method based on the calculation of the optical thicknesses of emission spectral lines in the framework of a homogeneous optically thick plasma in local thermodynamic equilibrium (LTE). In this approach, self-absorption is taken into account to retrieve the optically thin intensities and plasma characterization is achieved. The developed procedure is applied to magnesium (Mg) lines measured from plasmas generated in air at atmospheric pressure from calcium hydroxide samples using an infrared Nd:YAG laser. The influence of laser irradiance on both plasma shape and emission intensity was studied to select the most suitable experimental conditions. Spectral lines of Mg I-II were measured and analyzed for different laser energies, delay times, and concentrations of the analyte. In each case, the plasma temperature, the electron density, and the parameters Nl were determined, without employing curves-of-growth. The results obtained showed the practical usefulness of the method to provide valuable information in LIBS experiments. PMID:21986082

Pace, Diego M Díaz; D'Angelo, Cristian A; Bertuccelli, Graciela

2011-10-01

242

Spectrally-based quantification of plant heavy metal-induced stress  

NASA Astrophysics Data System (ADS)

Recent developments in environmental studies are greatly related to worldwide ecological problems associated with anthropogenic impacts on the biosphere and first of all on vegetation. Modern remote sensing technologies are involved in numerous ecology-related investigations dealing with problems of global importance, such as ecosystems preservation and biodiversity conservation. Agricultural lands are subjected to enormous pressure and their monitoring and assessment have become an important ecological issue. In agriculture, remote sensing is widely used for assessing plant growth, health condition, and detection of stress situations. Heavy metals constitute a group of environmentally hazardous substances whose deposition in soils and uptake by species affect soil fertility, plant development and productivity. This paper is devoted to the study of the impact of heavy metal contamination on the performance of agricultural species. The ability of different spectral indicators to detect heavy metal-induced stress in plants is examined and illustrated. Empirical relationships have been established between the pollutant concentration and plant growth variables and spectral response. This allows not only detection but quantification of the stress impact on plant performance.

Kancheva, Rumiana; Georgiev, Georgi

2012-09-01

243

Plasma property effects on spectral line broadening in double-pulse laser-induced breakdown spectroscopy  

NASA Astrophysics Data System (ADS)

Double-pulse Laser-Induced Breakdown Spectroscopy (LIBS) in an orthogonal configuration was used to investigate plasma temperature and electron density effects on Mg II emission spectral line broadening. The experiments were carried out with two Nd:YAG lasers, one operating at 355 nm for ablation and the other one at 1064 nm for plasma reheating in air at atmospheric pressure. Temporally resolved plasma temperature and electron density were measured at various delay times. Data in this study show prolonged emission of Mg II (280.27 nm) as well as enhancement of the signal intensity when using double-pulse excitation compared to the single-pulse case. An enhancement of ˜8× was attained with a delay between the laser pulses equal to 1 ?s. The enhancement was accompanied by higher plasma temperature and increased electron density. The double-pulse LIBS configuration provides energy to sustain the plasma emission at a period in time when the linewidth is minimum, thereby improving the analytical capabilities of low spectral resolution instrumentation typically used in LIBS system.

Choi, Inhee; Mao, Xianglei; Gonzalez, J. Jhanis; Russo, Richard E.

2013-03-01

244

Multilayer thin-film polarizer design for the far ultraviolet using the induced transmission and absorption technique  

Microsoft Academic Search

Good theoretical designs of far ultraviolet polarizers have been reported using a MgF(subscript 2)\\/Al\\/MgF(subscript 2) three layer structure on a thick Al layer as a substrate. The thicknesses were determined to induce transmission and absorption of p-polarized light. In these designs Al optical constants were used from films produced in ultrahigh vacuum (UHV:10(superscript -10) torr). Reflectance values for polarizers fabricated

Jongmin Kim; Muamer Zukic; Michele M. Wilson; Jong H. Park; Douglas G. Torr

1994-01-01

245

Detection of gravity-induced polarity of cytoplasmic streaming in Chara  

Microsoft Academic Search

Summary 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 µm\\/s at this interface, decreases with distance from the interface on either side of the cell to 0 µm\\/s near the middle. Therefore, when

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

1995-01-01

246

Quantitative predictions on auxin-induced polar distribution of PIN proteins during vein formation in leaves  

Microsoft Academic Search

.  The dynamic patterning of the plant hormone auxin and its efflux facilitator the PIN protein are the key regulators for the\\u000a spatial and temporal organization of plant development. In particular auxin induces the polar localization of its own efflux\\u000a facilitator. Due to this positive feedback, auxin flow is directed and patterns of auxin and PIN arise. During the earliest\\u000a stage

Karen Alim; Erwin Frey

2010-01-01

247

Laser-induced reactions between a Ca+ Coulomb crystal and polar molecules  

NASA Astrophysics Data System (ADS)

We have investigated laser-induced reactions between laser-cooled crystallized Ca+ ions and polar molecule NH3 at room temperature. Reaction rates of Ca+* (3d 2D3/2, 4p 2P1/2) + NH3 ? products have been determined from time variation of the size of fluorescence images of Ca+ Coulomb crystals. From the pressure dependence of the reaction rates we determined a lower limit of the reaction rate coefficients.

Kimura, N.; Okada, K.; Shiina, K.; Suganuma, T.; Wada, M.; Schuessler, H. A.

2012-11-01

248

Chemically induced dynamic spin polarization in two dimensional systems: Theoretical predictions  

Microsoft Academic Search

Theoretical predictions for chemically induced dynamic spin polarization [CIDN(E)P] and Heisenberg spin exchange in two dimensional fluid systems are developed. An idealized model, which yields simple limiting results is first discussed in order to illustrate the importance of the geometrical aspects of this problem upon the CIDN(E)P observables. Pedersen–Freed theory, which employs numerical solutions of the stochastic-Liouville equation is then

Gary P. Zientara; Jack H. Freed

1979-01-01

249

Chemically induced dynamic spin polarization in two dimensional systems: Theoretical predictions  

Microsoft Academic Search

Theoretical predictions for chemically induced dynamic spin polarization [CIDN(E)P] and Heisenberg spin exchange in two dimensional fluid systems are developed. An idealized model, which yields simple limiting results is first discussed in order to illustrate the importance of the geometrical aspects of this problem upon the CIDN(E)P observables. Pedersen-Freed theory, which employs numerical solutions of the stochastic-Liouville equation is then

Gary P. Zientara; Jack H. Freed

1979-01-01

250

Spread of HTLV-I Between Lymphocytes by Virus-Induced Polarization of the Cytoskeleton  

Microsoft Academic Search

Cell contact is required for efficient transmission of human T cell leukemia virus- type 1 (HTLV-I) between cells and between individuals, because naturally infected lymphocytes produce virtually no cell-free infectious HTLV-I particles. However, the mechanism of cell-to-cell spread of HTLV-I is not understood. We show here that cell contact rapidly induces polarization of the cytoskeleton of the infected cell to

Tadahiko Igakura; Jane C. Stinchcombe; Peter K. C. Goon; Graham P. Taylor; Jonathan N. Weber; Gillian M. Griffiths; Yuetsu Tanaka; Mitsuhiro Osame; Charles R. M. Bangham

2003-01-01

251

Photochemically Induced Dynamic Nuclear Polarization (Photo-CIDNP) Magic-Angle Spinning NMR  

Microsoft Academic Search

Photochemically induced dynamic nuclear polarization (photo-CIDNP) is non-Boltzmann nuclear magnetization which can be observed\\u000a by NMR spectroscopy as enhanced absorptive (positive) or emissive (negative) signals. In solids, photo-CIDNP has been observed\\u000a since its discovery in 1994 in various photosynthetic reaction centers (RCs) by magic angle spinning (MAS) solid-state NMR.\\u000a The photo-CIDNP effect in solids can be explained by a combination

Eugenio Daviso; Gunnar Jeschke; Jörg Matysik

252

Chemically induced dynamic nuclear polarization in systems containing large hyperfine coupling constants  

Microsoft Academic Search

Nuclear spin polarization effects induced in radical pairs with one or more strong (¹³C) hyperfine coupling constants have been evaluated. The pairs were generated by photoinduced α-cleavage or hydrogen abstraction reactions of carbonyl compounds. Several examples illustrate how changes in the magnetic field strength (Hâ) and the g-factor difference (Îg) affect the general appearance of the resulting CIDNP multiplets. The

Heinz D. Roth; Richard S. Hutton; Kuochu Hwang; Nicholas J. Turro; Kevin M. Welsh

1989-01-01

253

Heat-induced changes to lipid molecular structure in Vimy flaxseed: spectral intensity and molecular clustering.  

PubMed

Autoclaving was used to manipulate nutrient utilization and availability. The objectives of this study were to characterize any changes of the functional groups mainly associated with lipid structure in flaxseed (Linum usitatissimum, cv. Vimy), that occurred on a molecular level during the treatment process using infrared Fourier transform molecular spectroscopy. The parameters included lipid CH(3) asymmetric (ca. 2959 cm(-1)), CH(2) asymmetric (ca. 2928 cm(-1)), CH(3) symmetric (ca. 2871 cm(-1)) and CH(2) symmetric (ca. 2954 cm(-1)) functional groups, lipid carbonyl CO ester group (ca. 1745 cm(-1)), lipid unsaturation group (CH attached to CC) (ca. 3010 cm(-1)) as well as their ratios. Hierarchical cluster analysis (CLA) and principal components analysis (PCA) were conducted to identify molecular spectral differences. Flaxseed samples were kept raw for the control or autoclaved in batches at 120°C for 20, 40 or 60 min for treatments 1, 2 and 3, respectively. Molecular spectral analysis of lipid functional group ratios showed a significant decrease (P<0.05) in the CH(2) asymmetric to CH(3) asymmetric stretching band peak intensity ratios for the flaxseed. There were linear and quadratic effects (P<0.05) of the treatment time from 0, 20, 40 and 60 min on the ratios of the CH(2) asymmetric to CH(3) asymmetric stretching vibration intensity. Autoclaving had no significant effect (P>0.05) on lipid carbonyl CO ester group and lipid unsaturation group (CH attached to CC) (with average spectral peak area intensities of 138.3 and 68.8 IR intensity units, respectively). Multivariate molecular spectral analyses, CLA and PCA, were unable to make distinctions between the different treatment original spectra at the CH(3) and CH(2) asymmetric and symmetric region (ca. 2988-2790 cm(-1)). The results indicated that autoclaving had an impact to the mid-infrared molecular spectrum of flaxseed to identify heat-induced changes in lipid conformation. A future study is needed to quantify the relationship between lipid molecular structure changes and functionality/availability. PMID:21420356

Yu, Peiqiang; Damiran, Daalkhaijav

2011-03-21

254

Femtosecond laser-induced macular hole followed by spectral-domain optical coherence tomography.  

PubMed

There are rare reports of accidental macular injury caused by a laser-induced plasma flash.1,2 Here, we report a case of macular hole due to prolonged viewing of a plasma flash by a femtosecond laser that was followed with spectral domain OCT (SD-OCT). A 25-yearlevel while not wearing protective goggles. The pulsed titanium-sapphire femtosecond laser was operating at a repetition rate of 80 MHz, 0.5 mJ pulse energy, a central wavelength of 850 nm, and a pulse duration of 50 fs. The laser beam was focused by a lens with 50 cm focal length before delivery to a target tissue. The patient immediately had decreased vision and a paracentral scotoma in his left eye. -old postgraduate student stared at a bright flash from the plasma formed at the focus of a femtosecond laser from a distance of approximately 30 cm for >15 s at an ordinary indoor illumination. PMID:23448512

Cho, Ayashi; Sakai, Tsutomu; Akiyama, Goichi; Tsuneoka, Hiroshi

2013-02-28

255

Suppression of excitation and spectral broadening induced by interactions in a cold gas of Rydberg atoms.  

PubMed

We report on the observation of ultralong range interactions in a gas of cold rubidium Rydberg atoms. The van der Waals interaction between a pair of Rydberg atoms separated as far as 100,000 Bohr radii features two important effects: spectral broadening of the resonance lines and suppression of excitation with increasing density. The density dependence of these effects is investigated in detail for the S- and P-Rydberg states with principal quantum numbers n approximately 60 and n approximately 80 excited by narrow-band continuous-wave laser light. The density-dependent suppression of excitation can be interpreted as the onset of an interaction-induced local blockade. PMID:15524984

Singer, Kilian; Reetz-Lamour, Markus; Amthor, Thomas; Marcassa, Luis Gustavo; Weidemüller, Matthias

2004-10-13

256

Studies of polar mesosphere summer echoes with the EISCAT VHF and UHF radars: Information contained in the spectral shape  

NASA Astrophysics Data System (ADS)

The nature of PMSE in the VHF and UHF frequency range is considered taking into account the shape of corresponding Doppler spectra. Assuming a turbulence-based model of PMSE it is argued that for cases where a VHF radar detects strong PMSE, the UHF radar could either detect enhanced coherent scattering caused by the same physical process as in the VHF (i.e., turbulence with large charged ice particles), there could be incoherent scattering modified by the charged ice particles, or there could be a mixture of both. In order to distinguish these cases a simple but robust method is introduced to characterize the shape of the Doppler spectra derived from observations at both frequencies. Spectral shapes are quantified with one simple fitting parameter of a generalized fit to the autocorrelation function (=Fourier transform of the Doppler spectrum). This parameter takes a value of 1 for a Lorentzian spectrum indicative of pure incoherent scatter from the D-region, a value of 2 for coherent scatter owing to turbulence, and a value of less than 1 for incoherent scatter modified by the presence of charged aerosol particles. This method is applicable to observations at altitudes between ˜70 and ˜90 km. Simultaneous observations with the EISCAT VHF and UHF radar are presented in which all three cases mentioned above are identified. For the case of incoherent scatter modified by the presence of charged aerosol particles we quantify the radius of the involved ice particles to exceed ˜5 nm. Most importantly, however, for the case where the UHF-signal exceeded the incoherent scatter signal significantly, the spectrum revealed a clear Gaussian shape indicative of a coherent scattering process with identical spectral width as for the VHF-observations. This finding gives strong support that both echoes are created by the same turbulence-based mechanism and not by different mechanisms as speculated by several previous authors.

Strelnikova, Irina; Rapp, Markus

2010-01-01

257

Polarized spectral properties of a notable Yb3+: LaCa4O(BO3)3 crystal  

NASA Astrophysics Data System (ADS)

Yb3+: LaCa4O(BO3)3 single crystal, as a laser material with disordered structure, was successful grown by the Czochralski method. The important polarized spectra and laser performance parameters were analyzed in detail. The crystal has broad emission cross-section (FWHM = 57.1 nm for E?Y) at 1029 nm, wide gain cross-section (FWHM = 42.0 nm for E?Y) at 1029 nm, and long fluorescence lifetime of 2.88 ms, which are beneficial to the tunable laser emission and Q-switching ultra-short laser pulse. The results also report a lower pump threshold value which was calculated to be 0.4 kW/cm2 at 1029 nm compared with other well-known crystals.

Ji, Yuexia; Cao, Jiafeng; Tu, Chaoyang

2013-10-01

258

Laser-induced fluorescence and X-ray spectral analysis of carious process in hard dental tissues.  

PubMed

Morphological and spectral X-ray analysis of carious and noncarious extracted teeth showed the patterns of dentin ossification in caries of different degree. Parietal ectopic ossification of the canal and cavity lumens in stages III and IV dental caries is regarded as a specific structural marker of pathological regeneration. The X-ray spectral analysis showed that the progress of carious process is paralleled by loss of mineral components. Laser-induced fluorescent study of tissues in extracted teeth showed 4 spectral bands corresponding to mineral and protein components of the tooth. The progress of carious process was associated with reduction of the fluorescence intensities of the spectral bands characteristic of dental collagen and mineral components. PMID:21246104

Lidman, G Yu; Larionov, P M; Savchenko, S V; Lushnikova, E L; Orishich, A M; Rozhin, I A; Malov, A N; Maslov, N A; Titov, A T; Kositsyna, I G

2010-09-01

259

Measurement of the induced ?0(1116) polarization in K+ electroproduction at CLAS  

NASA Astrophysics Data System (ADS)

We are using the p(e, e' K+p)?- reaction to perform a measurement of the induced polarization of the electroproduced L(1116) using its p?- parity-violating weak decay. This study uses the CEBAF Large Acceptance Spectrometer (CLAS) to detect the scattered electron, the kaon, and the decay proton over the kinematics 0.8 <= Q2 <= 3.5 GeV2, 1.6 <= W <= 3.0 GeV, and the full kaon CM angle range. In this experiment a 5.5 GeV electron beam was incident upon an unpolarized liquid-hydrogen target. The goal is to map out the kinematic dependencies for this polarization observable to provide new constraints for models of the electromagnetic production of K-hyperon final states. Along with previously published photo- and electroproduction cross sections and polarization observables from CLAS, SAPHIR, LEPS, and GRAAL, these data are needed in a coupled-channel analysis to identify previously unobserved s-channel resonances. Preliminary polarization results will be presented.

Gabrielyan, M.; Raue, B.; Carman, D. S.; Park, K.; CLAS Collaboration

2012-04-01

260

RESIS: A Three-Dimensional Resistivity and Induced Polarization Computer Program Based on a Surface Integral Technique. Final Report.  

National Technical Information Service (NTIS)

A computer program that calculates apparent resistivity and induced polarization for the situation in which an anomalously conducting body is embedded in a homogeneous half- or whole-space is described. The program can deal with (1) fixed current probes, ...

J. M. Hanson

1986-01-01

261

Polarization induced effects in group-III-nitride heterostructures and devices  

NASA Astrophysics Data System (ADS)

Two dimensional electron and hole gases in AlInGaN/GaN hetero- and quantum well structures suitable for high electron mobility transistors (HEMT´s) are induced by strong polarization effects. The sheet carrier concentration and the confinement of the two dimensional carrier gases located close to one of the AlInGaN/GaN interfaces are sensitive to a high number of different physical properties such as polarity, alloy composition, strain, thickness and doping of the barriers. We have investigated the structural quality, the carrier concentration profiles and electrical transport properties of undoped, silicon and magnesium doped structures by a combination of high resolution X-ray diffraction, atomic force microscopy, PL-spectroscopy, Hall effect, C-V profiling and Shubnikov-de Haas measurements. The investigated samples with N- and Ga-face polarity were grown by metalorganic vapor phase (MOCVD) or plasma induced molecular beam epitaxy (PIMBE) covering a broad range of alloy compositions, barrier and quantum well thicknesses. We have measured and calculated the polarization induced sheet charge based on different sets of piezoelectric constants available in the literature and the sheet carrier concentration for 2DEGS and 2DHGs self-consistently from a coupled Schrödinger and Poisson equation for different alloy compositions and degree of relaxation of the barrier. By comparison of theoretical and experimental results we demonstrate that the formation of two dimensional carrier gases in AlGaInN/GaN structures both rely on the difference of piezoelectric and spontaneous polarization between the AlGaInN and the GaN layer. In addition, the experimental evidence for accumulation of free carriers at interfaces of lattice matched AlInN/GaN heterostructures and pseudomorphic InGaN/GaN quatum well structures due to gradients in spontaneous or piezoelectric polarization will be presented. The influence and relevance of the resulting carrier distribution on the performance of electronic and optoelectronic devices will be discussed in detail. O. Ambacher, J. Phys. D: Appl. Phys. 31 (1998) 2653. O. Ambacher et al., J. Appl. Phys. 85 (1999) 3222. O. Ambacher et al., J. Appl. Phys. 87 (2000) 334.

Ambacher, Oliver

2001-03-01

262

Relaxation behaviour of electrically induced polar orientation and of optically induced non-polar orientation in an azo-chromophore side group polymer  

NASA Astrophysics Data System (ADS)

We have investigated the relaxation of the polar order (P1icons/Journals/Common/langle" ALT="langle" ALIGN="TOP"/>cosicons/Journals/Common/theta" ALT="theta" ALIGN="TOP"/>icons/Journals/Common/rangle" ALT="rangle" ALIGN="TOP"/>) in a poled styrene-maleic anhydride copolymer with side groups of modified dispersed red chromophores - using pyroelectric studies - as well as the relaxation of the orientational order (P2icons/Journals/Common/langle" ALT="langle" ALIGN="TOP"/>cosicons/Journals/Common/theta" ALT="theta" ALIGN="TOP"/>icons/Journals/Common/rangle" ALT="rangle" ALIGN="TOP"/>) of the optical axes of the side groups previously induced by polarized light - using holographic techniques. Isomerization cycles of the chromophores cause in the latter case the formation of an optical grating. The relaxation processes were monitored within the glassy state. In addition we investigated molecular relaxation processes, in particular the glass relaxation, using dielectric techniques. The observation was that the relaxations of the pyroelectric response and of the holographic grating couple to the glass relaxation yet do not display identical kinetics within the solid glassy state, showing that the optical grating is less stable. The difference arises obviously from the excess free volume induced by the isomerization cycle in the optical storage experiment. The formation of this excess free volume is apparent from the formation of a surface relief pattern in the storage experiment. A straightforward conclusion is that the stability of the grating can be considerably enhanced if chromophores are used characterized by a significantly lower equilibrium concentration of cis-species during irradiation.

Stracke, A.; Bayer, A.; Zimmermann, S.; Wendorff, J. H.; Wirges, W.; Bauer-Gogonea, S.; Bauer, S.; Gerhard-Multhaupt, R.

1999-12-01

263

Photophysics of indole in polar solvent: Analysis of fluorescence lifetime distributions and time-dependence spectral shifts  

NASA Astrophysics Data System (ADS)

The fluorescence lifetime distribution of indole in isobutanol is described by the Maximum Entropy Method (MEM) by a main slow emission decay component and a second fast one which is due to spectral kinetics processes. These latter components are associated with positive amplitudes at short emission wavelengths and with negative amplitudes with the same mean decay time value at the long-wavelength edge of the fluorescence spectrum. Both positive and negative rapid components sharply decline or even disappear if the excitation is performed at the long-wavelength edge of the absorption spectrum (300 nm). As expected, these components are very sensitive to temperature. The variation is linear in Arrhenius coordinates and results in activation energies of 7.5 kcal/mol. The shifts of emission spectra as a function of time (TRES) have allowed to obtain relaxation times in the same range as observed in lifetime distributions. The C(t) function defined by the centers of the time-dependent emission spectrum, can be described by MEM as a sum of two or three discrete components depending on the temperature and not by continuous distributions. The longuest one displays a similar value as that of the longuest longitudinal relaxation time of isobutanol as determined by dielectric measurements in the same temperature range. The excited state stabilization energy is around 3.7 kcal/mol. This set of results are consistent with a mechanism of general dielectric solvent relaxation rather than formation of binary excited state complexes in the time range studied.

Vincent, Michel; Gallay, Jacques; Demchenko, Alexander P.

1996-04-01

264

Charge state dependent kinetic electron emission induced by slow Nq+ ions in a spin-polarized electron gas  

NASA Astrophysics Data System (ADS)

The screening of a Nq+ ion embedded in a spin-polarized electron gas is studied using density functional theory within the local spin density approximation. Results are presented for the dependence of the spin-polarization of the induced screening charge on the charge state (electronic configuration) of the Nq+ ion. The number and spin-polarization of the electrons excited when a slow Nq+ ion travels through the medium are calculated. It is observed that the degree of spin-polarization of the screening cloud and of the excited electrons depend crucially on the projectile L-shell filling.

Vincent, R.; Juaristi, J. I.

2005-05-01

265

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

266

Nanoscale infrared spectroscopy: improving the spectral range of the photothermal induced resonance technique.  

PubMed

Photothermal induced resonance (PTIR) is a new technique which combines the chemical specificity of infrared (IR) spectroscopy with the lateral resolution of atomic force microscopy (AFM). PTIR requires a pulsed tunable laser for sample excitation and an AFM tip to measure the sample expansion induced by light absorption. The limited tunability of commonly available laser sources constrains the application of the PTIR technique to a portion of the IR spectrum. In this work, a broadly tunable pulsed laser relying on a difference frequency generation scheme in a GaSe crystal to emit light tunable from 1.55 ?m to 16 ?m (from 6450 cm(-1) to 625 cm(-1)) was interfaced with a commercial PTIR instrument. The result is a materials characterization platform capable of chemical imaging, in registry with atomic force images, with a spatial resolution that notably surpasses the light diffraction limit throughout the entire mid-IR spectral range. PTIR nanoscale spectra and images allow the identification of compositionally and optically similar yet distinct materials; organic, inorganic, and composite samples can be studied with this nanoscale analog of infrared spectroscopy, suggesting broad applicability. Additionally, we compare the results obtained with the two tunable lasers, which have different pulse lengths, to experimentally assess the recently developed theory of PTIR signal generation. PMID:23363013

Katzenmeyer, Aaron M; Aksyuk, Vladimir; Centrone, Andrea

2013-02-04

267

Nuclear-Charge Polarization at Scission in Proton-Induced Fission of Light Actinides  

SciTech Connect

Fragment mass yields and the average neutron multiplicity in the proton-induced fission of {sup 232}Th and {sup 233}U were measured by a double time-of-flight method. The most probable charges of secondary fragments were evaluated from the fragment mass yields measured and the fractional cumulative yields reported. The nuclear charge polarization of primary fragments at scission was obtained by correcting the most probable charge of secondary fragments for neutron evaporation. The results show that the nuclear-charge polarization at scission is associated with the liquid-drop properties of nuclei and the proton shell effect with Z = 50 of heavy fragments and that it is practically insensitive to mass and excitation energy of the fissioning nucleus in the region of light actinides.

Nishinaka, I.; Nagame, Y. [Japan Atomic Energy Agency, Tokai-mura, Naka-gun, Ibaraki 319-1195 (Japan); Tanikawa, M. [School of Science, University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0032 (Japan); Nakahara, H. [Department of Chemistry, Tokyo Metropolitan University, Hachioji, Tokyo 192-0397 (Japan)

2009-03-04

268

13C hyperpolarization of a barbituric acid derivative via parahydrogen induced polarization  

NASA Astrophysics Data System (ADS)

Significant 13C NMR signal enhancement by a factor of 5000 of a barbituric acid derivative (5-methyl-5-propenyl-barbituric acid) via parahydrogen induced polarization is presented. This hyperpolarization is achieved by hydrogenating 5-methyl-5-propargyl-barbituric acid with 98% enriched para-H2 under elevated temperature and pressure and transferring the initially created 1H hyperpolarization with an INEPT-derived pulse sequence to 13C. The polarization can be selectively transferred to different carbons in the barbituric acid derivative by applying different pulse delays in the INEPT pulse sequence. These results demonstrate the potential of using hyperpolarized barbituric acid derivatives as “active” contrast agents in MRI and visualizing their pharmacokinetics in vivo.

Roth, Meike; Koch, Achim; Kindervater, Petra; Bargon, Joachim; Spiess, Hans Wolfgang; Münnemann, Kerstin

2010-05-01

269

Field-induced transitions between multilayer phases of polar smectic liquid crystals.  

PubMed

Recently Wang et al. [Phys. Rev. Lett. 104, 027801 (2010)] reported the discovery of a novel multilayer phase in polar liquid crystals. The phase was unambiguously assigned to a six-layer antiferroelectric structure (Sm-C(d6)(*)) by resonant x-ray diffraction. This discovery lead to essential progress in understanding the nature of polar phases. However, more recently, Chandani et al. [Liq. Cryst. 38, 663 (2011)] in the same material clearly identified the novel phase as a ferrielectric five-layer structure (Sm-C(d5)(*)) by the electric-field-induced birefringence. This contradiction seemed to be a mystery. In this paper we show that the two experiments are in agreement. Phenomenological Landau theory of the phase transitions shows that both phases (Sm-C(d6)(*) and Sm-C(d5)(*)) exist and transform into each other in a relatively low electric field. PMID:23005711

Dolganov, P V; Zhilin, V M; Dolganov, V K; Kats, E I

2012-08-15

270

Spatial gradient of dynamic nuclear spin polarization induced by breakdown of the quantum Hall effect  

NASA Astrophysics Data System (ADS)

We studied spatial distribution of dynamic nuclear polarization (DNP) in a Hall-bar device in a breakdown regime of the quantum Hall effect (QHE). We detected nuclear magnetic resonance (NMR) signals from the polarized nuclear spins by measuring the Hall voltage Vxy using three pairs of voltage probes attached to the conducting channel of the Hall bar. We find that the amplitude of the NMR signal depends on the position of the Hall voltage probes and that the largest NMR signal is obtained from the pair of probes farthest from the electron-injecting electrode. Combined with results on pump-and-probe measurements, we conclude that the DNP induced by QHE breakdown develops along the electron-drift direction.

Kawamura, M.; Kono, K.; Hashimoto, Y.; Katsumoto, S.; Machida, T.

2011-01-01

271

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

272

Semiclassical description of TRI asymmetry in ternary fission induced by cold polarized neutrons  

SciTech Connect

The possibility of semiclassically describing T-even TRI-type asymmetry in ternary fission induced by polarized neutrons is considered on the basis of employing Coriolis interaction that takes into account the coupling of a light charged particle to the collective rotation of a polarized fissile nucleus. It is shown that allowance for this interaction makes it possible to explain qualitatively the magnitudes of two asymmetry effects observed in light-charge-particle emission both within the semiclassical and within the quantum-mechanical approach. The difference in the relative magnitudes and signs of the effects between different target nuclei is associated with the interference contributions to the cross section from neighboring neutron resonances and therefore cannot be explained within the semiclassical approach.

Bunakov, V. E., E-mail: bunakov@vb13190.spb.edu [Russian Academy of Sciences, Petersburg Nuclear Physics Institute (Russian Federation); Kadmensky, S. G. [Voronezh State University (Russian Federation)

2011-11-15

273

Four-wave mixing using polarization grating induced thermal grating in liquids exhibiting circular dichroism  

SciTech Connect

A novel four-wave mixing technique for the detection of circular dichroism in optically active liquid samples is demonstrated. When two cross-polarized laser beams are crossed at a small angle in a circular dichroic liquid a weak thermal grating is produced with a phase depending on the sign of the circular dichroism. The authors show that the polarization of one of the beams can be modified to allow coherent interference with an intensity-grating induced thermal grating. A probe beam scattering from the composite grating results in a signal that reveals the sign and magnitude of the circular dichroism. The use of this technique to optimize the signal-to-noise ratio in the presence of scattered light and laser intensity noise is discussed.

Nunes, J.A.; Tong, W.G. [San Diego State Univ., CA (United States). Dept. of Chemistry; Chandler, D.W.; Rahn, L.A. [Sandia National Lab., Livermore, CA (United States). Combustion Research Facility

1995-04-01

274

Analysis of Seeing-induced Polarization Cross-talk and Modulation Scheme Performance  

NASA Astrophysics Data System (ADS)

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.

2012-09-01

275

The X-ray spectrum and spectral energy distribution of FIRST J155633.8+351758: a LoBAL quasar with a probable polar outflow  

NASA Astrophysics Data System (ADS)

We report the results of a new 60 ks Chandra X-ray Observatory Advanced CCD Imaging Spectrometer S-array (ACIS-S) observation of the reddened, radio-selected, highly polarized `FeLoBAL' quasar FIRST J1556+3517. We investigated a number of models of varied sophistication to fit the 531-photon spectrum. These models ranged from simple power laws to power laws absorbed by hydrogen gas in differing ionization states and degrees of partial covering. Preferred fits indicate that the intrinsic X-ray flux is consistent with that expected for quasars of similarly high luminosity, i.e. an intrinsic, dereddened and unabsorbed optical to X-ray spectral index of -1.7. We cannot tightly constrain the intrinsic X-ray power-law slope, but find indications that it is flat (photon index ? = 1.7 or flatter at a >99 per cent confidence for a neutral hydrogen absorber model). Absorption is present, with a column density a few times 1023 cm-2, with both partially ionized models and partially covering neutral hydrogen models providing good fits. We present several lines of argument that suggest the fraction of X-ray emissions associated with the radio jet is not large. We combine our Chandra data with observations from the literature to construct the spectral energy distribution of FIRST J1556+3517 from radio to X-ray energies. We make corrections for Doppler beaming for the pole-on radio jet, optical dust reddening and X-ray absorption, in order to recover a probable intrinsic spectrum. The quasar FIRST J1556+3517 seems to be an intrinsically normal radio-quiet quasar with a reddened optical/UV spectrum, a Doppler-boosted but intrinsically weak radio jet and an X-ray absorber not dissimilar from that of other broad absorption line quasars.

Berrington, Robert C.; Brotherton, Michael S.; Gallagher, Sarah C.; Ganguly, Rajib; Shang, Zhaohui; DiPompeo, Michael; Chatterjee, Ritaban; Lacy, Mark; Gregg, Michael D.; Hall, Patrick B.; Laurent-Muehleisen, S. A.

2013-10-01

276

Shock-induced polarized hydrogen emission lines in the Mira star o Ceti  

NASA Astrophysics Data System (ADS)

Context. In the spectra of variable pulsating stars, especially Mira stars, the detection of intense hydrogen emission lines has been explained by the presence of a radiative and hypersonic shock wave, periodically propagating throughout the stellar atmosphere. Previous observation of the Mira star o Ceti around one of its brightest maximum light led to the detection of a strong level of linear polarization associated to Balmer emissions, although the origin of this phenomenon is not fully explained yet. Aims: With the help of spectropolarimetry, we propose to investigate the nature of shock waves propagating throughout the stellar atmosphere and present, for o Ceti (the prototype of Mira stars), a full observational study of hydrogen emission lines formed in the radiative region of such a shock. Methods: Using the instrument NARVAL mounted on the Télescope Bernard Lyot (TBL) in Pic du Midi Observatory (France), we performed a spectropolarimetric monitoring of o Ceti during three consecutive pulsation cycles. For this survey, the four Stokes parameters (I for intensity, Q and U for linear polarization, and V for circular polarization) were systematically collected, with a particular emphasis on the maxima of luminosity, i.e. when a radiative shock wave is supposed to emerge from the photosphere and starts to propagate outward. Results: On hydrogen Balmer lines, over a large part of the luminosity cycle, we report clear detection of polarimetric structures in Q and U Stokes spectra (and also in V Stokes spectra but to a lesser extent). We report a temporal evolution of these spectropolarimetric signatures, which appear strongly correlated to the presence of an intense shock wave responsible for the hydrogen emission lines. We establish that the hydrogen lines are polarized by a physical process inherent to the mechanism responsible for the emission line formation: the shock wave itself. Two mechanisms are thus considered: a global one that implies a polarization induced by some giant convective cells located around the photosphere and a local one that implies a charge separation due to the passage of the shock wave, inducing an electrical current. Combined with the existing turbulence, this may generate a magnetic field, hence polarization. Based on spectropolarimetric observations obtained at the Télescope Bernard Lyot (TBL at Observatoire du Pic du Midi, CNRS and Université de Toulouse, France).

Fabas, N.; Lèbre, A.; Gillet, D.

2011-11-01

277

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

2013-04-08

278

Vortex oscillations induced by spin-polarized current in a magnetic nanopillar: Analytical versus micromagnetic calculations  

NASA Astrophysics Data System (ADS)

We investigate the vortex excitations induced by a spin-polarized current in a magnetic nanopillar by means of micromagnetic simulations and analytical calculations. Damped motion, stationary vortex rotation and the switching of the vortex core are successively observed for increasing values of the current. We demonstrate that even for small amplitude of the vortex motion, the analytical description based on the classical Thiele approach can yield quantitatively and qualitatively unsound results. We show that the energy dissipation function, which is calculated respecting rotational motion of the vortex, can be used for qualitative analytical description of the system.

Khvalkovskiy, A. V.; Grollier, J.; Dussaux, A.; Zvezdin, Konstantin A.; Cros, V.

2009-10-01

279

Laser-induced reactions between a Ca+ Coulomb crystal and polar molecules  

NASA Astrophysics Data System (ADS)

We have studied laser-induced reactions between a Ca+ Coulomb crystal and the polar molecules of NH3 and ND3 at room temperature. The reaction rates of Ca+*(3d2D3/2, 4p2P1/2) + NH3 (ND3) ? products have been determined from time variation of the size of fluorescence images of Ca+ Coulomb crystals. The results show that the reaction rates are very slow, and therefore the reaction-rate measurements between sympathetically cooled molecular ions and slow NH3 (ND3) molecules can be performed using a Ca+ Coulomb crystal as coolant.

Okada, K.; Kimura, N.; Suganuma, T.; Shiina, K.; Furukawa, T.; Takayanagi, T.; Wada, M.; Schuessler, H. A.

2012-11-01

280

Sustainable orientation of polar molecules induced by half-cycle pulses  

SciTech Connect

Subjecting polar linear molecules to appropriately designed half-cycle electromagnetic pulses induces strong orientation of the molecules. This is deduced by inspecting the quantum dynamics within a simplified model which yields analytical conditions for the parameters of the pulses that lead to strong molecular orientation sustainable for hundreds of picoseconds. These analytical predictions are largely confirmed by a full numerical time-dependent study of the orientation process for NaI molecules. Further strategies for increasing and maintaining the molecular orientation are proposed and numerically illustrated. Our finite-temperature calculations demonstrate that the molecular orientation persists at considerable temperatures.

Matos-Abiague, A.; Berakdar, J. [Max-Planck Institut fuer Mikrostrukturphysik, Weinberg 2, 06120 Halle (Germany)

2003-12-01

281

Evaluation of the effects of caffeine in the microcirculation and edema on thighs and buttocks using the orthogonal polarization spectral imaging and clinical parameters.  

PubMed

Gynoid lipodystrophy, also known as cellulite, is a common multifactorial entity that affects millions of women around the world. There have been few scientific articles dealing with its physiology and treatment in the past few years, and vascular changes seem to play an important role in its pathophysiology. Skin microvascular alterations can be observed noninvasively with a new method called orthogonal polarization spectral imaging, which was used to evaluate the effectiveness of an anticellulite drug composed mainly of a 7% caffeine solution. Microcirculatory parameters evaluated were functional capillary density (FCD; number of flowing capillaries per unit area), diameter of the dermic papilla (DPD), and capillary diameter (CD). The clinical parameters analyzed were centimetrical measurements of thighs and hips and the influence of tobacco, alcohol, and physical activities on the efficacy of the treatment. After 1 month of treatment, statistical application of chi-squared and Z approximation tests showed, in treated patients, statistically significant reduction of thigh circumferences in more than 80% of the cases and reduction of hip circumference in 67.7%. FCD, DPD, and CD did not change significantly after treatment. Smoking as well as alcohol consumption and regular physical activity were not significantly related to the centimetrical reduction observed in treated thighs and hips. PMID:17524126

Lupi, Omar; Semenovitch, Ivan Jorge; Treu, Curt; Bottino, Daniel; Bouskela, Eliete

2007-06-01

282

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

283

Lymphocyte-Polarized Dendritic Cells Are Highly Effective in Inducing Tumor-Specific CTLs  

PubMed Central

High activity of dendritic cells (DCs) in inducing cytotoxic T cells (CTLs) led to their application as therapeutic cancer vaccines. The ability of DCs to produce IL-12p70 is one of the key requirements for effective CTL induction and a predictive marker of their therapeutic efficacy in vivo. We have previously reported that defined cocktails of cytokines, involving TNF? and IFN?, induce mature type-1 polarized DCs (DC1s) which produce strongly elevated levels of IL-12 and CXCL10/IP10 upon CD40 ligation compared to “standard” PGE2-matured DCs (sDCs; matured with IL-1?, IL-6, TNF?, and PGE2) and show higher CTL-inducing activity. Guided by our observations that DC1s can be induced by TNF?- and IFN?-producing CD8+ T cells, we have tested the feasibility of using lymphocytes to generate DC1s in a clinically-compatible process, to limit the need for clinical-grade recombinant cytokines and the associated costs. CD3/CD28 activation of bulk lymphocytes expanded them and primed them for effective production of IFN?and TNF?following restimulation. Restimulated lymphocytes, or their culture supernatants, enhanced the maturation status of immature (i)DCs, elevating their expression of CD80, CD83 and CCR7, and the ability to produce IL-12p70 and CXCL10 upon subsequent CD40 ligation. The “lymphocyte-matured” DC1s showed elevated migration in response to the lymph-node-directing chemokine, CCL21, when compared to iDCs. When loaded with antigenic peptides, supernatant-matured DCs induced much high levels of CTLs recognizing tumor-associated antigenic epitope, than PGE2-matured DCs from the same donors. These results demonstrate the feasibility of generation of polarized DC1s using autologous lymphocytes.

Berk, Erik; Muthuswamy, Ravikumar; Kalinski, Pawel

2012-01-01

284

Nuclear Lamin A/C Deficiency Induces Defects in Cell Mechanics, Polarization, and Migration  

PubMed Central

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 deficiency induces significant separation of the microtubule organizing center (MTOC) from the nuclear envelope. Investigations using ballistic intracellular nanorheology reveal that lamin A/C deficiency also dramatically affects the micromechanical properties of the cytoplasm. Both the elasticity (stretchiness) and the viscosity (propensity of a material to flow) of the cytoplasm in Lmna?/? MEFs are significantly reduced. Disassembly of either the actin filament or microtubule networks in Lmna+/+ MEFs results in decrease of cytoplasmic elasticity and viscosity down to levels found in Lmna?/? MEFs. Together these results show that both the mechanical properties of the cytoskeleton and cytoskeleton-based processes, including cell motility, coupled MTOC and nucleus dynamics, and cell polarization, depend critically on the integrity of the nuclear lamina, which suggest the existence of a functional mechanical connection between the nucleus and the cytoskeleton. These results also suggest that cell polarization during cell migration requires tight mechanical coupling between MTOC and nucleus, which is mediated by lamin A/C.

Lee, Jerry S. H.; Hale, Christopher M.; Panorchan, Porntula; Khatau, Shyam B.; George, Jerry P.; Tseng, Yiider; Stewart, Colin L.; Hodzic, Didier; Wirtz, Denis

2007-01-01

285

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

286

Electromagnetic fields induced by a cuboidal inclusion with uniform spontaneous polarization and magnetization  

NASA Astrophysics Data System (ADS)

Exact closed-form solutions are derived for the electromagnetic fields induced by a cuboidal inclusion with uniform spontaneous polarization and magnetization embedded in an infinite uniaxial multiferroic solid. The method of Green's function and direct integration are employed to obtain the solution, with the results for the induced electric and magnetic potentials as well as the electric and magnetic fields being in terms of elementary functions. It is observed that all the electric and magnetic field components exhibit logarithmic singularities near the eight corners of the cuboid. There also exist logarithmic singularities for the electric and magnetic fields near certain edges of the cuboid. Numerical results are presented for a typical multiferroic composite to demonstrate the variation of electromagnetic fields in and near the cuboidal inclusion.

Wang, X.; Pan, E.

2007-05-01

287

Dynamical nuclear spin polarization induced by electronic current through double quantum dots  

NASA Astrophysics Data System (ADS)

We analyse electron-spin relaxation in electronic transport through coherently coupled double quantum dots (DQDs) in the spin blockade regime. In particular, we focus on hyperfine (HF) interaction as the spin-relaxation mechanism. We pay special attention to the effect of the dynamical nuclear spin polarization induced by the electronic current on the nuclear environment. We discuss the behaviour of the electronic current and the induced nuclear spin polarization versus an external magnetic field for different HF coupling intensities and interdot tunnelling strengths. We take into account, for each magnetic field, all HF-mediated spin-relaxation processes coming from different opposite spin level approaches. We find that the current as a function of the external magnetic field shows a peak or a dip and that the transition from a current dip to a current peak behaviour is obtained by decreasing the HF coupling or by increasing the interdot tunnelling strength. We give a physical picture in terms of the interplay between the electrons tunnelling out of the DQD and the spin-flip processes due to the nuclear environment.

López-Monís, Carlos; Iñarrea, Jesús; Platero, Gloria

2011-05-01

288

Interferon regulatory factor 4 regulates obesity-induced inflammation through regulation of adipose tissue macrophage polarization.  

PubMed

Interferon regulatory factors (IRFs) play functionally diverse roles in the transcriptional regulation of the immune system. We have previously shown that several IRFs are regulators of adipogenesis and that IRF4 is a critical transcriptional regulator of adipocyte lipid handling. However, the functional role of IRF4 in adipose tissue macrophages (ATMs) remains unclear, despite high expression there. Here we show that IRF4 expression is regulated in primary macrophages and in ATMs of high-fat diet-induced obese mice. Irf4(-/-) macrophages produce higher levels of proinflammatory cytokines, including interleukin-1? and tumor necrosis factor-?, in response to fatty acids. In coculture experiments, IRF4 deletion in macrophages leads to reduced insulin signaling and glucose uptake in 3T3-L1 adipocytes. To determine the macrophage-specific function of IRF4 in the context of obesity, we generated myeloid cell-specific IRF4 knockout mice, which develop significant insulin resistance on a high-fat diet, despite no difference in adiposity. This phenotype is associated with increased expression of inflammatory genes and decreased insulin signaling in adipose tissue, skeletal muscle, and liver. Furthermore, Irf4(-/-) ATMs express markers suggestive of enhanced M1 polarization. These findings indicate that IRF4 is a negative regulator of inflammation in diet-induced obesity, in part through regulation of macrophage polarization. PMID:23835343

Eguchi, Jun; Kong, Xingxing; Tenta, Masafumi; Wang, Xun; Kang, Sona; Rosen, Evan D

2013-07-08

289

The human Lgl polarity gene, Hugl-2, induces MET and suppresses Snail tumorigenesis.  

PubMed

Lethal giant larvae proteins have key roles in regulating polarity in a variety of cell types and function as tumour suppressors. A transcriptional programme initiated by aberrant Snail expression transforms epithelial cells to potentially aggressive cancer cells. Although progress in defining the molecular determinants of this programme has been made, we have little knowledge as to how the Snail-induced phenotype can be suppressed. In our studies we identified the human lethal giant larvae homologue 2, Hugl-2, (Llgl2/Lgl2) polarity gene as downregulated by Snail. Snail binds E-boxes in the Hugl-2 promoter and represses Hugl-2 expression, whereas removal of the E-boxes releases Hugl-2 from Snail repression. We demonstrate that inducing Hugl-2 in cells with constitutive Snail expression reverses the phenotype including changes in morphology, motility, tumour growth and dissemination in vivo, and expression of epithelial markers. Hugl-2 expression reduced the nuclear localization of Snail and thus binding of Snail to its target promoters. Our results placing Hugl-2 within the Snail network as well as its ability to suppress Snail carcinogenesis identifies Hugl-2 as a target molecule driving cascades, which may have preventative and therapeutic promise to minimize cancer progression. PMID:22580609

Kashyap, A; Zimmerman, T; Ergül, N; Bosserhoff, A; Hartman, U; Alla, V; Bataille, F; Galle, P R; Strand, S; Strand, D

2012-05-14

290

Theoretical investigation on degradation behaviors of spectral properties of thermal control coatings induced by charged particles  

NASA Astrophysics Data System (ADS)

The degradation of spectral properties of thermal control coatings on spacecrafts is investigated in this paper. By studying their physical components and geometry structure, the factors which determine the spectral properties of the coatings are founded. A theoretical model for calculating the spectral absorptance of coatings is proposed based on the Mie's theory and Stratified Media theory. Mathematical expressions are introduced for accounting for the effect of the complicated environment. Based on these work, a predicting model for the degradation of spectral absorptance properties of the coatings is established. To validate this model, the predicted degradation performance of spectral properties of zinc oxide based coatings under electrons and protons exposure are compared with the experimental data. A good agreement is found at the wavelength between 250 nm and 2500 nm. Finally, a useful approach for predicting the degradation behaviors of thermal control coatings on spacecrafts in orbit is established.

Han, Yuge; Ma, Wei; Xuan, Yimin

2013-10-01

291

Differential polarization of alveolar macrophages and bone marrow-derived monocytes following chemically and pathogen-induced chronic lung inflammation  

PubMed Central

Alveolar macrophages and BDMCs undergo sequential biochemical changes during the chronic inflammatory response to chemically induced lung carcinogenesis in mice. Herein, we examine two chronic lung inflammation models—repeated exposure to BHT and infection with Mycobacterium tuberculosis—to establish whether similar macrophage phenotype changes occur in non-neoplastic pulmonary disease. Exposure to BHT or M. tuberculosis results in pulmonary inflammation characterized by an influx of macrophages, followed by systemic effects on the BM and other organs. In both models, pulmonary IFN-? and IL-4 production coincided with altered polarization of alveolar macrophages. Soon after BHT administration or M. tuberculosis infection, IFN-? content in BALF increased, and BAL macrophages became classically (M1) polarized, as characterized by increased expression of iNOS. As inflammation progressed in both models, the amount of BALF IFN-? content and BAL macrophage iNOS expression decreased, and BALF IL-4 content and macrophage arginase I expression rose, indicating alternative/M2 polarization. Macrophages present in M. tuberculosis-induced granulomas remained M1-polarized, implying that these two pulmonary macrophage populations, alveolar and granuloma-associated, are exposed to different activating cytokines. BDMCs from BHT-treated mice displayed polarization profiles similar to alveolar macrophages, but BDMCs in M. tuberculosis-infected mice did not become polarized. Thus, only alveolar macrophages in these two models of chronic lung disease exhibit a similar progression of polarization changes; polarization of BDMCs was specific to BHT-induced pulmonary inflammation, and polarization of granuloma macrophages was specific to the M. tuberculosis infection.

Redente, Elizabeth F.; Higgins, David M.; Dwyer-Nield, Lori D.; Orme, Ian M.; Gonzalez-Juarrero, Mercedes; Malkinson, Alvin M.

2010-01-01

292

Note: Reducing polarization induced sidebands in Rayleigh backscattering spectra for accurate distributed strain measurement using optical frequency-domain reflectometry  

NASA Astrophysics Data System (ADS)

We describe a phenomenon called polarization-induced sidebands (PIS) in Rayleigh backscatter spectra (RBS) and discuss its deteriorating effects on the distributed strain measurement using an optical frequency-domain reflectometry. We propose using a special polarization diversity detection scheme to remove PIS and successfully demonstrate accurate distributed strain measurement in the range of 0.75 ??-225 ?? in a 50 m standard single mode fiber, with a good linearity between the strain and the spectra shift in RBS.

Ding, Zhenyang; Steve Yao, X.; Liu, Tiegen; Du, Yang; Liu, Kun; Han, Qun; Meng, Zhuo; Li, Dingjie

2013-02-01

293

The X-ray Spectrum and Spectral Energy Distribution of FIRST J155633.8+351758: A Beamed Radio-Quiet Quasar with a Polar Outflow  

NASA Astrophysics Data System (ADS)

We report the results of a 60 ks Chandra X-ray Observatory ACIS-S observation of the reddened, radio-selected, highly polarized "FeLoBAL" quasar FIRST J155633.8+351758. Our analyses of the 531 photon spectrum indicate that the intrinsic X-ray flux is consistent with that expected for quasars of similarly high luminosity. We cannot tightly constrain the intrinsic X-ray power-law slope, but find indications that it is flat (photon index ? = 1.7 or flatter). No iron K-? line is detected, and the X-rays appear to be down by only an order of magnitude below their intrinsic unabsorbed levels. Absorption is present with both partially ionized models and neutral hydrogen models with partial covering providing good fits. The level of partial covering in the latter model is consistent with the rest-frame ultraviolet maximum polarization of 13%, in the sense that light scattered by electrons around the X-ray absorber could account for both results. We present the spectral energy distribution (SED) of FIRST J155633.8+351758 from radio through X-ray energies, and make corrections for Doppler beaming for the pole-on radio-quiet jet, optical dust reddening, and X-ray absorption. The corrected SED appears to be that of a luminous radio-quiet quasar deficient in the mid and far-infrared, suggesting that the dust covering fraction of the quasar is not large and that star formation is not excessive. FIRST J155633.8+351758 seems to be an intrinsically normal radio-quiet quasar with an X-ray absorber not dissimilar from that of other broad absorption line quasars studied in detail at X-ray wavelengths. We acknowledge support from Chandra Award No. GO6-7105X, from the US NSF (grant AST 05-07781), from NASA under the grant NNG05GD03G, and from the National Natural Science Foundation of China (grant 10643001). This work was performed under the auspices of the US DOE by the University of California, LLNL (Contract No. W-7405-Eng-48).

Berrington, Robert C.; Brotherton, M. S.; Gallagher, S. C.; Ganguly, R.; Shang, Z.; Lacy, M.; Gregg, M. D.; Hall, P. B.; Laurent-Muehleisen, S. A.

2007-12-01

294

High spectral efficiency 1.6-b\\/s\\/Hz transmission (8×40 Gb\\/s with a 25GHz grid) over 200-km SSMF using RZ-DQPSK and polarization multiplexing  

Microsoft Academic Search

With relatively simple standard transmission equipment, we achieved a wavelength-division-multiplexing transmission with a record-high spectral efficiency of 1.6 b\\/s\\/Hz using return-to-zero differential quadrature phase-shift keying and polarization multiplexing over 200-km standard single-mode fiber with a 40-Gb\\/s capacity per wavelength but 10-GSymbol\\/s rate.

Christoph Wree; Nancy Hecker-Denschlag; Erich Gottwald; Peter Krummrich; Jochen Leibrich; Ernst-Dieter Schmidt; Berthold Lankl; Werner Rosenkranz

2003-01-01

295

Correlation-Induced Doppler-Like Frequency Shifts of Spectral Lines.  

National Technical Information Service (NTIS)

The question is examined whether there may be scattering media which could generate spectral frequency shifts in radiation from sources that are at rest relative to the observer and yet would imitate Doppler shifts. Scattering kernels of media whose physi...

E. Wolf

1989-01-01

296

Square-root law of turbulence-induced spectral broadening in Raman fiber lasers  

NASA Astrophysics Data System (ADS)

The output characteristics of the conventional one-stage Raman fiber laser are described theoretically by using the optical wave turbulence formalism. Simple analytical expressions describing RFL output power and its spectral shape are presented as well as square-root law for the output spectrum broadening law has been discovered. The indications of the turbulent-like spectral broadening in other types of CW fiber lasers and propagation phenomena in fibers are also discussed.

Babin, S. A.; Churkin, D. V.; Ismagulov, A. E.; Kablukov, S. I.; Podivilov, E. V.

2008-03-01

297

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.

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

2008-01-01

298

Spectral Jones vectors and spectral coherence matrices in analyzing modulated light  

NASA Astrophysics Data System (ADS)

In analyzing the polarization spectral structure of the time- varying spinorial fields obtained by light modulation, the notions of spectral Jones vector and spectral coherence matrix are introduced. The KDP longitudinal electrooptic modulator is presented as an example.

Tudor, Tiberiu S.; Vinkler, Istvan

1998-07-01

299

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

300

Measured Stark Widths of Several Sn I and Sn II Spectral Lines in a Laser-induced Plasma  

NASA Astrophysics Data System (ADS)

Data on Stark widths of spectral lines are of high interest for astrophysics and analytical techniques of stellar plasma diagnosis. Stark widths of 43 spectral lines of Sn I and 27 spectral lines of Sn II has been measured in a laser-induced plasma (LIP) at an electron temperature of 11,000 K and an electron density of 1.1×1016 cm-3. The LIP optical emission spectroscopy generated by a 10640 Å radiation, with a flux of 1.4×1010 W cm-2 on several tin and lead targets in an atmosphere of argon was recorded at 2.5 ?s and analyzed between 1890 and 7000 Å. The population level distribution and the corresponding temperatures were obtained using Boltzmann plots. The plasma electron densities were determined using well-known Stark broadening parameters of spectral lines. Special attention was dedicated to the possible self-absorption of the different transitions. The local thermodynamic equilibrium (LTE) conditions and plasma homogeneity have been checked. The experimental results obtained have been compared with the experimental and theoretical values given by other authors. The results obtained in this study will allow a substantial improvement in the interpretation of the data of the ultraviolet spectrum of the tin observed by the Goddard High Resolution Spectrograph aboard the Hubble Space Telescope. These atomic data are relevant to the analysis of the isotopic abundances of tin in stellar atmospheres.

Alonso-Medina, A.; Colón, C.

2008-01-01

301

Solar-blind AlxGa1-xN/AlN/SiC photodiodes with a polarization-induced electron filter  

NASA Astrophysics Data System (ADS)

Heterogeneous n-III-nitride/i-p silicon carbide (SiC) photodetectors have been demonstrated that enable the tailoring of the spectral response in the solar blind region below 280 nm. The negative polarization induced charge at the aluminum gallium nitride (AlxGa1-xN)/aluminum nitride (AlN) interface in conjunction with the positive polarization charge at the AlN/SiC interface creates a large barrier to carrier transport across the interface that results in the selective collection of electrons photoexcited to the ? and L valleys of SiC while blocking the transport of electrons generated in the M valley. In addition, the AlxGa1-xN alloys act as transparent windows that enhance the collection of carriers generated by high energy photons in the fully depleted SiC absorption regions. These two factors combine to create a peak external quantum efficiency of 76% at 242 nm, along with a strong suppression of the long-wavelength response from 260 nm to 380 nm.

Rodak, L. E.; Sampath, A. V.; Gallinat, C. S.; Chen, Y.; Zhou, Q.; Campbell, J. C.; Shen, H.; Wraback, M.

2013-08-01

302

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

NASA Astrophysics Data System (ADS)

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.

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

2013-10-01

303

Efficient calculation of the polarization induced by N coherent laser pulses.  

PubMed

We have developed a novel method, the equation-of-motion phase-matching approach (EOM-PMA), for the calculation of the response of a quantum system to N coherent laser fields. The N-pulse EOM-PMA is limited to weak fields (its domain of validity is equivalent to the traditional nonlinear response functions approach), but allows for arbitrary pulse durations and automatically accounts for pulse-overlap effects. The N-pulse EOM-PMA allows the evaluation of the time evolution of the N-pulse-induced polarization in any phase-matching direction by performing 2(N)-1 independent propagations of certain auxiliary density matrices. The N-pulse EOM-PMA can straightforwardly be incorporated into codes which provide the time evolution of the density matrix of material systems of interest and can efficiently be implemented on parallel computers. PMID:19929042

Gelin, Maxim F; Egorova, Dassia; Domcke, Wolfgang

2009-11-21

304

Contact-induced spin polarization in graphene/h-BN/Ni nanocomposites  

NASA Astrophysics Data System (ADS)

Atomic and electronic structure of graphene/Ni(111), h-BN/Ni(111) and graphene/h-BN/Ni(111) nanocomposites with different numbers of graphene and h-BN layers and in different mutual arrangements of graphene/Ni and h-BN/Ni at the interfaces was studied using LDA/PBC/PW technique. Using the same technique corresponding graphene, h-BN and graphene/h-BN structures without the Ni plate were calculated for the sake of comparison. It was suggested that C-top:C-fcc and N-top:B-fcc configurations are energetically favorable for the graphene/Ni and h-BN/Ni interfaces, respectively. The Ni plate was found to induce a significant degree of spin polarization in graphene and h-BN through exchange interactions of the electronic states located on different fragments.

Avramov, Pavel V.; Kuzubov, Alex A.; Sakai, Seiji; Ohtomo, Manabu; Entani, Shiro; Matsumoto, Yoshihiro; Naramoto, Hiroshi; Eleseeva, Natalia S.

2012-12-01

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.

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

2013-01-01

306

Modeling induced polarization with classical Drude oscillators: Theory and molecular dynamics simulation algorithm  

NASA Astrophysics Data System (ADS)

A simple treatment for incorporating induced polarization in computer simulations is formulated on the basis of the classical Drude oscillator model. In this model, electronic induction is represented by the displacement of a charge-carrying massless particle attached to a polarizable atom under the influence of the local electric field. The traditional self-consistent field (SCF) regime of induced polarization is reproduced if these auxiliary particles are allowed to relax instantaneously to their local energy minima for any given fixed configuration of the atoms in the system. In practice, such treatment is computationally prohibitive for generating molecular dynamics trajectories because the electric field must be recalculated several times iteratively to satisfy the SCF condition, and it is important to seek a more efficient way to simulate the classical Drude oscillator model. It is demonstrated that a close approximation to the SCF regime can be simulated efficiently by considering the dynamics of an extended Lagrangian in which a small mass is attributed to the auxiliary particles, and the amplitude of their oscillations away from the local energy minimum is controlled with a low-temperature thermostat. A simulation algorithm in this modified two-temperature isobaric-isothermal ensemble is developed. The algorithm is tested and illustrated using a rigid three-site water model with one additional Drude particle attached to the oxygen which is closely related to the polarizable SPC model of Ahlström et al. [Mol. Phys. 68, 563 (1989)]. The tests with the extended Lagrangian show that stable and accurate molecular dynamics trajectories for large integration time steps (1 or 2 fs) can be generated and that liquid properties equivalent to SCF molecular dynamics can be reproduced at a fraction of the computational cost.

Lamoureux, Guillaume; Roux, Benoît

2003-08-01

307

Azimuthally polarized laser mode generation by multilayer mirror with wideband grating-induced TM leakage in the TE stopband.  

PubMed

A new intracavity laser polarization-mode selection scheme relying upon a TE/TM diffractive dichroism principle in a grating multilayer mirror is proposed and demonstrated. The grating diffracts the first orders between the TE and TM band edges of the angular spectra of the laser mirror inducing a leakage of the TM polarization into the mirror substrate through the multilayer stack whereas TE diffraction into the substrate is forbidden. This mechanism is non-resonant, thus relatively wide-band. Applied with a circular-line grating in the 1.0 µm - 1.1 µm wavelength range, this mirror filters out the radially polarization mode and causes the emission of the azimuthally polarized mode. An original amorphous silicon grating technology was developed and the optical function demonstrated in a Nd:YAG laser. PMID:22418346

Kämpfe, Thomas; Tonchev, Svetlen; Tishchenko, Alexandre V; Gergov, Deyan; Parriaux, Olivier

2012-02-27

308

Multi-vortical flow inducing electrokinetic instability in ion concentration polarization layer  

NASA Astrophysics Data System (ADS)

In this work, we investigated multiple vortical flows inside the ion concentration polarization (ICP) layer that forms due to a coupling of applied electric fields and the semipermeable nanoporous junction between microchannels. While only a primary vortex near perm-selective membrane is traditionally known to lead to electrokinetic instability, multiple vortexes induced by the primary vortex were found to play a major role in the electrokinetic instability. The existence of multiple vortexes was directly confirmed by experiments using particle tracers and interdigitated electrodes were used to measure the local concentration profile inside the ICP layer. At larger applied electric fields, we observed aperiodic fluid motion due to electrokinetic instabilities which develop from a coupling of applied electric fields and electrical conductivity gradients induced by the ICP. The electrokinetic instability at micro-nanofluidic interfaces is important in the development of various electro-chemical-mechanical applications such as fuel cells, bio-analytical preconcentration methods, water purification/desalination and the fundamental study of ion electromigration through nanochannels and nonporous perm-selective membranes.In this work, we investigated multiple vortical flows inside the ion concentration polarization (ICP) layer that forms due to a coupling of applied electric fields and the semipermeable nanoporous junction between microchannels. While only a primary vortex near perm-selective membrane is traditionally known to lead to electrokinetic instability, multiple vortexes induced by the primary vortex were found to play a major role in the electrokinetic instability. The existence of multiple vortexes was directly confirmed by experiments using particle tracers and interdigitated electrodes were used to measure the local concentration profile inside the ICP layer. At larger applied electric fields, we observed aperiodic fluid motion due to electrokinetic instabilities which develop from a coupling of applied electric fields and electrical conductivity gradients induced by the ICP. The electrokinetic instability at micro-nanofluidic interfaces is important in the development of various electro-chemical-mechanical applications such as fuel cells, bio-analytical preconcentration methods, water purification/desalination and the fundamental study of ion electromigration through nanochannels and nonporous perm-selective membranes. Electronic supplementary information (ESI) available. See DOI: 10.1039/c2nr32467a

Kim, Sung Jae; Ko, Sung Hee; Kwak, Rhokyun; Posner, Jonathan D.; Kang, Kwan Hyoung; Han, Jongyoon

2012-11-01

309

Optic axis determination based on polarization flipping effect induced by optical feedback.  

PubMed

For many materials, particularly biological tissues, optic axis orientation directly correlates with the materials performance, such as refractive index. In this Letter, a system measuring the optic axis azimuth was built using the laser feedback method that the polarization state of laser output is linearly polarized when optic axis azimuth is consistent with the initial direction of the laser polarization, otherwise elliptical polarization will be observed. The polarization state of the laser output is highly sensitive to the relative position of the optic axis and the initial direction of the laser polarization. This may be used to determine the optic axis azimuth of a material with a high precision. PMID:23546250

Chen, Wenxue; Zhang, Shulian; Long, Xingwu

2013-04-01

310

Angular correlations in emission of prescission neutrons from {sup 235}U fission induced by slow polarized neutrons  

SciTech Connect

A new approach to searching for and studying scission neutrons, which is based on the analysis of specific angular correlations in nuclear fission induced by polarized neutrons, is described and used to evaluate the fraction of scission neutrons in the total number of prompt neutrons of {sup 235}U fission emitted perpendicularly to the fission axis.

Danilyan, G. V., E-mail: danilyan@itep.r [Institute of Theoretical and Experimental Physics (Russian Federation); Wilpert, T.; Granz, P. [Hahn-Meitner Institute (Germany); Krakhotin, V. A. [Institute of Theoretical and Experimental Physics (Russian Federation); Mezei, F. [Hahn-Meitner Institute (Germany); Novitsky, V. V.; Pavlov, V. S. [Institute of Theoretical and Experimental Physics (Russian Federation); Russina, M. V. [Hahn-Meitner Institute (Germany); Shatalov, P. B. [Institute of Theoretical and Experimental Physics (Russian Federation)

2008-12-15

311

Mechanism of the reaction between diazonium salts and potassium nitrite based on chemically induced dynamic nuclear polarization  

Microsoft Academic Search

The reaction between diazonium salts and nitrites of alkali metals in aprotic solvents takes place via a radical mechanism. This has been demonstrated by studies of chemically induced nuclear polarization [i] and by identifying the products of arylation in the presence of substituted benzenes [2]. In aqueous media, both the mechanism of the reaction and the final products are different.

L. A. Kiprianova; A. F. Levit; I. P. Gragerov

1977-01-01

312

Polar agents with differentiation inducing capacity potentiate tumor necrosis factor-mediated cytotoxicity in human myeloid cell lines  

Microsoft Academic Search

Cotreatment or pretreatment of several hu- man myeloid cell lines (KG!, HL6O, U937, THP1) with the differentiation inducer DMSO was found to potenti- ate the antiproliferative and cytotoxic effects of TNF. In addition, TNF-resistant monocytic cell lines could be sen- sitized to TNF cytotoxicity by DMSO treatment. Other highly polar molecules, known to be potent differentia- tion inducers, showed similar

Stany Depraetere; Bart Vanhaesebroeckt; Walter Fierst; Jean Willems; Marcel Joniau

313

Multi-vortical flow inducing electrokinetic instability in ion concentration polarization layer.  

PubMed

In this work, we investigated multiple vortical flows inside the ion concentration polarization (ICP) layer that forms due to a coupling of applied electric fields and the semipermeable nanoporous junction between microchannels. While only a primary vortex near perm-selective membrane is traditionally known to lead to electrokinetic instability, multiple vortexes induced by the primary vortex were found to play a major role in the electrokinetic instability. The existence of multiple vortexes was directly confirmed by experiments using particle tracers and interdigitated electrodes were used to measure the local concentration profile inside the ICP layer. At larger applied electric fields, we observed aperiodic fluid motion due to electrokinetic instabilities which develop from a coupling of applied electric fields and electrical conductivity gradients induced by the ICP. The electrokinetic instability at micro-nanofluidic interfaces is important in the development of various electro-chemical-mechanical applications such as fuel cells, bio-analytical preconcentration methods, water purification/desalination and the fundamental study of ion electromigration through nanochannels and nonporous perm-selective membranes. PMID:23085964

Kim, Sung Jae; Ko, Sung Hee; Kwak, Rhokyun; Posner, Jonathan D; Kang, Kwan Hyoung; Han, Jongyoon

2012-12-01

314

Beam-induced resonant depolarization effects in a polarized atomic hydrogen gas target at HERA  

Microsoft Academic Search

In the HERMES experiment at HERA deep inelastic scattering of polarized positrons from internal polarized gas targets is used to study the spin structure of the nucleons. For the hydrogen target, a strong magnetic field parallel to the positron beam direction is used to maintain the polarization of the atoms inside the target cell. Depolarization of the atoms due to

H. Kolster

1998-01-01

315

Suppression of Excitation and Spectral Broadening Induced by Interactions in a Cold Gas of Rydberg Atoms  

Microsoft Academic Search

We report on the observation of ultralong range interactions in a gas of cold rubidium Rydberg atoms. The vanderWaals interaction between a pair of Rydberg atoms separated as far as 100 000 Bohr radii features two important effects: spectral broadening of the resonance lines and suppression of excitation with increasing density. The density dependence of these effects is investigated in

Kilian Singer; Markus Reetz-Lamour; Thomas Amthor; Luis Gustavo Marcassa; Matthias Weidemüller

2004-01-01

316

Early stage expansion and time-resolved spectral emission of laser-induced plasma from polymer  

Microsoft Academic Search

In the nanosecond laser ablation regime, absorption of laser energy by the plasma during its early stage expansion critically influences the properties of the plasma and thus its interaction with ambient air. These influences can significantly alter spectral emission of the plasma. For organic samples especially, recombination of the plasma with the ambient air leads to interfering emissions with respect

Myriam Boueri; Matthieu Baudelet; Jin Yu; Xianglei Mao; Samuel S. Mao; Richard Russo

2009-01-01

317

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

2012-08-21

318

Spin-polarized current-induced magnetization reversal in single nanowires  

NASA Astrophysics Data System (ADS)

Using electrochemical deposition, 6 ?m long Ni nanowires, with typical diameters of the order of 80 nm, are grown in ion-track etched membranes. Electric contacts are established during the growth, allowing resistance measurements of a single magnetic wire. Whatever the angle of the applied magnetic field with the wire, the full loops of magnetoresistance of a nickel nanowire can be described quantitatively on the basis of anisotropic magnetoresistance of a uniform magnet, and exhibit a jump of the magnetization at the so-called switching field. Hybrid wires made half with nickel and half with a Co/Cu multilayer were also produced. The multilayer could be grown using either a single bath technique or a multiple bath setup, with the result of a different magnetic anisotropy in the Co layers. When the multilayer is made of an optimal number of layers, the two parts of the hybrid wire act as two resistances in series, having no magnetic interaction onto each other. In contrast, the action of a current pulse on the nickel magnetization is to provoke a switch, when injected before the unstable state of the hysteresis cycle has been reached. But the amount of applied field discrepancy where the current still has an effect is given by a measured value ?Hmax, which appears to be substantially dependent on the presence or not of a multilayer close enough to the nickel wire and on the orientation of the magnetization in the multilayer. The role of the multilayer’s presence or state evidences the role of spin polarization in the current-induced switches of nickel. This is confirmed by measurements of the amplitude of ?Hmax in homogeneous nickel wires that exclude spurious effects such as the induced oersted-field, heating, or a combination of the two to account for all the current-induced switches.

Kelly, Derek; Wegrowe, Jean-Eric; Truong, Trong-Kha; Hoffer, Xavier; Ansermet, Jean-Philippe

2003-10-01

319

FLIM and emission spectral analysis of caspase-3 activation inside single living cell during anticancer drug-induced cell death  

Microsoft Academic Search

Two-photon excitation (TPE) fluorescence lifetime imaging microscopy (FLIM) and emission spectral imaging (ESI) are powerful\\u000a tools for fluorescence resonance energy transfer (FRET) measurement. In this study, we use these two techniques to analyze\\u000a caspase-3 activation inside single living cells during anticancer drug-induced human lung adenocarcinoma (ASTC-a-1) cell death.\\u000a TPE-ESI of SCAT3, a caspase-3 indicator based on FRET, was performed inside

Wenliang Pan; Junle Qu; Tongsheng Chen; Lei Sun; Jing Qi

2009-01-01

320

Studies of X-ray Spectral Lines Polarization in Correlation with the Emission of Supra-thermal Electrons in Plasma-Focus Discharges  

Microsoft Academic Search

The correlation of the emission of polarized X-ray lines from highly-ionized argon ions and the emission of intense electron pulses has been observed. The paper presents a review of research on the polarization of the selected X-ray lines and their correlation with pulsed electron beams investigated within the MAJA-PF facility at SINS in Swierk, Poland.

L. Jakubowski; M. J. Sadowski; E. O. Baronova

2006-01-01

321

Studies of X-ray Spectral Lines Polarization in Correlation with the Emission of Supra-thermal Electrons in Plasma-Focus Discharges  

SciTech Connect

The correlation of the emission of polarized X-ray lines from highly-ionized argon ions and the emission of intense electron pulses has been observed. The paper presents a review of research on the polarization of the selected X-ray lines and their correlation with pulsed electron beams investigated within the MAJA-PF facility at SINS in Swierk, Poland.

Jakubowski, L.; Sadowski, M. J. [Andrzej Soltan Institute for Nuclear Studies, 05-400 Otwock-Swierk (Poland); Baronova, E. O. [Nuclear Fusion Institute, NRC Kurchatov Institute, 123182 Moscow (Russian Federation)

2006-12-04

322

Studies of X-ray Spectral Lines Polarization in Correlation with the Emission of Supra-thermal Electrons in Plasma-Focus Discharges  

NASA Astrophysics Data System (ADS)

The correlation of the emission of polarized X-ray lines from highly-ionized argon ions and the emission of intense electron pulses has been observed. The paper presents a review of research on the polarization of the selected X-ray lines and their correlation with pulsed electron beams investigated within the MAJA-PF facility at SINS in Swierk, Poland.

Jakubowski, L.; Sadowski, M. J.; Baronova, E. O.

2006-12-01

323

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

324

Polarizers at 1.053 um deposited on silica substrate for high laser flux applications in a vacuum  

Microsoft Academic Search

The French Megajoule Project requires polarizers with high laser-induced damage thresholds. Such polarizers must be deposited on silica substrates, which are commonly prone to stress leading to early failure. Better stress control in the films require an optimization of the stack design as well as the deposition parameters. The thermal e-beam technique is used. We present the spectral behavior of

Bernard Geenen; Herve Leplan; B. Pinot; W. Alexandre; P. Pally; Larry A. Roussel; Odile Lam

1996-01-01

325

Role of nitric oxide in modulation of afferent impulses in cutaneous branches of somatic nerves by polarized light.  

PubMed

Subcutaneous injection of L-NAME inhibited afferent impulse activity in n. ischiadicus and n. saphenus and abolished the increase in this activity induced by stimulation of mechanoreceptors after skin irradiation with polarized light with various spectral characteristics. Subsequent subcutaneous injection of sodium nitroprusside restored the pattern of afferent impulse activity in these nerves during repeated skin irradiation with polarized light. PMID:11177228

Chumak, A G; Chichkan, D N; Ulashchik, V S; Soltanov, V V; Kul'chitskii, V A

2000-08-01

326

Spectral Response of the Pulsationally-Induced Shocks in the Atmosphere of BW Vulpeculae  

Microsoft Academic Search

The star BW Vul excites an extremely strong radial pulsation that grows in\\u000aits envelope and is responsible for visible shock features in the continuum\\u000aflux and spectral line profiles emerging in the atmosphere At two phases\\u000aseparated by 0.8 cycles. Material propelled upwards in the atmosphere from the\\u000ashock returns to the lower photosphere where it creates a second

Myron A. Smith; C. Simon Jeffery

2002-01-01

327

Disorder-induced reversal of spin polarization in the Heusler alloy Co{sub 2}FeSi  

SciTech Connect

We study the spin polarization in the conduction band of Co{sub 2}FeSi layers with a different degree of structural order. The injected spin polarization in Co{sub 2}FeSi/(Al,Ga)As spin light-emitting diodes as well as the planar Hall effect measured for the Co{sub 2}FeSi injectors exhibit a sign reversal between injectors crystallized in the ordered L2{sub 1} phase and the Fe-Si disordered B2 phase. These results are explained by a disorder-induced change in the spin polarization at the Fermi energy of Co{sub 2}FeSi. Support for the occurrence of such a striking change in the electronic band structure is obtained by first principles calculations.

Bruski, P.; Ramsteiner, M.; Brandt, O.; Friedland, K.-J.; Farshchi, R.; Herfort, J.; Riechert, H. [Paul-Drude Institut fuer Festkoerperelektronik, Hausvogteiplatz 5-7, D-10117 Berlin (Germany); Erwin, S. C. [Center for Computational Materials Science, Naval Research Laboratory, Washington, DC 20375 (United States)

2011-04-01

328

Effects of polarization azimuth in dynamics of electrically assisted light-induced gliding of nematic liquid-crystal easy axis  

NASA Astrophysics Data System (ADS)

We experimentally study the reorientation dynamics of the nematic liquid crystal easy axis at photoaligned azo-dye films under the combined action of in-plane electric field and linearly polarized reorienting UV light at varying polarization azimuth, ?p. At non-zero values of the azimuth, ?p?0, as opposed to the case where the polarization vector of the light is parallel to the initial easy axis (?p=0), the easy axis reorientation was observed to be most pronounced outside the interelectrode gaps. In the regions between electrodes with non-vanishing electric field, it is found that the dynamics of reorientation slows down with ?p and the sense of easy axis rotation is independent of the sign of ?p. A generalized version of the phenomenological model that was previously developed to describe the electrically assisted light-induced gliding is applied to interpret the experimental data.

Dubtsov, A. V.; Shmeliova, D. V.; Pasechnik, S. V.; Kiselev, Alexei D.; Chigrinov, V. G.

2012-04-01

329

Gravity wave-induced polarization of the cosmic microwave background radiation  

NASA Astrophysics Data System (ADS)

We discuss the contribution of pure gravitational waves to the cosmic microwave background radiation (CMBR) anisotropy and polarization. It is found that the large-scale polarization of the CMBR is less than 1% of the anisotropy for an universe with standard recombination. The effect of early matter reionization will enhance the CMBR polarization to a 10% level. We have also computed the CMBR polarization for an universe having high baryon density and gravitational waves with a tilted spectrum and found that further enhancement of the polarization is possible. We conclude that measuring the polarization of the CMBR on large angular scales can probe the ionization history of the early universe and set constraints on cosmological models.

Ng, Ka Lok; Ng, Kin-Wang

1995-06-01

330

Level anti-crossings in ParaHydrogen Induced Polarization experiments with Cs-symmetric molecules  

NASA Astrophysics Data System (ADS)

Hyperpolarization by means of ParaHydrogen Induced Polarization (PHIP) has found increasing applications since its discovery. However, in the last decade only a few experiments have been reported describing the hydrogenation of symmetric molecules. A general AA?BB? system is studied here. Calculations of the spin dynamics with the density matrix formalism support the experimental findings, providing profound understanding of the experiments in Cs-symmetric molecules. Level anti-crossings between states related to the triplet and the singlet state of one pair of the protons are identified as being responsible for hyperpolarization transfer in a PHIP experiment, when the former p-H2 protons occupy the sites AA?.The hydrogenation of acetylene dicarboxylic acid dimethylester with parahydrogen is used to illustrate the case. The theoretical treatment applied to this particular reaction explains the signal enhancements in both groups of protons in the spectrum when the sample is placed in the proper magnetic field strength, including the phase inversion of the signal of the methyl group.The treatment described here can be extended to every molecule which can be approximated as an AA?BB? system.

Buljubasich, L.; Franzoni, M. B.; Spiess, H. W.; Münnemann, K.

2012-06-01

331

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

PubMed

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

2013-10-07

332

Gravity-Induced Polar Transport of Calcium across Root Tips of Maize 1  

PubMed Central

Calcium movement across primary roots of maize (Zea mays, L.) was determined by application of 45Ca2+ to one side of the root and collection of radioactivity in an agar receiver block on the opposite side. Ca movement across the root tip was found to be at least 20 times greater than movement across the elongation zone. The rapid movement of Ca across the tip was severely inhibited in roots from which the root cap had been removed. Ca movement across the tip was also strongly retarded in roots pretreated with 2,4-dinitrophenol or potassium cyanide. Orientation of roots horizontally had no effect on Ca movement across the elongation zone but caused a strong asymmetry in the pattern of Ca movement across the tip. In gravistimulated roots, the movement of Ca from top to bottom increased while movement from bottom to top decreased. The data indicate that gravistimulation induces polar movement of Ca toward the lower side of the root cap. An earlier report (Lee, Mulkey, Evans 1983 Science 220: 1375-1376) from this laboratory showed that artificial establishment of calcium gradients at the root tip can cause gravitropic-like curvature. Together, the two studies indicate that Ca plays a key role in linking gravistimulation to the gravitropic growth response in roots.

Lee, June S.; Mulkey, Timothy J.; Evans, Michael L.

1983-01-01

333

Electrical Resistivity and Induced Polarization as Tools for Mapping Near-Surface Weathered Hydrocarbon Bodies  

NASA Astrophysics Data System (ADS)

Induced polarization (IP) and electrical resistivity (ER) surveys were conducted at two legacy oil refinery sites in central Alberta during the fall of 2005 and summer of 2006. The first site had areas of near surface weathered hydrocarbons, and the second site had areas of saline soil and groundwater and areas of weathered hydrocarbons. The conductive saline environment of the second site posed significant challenges for the IP investigation. At the both sites, ER imaged weathered hydrocarbon bodies as resistive anomalies above background values. IP inversions yielded high values of chargeability at the boundaries of the resistive hydrocarbon bodies. At the second site, a resistivity high was associated with a change in subsurface lithology. Unlike the anomalies resulting from weathered hydrocarbons, there was no corresponding increase in chargeability associated with the high resistivity due to the lithology change. The results from these two surveys indicate that a combination of ER and IP is an effective tool for both mapping weathered hydrocarbons and in differentiating between resistivity increases associated with near surface hydrocarbons and resistivity increases due to subsurface lithology.

MacDonald, J.; Forte, S.; Bentley, L.

2006-12-01

334

A photochemically induced dynamic nuclear polarization study of denatured states of lysozyme  

SciTech Connect

Photochemically induced dynamic nuclear polarization (photo-CIDNP) techniques have been used to examine denatured states of lysozyme produced under a variety of conditions. {sup 1}H CIDNP difference spectra of lysozyme denatured thermally, by the addition of 10 M urea, or by the complete reduction of its four disulfide bonds were found to differ substantially not only from the spectrum of the native protein but also from that expected for a completely unstructured polypeptide chain. Specifically, denatured lysozyme showed a much reduced enhancement of tryptophan relative to tyrosine than did a mixture of blocked amino acids with the same composition as the intact protein. By contrast, the CIDNP spectrum of lysozyme denatured in dimethyl sulfoxide solution was found to be similar to that expected for a random coil. It is proposed that nonrandom hydrophobic interactions are present within the denatured states of lysozyme in aqueous solution and that these reduce the reactivity of tryptophan residues relative to tyrosine residues. Characterization of such interactions is likely to be of considerable significance for an understanding of the process of protein folding.

Broadhurst, R.W.; Dobson, C.M.; Hore, P.J.; Radford, S.E.; Rees, M.L. (Univ. of Oxford (United Kingdom))

1991-01-01

335

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.

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

2012-01-01

336

Polarization of the neutron induced by hadronic weak interactions in the photodisintegration of the deuteron  

NASA Astrophysics Data System (ADS)

New polarization observables with which we can study the two-nucleon weak interactions at low energies are considered. In the breakup of the deuteron by photons, polarization of outgoing neutrons can depend on the parity-violating component of two-nucleon interactions. We express the parity-violating polarization in general forms, and perform numerical calculations with a pionless effective field theory. The theory has three unknown parity-violating low energy constants, and new polarization observables are expressed in linear combinations of them. We discuss how the unknown constants may be determined and their implication to the understanding of the hadronic weak interactions.

Shin, J. W.; Hyun, C. H.; Ando, S.-I.; Hong, S. W.

2013-09-01

337

PPAR activation induces M1 macrophage polarization via cPLA?-COX-2 inhibition, activating ROS production against Leishmania mexicana.  

PubMed

Defence against Leishmania depends upon Th1 inflammatory response and, a major problem in susceptible models, is the turnoff of the leishmanicidal activity of macrophages with IL-10, IL-4, and COX-2 upregulation, as well as immunosuppressive PGE2, all together inhibiting the respiratory burst. Peroxisome proliferator-activated receptors (PPAR) activation is responsible for macrophages polarization on Leishmania susceptible models where microbicide functions are deactivated. In this paper, we demonstrated that, at least for L. mexicana, PPAR activation, mainly PPAR ? , induced macrophage activation through their polarization towards M1 profile with the increase of microbicide activity against intracellular pathogen L. mexicana. PPAR activation induced IL-10 downregulation, whereas the production of proinflammatory cytokines such as TNF- ? , IL-1 ? , and IL-6 remained high. Moreover, PPAR agonists treatment induced the deactivation of cPLA2-COX-2-prostaglandins pathway together with an increase in TLR4 expression, all of whose criteria meet the M1 macrophage profile. Finally, parasite burden, in treated macrophages, was lower than that in infected nontreated macrophages, most probably associated with the increase of respiratory burst in these treated cells. Based on the above data, we conclude that PPAR agonists used in this work induces M1 macrophages polarization via inhibition of cPLA2 and the increase of aggressive microbicidal activity via reactive oxygen species (ROS) production. PMID:23555077

Díaz-Gandarilla, J A; Osorio-Trujillo, C; Hernández-Ramírez, V I; Talamás-Rohana, P

2013-02-28

338

Dependence of InGaN solar cell performance on polarization-induced electric field and carrier lifetime  

NASA Astrophysics Data System (ADS)

The effects of Mg-induced net acceptor doping concentration and carrier lifetime on the performance of a p—i—n InGaN solar cell are investigated. It is found that the electric field induced by spontaneous and piezoelectric polarization in the i-region could be totally shielded when the Mg-induced net acceptor doping concentration is sufficiently high. The polarization-induced potential barriers are reduced and the short circuit current density is remarkably increased from 0.21 mA/cm2 to 0.95 mA/cm2 by elevating the Mg doping concentration. The carrier lifetime determined by defect density of i-InGaN also plays an important role in determining the photovoltaic properties of solar cell. The short circuit current density severely degrades, and the performance of InGaN solar cell becomes more sensitive to the polarization when carrier lifetime is lower than the transit time. This study demonstrates that the crystal quality of InGaN absorption layer is one of the most important challenges in realizing high efficiency InGaN solar cells.

Yang, Jing; Zhao, De-Gang; Jiang, De-Sheng; Liu, Zong-Shun; Chen, Ping; Li, Liang; Wu, Liang-Liang; Le, Ling-Cong; Li, Xiao-Jing; He, Xiao-Guang; Wang, Hui; Zhu, Jian-Jun; Zhang, Shu-Ming; Zhang, Bao-Shun; Yang, Hui

2013-09-01

339

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

PubMed

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. PMID:23872146

Fujii, Masakazu; Inoguchi, Toyoshi; Batchuluun, Battsetseg; Sugiyama, Naonobu; Kobayashi, Kunihisa; Sonoda, Noriyuki; Takayanagi, Ryoichi

2013-07-18

340

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

Microsoft Academic Search

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 ~200 nm thickness

David J. Hwang; Hojeong Jeon; Costas P. Grigoropoulos; Jong Yoo; Richard E. Russo

2008-01-01

341

Visual stress, its treatment with spectral filters, and its relationship to visually induced motion sickness.  

PubMed

We review the concept of visual stress and its relation to neurological disease. Visual stress can occur from the observation of images with unnatural spatial structure and an excess of contrast energy at spatial frequencies to which the visual system is generally most sensitive. Visual stress can often be reduced using spectral filters, provided the colour is selected with precision to suit each individual. The use of such filters and their effects on reading speed are reviewed. The filters have been shown to benefit patients with a variety of neurological conditions other than reading difficulty, all associated with an increased risk of seizures. PMID:19286164

Wilkins, Arnold Jonathan; Evans, Bruce J W

2009-03-14

342

Modeling the temporal spectral response of the thermally induced non-linearity of mechanical microresonators  

NASA Astrophysics Data System (ADS)

Optical techniques are widely used for the read-out of micro- and nanoresonators. Absorption of the employed light heats the device, thereby altering its mechanical properties, in particular, its eigenfrequency. To describe this effect, we present a model of a non-linear point mass resonator presuming an exponentially changing eigenfrequency, which is capable to predict the evolution of the resonators spectral response. The model was verified investigating the transient response of a hybrid microresonator and a silicon cantilever employing the gated frequency response method. This approach provides additionally a procedure to determine the thermo-mechanical time constant of resonators.

Radzio, B.; Oesterschulze, E.; Korsch, H. J.

2013-04-01

343

Observation of multiple electrically induced phase transitions and a decoupling of the induced strain and polarization in Sn-modified lead zirconate titanate  

SciTech Connect

Studies of Pb{sub 0.98}Nb{sub 0.02}[(Zr{sub 1{minus}x}Sn{sub x}){sub 0.97}Ti{sub 3}]{sub 1{minus}z}O{sub 3} (PZST x/3/2) were performed for 0{lt}x{lt}0.20 by electrically induced polarization and strain methods. Maximum electrically induced strains ({epsilon}) and polarizations (P) were found in the compositional range around x=0.15, where ferroelectric and antiferroelectric regions coexisted. In addition, these studies demonstrated evidence for two electrically induced phase transitions: (i) an antiferroelectric{endash}ferroelectric near 40 kV/cm, and (ii) a secondary ferroelectric{endash}ferroelectric near 60{endash}80 kV/cm. The dominate contribution to {epsilon} was associated with the secondary transition, whereas the dominate contribution to P was associated with the first. {copyright} {ital 1997 American Institute of Physics.}

Forst, D.; Li, J.; Viehland, D. [Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States)

1997-09-01

344

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

345

IR laser induced spectral kinetics of AgGaGe3Se8:Cu chalcogenide crystals  

NASA Astrophysics Data System (ADS)

The possibility to operate by optical spectra near the absorption edge gap was discovered for the AgGaGe3Se8:Cu semiconducting chalcogenide crystals under influence of microsecond CO2 laser with pulse energy 60 mJ operating at wavelength 10.6 ?m. An occurrence of substantial photoinduced optical density was observed at wavelengths in the spectral range of 610-620 nm. Introducing of Cu ions leads to substantial spectral asymmetry in the observed spectra. The process achieves its maximum value after the 80-120 s of CO2 laser treatment and relaxes with almost irreversible changes after the same time. The contribution of thermo heating did not exceed 5-6%. Only the irreversible changes of the sample's surface topography were observed during the CO2 laser treatment, which do not influence the treatment. So the surface states do not play a principal role and the effect is prevailingly originated from the. The observed effect may be used for control of the CO2 laser power density.

Al-Harbi, E.; Wojciechowski, A.; AlZayed, N.; Parasyuk, O. V.; Gondek, E.; Armatys, P.; El-Naggar, A. M.; Kityk, I. V.; Karasinski, P.

2013-07-01

346

Spontaneous-polarization-induced heterojunction asymmetry in III-nitride semiconductors  

SciTech Connect

We report on precise control of film crystal polarity in fully relaxed, thin InN/AlN heterojunctions grown on sapphire by plasma-assisted molecular beam epitaxy. Using these samples, we have measured asymmetric valence band offset values (0.8 {+-} 0.1 eV for the In/Al- and 1.8 {+-} 0.1 eV for the N-polar case) at polar InN/AlN heterojuncitons by synchrotron soft x-ray photoelectron spectroscopy. We confirm that the discontinuities of spontaneous polarizations at polar InN/AlN heterointerfaces lead to the large core level shift of the Al 2p peak related to the In 4d peak (1.0 eV).

Kuo, Cheng-Tai; Chang, Kai-Kuen; Lin, Shih-Chieh; Gwo, Shangjr [Department of Physics, National Tsing-Hua University, Hsinchu 30013, Taiwan (China); Shiu, Hung-Wei [Department of Physics, National Tsing-Hua University, Hsinchu 30013, Taiwan (China); National Synchrotron Radiation Research Center (NSRRC), Hsinchu 30076, Taiwan (China); Chen, Chia-Hao [National Synchrotron Radiation Research Center (NSRRC), Hsinchu 30076, Taiwan (China)

2011-07-11

347

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

348

A highly polar xanthophyll of 9?- cis -neoxanthin induces apoptosis in HCT116 human colon cancer cells through mitochondrial dysfunction  

Microsoft Academic Search

Highly polar xanthophylls of 9?-cis-neoxanthin (neoxanthin) and fucoxanthin, which have the characteristic structure of an epoxy group and an allenic bond, were\\u000a previously found to induce apoptosis in human prostate cancer cells. In the present study, we found apoptosis induction by\\u000a neoxanthin in HCT116 human colon cancer cells and examined the induction mechanism. The cells exposed to 20 ?M neoxanthin\\u000a clearly

Masaru Terasaki; Akira Asai; Hong Zhang; Akihiko Nagao

2007-01-01

349

Spectral and metabolic characteristics of mitochondrial fractions from rotenone-induced tumours.  

PubMed Central

Mitochondrial fractions isolated from tumours induced with the respiratory inhibitor rotenone lack respiratory control, oxidative phosphorylation, are partially or totally insensitive to cyanide and have a near-normal content of respiratory carriers. These characteristics are more similar to those of mitochondria from atrophic mammary gland than to those of mitochondria from spontaneous mammary adenomas. Thus, the characteristic structural and biochemical mitochondrial alteration of rotenone-induced tumours would represent a lack of mitochondrial differentiation as the tumour develops from the atrophic mammary gland. Slices of rotenone-induced tumours are insensitive to oligomycin and dinitrophenol, thus indicating that glycolysis would be their sole source of metabolic energy. Images Fig. 2

Gosalvez, M.; Diaz-Gil, J.; Coloma, J.; Salganicoff, L.

1977-01-01

350

Solar simulated radiation induced cell death depends on spectral distribution and irradiance but not output delivery.  

PubMed

Photo-biological investigations are dependent on calibration and characterisation to determine the relevance of an artificial irradiator to the study at hand. The importance of this has been voiced in the literature. However, the importance of output delivery is relatively unknown. The biological relevance of a high-energy, rapidly pulsing solar simulator was investigated using the clonogenic assay and was found to be reciprocity law compliant despite an exaggerated ultraviolet (UV) irradiance in excess of 1600 W m(-2) delivered per pulse. In fact, it was found to be the least cytotoxic irradiator compared with a second solar simulator and a UVB fluorescent lamp with continuous UV irradiances of 55 and 6.4 W m(-2), respectively. The reduced survival observed with the continuous irradiators is attributed to differences in spectral irradiance and distribution, particularly in the UVB, which in the absence of thorough calibration and characterisation may have resulted in erroneous conclusions. PMID:20203123

Maguire, Alanna; Lyng, Fiona M; Walsh, James E

2010-03-04

351

Modeling Robustness Tradeoffs in Yeast Cell Polarization Induced by Spatial Gradients  

PubMed Central

Cells localize (polarize) internal components to specific locations in response to external signals such as spatial gradients. For example, yeast cells form a mating projection toward the source of mating pheromone. There are specific challenges associated with cell polarization including amplification of shallow external gradients of ligand to produce steep internal gradients of protein components (e.g. localized distribution), response over a broad range of ligand concentrations, and tracking of moving signal sources. In this work, we investigated the tradeoffs among these performance objectives using a generic model that captures the basic spatial dynamics of polarization in yeast cells, which are small. We varied the positive feedback, cooperativity, and diffusion coefficients in the model to explore the nature of this tradeoff. Increasing the positive feedback gain resulted in better amplification, but also produced multiple steady-states and hysteresis that prevented the tracking of directional changes of the gradient. Feedforward/feedback coincidence detection in the positive feedback loop and multi-stage amplification both improved tracking with only a modest loss of amplification. Surprisingly, we found that introducing lateral surface diffusion increased the robustness of polarization and collapsed the multiple steady-states to a single steady-state at the cost of a reduction in polarization. Finally, in a more mechanistic model of yeast cell polarization, a surface diffusion coefficient between 0.01 and 0.001 µm2/s produced the best polarization performance, and this range is close to the measured value. The model also showed good gradient-sensitivity and dynamic range. This research is significant because it provides an in-depth analysis of the performance tradeoffs that confront biological systems that sense and respond to chemical spatial gradients, proposes strategies for balancing this tradeoff, highlights the critical role of lateral diffusion of proteins in the membrane on the robustness of polarization, and furnishes a framework for future spatial models of yeast cell polarization.

Chou, Ching-Shan

2008-01-01

352

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

353

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

354

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.

2011-02-01

355

Symmetry breaking in phase separation of binary polymer mixtures induced by linearly polarized light  

NASA Astrophysics Data System (ADS)

Symmetry breaking of concentration fluctuations was found in a binary polymer mixture with one component photo-cross-linked by linearly polarized light. As the reaction proceeds, the mixture undergoes phase separation, exhibiting lamellar morphologies with the direction closely perpendicular to the polarization (E) of the exciting light. It was also found that the phase separation is suppressed in the parallel direction and its kinetics strongly depends on the relative orientation with respect to the exciting polarization. Thus, these reacting mixtures provide a model system to study the directional phase separation driven by chemical reactions.

Tran-Cong, Qui; Kataoka, Katsunari; Urakawa, Osamu

1998-02-01

356

The influence of laser focusing on the intensity of spectral lines in femtosecond laser-induced breakdown spectroscopy of liquids  

NASA Astrophysics Data System (ADS)

The influence of the diameter of the beam of a femtosecond Ti:Sapphire laser (800 nm, 40 fs, 0.8 mJ) on the intensity of spectral lines upon optical breakdown on the surface of CaCl2 aqueous solution has been determined experimentally. It is shown that an increase in the laser-beam diameter from 7 to 14 mm on a focusing lens for identical pulse energy increases the intensities of the CaII (393.3 nm) and H? (656 nm) lines by factors of 3 and 20, respectively. This effect can be used to increase the intensities of emission lines of chemical elements in femtosecond laser-induced breakdown spectroscopy of liquids and, accordingly, improve the sensitivity of this method.

Golik, S. S.; Ilyin, A. A.; Kolesnikov, A. V.; Babiy, M. Yu.; Kul'chin, Yu. N.; Bukin, O. A.

2013-08-01

357

Analysis of the characters of chromophoric dissolved organic matter in water using laser induced fluorescence and spectral fluorescence signature  

NASA Astrophysics Data System (ADS)

A sort of analytical method of fast diagnosis of chromophoric dissolved matter (CDOM) in water is discussed. The total luminescence spectra (TLS) of CDOM in several types of water samples with laser-induced fluorescence (LIF) measurements using a 405 nm wavelength excitation source were measured in the laboratory, and the spectra of CDOM were pointed out and obtained with spectral fluorescence signature (SFS) technique. The spectrum of water Raman scattering and fluorescence of CDOM were separated from TLS with fitting Gaussian of the least squares method, and the curve of fluorescence peak intensity of CDOM against corresponding concentration of CDOM is showed. High correlation (R2 = 0.93) was observed between concentration of CDOM and fluorescence normalized to water Raman scattering. The results have presented the capability of the LIF technique as an integrated tool for research and observations.

Chen, Peng; Mao, Zhihua; Huang, Haiqing

2013-09-01

358

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

359

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

360

Chemotactic factor-induced polarization, receptor redistribution, and locomotion of human blood monocytes.  

PubMed Central

The locomotor response of human blood monocytes to chemotactic factors was studied using a polarization assay on cells in suspension and by filming locomotion on albumin-coated glass. Cells in optimal (5 x 10(-9) M) but uniform concentrations of N-formyl-methionyl-leucyl-phenylalanine (FMLP) polarized well and showed a 'persistent random walk' type of locomotion, whereas in supraoptimal concentrations (10(-7) M), the cells took erratic paths and polarized poorly, suggesting that monocytes cannot develop an anteroposterior polarity if hit by ligand molecules at many points on the cell surface simultaneously. Monocyte polarization in chemotactic factors at 37 degrees was transient and was gradually lost after 15-20 min. Likewise, the ability to form Fc rosettes after this time was gradually lost, suggesting loss of functional receptors from the cell surface with time. In optimally polarized cells, Fc rosettes were frequently localized at the head of the cell. This localization also was lost with time. Using pure chemotactic factors (FMLP, C5a, leukotriene B4) we found, as reported earlier (Cianciolo & Snyderman 1981), that polarization was restricted to a subpopulation (approximately 60% of cells) that responded to multiple attractants. However, 80-90% of monocytes polarized in response to combinations of any of the above pure attractants with candida-activated serum. This suggests that the subpopulation that lacks receptors for classical chemotactic factors nevertheless has locomotor capacity and can respond to undefined factors in activated serum, and that the great majority of blood monocytes is motile if appropriately stimulated. Images Figure 1 Figure 6

Islam, L N; Wilkinson, P C

1988-01-01

361

Confocal fluorescence polarization microscopy in turbid media: effects of scattering-induced depolarization  

Microsoft Academic Search

We present an experimental and theoretical study of confocal fluorescence polarization microscopy in turbid media. We have performed an experimental study using a fluorophore-embedded polymer rod immersed in aqueous suspensions of 0.1 and 0.5 mum diameter polystyrene microspheres. A Monte Carlo approach to simulate confocal fluorescence polarization imaging in scattering media is also presented. It incorporates a detailed model of

Chad E. Bigelow; Thomas H. Foster

2006-01-01

362

Transition probabilities of Ni II spectral lines measured by laser induced breakdown spectroscopy  

NASA Astrophysics Data System (ADS)

Experimental transition probabilities for 48 lines of the transition array 3d84s–3d84p of Ni II have been obtained by laser induced breakdown spectroscopy. A procedure based on the measurement and fitting of curves of growth that avoids the systematic error due to self-absorption has been used. The laser induced plasmas are generated using a Nd:YAG laser from a set of Ni–Cu alloys with different Ni concentrations. A comparison is made of our results with the available experimental and theoretical values.

Manrique, J.; Aguilera, J. A.; Aragón, C.

2013-05-01

363

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...

364

Spectral sensitivity of light induced respiratory activity of photoreceptor mitochondria in the intact fly  

Microsoft Academic Search

FlyCalliphora erythrocephala (white eyed) photoreceptors were investigated in intact, living animals by microspectrofluorometry in vivo. The fluorescence of mitochondrial flavoproteins (Tinbergen and Stavenga 1986) was used to monitor transient changes in oxidative metabolism, which were induced by a test light following a stimulus of variable intensity.

J. Tinbergen; D. G. Stavenga

1987-01-01

365

Polarization photography with partial polarization of light fluxes (photopolarimetry)  

Microsoft Academic Search

The polarization sensitivity of a yellow diazo dye to partially polarized light is investigated experimentally. Light-induced birefringence and dichroism are plotted versus the degree of polarization of actinic light polarization photographs of some objects producing partially polarized light are presented.

Z. V. Vardosanidze

1992-01-01

366

Spectral characteristics of the bioluminescence induced in the marine fish, Porichthys notatus , by Cypridina (ostracod) luciferin  

Microsoft Academic Search

Summary Specimens ofPorichthys notatus, which are naturally luminous along the coast of California, are non-luminous in Puget Sound. However, luminescence capability may be induced in the adult Puget SoundPorichthys by the administration of purifiedCypridina (ostracod) luciferin, syntheticCypridina luciferin, orCypridina organisms. The bioluminescence emission spectra produced by the Puget Sound fish following induction is similar, if not identical, to that of

Frederick I. Tsuji; Basil G. NAFPAKTITISt; Toshio Goto; Milton J. Cormier; John E. Wampler; James M. Anderson

1975-01-01

367

Microtubules induce self-organization of polarized PAR domains in C. elegans zygotes  

PubMed Central

A hallmark of polarized cells is the segregation of the PAR polarity regulators into asymmetric domains at the cell cortex1, 2. Antagonistic interactions involving two conserved kinases, atypical protein kinase C (aPKC) and PAR-1, have been implicated in polarity maintenance1, 2, but the mechanisms that initiate the formation of asymmetric PAR domains are not understood. Here, we describe one pathway used by the sperm-donated centrosome to polarize the PAR proteins in Caenorhabditis elegans zygotes. Before polarization, cortical aPKC excludes PAR-1 kinase and its binding partner PAR-2 by phosphorylation. During symmetry breaking, microtubules nucleated by the centrosome locally protect PAR-2 from phosphorylation by aPKC, allowing PAR-2 and PAR-1 to access the cortex nearest the centrosome. Cortical PAR-1 phosphorylates PAR-3, causing the PAR-3/aPKC complex to leave the cortex. Our findings illustrate how microtubules, independent of actin dynamics, stimulate the self-organization of PAR proteins by providing local protection against a global barrier imposed by aPKC.

Motegi, Fumio; Zonies, Seth; Hao, Yingsong; Cuenca, Adrian A.; Griffin, Erik; Seydoux, Geraldine

2011-01-01

368

Localized photo-induced voltage with controlled polarity in single K enriched MoO3 nanobundle.  

PubMed

The photo-induced voltage in an individual K enriched MoO(3) nanobundle was studied with localized focused laser beam irradiation. Without an external bias voltage, a significant photo-induced voltage (36.5 mV) was produced in a single nanobundle under low laser power (2.2 mW). Remarkably, the amplitude and polarity of the voltage could be controlled by the location of the focused laser spot. Unlike the common photo-response that comes from metal-semiconductor junction or PN junction in hybrid nanomaterial, the observed photo-induced effect is from the nanobundle itself, attributed to the small band gap of the material. PMID:23117865

Hu, Zhibin; Tok, Eng Soon; Sow, Chorng Haur

2012-11-01

369

Polarization control method for ultraviolet writing of advanced Bragg gratings.  

PubMed

We present a flexible and simple method for UV writing of Bragg gratings with advanced apodization profiles including discrete phase shifts. The method is based on a p phase shift between the refractive-index modulation profiles induced by s and p polarization of UV light. By changing the ratio of UV intensity in the two polarizations we are able to control the modulation strength and to induce phase shifts while keeping a constant effective refractive index throughout the Bragg grating. We demonstrate strong UV-written Bragg gratings with Gaussian or sinc apodizations with spectral shapes, in good agreement with theoretical predictions. PMID:18026346

Jensen, Jesper Bo; Plougmann, Nikolai; Deyerl, Hans-Jã Rgen; Varming, Poul; Hã Bner, Jã Rg; Kristensen, Martin

2002-06-15

370

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

371

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

372

Asymmetries in electron?induced breakup of polarized {sup 3}He  

SciTech Connect

The Jefferson Lab Experiment E05-102 "Measurement of A{sub x}' and A{sub z}' asymmetries in the quasi-elastic {sup 3}He(e,e'd) reaction" was performed in Hall A in 2009. The main physics motivation of the experiment was to investigate the effects of small components of the {sup 3}He ground-state wave-function by a simultaneous measurement of double-polarization asymmetries in quasi-elastic kinematics for three exclusive channels, (e,e'd), (e,e'p), and (e,e'n), at almost identical momentum transfers, as well as for (e,e'). This experiment will help map the spin structure of the {sup 3}He nucleus onto the picture of the "free" polarized neutron. As such, it is of great relevance to the polarized-neutron programs at Jefferson Lab and beyond.

Sirca, Simon [University of Ljubljana

2011-10-01

373

Curves of growth of spectral lines emitted by a laser-induced plasma: influence of the temporal evolution and spatial inhomogeneity of the plasma  

Microsoft Academic Search

The curves of growth (COG) of five Fe I lines emitted from a laser-induced plasma, generated with Fe–Ni alloys in air at atmospheric pressure, have been investigated. Spectral lines with different energy levels and line widths, emitted with a broad range of optical depths, have been included in the study in order to check the validity of theoretical models proposed

J. A. Aguilera; J. Bengoechea; C. Aragón

2003-01-01

374

The acidic pH-induced structural changes in Pin1 as revealed by spectral methodologies  

NASA Astrophysics Data System (ADS)

Pin1 is closely associated with the pathogenesis of cancers and Alzheimer's disease (AD). Previously, we have shown the characteristics of the thermal denaturation of Pin1. Herein, the acid-induced denaturation of Pin1 was determined by means of fluorescence emission, synchronous fluorescence, far-UV CD, ANS fluorescence and RLS spectroscopies. The fluorescence emission spectra and the synchronous fluorescence spectra suggested the partially reversible unfolding (approximately from pH 7.0 to 4.0) and refolding (approximately from pH 4.0 to 1.0) of the structures around the chromophores in Pin1, apparently with an intermediate state at about pH 4.0-4.5. The far-UV CD spectra indicated that acidic pH (below pH 4.0) induced the structural transition from ?-helix and random coils to ?-sheet in Pin1. The ANS fluorescence and the RLS spectra further suggested the exposure of the hydrophobic side-chains of Pin1 and the aggregation of it especially below pH 2.3, and the aggregation possibly resulted in the formation of extra intermolecular ?-sheet. The present work primarily shows that acidic pH can induce kinds of irreversible structural changes in Pin1, such as the exposure of the hydrophobic side-chains, the transition from ?-helix to ?-sheet and the aggregation of Pin1, and also explains why Pin1 loses most of its activity below pH 5.0. The results emphasize the important role of decreased pH in the pathogenesis of some Pin1-related diseases, and support the therapeutic approach for them by targeting acidosis and modifying the intracellular pH gradients.

Wang, Jing-Zhang; Xi, Lei; Zhu, Guo-Fei; Han, Yong-Guang; Luo, Yue; Wang, Mei; Du, Lin-Fang

2012-12-01

375

Optical-pumping-induced ring structures of polarized laser light propagating through sodium vapor  

NASA Astrophysics Data System (ADS)

We describe a sensitive technique for observing small transverse modifications to intensity, phase, and polarization arising in nonlinear propagation of a laser beam through an atomic vapor. The technique, which in essence is an interferometric one, is based on the use of crossed polarizers that are nearly but not exactly pure circular. Illustrative results are presented for cw dye-laser radiation propagating through collisionally broadened atomic sodium that is near resonant to the D1 line. Well-defined ring patterns produced by nonlinear interactions are observed at both positive and negative laser detunings.

Röhricht, B.; Rusch, U.; Dangel, S.; Schmid, H.; Eschle, P.; Holzner, R.; Sandle, W. J.

1995-08-01

376

Transverse voltage induced by circularly polarized obliquely incident light in plasmonic crystals  

NASA Astrophysics Data System (ADS)

By superposing two electric fields of light excited by s- and p-polarized light, respectively, it is possible to break the symmetry of the field intensity distribution in plasmonic crystals, which results in a DC voltage normal to the plane of incidence. Experimental results on 40 nm-thick Au film with square array of holes with diameter of 240 nm and period of 500 nm are compared with a numerical calculation based on the fast multipole boundary integral equation method. Dispersive behavior of transverse voltage around the surface plasmon resonance for circularly polarized light is elucidated in terms of the phase shift at the resonance.

Ishihara, T.; Hatano, T.; Kurosawa, H.; Kurami, Y.; Nishimura, N.

2012-10-01

377

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

378

Optical lattice polarization effects on magnetically induced optical atomic clock transitions  

SciTech Connect

We derive the frequency shift for a forbidden optical transition J=0{yields}J{sup '}=0 caused by the simultaneous actions of an elliptically polarized lattice field and a static magnetic field. We find that a simple configuration of lattice and magnetic fields leads to a cancellation of this shift to first order in lattice intensity and magnetic field. In this geometry, the second-order lattice intensity shift can be minimized as well by use of optimal lattice polarization. Suppression of these shifts could considerably enhance the performance of the next generation of atomic clocks.

Taichenachev, A. V.; Yudin, V. I.; Oates, C. W. [Institute of Laser Physics SB RAS, Novosibirsk 630090 (Russian Federation) and Novosibirsk State University, Novosibirsk 630090 (Russian Federation); National Institute of Standards and Technology, Boulder, Colorado 80305 (United States)

2007-08-15

379

In vivo near-infrared spectral detection of pressure-induced changes in breast tissue  

NASA Astrophysics Data System (ADS)

A diffuse near-infrared tomography system was used to measure dynamic changes in the absolute optical properties of the human breast that were induced through pressure applied to the tissue surface. Results from five subjects show that absorption and scattering coefficients changed measurably when pressure was increased and that these relative changes correlated with the subjects' body-mass index, indicating that the effect depends on tissue composition. Fitting the absolute absorption and scattering coefficients at six wavelengths to the molar absorption spectra of the three predominant chromophores revealed that both the average total hemoglobin and oxygen saturation increased by 10%, while water concentration decreased by more than 12%. These changes indicate that the pressure-induced variation is likely due to water displacement and vascular volume increase in the region being imaged, for mild application of pressure to the breast. These results suggest that the pressure applied during optical measurements of tissue may alter the tissue physiology, and care should be taken to factor this effect into the design of optical medical instrumentation. In addition, the technique provides a unique approach to measuring tissue elastic changes in vivo in the female breast and may offer a new method for dynamic contrast imaging based on elasto-optical measurements.

Jiang, Shudong; Pogue, Brian W.; Paulsen, Keith D.; Kogel, Christine; Poplack, Steven P.

2003-07-01

380

Exine dehiscing induces rape microspore polarity, which results in different daughter cell fate and fixes the apical-basal axis of the embryo.  

PubMed

The roles of cell polarity and the first asymmetric cell division during early embryogenesis in apical-basal cell fate determination remain unclear. Previously, a novel Brassica napus microspore embryogenesis system was established, by which rape exine-dehisced microspores were induced by physical stress. Unlike traditional microspore culture, cell polarity and subsequent asymmetric division appeared in the exine-dehisced microspore, which finally developed into a typical embryo with a suspensor. Further studies indicated that polarity is critical for apical-basal cell fate determination and suspensor formation. However, the pattern of the first division was not only determined by cell polarity but was also regulated by the position of the ruptured exine. The first division could be equal or unequal, with its orientation essentially perpendicular to the polar axis. In both types of cell division, the two daughter cells could have different cell fates and give rise to an embryo with a suspensor, similar to zygotic apical-basal cell differentiation. The alignment of the two daughter cells is consistent with the orientation of the apical-basal axis of future embryonic development. Thus, the results revealed that exine dehiscing induces rape microspore polarization, and this polarity results in a different cell fate and fixes the apical-basal axis of embryogenesis, but is uncoupled from cell asymmetric division. The present study demonstrated the relationships among cell polarity, asymmetric cell division, and cell fate determination in early embryogenesis. PMID:23162119

Tang, Xingchun; Liu, Yuan; He, Yuqing; Ma, Ligang; Sun, Meng-Xiang

2012-11-16

381

Curvature-induced microphase separation and lipid polar localization in cell membranes - I  

Microsoft Academic Search

Recent research has revealed the prevalence of lipid domains and heterogeneities in biological cell membranes: examples include lipid rafts found in the outer leaflet of eukaryotic plasma membranes and polar localization of the phospholipid, cardiolipin, in bacteria. One of the mysteries has been why domains obsereved in biological cell membranes, such as lipid rafts which are believed to be 10-100

Ranjan Mukhopadhyay; Kerwyn Huang; Ned Wingreen

2006-01-01

382

Polar charges induced electric hysteresis of ZnO nano/microwire for fast data storage.  

PubMed

We demonstrate an innovative memory device made of a single crystalline ZnO nanowire/microwire that works with a different mechanism from the p-n junction based memristor. A nonsymmetric, Schottky-Ohmic contacted ZnO nano/microwire can serve as a memristor if the channel length is short and the applied frequency is high. The observed phenomena could be explained based on a screening model of the polar charges at the two ends of the wire owing to the crystal structure of ZnO. The polar charges are usually fully screened by free electrons coming from the metal sides. But when the magnitude of the externally applied field exceeds a threshold value, the free electrons that screen the polar surfaces can be pulled away from the interface region, leading to a transient change in the effective height of the local Schottky barrier height owing to the electrical field formed by the polar surfaces of ZnO nanowires, which acts as a resistor with its magnitude depending on the total charges being transported. Such a phenomenon could be used for high density and fast writing/erasing data storage. PMID:21609005

Song, Jinhui; Zhang, Yan; Xu, Chen; Wu, Wenzuo; Wang, Zhong Lin

2011-05-24

383

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

Microsoft Academic Search

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

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

2008-01-01

384

Polarized rat uterine epithelium in vitro: constitutive expression of estrogen-induced proteins.  

PubMed

The hormonal responsiveness of immature rat primary uterine epithelial (UE) cells, cultured in a serum-free, phenol red-free defined medium, was examined under conditions which allowed the UE cells to reestablish their polarized phenotype. In the absence of estradiol and phenol red UE cells proliferated to confluence, achieving cell densities equal to those reached by UE cells cultured in the presence of estradiol. The expression of marker proteins, characteristic of the in vivo response of the uterus to estrogen, i.e. the adhesion molecule cell CAM 105, complement component C3, the secretory component of the immunoglobulin A receptor, and keratan sulfate proteoglycan, by polarized cultures of UE cells proved to be independent of estrogen in vitro. Polarized UE cells required the presence of estrogen to maintain integrity of their monolayer and did exhibit a dose-dependent response to estradiol in vitro in terms of cell growth (hypertrophy) and the secretion of two proteins not previously described as estrogen response markers. UE cell secretion, in particular apical secretion, was stimulated by estradiol but not by progesterone, dexamethasone, or testosterone. Progesterone failed to down-regulate the polarized UE cell responses to estradiol. Collectively, these observations suggest that many of the responses which nominally characterize the action of estrogen on the UE cell in vivo are likely to be initiated by agents other than estrogen, e.g. growth factors. PMID:1727726

Julian, J; Carson, D D; Glasser, S R

1992-01-01

385

Interaction-induced ferroelectricity in the rotational states of polar molecules  

Microsoft Academic Search

We show that a ferroelectric quantum phase transition can be driven by the dipolar interaction of polar molecules in the presence a microwave field. The obtained ferroelectricity crucially depends on the harmonic confinement potential, and the macroscopic dipole moment persists even when the external field is turned off adiabatically. The transition is shown to be second order for fermions and

C.-H. Lin; Y.-T. Hsu; Lee Hao; D.-W. Wang

2010-01-01

386

Simulation of streamers propagating along helium jets in ambient air: Polarity-induced effects  

SciTech Connect

Results of modeling of streamer propagation along helium jets for both positive and negative polarities of applied voltage are presented. Obtained patterns of streamer dynamics and structure in these two cases are similar to those observed in experiments with plasma jets.

Naidis, G. V. [Joint Institute for High Temperatures, RAS, 125412 Moscow (Russian Federation)

2011-04-04

387

Four-wave-mixing-induced turbulent spectral broadening in a long Raman fiber laser  

NASA Astrophysics Data System (ADS)

We present a detailed analytical self-consistent theory based on wave kinetic equations that describes generation spectrum and output power of a Raman fiber laser (RFL). It is shown both theoretically and experimentally that the quasi-degenerate four-wave mixing (FWM) between different longitudinal modes is the main broadening mechanism in the one-stage RFL at high powers. The shape and power dependence of the intracavity Stokes wave spectrum are in excellent quantitative agreement with predictions of the theory. FWM-induced stochasticity of the amplitude and the phase of each of the ˜106 longitudinal modes generated in the RFL cavity is an example of a light-wave turbulence in a fiber.

Babin, Sergey A.; Churkin, Dmitriy V.; Ismagulov, Arsen E.; Kablukov, Sergey I.; Podivilov, Evgeny V.

2007-08-01

388

Loop-induced photon spectral lines from neutralino annihilation in the NMSSM  

NASA Astrophysics Data System (ADS)

We have computed the loop-induced processes of neutralino annihilation into two photons and, for the first time, into a photon and a Z 0 boson in the framework of the NMSSM. The photons produced from these radiative modes are monochromatic and possess a clear "smoking gun" experimental signature. This numerical analysis has been done with the help of the SloopS code, initially developed for automatic one-loop calculation in the MSSM. We have computed the rates for different benchmark points coming from SUGRA and GMSB soft SUSY breaking scenarios and compared them with the MSSM. We comment on how this signal can be enhanced, with respect to the MSSM, especially in the low mass region of the neutralino. We also discuss the possibility of this observable to constrain the NMSSM parameter space, taking into account the latest limits from the FERMI collaboration on these two modes.

Chalons, G.; Semenov, A.

2011-12-01

389

Ionization-grating-induced nonlinear phase accumulation in spectrally resolved transient birefringence measurements at 400 nm.  

PubMed

We report experimental confirmation of the ionization-grating-induced transient birefringence predicted by Wahlstrand and Milchberg [Opt. Lett. 36, 3822 (2011)] and discuss its impact on the higher-order Kerr effect interpretation by Loriot et al. of pump-probe transient birefringence measurements made at 800 nm [Opt. Express 17, 13429 (2009)]. Measurement of the transient birefringence in air at 400 nm shows a negative contribution to the index of refraction at zero delay for frequencies within the pump bandwidth, the degenerate case, and no negative contribution for frequencies exceeding the pump bandwidth, the nondegenerate case. Our findings suggest that a reevaluation of the higher-order Kerr effect hypothesis of Loriot et al. is necessary. PMID:23006276

Odhner, J H; Romanov, D A; McCole, E T; Wahlstrand, J K; Milchberg, H M; Levis, R J

2012-08-07

390

Probing the Spin Polarization of Current by Soft X-Ray Imaging of Current-Induced Magnetic Vortex Dynamics  

NASA Astrophysics Data System (ADS)

Time-resolved soft x-ray transmission microscopy is applied to image the current-induced resonant dynamics of the magnetic vortex core realized in a micron sized Permalloy disk. The high spatial resolution better than 25 nm enables us to observe the resonant motion of the vortex core. The result also provides the spin polarization of the current to be 0.67±0.16 for Permalloy by fitting the experimental results with an analytical model in the framework of the spin-transfer torque.

Kasai, Shinya; Fischer, Peter; Im, Mi-Young; Yamada, Keisuke; Nakatani, Yoshinobu; Kobayashi, Kensuke; Kohno, Hiroshi; Ono, Teruo

2008-12-01

391

Measurements and polarization analysis of radio pulses from cosmic-ray-induced air showers at the Pierre Auger Observatory  

NASA Astrophysics Data System (ADS)

The Auger Engineering Radio Array (AERA) is designed to study the radio emissions from extensive air showers at the Pierre Auger Observatory. The array currently consists of a grid of 23 autonomous radio detector stations that measure the radio emissions from cosmic-ray-induced air showers since April 2011. The array is still under construction and is planned to be extended to 160 stations. The new detection technique provides an augmentation of the existing detectors, improves the sensitivity of the observatory and sheds new light on the shower physics. An analysis of the emission processes based on the polarization of the radio pulses is presented.

Fraenkel, Daniël; Pierre Auger Collaboration

2013-02-01

392

Ultrafast spin-induced polarization oscillations with tunable lifetime in vertical-cavity surface-emitting lasers  

NASA Astrophysics Data System (ADS)

We report spin-induced polarization oscillations in vertical-cavity surface-emitting lasers above threshold and at room temperature. The oscillation frequency is 11.6 GHz, which is significantly higher than the modulation bandwidth of less than 4 GHz in the device. The oscillation frequency is determined by an additional resonance frequency in birefringence containing microcavities, which is potentially much higher than the conventional relaxation oscillation frequency. The damping of the oscillations can be controlled by the current, allowing for oscillation lifetimes much longer than the spin lifetime in the device as well as for short bursts potentially interesting for information transmission.

Gerhardt, N. C.; Li, M. Y.; Jähme, H.; Höpfner, H.; Ackemann, T.; Hofmann, M. R.

2011-10-01

393

Spectral Effects in Quantum Teleportation  

SciTech Connect

We use a multimode description of polarization-encoded qubits to analyze the quantum teleportation protocol. Specifically, we investigate how the teleportation fidelity depends on the spectral correlations inherent to polarization-entangled photons generated by type-II spontaneous parametric down conversion. We find that the maximal obtainable fidelity depends on the spectral entanglement carried by the joint probability amplitude, a result which we quantify for the case of a joint spectrum approximated by a correlated Gaussian function. We contrast these results with a similar analysis of the visibility obtained in a polarization-correlation experiment.

Humble, Travis S [ORNL; Grice, Warren P [ORNL

2007-01-01

394

Spectral effects in quantum teleportation  

SciTech Connect

We use a multimode description of polarization-encoded qubits to analyze the quantum teleportation protocol. Specifically, we investigate how the teleportation fidelity depends on the spectral correlations inherent to polarization-entangled photons generated by type-II spontaneous parametric down conversion. We find that the maximal obtainable fidelity depends on the spectral entanglement carried by the joint probability amplitude, a result which we quantify for the case of a joint spectrum approximated by a correlated Gaussian function. We contrast these results with a similar analysis of the visibility obtained in a polarization-correlation experiment.

Humble, Travis S.; Grice, Warren P. [Center for Engineering Science Advanced Research, Computer Science and Mathematics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6016 (United States)

2007-02-15

395

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.

Barstow, Buz; Ando, Nozomi; Kim, Chae Un; Gruner, Sol M.

2009-01-01

396

Polarization-Induced Interfacial Reactions between Nickel and Selenium in Ni/Zirconia SOFC Anodes and Comparison with Sulfur Poisoning  

SciTech Connect

Three distinctly different characteristic responses of a nickel/yttria-stabilized zirconia (Ni/YSZ) cermet anode to the presence of hydrogen selenide in synthetic coal gas were observed, depending on temperature (650-800oC), H2Se concentration (0-40 ppm), and especially on the extent of anodic polarization (0 to ~0.5 V). The first level of response was characterized by a rapid but modest decrease in power density to a new steady state, with no further degradation observed in tests up to 700 hours in duration. Mostly observed at high temperatures, low H2Se concentrations, and low anodic polarizations, this response level was similar to effects caused by the presence of H2S, but with slower onset and lower reversibility. Higher anodic polarization at a constant current could trigger a second level of response characterized by oscillatory behavior involving cycles of rapid performance loss followed by rapid recovery. Oscillations at the constant current density were accompanied by the appearance and disappearance of a new feature in the electrochemical impedance spectrum with a summit frequency of ~100 Hz. Oscillatory behavior ceased when the current density was lowered. Such behavior was not observed for cells operated at a constant potential of similar magnitude, though. A third level of response, irreversible cell failure, could be induced by further increases in anodic polarization, additionally favored by low temperature and high H2Se concentration. Post-test analyses of failed cells by electron microscopy revealed the extensive microstructural changes including the appearance of nickel oxide and nickel selenide alteration phases, only at the anode/electrolyte interface. From bulk thermochemical considerations the formation of nickel selenides could not be expected. Local chemical conditions created at the anode/electrolyte interface appear to be of overriding importance with respect to the extent of Ni/YSZ anode interactions with H2Se in coal gas.

Marina, Olga A.; Pederson, Larry R.; Coyle, Christopher A.; Thomsen, Edwin C.; Edwards, Danny J.

2011-01-10

397

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

398

[Analysis of software for identifying spectral line of laser-induced breakdown spectroscopy based on LabVIEW].  

PubMed

Self-designed identifying software for LIBS spectral line was introduced. Being integrated with LabVIEW, the soft ware can smooth spectral lines and pick peaks. The second difference and threshold methods were employed. Characteristic spectrum of several elements matches the NIST database, and realizes automatic spectral line identification and qualitative analysis of the basic composition of sample. This software can analyze spectrum handily and rapidly. It will be a useful tool for LIBS. PMID:22582614

Hu, Zhi-yu; Zhang, Lei; Ma, Wei-guang; Yan, Xiao-juan; Li, Zhi-xin; Zhang, Yong-zhi; Wang, Le; Dong, Lei; Yin, Wang-bao; Jia, Suo-tang

2012-03-01

399

Light-induced phase transition in a quantum spin chain: Breakdown of the Haldane phase by circularly polarized laser  

NASA Astrophysics Data System (ADS)

We theoretically propose a new category of non-equilibrium phase transitions in quantum spin systems that can be induced by the magnetic component of strong lasers. As an example, we consider a Haldane chain with single ion anisotropy radiated by circularly polarized light. We study the spin dynamics by combining the numerical infinite time-evolving block decimation method and an analytical calculation via the Floquet theory, and demonstrate that the laser can magnetize even an antiferromagnet quantum mechanically. It is also shown that the string order is broken by the magnetization, which indicates that a photo-induced breakdown of the Haldane phase has occurred. This phenomenon can be realized using strong THz lasers.

Takayoshi, Shintaro; Aoki, Hideo; Oka, Takashi

2013-03-01

400

Diffractive optics based three-pulse photon echo peak shift studies of spectral diffusion in polar liquids: Evidence for long lived frequency correlations  

NASA Astrophysics Data System (ADS)

We report a three-pulse photon echo peak shift (3PEPS) apparatus adopting a diffractive beam splitter to generate triplets of femtosecond pulses with tilted wave front, which enhances the overlap over the entire aperture in a noncollinear geometry while preserving femtosecond pulse duration. The apparatus provides highly reproducible 3PEPS data including the long time peak shift, a critical parameter to recognize the spectral inhomogeneity in condensed phases. To demonstrate the high performance of our setup and to examine the inhomogeneous line broadening in liquids, we measured 3PEPS of a carbocyanine dye IR125 in several solvents. The solvation dynamics becomes slower for IR125 compared to the typical values reported previously probably due to the multipolar nature of the excitation in this large and flexible probe molecule. More importantly, inhomogeneity was observed unambiguously in all solvents, and it is excitation energy dependent. It was speculated that slow dielectric relaxation and conformational heterogeneity may be responsible for the inhomogeneity.

Park, Sohyun; Joo, Taiha

2009-10-01

401

Interaction-Induced Chiral Quantum States of the Ultracold Polar Molecules  

NASA Astrophysics Data System (ADS)

The ultracold polar molecules with the tunable dipole-dipole interaction, not only would enable explorations of a large class of exotic many-body physics phenomena, but also could be used for quantum information processing. In the present paper we demonstrate that this dipole-dipole interaction can generate the degenerate chiral quantum states acting as a qubit robust against noise when the ultracold polar molecules are confined by a triangular lattice. Moreover, we also find two first-order quantum phase transitions by controlling an external driving field. One is the transition with the change of the different degenerate chiral quantum states. The other is the transition with the breaking of the degenerate quantum chiral states to the nondegenerate state. In experiment, these first-order quantum phase transitions can be detected by measuring the collective molecular population.

Wang, Ming-Hao; Liang, Jiu-Qing; Ma, Jie; Chen, Gang; Jia, Suo-Tang

2012-11-01

402

Helicobacter pylori-Induced Disruption of Monolayer Permeability and Proinflammatory Cytokine Secretion in Polarized Human Gastric Epithelial Cells  

PubMed Central

Helicobacter pylori infection of the stomach is related to the development of diverse gastric pathologies. The ability of H. pylori to compromise epithelial junctional complexes and to induce proinflammatory cytokines is believed to contribute to pathogenesis. The purpose of this study was to use an in vitro human gastric epithelial model to investigate the ability of H. pylori to affect permeability and the extent and polarity of the host inflammatory response. NCI-N87 monolayers were cocultured with live or heat-killed H. pylori or culture supernatants. Epithelial barrier function was measured by transepithelial electric resistance (TEER) analysis, diffusion of fluorescein isothiocyanate (FITC)-labeled markers, and immunostaining for tight junction proteins. Supernatants from both apical and basolateral chambers were tested for cytokine production by multiplex analysis. H. pylori caused a significant decrease in TEER, an increased passage of markers through the infected monolayer, and severe disruption and mislocalization of ZO-1 and claudin-1 proteins. Cell viability was not altered by H. pylori, indicating that loss of barrier function could be attributed to a breakdown of tight junction integrity. Significantly high levels of cytokine secretion were induced by either viable or heat-killed H. pylori. H. pylori affects monolayer permeability of polarized human gastric epithelial cells. Proinflammatory cytokines were secreted in a polarized manner, mostly basolaterally. Live bacteria are required for disruption of tight junctions but not for the induction of cytokine secretion. The NCI-N87 cell line provides an excellent model for the in vitro study of H. pylori pathogenesis and the epithelial cell host response to infection.

Fiorentino, Maria; Ding, Hua; Blanchard, Thomas G.; Czinn, Steven J.; Sztein, Marcelo B.

2013-01-01

403

Optically induced dynamic polarization gratings for tunable, quasi-phase matched second harmonic generation  

Microsoft Academic Search

Light interference patterns can photoexcite mobile charge and generate periodic space charge fields with periods of typically 0.1 to 100 microns in photorefractive crystals. The space charge field attains values of 0.1 to 1 kV cm-1 in ferroelectrics such as Sr0.75Ba0.25Nb2O6 (SBN:75). A fundamental question is whether these periodic space charge fields can spatially modulate the ferroelectric polarization in materials

A. S. Kewitsch; M. Segev; A. Yariv; G. J. Salamo; T. Towe; E. J. Sharp; R. R. Neurgaonkar

1994-01-01

404

Insights into linear and rank correlation for material identification in laser-induced breakdown spectroscopy and other spectral techniques.  

PubMed

The purpose of this work was to critically assess the potential and limitations of linear and rank correlation methods, not only relevant to laser-induced breakdown spectroscopy (LIBS), but to other spectroscopic techniques as well. Through computer simulations, it was demonstrated that a linear correlation is a more suitable technique for material identification than a rank correlation due to its better stability toward noise and better ability to detect small systematic variations in line intensities. The effect of noise on the results of correlation analysis has been studied. It was found that random noise causes correlation coefficients to be distributed normally, whereas flicker noise (random fluctuations in line intensities) results in a gamma distribution of correlation coefficients. Hence, the distribution of correlation coefficients can be used for detection of the type of noise that dominates correlated spectra. A potential of linear correlation analysis for plasma diagnostics has been demonstrated. It is based on a strong dependence of the linear correlation coefficient upon the line shapes of correlated spectral lines and, consequently, upon plasma parameters (plasma temperature, number densities). PMID:18498696

Gornushkin, I B; Mueller, M; Panne, U; Winefordner, J D

2008-05-01

405

Helicobacter pylori-induced alteration of epithelial cell signaling and polarity: a possible mechanism of gastric carcinoma etiology and disparity.  

PubMed

Gastric cancer, a disease of disparity associated with Helicobacter pylori (H. pylori) infection, is the world's second leading cause of cancer deaths. The pathogen H. pylori target the epithelial adhesion receptors, E-cadherin, and ?1-integrin, to modulate the host cytoskeleton via disruption of the epithelial cell polarity necessary for maintaining the infection, but how this leads to the development of the carcinoma is widely unclear. While Rho family GTPases' signaling to the cytoskeleton and these receptors is required for initiating and maintaining the infection, the responsible effectors, and how they might influence the etiology of the carcinomas are currently unknown. Here we discuss the potential role of the Cdc42-IQGAP1 axis, a negative regulator of the tumor suppressors E-cadherin and ?1-integrin, as a potential driver of H. pylori-induced gastric carcinoma and propose avenues for addressing its disparity. Chronic dysfunction of the IQGAP1-signaling pathway, resulting from H. pylori-induced disruption of cell polarity, can explain the pathogenesis of the carcinoma, at least, in subsets of infected population, and thus could provide a potential means for personalized medicine. PMID:23629919

Osman, Mahasin A; Bloom, George S; Tagoe, Emmanuel A

2013-07-03

406

Spin-polarized transport induced by spin-pumping in a Rashba ring.  

PubMed

The Keldysh Green's function method is employed to study spin-dependent electron transport through a Rashba ring with a quantum dot (QD) embedded in one of its arms. Zero charge bias is applied on the system while a rotating magnetic field is considered in the QD to pump pure spin current. The Rashba spin-orbital coupling (RSOC) can cause a spin precession phase of the electron passing through the ring, so that the quantum interference in the ring can lead to a spin-polarized charge current flowing in the leads and the arm without a QD, whereas only pure spin current is flowing in the other arm with a QD. It is shown that for low frequency ? of the rotating magnetic field, the pumped charge current is proportional to ? unlike the charge current produced by mono-parametric quantum charge pumping, which is usually proportional to ?(2). Moreover, the magnitude, the direction, as well as the spin-polarization of the charge current can be controlled by tuning the device parameters such as the QD energy level, the RSOC strength, and the strength of the electron tunneling between the leads and the QD. Hence the studied device may serve as a generating source for tunable spin-polarized current in the spintronics field. PMID:21832514

Liang, F; Yang, Y H; Wang, J; Chan, K S

2009-11-06

407

Temporo-spectral imaging of intrinsic optical signals during hypoxia-induced spreading depression-like depolarization.  

PubMed

Spreading depression (SD) is characterized by a sustained near-complete depolarization of neurons, a massive depolarization of glia, and a negative deflection of the extracellular DC potential. These electrophysiological signs are accompanied by an intrinsic optical signal (IOS) which arises from changes in light scattering and absorption. Even though the underlying mechanisms are unclear, the IOS serves as non-invasive tool to define the spatiotemporal dynamics of SD in brain slices. Usually the tissue is illuminated by white light, and light reflectance or transmittance is monitored. Using a polychromatic, fast-switchable light source we now performed temporo-spectral recordings of the IOS associated with hypoxia-induced SD-like depolarization (HSD) in rat hippocampal slices kept in an interface recording chamber. Recording full illumination spectra (320-680 nm) yielded distinct reflectance profiles for the different phases of HSD. Early during hypoxia tissue reflectance decreased within almost the entire spectrum due to cell swelling. HSD was accompanied by a reversible reflectance increase being most pronounced at 400 nm and 460 nm. At 440 nm massive porphyrin absorption (Soret band) was detected. Hypotonic solutions, Ca(2+)-withdrawal and glial poisoning intensified the reflectance increase during HSD, whereas hypertonic solutions dampened it. Replacement of Cl(-) inverted the reflectance increase. Inducing HSD by cyanide distorted the IOS and reflectance at 340-400 nm increased irreversibly. The pronounced changes at short wavelengths (380 nm, 460 nm) and their cyanide sensitivity suggest that block of mitochondrial metabolism contributes to the IOS during HSD. For stable and reliable IOS recordings during HSD wavelengths of 460-560 nm are recommended. PMID:22952835

Mané, Maria; Müller, Michael

2012-08-29

408

Temporo-Spectral Imaging of Intrinsic Optical Signals during Hypoxia-Induced Spreading Depression-Like Depolarization  

PubMed Central

Spreading depression (SD) is characterized by a sustained near-complete depolarization of neurons, a massive depolarization of glia, and a negative deflection of the extracellular DC potential. These electrophysiological signs are accompanied by an intrinsic optical signal (IOS) which arises from changes in light scattering and absorption. Even though the underlying mechanisms are unclear, the IOS serves as non-invasive tool to define the spatiotemporal dynamics of SD in brain slices. Usually the tissue is illuminated by white light, and light reflectance or transmittance is monitored. Using a polychromatic, fast-switchable light source we now performed temporo-spectral recordings of the IOS associated with hypoxia-induced SD-like depolarization (HSD) in rat hippocampal slices kept in an interface recording chamber. Recording full illumination spectra (320–680 nm) yielded distinct reflectance profiles for the different phases of HSD. Early during hypoxia tissue reflectance decreased within almost the entire spectrum due to cell swelling. HSD was accompanied by a reversible reflectance increase being most pronounced at 400 nm and 460 nm. At 440 nm massive porphyrin absorption (Soret band) was detected. Hypotonic solutions, Ca2+-withdrawal and glial poisoning intensified the reflectance increase during HSD, whereas hypertonic solutions dampened it. Replacement of Cl- inverted the reflectance increase. Inducing HSD by cyanide distorted the IOS and reflectance at 340–400 nm increased irreversibly. The pronounced changes at short wavelengths (380 nm, 460 nm) and their cyanide sensitivity suggest that block of mitochondrial metabolism contributes to the IOS during HSD. For stable and reliable IOS recordings during HSD wavelengths of 460–560 nm are recommended.

Mane, Maria; Muller, Michael

2012-01-01

409

Development of a polarization hyperspectral image projector  

NASA Astrophysics Data System (ADS)

This paper describes the development of a new instrument for calibrating satellite imaging sensors - the Polarization Hyperspectral Image Projector (PHIP). The PHIP instrument is capable of producing realistic standards-based satellite imagery, simultaneously projecting spectral, spatial and polarization scenes. The feasibility study outlined here demonstrates that liquid crystal devices are capable of producing arbitrary polarization states. Boulder Nonlinear Systems is currently developing a complete spectral/spatial/polarization instrument to be delivered to NASA in 2013.

Ewing, Teresa K.; King, Sharon V.; Masterson, Hugh M.; Gonzales, Nicholas; Elshof, Dane

2012-05-01

410

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

411

Influence of the Grating Parameters on the Polarization Properties of Fiber Bragg Gratings  

Microsoft Academic Search

Due to the lateral inscription process, photo-induced birefringence is present in fiber Bragg gratings (FBGs) written into photosensitive single mode fiber. The birefringence value is generally too small to be perceived in the grating spectral response but it can lead to significant polarization dependent loss (PDL) and differential group delay (DGD) evolutions. In this paper, we first theoretically analyze the