Small-scale plasma turbulence and intermittency in the high latitude F region based on the ICI-2 sounding rocket experiment

NASA Astrophysics Data System (ADS)

Spicher, A.; Miloch, W.; Moen, J. I.; Clausen, L. B. N.

2015-12-01

Small-scale plasma irregularities and turbulence are common phenomena in the F layer of the ionosphere, both in the equatorial and polar regions. A common approach in analyzing data from experiments on space and ionospheric plasma irregularities are power spectra. Power spectra give no information about the phases of the waveforms, and thus do not allow to determine whether some of the phases are correlated or whether they exhibit a random character. The former case would imply the presence of nonlinear wave-wave interactions, while the latter suggests a more turbulent-like process. Discerning between these mechanisms is crucial for understanding high latitude plasma irregularities and can be addressed with bispectral analysis and higher order statistics. In this study, we use higher order spectra and statistics to analyze electron density data observed with the ICI-2 sounding rocket experiment at a meter-scale resolution. The main objective of ICI-2 was to investigate plasma irregularities in the cusp in the F layer ionosphere. We study in detail two regions intersected during the rocket flight and which are characterized by large density fluctuations: a trailing edge of a cold polar cap patch, and a density enhancement subject to cusp auroral particle precipitation. While these two regions exhibit similar power spectra, our analysis reveals that their internal structure is different. The structures on the edge of the polar cap patch are characterized by significant coherent mode coupling and intermittency, while the plasma enhancement associated with precipitation exhibits stronger random characteristics. This indicates that particle precipitation may play a fundamental role in ionospheric plasma structuring by creating turbulent-like structures.

A Binary Planet in Color

NASA Image and Video Library

2015-07-23

This image from NASA New Horizons highlights the contrasting appearance of the two worlds: Charon is mostly gray, with a dark reddish polar cap, while Pluto shows a wide variety of subtle color variations. Pluto and Charon are shown in enhanced color in this image, which is the highest-resolution color image of the pair so far returned to Earth by New Horizons. It was taken at 06:49 UT on July 14, 2015, five hours before Pluto closest approach, from a range of 150,000 miles (250,000 kilometers), with the spacecraft's Ralph instrument. The image highlights the contrasting appearance of the two worlds: Charon is mostly gray, with a dark reddish polar cap, while Pluto shows a wide variety of subtle color variations, including yellowish patches on the north polar cap and subtly contrasting colors for the two halves of Pluto's "heart," informally named Tombaugh Regio, seen in the upper right quadrant of the image. In order to fit Pluto and Charon in the same frame in their correct relative positions, the image has been rotated so the north pole on both Pluto and Charon is pointing towards the upper left. The image was made with the blue, red, and near-infrared color filters of Ralph's Multispectral Visible Imaging Camera, and shows colors that are similar, but not identical, to what would be seen with the human eye, which is sensitive to a narrower range of wavelengths. http://photojournal.jpl.nasa.gov/catalog/PIA19856

Morphology and composition of the surface of Mars: Mars Odyssey THEMIS results.

PubMed

Christensen, Philip R; Bandfield, Joshua L; Bell, James F; Gorelick, Noel; Hamilton, Victoria E; Ivanov, Anton; Jakosky, Bruce M; Kieffer, Hugh H; Lane, Melissa D; Malin, Michael C; McConnochie, Timothy; McEwen, Alfred S; McSween, Harry Y; Mehall, Greg L; Moersch, Jeffery E; Nealson, Kenneth H; Rice, James W; Richardson, Mark I; Ruff, Steven W; Smith, Michael D; Titus, Timothy N; Wyatt, Michael B

2003-06-27

The Thermal Emission Imaging System (THEMIS) on Mars Odyssey has produced infrared to visible wavelength images of the martian surface that show lithologically distinct layers with variable thickness, implying temporal changes in the processes or environments during or after their formation. Kilometer-scale exposures of bedrock are observed; elsewhere airfall dust completely mantles the surface over thousands of square kilometers. Mars has compositional variations at 100-meter scales, for example, an exposure of olivine-rich basalt in the walls of Ganges Chasma. Thermally distinct ejecta facies occur around some craters with variations associated with crater age. Polar observations have identified temporal patches of water frost in the north polar cap. No thermal signatures associated with endogenic heat sources have been identified.

Morphology and composition of the surface of Mars: Mars Odyssey THEMIS results

USGS Publications Warehouse

Christensen, P.R.; Bandfield, J.L.; Bell, J.F.; Gorelick, N.; Hamilton, V.E.; Ivanov, A.; Jakosky, B.M.; Kieffer, H.H.; Lane, M.D.; Malin, M.C.; McConnochie, T.; McEwen, A.S.; McSween, H.Y.; Mehall, G.L.; Moersch, J.E.; Nealson, K.H.; Rice, J. W.; Richardson, M.I.; Ruff, S.W.; Smith, M.D.; Titus, T.N.; Wyatt, M.B.

2003-01-01

The Thermal Emission Imaging System (THEMIS) on Mars Odyssey has produced infrared to visible wavelength images of the martian surface that show lithologically distinct layers with variable thickness, implying temporal changes in the processes or environments during or after their formation. Kilometer-scale exposures of bedrock are observed; elsewhere airfall dust completely mantles the surface over thousands of square kilometers. Mars has compositional variations at 100-meter scales, for example, an exposure of olivine-rich basalt in the walls of Ganges Chasma. Thermally distinct ejecta facies occur around some craters with variations associated with crater age. Polar observations have identified temporal patches of water frost in the north polar cap. No thermal signatures associated with endogenic heat sources have been identified.

Frost-free North Polar Layers in the Good Old Summertime

NASA Technical Reports Server (NTRS)

2006-01-01

17 October 2006 The middle portion of the northern summer season is the ideal time of year to capture relatively dust- and haze-free views of martian north polar terrain. This year, much more of the north polar cap has sublimed away than has been evident in previous northern summers going back to 1999, when Mars Global Surveyor (MGS) began the Mapping Phase of the mission. This MGS Mars Orbiter Camera (MOC) image shows a nearly ice-free view of layers exposed by erosion in the north polar region. The light-toned patches are remnants of water ice frost. The layers are generally considered by the Mars scientific community to be record of past depositions of ice and dust. This picture is located near 82.5oN, 118.6oW, and covers an area about 3 km by 10 km (1.9 by 6.2 miles). Sunlight illuminates the scene from the upper left; the image was acquired on 22 September 2006.

Two Types of Transpolar Arc Development, Event Studies with Data Set of ASTRID-2, DMSP, FAST, and SuperDARN

NASA Technical Reports Server (NTRS)

Narita, Yasuhito; Maezawa, Kiyoshi; Toshinori, Mukai; Kullen, A.; Ivchenko, N.; Marklund, G.; Frederick, R.; Carlson, C. W.; Spann, J. F.; Parks, G. K.;

A case-study of the evolution of polar-cap currents and auroral electrojets during polar geomagnetic disturbances with IMS magnetometer data

NASA Technical Reports Server (NTRS)

Iijima, T.; Kim, J. S.; Sugiura, M.

1984-01-01

The development of the polar cap current and the relationship of that development to the evolution of auroral electrojets during individual polar geomagnetic disturbances is studied using 1 min average data from US-Canada IMS network stations and standard magnetograms from sites on the polar cap and in the auroral zone. It is found that even when the auroral electrojet activity is weak, polar cap currents producing fields of magnitude approximately 100-200 nT almost always exist. A normal convection current system exists quasi-persistently in the polar cap during extended quiet or weakly disturbed periods of auroral electrojet activity. After one such period, some drastic changes occur in the polar cap currents, which are followed by phases of growth, expansion, and recovery. Polar cap currents cannot all be completely ascribed to a single source mechanism.

Cradle Cap

MedlinePlus

Cradle cap Overview Cradle cap causes crusty or oily scaly patches on a baby's scalp. The condition isn't painful or itchy. But it can ... scales that aren't easy to remove. Cradle cap usually clears up on its own in a ...

Comparisons of the North Polar Cap of Mars and the Earth's Northern Hemisphere snow cover

NASA Technical Reports Server (NTRS)

Foster, J.; Owe, M.; Capen, C.

1985-01-01

The boundaries of the polar caps of Mars have been measured on more than 3000 photographs since 1905 from the plate collection at the Lowell Observatory. For the Earth the polar caps have been accurately mapped only since the mid 1960's when satellites were first available to synoptically view the polar regions. The polar caps of both planets wax and wane in response to changes in the seasons, and interannual differences in polar cap behavior on Mars as well as Earth are intimately linked to global energy balance. In this study data on the year to year variations in the extent of the polar caps of Mars and Earth were assembled and analyzed together with data on annual variations in solar activity to determine if associations exist between these data. It was found that virtually no correlation exists between measurements of Mars north polar cap and solar variability. An inverse relationship was found between variations in the size of the north polar caps of Mars and Earth, although only 6 years of concurrent data were available for comparison.

Tracking the Martian CO2 Polar Ice Caps in Infrared Images

NASA Technical Reports Server (NTRS)

Wagstaff, Kiri L.; Castano, Rebecca; Chien, Steve

2006-01-01

Researchers at NASA s Jet Propulsion Laboratory have developed a method for automatically tracking the polar caps on Mars as they advance and recede each year (see figure). The seasonal Mars polar caps are composed mainly of CO2 ice and are therefore cold enough to stand out clearly in infrared data collected by the Thermal Emission Imaging System (THEMIS) onboard the Mars Odyssey spacecraft. The Bimodal Image Temperature (BIT) histogram analysis algorithm analyzes raw, uncalibrated data to identify images that contain both "cold" ("polar cap") and "warm" ("not polar cap") pixels. The algorithm dynamically identifies the temperature that separates these two regions. This flexibility is critical, because in the absence of any calibration, the threshold temperature can vary significantly from image to image. Using the identified threshold, the algorithm classifies each pixel in the image as "polar cap" or "not polar cap," then identifies the image row that contains the spatial transition from "polar cap" to "not polar cap." While this method is useful for analyzing data that has already been returned by THEMIS, it has even more significance with respect to data that has not yet been collected. Instead of seeking the polar cap only in specific, targeted images, the simplicity and efficiency of this method makes it feasible for direct, onboard use. That is, THEMIS could continuously monitor its observations for any detections of the polar-cap edge, producing detections over a wide range of spatial and temporal conditions. This effort can greatly contribute to our understanding of long-term climatic change on Mars.

Rash - child under 2 years

MedlinePlus

... can last for 12 to 18 months. Cradle cap (seborrheic dermatitis) causes greasy, scaling, crusty patches on ... acne medicines used by adolescents and adults. CRADLE CAP For cradle cap, wash the hair or scalp ...

Microelectromechanical Systems Actuator Based Reconfigurable Printed Antenna

NASA Technical Reports Server (NTRS)

Simons, Rainee N. (Inventor)

2005-01-01

A polarization reconfigurable patch antenna is disclosed. The antenna includes a feed element, a patch antenna element electrically connected to the feed element, and at least one microelectromechanical systems (MEMS) actuator, with a partial connection to the patch antenna element along an edge of the patch antenna element. The polarization of the antenna can be switched between circular polarization and linear polarization through action of the at least one MEMS actuator.

Measurements of the north polar cap of Mars and the earth's Northern Hemisphere ice and snow cover

NASA Technical Reports Server (NTRS)

Foster, J.; Owe, M.; Capen, C.

1986-01-01

The boundaries of the polar caps of Mars have been measured on more than 3000 photographs since 1905 from the plate collection at the Lowell Observatory. For the earth, the polar caps have been accurately mapped only since the mid 1960s when satellites were first available to synoptically view the polar regions. The polar caps of both planets wax and wane in response to changes in the seasons, and interannual differences in polar cap behavior on Mars as well as earth are intimately linked to global energy balance. Data on the year to year variations in the extent of the north polar caps of Mars and earth have been assembled and compared, although only 6 years of concurrent data were available for comparison.

In Vivo Evaluation of Wearable Head Impact Sensors.

PubMed

Wu, Lyndia C; Nangia, Vaibhav; Bui, Kevin; Hammoor, Bradley; Kurt, Mehmet; Hernandez, Fidel; Kuo, Calvin; Camarillo, David B

2016-04-01

Inertial sensors are commonly used to measure human head motion. Some sensors have been tested with dummy or cadaver experiments with mixed results, and methods to evaluate sensors in vivo are lacking. Here we present an in vivo method using high speed video to test teeth-mounted (mouthguard), soft tissue-mounted (skin patch), and headgear-mounted (skull cap) sensors during 6-13 g sagittal soccer head impacts. Sensor coupling to the skull was quantified by displacement from an ear-canal reference. Mouthguard displacements were within video measurement error (<1 mm), while the skin patch and skull cap displaced up to 4 and 13 mm from the ear-canal reference, respectively. We used the mouthguard, which had the least displacement from skull, as the reference to assess 6-degree-of-freedom skin patch and skull cap measurements. Linear and rotational acceleration magnitudes were over-predicted by both the skin patch (with 120% NRMS error for a(mag), 290% for α(mag)) and the skull cap (320% NRMS error for a(mag), 500% for α(mag)). Such over-predictions were largely due to out-of-plane motion. To model sensor error, we found that in-plane skin patch linear acceleration in the anterior-posterior direction could be modeled by an underdamped viscoelastic system. In summary, the mouthguard showed tighter skull coupling than the other sensor mounting approaches. Furthermore, the in vivo methods presented are valuable for investigating skull acceleration sensor technologies.

The Tordo 1 polar cusp barium plasma injection experiment

NASA Technical Reports Server (NTRS)

Wescott, E. M.; Stenbaek-Nielsen, H. C.; Davis, T. N.; Jeffries, R. A.; Roach, W. H.

1978-01-01

In January 1975, two barium plasma injection experiments were carried out with rockets launched into the upper atmosphere where field lines from the dayside cusp region intersect the ionosphere. The Tordo 1 experiment took place near the beginning of a worldwide magnetic storm. It became a polar cap experiment almost immediately as convection perpendicular to the magnetic field moved the fluorescent plasma jet away from the cusp across the polar cap in an antisunward direction. Convection across the polar cap with an average velocity of more than 1 km/s was observed for nearly 40 min until the barium flux tubes encountered large electron fields associated with a poleward bulge of the auroral oval near Greenland. Prior to the encounter with the aurora near Greenland there is evidence of upward acceleration of the barium ions while they were in the polar cap. The three-dimensional observations of the plasma orientation and motion give an insight into convection from the cusp region across the polar cap, the orientation of the polar cap magnetic field lines out to several earth radii, the causes of polar cap magnetic perturbations, and parallel acceleration processes.

Forcing of the Coupled Ionosphere-Thermosphere (IT) System During Magnetic Storms

NASA Technical Reports Server (NTRS)

Huang, Cheryl; Huang, Yanshi; Su, Yi-Jiun; Sutton, Eric; Hairston, Marc; Coley, W. Robin; Doornbos, Eelco; Zhang, Yongliang

2014-01-01

Poynting flux shows peaks around auroral zone AND inside polar cap. Energy enters IT system at all local times in polar cap. Track-integrated flux at DMSP often peaks at polar latitudes- probably due to increased area of polar cap during storm main phases. center dot lon temperatures at DMSP show large increases in polar region at all local times; cusp and auroral zones do not show distinctively high Ti. center dot I on temperatures in the polar cap are higher than in the auroral zones during quiet times. center dot Neutral densities at GRACE and GOCE show maxima at polar latitudes without clear auroral signatures. Response is fast, minutes from onset to density peaks. center dot GUVI observations of O/N2 ratio during storms show similar response as direct measurements of ion and neutral densities, i.e. high temperatures in polar cap during prestorm quiet period, heating proceeding from polar cap to lower latitudes during storm main phase. center dot Discrepancy between maps of Poynting flux and of ion temperatures/neutral densities suggests that connection between Poynting flux and Joule heating is not simple.

Polar Rain Gradients and Field-Aligned Polar Cap Potentials

NASA Technical Reports Server (NTRS)

Fairfield, D. H.; Wing, S.; Newell, P. T.; Ruohoniemi, J. M.; Gosling, J. T.; Skoug, R. M.

2008-01-01

ACE SWEPAM measurements of solar wind field-aligned electrons have been compared with simultaneous measurements of polar rain electrons precipitating over the polar cap and detected by DMSP spacecraft. Such comparisons allow investigation of cross-polar-cap gradients in the intensity of otherwise-steady polar rain. The generally good agreement of the distribution functions, f, from the two data sources confirms that direct entry of solar electrons along open field lines is indeed the cause of polar rain. The agreement between the data sets is typically best on the side of the polar cap with most intense polar rain but the DMSP f's in less intense regions can be brought into agreement with ACE measurements by shifting all energies by a fixed amounts that range from tens to several hundred eV. In most cases these shifts are positive which implies that field-aligned potentials of these amounts exist on polar cap field lines which tend to retard the entry of electrons and produce the observed gradients. These retarding potentials undoubtedly appear in order to prevent the entry of low-energy electrons and maintain charge quasi-neutrality that would otherwise be violated since most tailward flowing magnetosheath ions are unable to follow polar rain electrons down to the polar cap. In more limited regions near the boundary of the polar cap there is sometimes evidence for field-aligned potentials of the opposite sign that accelerate polar rain electrons. A solar electron burst is also studied and it is concluded that electrons from such bursts can enter the magnetotail and precipitate in the same manner as polar rain.

North-south geological differences between the residual polar caps on Mars

USGS Publications Warehouse

Thomas, P.C.; Malin, M.C.; Edgett, K.S.; Carr, M.H.; Hartmann, W.K.; Ingersoll, A.P.; James, P.B.; Soderblom, L.A.; Veverka, J.; Sullivan, R.

2000-01-01

Polar processes can be sensitive indicators of global climate, and the geological features associated with polar ice caps can therefore indicate evolution of climate with time. The polar regions on Mars have distinctive morphologic and climatologic features: thick layered deposits, seasonal CO2 frost caps extending to mid latitudes, and near-polar residual frost deposits that survive the summer. The relationship of the seasonal and residual frost caps to the layered deposits has been poorly constrained, mainly by the limited spatial resolution of the available data. In particular, it has not been known if the residual caps represent simple thin frost cover or substantial geologic features. Here we show that the residual cap on the south pole is a distinct geologic unit with striking collapse and erosional topography; this is very different from the residual cap on the north pole, which grades into the underlying layered materials. These findings indicate that the differences between the caps are substantial (rather than reflecting short-lived differences in frost cover), and so support the idea of long-term asymmetry in the polar climates of Mars.

The effect of polar caps on obliquity

NASA Technical Reports Server (NTRS)

Lindner, B. L.

1993-01-01

Rubincam has shown that the Martian obliquity is dependent on the seasonal polar caps. In particular, Rubincam analytically derived this dependence and showed that the change in obliquity is directly proportional to the seasonal polar cap mass. Rubincam concludes that seasonal friction does not appear to have changed Mars' climate significantly. Using a computer model for the evolution of the Martian atmosphere, Haberle et al. have made a convincing case for the possibility of huge polar caps, about 10 times the mass of the current polar caps, that exist for a significant fraction of the planet's history. Since Rubincam showed that the effect of seasonal friction on obliquity is directly proportional to polar cap mass, a scenario with a ten-fold increase in polar cap mass over a significant fraction of the planet's history would result in a secular increase in Mars' obliquity of perhaps 10 degrees. Hence, the Rubincam conclusion of an insignificant contribution to Mars' climate by seasonal friction may be incorrect. Furthermore, if seasonal friction is an important consideration in the obliquity of Mars, this would significantly alter the predictions of past obliquity.

Tordo 1 polar cusp barium plasma injection experiment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wescott, E.M.; Stenbaek-Nielsen, H.C.; Davis, T.N.

1978-04-01

In January 1975, two barium plasma injection experiments were carried out with rockets launched from Cape Parry, Northwest Territories, Canada, into the upper atmosphere where field lines from the dayside cusp region intersect the ionosphere. One experiment, Tordo 1, took place near the beginning of a worldwide magnetic storm. It became a polar cap experiment almost immediately as convection perpendicular to B moved the fluorescent plasma jet away from the cusp across the polar cap in an antisunward direction. Convection across the polar cap with an average velocity of more than 1 km/s was observed for nearly 40 min untilmore » the barium flux tubes encountered large E fields associated with a poleward bulge of the auroral oval near Greenland. Prior to the encounter with the aurora near Greenland there is evidence of upward acceleration of the barium ions while they were in the polar cap. The three-dimensional observations of the plasma orientation and motion give an insight into convection from the cusp region across the polar cap, the orientation of the polar cap magnetic field lines out to several earth radii, the causes of polar cap magnetic perturbations, and parallel acceleration processes.« less

Broadband Circularly Polarized Patch Antenna and Method

DTIC Science & Technology

2016-09-16

300152 1 of 14 BROADBAND CIRCULARLY POLARIZED PATCH ANTENNA AND METHOD STATEMENT OF GOVERNMENT INTEREST [0001] The invention described herein may...present invention provides a method and apparatus for a broadband circularly polarized patch antenna . (2) Description of the Prior Art [0004] A...patch antenna , also referred to as a microstrip antenna , is a type of radio antenna with a low profile that can be mounted on a flat surface. The

Reconfigurable Wideband Circularly Polarized Stacked Square Patch Antenna for Cognitive Radios

NASA Technical Reports Server (NTRS)

Barbosa Kortright, Miguel A.; Waldstein, Seth W.; Simons, Rainee N.

2017-01-01

An almost square patch and a square patch with corner truncation for circularly polarized (CP) and a stacked CP square patch are researched and developed at X-band for cognitive devices. A draft set of presentation charts are attached.

Reducing Cross-Polarized Radiation From A Microstrip Antenna

NASA Technical Reports Server (NTRS)

Huang, John

1991-01-01

Change in configuration of feed of nominally linearly polarized microstrip-patch transmitting array antenna reduces cross-polarized component of its radiation. Patches fed on opposing sides, in opposite phases. Combination of spatial symmetry and temporal asymmetry causes copolarized components of radiation from fundamental modes of patches to reinforce each other and cross-polarized components of radiation from higher-order modes to cancel each other.

Narrow-band imaging can increase the visibility of fibrin caps after bleeding of esophageal varices: a case with extensive esophageal candidiasis.

PubMed

Furuichi, Yoshihiro; Kasai, Yoshitaka; Takeuchi, Hirohito; Yoshimasu, Yuu; Kawai, Takashi; Sugimoto, Katsutoshi; Kobayashi, Yoshiyuki; Nakamura, Ikuo; Itoi, Takao

2017-08-01

A 58-year-old man with hepatitis B cirrhosis noticed black stools and underwent an endoscopy at a community hospital. The presence of esophageal varices (EVs) was confirmed, but the bleeding point was not found. He was referred to our institution and underwent a second endoscopy. Extensive white patches of esophageal candidiasis were visible on endoscopy by white-light imaging (WLI), but it was difficult to find the fibrin cap of the EVs. This was easier under narrow-band imaging (NBI), however, as the color turned red from absorption by hemoglobin adhered to it. We retrospectively measured the color differences (CD) between the fibrin cap and the surrounding mucosa 10 times using the CIE (L*a*b*) color space method. The median value of CD increased after NBI (13.9 → 43.0, p < 0.001), with increased visibility. However, the median CD between the white patch and surrounding mucosa decreased after NBI (44.8 → 30.3, p < 0.001). The fibrin cap was paler than the white patch of candidiasis, but the increased visibility of the fibrin cap by NBI enabled it to be found more easily. This is the first report of a case in which NBI was helpful in locating a fibrin cap of EVs.

"Cottage Cheese" Texture on the Martian North Polar Cap in Summer

NASA Image and Video Library

2000-04-24

This image is illuminated by sunlight from the upper left. Martian Dairy Products? If parts of the south polar cap can look like swiss cheese (see "Martian "Swiss Cheese""), then parts of the north polar cap might as well look like some kind of cheese, too. This picture shows a cottage cheese-like texture on the surface of a part of the residual--summertime--north polar cap. The north polar cap surface is mostly covered by pits, cracks, small bumps and knobs. In this image, the cap surface appears bright and the floors of pits look dark. Based upon observations made by the Mariner 9 and Viking orbiters in the 1970s, the north polar residual cap is thought to contain mostly water ice because its summertime temperature is usually near the freezing point of water and water vapor was observed by the Vikings to be coming off the cap during summer. The south residual cap is different--its temperatures in summer remain cold enough to freeze carbon dioxide, and very little to no water vapor has been observed to come off the south cap in summer. The pits that have developed on the north polar cap surface are closely-spaced relative to the very different depressions in the south polar cap. The pits are estimated from the length of shadows cast in them to be less than about 2 meters (5.5 feet) deep. These pits probably develop slowly over thousands of years of successive spring and summer seasons. This picture was taken by the Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) during northern summer on April 5, 1999. The picture is located near 82.1°N, 329.6°W and covers an area 1.5 km wide by 3 km long (0.9 x 1.8 miles) at a resolution of 3 meters (10 ft) per pixel. http://photojournal.jpl.nasa.gov/catalog/PIA02369

Optimization of a Circularly Polarized Patch Antenna for Two Frequency Bands

DTIC Science & Technology

2015-09-01

the various techniques that can be used to improve the performance of a circularly polarized microstrip patch antenna . These adjustments include... microstrip antenna . 15. SUBJECT TERMS Patch Antenna , Circular Polarization 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF ABSTRACT...Frequency Structural Simulator (HFSS) has allowed engineers to create scalable multiband microstrip antennas . Several factors were taken into

South Polar Cap, Summer 2000

NASA Technical Reports Server (NTRS)

2000-01-01

This is the south polar cap of Mars as it appeared to the Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) on April 17, 2000. In winter and early spring, this entire scene would be covered by frost. In summer, the cap shrinks to its minimum size, as shown here. Even though it is summer, observations made by the Viking orbiters in the 1970s showed that the south polar cap remains cold enough that the polar frost (seen here as white) consists of carbon dioxide. Carbon dioxide freezes at temperatures around -125o C (-193o F). Mid-summer afternoon sunlight illuminates this scene from the upper left from about 11.2o above the horizon. Soon the cap will experience sunsets; by June 2000, this pole will be in autumn, and the area covered by frost will begin to grow. Winter will return to the south polar region in December 2000. The polar cap from left to right is about 420 km (260 mi) across.

Sunlight penetration through the Martian polar caps: Effects on the thermal and frost budgets

NASA Technical Reports Server (NTRS)

Lindner, Bernhard Lee

1992-01-01

An energy balance model of the seasonal polar caps on Mars is modified to include penetration of solar radiation into and through the ice. Penetration of solar radiation has no effect on subsurface temperature or total frost sublimation if seasonal ice overlies a dust surface. An effect is noted for seasonal ice which overlies the residual polar caps. For the case of an exposed water-ice residual polar cap, the temperature at depth is calculated to be up to several degrees warmer and the calculated lifetime of seasonal CO2 frost is slightly lower when penetration of sunlight is properly treated in the model. For the case of a residual polar cap which is perennially covered by CO2 frost, the calculated lifetime of seasonal CO2 frost is very slightly increased as a result of sunlight penetration through the ice. Hence, penetration of sunlight into the ice helps to stabilize the observed dichotomy in the residual polar caps on Mars, although it is a small effect.

Sunlight penetration through the Martian polar caps - Effects on the thermal and frost budgets

NASA Technical Reports Server (NTRS)

Lindner, Bernhard L.

1992-01-01

An energy balance model of the seasonal polar caps on Mars is modified to include penetration of solar radiation into and through the ice. Penetration of solar radiation has no effect on subsurface temperature or total frost sublimation if seasonal ice overlies a dust surface. An effect is noted for seasonal ice which overlies the residual polar caps. For the case of an exposed water-ice residual polar cap, the temperature at depth is calculated to be up to several degrees warmer, and the calculated lifetime of seasonal CO2 frost is slightly lower when penetration of sunlight is properly treated in the model. For the case of a residual polar cap which is perennially covered by CO2 frost, the calculated lifetime of seasonal CO2 frost is very slightly increased as a result of sunlight penetration through the ice. Hence, penetration of sunlight into the ice helps to stabilize the observed dichotomy in the residual polar caps on Mars, although it is a small effect.

Polar Rain Gradients and Field-Aligned Polar Cap Potentials

NASA Technical Reports Server (NTRS)

Fairfield, D. H.; Wing, S.; Newell, P. T.; Ruohoniemi, J. M.; Gosling, J. T.; Skoug, R. M.

2008-01-01

ACE SWEPAM measurements of solar wind field-aligned electrons have been compared with simultaneous measurements of polar rain electrons precipitating over the polar cap and detected by DMSP spacecraft. Such comparisons allow investigation of cross-polarcap gradients in the intensity of otherwise-steady polar rain. The generally good agreement of the distribution functions, f, from the two data sources confirms that direct entry of solar electrons along open field lines is indeed the cause of polar rain. The agreement between the data sets is typically best on the side of the polar cap with most intense polar rain but the DMSP f's in less intense regions can be brought into agreement with ACE measurements by shifting all energies by a fixed amounts that range from tens to several hundred eV. In most cases these shifts are positive which implies that field-aligned potentials of these amounts exist on polar cap field lines which tend to retard the entry of electrons and produce the observed gradients. These retarding potentials undoubtedly appear in order to prevent the entry of low-energy electrons and maintain charge quasi-neutrality that would otherwise be violated since most tailward flowing magnetosheath ions are unable to follow polar rain electrons down to the polar cap. In more limited regions near the boundary of the polar cap there is sometimes evidence for field-aligned potentials of the opposite sign that accelerate polar rain electrons. A solar electron burst is also studied and it is concluded that electrons from such bursts can enter the magnetotail and precipitate in the same manner as polar rain.

Electron polar cap and the boundary of open geomagnetic field lines.

NASA Technical Reports Server (NTRS)

Evans, L. C.; Stone, E. C.

1972-01-01

A total of 333 observations of the boundary of the polar access region for electrons (energies greater than 530 keV) provides a comprehensive map of the electron polar cap. The boundary of the electron polar cap, which should occur at the latitude separating open and closed field lines, is consistent with previously reported closed field line limits determined from trapped-particle data. The boundary, which is sharply defined, seems to occur at one of three discrete latitudes. Although the electron flux is generally uniform across the polar cap, a limited region of reduced access is observed about 10% of the time.

Polar Cap Plasma and Convection

NASA Technical Reports Server (NTRS)

Elliott, Heather A.; Craven, Paul D.; Comfort, Richard H.; Chandler, Michael O.; Moore, Thomas E.; Ruohoniemi, J. M.

1998-01-01

This presentation will describe the character of the polar cap plasma in 10% AGU Spring 1998 particular the convection velocities at the perigee (about 1.8 Re) and apogee( about 8.9 Re) of Polar in relationship to Interplanetary Magnetic Field (IMF) and solar wind parameters. This plasma is thought to be due to several sources; the polar wind, cleft ion fountain, and auroral outflow. The plasma in the polar cap tends to be mostly field-aligned. At any given point in the polar cap, this plasma could be from a different regions since convection of magnetic field lines can transport this material. it is quite difficult to study such a phenomena with single point measurements. Current knowledge of the polar cap plasma obtained by in situ measurements will be presented along with recent results from the Polar mission. This study also examines the direct electrical coupling between the magnetosphere and ionosphere by comparing convection velocities measured by the Thermal Ion Dynamics Experiment (TIDE) and Magnetic Field Experiment (MFE) instruments in magnetosphere and measurements of the ionosphere by ground-based radars. At times such a comparison is difficult because the Polar satellite at apogee spends a large amount of time in the polar cap which is a region that is not coverage well by the current SuperDam coherent radars. This is impart due to the lack of irregularities that returns the radar signal.

South Polar Layers

NASA Image and Video Library

2016-08-25

Southern hemisphere spring has arrived at the south polar cap. The ice layers that make up the cap are easily seen in this image from NASA 2001 Mars Odyssey spacecraft. Southern hemisphere spring has arrived at the south polar cap. The ice layers that make up the cap are easily seen in this VIS image. Orbit Number: 64531 Latitude: -86.6334 Longitude: 97.7916 Instrument: VIS Captured: 2016-07-01 06:55 http://photojournal.jpl.nasa.gov/catalog/PIA20972

DEAD ZONE IN THE POLAR-CAP ACCELERATOR OF PULSARS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Alexander Y.; Beloborodov, Andrei M.

We study plasma flows above pulsar polar caps using time-dependent simulations of plasma particles in the self-consistent electric field. The flow behavior is controlled by the dimensionless parameter {alpha} = j/c{rho}{sub GJ}, where j is the electric current density and {rho}{sub GJ} is the Goldreich-Julian charge density. The region of the polar cap where 0 < {alpha} < 1 is a {sup d}ead zone{sup -}in this zone, particle acceleration is inefficient and pair creation is not expected even for young, rapidly rotating pulsars. Pulsars with polar caps near the rotation axis are predicted to have a hollow-cone structure of radiomore » emission, as the dead zone occupies the central part of the polar cap. Our results apply to charge-separated flows of electrons (j < 0) or ions (j > 0). In the latter case, we consider the possibility of a mixed flow consisting of different ion species, and observe the development of two-stream instability. The dead zone at the polar cap is essential for the development of an outer gap near the null surface {rho}{sub GJ} = 0.« less

Towards Onboard Orbital Tracking of Seasonal Polar Volatiles on Mars

NASA Technical Reports Server (NTRS)

Wagstaff, Kiri L.; Castano, Rebecca; Chien, Steve; Ivanov, anton B.; Titus, Timothy N.

2005-01-01

Current conditions on Mars support both a residual polar cap, composed mainly of water ice, and a seasonal cap, composed of CO2, which appears and disappears each winter. Kieffer and Titus characterized the recession of the seasonal south polar cap using an arctangent curve fit based on data from the Thermal Emission Spectrometer on Mars Global Surveyor [1]. They also found significant interannual deviations, at the regional scale, in the recession rate [2]. Further observations will enable the refinement of our models of polar cap evolution in both hemispheres. We have developed the Bimodal Image Temperature (BIT) Histogram Analysis method for the automated detection and tracking of the seasonal polar ice caps on Mars. It is specifically tailored for possible use onboard a spacecraft. We have evaluated BIT on uncalibrated data collected by the Thermal Emission Imaging System (THEMIS) instrument [3] on the Mars Odyssey spacecraft. In this paper, we focus on the northern seasonal cap, but our approach is directly applicable to the future analysis of the southern seasonal ice cap as well.

In vivo evaluation of wearable head impact sensors

PubMed Central

Wu, Lyndia C.; Nangia, Vaibhav; Bui, Kevin; Hammoor, Bradley; Kurt, Mehmet; Hernandez, Fidel; Kuo, Calvin; Camarillo, David B.

2015-01-01

Inertial sensors are commonly used to measure human head motion.(R1–3) Some sensors have been tested with dummy or cadaver experiments with mixed results, and methods to evaluate sensors in vivo are lacking. Here we present an in vivo(R3–10) method using high speed video to test teeth-mounted (mouthguard), soft tissue-mounted (skin patch), and headgear-mounted (skull cap) sensors during 6–13g(R1–20) sagittal soccer head impacts. Sensor coupling to the skull (R1–3) was quantified by displacement from an ear-canal reference. Mouthguard displacements were within video measurement error (<1mm), while the skin patch and skull cap displaced up to 4mm and 13mm from the ear-canal reference, respectively. We used the mouthguard, which had the least displacement from skull (R1–5), as the reference to assess 6-degree-of-freedom skin patch and skull cap measurements. Linear and rotational acceleration magnitudes were over-predicted by both the skin patch (with 120% NRMS error for amag, 290% for αmag(R1–6)) and the skull cap (320% NRMS error for amag, 500% for αmag(R1–6)). Such over-predictions were largely due to out-of-plane motion. To model sensor error, we found that in-plane skin patch acceleration peaks in the anterior-posterior direction could be modeled by an underdamped viscoelastic system. In summary, the mouthguard showed tighter skull coupling than the other sensor mounting approaches(R1–7). Furthermore, the in vivo methods presented are valuable for investigating skull acceleration sensor technologies. PMID:26289941

North Polar Cap

NASA Technical Reports Server (NTRS)

2004-01-01

7 September 2004 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a 1.4 m/pixel (5 ft/pixel) view of a typical martian north polar ice cap texture. The surface is pitted and rough at the scale of several meters. The north polar residual cap of Mars consists mainly of water ice, while the south polar residual cap is mostly carbon dioxide. This picture is located near 85.2oN, 283.2oW. The image covers an area approximately 1 km wide by 1.4 km high (0.62 by 0.87 miles). Sunlight illuminates this scene from the lower left.

Inclined Pulsar Magnetospheres in General Relativity: Polar Caps for the Dipole, Quadrudipole, and Beyond

NASA Astrophysics Data System (ADS)

Gralla, Samuel E.; Lupsasca, Alexandru; Philippov, Alexander

2017-12-01

In the canonical model of a pulsar, rotational energy is transmitted through the surrounding plasma via two electrical circuits, each connecting to the star over a small region known as a “polar cap.” For a dipole-magnetized star, the polar caps coincide with the magnetic poles (hence the name), but in general, they can occur at any place and take any shape. In light of their crucial importance to most models of pulsar emission (from radio to X-ray to wind), we develop a general technique for determining polar cap properties. We consider a perfectly conducting star surrounded by a force-free magnetosphere and include the effects of general relativity. Using a combined numerical-analytical technique that leverages the rotation rate as a small parameter, we derive a general analytic formula for the polar cap shape and charge-current distribution as a function of the stellar mass, radius, rotation rate, moment of inertia, and magnetic field. We present results for dipole and quadrudipole fields (superposed dipole and quadrupole) inclined relative to the axis of rotation. The inclined dipole polar cap results are the first to include general relativity, and they confirm its essential role in the pulsar problem. The quadrudipole pulsar illustrates the phenomenon of thin annular polar caps. More generally, our method lays a foundation for detailed modeling of pulsar emission with realistic magnetic fields.

Effects of Atmospheric Dust on Residual South Polar Cap Stability

NASA Technical Reports Server (NTRS)

Bonrv, B. P.; Bjorkman, J. E.; Hansen, G. B.; James, P. B.; Wolff, M. J.

2005-01-01

The Martian polar caps have been studied from the time of Herschel. Neither polar cap normally disappears in summer. The Residual North Polar Cap (portion that remains through summer) is composed of a mixture of water ice and dust, and its interannual stability is due to its low sublimation rate at the summer temperatures in the North Polar Region. The Residual South Polar Cap (RSPC) is more enigmatic, surviving the relatively hot perihelic summer season despite being composed of much more volatile CO2. It is able to do so because of its unusually high albedo, which is larger than that of other bright regions in the seasonal cap (e.g. Mountains of Mitchel). The proximity of the albedo of the RSPC to the critical albedo for stability raises the question of whether the RSPC exists in every Martian year. The ground based record is somewhat ambivalent. Douglass and Lowell reported that RSPC suddenly vanished at Ls=297deg in 1894 and did not reappear until Ls=0deg [1], and Kuiper reported that it disappeared in 1956 [2]; but both observations were questioned by contemporaries, who tended to attribute them to obscuring dust. Barker [3] reported a large amount of water vapor over the south polar cap in 1969 that could be attributed to exposure of near surface water ice during partial removal of the CO2 in the RSPC in 1969.

The polar caps

NASA Astrophysics Data System (ADS)

Akasofu, S.-I.

1985-12-01

According to the most common definition, the 'polar cap' is the region bounded by the average or statistical auroral oval. Studies of the effects of the interplanetary magnetic field (IMF) on various upper atmospheric phenomena are reviewed. The Antarctic region and the Arctic region represent an area for such investigations. Particular attention is given in this paper to those observations in the highest latitude region which provide some information concerning corresponding changes of the internal structure of the magnetosphere. A definition and working definition of the polar cap are considered along with the IMF and magnetospheric models, the entry of solar energetic electrons, statistical studies regarding the aurora, individual events, polar cap arcs, the cusp aurora, auroral electron precipitation, convection, ionospheric currents and field-aligned currents, the ionosphere, the thermosphere, polar rain, polar wind, and hopping motions of heavy ions.

Actin filament bundling by fimbrin is important for endocytosis, cytokinesis, and polarization in fission yeast.

PubMed

Skau, Colleen T; Courson, David S; Bestul, Andrew J; Winkelman, Jonathan D; Rock, Ronald S; Sirotkin, Vladimir; Kovar, David R

2011-07-29

Through the coordinated action of diverse actin-binding proteins, cells simultaneously assemble actin filaments with distinct architectures and dynamics to drive different processes. Actin filament cross-linking proteins organize filaments into higher order networks, although the requirement of cross-linking activity in cells has largely been assumed rather than directly tested. Fission yeast Schizosaccharomyces pombe assembles actin into three discrete structures: endocytic actin patches, polarizing actin cables, and the cytokinetic contractile ring. The fission yeast filament cross-linker fimbrin Fim1 primarily localizes to Arp2/3 complex-nucleated branched filaments of the actin patch and by a lesser amount to bundles of linear antiparallel filaments in the contractile ring. It is unclear whether Fim1 associates with bundles of parallel filaments in actin cables. We previously discovered that a principal role of Fim1 is to control localization of tropomyosin Cdc8, thereby facilitating cofilin-mediated filament turnover. Therefore, we hypothesized that the bundling ability of Fim1 is dispensable for actin patches but is important for the contractile ring and possibly actin cables. By directly visualizing actin filament assembly using total internal reflection fluorescence microscopy, we determined that Fim1 bundles filaments in both parallel and antiparallel orientations and efficiently bundles Arp2/3 complex-branched filaments in the absence but not the presence of actin capping protein. Examination of cells exclusively expressing a truncated version of Fim1 that can bind but not bundle actin filaments revealed that bundling activity of Fim1 is in fact important for all three actin structures. Therefore, fimbrin Fim1 has diverse roles as both a filament "gatekeeper" and as a filament cross-linker.

Space weather effects on airline communications in the high latitude regions

NASA Astrophysics Data System (ADS)

Stocker, Alan; Siddle, Dave; Warrington, Mike; Honary, Farideh; Zaalov, Nikolay; Homam, Mariyam; Boteler, David; Danskin, Donald; de Franceschi, Georgiana; Ascaneus, Svend

2013-04-01

In the polar regions, ground-based VHF facilities for air-traffic control are lacking (and non-existent on the Russian side of the pole) and satellite communication systems either not available or expensive to retrofit to current aircraft and hence there remains a need for HF communication systems. Unfortunately, at these latitudes space weather can significantly affect the propagation of HF radio signals and the forecasting techniques currently employed by the airline industry are somewhat crude. In this paper, a new project that aims to provide forecasting of HF propagation characteristics for use by civilian airlines operating over polar routes will be described and preliminary results presented. Previous work in this area [e.g. Stocker et al., 2007] has focussed on taking HF signal measurements (e.g. SNR, delay and Doppler spread, and direction of arrival) on a limited number of propagation paths and developing an ionospheric model that incorporates high latitude features (e.g. polar patches and arcs) which, when combined with raytracing, allows the broad characteristics of the observations to be reproduced [Warrington et al., 2012]. The new project will greatly extend this work and consists of a number of stages. Firstly, HF measurements from an extensive network of purpose built transmitters and receivers spanning the Arctic regions will be collected and analysed. In order to test a wide variety of scenarios, the propagation paths will have different characteristics, e.g. different lengths and covering different parts of the northern ionosphere (i.e. polar cap paths where both terminals are in the polar cap, trans-auroral paths, and sub-auroral paths) and observations will be taken at a range of HF frequencies for a period covering the current (so far weak) solar maximum and part of the declining phase. Simultaneously, high latitude absorption measurements utilising the Global Riometer Array (GLORIA) will be collected and analysed. Next, the observations of the signal characteristics (i.e. both reflection and absorption properties) will be related to prevailing space weather parameters. Following on from this, an auroral absorption prediction model based on solar wind and interplanetary data will be developed together with the further refinement of the existing ionospheric model taking into account the new observations and adding auroral and polar cap absorption models. Algorithms for nowcasting and forecasting of radio propagation conditions for trans-polar aircraft will then be developed from the ionospheric model. In addition to the approach described above, the benefits of ground station diversity using both the experimental data and the models developed during the project will also be investigated. Stocker A.J., E.M. Warrington, and D.R. Siddle, Comparison between the measured and predicted parameters of HF radio signals propagating along the mid-latitude trough and within the polar cap, Radio Science, 42, RS3019, doi:10.1029/2006RS003557, 2007. Warrington EM, Zaalov NY, Stocker AJ, Naylor JS, HF propagation modelling within the polar ionosphere, Radio Science, 47, Article number RS0L13, doi:10.1029/2011RS004909, 2012.

Possible recent and ancient glacial ice flow in the south polar region of Mars

NASA Technical Reports Server (NTRS)

Kargel, J. S.

1992-01-01

Martian polar science began almost as soon as small telescopes were trained on the planet. The seasonal expansion and contraction of the polar caps and their high albedoes led most astronomers to think that water ice is the dominant constituent. In 1911 Lowell perceived a bluish band around the retreating edge of the polar caps, and interpreted it as water from melting polar ice and seasonal snow. An alternative idea in his time was that the polar caps consist of frozen carbonic acid. Lowell rejected the carbonic acid hypothesis on account of his blue band. He also pointed out that carbonic acid would sublimate rather than melt at confining pressures near and below one bar, hence, carbonic acid could not account for the blue band. In comparing Lowell's theories with today's knowledge, it is recognized that (1) sublimation is mainly responsible for the growth and contraction of Mars' polar caps, (2) carbon dioxide is a major component of the southern polar cap, and (3) Lowell's blue band was probably seasonal dust and/or clouds. Geomorphic evidence that glacial ice and glacial melt waters once flowed over broad areas of the southern polar region. Two aspects of the south polar region suggest possible glacial processes during two distinct eras in Mars' history.

Different morphologic formation patterns of dark patches in the black-spotted frog (Pelophylax nigromaculata) and the Asiatic toad (Bufo gargarizans).

PubMed

Guangming, Gan; Tao, Zhao; Chao, Li; Moyan, Zhao

2017-01-01

The black-spotted frog (Pelophylax nigromaculata) and Asiatic toad (Bufo gargarizans), two relatively distantly related species, live in different habitats with different adaptive dark patches. To explain the formation of dark patches, the distribution patterns of melanin granules were examined with light microscopy and transmission electron microscopy. Melanin granules were produced and gathered into the "cap" structures on top of the nuclei in most epidermal cells. The "cap" structures may play a role in forming the dorsal dark patches coupled with three-layer melanophores, which can give rise to three layers of interconnected melanin networks in the dorsal dermis in P. nigromaculata. Epidermal melanocytes are rare and do not have a definitive role in forming dorsal dark patches in either P. nigromaculata or B. gargarizans. In B. gargarizans, the dermal melanophores only give rise to a single-layered melanin network, which hardly results in dark patches in the dorsal skin. However, the dermal melanophores migrate twice and form into pseudostratified networks, leading to dark patch formation in the ventral skin in B. gargarizans. The melanin granules precisely coregulate dark patches in the dermis and/or epidermis in P. nigromaculata and B. gargarizans. The dark patch formation depends on melanin granules in the epidermis or/and dermis in P. nigromaculata and B. gargarizans.

Polar CAP Boundary Identification Using Redline Imaging Data

NASA Astrophysics Data System (ADS)

Spanswick, E.; Roy, E. A.; Gallardo-Lacourt, B.; Donovan, E.; Ridley, A. J.; Gou, D.

2017-12-01

The location of the polar cap boundary is typically detected using low-orbit satellite measurements in which the boundary is identified by its unique signature of a sharp decrease in energy and particle flux poleward of the auroral oval. A previous study based in optical data by Blanchard et al. [1995] suggested that a dramatic gradient in redline aurora may also be an indicator of the polar cap boundary. While this study has been heavily cited, it was only based on few events and its findings have largely gone uncontested. Since the Blanchard study, satellite instrumentation and available auroral data have improved significantly. Auroral imaging has moved well beyond the capabilities of the instrumentation in the previous study in terms of sensitivity and both spatial and temporal resolution. We now have access to decades of optical data from arrays spanning a huge spatial range; none of which was available previously. In this study we have used data from FAST and DMSP satellites in conjunction with the University of Calgary's Narrow-band All-sky Cameras for Auroral Monitoring (NASCAM) ground based auroral imaging array and the REdline Geospace Observatory (REGO) data to assess the viability of automated detection of the polar cap boundary. In our analysis we used redline (630nm) auroral signatures from the ground based imagers around the location of the polar cap boundary observed in satellite data. We have characterized the polar cap boundary luminosity and location using the redline auroral data during different geomagnetic conditions. Our results enable a new tool to automatically identify the polar cap boundary to reach a deeper understanding of the connection between polar cap location and auroral activity.

Comparison of polar cap potential drops estimated from solar wind and ground magnetometer data - CDAW 6

NASA Technical Reports Server (NTRS)

Reiff, P. H.; Spiro, R. W.; Wolf, R. A.; Kamide, Y.; King, J. H.

1985-01-01

It is pointed out that the maximum electrostatic potential difference across the polar cap, Phi, is a fundamental measure of the coupling between the solar wind and the earth's magnetosphere/ionosphere sytem. During the Coordinated Data Analysis Workshop (CDAW) 6 intervals, no suitably instrumented spacecraft was in an appropriate orbit to determine the polar-cap potential drop directly. However, two recently developed independent techniques make it possible to estimate the polar-cap potential drop for times when direct spacecraft data are not available. The present investigation is concerned with a comparison of cross-polar-cap potential drop estimates calculated for the two CDAW 6 intervals on the basis of these two techniques. In the case of one interval, the agreement between the potential drops and Joule heating rates is relatively good. In the second interval, however, the agreement is not very good. Explanations for this discrepancy are discussed.

Pair Cascades and Deathlines in Magnetic Fields with Offset Polar Caps

NASA Technical Reports Server (NTRS)

Harding, Alice K.; Muslimov, Alex G.

2012-01-01

We present results of electron-positron pair cascade simulations in a dipole magnetic field whose polar cap is offset from the dipole axis. In such a field geometry, the polar cap is displaced a small fraction of the neutron star radius from the star symmetry axis and the field line radius of curvature is modified. Using the modified parallel electric field near the offset polar cap, we simulate pair cascades to determine the pair deathlines and pair multiplicities as a function of the offset. We find that the pair multiplicity can change dr;unatically with a modest offset, with a significant increase on one side of the polar cap. Lower pair deathlines allow a larger fraction of the pulsar population, that include old and millisecond pulsars, to produce cascades with high multiplicity. The results have some important implications for pulsar particle production, high-energy emission and cosmic-ray contribution.

The Mars water cycle at other epochs - Recent history of the polar caps and layered terrain

NASA Technical Reports Server (NTRS)

Jakosky, Bruce M.; Henderson, Bradley G.; Mellon, Michael T.

1993-01-01

A numerical model is presented of the integrated role of seasonal water cycle on the evolution of polar deposits on Mars over the last 10 million years. From the model, it is concluded that the only major difference between the polar caps which affects their long-term behavior is ultimately the difference in their elevations. Because of that difference, there is a preference for CO2 frost to stay longer on the northern polar cap. The average difference in sublimation at the caps results in a net south-to-north transport of water ice over long time scales. Superimposed on any long-term behavior is a transfer of water ice between the caps on the 10 exp 5 - 10 exp 6 yr time scales. The amount of water exchanged is small compared to the total ice content of the polar deposits.

The Mars water cycle at other epochs - Recent history of the polar caps and layered terrain

NASA Astrophysics Data System (ADS)

Jakosky, B. M.; Henderson, B. G.; Mellon, M. T.

1993-04-01

A numerical model is presented of the integrated role of seasonal water cycle on the evolution of polar deposits on Mars over the last 10 million years. From the model, it is concluded that the only major difference between the polar caps which affects their long-term behavior is ultimately the difference in their elevations. Because of that difference, there is a preference for CO2 frost to stay longer on the northern polar cap. The average difference in sublimation at the caps results in a net south-to-north transport of water ice over long time scales. Superimposed on any long-term behavior is a transfer of water ice between the caps on the 10 exp 5 - 10 exp 6 yr time scales. The amount of water exchanged is small compared to the total ice content of the polar deposits.

Ionospheric convection driven by NBZ currents

NASA Technical Reports Server (NTRS)

Rasmussen, C. E.; Schunk, R. W.

1987-01-01

Computer simulations of Birkeland currents and electric fields in the polar ionosphere during periods of northward IMF were conducted. When the IMF z component is northward, an additional current system, called the NBZ current system, is present in the polar cap. These simulations show the effect of the addition of NBZ currents on ionospheric convection, particularly in the polar cap. When the total current in the NBZ system is roughly 25 to 50 percent of the net region 1 and 2 currents, convection in the central portion of the polar cap reverses direction and turns sunward. This creates a pattern of four-cell convection with two small cells located in the polar cap, rotating in an opposite direction from the larger cells. When the Birkeland currents are fixed (constant current source), the electric field is reduced in regions of relatively high conductivity, which affects the pattern of ionospheric convection. Day-night asymmetries in conductivity change convection in such a way that the two polar-cap cells are located within the large dusk cell. When ionospheric convection is fixed (constant voltage source), Birkeland currents are increased in regions of relatively high conductivity. Ionospheric currents, which flow horizontally to close the Birkeland currents, are changed appreciably by the NBZ current system. The principal effect is an increase in ionospheric current in the polar cap.

North Polar Scarp

NASA Image and Video Library

2016-05-09

This image from NASA 2001 Mars Odyssey spacecraft shows the scarp face of the north polar cap near Abalos Mensa. The top part of the image is the polar cap. This image was collected during northern hemisphere summer.

Design of metamirrors for linear to circular polarization conversion with super-octave bandwidth

NASA Astrophysics Data System (ADS)

Fartookzadeh, Mahdi

2017-10-01

In this paper, bandwidth improvement of reflection-mode linear to circular polarization converters (RMCPs) is studied. The proposed RMCP is based on multi-layer rectangular patches. Equivalent transmission line circuit of multi-layer reflection-mode polarization converters is used for designing the proposed metamirror. In addition, the approximate equation of axial ratio (AR) of the reflected wave is obtained from the structures containing rectangular patches on each layer. Polarization converters containing multi-layer rectangular patches can be utilized for different ranges of frequencies. However, the frequency range of 2-8 THz is considered in this paper without losing generality. The incident wave is assumed to be linearly polarized with 45° polarization angle. AR equation is used for initial optimization of the dimensions of rectangular patches to obtain the widest possible bandwidth of RMCPs with two- and three-layer patches. Secondary optimization is applied after specifying largest dimensions of the unit cell and excluding them from the variables of optimization. Finally, modified dimensions of the three-layer RMCP are obtained using parametrical study in simulations. The proposed three-layer polarization converter has the 3 dB axial ratio bandwidth of more than 116% and the permitted incident angle of higher than 25°.

Polar Cap Formation on Ganymede

NASA Technical Reports Server (NTRS)

Pilcher, C. B.; Shaya, E. J.

1985-01-01

Since thermal migration is not an effective mechanism for water transport in the polar regions at the Galilean satellites, some other process must be responsible for the formation of Ganymede's polar caps. It is proposed that Ganymede's polar caps are the optical manifestation of a process that began with the distribution of an ice sheet over the surface of Ganymede. The combined processes of impact gardening and thermal migration led, in regions at latitudes less than 40 to 45 deg., to the burial of some fraction of this ice, the migration of some to the polar caps margins, and a depletion of free ice in the optical surface. At higher latitudes, no process was effective in removing ice from the optical surface, so the remanants of the sheet are visible today.

The hemispherical asymmetry of the residual polar caps on Mars

NASA Technical Reports Server (NTRS)

Lindner, Bernhard Lee

1991-01-01

A model of the polar caps of Mars was created which allows: (1) for light penetration into the cap; (2) ice albedo to vary with age, latitude, hemisphere, dust content, and solar zenith angle; and (3) for diurnal variability. The model includes the radiative effects of clouds and dust, and heat transport as represented by a thermal wind. The model reproduces polar cap regression data very well, including the survival of CO2 frost at the south pole and reproduces the general trend in the Viking Lander pressure data.

Textures in south polar ice cap #1

NASA Technical Reports Server (NTRS)

1998-01-01

Textures of the south polar permanent residual ice cap and polar layered terrains. This 30 x 29 km area image (frame 7709) is centered near 87 degrees south, 77 degrees west.

Figure caption from Science Magazine

Textures in south polar ice cap #2

NASA Technical Reports Server (NTRS)

1998-01-01

Textures of the south polar permanent residual ice cap and polar layered terrains. This 15 x 14 km area image (frame 7306) is centered near 87 degrees south, 341 degrees west.

Figure caption from Science Magazine

Spring Slide

NASA Image and Video Library

2013-10-30

The North Polar region of Mars is capped with layers of water ice and dust, called the polar layered deposits. This permanent polar cap is covered in the winter with a layer of seasonal carbon dioxide ice as seen by NASA Mars Reconnaissance Orbiter.

Observations of the north polar region of Mars from the Mars orbiter laser altimeter.

PubMed

Zuber, M T; Smith, D E; Solomon, S C; Abshire, J B; Afzal, R S; Aharonson, O; Fishbaugh, K; Ford, P G; Frey, H V; Garvin, J B; Head, J W; Ivanov, A B; Johnson, C L; Muhleman, D O; Neumann, G A; Pettengill, G H; Phillips, R J; Sun, X; Zwally, H J; Banerdt, W B; Duxbury, T C

1998-12-11

Elevations from the Mars Orbiter Laser Altimeter (MOLA) have been used to construct a precise topographic map of the martian north polar region. The northern ice cap has a maximum elevation of 3 kilometers above its surroundings but lies within a 5-kilometer-deep hemispheric depression that is contiguous with the area into which most outflow channels emptied. Polar cap topography displays evidence of modification by ablation, flow, and wind and is consistent with a primarily H2O composition. Correlation of topography with images suggests that the cap was more spatially extensive in the past. The cap volume of 1.2 x 10(6) to 1.7 x 10(6) cubic kilometers is about half that of the Greenland ice cap. Clouds observed over the polar cap are likely composed of CO2 that condensed out of the atmosphere during northern hemisphere winter. Many clouds exhibit dynamical structure likely caused by the interaction of propagating wave fronts with surface topography.

Dynamics of the High-latitude Ionospheric Irregularities During the 2015 St. Patrick's Day Storm

NASA Astrophysics Data System (ADS)

Cherniak, I.; Zakharenkova, I.; Redmon, R. J.; Andrzej, K.

2015-12-01

We presents results on the study of the high-latitude ionospheric irregularities observed in worldwide GPS data during the St. Patrick's Day geomagnetic storm (March 17, 2015). Multi-site GPS observations from more than 2500 ground-based GPS stations were used to analyze the dynamics of the ionospheric irregularities in the Northern and Southern Hemispheres. The most intense ionospheric irregularities lasted for more than 24 hours starting at 07 UT of March 17. This period correlates well with an increase of the auroral Hemispheric Power index. We find hemispheric asymmetries in the intensity and spatial structure of the ionospheric irregularities. Over North America the ionospheric irregularities zone expanded equatorward below ~45°N geographic latitude. Additionally, the strong mid and high latitude GPS phase irregularities in the auroral oval were found to be related to the formation of storm enhanced density, polar tongues of ionization and deepening of the main ionospheric trough through upper atmosphere ionization by energetic particle precipitations. Significant increases in the intensity of the irregularities within the polar cap region of both hemispheres were associated with the formation and evolution of the SED/TOI structures and polar patches.

Polar cap arcs from the magnetosphere to the ionosphere: kinetic modelling and observations by Cluster and TIMED

NASA Astrophysics Data System (ADS)

Maggiolo, R.; Echim, M.; Wedlund, C. Simon; Zhang, Y.; Fontaine, D.; Lointier, G.; Trotignon, J.-G.

2012-02-01

On 1 April 2004 the GUVI imager onboard the TIMED spacecraft spots an isolated and elongated polar cap arc. About 20 min later, the Cluster satellites detect an isolated upflowing ion beam above the polar cap. Cluster observations show that the ions are accelerated upward by a quasi-stationary electric field. The field-aligned potential drop is estimated to about 700 V and the upflowing ions are accompanied by a tenuous population of isotropic protons with a temperature of about 500 eV. The magnetic footpoints of the ion outflows observed by Cluster are situated in the prolongation of the polar cap arc observed by TIMED GUVI. The upflowing ion beam and the polar cap arc may be different signatures of the same phenomenon, as suggested by a recent statistical study of polar cap ion beams using Cluster data. We use Cluster observations at high altitude as input to a quasi-stationary magnetosphere-ionosphere (MI) coupling model. Using a Knight-type current-voltage relationship and the current continuity at the topside ionosphere, the model computes the energy spectrum of precipitating electrons at the top of the ionosphere corresponding to the generator electric field observed by Cluster. The MI coupling model provides a field-aligned potential drop in agreement with Cluster observations of upflowing ions and a spatial scale of the polar cap arc consistent with the optical observations by TIMED. The computed energy spectrum of the precipitating electrons is used as input to the Trans4 ionospheric transport code. This 1-D model, based on Boltzmann's kinetic formalism, takes into account ionospheric processes such as photoionization and electron/proton precipitation, and computes the optical and UV emissions due to precipitating electrons. The emission rates provided by the Trans4 code are compared to the optical observations by TIMED. They are similar in size and intensity. Data and modelling results are consistent with the scenario of quasi-static acceleration of electrons that generate a polar cap arc as they precipitate in the ionosphere. The detailed observations of the acceleration region by Cluster and the large scale image of the polar cap arc provided by TIMED are two different features of the same phenomenon. Combined together, they bring new light on the configuration of the high-latitude magnetosphere during prolonged periods of Northward IMF. Possible implications of the modelling results for optical observations of polar cap arcs are also discussed.

Polar cap formation on Ganymede

NASA Technical Reports Server (NTRS)

Shaya, E. J.; Pilcher, C. B.

1984-01-01

It is argued that Ganymede's polar caps are the remnants of a more extensive covering of water ice that formed during a period in which the satellite was geologically active. It is inferred that the initial thickness of this covering was a significant fraction of the gardening depth since the covering formed. This suggests an initial thickness of at least a few meters over heavily cratered regions such as the south polar grooved terrain. The absence of similar polar caps on Callisto apparently reflects the absence of comparable geologic activity in the history of this satellite.

Interplanetary magnetic field dependency of stable Sun-aligned polar cap arcs

NASA Technical Reports Server (NTRS)

Valladares, C. E.; Carlson, H. C., Jr.; Fukui, K.

1994-01-01

This is the first analysis, using a statistically significant data set, of the morphological dependence of the presence, orientation, and motion of stable sun-aligned polar cap arcs upon the vector interplanetary magnetic field (IMF). For the one winter season analyzed we had 1392 all-sky 630.0-nm images of 2-min resolution containing a total of 150 polar cap arcs, all with corresponding values of the IMF as measured by International Monitoring Platform (IMP) 8 or International Sun Earth Explorer (ISEE) 2. After demonstrating an unbiased data set with smooth normal distributions of events versus the dimensions of time, space, and IMF component, we examine IMF dependencies of the properties of the optical arcs. A well-defined dependence for B(sub z) is found for the presence/absence of stable Sun-aligned polar cap arcs. Consistent with previous statistical studies, the probability of observing polar cap aurora steadily increases for larger positive values of B(sub z), and linearly decreases when B(sub z) becomes more negative. The probability of observing Sun-aligned arcs within the polar cap is determined to vary sharply as a function of the arc location; arcs were observed 40% of the time on the dawnside and only 10% on the duskside. This implies an overall probability of at least 40% for the whole polar cap. 20% of the arcs were observed during 'southward IMF conditions,' but in fact under closer inspection were found to have been formed under northward IMF conditions; these 'residual' positive B(sub z) arcs ha d a delayed residence time in the polar cap of about what would be expected after a north to south transition of B(sub z). A firm dependence on B(sub y) is also found for both the orientation and the dawn-dusk direction of motion of the arcs. All the arcs are Sun-aligned to a first approximation, but present deviations from this orientation, depending primarily upon the location of the arc in corrected geomagnetic (CG) coordinates. The arcs populating the 06-12 and the 12-18 quadrants of the CG coordinate system point toward the cusp. The B(sub y) dependency of the arc alignment is consistent with a cusp displacement in local time according to the sign of B(sub y). We found that the arc direction of motion depended both on B(sub y) and the arc location within the polar cap. For a given value of B(sub y) two well-defined regions (or cells) exist. Within each cell the arcs move in the same direction toward the boundary between the cells. The arcs located in the duskside move dawnward; those in the dawnside move duskward. The relative size of these dusk and dawn regions (or cells) are controlled by the magnitude of B(sub y). This persistent dusk-dawn motion fo the polar cap arcs is interpreted in terms of newly open flux tubes entering the polar cap and exerting a displacement of the convective cells and the polar cap arcs that are embedded within them.

Idealized model of polar cap currents, fields, and auroras

NASA Technical Reports Server (NTRS)

Cornwall, J. M.

1985-01-01

During periods of northward Bz, the electric field applied to the magnetosphere is generally opposite to that occurring during southward Bz and complicated patterns of convection result, showing some features reversed in comparison with the southward Bz case. A study is conducted of a simple generalization of early work on idealized convection models, which allows for coexistence of sunward convection over the central polar cap and antisunward convection elsewhere in the cap. The present model, valid for By approximately 0, has a four-cell convection pattern and is based on the combination of ionospheric current conservation with a relation between parallel auroral currents and parallel potential drops. Global magnetospheric issues involving, e.g., reconnection are not considered. The central result of this paper is an expression giving the parallel potential drop for polar cap auroras (with By approximately 0) in terms of the polar cap convection field profile.

South Polar Cap

NASA Technical Reports Server (NTRS)

2005-01-01

8 December 2005 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows landforms created by sublimation processes on the south polar residual cap of Mars. The bulk of the ice in the south polar residual cap is frozen carbon dioxide.

Location near: 86.6oS, 342.2oW Image width: width: 3 km (1.9 mi) Illumination from: upper left Season: Southern Summer

South Polar Scarps

NASA Technical Reports Server (NTRS)

2003-01-01

MGS MOC Release No. MOC2-438, 31 July 2003

The terrain of the south polar residual ice cap, made up mostly of frozen carbon dioxide, has come to be known by many as 'swiss cheese terrain,' because many areas of the cap resemble slices of swiss cheese. However, not all of the south polar cap looks like a tasty lunch food. This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a series of curving scarps formed by erosion and sublimation of carbon dioxide from the south polar cap. This area is located near 86.3oS, 51.2oW. The image is illuminated by sunlight from the upper left; the area is about 1.5 km (0.9 mi) wide.

South Polar Cryptic Region Revisited: THEMIS Observations

NASA Technical Reports Server (NTRS)

Titus, T. N.; Kieffer, H. H.; Plaut, J. J.; Christensen, P. R.; Ivanov, A. B.

2003-01-01

The early part of the Mars Global Surveyor mission provided good TES coverage of the Mars south polar region. These data allow mapping of the polar cap recession, surface and atmospheric temperatures, and albedo features found within the seasonal cap itself over Ls = 180 - 270 deg. During this period, the seasonal south polar cap retreated continuously and asymmetrically around the geographic pole, similar to the observations of Viking in 1976- 1977 [3]. A prominent albedo feature on the seasonal cap is a region that appears almost as dark as bare ground, yet remains cold. We refer to this region, generally located between latitudes 85 deg. S and 75 deg. S and longitudes 150 deg. W and 310 deg. W, as the Cryptic region.

Martian Polar Caps: Folding, Faulting, Flowing Glaciers of Multiple Interbedded Ices

NASA Astrophysics Data System (ADS)

Kargel, J. S.

2001-12-01

The Martian south polar cap (permanent CO2 cap and polar layered deposits), exhibit abundant, varied, and widespread deformational phenomena. Folding and boudinage are very common. Strike-slip or normal faults are rarer. Common in the vicinity of major troughs and scarps are signs of convergent flow tectonics manifested as wrinkle-ridge-like surface folds, thrust faults, and viscous forebulges with thin-skinned extensional crevasses and wrinkle-ridge folds. Such flow convergence is predicted by theory. Boudinage and folding at the 300-m wavelength scale, indicating rheologically contrasting materials, is widely exposed at deep levels along erosional scarps. Independent morphologic evidence indicates south polar materials of contrasting volatility. Hence, the south polar cap appears to be a multiphase structure of interbedded ices. The north polar cap locally also exhibits flow indicators, though they are neither as common nor as varied as in the south. The large-scale quasi-spiral structure of the polar caps could be a manifestation of large-scale boudinage. According to this scenario, deep-level boudinage continuously originates under the glacial divide (the polar cap summit). Rod-like boudin structures are oriented transverse to flow and migrate outward with the large-scale flow field. Troughs develop over areas between major boudins. A dynamic competition, and possibly a rough balance, develops between the local flow field in the vicinity of a trough (which tends to close the trough by lateral closure and upwelling flow) and sublimation erosion (which tends to widen and deepen them). Over time, the troughs flow to the margins of the polar cap where they, along with other polar structures, are destroyed by sublimation. Major ice types contributing to rheological and volatility layering may include, in order of highest to lowest mechanical strength, CO2 clathrate hydrate, water ice containing inert/insoluble dust, pure water ice, water ice containing traces of liquid-soluble salts, water ice containing traces of solid-soluble acids, CO2 ice. This is also nearly the same sequence of highest to lowest melting/dissociation points, but it is different than the sequence of volatility. This geologic-structural interpretation and specific chemical models are amenable to testing by computational means and point the way toward future needed observations, including complete high-resolution imaging of the polar caps, measurement of flow fields (possibly by laser interferometry), mapping of subsurface structures (by radar and/or seismic methods), and determination of composition (by penetrators, drillers, or borers). New lab data are needed on the physical properties of candidate ices.

Determination of Martian Northern Polar Insolation Levels Using a Geodetic Elevation Model

NASA Technical Reports Server (NTRS)

Arrell, J. R.; Zuber, M. T.

2000-01-01

Solar insolation levels at the Martian polar caps bear significantly on the seasonal and climatic cycling of volatiles on that planet. In the northern hemisphere, the Martian surface slopes downhill from the equator to the pole such that the north polar cap is situated in a 5-km-deep hemispheric-scale depression. This large-scale topographic setting plays an important role in the insolation of the northern polar cap. Elevations measured by the Mars Orbiter Laser Altimeter (MOLA) provide comprehensive, high-accuracy topographical information required to precisely determine polar insolation. In this study, we employ a geodetic elevation model to quantify the north polar insolation and consider implications for seasonal and climatic changes. Additional information is contained in original extended abstract.

Elimination of surface band bending on N-polar InN with thin GaN capping

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kuzmík, J., E-mail: Jan.Kuzmik@savba.sk; Haščík, Š.; Kučera, M.

2015-11-09

0.5–1 μm thick InN (0001) films grown by molecular-beam epitaxy with N- or In-polarity are investigated for the presence of native oxide, surface energy band bending, and effects introduced by 2 to 4 monolayers of GaN capping. Ex situ angle-resolved x-ray photo-electron spectroscopy is used to construct near-surface (GaN)/InN energy profiles, which is combined with deconvolution of In3d signal to trace the presence of InN native oxide for different types of polarity and capping. Downwards surface energy band bending was observed on bare samples with native oxide, regardless of the polarity. It was found that the In-polar InN surface is mostmore » readily oxidized, however, with only slightly less band bending if compared with the N-polar sample. On the other hand, InN surface oxidation was effectively mitigated by GaN capping. Still, as confirmed by ultra-violet photo-electron spectroscopy and by energy band diagram calculations, thin GaN cap layer may provide negative piezoelectric polarization charge at the GaN/InN hetero-interface of the N-polar sample, in addition to the passivation effect. These effects raised the band diagram up by about 0.65 eV, reaching a flat-band profile.« less

Polar cap contraction and expansion during a period of substorms

NASA Astrophysics Data System (ADS)

Aikio, Anita; Pitkänen, Timo; Honkonen, Ilja; Palmroth, Minna; Amm, Olaf

We have studied the variations in the polar cap area and related parameters during a period of four substorms on February 18, 2004, following an extended quiet period. The measurements were obtained by the EISCAT incoherent scatter radars, MIRACLE magnetometers, Geotail and solar wind satellites. In addition, the event is modeled by the GUMICS-4 MHD simulation. By using the measured and modeled data, the dayside and nightside reconnection voltages are calculated. The results show a good general agreement in the polar cap boundary (PCB) location as estimated by the EISCAT radars and the GUMICS simulation. Deviations are found, too, like shorter durations of expansion phases in the simulation. Geotail measurements of the inclination angle of the magnetic field in the tail (Xgsm= -22 Re) agree with the PCB latitude variations measured by EISCAT at a different MLT. We conclude that a large polar cap corresponds to a stretched tail configuration in the near-Earth tail and a small polar cap to a more dipolar configuration. The substorm onsets took place during southward IMF. A specific feature is that the substorm expansion phases were not associated with significant contractions of the polar cap. Even though nightside reconnection voltages started to increase during expansion phases, maximum closure of open flux took place in the recovery phases. We shortly discuss implications of the observation to the definition of the recovery phase.

Perennial water ice identified in the south polar cap of Mars

NASA Astrophysics Data System (ADS)

Bibring, Jean-Pierre; Langevin, Yves; Poulet, François; Gendrin, Aline; Gondet, Brigitte; Berthé, Michel; Soufflot, Alain; Drossart, Pierre; Combes, Michel; Bellucci, Giancarlo; Moroz, Vassili; Mangold, Nicolas; Schmitt, Bernard; OMEGA Team; Erard, S.; Forni, O.; Manaud, N.; Poulleau, G.; Encrenaz, T.; Fouchet, T.; Melchiorri, R.; Altieri, F.; Formisano, V.; Bonello, G.; Fonti, S.; Capaccioni, F.; Cerroni, P.; Coradini, A.; Kottsov, V.; Ignatiev, N.; Titov, D.; Zasova, L.; Pinet, P.; Sotin, C.; Hauber, E.; Hoffman, H.; Jaumann, R.; Keller, U.; Arvidson, R.; Mustard, J.; Duxbury, T.; Forget, F.

2004-04-01

The inventory of water and carbon dioxide reservoirs on Mars are important clues for understanding the geological, climatic and potentially exobiological evolution of the planet. From the early mapping observation of the permanent ice caps on the martian poles, the northern cap was believed to be mainly composed of water ice, whereas the southern cap was thought to be constituted of carbon dioxide ice. However, recent missions (NASA missions Mars Global Surveyor and Odyssey) have revealed surface structures, altimetry profiles, underlying buried hydrogen, and temperatures of the south polar regions that are thermodynamically consistent with a mixture of surface water ice and carbon dioxide. Here we present the first direct identification and mapping of both carbon dioxide and water ice in the martian high southern latitudes, at a resolution of 2km, during the local summer, when the extent of the polar ice is at its minimum. We observe that this south polar cap contains perennial water ice in extended areas: as a small admixture to carbon dioxide in the bright regions; associated with dust, without carbon dioxide, at the edges of this bright cap; and, unexpectedly, in large areas tens of kilometres away from the bright cap.

HiRISE Observations of the Polar Regions of Mars

NASA Astrophysics Data System (ADS)

Herkenhoff, K. E.; Byrne, S.; Fishbaugh, K.; Russell, P.; Fortezzo, C.; McEwen, A.

2008-12-01

Digital elevation models (DEMs) derived from MRO HiRISE stereo images allow meter-scale topographic measurements in the north polar layered deposits (NPLD) and distinction of slope vs. albedo effects on apparent brightness of individual layers. HiRISE images do not show thin layers at the limit of resolution. Rather, fine layering, if it exists, appears to have been obscured by a more dust-rich mantling deposit which shows signs of eolian erosion and slumping. Stratigraphic sequences within the NPLD appear to be repeated within exposures observed by HiRISE, indicative of a record of periodic climate changes. Granular flows sourced from within the dark, basal unit are suggestive of, but do not require, the presence of water during their formation. Active mass wasting of frost and dust has been observed on steep NPLD scarps in early spring, similar to dry, loose snow avalanches on terrestrial slopes. Bright and dark streaks are seen to evolve during the northern summer, evidence for active eolian redistribution of frost and perhaps dark (non- volatile) material. Relatively dark reddish patches observed within the north polar residual cap during the summer indicate that the cap is very thin (<1 m) or more transparent in places. HiRISE images of exposures of the south polar layered deposits (SPLD) show rectilinear fractures that are continuous across several layers and whose orientation is not affected by the topography of the exposure, suggesting that they were formed before erosion of the SPLD. They appear to extend laterally and vertically through the SPLD, like a joint set. While NPLD tectonism appears limited to isolated grabens, several faults have been observed by HiRISE in the SPLD, showing structural details including reverse fault splays that merge into bedding planes and possible evidence for thrust duplication. The faults may be the result of basal sliding (decollements) ramping into thrust faults near the margin of the SPLD.

Martian Polar Impact Craters: A Preliminary Assessment Using Mars Orbiter Laser Altimeter (MOLA)

NASA Technical Reports Server (NTRS)

Sakimoto, S. E. H.; Garvin, J. B.

1999-01-01

Our knowledge of the age of the layered polar deposits and their activity in the volatile cycling and climate history of Mars is based to a large extent on their apparent ages as determined from crater counts. Interpretation of the polar stratigraphy (in terms of climate change) is complicated by reported differences in the ages of the northern and southern layered deposits. The north polar residual ice deposits are thought to be relatively young, based on the reported lack of any fresh impact craters in Viking Orbiter Images. Herkenhoff et al., report no craters at all on the North polar layered deposits or ice cap, and placed an upper bound on the surface age (or, alternatively, the vertical resurfacing rate) of 100 thousand years to 10 million years, suggesting that the north polar region is an active resurfacing site. In contrast, the southern polar region was found to have at least 15 impact craters in the layered deposits and cap. Plaut et al, concluded that the surface was less than or = 120 million years old. This reported age difference factor of 100 to 1000 increases complexity in climate and volatile modeling. Recent MOLA results for the topography of the northern polar cap document a handful or more of possible craters, which could result in revised age or resurfacing estimates for the northern cap. This study is a preliminary look at putative craters in both polar caps. Additional information is contained in the original extended abstract.

IMF B(y) and day-night conductivity effects in the expanding polar cap convection model

NASA Technical Reports Server (NTRS)

Moses, J. J.; Gorney, D. J.; Siscoe, G. L.; Crooker, N. U.

1987-01-01

During southward B(z) periods the open field line region in the ionosphere (polar cap) expands due to increased dayside merging. Ionospheric plasma flow patterns result which can be classified by the sign of the interplanetary magnetic field (IMF) B(y) component. In this paper, a time-dependent ionospheric convection model is constructed to simulate these flows. The model consists of a spiral boundary with a gap in it. The sign of the IMF B(y) component determines the geometry of the gap. A potential is applied across the gap and distributed around the boundary. A flow results which enters the polar cap through the gap and uniformly pushes the boundary outward. Results of the model show that B(y) effects are greatest near the gap and virtually unnoticeable on the nightside of the polar cap. Adding a day-night ionospheric conductivity gradient concentrates the polar cap electric field toward dawn. The resulting flow curvature gives a sunward component that is independent of B(y). These patterns are shown to be consistent with published observations.

Novel On-wafer Radiation Pattern Measurement Technique for MEMS Actuator Based Reconfigurable Patch Antennas

NASA Technical Reports Server (NTRS)

Simons, Rainee N.

2002-01-01

The paper presents a novel on-wafer, antenna far field pattern measurement technique for microelectromechanical systems (MEMS) based reconfigurable patch antennas. The measurement technique significantly reduces the time and the cost associated with the characterization of printed antennas, fabricated on a semiconductor wafer or dielectric substrate. To measure the radiation patterns, the RF probe station is modified to accommodate an open-ended rectangular waveguide as the rotating linearly polarized sampling antenna. The open-ended waveguide is attached through a coaxial rotary joint to a Plexiglas(Trademark) arm and is driven along an arc by a stepper motor. Thus, the spinning open-ended waveguide can sample the relative field intensity of the patch as a function of the angle from bore sight. The experimental results include the measured linearly polarized and circularly polarized radiation patterns for MEMS-based frequency reconfigurable rectangular and polarization reconfigurable nearly square patch antennas, respectively.

SPATIAL DISTRIBUTION OF PAIR PRODUCTION OVER THE PULSAR POLAR CAP

DOE Office of Scientific and Technical Information (OSTI.GOV)

Belyaev, Mikhail A.; Parfrey, Kyle, E-mail: mbelyaev@berkeley.edu

2016-10-20

Using an analytic, axisymmetric approach that includes general relativity, coupled to a condition for pair production deduced from simulations, we derive general results about the spatial distribution of pair-producing field lines over the pulsar polar cap. In particular, we show that pair production on magnetic field lines operates over only a fraction of the polar cap for an aligned rotator for general magnetic field configurations, assuming the magnetic field varies spatially on a scale that is larger than the size of the polar cap. We compare our result to force-free simulations of a pulsar with a dipole surface field andmore » find excellent agreement. Our work has implications for first-principles simulations of pulsar magnetospheres and for explaining observations of pulsed radio and high-energy emission.« less

Cylindrical Antenna Using Near Zero Index Metamaterial

DTIC Science & Technology

2012-07-24

circularly polarized microstrip patch antenna (SFCP-MPA). Simultaneous enhancement on antenna gain, impedance bandwidth (ZBW) and axial-ratio...K. L. Chung, and P. Akkaraekthalin, "Simultaneous gain and bandwidths enhancement of a single-feed circularly polarized microstrip patch antenna ...device for enhancing the directivity and port isolation of a dual-frequency dual- polarization (DFDP) microstrip antenna by using metamaterial

Martian North Polar Water-Ice Clouds During the Viking Era

NASA Technical Reports Server (NTRS)

Tamppari, L. K.; Bass, D. S.

2000-01-01

The Viking Orbiters determined that the surface of Mars' northern residual cap consists of water ice. Observed atmospheric water vapor abundances in the equatorial regions have been related to seasonal exchange between reservoirs such as the polar caps, the regolith and between different phases in the atmosphere. Kahn modeled the physical characteristics of ice hazes seen in Viking Orbiter imaging limb data, hypothesizing that ice hazes provide a method for scavenging water vapor from the atmosphere and accumulating it into ice particles. Given that Jakosky found that these particles had sizes such that fallout times were of order one Martian sol, these water-ice hazes provided a method for returning more water to the regolith than that provided by adsorption alone. These hazes could also explain the rapid hemispheric decrease in atmospheric water in late northern summer as well as the increase during the following early spring. A similar comparison of water vapor abundance versus polar cap brightness has been done for the north polar region. They have shown that water vapor decreases steadily between L(sub s) = 100-150 deg while polar cap albedo increases during the same time frame. As a result, they suggested that late summer water-ice deposition onto the ice cap may be the cause of the cap brightening. This deposition could be due to adsorption directly onto the cap surface or to snowfall. Thus, an examination of north polar waterice clouds could lend insight into the fate of the water vapor during this time period. Additional information is contained in the original extended abstract.

Gamma-Ray Pulsar Light Curves in Offset Polar Cap Geometry

NASA Technical Reports Server (NTRS)

Harding, Alice K.; DeCesar, Megan; Miller, M. Coleman

2011-01-01

Recent studies have shown that gamma-ray pulsar light curves are very sensitive to the geometry of the pulsar magnetic field. Pulsar magnetic field geometries, such as the retarded vacuum dipole and force-free magnetospheres, used to model high-energy light curves have distorted polar caps that are offset from the magnetic axis in the direction opposite to rotation. Since this effect is due to the sweepback of field lines near the light cylinder, offset polar caps are a generic property of pulsar magnetospheres and their effects should be included in gamma-ray pulsar light curve modeling. In slot gap models (having two-pole caustic geometry), the offset polar caps cause a strong azimuthal asymmetry of the particle acceleration around the magnetic axis. We have studied the effect of the offset polar caps in both retarded vacuum dipole and force-free geometry on the model high-energy pulse profile. We find that. corn pared to the profile:-; derived from :-;ymmetric caps, the flux in the pulse peaks, which are caustics formed along the trailing magnetic field lines. increases significantly relative to the off-peak emission. formed along leading field lines. The enhanced contrast produces greatly improved slot gap model fits to Fermi pulsar light curves like Vela, which show very little off-peak emIssIon.

Effects of cations on hormone transport in primary roots of Zea mays

NASA Technical Reports Server (NTRS)

Hasenstein, K. H.; Evans, M. L.

1988-01-01

We examined the influence of aluminum and calcium (and certain other cations) on hormone transport in corn roots. When aluminum was applied unilaterally to the caps of 15 mm apical root sections the roots curved strongly away from the aluminum. When aluminum was applied unilaterally to the cap and 3H-indole-3-acetic acid was applied to the basal cut surface twice as much radioactivity (assumed to be IAA) accumulated on the concave side of the curved root as on the convex side. Auxin transport in the apical region of intact roots was preferentially basipetal, with a polarity (basipetal transport divided by acropetal transport) of 6.3. In decapped 5 mm apical root segments, auxin transport was acropetally polar (polarity = 0.63). Application of aluminum to the root cap strongly promoted acropetal transport of auxin reducing polarity from 6.3 to 2.1. Application of calcium to the root cap enhanced basipetal movement of auxin, increasing polarity from 6.3 to 7.6. Application of the calcium chelator, ethylene-glycol-bis-(beta-aminoethylether)-N,N,N',N'-tetraacetic acid, greatly decreased basipetal auxin movement, reducing polarity from 6.3 to 3.7. Transport of label after application of tritiated abscisic acid showed no polarity and was not affected by calcium or aluminum. The results indicate that the root cap is particularly important in maintaining basipetal polarity of auxin transport in primary roots of corn. The induction of root curvature by unilateral application of aluminum or calcium to root caps is likely to result from localized effects of these ions on auxin transport. The findings are discussed relative to the possible role of calcium redistribution in the gravitropic curvature of roots and the possibility of calmodulin involvement in the action of calcium and aluminum on auxin transport.

Directly Driven Ion Outflow

NASA Technical Reports Server (NTRS)

Elliott, H. A.; Comfort, R. H.; Craven, P. D.; Moore, T. E.; Russell, C. T.; Rose, M. Franklin (Technical Monitor)

2001-01-01

We examine ionospheric outflows in the high altitude magnetospheric polar cap during the POLAR satellite's apogee on April 19, 1996 using the Thermal Ion Dynamics Experiment (TIDE) instrument. The elevated levels of O(+) observed in this pass may be due to the geophysical conditions during and prior to the apogee pass. In addition to the high abundance of O(+) relative to H(+), several other aspects of this data are noteworthy. We observe relationships between the density, velocity, and temperature which appear to be associated with perpendicular heating and the mirror force, rather than adiabatic expansion. The H(+) outflow is at a fairly constant flux which is consistent with being source limited by charge exchange at lower altitudes. Local centrifugal acceleration in the polar cap is found to be insufficient to account for the main variations we observe in the outflow velocity. The solar wind speed is high during this pass approximately 700 kilometers per second, and there are Alfve'n waves present in the solar wind such that the solar wind speed and IMF Bx are correlated. In this pass both the H(+) and O(+) outflow velocities correlate with both the solar wind speed and IMF fluctuations. Polar cap magnetometer and Hydra electron data show the same long period wave structure as found in the solar wind and polar cap ion outflow. In addition, the polar cap Poynting flux along the magnetic field direction correlates well with the H(+) temperature (R=0.84). We conclude that the solar wind can drive polar cap ion outflow particularly during polar squalls by setting up a parallel drop that is tens of eV which then causes the ion outflow velocity of O(+) and H(+), the electrons, and magnetic perturbations to vary in a similar fashion.

A multi-point perspective on the formation of polar cap arcs: kinetic modeling and observations by Cluster and TIMED

NASA Astrophysics Data System (ADS)

de Keyser, J. M.; Maggiolo, R.; Echim, M.; Simon, C.; Zhang, Y.; Trotignon, J.

2010-12-01

On April 1st, 2004 the GUVI imager onboard the TIMED spacecraft spots an isolated and elongated polar cap arc. Simultaneously, the Cluster spacecraft detects an isolated upflowing ion beam above the polar cap. Cluster observations show that the ions are accelerated upward by a quasi-stationary electric field. The field-aligned potential drop is estimated to about 600 V and the upflowing ions are accompanied by a tenuous population of isotropic protons with a temperature of about 300eV. The footprint of the magnetic field line on which the Cluster spacecraft are situated, is located just outside the GUVI field of view in the prolongation of the polar cap arc. This suggests that the upflowing ion beam and the polar cap arc may be different signatures of the same phenomenon, as suggested by a recent statistical study of polar cap ion beams using Cluster data. We use Cluster observations at high altitude as input to a quasi-stationary magnetosphere-ionosphere (MI) coupling model. Using a Knight-type current-voltage relationship and the current continuity at the topside ionosphere, the model computes the energy spectrum of precipitating electrons at ionospheric altitudes corresponding to the generator electric field observed by Cluster. The MI coupling model provides a field-aligned potential drop in agreement with Cluster observations of upflowing ions and a spatial scale of the polar cap arc consistent with the optical observations by TIMED. The energy spectrum of the precipitating electrons provided by the model is introduced as input to the Trans4 ionospheric transport code. This 1-D model, based on Boltzmann's kinetic formalism, takes into account ionospheric processes like photoionisation and electron/proton precipitation, and computes the optical and UV emissions due to precipitating electrons. The emission rates provided by the Trans4 code are then compared to the optical observations by TIMED. Data and modeling results are consistent with quasi-static acceleration of precipitating magnetospheric electrons. We also discuss possible implications of our modeling results for optical observations of polar cap arcs.

Ir Spectral Mapping of the Martian South Polar Residual CAP Using Crism

NASA Astrophysics Data System (ADS)

Campbell, Jacqueline; Sidiropoulos, Panagiotis; Muller, Jan-Peter

2016-06-01

Polycyclic aromatic hydrocarbons (PAHs) are considered to be important in theories of abiogenesis (Allamandola, 2011) . There is evidence that PAHs have been detected on two icy Saturnian satellites using the Visual and Infrared Mapping Spectrometer (VIMS) on the Cassini spacecraft (Cruikshank et al., 2007). The hypothesised presence of PAHs in Mars south polar cap has not been systematically examined even though the Mars south polar cap may allow the preservation of organic molecules that are typically destroyed at the Martian surface by UV radiation (Dartnell et al. 2012). This hypothesis is supported by recent analyses of South Polar Residual Cap (SPRC) structural evolution (Thomas et al., 2009) that suggest the possibility that seasonal and long term sublimation may excavate dust particles from within the polar ice. Periodic sublimation is believed to be responsible for the formation of so-called "Swiss Cheese Terrain", a unique surface feature found only in the Martian south polar residual cap consisting of flat floored, circular depressions (Byrne, 2009). We show the first examples of work towards the detection of PAHs in Swiss Cheese Terrain, using data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM), on board NASA's Mars Reconnaissance Orbiter (MRO). CRISM is designed to search for mineralogical indications of past and present water, thus providing extensive coverage of the south polar cap. In this work, we discuss whether CRISM infrared spectra can be used to detect PAHs in Swiss Cheese Terrain and demonstrate a number of maps showing shifts in spectral profiles over the SPRC.

The Mars water cycle at other epochs: History of the polar caps and layered terrain

NASA Technical Reports Server (NTRS)

Jakosky, Bruce M.; Henderson, Bradley G.; Mellon, Michael T.

1992-01-01

The atmospheric water cycle at the present epoch involves summertime sublimation of water from the north polar cap, transport of water through the atmosphere, and condensation on one or both winter CO2 caps. Exchange with the regolith is important seasonally, but the water content of the atmosphere appears to be controlled by the polar caps. The net annual transport through the atmosphere, integrated over long timescales, must be the driving force behind the long-term evolution of the polar caps; clearly, this feeds back into the evolution of the layered terrain. We have investigated the behavior of the seasonal water cycle and the net integrated behavior at the pole for the last 10 exp 7 years. Our model of the water cycle includes the solar input, CO2 condensation and sublimation, and summertime water sublimation through the seasonal cycles, and incorporates the long-term variations in the orbital elements describing the Martian orbit.

Mars South Polar Cap "Fingerprint" Terrain

NASA Image and Video Library

2000-04-24

This picture is illuminated by sunlight from the upper left. Some portions of the martian south polar residual cap have long, somewhat curved troughs instead of circular pits. These appear to form in a layer of material that may be different than that in which "swiss cheese" circles and pits form, and none of these features has any analog in the north polar cap or elsewhere on Mars. This picture shows the "fingerprint" terrain as a series of long, narrow depressions considered to have formed by collapse and widening by sublimation of ice. Unlike the north polar cap, the south polar region stays cold enough in summer to retain frozen carbon dioxide. Viking Orbiter observations during the late 1970s showed that very little water vapor comes off the south polar cap during summer, indicating that any frozen water that might be there remains solid throughout the year. This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image was obtained in early southern spring on August 4, 1999. It shows an area 3 x 5 kilometers (1.9 x 3.1 miles) at a resolution of about 7.3 meters (24 ft) per pixel. Located near 86.0°S, 53.9°W. http://photojournal.jpl.nasa.gov/catalog/PIA02373

Reconciling different observations of the CO2 ice mass loading of the Martian north polar cap

USGS Publications Warehouse

Haberle, R.M.; Mattingly, B.; Titus, T.N.

2004-01-01

The GRS measurements of the peak mass loading of the north polar CO2 ice cap on Mars are about 60% lower than those calculated from MGS TES radiation data and those inferred from the MOLA cap thicknesses. However, the GRS data provide the most accurate measurement of the mass loading. We show that the TES and MOLA data can be reconciled with the GRS data if (1) subsurface heat conduction and atmospheric heat transport are included in the TES mass budget calculations, and (2) the density of the polar deposits is ???600 kg m-3. The latter is much less than that expected for slab ice (???1600 kg m-3) and suggests that processes unique to the north polar region are responsible for the low cap density. Copyright 2004 by the American Geophysical Union.

Reduction of the field-aligned potential drop in the polar cap during large geomagnetic storms

NASA Astrophysics Data System (ADS)

Kitamura, N.; Seki, K.; Nishimura, Y.; Hori, T.; Terada, N.; Ono, T.; Strangeway, R. J.

2013-12-01

We have studied photoelectron flows and the inferred field-aligned potential drop in the polar cap during 5 large geomagnetic storms that occurred in the periods when the photoelectron observations in the polar cap were available near the apogee of the FAST satellite (~4000 km) at solar maximum, and the footprint of the satellite paths in the polar cap was under sunlit conditions most of the time. In contrast to the ~20 V potential drop during geomagnetically quiet periods at solar maximum identified by Kitamura et al. [JGR, 2012], the field-aligned potential drop frequently became smaller than ~5 V during the main and early recovery phases of the large geomagnetic storms. Because the potential acts to inhibit photoelectron escape, this result indicates that the corresponding acceleration of ions by the field-aligned potential drop in the polar cap and the lobe region is smaller during the main and early recovery phases of large geomagnetic storms compared to during geomagnetically quiet periods. Under small field-aligned current conditions, the number flux of outflowing ions should be nearly equal to the net escaping electron number flux. Since ions with large flux originating from the cusp/cleft ionosphere convect into the polar cap during geomagnetic storms [e.g., Kitamura et al., JGR, 2010], the net escaping electron number flux should increase to balance the enhanced ion outflows. The magnitude of the field-aligned potential drop would be reduced to let a larger fraction of photoelectrons escape.

Driving of Dramatic Geomagnetic Activity by Enhancement of Meso-Scale Polar-cap Flows

NASA Astrophysics Data System (ADS)

Lyons, L. R.; Gallardo-Lacourt, B.; Zou, Y.; Nishimura, Y.; Anderson, P. C.; Angelopoulos, V.; Ruohoniemi, J. M.; Mitchell, E. J.; Paxton, L. J.; Nishitani, N.

2017-12-01

Recent studies have shown that mesoscale flows are common within the polar cap ionosphere. They often cross the magnetic separatrix, and become are critical to the driving of geomagnetic activity. They lead, for example, to plasma sheet flow bursts, auroral poleward boundary intensifications, auroral streamers, substorms, auroral omega bands, and poleward motion of the polar cap boundary from reconnection. We have found large enhancements of these meso-scale ionospheric polar cap flows heading towards the nightside separatrix. These enhancements are common immediately after the impact of CME shocks under southward IMF, but can also occur in other situations, including without substantial change in the solar wind or IMF. These meso-scale flow enhancements, which must extent outward along magnetospheric field lines from the ionosphere, are seen to drive an almost immediate strong auroral, ionospheric and field-aligned current, and reconnection activity. The resulting activity is particularly dramatic during the initiation of CME storms, but may reflect a more generally occurring phenomenon of mesoscale flow enhancements leading to similar oval responses without a shock impact, including during and following the expansion phase some substorms. If this phenomenon is indeed common, it could lead to possibly fundamental questions, such as when do polar cap convection enhancements lead to a substorm growth phase versus leading directly to strong poleward expansion of, and strong activity within, the auroral oval field line region? Another critical question would be what leads to and causes the enhancements in meso-scale polar cap flows?

Rethinking the polar cap: Eccentric dipole structuring of ULF power at the highest corrected geomagnetic latitudes

NASA Astrophysics Data System (ADS)

Urban, Kevin D.; Gerrard, Andrew J.; Lanzerotti, Louis J.; Weatherwax, Allan T.

2016-09-01

The day-to-day evolution and statistical features of Pc3-Pc7 band ultralow frequency (ULF) power throughout the southern polar cap suggest that the corrected geomagnetic (CGM) coordinates do not adequately organize the observed hydromagnetic spatial structure. It is shown that that the local-time distribution of ULF power at sites along CGM latitudinal parallels exhibit fundamental differences and that the CGM latitude of a site in general is not indicative of the site's projection into the magnetosphere. Thus, ULF characteristics observed at a single site in the polar cap cannot be freely generalized to other sites of similar CGM latitude but separated in magnetic local time, and the inadequacy of CGM coordinates in the polar cap has implications for conjugacy/mapping studies in general. In seeking alternative, observationally motivated systems of "polar cap latitudes," it is found that eccentric dipole (ED) coordinates have several strengths in organizing the hydromagnetic spatial structure in the polar cap region. ED latitudes appear to better classify the local-time ULF power in both magnitude and morphology and better differentiate the "deep polar cap" (where the ULF power is largely UT dependent and nearly free of local-time structure) from the "peripheral polar cap" (where near-magnetic noon pulsations dominate at lower and lower frequencies as one increases in ED latitude). Eccentric local time is shown to better align the local-time profiles in the magnetic east component over several PcX bands but worsen in the magnetic north component. It is suggested that a hybrid ED-CGM coordinate system might capture the strengths of both CGM and ED coordinates. It is shown that the local-time morphology of median ULF power at high-latitude sites is dominantly driven by where they project into the magnetosphere, which is best quantified by their proximity to the low-altitude cusp on the dayside (which is not necessarily quantified by a site's CGM latitude), and that variations in the local-time morphology at sites similar in ED latitude are due to both geographic local-time control (relative amplification or dampening by the diurnal variation in the local ionospheric conductivity) and geomagnetic coastal effects (enhanced power in a coastally mediated direction). Regardless of cause, it is emphasized that the application of CGM latitudes in the polar cap region is not entirely meaningful and likely should be dispensed with in favor of a scheme that is in better accord with the observed hydromagnetic spatial structure.

Intense uniform precipitation of low-energy electrons over the polar cap

DOE Office of Scientific and Technical Information (OSTI.GOV)

Meng, C.; Kroehl, H.W.

1977-06-01

Analysis of precipitating electron data from the Defense Meteorological Satellite Program (DMSP) revealed significant enhancements (as large as two orders of magnitude) over the quiet time level of the low-energy electron flux over the polar cap during magnetic storms in September and October 1974. Strong asymmetry between the two polar caps was observed, and it may indicate that these electrons are of interplanetary (i.e., solar) origin and that their entry is influenced by the interplanetary magnetic field as illustrated by Yeager and Frank (1976) and Fennell et al., (1975). Energy spectra showing the spatial and temporal variations of the phenomenamore » are presented. There also is a region between the equatorward edge of the polar cap enhancement and the poleward edge of the evening auroral precipitation in which the electron flux drops down to the background level. If the observed intense polar cap precipitation is indeed of interplanetary origin, this void region implies that the poleward boundary of the auroral precipitation does not coincide with the equatorward boundary of the open field lines and that their separation cna be as wide as a few degrees in latitude.« less

Mars residual north polar cap - Earth-based spectroscopic confirmation of water ice as a major constituent and evidence for hydrated minerals

NASA Technical Reports Server (NTRS)

Clark, R. N.; Mccord, T. B.

1982-01-01

A description is presented of new earth-based reflectance spectra of the Martian north residual polar cap. The spectra indicate that the composition is at least mostly water ice plus another component with a 'gray' reflectance. The other minerals in the ice cap appear to be hydrated. The data were obtained with a cooled circular variable filter spectrometer on February 20, 1978, using the 2.2-m telescope on Mauna Kea, Hawaii. It is pointed out that the identification of water ice in the north polar cap alone does not indicate that water makes up all or even most of the bulk of the cap. Kieffer (1970) has shown that a small amount of water will mask the spectral features of CO2.

Upper Thermosphere Winds and Temperatures in the Geomagnetic Polar Cap: Solar Cycle, Geomagnetic Activity, and Interplanetary Magnetic Field Dependencies

NASA Technical Reports Server (NTRS)

Killeen, T. L.; Won, Y.-I.; Niciejewski, R. J.; Burns, A. G.

1995-01-01

Ground-based Fabry-Perot interferometers located at Thule, Greenland (76.5 deg. N, 69.0 deg. W, lambda = 86 deg.) and at Sondre Stromfjord, Greenland (67.0 deg. N, 50.9 deg. W, lambda = 74 deg.) have monitored the upper thermospheric (approx. 240-km altitude) neutral wind and temperature over the northern hemisphere geomagnetic polar cap since 1983 and 1985, respectively. The thermospheric observations are obtained by determining the Doppler characteristics of the (OI) 15,867-K (630.0-nm) emission of atomic oxygen. The instruments operate on a routine, automatic, (mostly) untended basis during the winter observing seasons, with data coverage limited only by cloud cover and (occasional) instrument failures. This unique database of geomagnetic polar cap measurements now extends over the complete range of solar activity. We present an analysis of the measurements made between 1985 (near solar minimum) and 1991 (near solar maximum), as part of a long-term study of geomagnetic polar cap thermospheric climatology. The measurements from a total of 902 nights of observations are compared with the predictions of two semiempirical models: the Vector Spherical Harmonic (VSH) model of Killeen et al. (1987) and the Horizontal Wind Model (HWM) of Hedin et al. (1991). The results are also analyzed using calculations of thermospheric momentum forcing terms from the Thermosphere-ionosphere General Circulation Model TGCM) of the National Center for Atmospheric Research (NCAR). The experimental results show that upper thermospheric winds in the geomagnetic polar cap have a fundamental diurnal character, with typical wind speeds of about 200 m/s at solar minimum, rising to up to about 800 m/s at solar maximum, depending on geomagnetic activity level. These winds generally blow in the antisunward direction, but are interrupted by episodes of modified wind velocity and altered direction often associated with changes in the orientation of the Interplanetary Magnetic Field (IMF). The central polar cap (greater than approx. 80 magnetic latitude) antisunward wind speed is found to be a strong function of both solar and geomagnetic activity. The polar cap temperatures show variations in both solar and geomagnetic activity, with temperatures near 800 K for low K(sub p) and F(sub 10.7) and greater than about 2000 K for high K(sub p) and F(sub 10.7). The observed temperatures are significantly greater than those predicted by the mass spectrometer/incoherent scatter model for high activity conditions. Theoretical analysis based on the NCAR TIGCM indicates that the antisunward upper thermospheric winds, driven by upstream ion drag, basically 'coast' across the polar cap. The relatively small changes in wind velocity and direction within the polar cap are induced by a combination of forcing terms of commensurate magnitude, including the nonlinear advection term, the Coriolis term, and the pressure gradient force term. The polar cap thennospheric thermal balance is dominated by horizontal advection, and adiabatic and thermal conduction terms.

A Ka-Band (26 GHz) Circularly Polarized 2x2 Microstrip Patch Sub-Array with Compact Feed

NASA Technical Reports Server (NTRS)

Chrysler, Andrew; Furse, Cynthia; Simons, Rainee N.; Miranda, Felix A.

2017-01-01

A Ka-band (26 GHz) 2x2 array consisting of square-shaped microstrip patch antenna elements with two truncated corners for circular polarization (CP) is presented. The array is being developed for satellite communications.

Is CO2 ice permanent?

NASA Technical Reports Server (NTRS)

Lindner, Bernhard Lee

1992-01-01

Carbon dioxide ice has been inferred to exist at the south pole in summertime, but Earth based measurements in 1969 of water vapor in the Martian atmosphere suggest that all CO2 ice sublined from the southern polar cap and exposed underlying water ice. This implies that the observed summertime CO2 ice is of recent origin. It appears possible to construct an energy balance model that maintains seasonal CO2 ice at the south pole year round and still reasonably simulates the polar cap regression and atmospheric pressure data. This implies that the CO2 ice observed in the summertime south polar cap could be seasonal in origin, and that minor changes in climate could cause CO2 ice to completely vanish, as would appear to have happened in 1969. However, further research remains before it is certain whether the CO2 ice observed in the summertime south polar cap is seasonal or is part of a permanent reservoir.

North Polar Cap

NASA Technical Reports Server (NTRS)

2004-01-01

[figure removed for brevity, see original site]

This week we will be looking at five examples of laminar wind flow on the north polar cap. On Earth, gravity-driven south polar cap winds are termed 'catabatic' winds. Catabatic winds begin over the smooth expanse of the cap interior due to temperature differences between the atmosphere and the surface. Once begun, the winds sweep outward along the surface of the polar cap toward the sea. As the polar surface slopes down toward sealevel, the wind speeds increase. Catabatic wind speeds in the Antartic can reach several hundreds of miles per hour.

In the images of the Martian north polar cap we can see these same type of winds. Notice the streamers of dust moving downslope over the darker trough sides, these streamers show the laminar flow regime coming off the cap. Within the trough we see turbulent clouds of dust, kicked up at the trough base as the winds slow down and enter a chaotic flow regime.

The horizontal lines in these images are due to framelet overlap and lighting conditions over the bright polar cap.

Image information: VIS instrument. Latitude 86.5, Longitude 64.5 East (295.5 West). 40 meter/pixel resolution.

Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

North Polar Cap

NASA Technical Reports Server (NTRS)

2004-01-01

[figure removed for brevity, see original site]

This week we will be looking at five examples of laminar wind flow on the north polar cap. On Earth, gravity-driven south polar cap winds are termed 'catabatic' winds. Catabatic winds begin over the smooth expanse of the cap interior due to temperature differences between the atmosphere and the surface. Once begun, the winds sweep outward along the surface of the polar cap toward the sea. As the polar surface slopes down toward sealevel, the wind speeds increase. Catabatic wind speeds in the Antartic can reach several hundreds of miles per hour.

In the images of the Martian north polar cap we can see these same type of winds. Notice the streamers of dust moving downslope over the darker trough sides, these streamers show the laminar flow regime coming off the cap. Within the trough we see turbulent clouds of dust, kicked up at the trough base as the winds slow down and enter a chaotic flow regime.

The horizontal lines in these images are due to framelet overlap and lighting conditions over the bright polar cap.

Image information:VIS instrument. Latitude 86.5, longitude 57.4 East (302.6 West). 40 meter/pixel resolution.

Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

North Polar Cap

NASA Technical Reports Server (NTRS)

2004-01-01

[figure removed for brevity, see original site]

This week we will be looking at five examples of laminar wind flow on the north polar cap. On Earth, gravity-driven south polar cap winds are termed 'catabatic' winds. Catabatic winds begin over the smooth expanse of the cap interior due to temperature differences between the atmosphere and the surface. Once begun, the winds sweep outward along the surface of the polar cap toward the sea. As the polar surface slopes down toward sealevel, the wind speeds increase. Catabatic wind speeds in the Antartic can reach several hundreds of miles per hour.

In the images of the Martian north polar cap we can see these same type of winds. Notice the streamers of dust moving downslope over the darker trough sides, these streamers show the laminar flow regime coming off the cap. Within the trough we see turbulent clouds of dust, kicked up at the trough base as the winds slow down and enter a chaotic flow regime.

The horizontal lines in these images are due to framelet overlap and lighting conditions over the bright polar cap.

Image information: VIS instrument. Latitude 84.3, Longitude 314.4 East (45.6 West). 40 meter/pixel resolution.

Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

North Polar Cap

NASA Technical Reports Server (NTRS)

2004-01-01

[figure removed for brevity, see original site]

This week we will be looking at five examples of laminar wind flow on the north polar cap. On Earth, gravity-driven south polar cap winds are termed 'catabatic' winds. Catabatic winds begin over the smooth expanse of the cap interior due to temperature differences between the atmosphere and the surface. Once begun, the winds sweep outward along the surface of the polar cap toward the sea. As the polar surface slopes down toward sealevel, the wind speeds increase. Catabatic wind speeds in the Antartic can reach several hundreds of miles per hour.

In the images of the Martian north polar cap we can see these same type of winds. Notice the streamers of dust moving downslope over the darker trough sides, these streamers show the laminar flow regime coming off the cap. Within the trough we see turbulent clouds of dust, kicked up at the trough base as the winds slow down and enter a chaotic flow regime.

The horizontal lines in these images are due to framelet overlap and lighting conditions over the bright polar cap.

Image information: VIS instrument. Latitude 84.2, Longitude 57.4 East (302.6 West). 40 meter/pixel resolution.

Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

Dual polarized, heat spreading rectenna

NASA Technical Reports Server (NTRS)

Epp, Larry W. (Inventor); Khan, Abdur R. (Inventor); Smith, R. Peter (Inventor); Smith, Hugh K. (Inventor)

1999-01-01

An aperture coupled patch splits energy from two different polarization components to different locations to spread heat. In addition, there is no physical electrical connection between the slot, patch and circuitry. The circuitry is located under a ground plane which shields against harmonic radiation back to the RF source.

Proceedings of the Fourth International Conference on Mars Polar Science and Exploration

NASA Technical Reports Server (NTRS)

2006-01-01

Sessions in this conference include: Mars polar geology and glaciology; Mars and terrestrial radar investigations; Observations, nature, and evolution of the Martian seasonal polar caps; Mars' residual south polar cap; Climate change, ice core analysis, and the redistribution of volatiles on Mars; errestrial Mars analog environments; The Phoenix Scout mission and the nature of the near-polar environment; Moderated Discussion: Key Issues Regarding Phoenix Scout Mission and the nature of the near-polar environment; Panel Discussion: Key Issues in Mars Polar Science and Exploration; Mars Reconnaissance Orbiter investigations of the Martian polar regions and climate; Mars Polar Scout Mission concepts; and Panel Discussion: New perspectives on Mars polar science and exploration

Mars Water Ice and Carbon Dioxide Seasonal Polar Caps: GCM Modeling and Comparison with Mars Express Omega Observations

NASA Technical Reports Server (NTRS)

Forget, F.; Levrard, B.; Montmessin, F.; Schmitt, B.; Doute, S.; Langevin, Y.; Bibring, J. P.

2005-01-01

To better understand the behavior of the Mars CO2 ice seasonal polar caps, and in particular interpret the the Mars Express Omega observations of the recession of the northern seasonal cap, we present some simulations of the Martian Climate/CO2 cycle/ water cycle as modeled by the Laboratoire de Meteorologie Dynamique (LMD) global climate model.

Signs of a Martian Ice Age

NASA Image and Video Library

2016-05-26

This image montage features a two-dimensional radar cross section of Mars north polar cap collected by SHARAD instrument on NASA Mars Reconnaissance Orbiter spacecraft top, and a color image mosaic of the polar cap from NASA Viking project bottom

North Polar Cap - False Color

NASA Image and Video Library

2015-01-28

The THEMIS VIS camera contains 5 filters. The data from different filters can be combined in multiple ways to create a false color image. This false color image from NASA 2001 Mars Odyssey spacecraft shows the margin of the north polar cap.

At the Edge of a Polar Cap

NASA Image and Video Library

2014-05-22

The deep chasm that formed on the polar cap edge is identified as an area of strong down-slope winds and has a clear connection to Mars largest dune field, Olympia Undae as observed by NASA Mars Reconnaissance Orbiter.

Basal sublimation and venting of the north seasonal cap of Mars

NASA Astrophysics Data System (ADS)

Piqueux, S.; Christensen, P. R.

2007-12-01

Spots, fans and dark polygonal patterns form during the spring on the southern seasonal cap of Mars as a consequence of 1) the basal sublimation of the translucent and impermeable slab of carbon dioxide and 2) the venting of the CO2 gas loaded with dust and sand size material scoured from the surface of the polar layered deposits. The dark polygons on the cap have a similar formation process as the spots but the dust and sand erupt from elongated vents rather than point sources. In the summer, spiders and etched polygons remain on the southern polar layered deposits. The spiders are shaped by the scouring action of confined CO2 gas flowing between the cap and the basement and converging toward point sources, whereas the etched polygons result form the forced migration of the CO2 gas over longer distances. Comparable observations during the spring near the north pole on the seasonal cap indicate that similar processes occur in both polar regions and that the venting model developed for the south seasonal cap also operates near the north pole. However, spider and etched polygonal features are extremely uncommon on the north substrate, indicating that the conditions for their formation (e.g. mechanical strength of the slab and the substrate, transparency of the seasonal cap) are not met. The continual erosion and re-sedimentation occurring at the surface of the polar layered deposits by the seasonal degassing is a major geomorphological agent shaping the polar regions. The polar layered deposits have been proposed to contain the stratigraphic record of climatic changes and catastrophic events of very high interest for future missions. Our observations suggest that both polar regions deposits may have been locally disrupted by the seasonal sub-ice gas flow and that the stratigraphic record may have been partially lost. The Phoenix landing site might have been affected in the past and the stratigraphic information associated with the original deposition of the polar material partially disrupted due to this surface reworking.

Evolving Technologies for In-Situ Studies of Mars Ice

NASA Technical Reports Server (NTRS)

Carsey, F. D.; Hecht, M. H.

2003-01-01

Icy sites on Mars continue to be of high scientific importance. These sites include the polar caps, the southern mid-latitude subsurface permafrost, and the seasonal frost. These sites have interest due to their roles in climate processes, past climates, surface and near-surface water, astrobiology, geomorphology, and other topics. As is the case for many planetary features, remote sensing, while of great value, cannot answer all questions; in-situ examination is essential, and the motivation for in-situ observations generally leads to the subsurface, which, fortunately, is accessible on Mars. It is clear in fact that a Mars polar cap subsurface mission is both scientifically compelling and practical. Recent data from orbiting platforms has provided a remarkable level of information about the Mars ice caps; we know, for example, the size, shape and annual cycle of the cap topography as well as we know that of Earth, and we have more information on stratification that we have of, for example, the ice of East Antarctica. To understand the roles that the Mars polar caps play, it is necessary to gather information on the ice cap surface, strata, composition and bed. In this talk the status of in-situ operations and observations will be summarized, and, since we have conveniently at hand another planet with polar caps, permafrost and ice, the role of testing and validation of experimental procedures on Earth will be addressed.

The global distribution, abundance, and stability of SO2 on Io

USGS Publications Warehouse

McEwen, A.S.; Johnson, T.V.; Matson, D.L.; Soderblom, L.A.

1988-01-01

Sulfur dioxide distribution and abundances, bolometric hemispheric albedos, and passive surface temperatures on Io are modeled and mapped globally from Voyager multispectral mosaics, Earth-based spectra, and photometric descriptions. Photometric models indicate global average values for regolith porosity of 75-95% and macroscopic roughness with a mean slope angle of ~30??. Abundances of SO2 suggested by observations at uv-visible wavelengths and at 4.08 ??m are partially reconciled by intimate-mixing models; 30-50% SO2 coverage of the integral disk is indicated. Three major spectral end members, with continuous mixing, are recognized from the Voyager multispectral mosaics; one of these end members is identified as SO2. Intimate-mixing models with the three spectal end members are used to produce abundance maps for the optical surface; ~30% of Io's total optical surface consists of SO2. The SO2 is concentrated in the bright equatorial band and is relatively deficient in the region of Pele-type volcanic reuptions (long 240??-360??) and the polar regions. Temperatures are computed to vary over a 40??K range, at the same illumination angle, according to variations in surface bolometric hemispheric albedo. The brightest (and locally coldest) areas correspond to areas rich in SO2 and are concentrated in an equatorial band (??30?? lat), but many small cold patches occur elsewhere. These cold patches have radiative equilibrium temperatures ???120??K at the subsolar point, resulting in SO2 saturation vapor pressures ???10-8 bar. Midlatitude areas and the region of Pele-type plume eruptions are generally warmer (due to lower albedos). These results for surface temperatures and SO2 abundances and distribution support the regional coldtrapping model for the surface and atmospheric SO2 presented by F.P. Fanale, W.B. Banerdt, L.S. Elson, T.V. Johnson, and R.W. Zurek (1982, In Satellites of Jupiter (D. Morrison, Ed.), pp. 756-781, Univ. of Arizona Press, Tucson), although the region of Pele-type volcanic eruptions may be better characterized by the regolith condtrapping/volcanic-venting model of D.L. Matson and D.B. Nash (1983, J. Geophys. Res. 88, 4771-4783). The bright equatorial band is especially effective at slowing the formation of polar caps of SO2, both by reducing the sublimation rate near the subsolar point and by coldtrapping the SO2 in the equatorial region, so that competing processes of sputtering and volcanic resurfacing may prevent the formation of polar SO2 caps.

Design of broadband single polarized antenna

NASA Astrophysics Data System (ADS)

Shin, Phoo Kho; Aziz, Mohamad Zoinol Abidin Abd.; Ahmad, Badrul Hisham; Ramli, Mohamad Hafize Bin; Fauzi, Noor Azamiah Md; Malek, Mohd Fareq Abd

2015-05-01

In practical wireless communication application, bandwidth enhancement becomes one of the major design considerations. At the same time, circular polarized (CP) antenna received much attention for the applications of modern wireless communication system when compared to linear polarized (LP) antenna. This is because CP antenna can reduce the multipath effect. Hence, broadband antenna with operating frequency at 2.4GHz for WLAN application is proposed. The proposed antenna is done by using L-probe amendment with rectangular patch. The rectangular patch and copper ground plane is separated with 10mm air gap. This approach is used to enhance the bandwidth and the gain of the proposed antenna. The bandwidth of the designed antenna is more than 200MHz which meet broadband application. The return loss for the antenna is below -10dB to achieved 90% matching efficiency. The position of L-probe feed is altered in order to obtained different polarizations. The broadband antenna had been designed and simulated by using Computer Simulation Technology (CST) software. In this paper, the comparison for single polarized antenna with the design of non-inverted patch and inverted patch is discussed. The characteristics of the S-parameter, axial ratio, gain, surface current for each designed antenna are analyzed.

Comportamento stagionale delle calote polari di Marte

NASA Astrophysics Data System (ADS)

di Giovanni, Giovanni

2004-08-01

The rhythms of progression and retraction of the polar ice caps on Mars have been studied to establish possible variations in polar meteorology over the course of the last centuries. The applied theoretical procedure offers a mathematical function that contains some significant physical parameters, for example the length and the beginning of spring and another parameter which depends on temperature. The numerical data for the South Polar Cap during the grand oppositions of the last 130 years has been studied with the suggested theory. Evident correlations emerge between parameters and form of the diagram of cap amplitude versus time.

Ionospheric convection inferred from interplanetary magnetic field-dependent Birkeland currents

NASA Technical Reports Server (NTRS)

Rasmussen, C. E.; Schunk, R. W.

1988-01-01

Computer simulations of ionospheric convection have been performed, combining empirical models of Birkeland currents with a model of ionospheric conductivity in order to investigate IMF-dependent convection characteristics. Birkeland currents representing conditions in the northern polar cap of the negative IMF By component are used. Two possibilities are considered: (1) the morning cell shifting into the polar cap as the IMF turns northward, and this cell and a distorted evening cell providing for sunward flow in the polar cap; and (2) the existence of a three-cell pattern when the IMF is strongly northward.

Determination of Polar Cap Boundary for the Substorm Event of 8 March 2008

NASA Astrophysics Data System (ADS)

Wang, Chi; Wang, Jiangyan; Lopez, Ramon; Li, Hui; Zhang, Jiaojiao; Tang, Binbin

2018-05-01

The polar cap boundary (PCB) is a fundamental indicator of magnetospheric activities especially during a substorm cycle. Taking a period on 8 March 2008 as an example, we investigate the location of PCB and its dynamics during a substorm event. The PCB location is determined from the Piecewise Parabolic Method with a Lagrangian Remap (PPMLR) -Magnetohydrodynamic (MHD) simulation data and Defense Meteorological Satellite Program (DMSP) observations, respectively. Model-observation comparison indicates that the PPMLR-MHD model gives a reliable estimate of PCB location during a complex substorm sequence. We further analyze the evolution of PCB in that period. The polar cap expands under southward interplanetary magnetic field (IMF), since the low-latitude dayside reconnection produces new open magnetic flux. Meanwhile, more solar wind energy enters and stores in the magnetosphere with the decreasing SML (SuperMAG Auroral Lower) index. After the substorm expansion onset, the polar cap contracts for a while due to the explosive increase of nightside reconnection. When the IMF direction turns northward, the polar cap contracts continuously, since the dayside reconnection ceases and no more open magnetic flux are supplied, and the storage energy in the magnetosphere releases with the increasing SML index. The model results are in good accord with the features from observations.

Microstrip Antenna for Remote Sensing of Soil Moisture and Sea Surface Salinity

NASA Technical Reports Server (NTRS)

Ramhat-Samii, Yahya; Kona, Keerti; Manteghi, Majid; Dinardo, Steven; Hunter, Don; Njoku, Eni; Wilson, Wiliam; Yueh, Simon

2009-01-01

This compact, lightweight, dual-frequency antenna feed developed for future soil moisture and sea surface salinity (SSS) missions can benefit future soil and ocean studies by lowering mass, volume, and cost of the antenna system. It also allows for airborne soil moisture and salinity remote sensors operating on small aircraft. While microstrip antenna technology has been developed for radio communications, it has yet to be applied to combined radar and radiometer for Earth remote sensing. The antenna feed provides a key instrument element enabling high-resolution radiometric observations with large, deployable antennas. The design is based on the microstrip stacked-patch array (MSPA) used to feed a large, lightweight, deployable, rotating mesh antenna for spaceborne L-band (approximately equal to 1 GHz) passive and active sensing systems. The array consists of stacked patches to provide dual-frequency capability and suitable radiation patterns. The stacked-patch microstrip element was designed to cover the required L-band center frequencies at 1.26 GHz (lower patch) and 1.413 GHz (upper patch), with dual-linear polarization capabilities. The dimension of patches produces the required frequencies. To achieve excellent polarization isolation and control of antenna sidelobes for the MSPA, the orientation of each stacked-patch element within the array is optimized to reduce the cross-polarization. A specialized feed-distribution network was designed to achieve the required excitation amplitude and phase for each stacked-patch element.

Testing Orbital Parameters as a Hypothesis for the Presence of CO2 Deposits on Mars's South Pole

NASA Astrophysics Data System (ADS)

Bain, Z. M.; Bierson, C. J.

2017-12-01

Observational data of Mars's polar caps shows large deposits of buried CO2 ice in the south polar cap and only seasonal CO2 ice in the north [1]. The lower elevation of Mars's north pole leads to higher surface pressures and therefore more favorable conditions for CO2 ice deposition. There are a few plausible reasons why the CO2 deposits are observed at the southern cap. The first is that during a past epochs of atmospheric collapse, CO2was deposited at both poles and only preserved in the south. Another is that the deposits represent a period where ice was preferentially deposited at the south polar cap. The latter could occur if the orbital parameters were such that the southern cap experienced colder summers (less insolation) than the north. The model of Bierson et. al. 2016 [2] used the observed difference in albedo between the north and the south polar caps and found several periods in the last one million years where deposition was favored at the south polar cap. Here we test if deposition is still favored in the south using the same albedo for both caps. For this work we are using the seasonally resolved KRC model [3]. We varied obliquity, longitude of perihelion, and eccentricity to match their expected values over the last one million years [4]. We modeled the annual CO2 deposition rate in 1,000 year increments. We tested both constant and insolation dependent albedo that was the same at both poles. While we did find periods of deposition on the south pole, this was always in conjunction with deposition in the north in much greater amounts. This finding favors the hypothesis that the deposits are only observed in the southern cap due to the deep pre-existing troughs that allowed the CO2 to be preserved to the modern day. These results also highlight the importance of understanding the observed difference in albedo between the polar caps. [1] Phillips et al. (2011) AAAS, Vol.332 Is.6031 pp.838-841 [2] Bierson et al. (2016) GRL, Vol.43 Is.9 pp.4172-4179 [3] Kieffer (2013) JGR, Vol.118 Is.3 pp.451-470 [4] Laskar et al. (2004) Icarus, Vol.170 Is.2 pp.343-364

Suspended Patch Antenna Array With Electromagnetically Coupled Inverted Microstrip Feed

NASA Technical Reports Server (NTRS)

Simons, Rainee N.

2000-01-01

The paper demonstrates a four-element suspended patch antenna array, with a parasitic patch layer and an electromagnetically coupled inverted microstrip feed, for linear polarization at K-Band frequencies. This antenna has the following advantages over conventional microstrip antennas: First, the inverted microstrip has lower attenuation than conventional microstrip; hence, conductor loss associated with the antenna corporate feed is lower resulting in higher gain and efficiency. Second, conventional proximity coupled patch antennas require a substrate for the feed and a superstrate for the patch. However, the inverted microstrip fed patch antenna makes use of a single substrate, and hence, is lightweight and low cost. Third, electromagnetic coupling results in wider bandwidth. Details regarding the design and fabrication will be presented as well as measured results including return loss, radiation patterns and cross-polarization levels.

Perspective of Life Search in Martian Econiches

NASA Astrophysics Data System (ADS)

Demidov, N. E.

2017-05-01

Mars may be divided on five ecological niches according to presence and state of water: permanent polar caps, dry regolith, subpermafrost aquifers, cryopegs and ice containing regolith. Basic limiting factors for the search of life in this econiches are: absence of water (dry regolith), depth of burial (cryopegs and subpermafrost aquifers), age (ice containing permafrost and polar caps). High priority targets for the search of life on Mars are represented by permanently frozen deposits of young polar volcanoes and ash layers in polar caps. During volcanic eruptions microorganisms from subpermafrost aquifers could propagate to the surface and survive in permafrost or ice for million years, as it is known to happen on Earth. Possibility of specific lithic habitats in dry layer must also be taken into account.

MGS TES observations of the water vapor above the seasonal and perennial ice caps during northern spring and summer

NASA Astrophysics Data System (ADS)

Pankine, Alexey A.; Tamppari, Leslie K.; Smith, Michael D.

2010-11-01

We report on new retrievals of water vapor column abundances from the Mars Global Surveyor (MGS) Thermal Emission Spectrometer (TES) data. The new retrievals are from the TES nadir data taken above the 'cold' surface areas in the North polar region ( Tsurf < 220 K, including seasonal frost and permanent ice cap) during spring and summer seasons, where retrievals were not performed initially. Retrievals are possible (with some modifications to the original algorithm) over cold surfaces overlaid by sufficiently warm atmosphere. The retrieved water vapor column abundances are compared to the column abundances observed by other spacecrafts in the Northern polar region during spring and summer and good agreement is found. We detect an annulus of water vapor growing above the edge of the retreating seasonal cap during spring. The formation of the vapor annulus is consistent with the previously proposed mechanism for water cycling in the polar region, according to which vapor released by frost sublimation during spring re-condenses on the retreating seasonal CO 2 cap. The source of the vapor in the vapor annulus, according to this model, is the water frost on the surface of the CO 2 at the retreating edge of the cap and the frost on the ground that is exposed by the retreating cap. Small contribution from regolith sources is possible too, but cannot be quantified based on the TES vapor data alone. Water vapor annulus exhibits interannual variability, which we attribute to variations in the atmospheric temperature. We propose that during spring and summer the water ice sublimation is retarded by high relative humidity of the local atmosphere, and that higher atmospheric temperatures lead to higher vapor column abundances by increasing the water holding capacity of the atmosphere. Since the atmospheric temperatures are strongly influenced by the atmospheric dust content, local dust storms may be controlling the release of vapor into the polar atmosphere. Water vapor abundances above the residual polar cap also exhibit noticeable interannual variability. In some years abundances above the cap are lower than the abundances outside of the cap, consistent with previous observations, while in the other years the abundances above the cap are higher or similar to abundances outside of the cap. We speculate that the differences may be due to weaker off-cap transport in the latter case, keeping more vapor closer to the source at the surface of the residual cap. Despite the large observed variability in water vapor column abundances in the Northern polar region during spring and summer, the latitudinal distribution of the vapor mass in the atmosphere is very similar during the summer season. If the variability in vapor abundances is caused by the variability of vapor sources across the residual cap then this would mean that they annually contribute relatively little vapor mass to significantly affect the vapor mass budget. Alternatively this may suggest that the vapor variability is caused by the variability of the polar atmospheric circulation. The new water vapor retrievals should be useful in tuning the Global Circulation Models of the martian water cycle.

Conditions for the formation of prominences as inferred from optical observations

NASA Technical Reports Server (NTRS)

Martin, Sara F.

1990-01-01

It is suggested that three conditions, if dynamically maintained for a sufficient period of time, will result in the formation of a solar prominence. These conditions are the presence of a coronal arcade that connects the magnetic fields on opposite sides of a prominence; the existence of a long-term (hours to days) converging flow of small patches of opposite-polarity magnetic flux toward a common-polarity inversion zone; and the cancellation of encountered patches of magnetic flux of opposite polarity at a photospheric polarity inversion boundary.

CO_2 Frost Halos on the South Polar Residual Cap of Mars

NASA Astrophysics Data System (ADS)

Becerra, P.; Byrne, S.; HiRISE Team

2012-03-01

We present observational analysis, and a numerical model to explain the formation of bright CO_2 frost halos seen by HiRISE on the edges of scarps and "swiss cheese" features in the south polar residual cap of Mars.

Mariner 9 observations of the south polar cap of Mars - Evidence for residual CO2 frost

NASA Technical Reports Server (NTRS)

Paige, D. A.; Herkenhoff, K. E.; Murray, B. C.

1990-01-01

The first spacecraft observations of the south residual polar cap of Mars were obtained by the Mariner 9 orbiter during the Martian southern summer season, 1971-1972. Analyses of Viking orbiter observations obtained 3 Mars years later have shown that residual carbon dioxide frost was present at the south polar cap in 1977. In this study, Mariner 9 infrared interferometer spectrometer spectra and television camera images are used in conjuction with multispectral thermal emission models to constrain the temperatures of dark bare ground and bright frost regions within the south residual cap. The results provide strong evidence that carbon dioxide frost was present throughout the summer season despite the fact that the residual frost deposits observed by Mariner 9 were less extensive than those observed by Viking.

Polar cap models of gamma-ray pulsars: Emision from single poles of nearly aligned rotators

NASA Technical Reports Server (NTRS)

Daugherty, Joseph K.; Harding, Alice K.

1994-01-01

We compare a new Monte Carlo simulation of polar cap models for gamma-ray pulsars with observations of sources detected above 10 MeV by the Compton Observatory (CGRO). We find that for models in which the inclination of the magnetic axis is comparable to the angular radius of the polar cap, the radiation from a single cap may exhibit a pusle with either a single broad peak as in PSR 1706-44 and PSR 1055-52, or a doubly peaked profile comparable to those observed from the Crab, Vela and Geminga pulsars. In general, double pulses are seen by observers whose line of sight penetrates into the cap interior and are due to enhanced emission near the rim. For cascades induced by culvature radiation, increased rim emission occurs even when electrons are accelerated over the entire cap, since electrons from the interior escape along magnetic field lines with less curvature and hence emit less radiation. However, we obtain better fits to the duty cycles of observed profiles if we make the empirical assumption that acceleration occurs only near the rim. In either case, the model energy spectra are consistent with most of the observed sources. The beaming factors expected from nearly aligned rotators, based on standard estimates for the cap radius, imply that their luminosities need not be as large as in the case of orthogonal rotators. However, small beam angles are also a difficutly with this model because they imply low detection probablities. In either case the polar cap radius is a critical factor, and in this context we point out that plasma loading of the field lines should make the caps larger than the usual estimates based on pure dipole fields.

A wide-band dual-polarized VHF microstrip antenna for global sensing of sea ice thickness

NASA Technical Reports Server (NTRS)

Huang, John; Hussein, Ziad; Petros, Argy

2005-01-01

A VHF microstrip patch antenna was developed to achieve a bandwidth of 45 MHz (30%) from 127 MHz to 172 MHz with dual-linear-polarization capability. This microstrip antenna used foam substrates and dual stacked patches with capacitive probe feeds to achieve wide bandwidth. Four such capacitive feeds were used to achieve dual polarizations with less than -20 dB of cross-polarization level. Twenty-four shorting pins were used on the lower patch to achieve acceptable isolation between the four feed probes. This antenna has a measured gain of 8.5 dB at 137 MHz and 10 dB at 162 MHz. By using the Method of Moments technique, multipath scattering patterns were calculated when the antenna is mounted on the outside of a Twin Otter aircraft.

Energetic Charged Particle Component or the NO(y) Budget of the Polar Middle Atmosphere

NASA Technical Reports Server (NTRS)

Vitt, F. M.; Jackman, C. H.

1999-01-01

Analysis of nitrates measured in polar ice cap snow at a high resolution shows large variations in the nitrates. It has been shown that the nitrate signal may contain a signature of solar activity [Zeller and Dreschhoff, 19951. Reactive odd nitrogen production associated with solar particle events (SPEs) and auroral activity may be a source of some of the nitrate anomalies observed in the polar ice caps. Periods of large SPEs can lead to a production of polar atmospheric odd nitrogen in excess of the ambient sources in the polar stratosphere and mesosphere, and may leave a large nitrate signal stratified in the polar ice cap. Auroral electrons and photoelectrons produce odd nitrogen in the thermosphere, some of which may be transported to the polar (>50 degrees) mesosphere and stratosphere. Sources of odd nitrogen in the polar middle atmosphere associated with SPEs, galactic cosmic rays, and auroral electron precipitation have been quantified. The relative contributions by the energetic particles sources to the Noy budget of the polar middle atmosphere (from tropopause to 50 km, from 50 degrees to 90 degrees latitude) are compared with the nitrates observed in the polar ice sheets.

The role of calcium in the desensitization of capsaicin responses in rat dorsal root ganglion neurons.

PubMed

Koplas, P A; Rosenberg, R L; Oxford, G S

1997-05-15

Capsaicin (Cap) is a pungent extract of the Capsicum pepper family, which activates nociceptive primary sensory neurons. Inward current and membrane potential responses of cultured neonatal rat dorsal root ganglion neurons to capsaicin were examined using whole-cell and perforated patch recording methods. The responses exhibited strong desensitization operationally classified as acute (diminished response during constant Cap exposure) and tachyphylaxis (diminished response to successive applications of Cap). Both acute desensitization and tachyphylaxis were greatly diminished by reductions in external Ca2+ concentration. Furthermore, chelation of intracellular Ca2+ by addition of either EGTA or bis(2-aminophenoxy)ethane-N,N,N',N'-tetra-acetic acid to the patch pipette attenuated both forms of desensitization even in normal Ca2+. Release of intracellular Ca2+ by caffeine triggered acute desensitization in the absence of extracellular Ca2+, and barium was found to effectively substitute for calcium in supporting desensitization. Cap activated inward current at an ED50 of 728 nM, exhibiting cooperativity (Hill coefficient, 2.2); however, both forms of desensitization were only weakly dependent on [Cap], suggesting a dissociation between activation of Cap-sensitive channels and desensitization. Removal of ATP and GTP from the intracellular solutions resulted in nearly complete tachyphylaxis even with intracellular Ca2+ buffered to low levels, whereas changes in nucleotide levels did not significantly alter the acute form of desensitization. These data suggest a key role for intracellular Ca2+ in desensitization of Cap responses, perhaps through Ca2+-dependent dephosphorylation at a locus that normally sustains Cap responsiveness via ATP-dependent phosphorylation. It also seems that the signaling mechanisms underlying the two forms of desensitization are not identical in detail.

Broadband Radio Polarimetry of Fornax A. I. Depolarized Patches Generated by Advected Thermal Material from NGC 1316

NASA Astrophysics Data System (ADS)

Anderson, C. S.; Gaensler, B. M.; Heald, G. H.; O’Sullivan, S. P.; Kaczmarek, J. F.; Feain, I. J.

2018-03-01

We present observations and analysis of the polarized radio emission from the nearby radio galaxy Fornax A over 1.28–3.1 GHz, using data from the Australia Telescope Compact Array. In this, the first of two associated papers, we use modern broadband polarimetric techniques to examine the nature and origin of conspicuous low-polarization (low-p) patches in the lobes. We resolve the (low-p) patches and find that their low fractional polarization is associated with complicated frequency-dependent interference in the polarized signal generated by Faraday effects along the line of sight (LOS). The low-p patches are spatially correlated with interfaces in the magnetic structure of the lobe, across which the LOS-projected magnetic field changes direction. Spatial correlations with the sky-projected magnetic field orientation and structure in total intensity are also identified and discussed. We argue that the (low-p) patches, along with associated reversals in the LOS magnetic field and other related phenomena, are best explained by the presence of { \\mathcal O }({10}9) {M}ȯ of magnetized thermal plasma in the lobes, structured in shells or filaments, and likely advected from the interstellar medium of NCG 1316 or its surrounding intracluster medium. Our study underscores the power and utility of spatially resolved, broadband, full-polarization radio observations to reveal new facets of flow behaviors and magneto-ionic structure in radio lobes and their interplay with the surrounding environment.

Reconfigurable Wideband Circularly Polarized Stacked Square Patch Antenna for Cognitive Radios

NASA Technical Reports Server (NTRS)

Barbosa Kortright, Miguel A.; Waldstein, Seth W.; Simons, Rainee N.

2017-01-01

An almost square patch, a square patch and a stacked square patch with corner truncation for circular polarization (CP) are researched and developed at X-band for cognitive radios. Experimental results indicate, first, that the impedance bandwidth of a CP almost square patch fed from the edge by a 50 ohm line is 1.70 percent and second, that of a CP square patch fed from the ground plane side by a surface launch connector is 1.87 percent. Third, the impedance bandwidth of a CP stacked square patch fed by a surface launch connector is 2.22 percent. The measured center frequency for the CP square patch fed by a surface launch connector without and with an identical stacked patch is 8.45 and 8.1017 GHz, respectively. By stacking a patch, separated by a fixed air gap of 0.254 mm, the center frequency is observed to shift by as much as 348.3 MHz. The shift in the center frequency can be exploited to reconfigure the operating frequency by mechanically increasing the air gap. The results indicate that a tuning bandwidth of about 100 MHz can be achieved when the distance of separation between the driven patch and the stacked patch is increased from its initial setting of 0.254 to 1.016 mm.

Polar cap ion beams during periods of northward IMF: Cluster statistical results

NASA Astrophysics Data System (ADS)

Maggiolo, R.; Echim, M.; de Keyser, J.; Fontaine, D.; Jacquey, C.; Dandouras, I.

2011-05-01

Above the polar caps and during prolonged periods of northward IMF, the Cluster satellites detect upward accelerated ion beams with energies up to a few keV. They are associated with converging electric field structures indicating that the acceleration is caused by a quasi-static field-aligned electric field that can extend to altitudes higher than 7 RE (Maggiolo et al., 2006; Teste et al., 2007). Using the AMDA science analysis service provided by the Centre de Données de la Physique des Plasmas, we have been able to extract about 200 events of accelerated upgoing ion beams above the polar caps from the Cluster database. Most of these observations are taken at altitudes lower than 7 RE and in the Northern Hemisphere. We investigate the statistical properties of these ion beams. We analyze their geometry, the properties of the plasma populations and of the electric field inside and around the beams, as well as their dependence on solar wind and IMF conditions. We show that ~40 % of the ion beams are collocated with a relatively hot and isotropic plasma population. The density and temperature of the isotropic population are highly variable but suggest that this plasma originates from the plasma sheet. The ion beam properties do not change significantly when the isotropic, hot background population is present. Furthermore, during one single polar cap crossing by Cluster it is possible to detect upgoing ion beams both with and without an accompanying isotropic component. The analysis of the variation of the IMF BZ component prior to the detection of the beams indicates that the delay between a northward/southward turning of IMF and the appearance/disappearance of the beams is respectively ~2 h and 20 min. The observed electrodynamic characteristics of high altitude polar cap ion beams suggest that they are closely connected to polar cap auroral arcs. We discuss the implications of these Cluster observations above the polar cap on the magnetospheric dynamics and configuration during prolonged periods of northward IMF.

IR spectral properties of dust and ice at the Mars south polar cap

NASA Astrophysics Data System (ADS)

Titus, T. N.; Kieffer, H. H.

2001-11-01

Removal of atmospheric dust effects is required to derive surface IR spectral emissivity. Commonly, the atmospheric-surface separation is based on radiative transfer (RT) spectral inversion methods using nadir-pointing observations. This methodology depends on a priori knowledge of the spectral shape of each atmospheric aerosol (e.g. dust or water ice) and a large thermal contrast between the surface and atmosphere. RT methods fail over the polar caps due to low thermal contrast between the atmosphere and the surface. We have used multi-angle Emission Phase Function (EPF) observations to estimate the opacity spectrum of dust over the springtime south polar cap and the underlying surface radiance, and thus, the surface emissivity. We include a few EPFs from Hellas Basin as a basis for comparisons between the spectral shape of polar and non-polar dust. Surface spectral emissivities over the seasonal cap are compared to CO2 models. Our results show that the spectral shape of the polar dust opacity is not constant, but is a two-parameter family that can be characterized by the 9 um and 20 um opacities. The 9 um opacity varies from 0.15 to 0.45 and characterizes the overall atmospheric conditions. The 9 um to 20 um opacity ratio varies from 2.0 to 5.1, suggesting changes in dust size distribution over the polar caps. Derived surface temperatures from the EPFs confirm that the slightly elevated temperatures (relative to CO2 frost temperature) observed in ``cryptic'' regions are a surface effect, not atmospheric. Comparison of broad-band reflectivity and surface emissivities to model spectra suggest the bright regions (e.g. perennial cap, Mountains of Mitchell) have higher albedos due to a thin surface layer of fine-grain CO2 (perhaps either frost or fractured ice) with an underlying layer of either coarse grain or slab CO2 ice.

Have a Nice Spring! MOC Revisits "Happy Face" Crater

NASA Image and Video Library

2005-05-16

Smile! Spring has sprung in the martian southern hemisphere. With it comes the annual retreat of the winter polar frost cap. This view of "Happy Face Crater"--officially named "Galle Crater"--shows patches of white water ice frost in and around the crater's south-facing slopes. Slopes that face south will retain frost longer than north-facing slopes because they do not receive as much sunlight in early spring. This picture is a composite of images taken by the Mars Global Surveyor Mars Orbiter Camera (MOC) red and blue wide angle cameras. The wide angle cameras were designed to monitor the changing weather, frost, and wind patterns on Mars. Galle Crater is located on the east rim of the Argyre Basin and is about 215 kilometers (134 miles) across. In this picture, illumination is from the upper left and north is up. http://photojournal.jpl.nasa.gov/catalog/PIA02325

Interactions between Auxin Transport and the Actin Cytoskeleton in Developmental Polarity of Fucus distichus Embryos in Response to Light and Gravity1

PubMed Central

Sun, Haiguo; Basu, Swati; Brady, Shari R.; Luciano, Randy L.; Muday, Gloria K.

2004-01-01

Land plants orient their growth relative to light and gravity through complex mechanisms that require auxin redistribution. Embryos of brown algae use similar environmental stimuli to orient their developmental polarity. These studies of the brown algae Fucus distichus examined whether auxin and auxin transport are also required during polarization in early embryos and to orient growth in already developed tissues. These embryos polarize with the gravity vector in the absence of a light cue. The auxin, indole-3-acetic acid (IAA), and auxin efflux inhibitors, such as naphthylphthalamic acid (NPA), reduced environmental polarization in response to gravity and light vectors. Young rhizoids are negatively phototropic, and NPA also inhibits rhizoid phototropism. The effect of IAA and NPA on gravity and photopolarization is maximal within 2.5 to 4.5 h after fertilization (AF). Over the first 6 h AF, auxin transport is relatively constant, suggesting that developmentally controlled sensitivity to auxin determines the narrow window during which NPA and IAA reduce environmental polarization. Actin patches were formed during the first hour AF and began to photolocalize within 3 h, coinciding with the time of NPA and IAA action. Treatment with NPA reduced the polar localization of actin patches but not patch formation. Latrunculin B prevented environmental polarization in a time frame that overlaps the formation of actin patches and IAA and NPA action. Latrunculin B also altered auxin transport. Together, these results indicate a role for auxin in the orientation of developmental polarity and suggest interactions between the actin cytoskeleton and auxin transport in F. distichus embryos. PMID:15122028

Rocket measurements within a polar cap arc - Plasma, particle, and electric circuit parameters

NASA Technical Reports Server (NTRS)

Weber, E. J.; Ballenthin, J. O.; Basu, S.; Carlson, H. C.; Hardy, D. A.; Maynard, N. C.; Kelley, M. C.; Fleischman, J. R.; Pfaff, R. F.

1989-01-01

Results are presented from the Polar Ionospheric Irregularities Experiment (PIIE), conducted from Sondrestrom, Greenland, on March 15, 1985, designed for an investigation of processes which lead to the generation of small-scale (less than 1 km) ionospheric irregularities within polar-cap F-layer auroras. An instrumented rocket was launched into a polar cap F layer aurora to measure energetic electron flux, plasma, and electric circuit parameters of a sun-aligned arc, coordinated with simultaneous measurements from the Sondrestrom incoherent scatter radar and the AFGL Airborne Ionospheric Observatory. Results indicated the existence of two different generation mechanisms on the dawnside and duskside of the arc. On the duskside, parameters are suggestive of an interchange process, while on the dawnside, fluctuation parameters are consistent with a velocity shear instability.

The role of in-situ measurements in scintillation modelling

NASA Astrophysics Data System (ADS)

Basu, S.; Basu, S.; Hanson, W. B.

It is shown that the conflicting equatorial scintillation observations obtained from greatly separated ground stations can be organized in the framework of a longitudinal variation of irregularity occurrence, given satellite-borne, in situ measurements of irregularity amplitude of the global F-region irregularity morphology's general features. High-inclination satellite data are used to delineate the morphological features of the polar cap by means of such a method. The lack of diurnal and magnetic control of the irregularity morphology within the low solar flux, northern winter polar cap distinguishes this region from the auroral oval regime. A polar-orbiting communication system sensitive to phase perturbations may observe large differences in the phase-to-amplitude scintillation ratio, as it traverses the auroral oval and proceeds into the polar cap, with its sun-aligned arc system.

Smoking Cessation Treatment for Patients With Mental Disorders Using CBT and Combined Pharmacotherapy.

PubMed

Loreto, Aline Rodrigues; Carvalho, Carlos Felipe Cavalcanti; Frallonardo, Fernanda Piotto; Ismael, Flavia; Andrade, Arthur Guerra de; Castaldelli-Maia, João Maurício

2017-01-01

The aim of this study was to investigate smoking treatment effectiveness and retention in a population with and without mental disorders (MD). Participants received cognitive behavioral therapy (CBT) plus nicotine patch alone or in combination with other medications (i.e., gum, bupropion, or nortriptyline) for smoking cessation treatment in a Brazilian Psychosocial Care Center unit (CAPS), taking into account sociodemographics and smoking profile covariates. The study involved comparison of treatment success (seven-day point prevalence abstinence at the end of the treatment) and retention (presence of the individual in all of the four medical consultations and six group sessions) in two subsamples of patients with MD (n = 267) and without MD (n = 397) who were included in a six-week treatment provided by a CAPS from 2007 to 2013. The treatment protocol comprised group CBT and pharmacotherapy (nicotine patches, nicotine gums, and bupropion and nortriptyline available, prescribed by psychiatrists). Within patients with MD, CBT plus nicotine patch plus bupropion (aOR = 2.00, 95% CI [1.14, 3.50], p = .015) and CBT plus nicotine patch plus gum (aOR = 2.10, 95% CI [1.04, 4.23], p = .036) were associated with treatment success. Within patients without MD, female gender (aOR = 0.60, 95% CI [0.37, 0.95], p = .031) and lower Heaviness of Smoking Index score (aOR = 0.80, 95% CI [0.65, 0.99], p = .048) were associated with treatment success. No variable was associated with dropout or retention within patients with or without MD. Our findings support the use of CBT plus nicotine patch plus bupropion as well as CBT plus nicotine patch plus gum in samples with high rates of medical, psychiatric, and addiction disorders. These findings support those of previous studies in the general population. Pharmacological treatment associated with group CBT based on cognitive-behavioral concepts and combined with ongoing MD treatment seems to be the best option for smoking cessation treatment among patients with MD. Units that deal with patients with MD, such as CAPS in Brazil, should be encouraged to treat smoking addiction in this population. Future studies should investigate retention rates in other samples of patients with MD.

A multi-instrument case study of high-latitude ionospheric GNSS scintillation due to drifting plasma irregularities

NASA Astrophysics Data System (ADS)

van der Meeren, C.; Oksavik, K.; Moen, J. I.; Romano, V.

2013-12-01

For this study, GPS receiver scintillation and Total Electron Content (TEC) data from high-latitude locations on Svalbard have been combined with several other data sets, including the EISCAT Svalbard Radar (ESR) and allsky cameras, to perform a multi-instrument case study of high-latitude GPS ionospheric scintillations in relation to drifting plasma irregularities at night over Svalbard on 31 October 2011. Scintillations are rapid amplitude and phase fluctuations of electromagnetic signals. GNSS-based systems may be disturbed by ionospheric plasma irregularities and structures such as plasma patches (areas of enhanced electron density in the polar cap) and plasma gradients. When the GNSS radio signals propagate through such areas, in particular gradients, the signals experience scintillations that at best increases positioning errors and at worst may break the receiver's signal lock, potentially resulting in the GNSS receiver losing track of its position. Due to the importance of many GNSS applications, it is desirable to study the scintillation environment to understand the limitations of the GNSS systems. We find scintillation mainly localised to plasma gradients, with predominantly phase scintillation at the leading edge of patches and both phase and amplitude scintillation at the trailing edge. A single edge may also contain different scintillation types at different locations.

Albedo models for the residual south polar cap on Mars: Implications for the stability of the cap under near-perihelion global dust storm conditions

NASA Astrophysics Data System (ADS)

Bonev, Boncho P.; Hansen, Gary B.; Glenar, David A.; James, Philip B.; Bjorkman, Jon E.

2008-02-01

It is uncertain whether the residual (perennial) south polar cap on Mars is a transitory or a permanent feature in the current Martian climate. While there is no firm evidence for complete disappearance of the cap in the past, clearly observable changes have been documented. Observations suggest that the perennial cap lost more CO 2 material in the spring/summer season prior to the Mariner 9 mission than in those same seasons monitored by Viking and Mars Global Surveyor. In this paper we examine one process that may contribute to these changes - the radiative effects of a planet encircling dust storm that starts during late Martian southern spring on the stability of the perennial south polar cap. To approach this, we model the radiative transfer through a dusty planetary atmosphere bounded by a sublimating CO 2 surface. A critical parameter for this modeling is the surface albedo spectrum from the near-UV to the thermal-IR, which was determined from both space-craft and Earth-based observations covering multiple wavelength regimes. Such a multi-wavelength approach is highly desirable since one spectral band by itself cannot tightly constrain the three-parameter space for polar surface albedo models, namely photon "scattering length" in the CO 2 ice and the amounts of intermixed water and dust. Our results suggest that a planet-encircling dust storm with onset near solstice can affect the perennial cap's stability, leading to advanced sublimation in a "dusty" year. Since the total amount of solid CO 2 removed by a single storm may be less than the total CO 2 thickness, a series of dust storms would be required to remove the entire residual CO 2 ice layer from the south perennial cap.

Assembly and Function of the Actin Cytoskeleton of Yeast: Relationships between Cables and Patches

PubMed Central

Karpova, Tatiana S.; McNally, James G.; Moltz, Samuel L.; Cooper, John A.

1998-01-01

Actin in eukaryotic cells is found in different pools, with filaments being organized into a variety of supramolecular assemblies. To investigate the assembly and functional relationships between different parts of the actin cytoskeleton in one cell, we studied the morphology and dynamics of cables and patches in yeast. The fine structure of actin cables and the manner in which cables disassemble support a model in which cables are composed of a number of overlapping actin filaments. No evidence for intrinsic polarity of cables was found. To investigate to what extent different parts of the actin cytoskeleton depend on each other, we looked for relationships between cables and patches. Patches and cables were often associated, and their polarized distributions were highly correlated. Therefore, patches and cables do appear to depend on each other for assembly and function. Many cell types show rearrangements of the actin cytoskeleton, which can occur via assembly or movement of actin filaments. In our studies, dramatic changes in actin polarization did not include changes in filamentous actin. In addition, the concentration of actin patches was relatively constant as cells grew. Therefore, cells do not have bursts of activity in which new parts of the actin cytoskeleton are created. PMID:9744880

Occurrence Locations, Dipole Tilt Angle Effects, and Plasma Cloud Drift Paths of Polar Cap Neutral Density Anomalies

NASA Astrophysics Data System (ADS)

Lin, C. S.; Sutton, E. K.; Huang, C. Y.; Cooke, D. L.

2018-02-01

Polar cap neutral density anomaly (PCNDA) with large mass density enhancements over the background has been frequently observed in the polar cap during magnetic storms. By tracing field lines to the magnetosphere from the polar ionosphere, we divide the polar cap into two regions, an open field line (OFL) region with field lines connecting to the magnetopause boundary and a distant tail field line (TFL) region threaded with magnetotail lobe field lines. A statistical study of neutral density observed by the Challenging Minisatellite Payload satellite during major magnetic storms with Dst < -100 from July 2001 to 2006 indicates that over 85% of density anomalies were detected in the TFL region, at about 18° to 25° equatorward the center of the OFL region. PCNDAs were frequently accompanied by plasma clouds with peak density greater than 105 #/cm3. Modeling of plasma cloud drift paths suggests that plasma clouds originating in the dayside ionosphere could convect through the OFL region following the zero-potential line and reach the PCNDA locations. Plasma clouds could become stagnate in the TFL region, allowing a long duration of collisions with the neutral gas and possibly contributing to heating of PCNDAs. The PCNDA observations are interpreted as evidence that traveling atmospheric disturbance could be generated in the nightside polar cap. From the PCNDA size and speed of sound at 400 km, we derive an initial energy deposition duration for producing traveling atmospheric disturbance in the range from 0.5 to 2.5 hr.

Mars South Polar Cap 'Fingerprint' Terrain

NASA Technical Reports Server (NTRS)

2000-01-01

This picture is illuminated by sunlight from the upper left.

Some portions of the martian south polar residual cap have long, somewhat curved troughs instead of circular pits. These appear to form in a layer of material that may be different than that in which 'swiss cheese' circles and pits form, and none of these features has any analog in the north polar cap or elsewhere on Mars. This picture shows the 'fingerprint' terrain as a series of long, narrow depressions considered to have formed by collapse and widening by sublimation of ice. Unlike the north polar cap, the south polar region stays cold enough in summer to retain frozen carbon dioxide. Viking Orbiter observations during the late 1970s showed that very little water vapor comes off the south polar cap during summer, indicating that any frozen water that might be there remains solid throughout the year.

This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image was obtained in early southern spring on August 4, 1999. It shows an area 3 x 5 kilometers (1.9 x 3.1 miles) at a resolution of about 7.3 meters (24 ft) per pixel. Located near 86.0oS, 53.9oW.

Malin Space Science Systems and the California Institute of Technology built the MOC using spare hardware from the Mars Observer mission. MSSS operates the camera from its facilities in San Diego, CA. The Jet Propulsion Laboratory's Mars Surveyor Operations Project operates the Mars Global Surveyor spacecraft with its industrial partner, Lockheed Martin Astronautics, from facilities in Pasadena, CA and Denver, CO.

Pluto: The Ice Plot Thickens

NASA Image and Video Library

2015-07-15

The latest spectra from New Horizons Ralph instrument reveal an abundance of methane ice, but with striking differences from place to place across the frozen surface of Pluto. In the north polar cap, methane ice is diluted in a thick, transparent slab of nitrogen ice resulting in strong absorption of infrared light. In one of the visually dark equatorial patches, the methane ice has shallower infrared absorptions indicative of a very different texture. An Earthly example of different textures of a frozen substance: a fluffy bank of clean snow is bright white, but compacted polar ice looks blue. New Horizons' surface composition team has begun the intricate process of analyzing Ralph data to determine the detailed compositions of the distinct regions on Pluto. This is the first detailed image of Pluto from the Linear Etalon Imaging Spectral Array, part of the Ralph instrument on New Horizons. The observations were made at three wavelengths of infrared light, which are invisible to the human eye. In this picture, blue corresponds to light of wavelengths 1.62 to 1.70 micrometers, a channel covering a medium-strong absorption band of methane ice, green (1.97 to 2.05 micrometers) represents a channel where methane ice does not absorb light, and red (2.30 to 2.33 micrometers) is a channel where the light is very heavily absorbed by methane ice. The two areas outlined on Pluto show where Ralph observations obtained the spectral traces at the right. Note that the methane absorptions (notable dips) in the spectrum from the northern region are much deeper than the dips in the spectrum from the dark patch. The Ralph data were obtained by New Horizons on July 12, 2015. http://photojournal.jpl.nasa.gov/catalog/PIA19712

Method for removing strongly adsorbed surfactants and capping agents from metal to facilitate their catalytic applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Adzic, Radoslav R.; Gong, Kuanping; Cai, Yun

A method of synthesizing activated electrocatalyst, preferably having a morphology of a nanostructure, is disclosed. The method includes safely and efficiently removing surfactants and capping agents from the surface of the metal structures. With regard to metal nanoparticles, the method includes synthesis of nanoparticle(s) in polar or non-polar solution with surfactants or capping agents and subsequent activation by CO-adsorption-induced surfactant/capping agent desorption and electrochemical oxidation. The method produces activated macroparticle or nanoparticle electrocatalysts without damaging the surface of the electrocatalyst that includes breaking, increasing particle thickness or increasing the number of low coordination sites.

Science goals for a Mars Polar Cap subsurface mission : optical approaches for investiagations of inclusions in ice

NASA Technical Reports Server (NTRS)

Mogensen, Claus T.; Carsey, Frank D.; Behar, Alberto; Engelhardt, Hermann; Lane, Arthur L.

2002-01-01

The Mars Polar Caps are highly interesting features of Mars and have received much recent attention with new and exciting data on morphology, basal units, and layered outcroppings. We have examined the climatological, glaciological, and geological issues associated with a subsurface exploration of the Mars North Polar Cap and have determined that a finescale optical examination of ice in a borehole, to examine the stratigraphy, geochemistry and geochronology of the ice, is feasible. This information will enable reconstruction of the development of the cap as well as predication of the properties of its ice. We present visible imagery taken of dust inclusions in archived Greenland ice cores as well as in-situ images of accreted lithologic inclusions in West Antarctica, and we argue for use of this kind of data in Mars climate reconstruction as has been successful with Greenland and Antarctic ice core anlaysis.

Science goals for a Mars Polar Cap subsurface mission : optical approaches for investigations of inclusions in ice

NASA Technical Reports Server (NTRS)

Carsey, Frank; Mogensen, Claus T.; Behar, Alberto; Engelhardt, Hermann; Lane, Arthur L.

2002-01-01

The Mars Polar Caps are highly interesting features of Mars and have received much recent attention with new and exciting data on morphology, basal units, and layered outcroppings. We have examined the climatological, glaciological, and geological issues associated with a subsurface exploration of the Mars North Polar Cap and have determined that a finescale optical examination of ice in a borehole, to examine the stratigraphy, geochemistry and geochronology of the ice, is feasible. This information will enable reconstruction of the development of the cap as well as prediction of the properties of its ice. We present visible imagery taken of dust inclusions in archived Greenland ice cores as well as in-situ images of accreted lithologic inclusions in West Antarctica, and we argue for use of this kind of data in Mars climate reconstruction as has been successful with Greenland and Antarctic ice core analysis. .

Reconfigurable Wideband Circularly Polarized Stacked Square Patch Antenna for Cognitive Radios

NASA Technical Reports Server (NTRS)

Barbosa Kortright, Miguel A.; Waldstein, Seth W.; Simons, Rainee N.

2017-01-01

An almost square patch, a square patch and a stacked square patch with corner truncation for circular polarization (CP) are researched and developed at X-band for cognitive radios. Experimental results indicate, first, that the impedance bandwidth of a CP almost square patch fed from the edge by a 50 ohm line is 1.70% and second, that of a CP square patch fed from the ground plane side by a surface launch connector is 1.87%. Third, the impedance bandwidth of a CP stacked square patch fed by a surface launch connector is 2.22%. The measured center frequency for the CP square patch fed by a surface launch connector without and with an identical stacked patch is 8.45 and 8.1017 GHz, respectively. By stacking a patch, separated by a fixed air gap of 0.254 mm, the center frequency is observed to shift by as much as 348.3 MHz. The shift in center frequency, brought about by the reconfiguring of the physical layer antenna, can be exploited in a cognitive system since it expands the usable frequency spectrum for software reconfiguration in the presence of interference. In addition, varying the fixed air gap in the stacked antenna geometry by increments of 0.254 mm further expands the usable frequency spectrum.

Gamma-Ray Pulsar Light Curves in Vacuum and Force-Free Geometry

NASA Technical Reports Server (NTRS)

Harding, Alice K.; DeCesar, Megan E.; Miller, M. Coleman; Kalapotharakos, Constantinos; Contopoulos, Ioannis

2011-01-01

Recent studies have shown that gamma-ray pulsar light curves are very sensitive to the geometry of the pulsar magnetic field. Pulsar magnetic field geometries, such as the retarded vacuum dipole and force-free magnetospheres have distorted polar caps that are offset from the magnetic axis in the direction opposite to rotation. Since this effect is due to the sweepback of field lines near the light cylinder, offset polar caps are a generic property of pulsar magnetospheres and their effects should be included in gamma-ray pulsar light curve modeling. In slot gap models (having two-pole caustic geometry), the offset polar caps cause a strong azimuthal asymmetry of the particle acceleration around the magnetic axis. We have studied the effect of the offset polar caps in both retarded vacuum dipole and force-free geometry on the model high-energy pulse profiles. We find that, compared to the profiles derived from symmetric caps, the flux in the pulse peaks, which are caustics formed along the trailing magnetic field lines, increases significantly relative to the off-peak emission, formed along leading field lines. The enhanced contrast produces improved slot gap model fits to Fermi pulsar light curves like Vela, with vacuum dipole fits being more favorable.

Convection flow structure in the central polar cap

NASA Astrophysics Data System (ADS)

Bristow, W. A.

2017-12-01

A previous study of spatially averaged flow velocity in the central polar cap [Bristow et al., 2015] observed under steady IMF conditions found that it was extremely rare for the average to exceed 850 m/s (less than 0.2 % of the time). Anecdotally, however it is not uncommon to observe line-of-sight velocities in excess of 100 m/s in the McMurdo radar field of view directly over the magnetic pole. This discrepancy motivated this study, which examines the conditions under which high-velocity flows are observed at latitudes greater than 80° magnetic latitude. It was found that highly structured flows are common in the central polar cap, which leads to the flow within regions to have significant deviation from the average. In addition, the high-speed flow regions are usually directed away from the earth-sun line. No specific set of driving conditions was identified to be associated with high-speed flows. The study did conclude that 1)Polar cap velocities are generally highly structured. 2)Flow patterns typically illustrate narrow channels, vortical flow regions, and propagating features. 3) Persistent waves are a regular occurrence. 3)Features are observed to propagate from day side to night side, and from night side to day side.. 4)Convection often exhibits significant difference between the two hemispheres. And 5)About 10% of the time the velocity somewhere in the cap exceeds 1 Km/s The presentation will conclude with a discussion of the physical reasons for the flow structure. Bristow, W. A., E. Amata, J. Spaleta, and M. F. Marcucci (2015), Observations of the relationship between ionospheric central polar cap and dayside throat convection velocities, and solar wind/IMF driving, J. Geophys. Res. Space Physics, 120, doi:10.1002/2015JA021199.

Interannual observations and quantification of summertime H2O ice deposition on the Martian CO2 ice south polar cap

USGS Publications Warehouse

Brown, Adrian J.; Piqueux, Sylvain; Titus, Timothy N.

2014-01-01

The spectral signature of water ice was observed on Martian south polar cap in 2004 by the Observatoire pour l'Mineralogie, l'Eau les Glaces et l'Activite (OMEGA) ( Bibring et al., 2004). Three years later, the OMEGA instrument was used to discover water ice deposited during southern summer on the polar cap ( Langevin et al., 2007). However, temporal and spatial variations of these water ice signatures have remained unexplored, and the origins of these water deposits remains an important scientific question. To investigate this question, we have used observations from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) instrument on the Mars Reconnaissance Orbiter (MRO) spacecraft of the southern cap during austral summer over four Martian years to search for variations in the amount of water ice. We report below that for each year we have observed the cap, the magnitude of the H2O ice signature on the southern cap has risen steadily throughout summer, particularly on the west end of the cap. The spatial extent of deposition is in disagreement with the current best simulations of deposition of water ice on the south polar cap (Montmessin et al., 2007). This increase in water ice signatures is most likely caused by deposition of atmospheric H2O ice and a set of unusual conditions makes the quantification of this transport flux using CRISM close to ideal. We calculate a ‘minimum apparent‘ amount of deposition corresponding to a thin H2O ice layer of 0.2 mm (with 70% porosity). This amount of H2O ice deposition is 0.6–6% of the total Martian atmospheric water budget. We compare our ‘minimum apparent’ quantification with previous estimates. This deposition process may also have implications for the formation and stability of the southern CO2 ice cap, and therefore play a significant role in the climate budget of modern day Mars.

A circularly polarized Ka-band stacked patch antenna with increased gain

NASA Technical Reports Server (NTRS)

Zawadzki, M.

2002-01-01

Stacking layers of microstrip patches is a technique often used to improve the bandwidth of a patch antenna, but rarely used to increase its gain. The work presented here scales the three-layer S-band work done in to Ka-band.

Monitoring Auroral Electrojet from Polar Cap Stations

NASA Astrophysics Data System (ADS)

Tan, A.; Lyatsky, W.; Lyatskaya, S.

2004-12-01

The auroral electrojet AL and AE geomagnetic activity indices are important for monitoring geomagnetic substorms. In the northern hemisphere these indices are derived from measurements at a set of geomagnetic observatories located in the auroral zone. In the southern hemisphere the major portion of the auroral zone is located on the ocean; this does not allow us to derive the auroral electrojet indices in the same way. We showed that monitoring the auroral electrojet is possible from magnetic field measurements at polar cap stations. For this purpose we used hourly values of geomagnetic field variations at four polar cap stations, distributed along polar cap boundary and occupying a longitudinal sector of about 14 hours, and calculated mean values of the total magnetic field disturbance T = (X2 + Y2 + Z2)1/2 where X, Y, and Z are geomagnetic field components measured at these polar cap stations. The set of the obtained values were called the T index. This index has a clear physical mining: it is the summary of geomagnetic disturbance in all three components averaged over the polar cap boundary. We found that correlation coefficients for the dependence of the T index on both AL and AE indices are as high as ~0.9 and higher. The high correlation of the T index with the AL and AE indices takes place for any UT hour when the stations were located at the night side. The T index further shows good correlation with solar wind parameters: the correlation coefficient for the dependence of the T index on the solar wind-geomagnetic activity coupling function is ~0.8 and higher, which is close to the correlation coefficient for AL index. The T index may be especially important in the cases when ground-based measurements in the auroral zone are impossible as in the southern hemisphere.

The Residual Polar Caps of Mars: Geological Differences and Possible Consequences

NASA Technical Reports Server (NTRS)

Thomas, P. C.; Sullivan, R.; Ingersoll, A. P.; Murray, B. C.; Danielson, G. E.; Herkenhoff, K. E.; Soderblom, L.; Malin, M. C.; Edgett, K. S.; James, P. B.

2000-01-01

The Martian polar regions have been known to have thick layered sequences (presumed to consist of silicates and ice), CO2 seasonal frost, and residual frosts that remain through the summer: H2O in the north, largely CO2 in the south. The relationship of the residual frosts to the underlying layered deposits could not be determined from Viking images. The Mars Orbiter Camera on Mars Global Surveyor has provided a 50-fold increase in resolution that shows more differences between the two poles. The north residual cap surface has rough topography of pits, cracks, and knobs, suggestive of ablational forms. This topography is less than a few meters in height, and grades in to surfaces exposing the layers underneath. In contrast, the south residual cap has distinctive collapse and possibly ablational topography emplaced in four or more layers, each approx. two meters thick. The top surface has polygonal depressions suggestive of thermal contraction cracks. The collapse and erosional forms include circular and cycloidal depressions, long sinuous troughs, and nearly parallel sets of troughs. The distinctive topography occurs throughout the residual cap area, but not outside it. Unconformities exposed in polar layers, or other layered materials, do not approximate the topography seen on the south residual cap. The coincidence of a distinct geologic feature, several layers modified by collapse, ablation, and mass movement with the residual cap indicates a distinct composition and/or climate compared to both the remainder of the south polar layered units and those in the north.

Effect of high-latitude ionospheric convection on Sun-aligned polar caps

NASA Technical Reports Server (NTRS)

Sojka, J. J.; Zhu, L.; Crain, D. J.; Schunk, R. W.

1994-01-01

A coupled magnetospheric-ionospheric (M-I) magnetohydrodynamic (MHD) model has been used to simulate the formation of Sun-aligned polar cap arcs for a variety of interplanetary magnetic field (IMF) dependent polar cap convection fields. The formation process involves launching an Alfven shear wave from the magnetosphere to the ionosphere where the ionospheric conductance can react self-consistently to changes in the upward currents. We assume that the initial Alfven shear wave is the result of solar wind-magnetosphere interactions. The simulations show how the E region density is affected by the changes in the electron precipitation that are associated with the upward currents. These changes in conductance lead to both a modified Alfven wave reflection at the ionosphere and the generation of secondary Alfven waves in the ionosphere. The ensuing bouncing of the Alfven waves between the ionosphere and magnetosphere is followed until an asymptotic solution is obtained. At the magnetosphere the Alfven waves reflect at a fixed boundary. The coupled M-I Sun-aligned polar cap arc model of Zhu et al.(1993a) is used to carry out the simulations. This study focuses on the dependence of the polar cap arc formation on the background (global) convection pattern. Since the polar cap arcs occur for northward and strong B(sub y) IMF conditions, a variety of background convection patterns can exist when the arcs are present. The study shows that polar cap arcs can be formed for all these convection patterns; however, the arc features are dramatically different for the different patterns. For weak sunward convection a relatively confined single pair of current sheets is associated with the imposed Alfven shear wave structure. However, when the electric field exceeds a threshold, the arc structure intensifies, and the conductance increases as does the local Joule heating rate. These increases are faster than a linear dependence on the background electric field strength. Furthermore, above the threshold, the single current sheet pair splits into multiple current sheet pairs. For the fixed initial ionospheric and magnetospheric conditions used in this study, the separation distance between the current pairs was found to be almost independent of the background electric field strength. For either three-cell or distorted two-cell background convection patterns the arc formation favored the positive B(sub y) case in the northern hemisphere.

Strong IMF By-Related Plasma Convection in the Ionosphere and Cusp Field-Aligned Currents Under Northward IMF Conditions

NASA Technical Reports Server (NTRS)

Le, G.; Lu, G.; Strangeway, R. J.; Pfaff, R. F., Jr.; Vondrak, Richard R. (Technical Monitor)

2001-01-01

We present in this paper an investigation of IMF-By related plasma convection and cusp field-aligned currents using FAST data and AMIE model during a prolonged interval with large positive IMF By and northward Bz conditions (By/Bz much greater than 1). Using the FAST single trajectory observations to validate the global convection patterns at key times and key locations, we have demonstrated that the AMIE procedure provides a reasonably good description of plasma circulations in the ionosphere during this interval. Our results show that the plasma convection in the ionosphere is consistent with the anti-parallel merging model. When the IMF has a strongly positive By component under northward conditions, we find that the global plasma convection forms two cells oriented nearly along the Sun-earth line in the ionosphere. In the northern hemisphere, the dayside cell has clockwise convection mainly circulating within the polar cap on open field lines. A second cell with counterclockwise convection is located in the nightside circulating across the polar cap boundary, The observed two-cell convection pattern appears to be driven by the reconnection along the anti-parallel merging lines poleward of the cusp extending toward the dusk side when IMF By/Bz much greater than 1. The magnetic tension force on the newly reconnected field lines drives the plasma to move from dusk to dawn in the polar cusp region near the polar cap boundary. The field-aligned currents in the cusp region flow downward into the ionosphere. The return field-aligned currents extend into the polar cap in the center of the dayside convection cell. The field-aligned currents are closed through the Peterson currents in the ionosphere, which flow poleward from the polar cap boundary along the electric field direction.

The Search for Subsurface Ice Caps on Mercury

NASA Astrophysics Data System (ADS)

Allen, R. A.; Barlow, N. G.; Vilas, F.

1996-03-01

Recent ground-based radar observations of Mercury have detected strong, highly depolarized echoes from the north and south polar regions which have been interpreted as possible polar ice deposits. These radar echoes have been correlated with a number of impact craters. Theoretical studies indicate that such surface ice can be stable within permanently shadowed areas, such as the floors of high latitude impact craters. One proposed hypothesis suggests that stable subsurface ice caps exist at the poles of Mercury, and that several of the impact events that created the high latitude craters exposed this subsurface ice. Thus, our study focused on the possibility of ice caps extending below the mercurian surface, down to some unknown latitude in the polar regions. We used the experiences from Mars, where the depth/diameter ratio (d/D) is smaller for ice rich areas, to investigate whether a comparable latitudinal change in d/D is detectable on Mercury. We found no significant latitudinal differences within the two polar regions of our study or between the north polar and equatorial quadrangles, but craters in the south polar region tend to have slightly lower d/D than those in the north polar region.

Modeling the Formation of CO2 Frost Halos on the South Polar Residual Cap of Mars

NASA Astrophysics Data System (ADS)

Becerra, P.; Byrne, S.; HiRISE Team

2011-03-01

We introduce a model for the formation of bright halos seen by HiRISE on the edges of scarps and "swiss cheese" features in the south polar residual cap of Mars. We propose that they are formed from differences between the sublimation rates of sloped and flat surfaces.

South Polar Cap

NASA Technical Reports Server (NTRS)

2005-01-01

17 March 2005 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows mesas and pits formed by sublimation of carbon dioxide of the south polar cap.

Location near: 85.8oS, 351.5oW Image width: 2 km (1.2 mi) Illumination from: upper left Season: Southern Summer

Non-linear vacuum polarization in strong fields

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gyulassy, M.

1981-07-01

The Wichmann-Kroll formalism for calculating the vacuum polarization density to first order in ..cap alpha.. but to all orders in Z..cap alpha.. is derived. The most essential quantity is shown to be the electrons Green's function in these calculations. The method of constructing that Green's function in the field of finite radius nuclei is then presented.

A model for polar cap electric fields

NASA Technical Reports Server (NTRS)

Dangelo, N.

1976-01-01

A model is proposed relating polar cap ionospheric electric fields to the parameters of the solar wind near the orbit of the earth. The model ignores the notion of field line merging. An essential feature is the role played by velocity shear instabilities in regions of the outer magnetosphere, in which mapping of the magnetosheath electric field would produce sunward convection. The anomalous resistivity which arises from velocity shear turbulence, suffices to essentially disconnect the magnetosphere from the magnetosheath, at any place where that resistivity is large enough. The magnetosheath-magnetosphere system, as a consequence, acts as a kind of diode or rectifier for the magnetosheath electric fields. Predictions of the model are compared with several observations related to polar cap convection.

An X-Ray Survey for Polar CAP Qpos in AM Herculis Systems

NASA Astrophysics Data System (ADS)

Wood, Kent

Five AM Herculis binary systems show an optical QPO that is known to be associated with magentically channeled polar cap accretion. Hard X-ray QPOs are predicted by the time-depndent hydrodynamic models. We propose to search selected AM Her systems for polar cap X-ray QPOs using the XTE PCA. Because of its large collecting area, the PCA is the only instrument that can do this job. No other accreting objects provide comparable high-quality observational diagnostics on the accretion flow. The detailed understanding of flow geometry, shock heating, ion-electron energy exchange, accretion column structure, and emission and radiative transfer mechanisms that go to make up the picture of AM Her accretion needs to be tested against X-ray timing information.

Leveraging the Polar Cap: Ground-Based Measurements of the Solar Wind

NASA Astrophysics Data System (ADS)

Urban, K. D.; Gerrard, A. J.; Weatherwax, A. T.; Lanzerotti, L. J.; Patterson, J. D.

2016-12-01

In this study, we look at and identify relationships between solar wind quantities that have previously been shown to have direct access into the very high-latitude polar cap as measured by ground-based riometers and magnetometers in Antarctica: ultra-low frequency (ULF) power in the interplanetary magnetic field (IMF) Bz component and solar energetic proton (SEP) flux (Urban [2016] and Patterson et al. [2001], respectively). It is shown that such solar wind and ground-based observations can be used to infer the hydromagnetic structure and magnetospheric mapping of the polar cap region in a data-driven manner, and that high-latitude ground-based instrumentation can be used to infer concurrent various state parameters of the geospace environment.

South Polar Variety

NASA Technical Reports Server (NTRS)

2005-01-01

28 July 2005 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a view of linear troughs and mesas formed in the frozen carbon dioxide of the martian south polar residual cap. This image, obtained in May 2005, is a reminder that not all of the south polar cap landscapes resemble 'swiss cheese.'

Location near: 86.7oS, 24.8oW Image width: width: 3 km (1.9 mi) Illumination from: upper left Season: Southern Spring

Triton Southern Hemisphere

NASA Image and Video Library

1998-06-08

This polar projection from NASA Voyager 2 of Triton southern hemisphere provides a view of the southern polar cap and bright equatorial fringe. The margin of the cap is scalloped and ranges in latitude from +10 degrees to -30 degrees. The bright fringe is closely associated with the cap's margin; from it, diffuse bright rays extend north-northeast for hundreds of kilometers. The bright fringe probably consists of very fresh nitrogen frost or snow, and the rays consist of bright-fringe materials that were redistributed by north-moving Coriolis-deflected winds. http://photojournal.jpl.nasa.gov/catalog/PIA00423

Convection and electrodynamic signatures in the vicinity of a Sun-aligned arc: Results from the Polar Acceleration Regions and Convection Study (Polar ARCS)

NASA Technical Reports Server (NTRS)

Weiss, L. A.; Weber, E. J.; Reiff, P. H.; Sharber, J. R.; Winningham, J. D.; Primdahl, F.; Mikkelsen, I. S.; Seifring, C.; Wescott, Eugene M.

1994-01-01

An experimental campaign designed to study high-latitude auroral arcs was conducted in Sondre Stromfjord, Greenland, on February 26, 1987. The Polar Acceleration Regions and Convection Study (Polar ARCS) consisted of a coordinated set of ground-based, airborne, and sounding rocket measurements of a weak, sun-aligned arc system within the duskside polar cap. A rocket-borne barium release experiment, two DMSP satellite overflights, all-sky photography, and incoherent scatter radar measurements provided information on the large-scale plasma convection over the polar cap region while a second rocket instrumented with a DC magnetometer, Langmuir and electric field probes, and an electron spectrometer provided measurements of small-scale electrodynamics. The large-scale data indicate that small, sun-aligned precipitation events formed within a region of antisunward convection between the duskside auroral oval and a large sun-aligned arc further poleward. This convection signature, used to assess the relationship of the sun-aligned arc to the large-scale magnetospheric configuration, is found to be consistent with either a model in which the arc formed on open field lines on the dusk side of a bifurcated polar cap or on closed field lines threading an expanded low-latitude boundary layer, but not a model in which the polar cap arc field lines map to an expanded plasma sheet. The antisunward convection signature may also be explained by a model in which the polar cap arc formed on long field lines recently reconnected through a highly skewed plasma sheet. The small-scale measurements indicate the rocket passed through three narrow (less than 20 km) regions of low-energy (less than 100 eV) electron precipitation in which the electric and magnetic field perturbations were well correlated. These precipitation events are shown to be associated with regions of downward Poynting flux and small-scale upward and downward field-aligned currents of 1-2 micro-A/sq m. The paired field-aligned currents are associated with velocity shears (higher and lower speed streams) embedded in the region of antisunward flow.

Year-to-year instability of the Mars south polar cap

NASA Technical Reports Server (NTRS)

Jakosky, Bruce M.; Haberle, Robert M.

1990-01-01

Models of the Mars polar cap energy balance suggest that the south cap has two possible configurations at the current epoch. It can be covered all year by CO2 frost, as was observed by the Viking spacecraft, or the CO2 frost can disappear at midsummer to expose an underlying surface. The difference between the two states depends on the role of energy conducted into the subsurface. If the cap was exposed the previous year, conducted energy will cause less CO2 frost to condense in winter, and the frost will disappear completely in summer. If the cap was covered the previous year, there will be no conducted energy, and it will stay covered again. Subtle effects in the atmosphere can perturb the cap energy balance sufficiently to cause the cap to jump between states. This behavior might provide an explanation for the large southern summer water vapor abundances observed in 1969. It also explains the observed differences between the north and the south residual caps as resulting in part from a difference in the role in the annual energy balance of energy conducted into the subsurface.

Ultra-Wideband, Dual-Polarized, Beam-Steering P-Band Array Antenna

NASA Technical Reports Server (NTRS)

duToit, Cornelis

2014-01-01

A dual-polarized, wide-bandwidth (200 MHz for one polarization, 100 MHz for the orthogonal polarization) antenna array at P-band was designed to be driven by NASA's EcoSAR digital beam former. EcoSAR requires two wide P-band antenna arrays mounted on the wings of an aircraft, each capable of steering its main beam up to 35deg off-boresight, allowing the twin radar beams to be steered at angles to the flight path. The science requirements are mainly for dual-polarization capability and a wide bandwidth of operation of up to 200 MHz if possible, but at least 100 MHz with high polarization port isolation and low cross-polarization. The novel design geometry can be scaled with minor modifications up to about four times higher or down to about half the current design frequencies for any application requiring a dual-polarized, wide-bandwidth steerable antenna array. EcoSAR is an airborne interferometric P-band synthetic aperture radar (SAR) research application for studying two- and three-dimensional fine-scale measurements of terrestrial ecosystem structure and biomass, which will ultimately aid in the broader study of the carbon cycle and climate change. The two 2×8 element Pband antenna arrays required by the system will be separated by a baseline of about 25 m, allowing for interferometry measurements. The wide 100-to- 200-MHz bandwidth dual-polarized beams employed will allow the determination of the amount of biomass and even tree height on the ground. To reduce the size of the patches along the boresight dimension in order to fit them into the available space, two techniques were employed. One technique is to add slots along the edges of each patch where the main electric currents are expected to flow, and the other technique is to bend the central part of the patch away from the ground plane. The latter also facilitates higher mechanical rigidity. The high port isolation of more than 40 dB was achieved by employing a highly symmetrical feed mechanism for each pair of elements: three apertures coupling to the patch elements were placed along the two symmetry lines of the antenna element pair. Two apertures were used in tandem to excite two of the stacked patch elements for one polarization; the other was used to excite one element from one side and the other element from the other side, opposite in phase, taking care of the remaining polarization. The apertures narrow down to a small gap where they are excited by a crossing microstrip line to prevent any asymmetrical excitation of the two sides of the aperture gap, minimizing port-to-port coupling. Using patches that are non-planar leads to higher mechanical rigidity and smaller patch sizes to fit into the available space. Aperture coupling minimizes direct metal-to-metal connections. Using an aperture coupling feed mechanism results in a feed network for two antenna elements with a total of three feed points, plus one simple in-phase combiner to reduce it to two ports. It greatly reduces the complexity of the alternative, but more conventional, way of feeding a pair of two dual-polarized elements with high port isolation.

Deferiprone

MedlinePlus

... as weekly pill minders and those for eye drops, creams, patches, and inhalers) are not child-resistant and young children can open them easily. To protect young children from poisoning, always lock safety caps and immediately place the medication in ...

Macitentan

MedlinePlus

... as weekly pill minders and those for eye drops, creams, patches, and inhalers) are not child-resistant and young children can open them easily. To protect young children from poisoning, always lock safety caps and immediately place the medication in ...

Busulfan

MedlinePlus

... as weekly pill minders and those for eye drops, creams, patches, and inhalers) are not child-resistant and young children can open them easily. To protect young children from poisoning, always lock safety caps and immediately place the medication in ...

Nevirapine

MedlinePlus

... as weekly pill minders and those for eye drops, creams, patches, and inhalers) are not child-resistant and young children can open them easily. To protect young children from poisoning, always lock safety caps and immediately place the medication in ...

Interannual Comparison of Water Vapor in the North Polar Region of Mars

NASA Technical Reports Server (NTRS)

Tamppari, L. K.; Smith, M. D.; Hale, A. S.; Bass, D. S.

2003-01-01

In order to better understand the current climate of Mars, we seek to understand atmospheric water in the north polar region. Our approach is to examine the water transport and cycling issues within the north polar region and in/out of the region on seasonal and annual timescales. Viking Mars Atmospheric Water Detector (MAWD) data showed that water vapor increased as the northern summer season progressed and temperatures increased, and that vapor appeared to be transported southward . However, there has been uncertainty about the amount of water cycling in and out of the north polar region, as evidenced by residual polar cap visible brightness changes between one Martian year (Mariner 9 data) and a subsequent year (Viking data). These changes were originally thought to be interannual variations in the amount of frost sublimed based on global dust storm activity . However, Viking thermal and imaging data were re-examined and it was found that 14-35 pr m of water -ice appeared to be deposited on the cap later in the summer season, indicating that some water may be retained and redistributed within the polar cap region. This late summer deposition could be due to adsorption directly onto the cap surface or due to snowfall. We seek to understand what happens to the water on seasonal and interannual timescales. We address these issues by examining water vapor in the north polar region of Mars during the north spring and summer period from MGS TES data and by comparing these results to the Viking MAWD results.

ST5 Observations of the Imbalance of Region 1 and 2 Field-Aligned Currents and Its Implication to the Cross-Polar Cap Pedersen Currents

NASA Technical Reports Server (NTRS)

Le, Guan; Slavin, J. A.; Strangeway, Robert

2011-01-01

In this study, we use the in-situ magnetic field observations from Space Technology 5 mission to quantify the imbalance of Region 1 (R1) and Region 2 (R2) currents. During the three-month duration of the ST5 mission, geomagnetic conditions range from quiet to moderately active. We find that the R1 current intensity is consistently stronger than the R2 current intensity both for the dawnside and the duskside large-scale field-aligned current system. The net currents flowing into (out of) the ionosphere in the dawnside (duskside) are in the order of 5% of the total R1 currents. We also find that the net currents flowing into or out of the ionosphere are controlled by the solar wind-magnetosphere interaction in the same way as the field-aligned currents themselves are. Since the net currents due to the imbalance of the R1 and R2 currents require that their closure currents flow across the polar cap from dawn to dusk as Pedersen currents, our results indicate that the total amount of the cross-polar cap Pedersen currents is in the order of 0.1 MA. This study, although with a very limited dataset, is one of the first attempts to quantify the cross-polar cap Pedersen currents. Given the importance of the Joule heating due to Pedersen currents to the high-latitude ionospheric electrodynamics, quantifying the cross-polar cap Pedersen currents and associated Joule heating is needed for developing models of the magnetosphere-ionosphere coupling.

ST5 Observations of the Imbalance of Region 1 and 2 Field-Aligned Currents and its Implication to the Cross-Polar Cap Pedersen Currents

NASA Technical Reports Server (NTRS)

Le, Guan; Slavin, J. A.; Strangeway, Robert

2010-01-01

In this study, we use the in-situ magnetic field observations from Space Technology 5 mission to quantify the imbalance of Region 1 (R1) and Region 2 (R2) currents. During the three-month duration of the ST5 mission, geomagnetic conditions range from quiet to moderately active. We find that the R1 current intensity is consistently stronger than the R2 current intensity both for the dawnside and the duskside large-scale field-aligned current system. The net currents flowing into (out of) the ionosphere in the dawnside (duskside) are in the order of 5% of the total R1 currents. We also find that the net currents flowing into or out of the ionosphere are controlled by the solar windmagnetosphere interaction in the same way as the field-aligned currents themselves are. Since the net currents due to the imbalance of the R1 and R2 currents require that their closure currents flow across the polar cap from dawn to dusk as Pedersen currents, our results indicate that the total amount of the cross-polar cap Pedersen currents is in the order of approximately 0.1 MA. This study, although with a very limited dataset, is one of the first attempts to quantify the cross-polar cap Pedersen currents. Given the importance of the Joule heating due to Pedersen currents to the high-latitude ionospheric electrodynamics, quantifying the cross-polar cap Pedersen currents and associated Joule heating is needed for developing models of the magnetosphere-ionosphere coupling.

Ionization rate from the electron precipitation during August 2011 storm

NASA Astrophysics Data System (ADS)

Huang, Y.; Huang, C. Y.; Su, Y.

2013-12-01

We apply a parameterization by Fang et al. [2010] (Fang2010) to the complex energy spectra measured by DMSP F16 satellites to calculate the ionization rate from electron precipitation during a moderate storm on August 6th, 2011. The DMSP electron flux measurements show that there is clear enhancement of electron fluxes in the polar cap. The mean energy in the polar cap is mostly above 100 eV, while the mean energy of auroral zone is above 1 keV. F16 also captures a strong Poynting flux enhancement in the polar cap. The electron impact ionization rates using thermospheric densities and temperatures from NRLMSISE-00, TIE-GCM and GITM show clear enhancement at F-region altitudes in the polar cap region due to the low-energy electrons precipitated. Using the default empirical formulations of electron impact ionization in GCMs, TIE-GCM and GITM do not capture the F-region ionization shown in the results of Fang2010 parameterization. Fang, X, C. E. Randall, D. Lummerzheim, W. Wang, G. Lu, S. C. Solomon, and R. A. Frahm (2010), Geophys. Res. Lett., 37, L22106, doi:10.1029/2010GL045406.

Enoxaparin Injection

MedlinePlus

... as weekly pill minders and those for eye drops, creams, patches, and inhalers) are not child-resistant and young children can open them easily. To protect young children from poisoning, always lock safety caps and immediately place the medication in ...

Surface Plasmon Coupling and Control Using Spherical Cap Structures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gong, Yu; Joly, Alan G.; Zhang, Xin

2017-06-05

Propagating surface plasmons (PSPs) launched from a protruded silver spherical cap structure are investigated using photoemission electron microscopy (PEEM) and finite difference time domain (FDTD) calculations. Our combined experimental and theoretical findings reveal that PSP coupling efficiency is comparable to conventional etched-in plasmonic coupling structures. Additionally, plasmon propagation direction can be varied by a linear rotation of the driving laser polarization. A simple geometric model is proposed in which the plasmon direction selectivity is proportional to the projection of the linear laser polarization on the surface normal. An application for the spherical cap coupler as a gate device is proposed.more » Overall, our results indicate that protruded cap structures hold great promise as elements in emerging surface plasmon applications.« less

Polarized Exocytosis Induces Compensatory Endocytosis by Sec4p-Regulated Cortical Actin Polymerization

PubMed Central

Johansen, Jesper; Alfaro, Gabriel; Beh, Christopher T.

2016-01-01

Polarized growth is maintained by both polarized exocytosis, which transports membrane components to specific locations on the cell cortex, and endocytosis, which retrieves these components before they can diffuse away. Despite functional links between these two transport pathways, they are generally considered to be separate events. Using live cell imaging, in vivo and in vitro protein binding assays, and in vitro pyrene-actin polymerization assays, we show that the yeast Rab GTPase Sec4p couples polarized exocytosis with cortical actin polymerization, which induces endocytosis. After polarized exocytosis to the plasma membrane, Sec4p binds Las17/Bee1p (yeast Wiskott—Aldrich Syndrome protein [WASp]) in a complex with Sla1p and Sla2p during actin patch assembly. Mutations that inactivate Sec4p, or its guanine nucleotide exchange factor (GEF) Sec2p, inhibit actin patch formation, whereas the activating sec4-Q79L mutation accelerates patch assembly. In vitro assays of Arp2/3-dependent actin polymerization established that GTPγS-Sec4p overrides Sla1p inhibition of Las17p-dependent actin nucleation. These results support a model in which Sec4p relocates along the plasma membrane from polarized sites of exocytic vesicle fusion to nascent sites of endocytosis. Activated Sec4p then promotes actin polymerization and triggers compensatory endocytosis, which controls surface expansion and kinetically refines cell polarization. PMID:27526190

High Latitude Energetic Particle Boundaries: The SAMPEX Database

NASA Astrophysics Data System (ADS)

Kanekal, S. G.; Baker, D. N.

2006-11-01

The size of the polar cap or the open field line region depends, upon the difference in reconnection rates at the dayside between the IMF and the geomagnetic field, and those occurring in the magnetotail. The dayside merging adds flux to the open field region increasing the polar cap size and the magnetic flux in the lobes of the tail, thereby causing energy to be stored in the magnetosphere. Night side reconnection, geomagnetic storms and substorms dissipate this energy removing flux and shrink the polar cap. The dynamics of the polar cap can therefore be useful in the study of the energy dynamics of the magnetosphere. Energetic particles delineate magnetospheric regions, since their motions are governed by the geomagnetic field. Convection and corotation electric fields control the drift of low energy particles whereas magnetic field gradient and curvature are the dominant factors for higher energy (> ~30 keV) particles. High latitude energetic particle boundaries are related to the polar cap and therefore useful in determining the size of the open field line regions We will provide a long database of energetic particle boundaries in the polar regions using instruments aboard SAMPEX, the first of the Small explorer (SMEX) spacecraft. It was launched on July 3, 1992 into a low earth polar orbit. There are four particle detectors, HILT, LICA, PET and MAST on board which point toward the zenith over the poles of the Earth. These detectors measure electrons, protons and ions ranging in energy from tens of keV to a few MeV. This database will comprise the latitudinal (geographic, magnetic and invariant) and longitudinal (geographic and magnetic local time) positions of energetic particle boundaries in the polar regions. The database will cover a time period from launch to about mid 2004. It will therefore cover a significant portion of the solar cycles 22 and 23. Together with interplanetary data obtainable from public databases, such as the NASA OMNI database the SAMPEX energetic particle database can be used to relate Earth's magnetospheric response to the interplanetary drivers such as solar wind speed, density and magnetic field.

Four Mars Years of South Polar Changes

NASA Technical Reports Server (NTRS)

2005-01-01

[figure removed for brevity, see original site] [figure removed for brevity, see original site] View in 1999View in 2001View in 2003View in 2005

One of the most profound discoveries that would not have been possible if NASA's Mars Global Surveyor mission had not been extended beyond its primary mission of one Mars year (687 Earth days) is that of dramatic changes that take place in the south polar residual ice cap each martian year. To make this discovery, the Mars Orbiter Camera on the spacecraft had to be employed during a second Mars year to repeat images of sites on the south polar cap that had been imaged during the primary mission.

The initial discovery was made in 2001, when the camera team repeated images of portions of the south polar cap that had already been imaged in 1999. The goal of these images was to obtain stereo views, which would allow investigators to see the topography of the cap in three dimensions and to measure the thickness of the polar ice layers.

It was not possible to produce the desired 3-D views. To the team's surprise, the landforms of the south polar cap had changed.

The south polar residual cap -- that is, the portion of the ice cap that remains bright and retains ice throughout the southern summer season -- was seen in 1997 and 1999 images to have a complex terrain of broad, relatively flat mesas, small buttes, and many pits and troughs. Pits are generally circular and in some areas visually resemble a stack of thin slices of Swiss cheese. Very early in the Mars Global Surveyor mission, the Mars Orbiter Camera team speculated that these landforms must be carved into frozen carbon dioxide, because they look so unfamiliar and because Viking orbiter infrared measurements indicated that the south polar cap is cold enough consist of frozen carbon dioxide, even in summer.

The observations made by Mars Orbiter Camera in 2001, during the first part of the extended mission, showed that the scarps and pit walls of the south polar cap had retreated at an average rate of about 3 meters (10 feet) since 1999. In other words, they were retreating 3 meters per Mars year (and, of course, most of that retreat takes place during the summer). In some places on the cap, the scarps retreat less than 3 meters a Mars year, and in others it can retreat as much as 8 meters (26 feet) per martian year.

Of the two volatile materials one is likely to find in a frozen state on Mars -- water and carbon dioxide -- it is carbon dioxide that is volatile enough to permit scarp retreat rates like those observed by the Mars Orbiter Camera.

Over time, south polar pits merge to become plains, mesas turn into buttes, and buttes vanish forever. Since 2001, two additional Mars years have elapsed. A scientific benefit of having a long extended mission for Mars Global Surveyor has been the opportunity to document how the polar cap is changing each year.

Four images are shown here, plus an animation at left presenting the four frames in sequence. The location is near 86.3 degrees south latitude, 49.4 degrees west longitude, and the images show the same portion of the south polar residual cap as it appeared in 1999, 2001, 2003, and 2005. Comparing the images or viewing the animation makes it evident that the landscape of the south polar cap has been changing rapidly over the past four martian years.

Each year that Mars Global Surveyor has been in orbit, the landforms of the south polar residual cap have gotten smaller, and the carbon dioxide removed from the cap has not been re-deposited. The implication is that Mars presently has a warm (and possibly warming) climate, with new carbon dioxide going into the atmosphere every year. The other implication is that, at some time in the not-too-distant past, the planet had a colder climate, so that the layers of carbon dioxide could be deposited in the first place. If one takes the rate of scarp retreat and projects it backwards to fill in all of the pits and troughs with the carbon dioxide that has been removed from them, one finds that the colder climate might only have occurred a few centuries to a few tens of thousands of years ago. This kind of time scale is not unlike that of the climate changes that have been recorded on Earth, including the Ice Ages and the smaller fluctuations that have occurred since the last Ice Age (e.g., the 'Little Ice Age' of the mid-14th through mid-19th centuries).

After the discovery that the pits were enlarging and that we were not seeing carbon-dioxide deposition, it was suggested that interannual variations might be large enough to permit such deposition on a short timescale. However, two Mars years of additional observations show no large magnitude annual differences. Variations that would permit carbon dioxide deposition may require decades. And to see such variations may require many more Mars years of observations by orbiting spacecraft.

The Mars Orbiter Camera was built and is operated by Malin Space Science Systems, San Diego, Calif. Mars Global Surveyor left Earth on Nov. 7, 1996, and began orbiting Mars on Sept. 12, 1997. JPL, a division of the California Institute of Technology, Pasadena, manages Mars Global Surveyor for NASA's Science Mission Directorate, Washington.

Polar Winds

NASA Image and Video Library

2018-04-05

This VIS image shows 'streamers' of clouds created by katabatic winds at the north polar cap. Katabatic winds are created by cold air sinking at the pole and then speeding along the ice surface towards the edge of the polar cap. When the winds enter troughs the wind regime changes from laminar flow to choatic and clouds of ice particles and/or dust are visible. This wind activity peaks at the start of northern hemisphere summer. Orbit Number: 53942 Latitude: 86.8433 Longitude: 99.3149 Instrument: VIS Captured: 2014-02-10 10:50 https://photojournal.jpl.nasa.gov/catalog/PIA22362

A Sublimation Model for the Martian Polar Swiss-Cheese Features. Observational and Modeling Studies of the South Polar Residual Cap

NASA Technical Reports Server (NTRS)

Byrne, Shane; Ingersoll, Andrew P.

2002-01-01

In their pioneering work Leighton and Murray argued that the Mars atmosphere, which is 95 percent CO2 today, is controlled by vapor equilibrium with a much larger polar reservoir of solid CO2. Here we argue that the polar reservoir is small and cannot function as a long-term buffer to the more massive atmosphere. Our work is based on modeling the circular depressions (Swiss-cheese features) in the south polar cap. We argue that a solid CO2 layer approximately 8 meters thick is being etched away to reveal water ice underneath. Preliminary results from the THEMIS (Thermal Emission Imaging System) instrument seem to confirm our model.

A study of the relationship between interplanetary parameters and large displacements of the nightside polar cap boundary

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lester, M.; Freeman, M.P.; Southwood, D.J.

On July 14, 1982 the Sweden and Britain Radar-Aurora Experiment (SABRE) observed the ionospheric flow reversal boundary at {approximately} 0400 MLT to move equatorward across the radar field of view and then later to return poleward. The polar cap appeared to be considerably inflated at this time. Concurrent observations by ISEE-3 at the L1 libration point of the solar wind speed and density, and of the interplanetary magnetic field (IMF) indicated that the solar wind conditions were unusual throughout the interval under consideration. A mapping of the solar wind parameters from the L1 point to the subsolar magnetopause and thencemore » to the SABRE local time sector indicates that the equatorward motion of the polar cap boundary was controlled by a southward turning of the IMF. The inference of a concomitant increase in open magnetic flux is supported by a comparison of the magnetopause location observed by ISEE-1 on an inbound pass in the 2,100 MLT sector with a magnetopause model based upon the solar wind measurements made by ISEE-3. Some 20 minutes after the expansion of the polar cap boundary was first seen by SABRE, there was a rapid contraction of the boundary, the casue of which was independent of the INF and solar wind parameters, and which had a poleward velocity component in excess of 1,900 m s{sup {minus}1}. the boundary as it moved across the radar field of view was highly structured and oriented at a large angle to the ionospheric footprints of the magnetic L shells. Observations in the premidnight sector by the Air Force Geophysics Laboratory (AFGL) magnetometer array indicate that the polar cap contraction is caused by substorm draining of the polar cap flux and occurs without a clearly associated trigger in the interplanetary medium. The response time in the early morning local time sector to the substorm onset switch is approximately 20 minutes, equivalent to an ionospheric azimuthal phase velocity of some 5 km s{sup {minus}1}.« less

The Martian North Polar Cap in Summer - One Year Later

NASA Technical Reports Server (NTRS)

2001-01-01

In the middle of January 2001, Mars Global Surveyor (MGS) completed one Mars year in its 380 km-high (236 mi) mapping orbit. The mapping orbit was originally achieved in late February 1999. In March of that year, MGS conducted a series of operations in preparation for full-up mapping, first calibrating its scientific instruments and then operating in a mode in which the high gain antenna was held fixed against the body of the spacecraft. During this Fixed High Gain Antenna period, 'contingency science' observations were made in case the high gain antenna failed to properly deploy. The wide angle view of the martian north polar cap shown on the left was acquired on March 13, 1999, during early northern summer. The image on the right was acquired almost exactly one Mars year later, on January 26, 2001. The light-toned surfaces are residual water ice that remains through the summer season. The nearly circular band of dark material surrounding the cap consists mainly of sand dunes formed and shaped by wind. The north polar cap is roughly 1100 kilometers (680 miles) across. Close inspection will show that there are differences in the frost cover between the two images (for example, in the upper center of each image, and on the left edge center). Although these changes appear small, they are in fact quite large--the change in frost covering is equivalent to the amount of frost that would be evaporated (in the case of areas that are darker) or deposited (in areas where frost is still on the ground) in almost 5 months. What gives rise to such large changes in the heat budget for the polar caps from one year to the next is not known. Changes in the coloration and brightness of the polar cap suggest dust, deposited perhaps by dust storms during critical periods of the year, may play an important role.

Mars Seasonal Polar Caps as a Test of the Equivalence Principle

NASA Technical Reports Server (NTRS)

Rubincam, Daivd Parry

2011-01-01

The seasonal polar caps of Mars can be used to test the equivalence principle in general relativity. The north and south caps, which are composed of carbon dioxide, wax and wane with the seasons. If the ratio of the inertial to gravitational masses of the caps differs from the same ratio for the rest of Mars, then the equivalence principle fails, Newton's third law fails, and the caps will pull Mars one way and then the other with a force aligned with the planet's spin axis. This leads to a secular change in Mars's along-track position in its orbit about the Sun, and to a secular change in the orbit's semimajor axis. The caps are a poor E6tv6s test of the equivalence principle, being 4 orders-of-magnitude weaker than laboratory tests and 7 orders-of-magnitude weaker than that found by lunar laser ranging; the reason is the small mass of the caps compared to Mars as a whole. The principal virtue of using Mars is that the caps contain carbon, an element not normally considered in such experiments. The Earth with its seasonal snow cover can also be used for a similar test.

A study of the electric field in an open magnetospheric model

NASA Technical Reports Server (NTRS)

Stern, D. P.

1972-01-01

The qualitative properties of an open magnetosphere and its electric field are examined and compared to a simple model of a dipole in a constant field and to actual observations. Many of these properties are found to depend on the separatrix, a curve connecting neutral points and separating different field-line regimes. In the simple model, the electric field in the central polar cap tends to point from dawn to dusk for a wide choice of external fields. Near the boundary of the polar cap electric equipotentials curve and become crescent-shaped, which may explain the correlation of polar magnetic variations with the azimuthal component of the interplanetary magnetic field, reported by Svalgaard. Modifications expected to occur in the actual magnetosphere are also investigated: in particular, it appears that bending of equipotentials may be reduced by cross-field flow during the merging of field lines and that open field lines connected to the polar caps emerge from a long and narrow slot extending along the tail.

Magnetospheric access of solar particles and the configuration of the distant geomagnetic field, volume 1. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Evans, L. C.

1972-01-01

The access of 1.2 to 40 MeV protons and 0.4 to 1.0 MeV electrons from interplanetary space to the polar cap regions was investigated with an experiment on board a low altitude, polar-orbiting satellite (0G0 4). A total of 333 quiet time observations of the electron polar cap boundary give a mapping of the boundary between open and closed geomagnetic field lines. Observations of events associated with co-rotating regions of enhanced proton flux in interplanetary space were used to establish the characteristics of the 1.2 to 40 MeV proton access windows. The results were compared to particle access predictions of the distant geomagnetic tail configurations. The role played by interplanetary anisotropies in the observation of persistent polar cap features is discussed. Special emphasis is given to the problem of nonadiabatic particle entry through regions where the magnetic field is changing direction.

Mars south polar spring and summer temperatures - A residual CO2 frost

NASA Technical Reports Server (NTRS)

Kieffer, H. H.

1979-01-01

Viking infrared thermal mapper (IRTM) energy measurements over the Mars south polar cap throughout the Martian spring and summer revealed complex spatial, spectral, and temporal variations. High albedos did not directly correspond with low temperatures, and as the cap shrank to its residual position, it maintained large differences in brightness temperature between the four IRTM surface-sensing bands at 7, 9, 11, and 20 microns. The late summer infrared spectral pattern can be matched by a surface consisting of CO2 frost with 20 micron emissivity of 0.8 and about 6% dark, warm soil under a dusty atmosphere of moderate infrared opacity and spectral properties similar to those measured for the Martian global dust storms. Low temperature, the absence of appreciable water vapor in the south polar atmosphere, and the absence of surface warming expected if H2O were to become exposed, all imply that the residual south polar cap was covered by solid CO2.

South Polar Cap Erosion and Aprons

NASA Technical Reports Server (NTRS)

2000-01-01

This scene is illuminated by sunlight from the upper left.

While Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) images have shown that the north and south polar cap surfaces are very different from each other, one thing that the two have in common is that they both seem to have been eroded. Erosion in the north appears mostly to come in the form of pits from which ice probably sublimed to vapor and was transported away from the polar cap by wind. Erosion in the south takes on a wider range of possible processes that include collapse, slumping and mass-movement on slopes, and probably sublimation. Among the landforms created by these process on the south polar cap are the 'aprons' that surround mesas and buttes of remnant layers such as the two almost triangular features in the lower quarter of this image. The upper slopes of the two triangular features show a stair-stepped pattern that suggest these hills are layered.

This image shows part of the south polar residual cap near 86.9oS, 78.5oW, and covers an area approximately 1.2 by 1.0 kilometers (0.7 x 0.6 miles) in size. The image has a resolution of 2.2 meters per pixel. The picture was taken on September 11, 1999.

Malin Space Science Systems and the California Institute of Technology built the MOC using spare hardware from the Mars Observer mission. MSSS operates the camera from its facilities in San Diego, CA. The Jet Propulsion Laboratory's Mars Surveyor Operations Project operates the Mars Global Surveyor spacecraft with its industrial partner, Lockheed Martin Astronautics, from facilities in Pasadena, CA and Denver, CO.

Strategy for Improved Representation of Magnetospheric Electric Potential Structure on a Polar-Capped Ionosphere

NASA Astrophysics Data System (ADS)

Schulz, M.

2016-12-01

In some simple models of magnetospheric electrodynamics [e.g., Volland, Ann. Géophys., 31, 159-173, 1975], the normal component of the convection electric field is discontinuous across the boundary between closed and open magnetic field lines, and this discontinuity facilitates the formation of auroral arcs there. The requisite discontinuity in E is achieved by making the scalar potential proportional to a positive power (typically 1 or 2) of L on closed field lines and to a negative power (typically -1/2) of L on open (i.e., polar-cap) field lines. This suggests that it may be advantageous to construct more realistic (and thus more complicated) empirical magnetospheric and ionospheric electric-field models from superpositions of mutually orthogonal (or not) vector basis functions having this same analytical property (i.e., discontinuity at L = L*, the boundary surface between closed and open magnetic field lines). The present work offers a few examples of such constructions. A major challenge in this project has been to devise a coordinate system that simplifies the required analytical expansions of electric scalar potentials and accommodates the anti-sunward offset of each polar-cap boundary's centroid with respect to the corresponding magnetic pole. For circular northern and southern polar caps containing equal amounts of magnetic flux, one can imagine a geometrical construction of nested circular (but non-concentric) contours of constant quasi-latitude whose centers converge toward the magnetic poles as the contours themselves approach the magnetic equator. For more general polar-cap shapes and (in any case) to assure mutual orthogonality of respective coordinate surfaces on a spherical ionosphere, a formulation based on harmonic coordinates (expanded from eigen-solutions of the two-dimensional Laplace equation) may be preferable.

The Contribution of Water Ice Clouds to the Water Cycle in the North Polar Region of Mars: Preliminary Analysis

NASA Technical Reports Server (NTRS)

Bass, D. S.; Tamppari, L. K.

2000-01-01

While it has long been known that Mars' north residual polar cap and the Martian regolith are significant sources of atmospheric water vapor, the amount of water vapor observed in the northern spring season by the Viking Mars Atmospheric Water Detector instrument (MAWD) cannot be attributed to cap and regolith sources alone. Kahn suggested that ice hazes may be the mechanism by which additional water is supplied to the Martian atmosphere. Additionally, a significant decrease in atmospheric water vapor was observed in the late northern summer that could not be correlated with the return of the cold seasonal C02 ice. While the detection of water ice clouds on Mars indicate that water exists in Mars' atmosphere in several different phases, the extent to which water ice clouds play a role in moving water through the Martian atmosphere remains uncertain. Work by Bass et. al. suggested that the time dependence of water ice cap seasonal variability and the increase in atmospheric water vapor depended on the polar cap center reaching 200K, the night time saturation temperature. Additionally, they demonstrated that a decrease in atmospheric water vapor may be attributed to deposition of water ice onto the surface of the polar cap; temperatures were still too warm at this time in the summer for the deposition of carbon dioxide. However, whether water ice clouds contribute significantly to this variability is unknown. Additional information is contained in original extended abstract.

Impact of the CO2 and H2O clouds of the Martian polar hood on the polar energy balance

NASA Technical Reports Server (NTRS)

Forget, Francois; Pollack, James B.

1993-01-01

Clouds covering extensive areas above the martian polar caps have regularly been observed during the fall and winter seasons of each hemisphere. These 'polar hoods' are thought to be made of H2O and CO2. In particular, the very cold temperatures observed during the polar night by Viking and Mariner 9 around both poles have been identified as CO2 clouds and several models, including GCM, have indicated that the CO2 can condense in the atmosphere at all polar latitudes. Estimating the impact of the polar hood clouds on the energy balance of the polar regions is necessary to model the CO2 cycle and address puzzling problems like the polar caps assymetry. For example, by altering the thermal radiation emitted to space, CO2 clouds alter the amount of CO2 that condenses during the fall and winter season. The complete set of Viking IRTM data was analyzed to define the spatial and temporal properties of the polar hoods, and how their presence affects the energy radiated by the atmosphere/caps system to space was estimated. The IRTM observations provide good spatial and temporal converage of both polar regions during fall, winter, and spring, when a combination of the first and the second Viking year is used. Only the IRTM brightness temperatures at 11, 15, and 20 microns are reliable at martian polar temperatures. To recover the integrated thermal fluxes from the IRTM data, a simple model of the polar hood, thought to consist of 'warm' H2O clouds lying above colder and opaque CO2 clouds was developed. Such a model is based on the analysis of the IRIS spectra, and is consistent with the IRTM data used.

The Mars water cycle at other epochs: Recent history of the polar caps and layered terrain

NASA Technical Reports Server (NTRS)

Jakosky, Bruce M.; Henderson, Bradley G.; Mellon, Michael T.

1992-01-01

The Martian polar caps and layered terrain presumably evolves by the deposition and removal of small amounts of water and dust each year, the current cap attributes therefore represent the incremental transport during a single year as integrated over long periods of time. The role was studied of condensation and sublimation of water ice in this process by examining the seasonal water cycle during the last 10(exp 7) yr. In the model, axial obliquity, eccentricity, and L sub s of perihelion vary according to dynamical models. At each epoch, the seasonal variations in temperature are calculated at the two poles, keeping track of the seasonal CO2 cap and the summertime sublimation of water vapor into the atmosphere; net exchange of water between the two caps is calculated based on the difference in the summertime sublimation between the two caps (or on the sublimation from one cap if the other is covered with CO2 frost all year). Results from the model can help to explain (1) the apparent inconsistency between the timescales inferred for layer formation and the much older crater retention age of the cap and (2) the difference in sizes of the two residual caps, with the south being smaller than the north.

Auroral-polar cap environment and its impact on spacecraft plasma interactions

NASA Technical Reports Server (NTRS)

Garrett, H. B.

1985-01-01

The high density of the plasma at shuttle altitude is likely to increase greatly the possibility of arcing and shorting of exposed high voltage surfaces. For military missions over the polar caps and through the auoroal zones, the added hazards of high energy auroral particle fluxes or solar flares will further increase the hazard to shuttle, its crew, and its mission. A review of the role that the auroral and polar cap environment play in causing these interactions was conducted. A simple, though comprehensive attempt at modelling the shuttle environment at 400 km will be described that can be used to evaluate the importance of the interactions. The results of this evaluation are then used to define areas where adequate environmental measurements will be necessary if a true spacecraft interactions technology is to be developed for the shuttle.

Parameterized study of the ionospheric modification associated with sun-aligned polar cap arcs

NASA Technical Reports Server (NTRS)

Crain, D. J.; Sojka, J. J.; Schunk, R. W.; Zhu, L.

1993-01-01

The local ionospheric modification that is due to a generalized steady state solar aligned (SA) arc structure is addressed. For a representative set of SA arc parameters which includes both convection and precipitation, emphasis is placed on the modification by SA polar cap arcs upon the F region electron density and the height integrated conductivity. At low fluxes and low characteristic energies, SA polar cap arcs have the most pronounced relative effect at F region altitudes in darkness for winter solar minimum conditions. The absolute enhancement in summer solar minimum and winter solar maximum is equivalent to that of winter solar minimum, but the higher ambient densities make the relative enhancement less. The TEC enhancement associated with an SA arc may be used to indicate the degree of plasma cross flow across the arc.

Cosmic ray electrons and positrons from supernova explosions of massive stars.

PubMed

Biermann, P L; Becker, J K; Meli, A; Rhode, W; Seo, E S; Stanev, T

2009-08-07

We attribute the recently discovered cosmic ray electron and cosmic ray positron excess components and their cutoffs to the acceleration in the supernova shock in the polar cap of exploding Wolf-Rayet and red supergiant stars. Considering a spherical surface at some radius around such a star, the magnetic field is radial in the polar cap as opposed to most of 4pi (the full solid angle), where the magnetic field is nearly tangential. This difference yields a flatter spectrum, and also an enhanced positron injection for the cosmic rays accelerated in the polar cap. This reasoning naturally explains the observations. Precise spectral measurements will be the test, as this predicts a simple E;{-2} spectrum for the new components in the source, steepened to E;{-3} in observations with an E;{-4} cutoff.

Mars polar cap: a habitat for elementary life1

NASA Astrophysics Data System (ADS)

Wallis, M. K.; Wickramasinghe, N. C.

2009-04-01

Ices in the Martian polar caps are potential habitats for various species of microorganisms. Salts in the ice and biological anti-freeze polymers maintain liquid in cracks in the ices far below 0°C, possibly down to the mean 220-240 K. Sub-surface microbial life is shielded from ultraviolet (UV) radiation, but could potentially be activated on south-facing slopes under the midday, midsummer Sun. Such life would be limited by low levels of vapour, little transport of nutrients, low light levels below a protective dirt-crust, frost accumulation at night and in shadows, and little if any active translocation of organisms. As in the Antarctic and in permafrost, movement to new habitats depends on geo-climatic changes, which for Mars's north polar cap occur on a 50 000 year scale, except for rare meteorite impacts.

The neutral wind 'flywheel' as a source of quiet-time, polar-cap currents

NASA Technical Reports Server (NTRS)

Lyons, L. R.; Walterscheid, R. L.; Killeen, T. L.

1985-01-01

The neutral wind pattern over the summer polar cap can be driven by plasma convection to resemble the convection pattern. For a north-south component of the interplanetary magnetic field Bz directed southward, the wind speeds in the conducting E-region can become approximately 25 percent of the electric field drift speeds. If convection ceases, this neutral wind distribution can drive a significant polar cap current system for approximately 6 hours. The currents are reversed from those driven by the electric fields for southward Bz, and the Hall and field-aligned components of the current system resemble those observed during periods of northward Bz. The current magnitudes are similar to those observed during periods of small, northward Bz; however, observations indicate that electric fields often contribute to the currents as much as, or more than, the neutral winds.

Localized Patch Clamping of Plasma Membrane of a Polarized Plant Cell 1

PubMed Central

Taylor, Alison R.; Brownlee, Colin

1992-01-01

We used an ultraviolet laser to rupture a small region of cell wall of a polarized Fucus spiralis rhizoid cell and gained localized access to the plasma membrane at the growing apex. Careful control of cell turgor enabled a small portion of plasma membrane-bound cytoplasm to be exposed. Gigaohm seals allowing single-channel recordings were obtained with a high success rate using this method with conventional patch clamp techniques. ImagesFigure 1 PMID:16669092

Residual Cap

NASA Image and Video Library

2006-05-10

This MOC image shows a summertime view of the south polar residual cap of Mars. In this image, mesas composed largely of solid carbon dioxide are separated from one another by irregularly-shaped depressions

Design of triple-band polarization controlled terahertz metamaterial absorber

NASA Astrophysics Data System (ADS)

Wang, Ben-Xin; Xie, Qin; Dong, Guangxi; Huang, Wei-Qing

2018-02-01

A kind of triple-band polarization tunable terahertz absorber based on a metallic mirror and a metallic patch structure with two indentations spaced by an insulating medium layer is presented. Results prove that three near-perfect absorption peaks with average absorption coefficients of 98.25% are achieved when the polarization angle is equal to zero, and their absorptivities gradually decrease (and even disappear) by increasing the angle of polarization. When the polarization angle is increased to 90°, three new resonance modes with average absorption rates of 96.59% can be obtained. The field distributions are given to reveal the mechanisms of the triple-band absorption and the polarization tunable characteristics. Moreover, by introducing photosensitive silicon materials (its conductivity can be changed by the pump beam) in the indentations of the patch structure, the number of resonance peaks of the device can be actively tuned from triple-band to dual-band. The presented absorbers have potential applications, such as controlling thermal emissivity, and detection of polarization direction of the incident waves.

Polar Cap and Polar Cap Boundary Phenomena

DTIC Science & Technology

2009-06-25

of the high-latitude ionospheric plasma. Incoherent scatter radar and radio tomography measurements were used to directly observe the remnants of...On the relationship between thin Birkeland current arcs and reversed flow channels in the winter cusp/cleft ionosphere Moen J., Y. Rinne, H...current arcs in the winter cusp ionosphere above Svalbard. An RFE is a longitudinally elongated, 100–200 km wide channel, in which the flow direction is

Quantitative Mapping of Surface Texture on the Northern Polar Residual Cap of Mars

NASA Astrophysics Data System (ADS)

Milkovich, S. M.; Byrne, S.; Russell, P. S.

2010-12-01

The northern polar residual cap (NPRC) of Mars is a water ice deposit with a rough surface made up of pits, knobs, and linear depressions on scales of tens of meters [1]. This roughness manifests as a series of bright and dark patches in visible images. Spectral data indicate that the surface of the NPRC is composed of large-grained (and therefore old) water ice. Due to the presence of this old ice, it is thought that the NPRC is in a current state of net loss of material [2]. The NPRC provides a link between the current martian climate and the historical climate recorded within the layers of the underlying north polar layered deposits. By characterizing and mapping the variations in surface texture of the NPRC, we seek to understand what factors (distance from the pole, GCM and mesoscale wind direction predictions, etc) are currently at work in resurfacing the deposit, and may have been at work in shaping the layers below. Maps of NPRC texture wavelength and orientation are being produced from HiRISE images. Two-dimensional Fourier analysis is performed upon a 256 meter x 256 meter region (corresponding to 512 x 512 pixels in 0.5 cm/pxl images, or 1024 x 1024 pixels in 0.25 cm/pxl images) within each image analyzed. The dominant wavelength of the resulting peak power spectrum corresponds to the average size of a pit-knob pair in the image, and so is a proxy for the scale of the surface roughness. The orientation of the surface roughness (i.e., the orientation of a chain of pits and mounds) is measured from a narrow range of wavelengths encompassing the dominant wavelength. We will report on how the dominant wavelengths and orientations of this surface texture vary with location and what that implies for the processes currently shaping this landscape. [1] P. C. Thomas et al, Nature 404, 161-164, 2000 [2]Y. Langevin et al, Science 307, 5715, 1581-1584, 2005.

The 20 GHz circularly polarized, high temperature superconducting microstrip antenna array

NASA Technical Reports Server (NTRS)

Morrow, Jarrett D.; Williams, Jeffery T.; Long, Stuart A.; Wolfe, John C.

1994-01-01

The primary goal was to design and characterize a four-element, 20 GHz, circularly polarized microstrip patch antenna fabricated from YBa2Cu3O(x) superconductor. The purpose is to support a high temperature superconductivity flight communications experiment between the space shuttle orbiter and the ACTS satellite. This study is intended to provide information into the design, construction, and feasibility of a circularly polarized superconducting 20 GHz downlink or cross-link antenna. We have demonstrated that significant gain improvements can be realized by using superconducting materials for large corporate fed array antennas. In addition, we have shown that when constructed from superconducting materials, the efficiency, and therefore the gain, of microstrip patches increases if the substrate is not so thick that the dominant loss mechanism for the patch is radiation into the surface waves of the conductor-backed substrate. We have considered two design configurations for a superconducting 20 GHz four-element circularly polarized microstrip antenna array. The first is the Huang array that uses properly oriented and phased linearly polarized microstrip patch elements to realize a circularly polarized pattern. The second is a gap-coupled array of circularly polarized elements. In this study we determined that although the Huang array operates well on low dielectric constant substrates, its performance becomes extremely sensitive to mismatches, interelement coupling, and design imperfections for substrates with high dielectric constants. For the gap-coupled microstrip array, we were able to fabricate and test circularly polarized elements and four-element arrays on LaAlO3 using sputtered copper films. These antennas were found to perform well, with relatively good circular polarization. In addition, we realized a four-element YBa2Cu3O(x) array of the same design and measured its pattern and gain relative to a room temperature copper array. The patterns were essentially the same as that for the copper array. The measured gain of the YBCO antenna was greater than that for the room temperature copper design at temperatures below 82K, reaching a value of 3.4 dB at the lowest temperatures.

Vortex circulation and polarity patterns in closely packed cap arrays

DOE PAGES

Streubel, Robert; Kronast, Florian; Reiche, Christopher F.; ...

2016-01-25

For this work, we studied curvature-driven modifications to the magnetostatic coupling of vortex circulation and polarity in soft-magnetic closely packed cap arrays. A phase diagram for the magnetic remanent/transition states at room temperature as a function of diameter and thickness was assembled. For specimens with vortex remanent state (40 nm-thick Permalloy on 330 nm spherical nanoparticles), both vortex circulation and polarity were visualized. Intercap coupling upon vortex nucleation leads to the formation of vortex circulation patterns in closely packed arrays. The remanent circulation pattern can be tailored choosing the direction of the applied magnetic field with respect to the symmetrymore » axis of the hexagonal array. An even and random distribution of vortex polarity indicates the absence of any circulation-polarity coupling.« less

Circularly Polarized S Band Dual Frequency Square Patch Antenna Using Glass Microfiber Reinforced PTFE Composite

PubMed Central

Samsuzzaman, M.; Islam, M. T.; Arshad, Haslina; Mandeep, J. S.; Misran, N.

2014-01-01

Circularly polarized (CP) dual frequency cross-shaped slotted patch antenna on 1.575 mm thick glass microfiber reinforced polytetrafluoroethylene (PTFE) composite material substrate is designed and fabricated for satellite applications. Asymmetric cross-shaped slots are embedded in the middle of the square patch for CP radiation and four hexagonal slots are etched on the four sides of the square patch for desired dual frequency. Different substrate materials have been analysed to achieve the desired operating band. The experimental results show that the impedance bandwidth is approximately 30 MHz (2.16 GHz to 2.19 GHz) for lower band and 40 MHz (3.29 GHz to 3.33 GHz) for higher band with an average peak gain of 6.59 dBiC and 5.52 dBiC, respectively. Several optimizations are performed to obtain the values of the antenna physical parameters. Moreover, the proposed antenna possesses compactness, light weight, simplicity, low cost, and circularly polarized. It is an attractive candidate for dual band satellite antennas where lower band can be used for uplink and upper band can be used for downlink. PMID:24982943

Polar cap particle precipitation and aurora: Review and commentary

NASA Astrophysics Data System (ADS)

Newell, Patrick T.; Liou, Kan; Wilson, Gordon R.

2009-02-01

Polar rain has a beautiful set of symmetry properties, individually established, but not previously discussed collectively, which can be organized by a single unifying principle. The key polar rain properties are favored hemisphere (controlled by the interplanetary magnetic field Bx), dawn/dusk gradient (IMF By), merging rate (IMF Bz or more generally d[Phi]MP/dt), nightside/dayside gradient, and seasonal effect. We argue that all five properties involve variants on a single theme: the further downstream a field line exits the magnetosphere (or less directly points toward the solar wind electron heat flux), the weaker the polar rain. This effect is the result of the requirements of charge quasi-neutrality, and because the ion thermal velocity declines and the tailward ion bulk flow velocity rises moving down tail from the frontside magnetopause. Polar cap arcs (or more properly, high-latitude sun-aligned arcs) are largely complementary to the polar rain, occurring most frequently when the dayside merging rate is low, and thus when polar rain is weak. Sun-aligned arcs are often considered as originating either in the polar rain or the expansion of the plasma sheet into the polar cap. In fact three quite distinct types of sun-aligned high-latitude arcs exist, two common, and one rare. One type of arc occurs as intensifications of the polar rain, and is common, but weak, typically <0.1 ergs/cm2 s, and lacks associated ion precipitation. A second category of Sun-aligned arcs with energy flux >0.1 ergs/cm2 s usually occurs adjacent to the auroral oval, and includes ion precipitation. The plasma regime of these common, and at times intense, arcs is often distinct from the oval which they abut. Convection alone does not specify the open/closed nature of these arcs, because multiple narrow convection reversals are common around such arcs, and the arcs themselves can be embedded within flows that are either sunward or anti-sunward. These observational facts do not neatly fit into either a plasma sheet origin or a polar rain origin (e.g., the necessity to abut the auroral oval, and the presence of ions does not fit the properties of polar rain, which can in any event be nearly absent for northward interplanetary magnetic field). One theory is that such arcs are associated with merging tailward of the cusp. Both of these common types of sun-aligned arcs fade within about 30 min of a southward IMF turning. The third, and rarest, category of sun-aligned arcs are intense, well detached from the auroral oval, contain plasma sheet origin ion precipitation as well as electrons, and persist for hours after a southward turning. These intense detached sun-aligned arcs can rapidly cross the polar cap, sometimes multiple times. Most events discussed in the literature as "theta-aurora" do not fit into this category (for example, although they may appear detached in images, they abut the oval in particle data, and do not have the persistence of detached events under southward IMF turnings). It is possible that no single theory can account for all three types of sun-aligned arcs. Solar energetic particle (SEP) events are at times used to demarcate polar cap open/closed boundaries. Although this works at times, examples exist where this method fails (e.g., very quiet conditions for which SEP reaches below L=4), and the method should be used with caution. Finally, it is shown that, although it is rare, the polar cap can at times completely close.

Katabatic jumps in the Martian northern polar regions

NASA Astrophysics Data System (ADS)

Spiga, Aymeric; Smith, Isaac

2018-07-01

Martian polar regions host active regional wind circulations, such as the downslope katabatic winds which develop owing to near-surface radiative cooling and sloped topography. Many observations (stratigraphy from radar profiling, frost streaks, spectral analysis of ices) concur to show that aeolian processes play a key role in glacial processes in Martian polar regions. A spectacular manifestation of this resides in elongated clouds that forms within the polar spiral troughs, a series of geological depressions in Mars' polar caps. Here we report mesoscale atmospheric modeling in Martian polar regions making use of five nested domains operating a model downscaling from horizontal resolutions of twenty kilometers to 200 m in a typical polar trough. We show that strong katabatic jumps form at the bottom of polar troughs with an horizontal morphology and location similar to trough clouds, large vertical velocity (up to +3 m/s) and temperature perturbations (up to 20 K) propitious to cloud formation. This strongly suggests that trough clouds on Mars are caused by katabatic jumps forming within polar troughs. This phenomena is analogous to the terrestrial Loewe phenomena over Antarctica's slopes and coastlines, resulting in a distinctive "wall of snow" during katabatic events. Our mesoscale modeling results thereby suggest that trough clouds might be present manifestations of the ice migration processes that yielded the internal cap structure discovered by radar observations, as part of a "cyclic step" process. This has important implications for the stability and possible migration over geological timescales of water ice surface reservoirs-and, overall, for the evolution of Mars' polar caps over geological timescales.

Zonally averaged thermal balance and stability models for nitrogen polar caps on Triton

NASA Technical Reports Server (NTRS)

Stansberry, John A.; Lunine, J. I.; Porco, C. C.; Mcewen, A. S.

1990-01-01

Voyager four-color imaging data of Triton are analyzed to calculate the bolometric hemispheric albedo as a function of latitude and longitude. Zonal averages of these data have been incorporated into a thermal balance model involving insolation, reradiation, and latent heat of sublimation of N2 ice for the surface. The current average bolometric albedo of Triton's polar caps is 0.8, implying an effective temperature of 34.2 K and a surface pressure of N2 of 1.6 microbar for unit emissivity. This pressure is an order of magnitude lower than the surface pressure of 18 microbar inferred from Voyager data (Broadfoot et al., 1989; Conrath et al., 1989), a discrepancy that can be reconciled if the emissivity of the N2 on Triton's surface is 0.66. The model predicts that Triton's surface north of 15 deg N latitude is experiencing deposition of N2 frosts, as are the bright portions of the south polar cap near the equator. This result explains why the south cap covers nearly the entire southern hemisphere of Triton.

Fourier analysis of polar cap electric field and current distributions

NASA Technical Reports Server (NTRS)

Barbosa, D. D.

1984-01-01

A theoretical study of high-latitude electric fields and currents, using analytic Fourier analysis methods, is conducted. A two-dimensional planar model of the ionosphere with an enhanced conductivity auroral belt and field-aligned currents at the edges is employed. Two separate topics are treated. A field-aligned current element near the cusp region of the polar cap is included to investigate the modifications to the convection pattern by the east-west component of the interplanetary magnetic field. It is shown that a sizable one-cell structure is induced near the cusp which diverts equipotential contours to the dawnside or duskside, depending on the sign of the cusp current. This produces characteristic dawn-dusk asymmetries to the electric field that have been previously observed over the polar cap. The second topic is concerned with the electric field configuration obtained in the limit of perfect shielding, where the field is totally excluded equatorward of the auroral oval. When realistic field-aligned current distributions are used, the result is to produce severely distorted, crescent-shaped equipotential contours over the cap. Exact, analytic formulae applicable to this case are also provided.

Polar Cap Energy Deposition Events During the 5-6 August 2011 Magnetic Storm

NASA Astrophysics Data System (ADS)

Horvath, Ildiko; Lovell, Brian C.

2018-03-01

We study the 5-6 August 2011 storm for its energy deposition events occurring deep in the polar cap region, where the consequential localized intensifications of earthward directed Poynting flux led to the development of their related localized neutral density increases. For unraveling the underlying physical processes, we investigate the relations among Poynting flux intensifications, flow channels (FCs), and localized neutral density enhancements plus the nature of the underlying reconnection events. Observational results demonstrate Poynting flux increase deep in the polar cap in a FC-2 type FC during magnetopause reconnections and in a FC-4 type FC during lobe reconnections. During the latter stages of these different types of reconnection events, energy/momentum transfer occurred along old-open field lines and commonly led to the development of localized neutral density increases during their respective upwelling events fueled by field-aligned currents and above/within these polar FCs. The prevailing BY domination and the pulsed nature of this storm created favorable conditions for the development of these FC-2 and FC-4 types in the sunlit northern summer hemisphere and caused the observed Poynting flux intensifications deep in the polar cap. The solar wind source of these reconnections taking place along old-open field lines was situated in the high-latitude boundary layer. Thus, the high-latitude boundary layer dynamo provided a vigorous source of energy/momentum transfer during the latter-stage reconnections unfolding along old-open field lines.

Observations of the northern seasonal polar cap on Mars: I. Spring sublimation activity and processes

USGS Publications Warehouse

Hansen, C.J.; Byrne, S.; Portyankina, G.; Bourke, M.; Dundas, C.; McEwen, A.; Mellon, M.; Pommerol, A.; Thomas, N.

2013-01-01

Spring sublimation of the seasonal CO2 northern polar cap is a dynamic process in the current Mars climate. Phenomena include dark fans of dune material propelled out onto the seasonal ice layer, polygonal cracks in the seasonal ice, sand flow down slipfaces, and outbreaks of gas and sand around the dune margins. These phenomena are concentrated on the north polar erg that encircles the northern residual polar cap. The Mars Reconnaissance Orbiter has been in orbit for three Mars years, allowing us to observe three northern spring seasons. Activity is consistent with and well described by the Kieffer model of basal sublimation of the seasonal layer of ice applied originally in the southern hemisphere. Three typical weak spots have been identified on the dunes for escape of gas sublimed from the bottom of the seasonal ice layer: the crest of the dune, the interface of the dune with the interdune substrate, and through polygonal cracks in the ice. Pressurized gas flows through these vents and carries out material entrained from the dune. Furrows in the dunes channel gas to outbreak points and may be the northern equivalent of southern radially-organized channels (“araneiform” terrain), albeit not permanent. Properties of the seasonal CO2 ice layer are derived from timing of seasonal events such as when final sublimation occurs. Modification of dune morphology shows that landscape evolution is occurring on Mars today, driven by seasonal activity associated with sublimation of the seasonal CO2 polar cap.

The Strategy for Polar Exploration: Planes, Trains, and Automobiles

NASA Technical Reports Server (NTRS)

Stoker, C.; Lemke, L.

2000-01-01

The polar regions are both interesting and challenging to explore. The record of climate history and the behavior of Martian volatiles over time are thought to be contained in the polar terrains. Furthermore, the polar regions are probably the best environment to search for evidence of living organisms on Mars because they have both the presence of water ice and summertime temperatures at the surface that exceed the freezing point of water. In addition, melting at the base of the polar caps is predicted to occur which could result in a deep aquifer beneath the polar caps. Such an aquifer is potentially another habitat for life. Clearly, assessing the question of volaties, climate, and life in the polar regions would benefit from landed missions that can sample and interact with the surface. Mobility on the surface is also important for polar exploration due to the apparent wide diversity of terrains that occur on both local and regional scales. Additional information is contained in the original extended abstract.

Mars Polar Thermal Inertia and Albedo Properties Using TES Data

NASA Astrophysics Data System (ADS)

Scherbenski, J. M.; Paige, D. A.

2002-12-01

We present north and south polar thermal inertia and albedo maps derived from MGS TES observations. The maps were derived using the same robust approach developed to make polar thermal and inertia and albedo maps using IRTM observationsby Paige, Bachman, and Keegan (1994) and Paige and Keegan (1994). The data processing approach involved reading TES reduced data records in PDS format using the Vanilla software tool, and sending the data down a processing pipeline that constrains and bins the data, and compares it to the results of a diurnal and seasonal thermal model to obtain the best fit thermal inertia and apparent albedo. To facilitate comparison, the TES maps were created at the same Ls ranges as the published IRTM maps using TES spectral surface temperature results. The north polar maps used TES nadir observations obtained during a 50-day period from Ls 98.39 to Ls 121.25. The south polar maps used TES nadir observations obtained during a 30-day period from Ls 321.58 to 338.07. The creation of these maps employ a basic thermal model that does not include the effects of the atmosphere, as well as a one-dimensional radiative-convective model that does include the effects of the atmosphere. The spatial resolution of the north polar maps is 0.1 degrees of latitude and 1.0 degrees of longitude. The spatial resolution of the south polar maps is 2 degrees of latitude and 2 degrees of longitude. The TES north polar maps show the residual cap area in significantly greater detail than has been available previously. The IRTM maps showed that the north polar sand sea that surrounds the cap has unusually low thermal inertia. The TES maps confirm this conclusion, but also show that the dark renetrant features in chama boreal and elsewhere on the cap also have low thermal inertias. This strongly supports the proposal that these dark rentrants are the sources of the dune material. The TES maps also show that the darker layered deposits which are found at the periphery of the cap have high thermal inertias, just like the brighter water ice deposits elsewhere on the cap. This strongly supports the conclusion that even the darker north polar layered deposits are mostly ice. The TES south polar maps show similar features to those observed by IRTM, including the presence of a low thermal inertia region centered on the south pole, and a region of anomalously high apparent albedo southward of 78 degrees latitude. References: Paige, D. A., J. E. Bachman and K. D. Keegan, Thermal and albedo mapping of the polar regions of Mars using Viking thermal mapper observations: 1. North polar region, J. Geophys. Res. 99, 24,959-25,991, 1994. Paige, D. A. and K. D. Keegan, Thermal and albedo mapping of the polar regions of Mars using Viking thermal mapper observations: 1. South polar region, J. Geophys. Res. 99, 24,993-26,013, 1994.

Comparison of Mars Northern Cap Edge Advance and Recession Rates over the Last 6 Mars Years

NASA Astrophysics Data System (ADS)

Titus, T. N.; Cushing, G. E.; Langevin, Y.; Brown, A. J.; Themis Science Team; CRISM Science Team

2011-12-01

The most observable parameter that describes the Mars polar seasonal caps is their size, which has been measured since the days of Herschel. The advance and retreat of the polar cap from year to year may exhibit many clues to help elucidate little understood physical processes. For example, summertime heat storage in the regolith could delay the onset of seasonal CO2 cap formation. The evolution of the seasonal cap could also be directly affected by the thermal inertia of the near-surface regolith and place constraints on the depth of the ice table. Parameterizations of the seasonal cap edges provide useful constraints on atmospheric GCMs and mesoscale models. Longitudinally resolving the cap edges as they advance and retreat constrains the times when zonal means are appropriate and when longitudinal asymmetries make zonal means invalid. These same kinds of parameterizations can also be used when modeling other data that have low spatial resolutions, such as Gamma Ray Spectrometer (GRS )and Neutron Spectrometer (NS) data. By knowing where the cap edge should be, coarse spatial data can correct for subpixel mixing caused by large point-spread functions including both frosted and frost-free areas. The northern cap exhibits a near symmetric retreat, which has been well characterized at visible wavelengths by both telescopic and spacecraft observations. However, the advance of the cap has not been well characterized until the 21st century. Kieffer and Titus (2001) have used zonal means to observe surface temperature and visible bolometric albedo variations with season using MGS/TES. The TES thermal observations show an almost perfectly symmetrical advance; i.e., condensation at consistent latitude across all longitudes, with the most northern edge of the seasonal cap occurring between longitudes 245°E to 265°E and the most southern edge of the seasonal cap occurring between 280°E and 30°E. The advance of the northern cap typically leads the advance of the edge of polar night by 10° of latitude. The northern spring retreat is also nearly symmetric in both visual and thermal observations, and follows the same small asymmetries as seen in the advance. In addition to four Mars years of seasonal observations by TES and MOC, the northern seasonal cap was observed in detail by OMEGA in 2004 and 2006. The bright ring at intermediate temperatures (~ 180 K) observed by TES (Kieffer and Titus, 2001) in early spring is confirmed by OMEGA as resulting from H2O ice frost, with a sublimation front which lags by up to 4° in latitude south of the CO2 ice sublimation front. H2O ice contamination of CO2 ice is ubiquitous in the northern seasonal cap at all stages of its evolution. H2O ice dominates the spectral signatures over most of the seasonal cap after mid-spring. This paper will compare the inter-annual variations in the advance and recession of the Mars northern polar cap over the last 6 Mars years using TES, THEMIS, OMEGA, and CRISM.

TES premapping data: Slab ice and snow flurries in the Martian north polar night

USGS Publications Warehouse

Titus, T.N.; Kieffer, H.H.; Mullins, K.F.; Christensen, P.R.

2001-01-01

In the 1970s, Mariner and Viking spacecraft observations of the north polar region of Mars revealed polar brightness temperatures that were significantly below the expected kinetic temperatures for CO2 sublimation. For the past few decades, the scientific community has speculated as to the nature of these Martian polar cold spots. Thermal Emission Spectrometer (TES) thermal spectral data have shown these cold spots to result largely from fine-grained, CO2 and have constrained most of these cold spots to the surface (or near-surface). Cold spot formation is strongly dependent on topography, forming preferentially near craters and on polar slopes. TES data, combined with Mars Orbiter Laser Altimeter (MOLA) cloud data, suggest atmospheric condensates form a small fraction of the observed cold spots. TES observations of spectra close to a blackbody indicate that another major component of the polar cap is slab CO2 ice; these spectrally bland regions commonly have a low albedo. The cause is uncertain but may result from most of the light being reflected toward the specular direction, from the slab ice being intrinsically dark, or from it being transparent. Regions of the cap where the difference between the brightness temperatures at 18 ??m (T18) and 25 ??m (T25) is less than 5?? are taken to indicate deposits of slab ice. Slab ice is the dominant component of the polar cap at latitudes outside of the polar night. Copyright 2001 by the American Geophysical Union.

High LMD GCM Resolution Modeling of the Seasonal Evolution of the Martian Northern Permanent Cap: Comparison with Mars Express OMEGA Observations

NASA Technical Reports Server (NTRS)

Levrard, B.; Forget, F.; Montmessin, F.; Schmitt, B.; Doute, S.; Langevin, Y.; Poulet, F.; Bibring, J. P.; Gondet, B.

2005-01-01

Analyses of imaging data from Mariner, Viking and MGS have shown that surface properties (albedo, temperature) of the northern cap present significant differences within the summer season and between Mars years. These observations include differential brightening and/or darkening between polar areas from the end of the spring to midsummer. These differences are attributed to changes in grain size or dust content of surface ice. To better understand the summer behavior of the permanent northern polar cap, we perfomed a high resolution modeling (approximately 1 deg x 1 deg.) of northern cap in the Martian Climate/water cycle as simulated by the Laboratoire de Meteorologie Dynamique (LMD) global climate model. We compare the predicted properties of the surface ice (ice thickness, temperature) with the Mars Express Omega summer observations of the northern cap. albedo and thermal inertia svariations model. In particular, albedo variations could be constrained by OMEGA data. Meteorological predictions of the LMD GCM wil be presented at the conference to interpret the unprecedently resolved OMEGA observations. The specific evolution of regions of interest (cap center, Chasma Boreal...) and the possibility of late summer global cap brightening will be discussed.

Thermal and albedo mapping of the north and south polar regions of Mars

NASA Technical Reports Server (NTRS)

Paige, D. A.; Keegan, K. D.

1991-01-01

The first maps of the thermal properties of the north and south polar region of Mars are presented. The maps complete the mapping of the entire planet. The maps for the north polar region were derived from Viking Infrared Thermal Mapper (IRTM) observations obtained from 10 Jun. to 30 Sep. 1978. This period corresponds to the early summer season in the north, when the north residual water ice cap was exposed, and the polar surface temperatures were near their maximum. The maps in the south were derived from observations obtained between 24 Aug. to 23 Sep. 1977. This period corresponds to the late summer season in the south, when the seasonal polar cap had retreated to close to its residual configuration, and the second global dust storm of 1977 had largely subsided. The major results concerning the following topics are summarized: (1) surface water ice; (2) polar dune material; and (3) dust deposits.

Esr Observations of Tid In The Polar Cusp/cap Ionosphere

NASA Astrophysics Data System (ADS)

Yin, F.; Ma, S. Y.; Schlegel, K.

EISCAT-Svalbard radar provides new opportunity to study TIDs in the polar cusp/cap ionosphere. Propagation characteristics of AGW-caused TIDs in quiet days are stud- ied by means of maximum entropy cross-spectral analysis of ESR CP1 and CP2 data. Apparent vertical wave-number of the TIDs as a function of height and the horizontal wave-number vector are obtained for main period of disturbances. It is observed as the first time that some of TIDs in the polar cap/cusp ionosphere can propagate vertically from the height lower than 200 km up to as high as about 700 km with little attenu- ation. In the auroral ionosphere, however, they usually fade away below 500 km. In the region from about 100 to 180 km height, downward propagating mode is seen ob- viously. The possible relations of the TIDs with cusp particle precipitation and upper E-region heating are discussed.

Summer South Polar Cap

NASA Technical Reports Server (NTRS)

2004-01-01

13 April 2004 The martian south polar residual ice cap is composed mainly of frozen carbon dioxide. Each summer, a little bit of this carbon dioxide sublimes away. Pits grow larger, and mesas get smaller, as this process continues from year to year. This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a view of a small portion of the south polar cap as it appeared in mid-summer in January 2004. The dark areas may be places where the frozen carbon dioxide contains impurities, such as dust, or places where sublimation of ice has roughened the surface so that it appears darker because of small shadows cast by irregularities in the roughened surface. The image is located near 86.9oS, 7.6oW. The image covers an area about 3 km (1.9 mi) across. Sunlight illuminates the scene from the upper left.

CO2 cycle

USGS Publications Warehouse

Titus, Timothy N.; Byrne, Shane; Colaprete, Anthony; Forget, Francois; Michaels, Timothy I.; Prettyman, Thomas H.

2017-01-01

This chapter discusses the use of models, observations, and laboratory experiments to understand the cycling of CO2 between the atmosphere and seasonal Martian polar caps. This cycle is primarily controlled by the polar heat budget, and thus the emphasis here is on its components, including solar and infrared radiation, the effect of clouds (water- and CO2-ice), atmospheric transport, and subsurface heat conduction. There is a discussion about cap properties including growth and regression rates, albedos and emissivities, grain sizes and dust and/or water-ice contamination, and curious features like cold gas jets and araneiform (spider-shaped) terrain. The nature of the residual south polar cap is discussed as well as its long-term stability and ability to buffer atmospheric pressures. There is also a discussion of the consequences of the CO2 cycle as revealed by the non-condensable gas enrichment observed by Odyssey and modeled by various groups.

The CAMEO barium release - E/parallel/ fields over the polar cap

NASA Technical Reports Server (NTRS)

Heppner, J. P.; Miller, M. L.; Pongratz, M. B.; Smith, G. M.; Smith, L. L.; Mende, S. B.; Nath, N. R.

1981-01-01

Four successive thermite barium releases at an altitude of 965 km over polar cap invariant latitudes 84 to 76 deg near magnetic midnight were conducted from the orbiting second stage of the vehicle that launched Nimbus 7; the releases were made as part of the CAMEO (Chemically Active Material Ejected in Orbit) program. This was the first opportunity to observe the behavior of conventional barium release when conducted at orbital velocity in the near-earth magnetic field. The principal unexpected characteristic in the release dynamics was the high, 1.4 to 2.6 km/s, initial Ba(+) expansion velocity relative to an expected velocity of 0.9 km/s. Attention is also given to neutral cloud expansion, initial ion cloud expansion, convective motion, and the characteristics of field-aligned motion. The possibility of measuring parallel electric fields over the polar cap by observing perturbations in the motion of the visible ions is assessed.

Low-Energy Electron Effects on the Polar Wind Observed by the POLAR Spacecraft

NASA Technical Reports Server (NTRS)

Horwitz, J. L.; Su, Y.-J.; Dors, E. E.; Moore, Thomas E.; Giles, Barbara L.; Chandler, Michael O.; Craven, Paul D.; Chang, S.-W.; Scudder, J.

1998-01-01

Large ion outflow velocity variation at POLAR apogee have been observed. The observed H+ flow velocities were in the range of 23-110 km/s and 0+ flow velocities were in the range of 5-25 km/s. These velocity ranges lie between those predicted by simulations of the photoelectron-driven polar wind and "baseline" polar wind. The electric current contributions of the photoelectrons and polar rain are expected to control the size and altitude of an electric potential drop which accelerates the polar wind at relatively high altitudes. In this presentation, we compare polar wind characteristics observed near 5000 km and 8 RE altitudes by the Thermal Ion Dynamics Experiment (TIDE) with measurements of low-energy electrons sampled by HYDRA, both from the POLAR spacecraft, to examine possible effects of the polar rain and photoelectrons on the polar wind. Both correlations and anti-correlations are found between the polar wind velocities and the polar rain fluxes at POLAR apogee during different polar cap crossings. Also, the low-altitude upward/downward photoelectron spectra are used to estimates the potential drops above the spacecraft. We interpret these observations in terms of the effects that both photoelectrons and polar rain may have on the electric potential and polar wind acceleration along polar cap magnetic field lines.

Mars seasonal polar caps as a test of the equivalence principle

NASA Astrophysics Data System (ADS)

Rubincam, David Parry

2011-08-01

The seasonal polar caps of Mars can be used to test the equivalence principle in general relativity. The north and south caps, which are composed of carbon dioxide, wax and wane with the seasons. If the ratio of the inertial (passive) to gravitational (active) masses of the caps differs from the same ratio for the rest of Mars, then the equivalence principle fails, Newton’s third law fails, and the caps will pull Mars one way and then the other with a force aligned with the planet’s spin axis. This leads to a secular change in Mars’s along-track position in its orbit about the Sun, and to a secular change in the orbit’s semimajor axis. The caps are a poor Eötvös test of the equivalence principle, being 4 orders-of-magnitude weaker than laboratory tests and 7 orders-of-magnitude weaker than that found by lunar laser ranging; the reason is the small mass of the caps compared to Mars as a whole. The principal virtue of using Mars is that the caps contain carbon, an element not normally considered in such experiments. The Earth with its seasonal snow cover can also be used for a similar test.

Suppression of gate leakage current in in-situ grown AlN/InAlN/AlN/GaN heterostructures based on the control of internal polarization fields

NASA Astrophysics Data System (ADS)

Kotani, Junji; Yamada, Atsushi; Ishiguro, Tetsuro; Yamaguchi, Hideshi; Nakamura, Norikazu

2017-03-01

This paper investigates the gate leakage characteristics of in-situ AlN capped InAlN/AlN/GaN heterostructures grown by metal-organic vapor phase epitaxy. It was revealed that the leakage characteristics of AlN capped InAlN/AlN/GaN heterostructures are strongly dependent on the growth temperature of the AlN cap. For an AlN capped structure with an AlN growth temperature of 740 °C, the leakage current even increased although there exists a large bandgap material on InAlN/AlN/GaN heterostructures. On the other hand, a large reduction of the gate leakage current by 4-5 orders of magnitudes was achieved with a very low AlN growth temperature of 430 °C. X-ray diffraction analysis of the AlN cap grown at 740 °C indicated that the AlN layer is tensile-strained. In contrast to this result, the amorphous structure was confirmed for the AlN cap grown at 430 °C by transmission electron microscopy. Furthermore, theoretical analysis based on one-dimensional band simulation was carried out, and the large increase in two-dimensional electron gas (2DEG) observed in Hall measurements was well reproduced by taking into account the spontaneous and piezo-electric polarization in the AlN layer grown at 740 °C. For the AlN capped structure grown at 430 °C, it is believed that the reduced polarization field in the AlN cap suppressed the penetration of 2DEG into the InAlN barrier layer, resulting in a small impact on 2DEG mobility and density. We believe that an in-situ grown AlN cap with a very low growth temperature of 430 °C is a promising candidate for high-frequency/high-power GaN-based devices with low gate leakage current.

Host-guest chemistry for tuning colloidal solubility, self-organization and photoconductivity of inorganic-capped nanocrystals

NASA Astrophysics Data System (ADS)

Bodnarchuk, Maryna I.; Yakunin, Sergii; Piveteau, Laura; Kovalenko, Maksym V.

2015-12-01

Colloidal inorganic nanocrystals (NCs), functionalized with inorganic capping ligands, such as metal chalcogenide complexes (MCCs), have recently emerged as versatile optoelectronic materials. As-prepared, highly charged MCC-capped NCs are dispersible only in highly polar solvents, and lack the ability to form long-range ordered NC superlattices. Here we report a simple and general methodology, based on host-guest coordination of MCC-capped NCs with macrocyclic ethers (crown ethers and cryptands), enabling the solubilization of inorganic-capped NCs in solvents of any polarity and improving the ability to form NC superlattices. The corona of organic molecules can also serve as a convenient knob for the fine adjustment of charge transport and photoconductivity in films of NCs. In particular, high-infrared-photon detectivities of up to 3.3 × 1011 Jones with a fast response (3 dB cut-off at 3 kHz) at the wavelength of 1,200 nm were obtained with films of PbS/K3AsS4/decyl-18-crown-6 NCs.

Drill/borescope System for the Mars Polar Pathfinder

NASA Technical Reports Server (NTRS)

Paige, D. A.; Wood, S. E.; Vasavada, A. R.

1993-01-01

The primary goals of the Mars Polar Pathfinder (MPP) Discovery Mission are to characterize the composition and structure of Mars' north polar ice cap, and to determine whether a climate record may be preserved in layers of ice and dust. The MPP would land as close as possible to the geographic north pole of Mars and use a set of instruments similar to those used by glaciologists to study polar ice caps on Earth: a radar sounder, a drill/borescope system, and a thermal probe. The drill/borescope system will drill approximately 50 cm into the surface and image the sides of the hole at 10 micron resolution for compositional and stratigraphic analysis. Several uncertainties have guided the development of this instrument, and they are discussed.

Diagnostic performance of the atopy patch test with inhalant allergens.

PubMed

Fuiano, N; Diddi, G; Delvecchio, M; Incorvaia, C

2015-01-01

This study evaluated the diagnostic performance of the atopy patch test (APT) compared with skin prick testing (SPT) and in vitro IgE measurement in a large group of patients with atopic dermatitis (AD) with or without respiratory symptoms (RS). The study included 521 patients (292 males, 229 females; age, 0.5-18 years; median age, 6 years) with AD and RS with different clinical presentations: current AD, 47 patients (Group A); current AD and RS, 72 patients (Group B), past AD and RS, 69 patients (Group C); and RS only, 280 patients (Group D). Fifty-three healthy individuals served as controls. All participants underwent the APT, SPT, and CAP/RAST with the most common inhalant allergens. The presence of a control group allowed calculation of specificity and positive and negative predictive values. A significant difference was found for a positive APT versus both SPT and CAP/RAST (P < .0001) but not for SPT versus CAP/RAST. The differences for APT were significant in all group comparisons except group B vs C and group C vs D. In the control group, the APT was positive in 2% of cases (specificity of 96.2%), SPT was positive in 6% of cases (specificity of 88.4%), and CAP/RAST was positive in 4% of cases (specificity of 92.5%). In young patients sensitized to inhalant allergens with AD in addition to RS, the APT has a superior diagnostic performance to SPT and in vitro IgE measurement.

Water Cycling in the North Polar Region of Mars

NASA Technical Reports Server (NTRS)

Tamppari, L. K.; Smith, M. D.; Bass, D. S.

2003-01-01

To date, there has been no comprehensive study to understand the partitioning of water into vapor and ice clouds, and the associated effects of dust and surface temperature in the north polar region. Ascertaining the degree to which water is transported out of the cap region versus within the cap region will give much needed insight into the overall story of water cycling on a seasonal basis. In particular, understanding the mechanism for the polar cap surface albedo changes would go along way in comprehending the sources and sinks of water in the northern polar region. We approach this problem by examining Thermal Emission Spectrometer (TES) atmospheric and surface data acquired in the northern summer season and comparing it to Viking data when possible. Because the TES instrument spans the absorption bands of water vapor, water ice, dust, and measures surface temperature, all three aerosols and surface temperature can be retrieved simultaneously. This presentation will show our latest results on the water vapor, water-ice clouds seasonal and spatial distributions, as well as surface temperatures and dust distribution which may lend insight into where the water is going.

Multiport Circular Polarized RFID-Tag Antenna for UHF Sensor Applications.

PubMed

Zaid, Jamal; Abdulhadi, Abdulhadi; Kesavan, Arun; Belaizi, Yassin; Denidni, Tayeb A

2017-07-05

A circular polarized patch antenna for UHF RFID tag-based sensor applications is presented, with the circular polarization (CP) generated by a new antenna shape, an asymmetric stars shaped slotted microstrip patch antenna (CP-ASSSMP). Four stars etched on the patch allow the antenna's size to be reduced by close to 20%. The proposed antenna is matched with two RFID chips via inductive-loop matching. The first chip is connected to a resistive sensor and acts as a sensor node, and the second is used as a reference node. The proposed antenna is used for two targets, serving as both reference and sensor simultaneously, thereby eliminating the need for a second antenna. Its reader can read the RFID chips at any orientation of the tag due to the CP. The measured reading range is about 25 m with mismatch polarization. The operating frequency band is 902-929 MHz for the two ports, which is covered by the US RFID band, and the axial-ratio bandwidth is about 7 MHz. In addition, the reader can also detect temperature, based on the minimum difference in the power required by the reference and sensor.

Multiport Circular Polarized RFID-Tag Antenna for UHF Sensor Applications

PubMed Central

Zaid, Jamal; Abdulhadi, Abdulhadi; Kesavan, Arun; Belaizi, Yassin; Denidni, Tayeb A.

2017-01-01

A circular polarized patch antenna for UHF RFID tag-based sensor applications is presented, with the circular polarization (CP) generated by a new antenna shape, an asymmetric stars shaped slotted microstrip patch antenna (CP-ASSSMP). Four stars etched on the patch allow the antenna’s size to be reduced by close to 20%. The proposed antenna is matched with two RFID chips via inductive-loop matching. The first chip is connected to a resistive sensor and acts as a sensor node, and the second is used as a reference node. The proposed antenna is used for two targets, serving as both reference and sensor simultaneously, thereby eliminating the need for a second antenna. Its reader can read the RFID chips at any orientation of the tag due to the CP. The measured reading range is about 25 m with mismatch polarization. The operating frequency band is 902–929 MHz for the two ports, which is covered by the US RFID band, and the axial-ratio bandwidth is about 7 MHz. In addition, the reader can also detect temperature, based on the minimum difference in the power required by the reference and sensor. PMID:28678178

An examination of Mars' north seasonal polar cap using MGS: Composition and infrared radiation balance

NASA Astrophysics Data System (ADS)

Hansen, Gary B.

2013-08-01

A detailed analysis of data from one revolution of the Mars Global Surveyor (MGS) is presented. Approximately 80% of this revolution observes the mid-winter northern seasonal polar cap, which covers the surface to <60°N, and which is predominantly within polar night. The surface composition and temperature are determined through analysis of 6-50 μm infrared spectra from the Thermal Emission Spectrometer (TES). The infrared radiative balance, which is the entire heat balance in the polar night except for small subsurface and atmospheric advection terms, is calculated for the surface and atmospheric column. The primary constituent, CO2 ice, also dominates the infrared spectral properties by variations in its grain size and by admixtures of dust and water ice, which cause large variations in the 20-50 μm emissivity. This is modified by incomplete areal coverage, and clouds or hazes. This quantitative analysis reveals CO2 grain radii ranging from ˜100 μm in isolated areas, to 1-5 mm in more widespread regions. The water ice content varies from none to about one part per thousand by mass, with a clear increase towards the periphery of the polar cap. The dust content is typically a few parts per thousand by mass, but is as much as an order of magnitude less abundant in "cold spot" regions, where the low emissivity of pure CO2 ice is revealed. This is the first quantitative analysis of thermal spectra of the seasonal polar cap and the first to estimate water ice content. Our models show that the cold spots represent cleaner, dust-free ice rather than finer grained ice than the background. Our guess is that the dust in cold spots is hidden in the center of the CO2 frost particles rather than not present. The fringes of the cap have more dust and water ice, and become patchy, with warmer water snow filling the gaps on the night side, and warmer bare soil on the day side. A low optical depth (<1 in the visible) water ice atmospheric haze is apparent on the night side, and appears with smaller optical depth on the day side. The infrared radiative balance at the surface is typically 20-25 W m-2 in the central polar cap, with ˜25% dips in the regions of dust-free CO2. The atmospheric radiative terms are typically 1-3 W m-2.

Frozen Frozen CO2

NASA Technical Reports Server (NTRS)

2005-01-01

2 October 2005 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a view of frozen carbon dioxide in the south polar residual cap of Mars. Much of the south polar residual cap exhibits terrain that resembles stacks of sliced Swiss cheese, but this portion of the cap lacks the typical, circular depressions that characterize much of the region. Carbon dioxide on Mars freezes at a temperature of around 148 Kelvins, which is -125oC or about -193oF.

Location near: 87.2oS, 28.4oW Image width: width: 3 km (1.9 mi) Illumination from: upper left Season: Southern Spring

Regional Climate Modeling of Volcanic Eruptions and the Arctic Climate System: A Baffin Island Case Study

NASA Astrophysics Data System (ADS)

Losic, M.; Robock, A.

2010-12-01

It is well-understood that the effects of volcanic aerosol loading into the stratosphere are transient, with global cooling lasting only a few years after a single large eruption. Geological evidence collected from Northern Baffin Island, Canada, suggests ice cap growth began soon after a succession of several large eruptions in the 13th century, and they did not start to melt until roughly a century ago. We investigate which feedbacks allowed these ice caps to be maintained long after the transient forcing of the volcanic aerosols, by conducting sensitivity studies with the Weather Research and Forecasting (WRF) Model and Polar WRF, a version of WRF developed specifically for the polar regions. Results from an ensemble of month-long regional simulations over Baffin Island suggest that better treatment of snow and ice in Polar WRF improves our regional climate simulations. Thus, sensitivity test results from decade-long runs with imposed changes to boundary condition temperatures and carbon dioxide concentrations using Polar WRF are presented. Preliminary findings suggest that not only large scale but localized climate feedbacks play an important role in the responses of the ice caps after temperature and carbon dioxide forcings are applied. The results from these and further sensitivity tests will provide insight into the influence of regional feedbacks on the persistence of these ice caps long after the 13th century eruptions.

Telescopic observations - Visual, photographic, polarimetric. [of planet Mars

NASA Technical Reports Server (NTRS)

Martin, Leonard J.; James, Philip B.; Dollfus, Audouin; Iwasaki, Kyosuke; Beish, Jeffrey D.

1992-01-01

The paper divides the high points of telescopic observations of Mars into three time periods: historical, missions support (recent), and present. Particular attention is given to visual and photographic observations, with brief discussions of spectroscopic and polarization studies. Major topics of Martian phenomena included are albedo features, polar caps, dust storms, and white clouds. The interannual variability of the recessions of seasonal polar caps has been compared to dust storm activity, but this relationship remains uncertain. Only a very limited number of canals can be related to markings on the Viking images. The remainder are argued to be optical illusions created by observers pushing their perceived resolution beyond practical limits.

The sun's magnetic sector structure

NASA Technical Reports Server (NTRS)

Svalgaard, L.; Wilcox, J. M.; Scherrer, P. H.; Howard, R.

1975-01-01

The synoptic appearance of solar magnetic sectors is studied using 454 sector boundaries observed at earth during 1959-1973. The sectors are clearly visible in the photospheric magnetic field. Sector boundaries can be clearly identified as north-south running demarcation lines between regions of persistent magnetic polarity imbalances. These regions extend up to about 35 deg of latitude on both sides of the equator. They generally do not extend into the polar caps. The polar cap boundary can be identified as an east-west demarcation line marking the poleward limit of the sectors. The typical flux imbalance for a magnetic sector is about 4 x 10 to the 21st power Maxwells.

MECA Symposium on Mars: Evolution of its Climate and Atmosphere

NASA Technical Reports Server (NTRS)

Baker, Victor (Editor); Carr, Michael (Editor); Fanale, Fraser (Editor); Greeley, Ronald (Editor); Haberle, Robert (Editor); Leovy, Conway (Editor); Maxwell, Ted (Editor)

1987-01-01

The geological, atmospheric, and climatic history of Mars is explored in reviews and reports of recent observational and interpretive investigations. Topics addressed include evidence for a warm wet climate on early Mars, volatiles on Earth and on Mars, CO2 adsorption on palagonite and its implications for Martian regolith partitioning, and the effect of spatial resolution on interpretations of Martian subsurface volatiles. Consideration is given to high resolution observations of rampart craters, ring furrows in highland terrains, the interannual variability of the south polar cap, telescopic observations of the north polar cap and circumpolar clouds, and dynamical modeling of a planetary wave polar warming mechanism.

Design of a dual linear polarization antenna using split ring resonators at X-band

NASA Astrophysics Data System (ADS)

Ahmed, Sadiq; Chandra, Madhukar

2017-11-01

Dual linear polarization microstrip antenna configurations are very suitable for high-performance satellites, wireless communication and radar applications. This paper presents a new method to improve the co-cross polarization discrimination (XPD) for dual linear polarized microstrip antennas at 10 GHz. For this, three various configurations of a dual linear polarization antenna utilizing metamaterial unit cells are shown. In the first layout, the microstrip patch antenna is loaded with two pairs of spiral ring resonators, in the second model, a split ring resonator is placed between two microstrip feed lines, and in the third design, a complementary split ring resonators are etched in the ground plane. This work has two primary goals: the first is related to the addition of metamaterial unit cells to the antenna structure which permits compensation for an asymmetric current distribution flow on the microstrip antenna and thus yields a symmetrical current distribution on it. This compensation leads to an important enhancement in the XPD in comparison to a conventional dual linear polarized microstrip patch antenna. The simulation reveals an improvement of 7.9, 8.8, and 4 dB in the E and H planes for the three designs, respectively, in the XPD as compared to the conventional dual linear polarized patch antenna. The second objective of this paper is to present the characteristics and performances of the designs of the spiral ring resonator (S-RR), split ring resonator (SRR), and complementary split ring resonator (CSRR) metamaterial unit cells. The simulations are evaluated using the commercial full-wave simulator, Ansoft High-Frequency Structure Simulator (HFSS).

Nature and Stability of the Martian Seasonal Water Cycle

NASA Astrophysics Data System (ADS)

Richardson, M. I.; Wilson, R. J.

2001-12-01

Which components control the contemporary water cycle and what is the nature of the control mechanisms? These questions are at the heart of understanding how the Martian exchangeable water budget adjusts to perturbations and changes in the climate system. Analysis of a water cycle model embedded in the GFDL Mars GCM provides a paradigm for the water cycle as a feedback system, providing information on the important control points and response times. Much information on this system derives from monitoring the evolution towards steady state--one that resembles the observed water vapour and ice cloud distributions. The most important exchange balance in the system is that between the northern polar atmosphere and the rest of the planet. As the major net source for water, the northern residual water ice cap is active during summer, in the window of time between the sublimation and recondensation of the seasonal CO2 cap. At this time, water is exported from the northern polar atmosphere at a rate determined by the mixing capacity of the atmosphere and the amount of water held in the polar atmosphere. The latter is determined by the cap surface temperature. During the remainder of the year, water is returned to the pole. This return flux is determined by the atmospheric mixing capacity and the amount of water vapour held in the tropical and winter extratropical atmosphere. Steady-state is achieved when these fluxes balance. For a given climate state (and a roughly repeatable annual cycle of mixing), the outflux and influx of polar water are controlled by separate variables. Holding the cap temperature constant, the outflux will remain constant. Any perturbation to the global water budget will result in a change in the return flux that tends to oppose the sense of the perturbation--the perturbation will be damped. In the same way, a change in cap temperature (e.g. associated with a change in albedo) will result in changed water outflow. Again, this will tend to change the non-polar water vapour budget and hence the polar water influx so as to develop a new steady-state. It is important to note that only in this case is the steady-state global humidity changed: a given cap temperature and seasonal cycle of mixing capacity specifies a bulk steady-state atmospheric humidity. In all cases, the regolith acts as a damper on the system and adjusts to the global water distribution dictated ultimately by the northern cap. The model also suggests fast adjustment times, on order decades. A number of factors can affect atmospheric mixing capacity. As climate forcing factors change (associated with obliquity or greenhouse gas loading) the mixing capacity will change--an area for future study. The current mixing capacity of the atmosphere is also different from one that would obtain without atmospheric water condensation and sedimentation. Model clouds play important roles in returning water to the residual ice cap in northern summer, and significantly altering interhemispheric transport from that which would occur without clouds. As with previous studies, the southern polar cap acts as a permanent sink for water. The model and resulting paradigm for the water cycle can be used in very preliminary studies of past climate states. Forcing the model with an obliquity of 45 deg., the seasonal water ice caps become significantly more extended, reaching into the summer hemisphere. In fact, the seasonal caps "overlap" in the northern tropics, generating a year-round surface ice belt. Much work remains to be done in understanding water ice transport and exchange processes before models of paleoclimate can be of widespread utility--of which analysis of data from MGS and future missions will be key.

Characteristics of ionospheric electron density profiles in the auroral and polar cap regions from long-term incoherent scatter radar observations

NASA Astrophysics Data System (ADS)

Jee, G.; Kim, E.; Kwak, Y. S.; Kim, Y.; Kil, H.

2017-12-01

We investigate the climatological characteristics of the ionospheric electron density profiles in the auroral and polar cap regions in comparison with the mid-latitude ionosphere using incoherent scatter radars (ISR) observations from Svalbard (78.15N, 16.05E), Tromso (69.59N, 19.23E), and Millstone Hill (42.6N, 288.5E) during a period of 1995 - 2015. Diurnal variations of electron density profiles from 100 to 500 km are compared among the three radar observations during equinox, summer and winter solstice for different solar and geomagnetic activities. Also investigated are the physical characteristics of E-region and F-region peak parameters of electron density profiles in the auroral and polar cap regions, which are significantly different from the mid-latitude ionosphere. In the polar ionosphere, the diurnal variations of density profiles are extremely small in summer hemisphere. Semiannual anomaly hardly appears for all latitudes, but winter anomaly occurs at mid-latitude and auroral ionospheres for high solar activity. Nighttime density becomes larger than daytime density in the winter polar cap ionosphere for high solar activity. The E-region peak is very distinctive in the nighttime auroral region and the peak height is nearly constant at about 110 km for all conditions. Compared with the F-region peak density, the E-region peak density does not change much with solar activity. Furthermore, the E-region peak density can be even larger than F-region density for low solar activity in the auroral region, particularly during disturbed condition.

Role of actin in auxin transport and transduction of gravity

NASA Astrophysics Data System (ADS)

Hu, S.; Basu, S.; Brady, S.; Muday, G.

Transport of the plant hormone auxin is polar and the direction of the hormone movement appears to be controlled by asymmetric distribution of auxin transport protein complexes. Changes in the direction of auxin transport are believed to drive asymmetric growth in response to changes in the gravity vector. To test the possibility that asymmetric distribution of the auxin transport protein complex is mediated by attachment to the actin cytoskeleton, a variety of experimental approaches have been used. The most direct demonstration of the role of the actin cytoskeleton in localization of the protein complex is the ability of one protein in this complex to bind to affinity columns containing actin filaments. Additionally, treatments of plant tissues with drugs that fragment the actin c toskeleton reducey polar transport. In order to explore this actin interaction and the affect of gravity on auxin transport and developmental polarity, embryos of the brown alga, Fucus have been examined. Fucus zygotes are initially symmetrical, but develop asymmetry in response to environmental gradients, with light gradients being the best- characterized signal. Gravity will polarize these embryos and gravity-induced polarity is randomized by clinorotation. Auxin transport also appears necessary for environmental controls of polarity, since auxin efflux inhibitors perturb both photo- and gravity-polarization at a very discrete temporal window within six hours after fertilization. The actin cytoskeleton has previously been shown to reorganize after fertilization of Fucus embryos leading to formation of an actin patch at the site of polar outgrowth. These actin patches still form in Fucus embryos treated with auxin efflux inhibitors, yet the position of these patches is randomized. Together, these results suggest that there are connections between the actin cytoskeleton, auxin transport, and gravity oriented growth and development. (Supported by NASA Grant: NAG2-1203)

Targeting of Chitin Synthase 3 to Polarized Growth Sites in Yeast Requires Chs5p and Myo2p

PubMed Central

Santos, Beatriz; Snyder, Michael

1997-01-01

Chitin is an essential structural component of the yeast cell wall whose deposition is regulated throughout the yeast life cycle. The temporal and spatial regulation of chitin synthesis was investigated during vegetative growth and mating of Saccharomyces cerevisiae by localization of the putative catalytic subunit of chitin synthase III, Chs3p, and its regulator, Chs5p. Immunolocalization of epitope-tagged Chs3p revealed a novel localization pattern that is cell cycledependent. Chs3p is polarized as a diffuse ring at the incipient bud site and at the neck between the mother and bud in small-budded cells; it is not found at the neck in large-budded cells containing a single nucleus. In large-budded cells undergoing cytokinesis, it reappears as a ring at the neck. In cells responding to mating pheromone, Chs3p is found throughout the projection. The appearance of Chs3p at cortical sites correlates with times that chitin synthesis is expected to occur. In addition to its localization at the incipient bud site and neck, Chs3p is also found in cytoplasmic patches in cells at different stages of the cell cycle. Epitope-tagged Chs5p also localizes to cytoplasmic patches; these patches contain Kex2p, a late Golgi-associated enzyme. Unlike Chs3p, Chs5p does not accumulate at the incipient bud site or neck. Nearly all Chs3p patches contain Chs5p, whereas some Chs5p patches lack detectable Chs3p. In the absence of Chs5p, Chs3p localizes in cytoplasmic patches, but it is no longer found at the neck or the incipient bud site, indicating that Chs5p is required for the polarization of Chs3p. Furthermore, Chs5p localization is not affected either by temperature shift or by the myo2-66 mutation, however, Chs3p polarization is affected by temperature shift and myo2-66. We suggest a model in which Chs3p polarization to cortical sites in yeast is dependent on both Chs5p and the actin cytoskeleton/Myo2p. PMID:9008706

Passive millimeter wave differential interference contrast polarimetry

DOEpatents

Bernacki, Bruce E; Kelly, James F; Sheen, David M; Tedeschi, Jonathan R; Hall, Thomas E; Hatchell, Brian K; Valdez, Patrick; McMakin, Douglas L

2014-04-29

Differential polarization imaging systems include an axicon configured to provide a displacement of ray bundles associated with different image patches. The displaced ray bundles are directed to antenna horns and orthomode transducers so as to provide outputs correspond to orthogonal linear states of polarization (SOPs). The outputs are directed to a differential radiometer so that Stokes parameter differences between image patches can be obtained. The ray bundle displacements can be selected to correspond to a mechanical spacing of antenna horns. In some examples, ray bundle displacement corresponds to a displacement less than the diffraction limit.

Field Line Mapping of the Polar Cap Neutral Density Anomaly

NASA Astrophysics Data System (ADS)

Sutton, E. K.; Lin, C. S.; Huang, C. Y.; Cooke, D. L.

2016-12-01

Polar cap neutral density anomaly (PCNDA) events of localized density enhancement with a half size around 700-1000 km had been frequently detected by CHAMP satellite at around 400 km during major magnetic storms with Dst < -100 nT. Density enhancement is probably produced via Joule heating of the thermosphere when a significant amount of energy is deposited in the polar cap. We have identified 12 PCNDA events measured by CHAMP during two major magnetic storms including one initiated by a large solar wind pressure pulse. Their density anomaly locations are found to scatter randomly within the polar circle of 80o magnetic latitude in the geomagnetic coordinate. However after transformed to the Geocentric Solar Wind (GSW) coordinates, their locations become aligned in the direction of solar wind velocity. To better understand the polar cap energy deposition we trace magnetic field lines to the magnetosphere up to 30 earth radii from the ionosphere at 400 km using the data-based Tsyganenko T95 and TS05 magnetic field models. Field line tracing is performed in the GSW coordinate along the CHAMP orbit as well as for the whole polar cap. Each traced magnetic field line is classified into one of the three categories, (1) magnetosphere closed field line (MC) crossing the equatorial plane within 30 earth radii, (2) open field line connected to the magnetopause (MP), or (3) open field line connected to the magnetotail lobe (MT). For nine PCNDA events among the 10 events that we are able to conduct tracing, field lines originated from the density anomaly regions are classified as MT. Only one outlier event in association with a very large IMF BZ is classified as MP. Furthermore the separation angle between the density anomaly peak and the MP-MT field line separation point at 400 km on the X- and Z-axes meridian plane varies from -4o to 16o. Based on these results we speculate that convective electric fields and field aligned currents in the ionosphere might be enhanced near the MP-MT separation point during magnetic storms, resulting in intense localized Joule heating of the thermosphere.

A GCM Recent History of Northern Martian Polar Layered Deposits: Contribution from Past Equatorial Ice Reservoirs

NASA Technical Reports Server (NTRS)

Levrard, B.; Laskar, J.; Montmessin, F.; Forget, F.

2005-01-01

Polar layered deposits are exposed in the walls of the troughs cutting the north polar cap of Mars. They consist of alternating ice and dust layers or layers of an ice-dust mixture with varying proportions and are found throughout the cap. Layers thickness ranges from meters to several tens of meters with an approximately 30 meter dominant wavelength. Although their formation processes is not known, they are presumed to reflect changes in ice and dust stability over orbital and axial variations. Intensive 3-D LMD GCM simulations of the martian water cycle have been thus performed to determine the annual rates of exchange of surface ice between the northern cap and tropical areas for a wide range of obliquity and orbital parameters values.These rates have been employed to reconstruct an history of the northern cap and test simple models of dust-ice layers formation over the last 10 Ma orbital variations. We use the 3-D water cycle model simulated by the 3-D LMD GCM with an intermediate grid resolution (7.5 longitude x 5.625 latitude) and 25 vertical levels. The dust opacity is constant and set to 0,15. No exchange of ice with regolith is allowed. The evolution of the northern cap over obliquity and orbital changes (eccentricity, Longitude of perihelion) has been recently described with this model. High summer insolation favors transfer of ice from the northern pole to the Tharsis and Olympus Montes, while at low obliquity, unstable equatorial ice is redeposited in high-latitude and polar areas of both hemisphere. The disappearance of the equatorial ice reservoir leads to a poleward recession of icy high latitude reservoirs, providing an additional source for the cap accumulation during each obliquity or orbital cycle. Furthering the efforts, a quantitative evolution of ice reservoirs is here investigated for various astronomical conditions.

Stripline feed for a microstrip array of patch elements with teardrop shaped probes

NASA Technical Reports Server (NTRS)

Huang, John (Inventor)

1990-01-01

A circularly polarized microstrip array antenna utilizing a honeycomb substrate made of dielectric material to support on one side the microstrip patch elements in an array, and on the other side a stripline circuit for feeding the patch elements in subarray groups of four with angular orientation and phase for producing circularly polarized radiation, preferably at a 0.degree., 90.degree., 180.degree. and 270.degree. relationship. The probe used for coupling each feed point in the stripline circuit to a microstrip patch element is teardrop shaped in order to introduce capacitance between the coupling probe and the metal sheet of the stripline circuit that serves as an antenna ground plane. The capacitance thus introduced tunes out inductance of the probe. The shape of the teardrop probe is not critical. The probe capacitance required is controlled by the maximum diameter for the teardrop shaped probe, which can be empirically determined for the operating frequency. An aluminum baffle around each subarray blocks out surface waves between subarrays.

Broadbanding of circularly polarized patch antenna by waveguided magneto-dielectric metamaterial

NASA Astrophysics Data System (ADS)

Yang, Xin Mi; Wen, Juan; Liu, Chang Rong; Liu, Xue Guan; Cui, Tie Jun

2015-12-01

Design of bandwidth-enhanced circularly polarized (CP) patch antenna using artificial magneto-dielectric substrate was investigated. The artificial magneto-dielectric material adopted here takes the form of waveguided metamaterial (WG-MTM). In particular, the embedded meander line (EML) structure was employed as the building element of the WG-MTM. As verified by the retrieved effective medium parameters, the EML-based waveguided magneto-dielectric metamaterial (WG-MDM) exhibits two-dimensionally isotropic magneto-dielectric property with respect to TEM wave excitations applied in two orthogonal directions. A CP patch antenna loaded with the EML-based WG-MDM (WG-MDM antenna) has been proposed and its design procedure is described in detail. Simulation results show that the impedance and axial ratio bandwidths of the WG-MDM antenna have increased by 125% and 133%, respectively, compared with those obtained with pure dielectric substrate offering the same patch size. The design of the novel WG-MDM antenna was also validated by measurement results, which show good agreement with their simulated counterparts.

Evolution of Martian polar landscapes - Interplay of long-term variations in perennial ice cover and dust storm intensity

NASA Technical Reports Server (NTRS)

Cutts, J. A.; Blasius, K. R.; Roberts, W. J.

1979-01-01

The discovery of a new type of Martian polar terrain, called undulating plain, is reported and the evolution of the plains and other areas of the Martian polar region is discussed in terms of the trapping of dust by the perennial ice cover. High-resolution Viking Orbiter 2 observations of the north polar terrain reveal perennially ice-covered surfaces with low relief, wavelike, regularly spaced, parallel ridges and troughs (undulating plains) occupying areas of the polar terrain previously thought to be flat, and associated with troughs of considerable local relief which exhibit at least partial annual melting. It is proposed that the wavelike topography of the undulating plains originates from long-term periodic variations in cyclical dust precipitation at the margin of a growing or receding perennial polar cap in response to changes in insolation. The troughs are proposed to originate from areas of steep slope in the undulating terrain which have lost their perennial ice cover and have become incapable of trapping dust. The polar landscape thus appears to record the migrations, expansions and contractions of the Martian polar cap.

Comparison of Polar Cap (PC) index calculations.

NASA Astrophysics Data System (ADS)

Stauning, P.

2012-04-01

The Polar Cap (PC) index introduced by Troshichev and Andrezen (1985) is derived from polar magnetic variations and is mainly a measure of the intensity of the transpolar ionospheric currents. These currents relate to the polar cap antisunward ionospheric plasma convection driven by the dawn-dusk electric field, which in turn is generated by the interaction of the solar wind with the Earth's magnetosphere. Coefficients to calculate PCN and PCS index values from polar magnetic variations recorded at Thule and Vostok, respectively, have been derived by several different procedures in the past. The first published set of coefficients for Thule was derived by Vennerstrøm, 1991 and is still in use for calculations of PCN index values by DTU Space. Errors in the program used to calculate index values were corrected in 1999 and again in 2001. In 2005 DMI adopted a unified procedure proposed by Troshichev for calculations of the PCN index. Thus there exists 4 different series of PCN index values. Similarly, at AARI three different sets of coefficients have been used to calculate PCS indices in the past. The presentation discusses the principal differences between the various PC index procedures and provides comparisons between index values derived from the same magnetic data sets using the different procedures. Examples from published papers are examined to illustrate the differences.

Plasma characteristics of upflowing ion beams in the polar cap region

NASA Technical Reports Server (NTRS)

Chen, M. W.; Ashour-Abdalla, M.; Peterson, W. K.; Moore, T. E.; Persoon, A. M.

1990-01-01

The plasma characteristics of upflowing ion stream events with energies greater than 10 eV in the polar cap region near solar maximum are analyzed. It is found that, in 22 of the 41 polar ion streaming events studied, O(+) is the dominant ion constituent in the upflowing beam components. There are significant amounts of upflowing O(+) in the plasma even during quiet auroral conditions. In one event, the upflowing O(+) population had two components, a cold distribution and a warm one. In another event the O(+) and H(+) temperatures suggested that ionospheric ions are heated. The cold upflowing ion stream component observed in some of the polar ion streaming events exhibited a filamentary nature. A significant amount of He(+) was also found in some of the events studied.

Simulations of the general circulation of the Martian atmosphere. I - Polar processes

NASA Technical Reports Server (NTRS)

Pollack, James B.; Haberle, Robert M.; Schaeffer, James; Lee, Hilda

1990-01-01

Numerical simulations of the Martian atmosphere general circulation are carried out for 50 simulated days, using a three-dimensional model, based on the primitive equations of meteorology, which incorporated the radiative effects of atmospheric dust on solar and thermal radiation. A large number of numerical experiments were conducted for alternative choices of seasonal date and dust optical depth. It was found that, as the dust content of the winter polar region increased, the rate of atmospheric CO2 condensation increased sharply. It is shown that the strong seasonal variation in the atmospheric dust content observed might cause a number of hemispheric asymmetries. These asymmetries include the greater prevalence of polar hoods in the northern polar region during winter, the lower albedo of the northern polar cap during spring, and the total dissipation of the northern CO2 ice cap during the warmer seasons.

North Polar Cap Layers and Ledges

NASA Image and Video Library

2016-08-24

At the edge of Mars' permanent North Polar cap, we see an exposure of the internal layers, each with a different mix of water ice, dust and dirt. These layers are believed to correspond to different climate conditions over the past tens of thousands of years. When we zoom in closer, we see that the distinct layers erode differently. Some are stronger and more resistant to erosion, others only weakly cemented. The strong layers form ledges. http://photojournal.jpl.nasa.gov/catalog/PIA21022

Pulsar Polar Cap and Slot Gap Models: Confronting Fermi Data

NASA Technical Reports Server (NTRS)

Harding, Alice K.

2012-01-01

Rotation-powered pulsars are excellent laboratories for studying particle acceleration as well as fundamental physics of strong gravity, strong magnetic fields and relativity. I will review acceleration and gamma-ray emission from the pulsar polar cap and slot gap. Predictions of these models can be tested with the data set on pulsars collected by the Large Area Telescope on the Fermi Gamma-Ray Telescope over the last four years, using both detailed light curve fitting and population synthesis.

Reconciling the MOLA, TES, and Neutron Observations of the North Polar CO2 Mass Budget on Mars

NASA Technical Reports Server (NTRS)

Haberle, Robert M.; Mattingly, B.; Titus, T. N.

2003-01-01

There are now three independent observations of the CO2 polar cap mass budget of Mars' north polar cap. The first is based elevation changes detected by the Mars Orbiter Laser Altimeter (MOLA) on the Mars Global Surveyor (MGS). The second is based on MGS Thermal Emission Spectrometer (TES) broadband observations of the solar and infrared radiation fields at the top of the atmosphere. The third is based on neutron counts measured by the neutron spectrometer (NS) on Odyssey. If one assumes a cap density of 910 kg/cu m, then the peak mass loading poleward of 85 N inferred from the MOLA data is approx. 1090 kg/sq m, which compares to approx. 1150 kg/sq m inferred from TES for the same region, and 700 kg/sq m from the NS data. TES and MOLA are in good agreement, but are about 60% higher than the NS data. Is there a way to reconcile these discrepancies?

ARC-1989-AC89-7046

NASA Image and Video Library

1989-08-25

P-34764 Voyager 2 obtained this high resolution color image of Neptune's large satellite Triton during its close flyby. Approximately a dozen individual images were combined to produce this comprehensive view of the Neptune-facing hemisphere of Triton. Fine detail is provided by high resolution, clear-filter images, with color information added from lower resolution frames. The large south polar cap at the bottom of the image is highly refective and slightly pink in color , and may consist of a slowly evaporating layer of nitrogen ice deposited during the previous winter. From the ragged edge of the polar cap northward the satellite's face is generously darker and redder in color. This coloring may be produced by the action of ultraviolet light and magnetospheric radiation upon methane in the atmosphere and surface. Running across this darker region , approximately parallel to the edge of the polar cap, is a band of brighter white material that is almost bluish in color. The underlying topography in this bright band is similiar, however to that in the darker, redder regions surrounding it.

Why do horseflies need polarization vision for host detection? Polarization helps tabanid flies to select sunlit dark host animals from the dark patches of the visual environment

PubMed Central

Szörényi, Tamás; Pereszlényi, Ádám; Gerics, Balázs; Hegedüs, Ramón; Barta, András

2017-01-01

Horseflies (Tabanidae) are polarotactic, being attracted to linearly polarized light when searching for water or host animals. Although it is well known that horseflies prefer sunlit dark and strongly polarizing hosts, the reason for this preference is unknown. According to our hypothesis, horseflies use their polarization sensitivity to look for targets with higher degrees of polarization in their optical environment, which as a result facilitates detection of sunlit dark host animals. In this work, we tested this hypothesis. Using imaging polarimetry, we measured the reflection–polarization patterns of a dark host model and a living black cow under various illumination conditions and with different vegetation backgrounds. We focused on the intensity and degree of polarization of light originating from dark patches of vegetation and the dark model/cow. We compared the chances of successful host selection based on either intensity or degree of polarization of the target and the combination of these two parameters. We show that the use of polarization information considerably increases the effectiveness of visual detection of dark host animals even in front of sunny–shady–patchy vegetation. Differentiation between a weakly polarizing, shady (dark) vegetation region and a sunlit, highly polarizing dark host animal increases the efficiency of host search by horseflies. PMID:29291065

Why do horseflies need polarization vision for host detection? Polarization helps tabanid flies to select sunlit dark host animals from the dark patches of the visual environment.

PubMed

Horváth, Gábor; Szörényi, Tamás; Pereszlényi, Ádám; Gerics, Balázs; Hegedüs, Ramón; Barta, András; Åkesson, Susanne

2017-11-01

Horseflies (Tabanidae) are polarotactic, being attracted to linearly polarized light when searching for water or host animals. Although it is well known that horseflies prefer sunlit dark and strongly polarizing hosts, the reason for this preference is unknown. According to our hypothesis, horseflies use their polarization sensitivity to look for targets with higher degrees of polarization in their optical environment, which as a result facilitates detection of sunlit dark host animals. In this work, we tested this hypothesis. Using imaging polarimetry, we measured the reflection-polarization patterns of a dark host model and a living black cow under various illumination conditions and with different vegetation backgrounds. We focused on the intensity and degree of polarization of light originating from dark patches of vegetation and the dark model/cow. We compared the chances of successful host selection based on either intensity or degree of polarization of the target and the combination of these two parameters. We show that the use of polarization information considerably increases the effectiveness of visual detection of dark host animals even in front of sunny-shady-patchy vegetation. Differentiation between a weakly polarizing, shady (dark) vegetation region and a sunlit, highly polarizing dark host animal increases the efficiency of host search by horseflies.

South Polar Autumn

NASA Image and Video Library

2006-04-22

This MOC image shows a portion of the south polar residual cap; darkened edges of the pits and mesas are evidence of the removal, by sublimation, of frozen carbon dioxide during the recent martian summer

Planar microstrip YAGI antenna array

NASA Technical Reports Server (NTRS)

Huang, John (Inventor)

1993-01-01

A directional microstrip antenna includes a driven patch surrounded by an isolated reflector and one or more coplanar directors, all separated from a ground plane on the order of 0.1 wavelength or less to provide end fire beam directivity without requiring power dividers or phase shifters. The antenna may be driven at a feed point a distance from the center of the driven patch in accordance with conventional microstrip antenna design practices for H-plane coupled or horizontally polarized signals. The feed point for E-plane coupled or vertically polarized signals is at a greater distance from the center than the first distance. This feed point is also used for one of the feed signals for circularly polarized signals. The phase shift between signals applied to feed points for circularly polarized signals must be greater than the conventionally required 90 degrees and depends upon the antenna configuration.

Host-guest chemistry for tuning colloidal solubility, self-organization and photoconductivity of inorganic-capped nanocrystals.

PubMed

Bodnarchuk, Maryna I; Yakunin, Sergii; Piveteau, Laura; Kovalenko, Maksym V

2015-12-09

Colloidal inorganic nanocrystals (NCs), functionalized with inorganic capping ligands, such as metal chalcogenide complexes (MCCs), have recently emerged as versatile optoelectronic materials. As-prepared, highly charged MCC-capped NCs are dispersible only in highly polar solvents, and lack the ability to form long-range ordered NC superlattices. Here we report a simple and general methodology, based on host-guest coordination of MCC-capped NCs with macrocyclic ethers (crown ethers and cryptands), enabling the solubilization of inorganic-capped NCs in solvents of any polarity and improving the ability to form NC superlattices. The corona of organic molecules can also serve as a convenient knob for the fine adjustment of charge transport and photoconductivity in films of NCs. In particular, high-infrared-photon detectivities of up to 3.3 × 10(11) Jones with a fast response (3 dB cut-off at 3 kHz) at the wavelength of 1,200 nm were obtained with films of PbS/K3AsS4/decyl-18-crown-6 NCs.

Host–guest chemistry for tuning colloidal solubility, self-organization and photoconductivity of inorganic-capped nanocrystals

PubMed Central

Bodnarchuk, Maryna I.; Yakunin, Sergii; Piveteau, Laura; Kovalenko, Maksym V.

2015-01-01

Colloidal inorganic nanocrystals (NCs), functionalized with inorganic capping ligands, such as metal chalcogenide complexes (MCCs), have recently emerged as versatile optoelectronic materials. As-prepared, highly charged MCC-capped NCs are dispersible only in highly polar solvents, and lack the ability to form long-range ordered NC superlattices. Here we report a simple and general methodology, based on host–guest coordination of MCC-capped NCs with macrocyclic ethers (crown ethers and cryptands), enabling the solubilization of inorganic-capped NCs in solvents of any polarity and improving the ability to form NC superlattices. The corona of organic molecules can also serve as a convenient knob for the fine adjustment of charge transport and photoconductivity in films of NCs. In particular, high-infrared-photon detectivities of up to 3.3 × 1011 Jones with a fast response (3 dB cut-off at 3 kHz) at the wavelength of 1,200 nm were obtained with films of PbS/K3AsS4/decyl-18-crown-6 NCs. PMID:26647828

CryoScout: A Descent Through the Mars Polar Cap

NASA Technical Reports Server (NTRS)

Hecht, M. H.; Saunders, R. S.

2003-01-01

CryoScout was proposed as a subsurface investigation of the stratigraphic climate record embedded in Mars North Polar cap. After landing on a gentle landscape in the midst of the mild summer season, CryoScout was to use the continuous polar sunlight to power the descent of a cryobot, a thermal probe, into the ice at a rate of about 1 m per day. CryoScout would probe deep enough into this time capsule to see the effects of planetary obliquity variations and discrete events such as dust storms or volcanic eruptions. By penetrating tens of meters of ice, the mission would explore at least one of the dominant "MOC layers" observed in exposed layered terrain.

Studies of Martian polar regions. [using CO2 flow

NASA Technical Reports Server (NTRS)

Smith, C. I.; Clark, B. R.; Eschman, D. F.

1974-01-01

The flow law determined experimentally for solid CO2 establishes that an hypothesis of glacial flow of CO2 at the Martian poles is not physically unrealistic. Compression experiments carried out under 1 atmosphere pressure and constant strain rate conditions demonstrate that the strength of CO2 near its sublimation point is considerably less than the strength of water ice near its melting point. A plausible glacial model for the Martian polar caps was constructed. The CO2 deposited near the pole would have flowed outward laterally to relieve high internal shear stresses. The topography of the polar caps, and the uniform layering and general extent of the layered deposits were explained using this model.

Ridges Down South

NASA Image and Video Library

2005-11-04

This image captured by NASA 2001 Mars Odyssey spacecraft shows part of an area just off the margin of the south polar cap. The bright and dark markings are identical to some seen on the cap, telling us that ice is located at the surface.

The source of the electric field in the nightside magnetosphere

NASA Technical Reports Server (NTRS)

Stern, D. P.

1975-01-01

In the open magnetosphere model magnetic field lines from the polar caps connect to the interplanetary magnetic field and conduct an electric field from interplanetary space to the polar ionosphere. By examining the magnetic flux involved it is concluded that only slightly more than half of the magnetic flux in the polar caps belongs to open field lines and that such field lines enter or leave the magnetosphere through narrow elongated windows stretching the tail. These window regions are identified with the tail's boundary region and shift their position with changes in the interplanetary magnetic field, in particular when a change of interplanetary magnetic sector occurs. The circuit providing electric current in the magnetopause and the plasma sheet is extended across those windows; thus energy is drained from the interplanetary electric field and an electric potential drop is produced across the plasma sheet. The polar cap receives its electric field from interplanetary space on the day side from open magnetic field lines and on the night side from closed field lines leading to the plasma sheet. The theory described provides improved understanding of magnetic flux bookkeeping, of the origin of Birkeland currents, and of the boundary layer of the geomagnetic tail.

Space Plasma Physics

NASA Technical Reports Server (NTRS)

Wu, S. T.

2000-01-01

Dr. James L. Horwitz and R. Hugh Comfort's studies with the high altitude TIDE data have been progressing well. We concluded a study on the relationship of polar cap ion properties observed by TIDE near apogee with solar wind and IMF conditions. We found that in general H+ did not correlate as well as O+ with solar wind and IMF parameters. O+ density correlated(sub IMF), and Kp. At lower solar wind speeds, O+ density decreased with increasing latitude, but this trend was not observed at higher solar wind speeds. By comparing these results with results from other studies of O+ in different parts of the magnetosphere, we concluded that O+ ions often leave the ionosphere near the foot point of the cusp/cleft region, pass through the high-altitude polar cap lobes, and eventually arrive in the plasma sheet. We found that H+ outflows are a persistent feature of the polar cap and are not as dependent on the geophysical conditions; even classical polar wind models show H+ ions readily escaping owing to their low mass. Minor correlations with solar wind drivers were found; specifically, H+ density correlated best with IMF By, V(sub sw)B(sub IMF), and ESW(sub sw).

Recession of the Northern polar cap from the PFS Mars Express observations

NASA Astrophysics Data System (ADS)

Zasova, L. V.; Formisano, V.; Moroz, V. I.; Giuranna, M.; Grassi, D.; Hansen, G.; Ignatiev, N. I.; Maturilli, A.; Pfs Team

Planetary Fourier Spectrometer (PFS) has two spectral channels, devoted to the thermal and solar reflected spectral range investigations. The first observations by PFS of the Northern hemisphere ,which includes the North pole, occurred at Ls= 342 (northern winter). Surface temperature alone the orbit shows that the CO2 ice polar cap, where the surface temperature is found around 150K and below, is extended down to about 62 N. The spectra at latitudes above 80 N are obtained at polar darkness and at latitudes below 80 at illumination by the low Sun. Retrieved temperature profiles of the atmosphere at darkness show that temperature of the atmosphere is low enough to allow the CO2 condensation up to about 25 km. Between 70 and 80 latitude the upper levels of the atmosphere are heated by the Sun, but condensation of the CO2 may occur in the near surface layer below 5 km. The water ice clouds exist at lower latitudes with maximum opacity at the edge of the polar cap. More detailed investigation of the data obtained in winter as well as of the measurements in the northern spring will be presented.

The First International Conference on Mars Polar Science and Exploration

NASA Technical Reports Server (NTRS)

1998-01-01

This volume contains abstracts of articles that have been accepted for presentation at the First International Conference on Mars Polar Science and Exploration. Articles about the geology of the Martian Polar regions were presented, and analogs from Earth's geology were also presented. Presentations also were given about the probable contents of the Martian polar caps

Seasonal Changes in Mars' North Polar Ice Cap

NASA Technical Reports Server (NTRS)

1997-01-01

These images, which seem to have been taken while NASA's Hubble Space Telescope (HST) was looking directly down on the Martian North Pole, were actually created by assembling mosaics of three sets of images taken by HST in October, 1996 and in January and March, 1997 and projecting them to appear as they would if seen from above the pole. This first mosaic is a view which could not actually be seen in nature because at this season a portion of the pole would have actually been in shadow; the last view, taken near the summer solstice, would correspond to the Midnight Sun on Earth with the pole fully illuminated all day. The resulting polar maps begin at 50 degrees N latitude and are oriented with 0 degrees longitude at the 12 o'clock position. This series of pictures captures the seasonal retreat of Mars' north polar cap.

October 1996 (early spring in the Northern hemisphere): In this map, assembled from images obtained between Oct. 8 and 15, the cap extends down to 60 degrees N latitude, nearly it's maximum winter extent. (The notches are areas where Hubble data were not available). A thin, comma-shaped cloud of dust can be seen as a salmon-colored crescent at the 7 o'clock position. The cap is actually fairly circular about the geographic pole at this season; the bluish 'knobs' where the cap seems to extend further are actually clouds that occurred near the edges of the three separate sets of images used to make the mosaic.

January 1997 (mid-spring): Increased warming as spring progresses in the northern hemisphere has sublimated the carbon dioxide ice and frost below 70 degrees north latitude. The faint darker circle inside the cap boundary marks the location of circumpolar sand dunes (see March '97 map); these dark dunes are warmed more by solar heating than are the brighter surroundings, so the surface frost sublimates from the dunes earlier than from the neighboring areas. Particularly evident is the marked hexagonal shape of the polar cap at this season, noted previously by HST in 1995 and Mariner 9 in 1972; this may be due to topography, which isn't well known, or to wave structure in the circulation. This map was assembled from WFPC2 images obtained between Dec. 30, 1996 and Jan. 4, 1997.

March 30, 1997 (early summer): The cap has fully retreated to its remnant core of water-ice. This residual cap is actually almost cut into two by a large, horn-shaped canyon called Chasma Borealis which is cut deeply into the polar terrain. The HST images also reveal a curious layered terrain which is evidence of past climatic changes on Mars. The sublimation of all of the carbon dioxide has exposed the ring of dark sand dunes which encircle the North Polar Cap. Outliers of ice persist south of the polar sand sea (between the 3 o'clock and 9 o'clock positions). The bright circular features at 3, 6, and 9 o'clock are ice-filled craters.

All images were taken with the Wide Field and Planetary Camera 2. The color is constructed from images taken in red (673 nm) , blue (410 nm) and green (502 nm) light. The resolution at the North Pole ranges from about 115 km/pixel in October '96 to about 45 km/pixel in March '97.

This image and other images and data received from the Hubble Space Telescope are posted on the World Wide Web on the Space Telescope Science Institute home page at URL http://oposite.stsci.edu/pubinfo/

Space Technology 5 (ST-5) Observations of the Imbalance of Region 1 and 2 Field-Aligned Currents

NASA Technical Reports Server (NTRS)

Le, Guan

2010-01-01

Space Technology 5 (ST-5) is a three micro-satellite constellation deployed into a 300 x 4500 km, dawn-dusk, sun-synchronous polar orbit from March 22 to June 21, 2006, for technology validations. In this study, we use the in-situ magnetic field observations from Space Technology 5 mission to quantify the imbalance of Region 1 (R1) and Region 2 (R2) currents. During the three-month duration of the ST5 mission, geomagnetic conditions range from quiet to moderately active. We find that the R1 current intensity is consistently stronger than the R2 current intensity both for the dawnside and the duskside large-scale field-aligned current system. The net currents flowing into (out of) the ionosphere in the dawnside (duskside) are in the order of 5% of the total RI currents. We also find that the net currents flowing into or out of the ionosphere are controlled by the solar wind-magnetosphere interaction in the same way as the field-aligned currents themselves are. Since the net currents due to the imbalance of the R1 and R2 currents require that their closure currents flow across the polar cap from dawn to dusk as Pedersen currents, our results indicate that the total amount of the cross-polar cap Pedersen currents is in the order of approx. 0.1 MA. This study, although with a very limited dataset, is one of the first attempts to quantify the cross-polar cap Pedersen currents. Given the importance of the Joule heating due to Pedersen currents to the high-latitude ionospheric electrodynamics, quantifying the cross-polar cap Pedersen currents and associated Joule heating is needed for developing models of the magnetosphere-ionosphere coupling.

Intermediate-scale plasma irregularities in the polar ionosphere inferred from GPS radio occultation

NASA Astrophysics Data System (ADS)

Shume, E. B.; Komjathy, A.; Langley, R. B.; Verkhoglyadova, O.; Butala, M. D.; Mannucci, A. J.

2015-02-01

We report intermediate-scale plasma irregularities in the polar ionosphere inferred from high-resolution radio occultation (RO) measurements using GPS (Global Positioning System) to CASSIOPE (CAScade Smallsat and IOnospheric Polar Explorer) satellite radio links. The high inclination of CASSIOPE and the high rate of signal reception by the GPS Attitude, Positioning, and Profiling RO receiver on CASSIOPE enable a high-resolution investigation of the dynamics of the polar ionosphere with unprecedented detail. Intermediate-scale, scintillation-producing irregularities, which correspond to 1 to 40 km scales, were inferred by applying multiscale spectral analysis on the RO phase measurements. Using our multiscale spectral analysis approach and satellite data (Polar Operational Environmental Satellites and Defense Meteorological Satellite Program), we discovered that the irregularity scales and phase scintillations have distinct features in the auroral oval and polar cap. We found that large length scales and more intense phase scintillations are prevalent in the auroral oval compared to the polar cap implying that the irregularity scales and phase scintillation characteristics are a function of the solar wind and magnetospheric forcings.

What can stimulus polarity and interphase gap tell us about auditory nerve function in cochlear-implant recipients?

PubMed

Hughes, Michelle L; Choi, Sangsook; Glickman, Erin

2018-03-01

Modeling studies suggest that differences in neural responses between polarities might reflect underlying neural health. Specifically, large differences in electrically evoked compound action potential (eCAP) amplitudes and amplitude-growth-function (AGF) slopes between polarities might reflect poorer peripheral neural health, whereas more similar eCAP responses between polarities might reflect better neural health. The interphase gap (IPG) has also been shown to relate to neural survival in animal studies. Specifically, healthy neurons exhibit larger eCAP amplitudes, lower thresholds, and steeper AGF slopes for increasing IPGs. In ears with poorer neural survival, these changes in neural responses are generally less apparent with increasing IPG. The primary goal of this study was to examine the combined effects of stimulus polarity and IPG within and across subjects to determine whether both measures represent similar underlying mechanisms related to neural health. With the exception of one measure in one group of subjects, results showed that polarity and IPG effects were generally not correlated in a systematic or predictable way. This suggests that these two effects might represent somewhat different aspects of neural health, such as differences in site of excitation versus integrative membrane characteristics, for example. Overall, the results from this study suggest that the underlying mechanisms that contribute to polarity and IPG effects in human CI recipients might be difficult to determine from animal models that do not exhibit the same anatomy, variance in etiology, electrode placement, and duration of deafness as humans. Copyright © 2017 Elsevier B.V. All rights reserved.

South Polar Textures

NASA Image and Video Library

2014-10-07

While yesterday image showed a texture of oval depressions swiss cheese, this image from NASA 2001 Mars Odyssey spacecraft shows a linear surface texture of the south polar cap. This texture is described as looking like a thumbprint.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Galati, Elizabeth; Tebbe, Moritz; Querejeta-Fernández, Ana

Chemically and topographically patterned nanoparticles (NPs) with dimensions on the order of tens of nanometers have a diverse range of applications and are a valuable system for fundamental research. Recently, thermodynamically controlled segregation of a smooth layer of polymer ligands into pinned micelles (patches) offered an approach to nanopatterning of polymer-functionalized NPs. Control of the patch number, size, and spatial distribution on the surface of spherical NPs has been achieved, however, the role of NP shape remained elusive. Here, we report the role of NP shape, namely, the effect of the local surface curvature, on polymer segregation into surface patches.more » For polymer-functionalized metal nanocubes, we show experimentally and theoretically that the patches form preferentially on the high-curvature regions such as vertices and edges. An in situ transformation of the nanocubes into nanospheres leads to the change in the number and distribution of patches; a process that is dominated by the balance between the surface energy and the stretching energy of the polymer ligands. The experimental and theoretical results presented in this work are applicable to surface patterning of polymer-capped NPs with different shapes, which then enables the exploration of patch-directed self-assembly, as colloidal surfactants, and as templates for the synthesis of hybrid nanomaterials.« less

Tuning the interfacial charge, orbital, and spin polarization properties in La0.67Sr0.33MnO3/La1-xSrxMnO3 bilayers

NASA Astrophysics Data System (ADS)

Carreira, Santiago J.; Aguirre, Myriam H.; Briatico, Javier; Weschke, Eugen; Steren, Laura B.

2018-01-01

The possibility of controlling the interfacial properties of artificial oxide heterostructures is still attracting researchers in the field of materials engineering. Here, we used surface sensitive techniques and high-resolution transmission electron microscopy to investigate the evolution of the surface spin-polarization and lattice strains across the interfaces between La0.66Sr0.33MnO3 thin films and low-doped manganites as capping layers. We have been able to fine tune the interfacial spin-polarization by changing the capping layer thickness and composition. The spin-polarization was found to be the highest at a critical capping thickness that depends on the Sr doping. We explain the non-trivial magnetic profile by the combined effect of two mechanisms: On the one hand, the extra carriers supplied by the low-doped manganites that tend to compensate the overdoped interface, favouring locally a ferromagnetic double-exchange coupling. On the other hand, the evolution from a tensile-strained structure of the inner layers to a compressed structure at the surface that changes gradually the orbital occupation and hybridization of the 3d-Mn orbitals, being detrimental for the spin polarization. The finding of an intrinsic spin-polarization at the A-site cation observed in x-ray magnetic circular dichroism (XMCD) measurements also reveals the existence of a complex magnetic configuration at the interface, different from the magnetic phases observed at the inner layers.

Evaluations of dielectric property and drug release profile of 5-FU patches based on plasma charged electrets

NASA Astrophysics Data System (ADS)

Wang, YUAN; Hejuan, LIANG; Ping, HUANG; Xiaoqiang, AN; Jian, JIANG; Lili, CUI

2018-05-01

In the present study, the electret 5-fluorouracil patch was developed, the effective surface potential, piezoelectric coefficient d 33, open-circuit thermally stimulated discharge (TSD) current spectra and shear adhesion of the patch were measured. The drug release profile of the patch was determined by using high performance liquid chromatography method. A stable potential difference which was positively dependent on the surface potential of the electret was generated on two sides of the patch. The measurements of d 33 coefficient, TSD current spectra and adhesion performance showed that the electrostatic field of the electret could cause polarization and cohesive strength decreasing of the matrix molecules, change the distribution and interaction of the drug molecules in patch, therefore to increase the release of drug from the transdermal patch.

CO2 jets formed by sublimation beneath translucent slab ice in Mars' seasonal south polar ice cap

USGS Publications Warehouse

Kieffer, H.H.; Christensen, P.R.; Titus, T.N.

2006-01-01

The martian polar caps are among the most dynamic regions on Mars, growing substantially in winter as a significant fraction of the atmosphere freezes out in the form of CO2 ice. Unusual dark spots, fans and blotches form as the south-polar seasonal CO2 ice cap retreats during spring and summer. Small radial channel networks are often associated with the location of spots once the ice disappears. The spots have been proposed to be simply bare, defrosted ground; the formation of the channels has remained uncertain. Here we report infrared and visible observations that show that the spots and fans remain at CO2 ice temperatures well into summer, and must be granular materials that have been brought up to the surface of the ice, requiring a complex suite of processes to get them there. We propose that the seasonal ice cap forms an impermeable, translucent slab of CO2 ice that sublimates from the base, building up high-pressure gas beneath the slab. This gas levitates the ice, which eventually ruptures, producing high-velocity CO 2 vents that erupt sand-sized grains in jets to form the spots and erode the channels. These processes are unlike any observed on Earth. ?? 2006 Nature Publishing Group.

Polar Cap Retreat

NASA Technical Reports Server (NTRS)

2004-01-01

13 August 2004 This red wide angle Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a view of the retreating seasonal south polar cap in the most recent spring in late 2003. Bright areas are covered with frost, dark areas are those from which the solid carbon dioxide has sublimed away. The center of this image is located near 76.5oS, 28.2oW. The scene is large; it covers an area about 250 km (155 mi) across. The scene is illuminated by sunlight from the upper left.

Low-energy electron intensities at large distances over the earth's polar cap

NASA Technical Reports Server (NTRS)

Yeager, D. M.; Frank, L. A.

1975-01-01

The results of the character and temporal fluctuations study of electron intensities in the energy range of hundreds of electron volts, are reported which were measured at high latitudes and altitudes on geomagnetic field lines corresponding to those of the polar cap and magnetotail lobes. It is concluded that such electron intensities are diminutive relative to those found in other regions of the magnetosphere. Severe variations of intensities were found and the magnitudes of electron intensities appear to be strongly coupled to the directions of the interplanetary magnetic fields.

Simulated Martian pressure cycle based on the sublimation and deposition of polar CO2

NASA Astrophysics Data System (ADS)

Kemppinen, Osku; Paton, Mark; Savijärvi, Hannu; Harri, Ari-Matti

2014-05-01

The Martian atmospheric pressure cycle is driven by sublimation and deposition of CO2 at polar caps. In the thin atmosphere of Mars the surface energy balance and thus the phase changes of CO2 are dominated by radiation. Additionally, because the atmosphere is so thin, the annual polar cap cycle can have a large relative effect on the pressure. In this work we utilize radiative transfer models to calculate the amount of radiation incoming to Martian polar latitudes over each sol of the year, as well as the amount of energy lost from the surface due to thermal radiation. The energy budget calculated in this way allows us to estimate the amount of CO2 sublimating and depositing at each hour of the Martian year. Since virtually all of the sublimated CO2 is believed to enter and stay in the atmosphere until depositing, this estimate allows us to calculate the annual pressure cycle, assuming that the CO2 is distributed approximately evenly over the planet. The model is running with physically plausible parameters and producing encouragingly good fits to in situ measured data made by e.g. Viking landers. In the next phase we will validate the simulation runs against polar ice cap thickness measurements as well as compare the calculated CO2 source and sink strengths to the sources and sinks of global atmospheric models.

Interaction of capsaicinoids with cell membrane models does not correlate with pungency of peppers

NASA Astrophysics Data System (ADS)

Geraldo, Vananélia P. N.; Ziglio, Analine C.; Gonçalves, Débora; Oliveira, Osvaldo N.

2017-04-01

Mixed monolayers were prepared using phospholipids in order to mimic cell membranes and fractions of capsaicinoids (extracted from Malagueta, Caps-M, and Bhut Jolokia, Caps-B, peppers). According to their surface-pressure isotherms and polarization-modulated infrared reflection absorption spectra (PM-IRRAS), weak molecular-level interactions were observed between Caps and phospholipids. Both Caps-M and Caps-B penetrated into the alkyl tail region of the monolayer, interacted with the phosphate group of the phospholipids and affected hydration of their Cdbnd O groups. Since the physiological activity of Caps is not governed solely by interaction with cell membranes, it should require participation of a neuronal membrane receptor, e.g. vanilloid receptor (TRPV1).

DC Potentials Applied to an End-cap Electrode of a 3-D Ion Trap for Enhanced MSn Functionality

PubMed Central

Prentice, Boone M.; Xu, Wei; Ouyang, Zheng; McLuckey, Scott A.

2010-01-01

The effects of the application of various DC magnitudes and polarities to an end-cap of a 3-D quadrupole ion trap throughout a mass spectrometry experiment were investigated. Application of a monopolar DC field was achieved by applying a DC potential to the exit end-cap electrode, while maintaining the entrance end-cap electrode at ground potential. Control over the monopolar DC magnitude and polarity during time periods associated with ion accumulation, mass analysis, ion isolation, ion/ion reaction, and ion activation can have various desirable effects. Included amongst these are increased ion capture efficiency, increased ion ejection efficiency during mass analysis, effective isolation of ions using lower AC resonance ejection amplitudes, improved temporal control of the overlap of oppositely charged ion populations, and the performance of “broad-band” collision induced dissociation (CID). These results suggest general means to improve the performance of the 3-D ion trap in a variety of mass spectrometry and tandem mass spectrometry experiments. PMID:21927573

Quasi-periodic climatic changes on Mars and earth

NASA Technical Reports Server (NTRS)

Cutts, J. A.; Pollack, J. B.; Toon, O. B.; Howard, A. D.

1981-01-01

Evidence of climatic changes on Mars and the earth due to geologic and astronomical variations is discussed. Finely striped ice-free bands in the Martian polar caps have been taken to indicate that long term variations in the orbit and axial tilt of Mars have precipitated these features at the rate of a mm/yr. Photogrammetric and photometric methods have contributed to measurements of the composition and depth of the Martian caps (14-46 m), and observations of higher solar energy absorption in the northern ice cap implies greater dust deposition in that region than on the south cap; however, the transport mechanisms are not well understood. Comparisons of earth and Martian climatic variations data are made, noting a lack of information on the age intervals of marine and nonmarine sediments on the earth. The possibilities of using quantitative data other than layer thickness to constrain climate models are discussed, and the slope or albedo of layers, or the spacing of polar undulations are suggested.

Albedo of the south pole on Mars determined by topographic forcing of atmosphere dynamics

USGS Publications Warehouse

Colaprete, A.; Barnes, J.R.; Haberle, R.M.; Hollingsworth, J.L.; Kieffer, H.H.; Titus, T.N.

2005-01-01

The nature of the martian south polar cap has remained enigmatic since the first spacecraft observations. In particular, the presence of a perennial carbon dioxide ice cap, the formation of a vast area of black 'slab ice' known as the Cryptic region and the asymmetric springtime retreat of the cap have eluded explanation. Here we present observations and climate modelling that indicate the south pole of Mars is characterized by two distinct regional climates that are the result of dynamical forcing by the largest southern impact basins, Argyre and Hellas. The style of surface frost deposition is controlled by these regional climates. In the cold and stormy conditions that exist poleward of 60?? S and extend 180?? in longitude west from the Mountains of Mitchel (???30?? W), surface frost accumulation is dominated by precipitation. In the opposite hemisphere, the polar atmosphere is relatively warm and clear and frost accumulation is dominated by direct vapour deposition. It is the differences in these deposition styles that determine the cap albedo.

The 1997 Spring Regression of the Martian South Polar Cap: Mars Orbiter Camera Observations

USGS Publications Warehouse

James, P.B.; Cantor, B.A.; Malin, M.C.; Edgett, K.; Carr, M.H.; Danielson, G.E.; Ingersoll, A.P.; Davies, M.E.; Hartmann, W.K.; McEwen, A.S.; Soderblom, L.A.; Thomas, P.C.; Veverka, J.

2000-01-01

The Mars Orbiter cameras (MOC) on Mars Global Surveyor observed the south polar cap of Mars during its spring recession in 1997. The images acquired by the wide angle cameras reveal a pattern of recession that is qualitatively similar to that observed by Viking in 1977 but that does differ in at least two respects. The 1977 recession in the 0o to 120o longitude sector was accelerated relative to the 1997 observations after LS = 240o; the Mountains of Mitchel also detached from the main cap earlier in 1997. Comparison of the MOC images with Mars Orbiter Laser Altimeter data shows that the Mountains of Mitchel feature is controlled by local topography. Relatively dark, low albedo regions well within the boundaries of the seasonal cap were observed to have red-to-violet ratios that characterize them as frost units rather than unfrosted or partially frosted ground; this suggests the possibility of regions covered by CO2 frost having different grain sizes.

Structure of Colloidal Quantum Dots from Dynamic Nuclear Polarization Surface Enhanced NMR Spectroscopy.

PubMed

Piveteau, Laura; Ong, Ta-Chung; Rossini, Aaron J; Emsley, Lyndon; Copéret, Christophe; Kovalenko, Maksym V

2015-11-04

Understanding the chemistry of colloidal quantum dots (QDs) is primarily hampered by the lack of analytical methods to selectively and discriminately probe the QD core, QD surface and capping ligands. Here, we present a general concept for studying a broad range of QDs such as CdSe, CdTe, InP, PbSe, PbTe, CsPbBr3, etc., capped with both organic and inorganic surface capping ligands, through dynamic nuclear polarization (DNP) surface enhanced NMR spectroscopy. DNP can enhance NMR signals by factors of 10-100, thereby reducing the measurement times by 2-4 orders of magnitude. 1D DNP enhanced spectra acquired in this way are shown to clearly distinguish QD surface atoms from those of the QD core, and environmental effects such as oxidation. Furthermore, 2D NMR correlation experiments, which were previously inconceivable for QD surfaces, are demonstrated to be readily performed with DNP and provide the bonding motifs between the QD surfaces and the capping ligands.

Carbon dioxide-water clathrate as a reservoir of CO2 on Mars

NASA Technical Reports Server (NTRS)

Dobrovolskis, A.; Ingersell, A. P.

1975-01-01

It has been suggested that the residual polar caps of Mars contain a resorvoir of permanently frozen carbon dioxide which is controlling the atmospheric pressure. However, observational data and models of the polar heat balance suggest that the temperatures of the Martian poles are too high for solid CO2 to survive permanently. On the other hand, the icelike compound carbon dioxide-water clathrate could function as a CO2 reservoir instead of solid CO2, because it is stable at higher temperatures. This paper shows that the permanent polar caps may contain several millibars of CO2 in the form of clathrate, and discusses the implications of this permanent clathrate reservoir for the present and past atmospheric pressure on Mars.

Surface Ages and Resurfacing Rates of the Polar Layered Deposits on Mars

USGS Publications Warehouse

Herkenhoff, K. E.; Plaut, J.J.

2000-01-01

Interpretation of the polar stratigraphy of Mars in terms of global climate changes is complicated by the significant difference in surface ages between the north and south polar layered terrains inferred from crater statistics. We have reassessed the cratering record in both polar regions using Viking Orbiter and Mariner 9 images. No craters have been found in the north polar layered terrain, but the surface of most of the south polar layered deposits appears to have been stable for many of the orbital/axial cycles that are thought to have induced global climate changes on Mars. The inferred surface age of the south polar layered deposits (about 10 Ma) is two orders of magnitude greater than the surface age of the north polar layered deposits and residual cap (at most 100 ka). Similarly, modeled resurfacing rates are at least 20 times greater in the north than in the south. These results are consistent with the hypotheses that polar layered deposit resurfacing rates are highest in areas covered by perennial ice and that the differences in polar resurfacing rates result from the 6.4 km difference in elevation between the polar regions. Deposition on the portion of the south polar layered deposits that is not covered by the perennial ice cap may have ceased about 5 million years ago when the obliquity of Mars no longer exceeded 40??. ?? 2000 Academic Press.

Modeling the Quiet Time Outflow Solution in the Polar Cap

NASA Technical Reports Server (NTRS)

Glocer, Alex

2011-01-01

We use the Polar Wind Outflow Model (PWOM) to study the geomagnetically quiet conditions in the polar cap during solar maximum, The PWOM solves the gyrotropic transport equations for O(+), H(+), and He(+) along several magnetic field lines in the polar region in order to reconstruct the full 3D solution. We directly compare our simulation results to the data based empirical model of Kitamura et al. [2011] of electron density, which is based on 63 months of Akebono satellite observations. The modeled ion and electron temperatures are also compared with a statistical compilation of quiet time data obtained by the EISCAT Svalbard Radar (ESR) and Intercosmos Satellites (Kitamura et al. [2011]). The data and model agree reasonably well. This study shows that photoelectrons play an important role in explaining the differences between sunlit and dark results, ion composition, as well as ion and electron temperatures of the quiet time polar wind solution. Moreover, these results provide validation of the PWOM's ability to model the quiet time ((background" solution.

Ion Outflow and Convection in the Polar Cap and Cleft as Measured by Tide, EFI, MFE and Timas

NASA Technical Reports Server (NTRS)

Elliott, H. A.; Craven, P. D.; Chandler, M. O.; Moore, T. E.; Maynard, N. C.; Peterson, W. K.; Lennartsson, O. W.; Shelley, E. G.; Mozer, F. S.; Russell, C. T.

1997-01-01

This study examines high-latitude ion outflows and velocities perpendicular to the magnetic field derived from moments of ion distributions measured by the TIDE (Thermal Ion Dynamics Experiment) instrument on the Polar satellite. Hydrogen and oxygen ions are shown to be E X B drifting in the polar cap and cleft regions with a speed of about 5-20 km/s at apogee (approximately 9 Re) and a speed of 1-2 km/s at perigee (approximately 1. 8 Re). E X B drifts are calculated from electric fields measured by EFI (Electric Field Instrument) and magnetic fields measured by MFE (Magnetic Field Experiment) both of which are also on Polar. How convection at Polar's perigee relates to potential patterns of the ionosphere will be discussed. In the cusp/cleft the distribution of hydrogen extends over a large enough range of energy to be measured by both TIDE and the Toroidal Imaging Mass-Angle Spectrograph (TIMAS). Such comparisons will be also be presented.

Plasma Irregularity Production in the Polar Cap F-Region Ionosphere

NASA Astrophysics Data System (ADS)

Lamarche, Leslie

Plasma in the Earth's ionosphere is highly irregular on scales ranging between a few centimeters and hundreds of kilometers. Small-scale irregularities or plasma waves can scatter radio waves resulting in a loss of signal for navigation and communication networks. The polar region is particularly susceptible to strong disturbances due to its direct connection with the Sun's magnetic field and energetic particles. In this thesis, factors that contribute to the production of decameter-scale plasma irregularities in the polar F region ionosphere are investigated. Both global and local control of irregularity production are studied, i.e. we consider global solar control through solar illumination and solar wind as well as much more local control by plasma density gradients and convection electric field. In the first experimental study, solar control of irregularity production is investigated using the Super Dual Auroral Radar Network (SuperDARN) radar at McMurdo, Antarctica. The occurrence trends for irregularities are analyzed statistically and a model is developed that describes the location of radar echoes within the radar's field-of-view. The trends are explained through variations in background plasma density with solar illumination affecting radar beam propagation. However, it is found that the irregularity occurrence during the night is higher than expected from ray tracing simulations based on a standard ionospheric density model. The high occurrence at night implies an additional source of plasma density and it is proposed that large-scale density enhancements called polar patches may be the source of this density. Additionally, occurrence maximizes around the terminator due to different competing irregularity production processes that favor a more or less sunlit ionosphere. The second study is concerned with modeling irregularity characteristics near a large-scale density gradient reversal, such as those expected near polar patches, with a particular focus on the asymmetry of the irregularity growth rate across the gradient reversal. Directional dependencies on the plasma density gradient, plasma drift, and wavevector are analyzed in the context of the recently developed general fluid theory of the gradient-drift instability. In the ionospheric F region, the strongest asymmetry is found when an elongated structure is oriented along the radar's boresight and moving perpendicular to its direction of elongation. These results have important implications for finding optimal configurations for oblique-scanning ionospheric radars such as SuperDARN to observe gradient reversals. To test the predictions of the developed model and the general theory of the gradient-drift instability, an experimental investigation is presented focusing on decameter-scale irregularities near a polar patch and the previously uninvestigated directional dependence of irregularity characteristics. Backscatter power and occurrence of irregularities are analyzed using measurements from the SuperDARN radar at Rankin Inlet, Canada, while background density gradients and convection electric fields are found from the north face of the Resolute Bay Incoherent Scatter Radar. It is shown that irregularity occurrence tends to follow the expected trends better than irregularity power, suggesting that while the gradient-drift instability may be a dominant process in generating small-scale irregularities, other mechanisms such as a shear-driven instability or nonlinear process may exert greater control over their intensity. It is concluded from this body of work that the production of small-scale plasma irregularities in the polar F-region ionosphere is controlled both by global factors such as solar illumination as well as local plasma density gradients and electric fields. In general, linear gradient-drift instability theory describes small-scale irregularity production well, particularly for low-amplitude perturbations. The production of irregularities is complex, and while ground-based radars are invaluable tools to study the ionosphere, care must be taken to interpret results correctly.

Volatile-rich Crater Interior Deposits in the Polar Regions of Mars: Evidence for Ice Cap Advance and Retreat

NASA Technical Reports Server (NTRS)

Russell, Patrick S.; Head, James W.; Hecht, Michael H.

2003-01-01

Many craters on Mars are partially filled by distinctive material emplaced by post-impact processes. This crater fill material is an interior mound which is generally separated from the walls of the crater by a trough that may be continuous along the crater circumference (i.e. a ring-shaped trough), or which may only partially contact the crater walls (i.e. a crescent-shaped trough). The fill deposit is frequently offset from the crater center and may be asymmetric in plan view. Populations of such craters include those in the circum-south polar cap region, in Arabia Terra, associated with the Medusae Fossae Formation, and in the northern lowlands proximal to the north polar cap. We focus on those craters in circumpolar regions and assess their relationship to polar cap advance and retreat, especially the possibility that fill material represents remnants of a formerly larger contiguous cap. Volatile-rich deposits have the property of being modifiable by the local stability of the solid volatile, which is governed by local energy balance. Here we test the hypothesis that asymmetries in volatile fill shape, profile, and center-location within a crater result from asymmetries in local energy balance within the crater, due mainly to variation of solar insolation and radiative effects of the crater walls over the crater interior. Model profiles of crater fill are compared with MOLA topographic profiles to assess this hypothesis. If asymmetry in morphology and location of crater fill are consistent with radiative-dominated asymmetries in energy budget within the crater, then 1) the volatile-rich composition of the fill is supported (this process should not be effective at shaping volcanic or sedimentary deposits), and 2) the dominant factor determining the observed shape of volatile-rich crater fill is the local radiative energy budget (and erosive processes such as eolian deflation are secondary or unnecessary). We also use a geographic and energy model approach to specifically test the idea that material in partially filled craters around the south pole may once have been contiguous to the cap and may have been sustained and modified by radiative processes specific to the crater environment (as opposed to the surrounding plains) as the cap retreated.

Broadband Circularly Polarized Slot Antenna Loaded by a Multiple-Circular-Sector Patch

PubMed Central

Trinh-Van, Son; Yang, Youngoo; Lee, Kang-Yoon

2018-01-01

In this paper, a microstrip-fed broadband circularly polarized (CP) slot antenna is presented. CP operation can be attained simply by embedding an S-shaped strip. By loading with a multiple-circular-sector patch, which consists of 12 circular-sector patches with identical central angles of 30° and different radii, the 3 dB axial ratio (AR) bandwidth is significantly broadened. To validate the performance of the proposed antenna, an antenna prototype is fabricated and tested. The fabricated antenna is 54 mm × 54 mm × 0.8 mm in size. The measured −10 dB reflection and 3 dB AR bandwidths are 81.06% (1.68–3.97 GHz) and 70.55% (1.89–3.95 GHz), respectively. Within the 3 dB AR bandwidth, the measured peak gain is 3.81 dBic. Reasonable agreement is also obtained between the measured and simulated results. PMID:29762530

Broadband Circularly Polarized Slot Antenna Loaded by a Multiple-Circular-Sector Patch.

PubMed

Trinh-Van, Son; Yang, Youngoo; Lee, Kang-Yoon; Hwang, Keum Cheol

2018-05-15

In this paper, a microstrip-fed broadband circularly polarized (CP) slot antenna is presented. CP operation can be attained simply by embedding an S-shaped strip. By loading with a multiple-circular-sector patch, which consists of 12 circular-sector patches with identical central angles of 30° and different radii, the 3 dB axial ratio (AR) bandwidth is significantly broadened. To validate the performance of the proposed antenna, an antenna prototype is fabricated and tested. The fabricated antenna is 54 mm × 54 mm × 0.8 mm in size. The measured -10 dB reflection and 3 dB AR bandwidths are 81.06% (1.68⁻3.97 GHz) and 70.55% (1.89⁻3.95 GHz), respectively. Within the 3 dB AR bandwidth, the measured peak gain is 3.81 dBic. Reasonable agreement is also obtained between the measured and simulated results.

Magnetohydrodynamic Simulations of Black Hole Accretion Flows Using PATCHWORK, a Multi-Patch, multi-code approach

NASA Astrophysics Data System (ADS)

Avara, Mark J.; Noble, Scott; Shiokawa, Hotaka; Cheng, Roseanne; Campanelli, Manuela; Krolik, Julian H.

2017-08-01

A multi-patch approach to numerical simulations of black hole accretion flows allows one to robustly match numerical grid shape and equations solved to the natural structure of the physical system. For instance, a cartesian gridded patch can be used to cover coordinate singularities on a spherical-polar grid, increasing computational efficiency and better capturing the physical system through natural symmetries. We will present early tests, initial applications, and first results from the new MHD implementation of the PATCHWORK framework.

Analysis of proton and electron spectrometer data from OGO-5 spacecraft

NASA Technical Reports Server (NTRS)

Pomerantz, M. A.

1975-01-01

The interaction between the geomagnetic and interplanetary magnetic fields is studied through its effects upon the intensities of solar electrons reaching the polar caps during times of strongly anisotropic electron fluxes in the magnetosheath. During the particle event of November 18, 1968, electrons of solar origin were observed outside the magnetopause with detectors aboard OGO-5. Correlative studies of these satellite observations and concurrent measurements by riometers and ionospheric forward scatter systems in both polar regions revealed that the initial stage of the associated polar cap absorption event is attributable to the arrival of solar electrons. Evidence of a north-south asymmetry in the solar electron flux, at a time when the interplanetary magnetic field vector was nearly parallel with the ecliptic plane, supports an open magnetospheric model. The analysis indicates that an anisotropic electron flux may be isotropized at the magnetopause before propagating into the polar regions.

An onboard data analysis method to track the seasonal polar caps on Mars

NASA Technical Reports Server (NTRS)

Wagstaff, Kiri L.; Castano, Rebecca; Chien, Steve; Ivanov, Anton B.; Pounders, Erik; Titus, Timothy N.

2005-01-01

In this paper, we evaluate our method on uncalibrated THEMIS data and find 1) agreement with manual cap edge identifications to within 28.2 km, and 2) high accuracy even with a reduced context window, yielding large reductions in memory requirements.

Measurement of the magnetotail reconnection rate

NASA Astrophysics Data System (ADS)

Blanchard, G. T.; Lyons, L. R.; de la Beaujardière, O.; Doe, R. A.; Mendillo, M.

1996-07-01

A technique to measure the magnetotail reconnection rate from the ground is described and applied to 71 hours of measurements from 20 nights. The reconnection rate is obtained from the ionospheric flow across the polar cap boundary in the frame of reference of the boundary, measured by the Sondrestrom incoherent scatter radar. For our measurements, the polar cap boundary is located using 6300 Å auroral emissions and E region electron density. The average experimental uncertainty of the reconnection rate measurement is 11.6 mVm-1 in the ionospheric electric field. By using a large data set, we obtain the dependence of the reconnection rate on magnetic local time, the interplanetary magnetic field, and substorm activity, with much higher accuracy. We find that two thirds of the average polar cap potential drop occurs over the 4-hour segment of the separatrix centered on 2330 MLT, that the linear correlation between the reconnection electric field and the half-wave rectified dawn-dusk solar wind electric field VBs peaks between 1.0 and 1.5 hours, with a maximum linear correlation coefficient of 0.46 at 70 min; and that following substorm expansion phase onset, the reconnection electric field becomes larger than the experimental uncertainty, with an average delay of 23 min. The 70-min delay of the reconnection rate with respect to VBs is a typical convection time for a flux tube across the polar cap. This result indicates that reconnection in the magnetotail is influenced by the solar wind electric field VBs on the field line being reconnected.

The effects of seasonal and diurnal variations in the Earth's magnetic dipole orientation on solar wind-magnetosphere-ionosphere coupling

NASA Astrophysics Data System (ADS)

Cnossen, Ingrid; Wiltberger, Michael; Ouellette, Jeremy E.

2012-11-01

The angle μ between the geomagnetic dipole axis and the geocentric solar magnetospheric (GSM) z axis, sometimes called the “dipole tilt,” varies as a function of UT and season. Observations have shown that the cross-polar cap potential tends to maximize near the equinoxes, when on average μ = 0, with smaller values observed near the solstices. This is similar to the well-known semiannual variation in geomagnetic activity. We use numerical model simulations to investigate the role of two possible mechanisms that may be responsible for the influence of μ on the magnetosphere-ionosphere system: variations in the coupling efficiency between the solar wind and the magnetosphere and variations in the ionospheric conductance over the polar caps. Under southward interplanetary magnetic field (IMF) conditions, variations in ionospheric conductance at high magnetic latitudes are responsible for 10-30% of the variations in the cross-polar cap potential associated with μ, but variations in solar wind-magnetosphere coupling are more important and responsible for 70-90%. Variations in viscous processes contribute slightly to this, but variations in the reconnection rate with μ are the dominant cause. The variation in the reconnection rate is primarily the result of a variation in the length of the section of the separator line along which relatively strong reconnection occurs. Changes in solar wind-magnetosphere coupling also affect the field-aligned currents, but these are influenced as well by variations in the conductance associated with variations in μ, more so than the cross-polar cap potential. This may be the case for geomagnetic activity too.

The Role of Ionospheric Conductivity in the Response of the Magnetosphere and Ionosphere to Changes in the Earth's Magnetic Field

NASA Astrophysics Data System (ADS)

Cnossen, I.; Wiltberger, M. J.; Richmond, A. D.; Ouellette, J.

2014-12-01

The strength and orientation of the Earth's magnetic field play an important role in the magnetosphere-ionosphere-thermosphere system. This is demonstrated in a set of idealized experiments with the Coupled Magnetosphere-Ionosphere-Thermosphere model using a dipolar magnetic field. A decrease of the dipole moment (M) causes an increase in ionospheric conductance. This increase in conductance results in enhanced field-aligned currents (FACs), which change the shape of the magnetosphere, and causes a deviation from theoretical scaling relations of the stand-off distance, the size of the polar cap, and the cross-polar cap potential with M. The orientation of the Earth's magnetic field determines how the angle μ between the geomagnetic dipole axis and the geocentric solar magnetospheric (GSM) z-axis varies with season and universal time (UT). The angle μ can affect solar wind-magnetosphere-ionosphere coupling in two distinct ways: via variations in ionospheric conductivity over the polar caps or via a change in the coupling efficiency between the solar wind and magnetosphere as a result of changes in geometry. Simulations in which the ionospheric conductivity was either kept fixed or allowed to vary realistically demonstrated that variations in ionospheric conductance are responsible for ~10-30% of the variations in the cross-polar cap potential associated with variations in μ for southward interplanetary magnetic field (IMF). The remainder was mostly due to variations in the magnetic reconnection rate, which were associated with variations in the length of the section of the separator line along which relatively strong reconnection occurs.

Springtime Dust Storm Swirls at Martian North Pole

NASA Technical Reports Server (NTRS)

1996-01-01

Two Hubble Space Telescope images of Mars, taken about a month apart on September 18 and October 15, 1996, reveal a state-sized dust storm churning near the edge of the Martian north polar cap. The polar storm is probably a consequence of large temperature differences between the polar ice and the dark regions to the south, which are heated by the springtime sun. The increased sunlight also causes the dry ice in the polar cap to sublime and shrink.

Mars is famous for large, planet-wide dust storms. Smaller storms resembling the one seen here were observed in other regions by Viking orbiters in the late 1970s. However, this is the first time that such an event has been caught near the receding north polar cap. The Hubble images provide valuable new insights into the behavior of localized dust storms on Mars, which are typically below the resolution of ground-based telescopes. This kind of advanced planetary 'weather report' will be invaluable for aiding preparation for the landing of NASA's Pathfinder spacecraft in July 1997 and the arrival of Mars Global Surveyor orbiter in September 1997.

Top (September 18, 1996) - The salmon colored notch in the white north polar cap is a 600-mile (1,000 kilometer) long storm -- nearly the width of Texas. The bright dust can also be seen over the dark surface surrounding the cap, where it is caught up in the Martian jet stream and blown easterly. The white clouds at lower latitudes are mostly associated with major Martian volcanos such as Olympus Mons. This image was taken when Mars was more than 186 million miles (300 million kilometers) from Earth, and the planet was smaller in angular size than Jupiter's Great Red Spot!

Bottom (October 15, 1996) - Though the storm has dissipated by October, a distinctive dust-colored comma-shaped feature can be seen curving across the ice cap. The shape is similar to cold fronts on Earth, which are associated with low pressure systems. Nothing quite like this feature has been seen previously either in ground-based or spacecraft observation. The snow line marking the edge of the cap receded northward by approximately 120 miles (200 kilometers), while the distance to the Red Planet narrowed to 170 million miles (275 million kilometers).

Technical notes: To help compare locations and sizes of features, map projections (right of each disk) are centered on the geographic north pole. Maps are oriented with 0 degrees longitude at the top and show meridians every 45 degrees of longitude (longitude increases clockwise); latitude circles are also shown for 40, 60, and 80 degrees north latitude. The color images were assembled from separate exposures taken with the Wide Field Planetary Camera 2.

This image and other images and data received from the Hubble Space Telescope are posted on the World Wide Web on the Space Telescope Science Institute home page at URL http:// oposite.stsci.edu/pubinfo/

Field-aligned Currents Induced by Electrostatic Polarization at the Ionosphere: Application to the Poleward Boundary Intensification (PBI) of Auroral Emission

NASA Astrophysics Data System (ADS)

Ohtani, S.; Yoshikawa, A.

2016-12-01

Although the field-aligned currents (Birkeland currents) are generally considered to be driven by magnetospheric processes, it is possible that some field-aligned currents are locally induced in the ionosphere in the presence of sharp conductance gradient. In this presentation we shall discuss the poleward boundary intensification (PBI) of auroral emission as an example effect of such electrostatic polarization. The observations show that the PBIs are very often preceded by the fast polar cap convection approaching the nightside auroral oval. We propose that the ionospheric currents driven by the associated electric field diverges/converges at the poleward boundary of the auroral oval as the background ionospheric conductance changes sharply in space, and they close with field-aligned currents. The associated upward field-aligned current is accompanied by electron precipitation, which may cause auroral emission as observed as PBIs. We test this idea by modeling the ionosphere as a slab-shaped enhancement of conductance and the polar cap flow channel as a pair of upward and downward FACs. The results show that (i) a pair of upward and downward FACs is induced at the poleward boundary when the front of the polar cap flow channel approaches the auroral oval; (ii) the upward FAC extends westward much wider in longitude than the flow channel; (iii) the peak FAC density is significantly larger than the incident FAC; and (iv) the induced upward and downward FACs are distributed almost symmetrically in longitude, indicating that the Pedersen polarization dominates the Hall polarization. These results are consistent with some general characteristics of PBIs, which are rather difficult to explain if the PBIs are the ionospheric manefestation of distant reconnection as often suggested.

Lipid Domain Structure of the Plasma Membrane Revealed by Patching of Membrane Components

PubMed Central

Harder, Thomas; Scheiffele, Peter; Verkade, Paul; Simons, Kai

1998-01-01

Lateral assemblies of glycolipids and cholesterol, “rafts,” have been implicated to play a role in cellular processes like membrane sorting, signal transduction, and cell adhesion. We studied the structure of raft domains in the plasma membrane of non-polarized cells. Overexpressed plasma membrane markers were evenly distributed in the plasma membrane. We compared the patching behavior of pairs of raft markers (defined by insolubility in Triton X-100) with pairs of raft/non-raft markers. For this purpose we cross-linked glycosyl-phosphatidylinositol (GPI)-anchored proteins placental alkaline phosphatase (PLAP), Thy-1, influenza virus hemagglutinin (HA), and the raft lipid ganglioside GM1 using antibodies and/or cholera toxin. The patches of these raft markers overlapped extensively in BHK cells as well as in Jurkat T–lymphoma cells. Importantly, patches of GPI-anchored PLAP accumulated src-like protein tyrosine kinase fyn, which is thought to be anchored in the cytoplasmic leaflet of raft domains. In contrast patched raft components and patches of transferrin receptor as a non-raft marker were sharply separated. Taken together, our data strongly suggest that coalescence of cross-linked raft elements is mediated by their common lipid environments, whereas separation of raft and non-raft patches is caused by the immiscibility of different lipid phases. This view is supported by the finding that cholesterol depletion abrogated segregation. Our results are consistent with the view that raft domains in the plasma membrane of non-polarized cells are normally small and highly dispersed but that raft size can be modulated by oligomerization of raft components. PMID:9585412

The Triggering Mechanism of Quiet-Region Coronal Jet Eruptions: Flux Cancelation

NASA Technical Reports Server (NTRS)

Panesar, Navdeep K.; Sterling, Alphonse C.; Moore, Ronald L.

2017-01-01

Coronal jets are frequent transient features on the Sun, observed in EUV and X-ray emissions. They occur in active regions, quiet Sun and coronal holes, and appear as a bright spire with base brightenings. Recent studies show that many coronal jets are driven by the eruption of a minifilament. Here we investigate the magnetic cause of jet-driving minifilament eruptions. We study ten randomly-found on-disk quiet-region coronal jets using SDO/AIA intensity images and SDO/HMI magnetograms. For all ten events, we track the evolution of photospheric magnetic flux in the jet-base region in EUV images and find that (a) a cool (transition-region temperature) minifilament is present prior to each jet eruption; (b) the pre-eruption minifilament resides above the polarity-inversion line between majority-polarity and minority-polarity magnetic flux patches; (c) the opposite-polarity flux patches converge and cancel with each other; (d) the cancelation between the majority-polarity and minority-polarity flux patches eventually destabilizes the field holding the minifilament to erupt outwards; (e) the envelope of the erupting field barges into ambient oppositely-directed far-reaching field and undergoes external reconnection (interchange reconnection); (f) the external reconnection opens the envelope field and the minifilament field inside, allowing reconnected-heated hot material and cool minifilament material to escape along the far-reaching field, producing the jet spire. In summary, we found that each of our ten jets resulted from a minifilament eruption following flux cancelation at the magnetic neutral line under the pre-eruption minifilament. These observations show that flux cancelation is usually the trigger of quiet-region coronal jet eruptions.

H2O grain size and the amount of dust in Mars' residual north polar cap

NASA Technical Reports Server (NTRS)

Kieffer, Hugh H.

1990-01-01

In Mars' north polar cap, the probable composition of material residual from the annual condensation cycle is a mixture of fine dust and H2O grains of comparable size and abundance. However, metamorphism of such material will gradually lower its albedo by increasing the size of the H2O grains only. If the cap is undergoing net annual sublimation (as inferred from water vapor observations), late summer observations should be of old ice with H2O grain sizes of 100 microns or more. Ice of this granularity containing 30 percent fine dust has a reflectivity similar to that of dust alone; the observed albedo and computed ice grain size imply dust concentrations of 1 part per 1000 or less. The brightness of the icy areas conflicts with what would be expected for a residual cap deposited by an annual cycle similar to that observed by Viking and aged for thousands of years. The residual cap surface cannot be 'old dirty' ice. It could be old, coarse, and clean; or it could be young, fine, and dirty. This brings into question both the source of the late summer water vapor and the formation rate of laminated terrain.

Surface mass balance of Greenland mountain glaciers and ice caps

NASA Astrophysics Data System (ADS)

Benson, R. J.; Box, J. E.; Bromwich, D. H.; Wahr, J. M.

2009-12-01

Mountain glaciers and ice caps contribute roughly half of eustatic sea-level rise. Greenland has thousands of small mountain glaciers and several ice caps > 1000 sq. km that have not been included in previous mass balance calculations. To include small glaciers and ice caps in our study, we use Polar WRF, a next-generation regional climate data assimilation model is run at grid resolution less than 10 km. WRF provides surface mass balance data at sufficiently high resolution to resolve not only the narrow ice sheet ablation zone, but provides information useful in downscaling melt and accumulation rates on mountain glaciers and ice caps. In this study, we refine Polar WRF to simulate a realistic surface energy budget. Surface melting is calculated in-line from surface energy budget closure. Blowing snow sublimation is computed in-line. Melt water re-freeze is calculated using a revised scheme. Our results are compared with NASA's Gravity Recovery and Climate Experiment (GRACE) and associated error is calculated on a regional and local scale with validation from automated weather stations (AWS), snow pits and ice core data from various regions along the Greenland ice sheet.

H2O grain size and the amount of dust in Mars' residual North polar cap

USGS Publications Warehouse

Kieffer, H.H.

1990-01-01

In Mars' north polar cap the probable composition of material residual from the annual condensation cycle is a mixture of fine dust and H2O grains of comparable size and abundance. However, metamorphism of such material will gradually lower its albedo by increasing the size of the H2O grains only. If the cap is undergoing net annual sublimation (as inferred from water vapor observations), late summer observations should be of old ice with H2O grain sizes of 100 ??m or more. Ice of this granularity containing 30% fine dust has a reflectivity similar to that of dust alone; the observed albedo and computed ice grain size imply dust concentrations of 1 part per 1000 or less. The brightness of the icy areas conflicts with what would be expected for a residual cap deposited by an annual cycle similar to that observed by Viking and aged for thousands of years. The residual cap surface cannot be "old dirty' ice. It could be old, coarse, and clean; or it could be young, fine, and dirty. This brings into question both the source of the late summer water vapor and the formation rate of laminated terrain. -Author

Unidirectional Magneto-Electric Dipole Antenna for Base Station: A Review

NASA Astrophysics Data System (ADS)

Idayachandran, Govindanarayanan; Nakkeeran, Rangaswamy

2018-04-01

Unidirectional base station antenna design using Magneto-Electric Dipole (MED) has created enormous interest among the researchers due to its excellent radiation characteristics like low back radiation, symmetrical radiation at E-plane and H-plane compared to conventional patch antenna. Generally, dual polarized antennas are used to increase channel capacity and reliability of the communication systems. In order to serve the evolving mobile communication standards like long term evolution LTE and beyond, unidirectional dual polarized MED antenna are required to have broad impedance bandwidth, broad half power beamwidth, high port isolation, low cross polarization level, high front to back ratio and high gain. In this paper, the critical electrical requirements of the base station antenna and frequently used frequency bands for modern mobile communication have been presented. It is followed by brief review on broadband patch antenna and discussion on complementary antenna concepts. Finally, the performance of linearly polarized and dual polarized magneto-electric dipole antennas along with their feeding techniques are discussed and summarized. Also, design and modeling of developed MED antenna is presented.

Influence of the interplanetary magnetic field orientation on polar cap ion trajectories - Energy gain and drift effects

NASA Technical Reports Server (NTRS)

Delcourt, D. C.; Horwitz, J. L.; Swinney, K. R.

1988-01-01

The influence of the interplanetary magnetic field (IMF) orientation on the transport of low-energy ions injected from the ionosphere is investigated using three-dimensional particle codes. It is shown that, unlike the auroral zone outflow, the ions originating from the polar cap region exhibit drastically different drift paths during southward and northward IMF. During southward IMF orientation, a 'two-cell' convection pattern prevails in the ionosphere, and three-dimensional simulations of ion trajectories indicate a preferential trapping of the light ions H(+) in the central plasma sheet, due to the wide azimuthal dispersion of the heavy ions, O(+). In contrast, for northward IMF orientation, the 'four-cell' potential distribution predicted in the ionosphere imposes a temporary ion drift toward higher L shells in the central polar cap. In this case, while the light ions can escape into the magnetotail, the heavy ions can remain trapped, featuring more intense acceleration (from a few electron volts up to the keV range) followed by precipitation at high invariant latitudes, as a consequence of their further travel into the tail.

Microorganisms on comets, Europa, and the polar ice caps of Mars

NASA Astrophysics Data System (ADS)

Hoover, Richard B.; Pikuta, Elena V.

2004-02-01

Microbial extremophiles live on Earth wherever there is liquid water and a source of energy. Observations by ground-based observatories, space missions, and satellites have provided strong evidence that water ice exists today on comets, Europa, Callisto, and Ganymede and in the snow, permafrost, glaciers and polar ice caps of Mars. Studies of the cryoconite pools and ice bubble systems of Antarctica suggest that solar heating of dark rocks entrained in ice can cause localized melting of ice providing ideal conditions for the growth of microbial communities with the creation of micro-environments where trapped metabolic gasses produce entrained isolated atmospheres as in the Antarctic ice-bubble systems. It is suggested that these considerations indicate that several groups of microorganisms should be capable of episodic growth within liquid water envelopes surrounding dark rocks in cometary ices and the permafrost and polar caps of Mars. We discuss some of the types of microorganisms we have encountered within the permafrost and snow of Siberia, the cryoconite pools of Alaska, and frozen deep within the Antarctic ice sheet above Lake Vostok.

A Case for Microorganisms on Comets, Europa and the Polar Ice Caps of Mars

NASA Technical Reports Server (NTRS)

Hoover, Richard B.; Pikuta, Elena V.

2003-01-01

Microbial extremophiles live on Earth wherever there is liquid water and a source of energy. Observations by ground-based observatories, space missions, and satellites have provided strong evidence that water ice exists today on comets, Europa, Callisto, and Ganymede and in the snow, permafrost, glaciers and polar ice caps of Mars. Studies of the cryoconite pools and ice bubble systems of Antarctica suggest that solar heating of dark rocks entrained in ice can cause localized melting of ice providing ideal conditions for the growth of microbial communities with the creation of micro-environments where trapped metabolic gasses produce entrained isolated atmospheres as in the Antarctic ice-bubble systems. It is suggested that these considerations indicate that several groups of microorganisms should be capable of episodic growth within liquid water envelopes surrounding dark rocks in cometary ices and the permafrost and polar caps of Mars. We discuss some of the types of microorganisms we have encountered within the permafrost and snow of Siberia, the cryoconite pools of Alaska, and frozen deep within the Antarctic ice sheet above Lake Vostok.

Chronological changes in the eighth cranial nerve compound action potential (CAP) in experimental endolymphatic hydrops: the effects of altering the polarity of click sounds.

PubMed

Morizono, Tetsuo; Kondo, Tsuyoshi; Yamano, Takafumi; Miyagi, Morimichi; Shiraishi, Kimio

2009-02-01

Using a guinea pig model of experimental endolymphatic hydrops, click sounds of altered polarity showed different latencies and amplitudes in hydropic compared with normal cochleae. Latency changes appeared as early as 1 week after endolymphatic obstruction. This method can help diagnose endolymphatic hydrops. The goal of the study was to develop an objective electrophysiological diagnosis of endolymphatic hydrops. Endolymphatic hydrops were created surgically in guinea pigs. The latency and the amplitude of the eighth cranial nerve compound action potential (CAP) for click sounds of altered polarity were measured up to 8 weeks after the surgery. At early stages after surgery, the latency for condensation clicks became longer, and at later stages the latencies for both condensation and rarefaction became longer. The discrepancy in the latencies for rarefaction and condensation click sounds (rarefaction minus condensation) became larger by the first week after surgery, but no further discrepancy occurred thereafter. Compared with latency changes, amplitude changes in the CAP were rapid and progressive following surgery, suggesting ongoing damage to hair cells.

The Canadian High Arctic Ionospheric Network (CHAIN)

NASA Astrophysics Data System (ADS)

Jayachandran, P. T.; Langley, R. B.; MacDougall, J. W.; Mushini, S. C.; Pokhotelov, D.; Chadwick, R.; Kelly, T.

2009-05-01

Polar cap ionospheric measurements are important for the complete understanding of the various processes in the solar wind - magnetosphere - ionosphere (SW-M-I) system as well as for space weather applications. Currently the polar cap region is lacking high temporal and spatial resolution ionospheric measurements because of the orbit limitations of space-based measurements and the sparse network providing ground- based measurements. Canada has a unique advantage in remedying this shortcoming because it has the most accessible landmass in the high Arctic regions and the Canadian High Arctic Ionospheric Network (CHAIN) is designed to take advantage of Canadian geographic vantage points for a better understanding of the Sun-Earth system. CHAIN is a distributed array of ground-based radio instruments in the Canadian high Arctic. The instruments components of CHAIN are ten high data-rate Global Positioning System ionospheric scintillation and total electron content monitors and six Canadian Advanced Digital Ionosondes. Most of these instruments have been sited within the polar cap region except for two GPS reference stations at lower latitudes. This paper briefly overviews the scientific capabilities, instrument components, and deployment status of CHAIN.

Experimental investigation of insolation-driven dust ejection from Mars' CO2 ice caps

NASA Astrophysics Data System (ADS)

Kaufmann, E.; Hagermann, A.

2017-01-01

Mars' polar caps are - depending on hemisphere and season - partially or totally covered with CO2 ice. Icy surfaces such as the polar caps of Mars behave differently from surfaces covered with rock and soil when they are irradiated by solar light. The latter absorb and reflect incoming solar radiation within a thin layer beneath the surface. In contrast, ices are partially transparent in the visible spectral range and opaque in the infrared. Due to this fact, the solar radiation can penetrate to a certain depth and raise the temperature of the ice or dust below the surface. This may play an important role in the energy balance of icy surfaces in the solar system, as already noted in previous investigations. We investigated the temperature profiles inside CO2 ice samples including a dust layer under Martian conditions. We have been able to trigger dust eruptions, but also demonstrated that these require a very narrow range of temperature and ambient pressure. We discuss possible implications for the understanding of phenomena such as arachneiform patterns or fan shaped deposits as observed in Mars' southern polar region.

Origin of Pre-Coronal-Jet Minifilaments: Flux Cancellation

NASA Astrophysics Data System (ADS)

Panesar, N. K.; Sterling, A. C.; Moore, R. L.

2017-12-01

We recently investigated the triggering mechanism of ten quiet-region coronal jet eruptions and found that magnetic flux cancellation at the neutral line of minifilaments is the main cause of quiet-region jet eruptions (Panesar et al 2016). However, what leads to the formation of the pre-jet minifilaments remained unknown. In the present work, we study the longer-term evolution of the magnetic field that leads to the formation of pre-jet minifilaments by using SDO/AIA intensity images and concurrent line of sight SDO/HMI magnetograms. We find that each of the ten pre-jet minifilaments formed due to progressive flux cancellation between the minority-polarity and majority-polarity flux patches (with a minority-polarity flux loss of 10% - 40% prior to minifilament birth). Apparently, the flux cancellation between the opposite polarity flux patches builds a highly-sheared field at the magnetic neutral line, and that field holds the cool transition region minifilament plasma. Even after the formation of minifilaments, the flux continues to cancel, making the minifilament body more thick and prominent. Further flux cancellation between the opposite-flux patches leads to the minifilament eruption and a resulting jet. From these observations, we infer that flux cancellation is usually the process that builds up the sheared and twisted field in pre-jet minifilaments, and that triggers it to erupt and drive a jet.

Impedance properties of circular microstrip antenna

NASA Technical Reports Server (NTRS)

Deshpande, M. D.; Bailey, M. C.

1983-01-01

A moment method solution to the input impedance of a circular microstrip antenna excited by either a microstrip feed or a coaxial probe is presented. Using the exact dyadic Green's function and the Fourier transform the problem is formulated in terms of Richmond's reaction integral equation from which the unknown patch current can be solved for. The patch current is expanded in terms of regular surface patch modes and an attachment mode (for probe excited case) which insures continuity of the current at probe/patch junction, proper polarization and p-dependance of patch current in the vicinity of the probe. The input impedance of a circular microstrip antenna is computed and compared with earlier results. Effect of attachment mode on the input impedance is also discussed.

Department of Defense’s Waiver of Competitive Prototyping Requirement for Enhanced Polar System Program

DTIC Science & Technology

2012-08-23

objectives. Finally, the CAPS acquisition strategy anticipates the use of a cost- reimbursement contract for designing and building the system...The CAPS acquisition strategy anticipates the use of a cost- reimbursement contract for designing and building the system; however, it may be... reimbursement contract was chosen for the basic CAPS contract because of the nature of the design work, which includes software design and development

Topography of the South Polar Cap and Layered Deposits of Mars: Viking Stereo Grametry at Regional and Local Scales

NASA Technical Reports Server (NTRS)

Schenk, P.; Moore, J.; Stoker, C.

1998-01-01

Layered deposits and residual polar caps on Mars may record the deposition of ice and sediment modulated by periodic climate change. Topographic information relating to layer thicknesses, erosional processes, and formation of dark spirals within these deposits has been sparce or unreliable until the arrival of MOLA in orbit in September 1997. To assist in evaluating these terrains prior to launch and to assess formation and erosion processes in the polar deposits, we have assembled Viking stereo mosaics of the region and have produced the first reliable DEM models of the south polar deposits using automated stereogrammetry tools. Here we report our preliminary topographic results, pending final image pointing updates. The maximum total thickness of the layered deposits in the south polar region is 2.5 km. The thick layered deposits consist of a series of megaterraces. Each terrace is several tens of kilometers wide and is flat or slopes very gently toward the pole. These terraces step downward from a central plateau near the south pole. Terraces are bounded by relatively steep scarps 100-500 meters high that face toward the equator. These scarps correspond to the pattern of dark spirals observed within the residual cap in southern summer, and are interpreted as ice or frost-free surfaces warmed by solar insolation. Several tongue-shaped troughs, with rounded cirquelike heads, are observed near the margins of the deposit. These troughs are 300-600 meters in deep and may be similar to troughs observed in the northern polar deposit.

Improved Dual-Polarized Microstrip Antenna

NASA Technical Reports Server (NTRS)

Huang, John

1993-01-01

Dual-polarized microstrip antenna features microstrip transmission-line feeds arranged in such configuration that cross-polarized components of radiation relatively low and degree of isolation between feed ports relatively high. V and H feed ports offset from midpoints of feed lines to obtain required opposite phases at feed-point connections to microstrip patches. Two independent beams of same frequency with electric fields polarized orthogonally to each other transmitted or received via antenna. Improved design saves space.

The Residual South Polar Cap of Mars: Stable or Transitory?

NASA Astrophysics Data System (ADS)

Glenar, David A.; Bonev, B. P.; Hansen, G. B.; James, P. B.; Bjorkman, J. E.

2006-09-01

It remains uncertain whether the CO2 residual south polar cap (RSPC) is a permanent feature of the present Mars climate, or whether it occasionally sublimes completely during years marked by dramatic dust storm activity. While there is no firm evidence for complete disappearance of the cap in the past, observations show that the residual cap lost significant CO2 material in the spring / summer season prior to the Mariner 9 encounter. On the other hand, little interannual change has been observed in the RSPC during the MGS mission [1], despite the massive early-spring dust storm which occurred in 2001. We discuss whether a global dust storm beginning near perihelion could enhance the net CO2 sublimation sufficiently to completely remove the RSPC. We utilize a surface-plus-aerosol radiative transfer model under conditions of both modest and heavy atmospheric dust loading. The sublimination behavior depends critically on the extended (visible to thermal IR) albedo spectrum of the polar CO2 ice, which we have strongly constrained [2] from a combination of HST photometric imaging, ground based near-IR imaging spectroscopy and spectroscopic measurements by the Mars Express PFS. The extension of the cap spectrum to thermal IR wavelengths was accomplished by forward modeling using a semi-infinite grid of scattering grains. Results of this analysis depend on the strength of possible feedback mechanisms (increased surface dust content; exposure of water ice) as well as on the possibility of dust confinement by the polar vortex; but the general conclusion is that it would require multiple, intense dust storms in a given year in order to completely remove the CO2 ice veneer layer. This work has been supported by the NASA Planetary Astronomy and Mars Data Analysis Programs. [1] Benson and James, Icarus 174, 513, 2005; [2] Bonev et al., Planet Space Sci. 2006 (accepted).

Parallel and series FED microstrip array with high efficiency and low cross polarization

NASA Technical Reports Server (NTRS)

Huang, John (Inventor)

1995-01-01

A microstrip array antenna for vertically polarized fan beam (approximately 2 deg x 50 deg) for C-band SAR applications with a physical area of 1.7 m by 0.17 m comprises two rows of patch elements and employs a parallel feed to left- and right-half sections of the rows. Each section is divided into two segments that are fed in parallel with the elements in each segment fed in series through matched transmission lines for high efficiency. The inboard section has half the number of patch elements of the outboard section, and the outboard sections, which have tapered distribution with identical transmission line sections, terminated with half wavelength long open-circuit stubs so that the remaining energy is reflected and radiated in phase. The elements of the two inboard segments of the two left- and right-half sections are provided with tapered transmission lines from element to element for uniform power distribution over the central third of the entire array antenna. The two rows of array elements are excited at opposite patch feed locations with opposite (180 deg difference) phases for reduced cross-polarization.

A compact microwave patch applicator for hyperthermia treatment of cancer.

PubMed

Chakaravarthi, Geetha; Arunachalam, Kavitha

2014-01-01

Design and development of a compact microstrip C-type patch applicator for hyperthermia treatment of cancer is presented. The patch antenna is optimized for resonance at 434 MHz, return loss (S11) better than -15dB and co-polarized electric field in tissue. Effect of water bolus thickness on power delivery is studied for improved power coupling. Numerical simulations for antenna design optimization carried out using EM simulation software, Ansys HFSS(®), USA were experimentally verified. The effective field coverage for the optimized patch antenna and experimental results indicate that the compact antenna resonates at ISM frequency 434 MHz with better than -15 dB power coupling.

Mars Odyssey All Stars: Polar Dunes

NASA Image and Video Library

2010-12-09

A sea of dark dunes, sculpted by the wind into long lines, surrounds the northern polar cap covering an area as big as Texas in this false-color image from NASA Mars Odyssey, the longest-working Mars spacecraft in history.

Investigation of Martian H2O and CO2 via gamma-ray spectroscopy

NASA Technical Reports Server (NTRS)

Squyres, Steven W.; Evans, Larry G.

1987-01-01

The evolution and present state of water and carbon dioxide on Mars are discussed. Researchers wished to determine how effectively questions regarding the distribution of water and carbon dioxide on Mars may be addressed with orbital gamma ray spectrometer data. Several simple, multi-layer models of the Martian surface were formulated to address problems such as the ice/dust ratio of layered deposits; the distribution, depth and concentration of ground ice; the thickness of north polar perennial ice; the thickness of the carbon dioxide layer over the south polar cap; the thickness of the seasonal carbon dioxide frost cap; and the water content of the seasonal frost cap. The results indicate that the Mars Observer gamma ray spectrometer will be a powerful tool for investigating the distribution and stratigraphy of volatiles on Mars.

Molecular biology of Streptococcus pneumoniae: an everlasting challenge.

PubMed

Sicard, M; Gasc, A M; Giammarinaro, P; Lefrançois, J; Pasta, F; Samrakandi, M

2000-01-01

Streptococcus pneumoniae is a model for elucidating: 1) recombination steps of DNA, from its discovery to polarity of integration; 2) long-patch mismatch repair, short-patch repair triggered by A/G and exclusion of deletions; 3) resistance to beta-lactam antibiotics; and 4) factors of virulence. Several of these topics remain a challenge for future investigations.

Digisonde at Sondrestrom to monitor the ionospheric polar cap and cusp region. Technical report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Crowley, G.; Reinisch, B.W.; Kitrosser, D.F.

1990-01-01

In July 1989, the Air Force meridional chain of Digisondes was completed by the installation of a system in Sondrestromfjord, Greenland (66.98 deg N, 50.94 deg W). In this report we describe the Sondrestrom site and instrument, and the relationship between Sondrestrom and the other AF sites. We also established the importance of this site by describing its geophysically unique features. Finally, some of the first measurements from Sondrestrom are presented, and interpreted in terms of high latitude features. Keywords: Geomagnetism; Plasmas physics drift; Magnetosphere; Ionosphere; Polar cap; Ionosondes.

Shape-Specific Patterning of Polymer-Functionalized Nanoparticles

DOE PAGES

Galati, Elizabeth; Tebbe, Moritz; Querejeta-Fernández, Ana; ...

2017-05-01

Chemically and topographically patterned nanoparticles (NPs) with dimensions on the order of tens of nanometers have a diverse range of applications and are a valuable system for fundamental research. Recently, thermodynamically controlled segregation of a smooth layer of polymer ligands into pinned micelles (patches) offered an approach to nanopatterning of polymer-functionalized NPs. Control of the patch number, size, and spatial distribution on the surface of spherical NPs has been achieved, however, the role of NP shape remained elusive. Here, we report the role of NP shape, namely, the effect of the local surface curvature, on polymer segregation into surface patches.more » For polymer-functionalized metal nanocubes, we show experimentally and theoretically that the patches form preferentially on the high-curvature regions such as vertices and edges. An in situ transformation of the nanocubes into nanospheres leads to the change in the number and distribution of patches; a process that is dominated by the balance between the surface energy and the stretching energy of the polymer ligands. The experimental and theoretical results presented in this work are applicable to surface patterning of polymer-capped NPs with different shapes, which then enables the exploration of patch-directed self-assembly, as colloidal surfactants, and as templates for the synthesis of hybrid nanomaterials.« less

A study of the electric field in an open magnetospheric model

NASA Technical Reports Server (NTRS)

Stern, D. P.

1973-01-01

Recently, Svalgaard and Heppner reported two separate features of the polar electromagnetic field that correlate with the dawn-dusk component of the interplanetary magnetic field. This work attempts to explain these findings in terms of properties of the open magnetosphere. The topology and qualitative properties of the open magnetosphere are first studied by means of a simple model, consisting of a dipole in a constant field. Many such properties are found to depend on the separation line, a curve connecting neutral points and separating different field line regimes. In the simple model it turns out that the electric field in the central polar cap tends to point from dawn to dusk for a wide variety of external fields, but, near the boundary of the polar cap, electric equipotentials are deformed into crescents.

PolarWinds I & II

Atmospheric Science Data Center

2018-04-20

... (Organized Large Eddies), and near surface winds over open water, transitional ice zones and the Greenland Ice Cap. Polar Winds I was ... total, twenty-four individual missions with over 80 hours of research flights were flown in the Arctic region near Greenland and Iceland ...

Effects of deliquescent salts in soils of polar Mars on the flow of the Northern Ice Cap

NASA Astrophysics Data System (ADS)

Fisher, D. A.; Hecht, M. H.; Kounaves, S.; Catling, D.

2008-12-01

The discovery of substantial amounts of magnesium and perchlorate by Phoenix' "Wet Chemistry Lab" (WCL) in the soil of Polar Mars suggests that magnesium perchlorate could be the dominant salt in the polar region's soils. This prospect opens some unexpected doors for moving liquid water around at temperatures as low as -68C. In its fully hydrated form ,this salt water mixture has a high density (~ 1700 kgm /cubic meter) (Besley and Bottomley,1969) and a freezing point of -68C (Pestova et al., 2005).This perchlorate is very deliquescent and gives off heat as it melts ice. About 1.8 gram of ice can be 'melted' by 1 gm of pure magnesium perchlorate . If the reported 1 percent perchlorate is typical of polar soils and if 5 percent of the Northern Permanent Ice Cap is soil then the perchorate , makes up about 0.0005 the of the ice cap. Given the average thickness of the ice cap is about 2000 meters,this suggests there enough perchorate in the ice cap to generate about 2m of salty water at the bed. Because of its density the perclorate salty water would pool over impervious layers and make the bed into a perchorate sludge that could be mobilized and deformed by the overburden of ice. The deformation of mobile beds is a well known phenomenon on some terrestrial glaciers presently and was thought to have played a major role during the Wisconsinan ice age (Fisher et al., 1985) . The perchorate sludge would be deformed and moved outwards possibly resulting its re-introduction to the polar environment. Having a deliquescent salt sludge at the bed whose melting point is -68C would mean that the ice cap could slide on its deformable bed while the ice itself was still very cold and stiff . This possibility has been modeled with a 2D time varying model . Adding the deformable bed material allows ice cap motion even at ice temperatures cold enough to generate and preserve the scarp/trough features. When the perchlorate formation mechanisms and rates are known the ultimate importance of it in the water cycle of Mars will be clearer. The ice cap has long been thought of as a possible re-charge area for the deep water return flow (Clifford , 1987) . If perchlorate is formed sufficiently quickly, this view would be strengthened in spite of the low temperatures. Clifford S.M. 1987. Polar basal melting. JGR. Vol. 92, No. B9, pp 9135-9152. Besley L. M. and G.A. Bottomley. 1969. The water vapour equilibria over magnesium perchlorate hydrates. Journal of Chemical Thermodynamics. 1, pp13-19. Fisher, D.A., Reeh, N., and Langley, K. 1985. Objective reconstructions of the late Wisconsinan Laurentide Ice Sheet and the significance of deformable beds. Géographie physique et Quaternaire, v. 39, no. 3, p. 229-238. Pestova O. N.,Myund L.A.,Khripun M.K. and A.V. Prigaro. 2005. Polythermal study of systems M(ClO4)2-H2O (M2+=Mg2+, Ca2+, Sr2+, Ba2+). Russian Journal of Applied Chemistry , Vol.78.No.3,pp409-413. class="ab'>

Occupational protein contact dermatitis from spices in a butcher: a new presentation of the mugwort-spice syndrome.

PubMed

Anliker, Mark David; Borelli, Siegfried; Wüthrich, Brunello

2002-02-01

Protein contact dermatitis to meat is well known in butchers; spices are another source of potential contact allergy and usually are not recognized. We present a first case of contact-dermatitis to spice mix in a 39-year-old-butcher. The patient underwent skin prick testing (SPT) with standard allergens (ALK) and different meat and spice extracts (Stallergènes), scratch-patch testing with spice mix containing glutamate, paprika and other spices. Specific serum-IgE was measured with CAP-FEIA. SPT only showed an immediate-type sensitization to mugwort (+ +), as well as different spices (paprika +, curry +, cumin +) and camomile (+ + +). Scratch-patch tests were negative for different meat, but strongly positive for spice mix (+ + +) after 30 min (wheal and flare) and (+ +) after 48 h (infiltration and vesiculation). Two healthy controls were tested negative for spice mix used from that patient (scratch-patch). Specific IgE was slightly elevated for paprika 0.47 kU/L (CAP class 1), anise 0.43 kU/L, curry 0.36 kU/L and mugwort 3.83 kU/L. Sx1 atopy-multiscreen was 3.8 kU/L due to a sensitization to mugwort alone. The tests performed demonstrate an IgE-mediated contact allergy to spices but also a delayed type allergy to spice mix as a manifestation of the mugwort-spice syndrome in this individual. When testing for occupational dermatitis in butchers, protein contact allergy to spices must also be taken into consideration.

Particle Acceleration in Dissipative Pulsar Magnetospheres

NASA Technical Reports Server (NTRS)

Kazanas, Z.; Kalapotharakos, C.; Harding, A.; Contopoulos, I.

2012-01-01

Pulsar magnetospheres represent unipolar inductor-type electrical circuits at which an EM potential across the polar cap (due to the rotation of their magnetic field) drives currents that run in and out of the polar cap and close at infinity. An estimate ofthe magnitude of this current can be obtained by dividing the potential induced across the polar cap V approx = B(sub O) R(sub O)(Omega R(sub O)/c)(exp 2) by the impedance of free space Z approx eq 4 pi/c; the resulting polar cap current density is close to $n {GJ} c$ where $n_{GJ}$ is the Goldreich-Julian (GJ) charge density. This argument suggests that even at current densities close to the GJ one, pulsar magnetospheres have a significant component of electric field $E_{parallel}$, parallel to the magnetic field, a condition necessary for particle acceleration and the production of radiation. We present the magnetic and electric field structures as well as the currents, charge densities, spin down rates and potential drops along the magnetic field lines of pulsar magnetospheres which do not obey the ideal MHD condition $E cdot B = 0$. By relating the current density along the poloidal field lines to the parallel electric field via a kind of Ohm's law $J = sigma E_{parallel}$ we study the structure of these magnetospheres as a function of the conductivity $sigma$. We find that for $sigma gg OmegaS the solution tends to the (ideal) Force-Free one and to the Vacuum one for $sigma 11 OmegaS. Finally, we present dissipative magnetospheric solutions with spatially variable $sigma$ that supports various microphysical properties and are compatible with the observations.

Spider Web Pattern

NASA Technical Reports Server (NTRS)

2006-01-01

A delicate pattern, like that of a spider web, appears on top of the Mars residual polar cap, after the seasonal carbon-dioxide ice slab has disappeared. Next spring, these will likely mark the sites of vents when the carbon-dioxide ice cap returns. This Mars Global Surveyor, Mars Orbiter Camera image is about 3-kilometers wide (2-miles).

Obliquity variation in a Mars climate evolution model

NASA Technical Reports Server (NTRS)

Tyler, D.; Haberle, Robert M.

1993-01-01

The existence of layered terrain in both polar regions of Mars is strong evidence supporting a cyclic variation in climate. It has been suggested that periods of net deposition have alternated with periods of net erosion in creating the layered structure that is seen today. The cause for this cyclic climatic behavior is variation in the annually averaged latitudinal distribution of solar insolation in response to obliquity cycles. For Mars, obliquity variation leads to major climatological excursion due to the condensation and sublimation of the major atmospheric constituent, CO2. The atmosphere will collapse into the polar caps, or existing caps will rapidly sublimate into the atmosphere, dependent upon the polar surface heat balance and the direction of the change in obliquity. It has been argued that variations in the obliquity of Mars cause substantial departures from the current climatological values of the surface pressure and the amount of CO2 stored in both the planetary regolith and polar caps. In this new work we have modified the Haberle et al. model to incorporate variable obliquity by allowing the polar and equatorial insolation to become functions of obliquity, which we assume to vary sinusoidally in time. As obliquity varies in the model, there can be discontinuities in the time evolution of the model equilibrium values for surface pressure, regolith, and polar cap storage. The time constant, tau r, for the regolith to find equilibrium with the climate is estimated--depending on the depth, thermal conductivity, and porosity of the regolith--between 10(exp 4) and 10(exp 6) yr. Thus, using 2000-yr timesteps to move smoothly through the 0.1250 m.y. obliquity cycles, we have an atmosphere/regolith system that cannot be assumed in equilibrium. We have dealt with this problem by limiting the rate at which CO2, can move between the atmosphere and regolith, mimicking the diffusive nature and effects of the temperature and pressure waves, by setting the time rate of change of regolith storage proportional to the difference between equilibrium storage and current storage.

Shallow groundwater systems in a polar desert, McMurdo Dry Valleys, Antarctica

NASA Astrophysics Data System (ADS)

Gooseff, Michael N.; Barrett, John E.; Levy, Joseph S.

2013-02-01

The McMurdo Dry Valleys (MDVs), Antarctica, exist in a hyperarid polar desert, underlain by deep permafrost. With an annual mean air temperature of -18 °C, the MDVs receive <10 cm snow-water equivalent each year, collecting in leeward patches across the landscape. The landscape is dominated by expansive ice-free areas of exposed soils, mountain glaciers, permanently ice-covered lakes, and stream channels. An active layer of seasonally thawed soil and sediment extends to less than 1 m from the surface. Despite the cold and low precipitation, liquid water is generated on glaciers and in snow patches during the austral summer, infiltrating the active layer. Across the MDVs, groundwater is generally confined to shallow depths and often in unsaturated conditions. The current understanding and the biogeochemical/ecological significance of four types of shallow groundwater features in the MDVs are reviewed: local soil-moisture patches that result from snow-patch melt, water tracks, wetted margins of streams and lakes, and hyporheic zones of streams. In general, each of these features enhances the movement of solutes across the landscape and generates soil conditions suitable for microbial and invertebrate communities.

Carbon Dioxide Landforms

NASA Technical Reports Server (NTRS)

2004-01-01

19 March 2004 The martian south polar residual ice cap is mostly made of frozen carbon dioxide. There is no place on Earth that a person can go to see the landforms that would be produced by erosion and sublimation of hundreds or thousands of cubic kilometers of carbon dioxide. Thus, the south polar cap of Mars is as alien as alien can get. This image, acquired in February 2004 by the Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC), shows how the cap appears in summer as carbon dioxide is subliming away, creating a wild pattern of pits, mesas, and buttes. Darker surfaces may be areas where the ice contains impurities, such as dust, or where the surface has been roughened by the removal of ice. This image is located near 86.3oS, 0.8oW. This picture covers an area about 3 km (1.9 mi) across. Sunlight illuminates the scene from the top/upper left.

Response of the equatorial and polar magnetosphere to the very tenuous solar wind on May 11, 1999

NASA Astrophysics Data System (ADS)

Farrugia, C. J.; Singer, H. J.; Evans, D.; Berdichevsky, D.; Scudder, J. D.; Ogilvie, K. W.; Fitzenreiter, R. J.; Russell, C. T.

2000-12-01

We examine effects in the equatorial and polar magnetosphere during 9-13 May, 1999. Earth's field at geostationary orbit became closely dipolar for ˜16 hours when solar wind densities nsw were <1 cm-3. Electron precipitation in the northern polar cap intensified as nsw decreased, with significant fluxes up to ˜15 keV energy on May 11. The simultaneous precipitation void in the southern polar cap implies a very pronounced north-south asymmetry, also reflected in the hemispherical power deposition. With an intense and collimated strahl, these observations support the ideas of Fairfield and Scudder [1985] on the preferential entry of the strahl into the northern hemisphere under the observed IMF away sector as a source of the north-south precipitation asymmetry. The polar rain north-south asymmetry argues against an ejecta source for the solar wind drop-out. The temporal profiles of solar wind parameters were very asymmetric with respect to the time of minimum nsw, and strong compressions and substorm activity prevailed as nsw recovered.

Statistical Patterns of Ionospheric Convection Derived From Mid-latitude, High-Latitude, and Polar SuperDARN HF Radar Observations

NASA Astrophysics Data System (ADS)

Thomas, E. G.; Shepherd, S. G.

2018-04-01

Over the last decade, the Super Dual Auroral Radar Network (SuperDARN) has undergone a dramatic expansion in the Northern Hemisphere with the addition of more than a dozen radars offering improved coverage at mid-latitudes (50°-60° magnetic latitude) and in the polar cap (80°-90° magnetic latitude). In this study, we derive a statistical model of ionospheric convection (TS18) using line-of-sight velocity measurements from the complete network of mid-latitude, high-latitude, and polar radars for the years 2010-2016. These climatological patterns are organized by solar wind, interplanetary magnetic field (IMF), and dipole tilt angle conditions. We find that for weak solar wind driving conditions the TS18 model patterns are largely similar to the average patterns obtained using high-latitude radar data only. For stronger solar wind driving the inclusion of mid-latitude radar data at the equatorward extent of the ionospheric convection can increase the measured cross-polar cap potential (ΦPC) by as much as 40%. We also derive an alternative model organized by the Kp index to better characterize the statistical convection under a range of magnetic activity conditions. These Kp patterns exhibit similar IMF By dependencies as the TS18 model results and demonstrate a linear increase in ΦPC with increasing Kp for a given IMF orientation. Overall, the mid-latitude radars provide a better specification of the flows within the nightside Harang reversal region for moderate to strong solar wind driving or geomagnetic activity, while the polar radars improve the quality of velocity measurements in the deep polar cap under all conditions.

The Energy Budget of the Polar Atmosphere in MERRA

NASA Technical Reports Server (NTRS)

Cullather, Richard I.; Bosilovich, Michael G.

2010-01-01

Components of the atmospheric energy budget from the Modern Era Retrospective-analysis for Research and Applications (MERRA) are evaluated in polar regions for the period 1979-2005 and compared with previous estimates, in situ observations, and contemporary reanalyses. Closure of the energy budget is reflected by the analysis increments term, which results from virtual enthalpy and latent heating contributions and averages -11 W/sq m over the north polar cap and -22 W/sq m over the south polar cap. Total energy tendency and energy convergence terms from MERRA agree closely with previous study for northern high latitudes but convergence exceeds previous estimates for the south polar cap by 46 percent. Discrepancies with the Southern Hemisphere transport are largest in autumn and may be related to differences in topography with earlier reanalyses. For the Arctic, differences between MERRA and other sources in TOA and surface radiative fluxes maximize in May. These differences are concurrent with the largest discrepancies between MERRA parameterized and observed surface albedo. For May, in situ observations of the upwelling shortwave flux in the Arctic are 80 W/sq m larger than MERRA, while the MERRA downwelling longwave flux is underestimated by 12 W/sq m throughout the year. Over grounded ice sheets, the annual mean net surface energy flux in MERRA is erroneously non-zero. Contemporary reanalyses from the Climate Forecast Center (CFSR) and the Interim Re-Analyses of the European Centre for Medium Range Weather Forecasts (ERA-I) are found to have better surface parameterizations, however these collections are also found to have significant discrepancies with observed surface and TOA energy fluxes. Discrepancies among available reanalyses underscore the challenge of reproducing credible estimates of the atmospheric energy budget in polar regions.

Rectangular microstrip antenna with corrugation like defects at radiating edge: A new approach to reduce cross polarization radiation

NASA Astrophysics Data System (ADS)

Pawar, U. A.; Mondal, D.; Nagaraju, A.; Chakraborty, S.; Singh, L. L. K.; Chattopadhyay, S.

2018-03-01

In this paper, single layer, simple and compact RMA, with corrugation like defects at the radiating edge, is studied thoroughly to reduce XP radiation from the patch. Unlike the earlier works reported on defected ground structure integrated patches and defect patch structures, in this work, corrugation like linear defects have been placed at the radiating edges of the patch to reduce cross polarisation radiation. Around 30-40 dB of CP-XP isolation is observed in H-plane with 7% impedance bandwidth and in E-plane also, more than 55 dB CP-XP isolation is found. The proposed structure is very simple to design and easy to fabricate.

Tracking Retreat of the North Seasonal Ice Cap on Mars: Results from the THEMIS Investigation

NASA Technical Reports Server (NTRS)

Ivanov, A. B.; Wagstaff, K. L.; Ttus, T. N.

2005-01-01

The CO2 ice caps on Mars advance and retreat with the seasons. This phenomenon was first observed by Cassini and then confirmed by numerous ground based observations in 19th and 20th centuries. With the advent of the space age observations of the seasonal ice cap were done by all orbiting spacecraft starting with Mariner 7. Viking Orbiters and more recently the Mars Global Surveyor (particularly Mars Orbiter Camera (MOC) and Thermal Emission Spectrometer (TES) instruments) have accumulated significant data on the retreat of the CO2 seasonal cap. During Mars year 2 of THEMIS operations at Mars, we planned an observational campaign in which the THEMIS instrument (onboard the Mars Odyssey spacecraft) repeatedly observed the north seasonal polar cap from midwinter to late spring. THEMIS allows simultaneous observations in both Thermal IR (12.57 m) and Visible wavelengths (0.65 m). One of the goals for this work is to initiate an interannual program for observations of the seasonal ice caps using the THEMIS instrument. The most efficient way to detect the edge between frost and bare ground is directly onboard of the spacecraft. Prior to onboard software design effort, we have developed two groundbased algorithms for automatically finding the edge of the seasonal polar cap in THEMIS IR data. The first algorithm relies on fully calibrated data and can be used for highly reliable groundbased analyses. The second method was specifically developed for processing raw, uncalibrated data in a highly efficient way. It has the potential to enable automatic, onboard detections of the seasonal cap retreat. We have experimentally confirmed that both methods produce similar results, and we have validated both methods against a model constructed from the MGS TES data from the same season.

La calotta polare sud di Mars

NASA Astrophysics Data System (ADS)

di Giovanni, Giovanni

2006-06-01

The paper discusses the variations in the ice-retreat rate of the south polar cap of Mars in springtime during the 2003 and 2005 apparitions. For this we have measured the planetocentric cap amplitude on images of the Mars Sections of the Italian Union of Amateur Astronomers (UAI), the American Association of Lunar and Planetary Observers (ALPO) and ALPO Japan in the relevant Internet sites. A reasonable first approach to the problem was to perform a simple heat-balance model of Mars' ice cap including solar insolation, surface thermal emission, condensation and sublimation of carbon dioxide frost. The model doesn't include several important physical conditions, such as atmospherical absorption of radiation etc. and other components of ice (i.e. dust, H2O etc.). A suitable mathematical continue function θ(Ls) concerning the planetocentric amplitude of the cap as a function of the areocentric solar longitude on Mars (Ls) has been used to fit the experimental points in a classical diagram cap amplitude versus Ls. The correlation coefficient resulted 0.95. The second derivative of the function (d2θ/dLs2) suggests the existence of three important points during the spring recession: a) at Ls≍228° the highest sublimation rate is observe; b) at Ls≍245° (near perihelion) the highest retraction speed of the edge cap occurs, when the solar radiation flux over the south pole exceeds the flux over the equatorial zone; c) at Ls>285° the retraction speed of the cap's edge is constant. With the same function θ(Ls) we have worked out the ice thickness for every degrees in Ls, sublimation diurnal rate and total mass of seasonal cap. The ring of ice around to the pole, whose existence was suggested by Cross, was not revealed.

Resonant frequencies of irregularly shaped microstrip antennas using method of moments

NASA Technical Reports Server (NTRS)

Deshpande, Manohar D.; Shively, David G.; Cockrell, C. R.

1993-01-01

This paper describes an application of the method of moments to determine resonant frequencies of irregularly shaped microstrip patches embedded in a grounded dielectric slab. For analysis, the microstrip patch is assumed to be excited by a linearly polarized plane wave that is normal to the patch. The surface-current density that is induced on the patch because of the incident field is expressed in terms of subdomain functions by dividing the patch into identical rectangular subdomains. The amplitudes of the subdomain functions, as a function of frequency, are determined using the electric-field integral equation (EFIE) approach in conjunction with the method of moments. The resonant frequencies of the patch are then obtained by selecting the frequency at which the amplitude of the surface-current density is real. The resonant frequencies of the equilateral triangular and other nonrectangular patches are computed using the present technique, and these frequencies are compared with measurements and other independent calculations.

Asymmetric ion trap

DOEpatents

Barlow, Stephan E.; Alexander, Michael L.; Follansbee, James C.

1997-01-01

An ion trap having two end cap electrodes disposed asymmetrically about a center of a ring electrode. The inner surface of the end cap electrodes are conformed to an asymmetric pair of equipotential lines of the harmonic formed by the application of voltages to the electrodes. The asymmetry of the end cap electrodes allows ejection of charged species through the closer of the two electrodes which in turn allows for simultaneously detecting anions and cations expelled from the ion trap through the use of two detectors charged with opposite polarity.

Goldstone/VLA 3.5cm Mars Radar Observations - "Stealths" and South Polar Regions

NASA Astrophysics Data System (ADS)

Butler, Bryan; Chizek, M. R.; Slade, M. A.; Haldemann, A. F.; Muhleman, D. O.; Mao, T. F.

2006-09-01

The opposition of Mars in 2003 provided a fantastic opportunity to use the combined Goldstone/VLA radar to probe the surface with the highest resolution ever obtained on Mars with that instrument (as good as 70 km). Observations were made on August 11, 19, 28, and September 8. Details of data reduction and analysis of the radar echoes from the volcanic regions of the planet are presented in a companion paper in these proceedings (Chizek et al.). We will present results related to "Stealth" (and other radar-dark regions of the planet, including the Argyre and Hellas Planitiae, and a region to the west of the Elysium Mons caldera), and the south polar residual and seasonal ice caps. The size, shape, and reflectivity characteristics of Stealth and "mega-Stealth" (Edgett et al. 1997) are reaffirmed, with a better viewing geometry of the western extent of the feature than had been obtained previously. It had been speculated previously that Hellas Planitia should also be radar dark - this is confirmed by our imaging, though the reflectivity is not as low as for Stealth. We find a new radar dark area to the west of Elysium Mons, which is likely an ash fall from that volcano (similar to the relationship between Stealth and the Tharsis volcanoes). The south polar residual ice cap is a very bright reflector, as seen previously, but we now also see a very bright reflection from the seasonal cap, not seen previously. The cap is not uniformly bright, however, and the extent of the bright reflection does not correspond to that expected from the retreat of the cap as measured either from albedo or thermal emission characteristics. The NRAO is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

THE HANLE AND ZEEMAN POLARIZATION SIGNALS OF THE SOLAR Ca II 8542 Å LINE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Štěpán, Jiri; Bueno, Javier Trujillo

We highlight the main results of a three-dimensional (3D) multilevel radiative transfer investigation about the solar disk-center polarization of the Ca ii 8542 Å line. First, through the use of a 3D model of the solar atmosphere, we investigate the linear polarization that occurs due to the atomic level polarization produced by the absorption and scattering of anisotropic radiation, taking into account the symmetry-breaking effects caused by its thermal, dynamic, and magnetic structure. Second, we study the contribution of the Zeeman effect to the linear and circular polarization. Finally, we show examples of the Stokes profiles produced by the jointmore » action of the atomic level polarization and the Hanle and Zeeman effects. We find that the Zeeman effect tends to dominate the linear polarization signals only in the localized patches of opposite magnetic polarity, where the magnetic field is relatively strong and slightly inclined; outside such very localized patches, the linear polarization is often dominated by the contribution of atomic level polarization. We demonstrate that a correct modeling of this last contribution requires taking into account the symmetry-breaking effects caused by the thermal, dynamic, and magnetic structure of the solar atmosphere, and that in the 3D model used the Hanle effect in forward-scattering geometry (disk-center observation) mainly reduces the polarization corresponding to the zero-field case. We emphasize that, in general, a reliable modeling of the linear polarization in the Ca ii 8542 Å line requires taking into account the joint action of atomic level polarization and the Hanle and Zeeman effects.« less

South Polar Texture

NASA Image and Video Library

2016-08-26

This VIS image of the south polar cap shows a surface with hundreds of circular depressions. This texture similar in appearance to swiss cheese. Orbit Number: 64535 Latitude: -86.8715 Longitude: 354.786 Instrument: VIS Captured: 2016-07-01 14:50 http://photojournal.jpl.nasa.gov/catalog/PIA20974

More South Polar "Swiss Cheese"

NASA Image and Video Library

2000-04-24

This image is illuminated by sunlight from the upper left. Some of the surface of the residual south polar cap has a pattern that resembles that of sliced, swiss cheese. Shown here at the very start of southern spring is a frost-covered surface in which there are two layers evident--a brighter upper layer into which are set swiss cheese-like holes, and a darker, lower layer that lies beneath the "swiss cheese" pattern. Nothing like this exists anywhere on Mars except within the south polar cap. This is a Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image acquired on August 2, 1999. It is located near 84.8°S, 71.8°W, and covers an area 3 km across and about 6.1 km long (1.9 by 3.8 miles). http://photojournal.jpl.nasa.gov/catalog/PIA02368

Nuclear physics of reverse electron flow at pulsar polar caps

NASA Astrophysics Data System (ADS)

Jones, P. B.

2010-01-01

Protons produced in electromagnetic showers formed by the reverse electron flux are usually the largest component of the time-averaged polar cap open magnetic flux line current in neutron stars with positive corotational charge density. Although the electric field boundary conditions in the corotating frame are time independent, instabilities on both medium and short time-scales cause the current to alternate between states in which either protons or positrons and ions form the major component. These properties are briefly discussed in relation to nulling and microstructure in radio pulsars, pair production in an outer gap and neutron stars with high surface temperatures.

South Polar Ice Cap

NASA Technical Reports Server (NTRS)

2003-01-01

MGS MOC Release No. MOC2-337, 21 April 2003

This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows the 'swiss cheese' pattern of frozen carbon dioxide on the south polar residual cap. Observation of these materials over two Mars years has revealed that the scarps that bound the mesas and small buttes are retreating-the carbon dioxide ice is subliming away-at a rate of about 3 meters (3 yards) per Mars year in some places. The picture covers an area about 900 m (about 900 yards) wide near 87.1oS, 93.7oW. Sunlight illuminates the scene from the upper left.

The planet Mars - From antiquity to the present

NASA Astrophysics Data System (ADS)

Kieffer, Hugh H.; Jakosky, Bruce M.; Snyder, Conway W.

Telescopic observations of Mars, from those of Galileo in 1610 to the late 19th century, were summarized by Flammarion (1892, 1909). Major compilations of knowledge of Mars were produced by Antoniadi (1930) and de Vaucouleurs (1954). Polar cap composition was debated until the discovery by the Viking mission that the north and south perennial polar caps are composed of different materials. Spacecraft data indicate a rich and diverse geologic history as well as many unsolved puzzles. An annotated list of books about Mars is provided. Basic physical and chemical data on Mars are summarized in tabular form, and a guide to the Martian seasons is given.

Monitoring the perennial martian northern polar cap with MGS MOC

NASA Astrophysics Data System (ADS)

Hale, A. Snyder; Bass, D. S.; Tamppari, L. K.

2005-04-01

We have used the Mars Global Surveyor Mars Orbiter Camera Wide Angle (MGS MOC WA) dataset to study albedo trends on the martian northern residual cap. Six study regions were selected, the Chasma Boreale source region, three regions near the center of the cap ("fish hook" region, latitude = 87°; "bottle opener" region, latitude = 87°, "steep-shallow" region, latitude = 85°), and two lower latitude regions (crater, latitude = 77°, and polar outlier, latitude = 82°), and the albedos of these six regions were examined. These regions were chosen due to their good temporal coverage in the MOC dataset, as well as having been studied by other researchers (Bass et al., 2000, Icarus 144, 382-396; Calvin and Titus, 2004, Lunar Planet. Sci. XXXV, Abstract 1455). The picture which emerges is complex. Most areas experience a combination of darkening and brightening through the northern summer; only one area consistently brightens (the polar outlier region). A good deal of interannual repeatability in each region's albedo behavior is seen, however. Possible causes for the observed complex behaviors include dust deposition from late summer storms, sintering of frost grains over the course of the summer, and cold trapping of volatiles on bright, cold surfaces.

Sedimentation Waves on the Martian North Polar Cap: Analogy with Megadunes in Antarctica

NASA Astrophysics Data System (ADS)

Herny, C.; Masse, M.; Bourgeois, O.; Carpy, S.; Le Mouelic, S.; Appéré, T.; Smith, I. B.; Spiga, A.; Perret, L.; Rodriguez, S.; Piquet, T.; Gaudin, D.; Le Menn, E.

2014-12-01

Complex feedbacks between katabatic winds and the cryosphere may lead to the development of sedimentation waves at the surface of ice sheets. These have been first described and named megadunes in Antarctica. Here we use topographic data, optical images, spectroscopic data and radar soundings, acquired by Mars orbiters, to show that the surface of the Martian North Polar Cap displays two superimposed sets of sedimentation waves with differing wavelengths. These sedimentation waves grow and migrate upwind in response to the development of periodic accumulation/ablation patterns controlled by katabatic winds. They have similarities with Antarctic megadunes regarding their surface morphology, texture, grain size, and internal stratigraphic architecture. Based on this analogy, we are currently developing a model of ice/wind interaction at the surface of ice sheets. In Antarctica the accumulation processes on megadunes fields is generally attributed to the wind-blown snow transport while on sedimentation waves of the North Polar Cap of Mars the accumulation seems to be dominated by sublimation/condensation processes at the surface. The model is designed to explore the implication of the water vapor mass transfer and heat transfer on the development of sedimentation waves both on Mars and Earth.

VISIONS: Remote Observations of a Spatially-Structured Filamentary Source of Energetic Neutral Atoms near the Polar Cap Boundary During an Auroral Substorm

NASA Technical Reports Server (NTRS)

Collier, Michael R.; Chornay, D.; Clemmons, J.; Keller, J. W.; Klenzing, J.; Kujawski, J.; McLain, J.; Pfaff, R.; Rowland, D.; Zettergren, M.

2015-01-01

We report initial results from the VISualizing Ion Outflow via Neutral atom imaging during a Substorm (VISIONS) rocket that flew through and near several regions of enhanced auroral activity and also sensed regions of ion outflow both remotely and directly. The observed neutral atom fluxes were largest at the lower energies and generally higher in the auroral zone than in the polar cap. In this paper, we focus on data from the latter half of the VISIONS trajectory when the rocket traversed the polar cap region. During this period, many of the energetic neutral atom spectra show a peak at 100 electronvolts. Spectra with peaks around 100 electronvolts are also observed in the Electrostatic Ion Analyzer (EIA) data consistent with these ions comprising the source population for the energetic neutral atoms. The EIA observations of this low energy population extend only over a few tens of kilometers. Furthermore, the directionality of the arriving energetic neutral atoms is consistent with either this spatially localized source of energetic ions extending from as low as about 300 kilometers up to above 600 kilometers or a larger source of energetic ions to the southwest.

Pits in Polar Cap

NASA Technical Reports Server (NTRS)

2006-01-01

This full-frame image from the High Resolution Imaging Science Experiment camera on NASA's Mars Reconnaissance Orbiter shows faults and pits in Mars' north polar residual cap that have not been previously recognized.

The faults and depressions between them are similar to features seen on Earth where the crust is being pulled apart. Such tectonic extension must have occurred very recently because the north polar residual cap is very young, as indicated by the paucity of impact craters on its surface. Alternatively, the faults and pits may be caused by collapse due to removal of material beneath the surface. The pits are aligned along the faults, either because material has drained into the subsurface along the faults or because gas has escaped from the subsurface through them.

NASA's Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Mars Reconnaissance Orbiter for NASA's Science Mission Directorate, Washington. Lockheed Martin Space Systems, Denver, is the prime contractor for the project and built the spacecraft. The High Resolution Imaging Science Experiment is operated by the University of Arizona, Tucson, and the instrument was built by Ball Aerospace and Technology Corp., Boulder, Colo.

Gamma-ray Pulsars: Models and Predictions

NASA Technical Reports Server (NTRS)

Harding Alice K.; White, Nicholas E. (Technical Monitor)

2000-01-01

Pulsed emission from gamma-ray pulsars originates inside the magnetosphere, from radiation by charged particles accelerated near the magnetic poles or in the outer gaps. In polar cap models, the high energy spectrum is cut off by magnetic pair production above an energy that is, dependent on the local magnetic field strength. While most young pulsars with surface fields in the range B = 10(exp 12) - 10(exp 13) G are expected to have high energy cutoffs around several GeV, the gamma-ray spectra of old pulsars having lower surface fields may extend to 50 GeV. Although the gamma-ray emission of older pulsars is weaker, detecting pulsed emission at high energies from nearby sources would be an important confirmation of polar cap models. Outer gap models predict more gradual high-energy turnovers of the primary curvature emission around 10 GeV, but also predict an inverse Compton component extending to TeV energies. Detection of pulsed TeV emission, which would not survive attenuation at the polar caps, is thus an important test of outer gap models. Next-generation gamma-ray telescopes sensitive to GeV-TeV emission will provide critical tests of pulsar acceleration and emission mechanisms.

High-latitude convection on open and closed field lines for large IMF B(y)

NASA Technical Reports Server (NTRS)

Moses, J. J.; Crooker, N. U.; Gorney, D. J.; Siscoe, G. L.

1985-01-01

S3-3 electric field observations for August 23, 1976, show a single convection cell engulfing the northern polar cap. The flow direction is that for a positive IMF B(y) component. The particle data indicate that nearly half the duskside sunward flow occurs on closed field lines whereas the dawnside flow is entirely on open field lines. This is interpreted in terms of an IMF B(y)-induced deformation in the polar cap boundary, where the deformation moves with the convective flow. Thus, convection streamlines cross the deformed polar cap boundary, but no flow crosses the boundary because it is carried by the flow. Since southern hemisphere convection is expected to occur with the opposite sense of rotation, closed field lines that will be forced to tilt azimuthally are predicted. On the nightside the tilt produces a y component of the magnetic field in the same direction as the IMF for either sign of IMF B(y). This interpretation is consistent with observations of a greater y component in the plasma sheet than the tail lobes, which are difficult to understand in terms of the common explanation of IMF penetration. Alternatives to this interpretation are also discussed.

Quadrature transmit array design using single-feed circularly polarized patch antenna for parallel transmission in MR imaging.

PubMed

Pang, Yong; Yu, Baiying; Vigneron, Daniel B; Zhang, Xiaoliang

2014-02-01

Quadrature coils are often desired in MR applications because they can improve MR sensitivity and also reduce excitation power. In this work, we propose, for the first time, a quadrature array design strategy for parallel transmission at 298 MHz using single-feed circularly polarized (CP) patch antenna technique. Each array element is a nearly square ring microstrip antenna and is fed at a point on the diagonal of the antenna to generate quadrature magnetic fields. Compared with conventional quadrature coils, the single-feed structure is much simple and compact, making the quadrature coil array design practical. Numerical simulations demonstrate that the decoupling between elements is better than -35 dB for all the elements and the RF fields are homogeneous with deep penetration and quadrature behavior in the area of interest. Bloch equation simulation is also performed to simulate the excitation procedure by using an 8-element quadrature planar patch array to demonstrate its feasibility in parallel transmission at the ultrahigh field of 7 Tesla.

Circularly polarized triple band glass shaped monopole patch antenna with metallic reflector for bluetooth & wireless applications

NASA Astrophysics Data System (ADS)

Jangid, K. G.; Choudhary, N.; Jain, P.; Sharma, B. R.; Saini, J. S.; Kulhar, V. S.; Bhatnagar, D.

2016-03-01

This paper presents the design and performance of strip line fed glass shaped monopole patch antenna having with overall size 30mm × 30 mm × 1.59 mm. In the patch; an eight shaped slot and in the ground plane an eight shaped ring are introduced. A metallic ground plane is also introduced at appropriate location beneath the ground plane. The proposed antenna is simulated by applying CST Microwave Studio simulator. Antenna provides circularly polarized radiations, triple broad impedance bandwidth of 203MHz (2.306GHz to 2.510GHz), 42MHz (2.685GHz to 2.757GHz) & GHz (3.63 GHz to 6.05 GHz), high flat gain (close to 5dBi) and good radiation properties in the desired frequency range. This antenna may be a very useful tool for 2.45GHz Bluetooth communication band as well as for 2.4GHz/5.2 GHz /5.8 GHz WLAN bands & 3.7GHz/5.5 GHz Wi-Max bands.

Relativistic Effects and Polarization in Three High-Energy Pulsar Models

NASA Technical Reports Server (NTRS)

Dyks, J.; Harding, Alice K.; Rudak, B.

2004-01-01

We present the influence of the special relativistic effects of aberration and light travel time delay on pulsar high-energy lightcurves and polarization characteristics predicted by three models: the two-pole caustic model, the outer gap model, and the polar cap model. Position angle curves and degree of polarization are calculated for the models and compared with the optical data on the Crab pulsar. The relative positions of peaks in gamma-ray and radio lightcurves are discussed in detail for the models. We find that the two-pole caustic model can reproduce qualitatively the optical polarization characteristics of the Crab pulsar - fast swings of the position angle and minima in polarization degree associated with both peaks. The anticorrelation between the observed flux and the polarization degree (observed in the optical band also for B0656+14) naturally results from the caustic nature of the peaks which are produced in the model due to the superposition of radiation from many different altitudes, ie. polarized at different angles. The two-pole caustic model also provides an acceptable interpretation of the main features in the Crab's radio profile. Neither the outer gap model nor the polar cap model are able to reproduce the optical polarization data on the Crab. Although the outer gap model is very successful in reproducing the relative positions of gamma-ray and radio peaks in pulse profiles, it can reproduce the high-energy lightcurves only when photon emission from regions very close to the light cylinder is included.

A New Polar Magnetic Index of Geomagnetic Activity and its Application to Monitoring Ionospheric Parameters

NASA Technical Reports Server (NTRS)

Lyatsky, Wladislaw; Khazanov, George V.

2008-01-01

For improving the reliability of Space Weather prediction, we developed a new, Polar Magnetic (PM) index of geomagnetic activity, which shows high correlation with both upstream solar wind data and related events in the magnetosphere and ionosphere. Similarly to the existing polar cap PC index, the new, PM index was computed from data from two near-pole geomagnetic observatories; however, the method for computing the PM index is different. The high correlation of the PM index with both solar wind data and events in Geospace environment makes possible to improve significantly forecasting geomagnetic disturbances and such important parameters as the cross-polar-cap voltage and global Joule heating in high latitude ionosphere, which play an important role in the development of geomagnetic, ionospheric and thermospheric disturbances. We tested the PM index for 10-year period (1995-2004). The correlation between PM index and upstream solar wind data for these years is very high (the average correlation coefficient R approximately equal to 0.86). The PM index also shows the high correlation with the cross-polar-cap voltage and hemispheric Joule heating (the correlation coefficient between the actual and predicted values of these parameters is approximately 0.9), which results in significant increasing the prediction reliability of these parameters. Using the PM index of geomagnetic activity provides a significant increase in the forecasting reliability of geomagnetic disturbances and related events in Geospace environment. The PM index may be also used as an important input parameter in modeling ionospheric, magnetospheric, and thermospheric processes.

Solar photospheric network properties and their cycle variation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Thibault, K.; Charbonneau, P.; Béland, M., E-mail: kim@astro.umontreal.ca-a, E-mail: paulchar@astro.umontreal.ca-b, E-mail: michel.beland@calculquebec.ca-c

We present a numerical simulation of the formation and evolution of the solar photospheric magnetic network over a full solar cycle. The model exhibits realistic behavior as it produces large, unipolar concentrations of flux in the polar caps, a power-law flux distribution with index –1.69, a flux replacement timescale of 19.3 hr, and supergranule diameters of 20 Mm. The polar behavior is especially telling of model accuracy, as it results from lower-latitude activity, and accumulates the residues of any potential modeling inaccuracy and oversimplification. In this case, the main oversimplification is the absence of a polar sink for the flux,more » causing an amount of polar cap unsigned flux larger than expected by almost one order of magnitude. Nonetheless, our simulated polar caps carry the proper signed flux and dipole moment, and also show a spatial distribution of flux in good qualitative agreement with recent high-latitude magnetographic observations by Hinode. After the last cycle emergence, the simulation is extended until the network has recovered its quiet Sun initial condition. This permits an estimate of the network relaxation time toward the baseline state characterizing extended periods of suppressed activity, such as the Maunder Grand Minimum. Our simulation results indicate a network relaxation time of 2.9 yr, setting 2011 October as the soonest the time after which the last solar activity minimum could have qualified as a Maunder-type Minimum. This suggests that photospheric magnetism did not reach its baseline state during the recent extended minimum between cycles 23 and 24.« less

Patient adherence to transdermal rivastigmine after switching from oral donepezil: a retrospective claims database study.

PubMed

Tian, Haijun; Abouzaid, Safiya; Chen, Wei; Kahler, Kristijan H; Kim, Edward

2013-01-01

To examine patient adherence before and after switching from donepezil to the rivastigmine patch. This retrospective cohort study used the MarketScan Commercial and Medicare data sets (2004 to 2009). Patients with a diagnosis of Alzheimer disease who were new donepezil users and were subsequently switched to the rivastigmine patch were included. The proportion of days covered (PDC) and PDC difference between donepezil and the rivastigmine patch were calculated from the time of initiation to the switch, capped at 1 year after the first respective claim. PDC was calculated as the number of days with drugs available divided by the number of days in the respective follow-up periods. The sample included 772 patients (mean age 77 y; 58% female). The mean time between switching from donepezil to the rivastigmine patch was 579 (SD=317.3) days. The mean PDC for the rivastigmine patch was highest among patients who switched within 3 months (80.4% vs. 90.7%; P=0.04) and within 7 to 9 months (61.3% vs. 71.0%; P=0.05) of initiating donepezil. When adherence was analyzed in increments of 1 year, patients who switched to the rivastigmine patch within the first year of treatment had significantly greater adherence to rivastigmine compared with those who were on donepezil (PDC 69.3% vs. 60.6%; P=0.0004). Switching from donepezil to the rivastigmine patch seems to be associated with increased adherence, especially in patients who switched within the first year of initiating donepezil.

Dermal exposure to monoterpenes during wood work.

PubMed

Eriksson, Kare; Wiklund, Leif

2004-06-01

The dermal exposure to the suspected allergenic monoterpenes [small alpha]-pinene, [small beta]-pinene and [capital Delta](3)-carene was assessed with a patch sampling technique. The patch used was made of activated charcoal sandwiched between two layers of cotton cloth. Patches were fastened at 12 different spots on a sampling overall and at the front of a cap to estimate the potential exposure of the body. Fastening two patches on a cotton glove, one patch representing the dorsal side and one patch representing the palm of the hand respectively, assessed the exposure on the hands. Sampling was carried out during collecting of pine and spruce boards in sawmills and during sawing of pine wood pieces in joinery shops respectively. The potential dermal exposure of the total body was 29.0-1 890 mg h(-1) with a geometric mean (GM) of 238 mg h(-1) during sawing. During collecting the GM was estimated to 100 mg h(-1) with a range of 12.2-959 mg h(-1). The hands had a mean exposure of 9.24 mg h(-1) during sawing and 3.25 mg h(-1) during collecting respectively. The good correlation between the mass of contamination on the individual body parts and the potential body exposure indicates that sampling can be performed on one body part to give a good estimation of the potential body exposure. Monoterpenes were detected at patches fastened underneath the protective clothing indicating a contamination of the skin of the worker. The patch used may overestimate the dermal exposure.

Polar Stratigraphy

NASA Technical Reports Server (NTRS)

1999-01-01

These three images were taken on three different orbits over the north polar cap in April 1999. Each shows a different part of the same ice-free trough. The left and right images are separated by a distance of more than 100 kilometers (62 miles). Note the similar layers in each image.

Observations of the north polar water ice annulus on Mars using THEMIS and TES

USGS Publications Warehouse

Wagstaff, K.L.; Titus, T.N.; Ivanov, A.B.; Castano, R.; Bandfield, J.L.

2008-01-01

The Martian seasonal CO2 ice caps advance and retreat each year. In the spring, as the CO2 cap gradually retreats, it leaves behind an extensive defrosting zone from the solid CO2 cap to the location where all CO2 frost has sublimated. We have been studying this phenomenon in the north polar region using data from the THermal EMission Imaging System (THEMIS), a visible and infra-red (IR) camera on the Mars Odyssey spacecraft, and the Thermal Emission Spectrometer (TES) on Mars Global Surveyor. Recently, we discovered that some THEMIS images of the CO2 defrosting zone contain evidence for a distinct defrosting phenomenon: some areas just south of the CO2 cap edge are too bright in visible wavelengths to be defrosted terrain, but too warm in the IR to be CO2 ice. We hypothesize that we are seeing evidence for a seasonal annulus of water ice (frost) that recedes with the seasonal CO2 cap, as predicted by previous workers. In this paper, we describe our observations with THEMIS and compare them to simultaneous observations by TES and OMEGA. All three instruments find that this phenomenon is distinct from the CO2 cap and most likely composed of water ice. We also find strong evidence that the annulus widens as it recedes. Finally, we show that this annulus can be detected in the raw THEMIS data as it is collected, enabling future long-term onboard monitoring. ?? 2007.

Near-infrared light-controlled regulation of intracellular calcium to modulate macrophage polarization.

PubMed

Kang, Heemin; Zhang, Kunyu; Wong, Dexter Siu Hong; Han, Fengxuan; Li, Bin; Bian, Liming

2018-04-21

Macrophages are multifunctional immune cells with diverse physiological functions such as fighting against infection, influencing progression of pathologies, maintaining homeostasis, and regenerating tissues. Macrophages can be induced to adopt distinct polarized phenotypes, such as classically activated pro-inflammatory (M1) phenotypes or alternatively activated anti-inflammatory and pro-healing (M2), to execute diverse and dynamic immune functions. However, unbalanced polarizations of macrophage can lead to various pathologies, such as atherosclerosis, obesity, tumor, and asthma. Thus, the capability to remotely control macrophage phenotypes is important to the success of treating many pathological conditions involving macrophages. In this study, we developed an upconversion nanoparticle (UCNP)-based photoresponsive nanocarrier for near-infrared (NIR) light-mediated control of intracellular calcium levels to regulate macrophage polarization. UCNP was coated with mesoporous silica (UCNP@mSiO 2 ), into which loaded calcium regulators that can either supply or deplete calcium ions. UCNP@mSiO 2 was chemically modified through serial coupling of photocleavable linker and Arg-Gly-Asp (RGD) peptide-bearing molecular cap via cyclodextrin-adamantine host-guest complexation. The RGD-bearing cap functioned as the photolabile gating structure to control the release of calcium regulators and facilitated the cellular uptake of UCNP@mSiO 2 nanocarrier. The upconverted UV light emission from the UCNP@mSiO 2 under NIR light excitation triggered the cleavage of cap and intracellular release of calcium regulators, thereby allowing temporal regulation on the intracellular calcium levels. Application of NIR light through skin tissue promoted M1 or M2 polarization of macrophages, by elevating or depleting intracellular calcium levels, respectively. To the best of our knowledge, this is the first demonstration of NIR light-mediated remote control on macrophage polarization. This photoresponsive nanocarrier offers the potential to remotely manipulate in vivo immune functions, such as inflammation or tissue regeneration, via NIR light-controlled macrophage polarization. Copyright © 2018 Elsevier Ltd. All rights reserved.

Polarization patterns of the twilight sky

NASA Astrophysics Data System (ADS)

Cronin, Thomas W.; Warrant, Eric J.; Greiner, Birgit

2005-08-01

Although natural light sources produce depolarized light, patterns of partially linearly polarized light appear in the sky due to scattering from air molecules, dust, and aerosols. Many animals, including bees and ants, orient themselves to patterns of polarization that are present in daytime skies, when the intensity is high and skylight polarization is strong and predictable. The halicitid bee Megalopta genalis inhabits rainforests in Central America. Unlike typical bees, it forages before sunrise and after sunset, when light intensities under the forest canopy are very low, and must find its way to food sources and return to its nest in visually challenging circumstances. An important cue for the orientation could be patterns of polarization in the twilight sky. Therefore, we used a calibrated digital camera to image skylight polarization in an overhead patch of sky, 87.6° across, before dawn on Barro Colorado Island in Panama, where the bees are found. We simultaneously measured the spectral properties of polarized light in a cloudless patch of sky 15° across centered on the zenith. We also performed full-sky imaging of polarization before dawn and after dusk on Lizard Island in Australia, another tropical island. During twilight, celestial polarized light occurs in a wide band stretching perpendicular to the location of the hidden sun and reaching typical degrees of polarization near 80% at wavelengths >600 nm. This pattern appears about 45 minutes before local sunrise or disappears 45 minutes after local sunset (about 20 minutes after the onset of astronomical twilight at dawn, or before its end at dusk) and extends with little change through the entire twilight period. Such a strong and reliable orientation cue could be used for flight orientation by any animal with polarization sensitivity that navigates during twilight.

Microstrip antenna developments at JPL

NASA Technical Reports Server (NTRS)

Huang, John

1991-01-01

The in-house development of microstrip antennas, initiated in 1981, when a spaceborne lightweight and low-profile planar array was needed for a satellite communication system, is described. The work described covers the prediction of finite-ground-plane effects by the geometric theory of diffraction, higher-order-mode circularly polarized circular patch antennas, circularly polarized microstrip arrays with linearly polarized elements, an impedance-matching teardrop-shaped probe feed, a dual-polarized microstrip array with high isolation and low cross-polarization, a planar microstrip Yagi array, a microstrip reflectarray, a Ka-band MMIC array, and a series-fed linear arrays.

Polar Textures

NASA Image and Video Library

2016-09-21

This VIS image shows part of the South Polar cap. In this region the surface has numerous circular depressions, which give the appearance of a slice of swiss cheese. Orbit Number: 64848 Latitude: -86.7725 Longitude: 355.096 Instrument: VIS Captured: 2016-07-27 09:35 http://photojournal.jpl.nasa.gov/catalog/PIA20993

Atmospheric Modeling of the Martian Polar Regions: One Mars Year of CRISM EPF Observations of the South Pole

NASA Astrophysics Data System (ADS)

Brown, A. J.; Wolff, M. J.

2009-03-01

We have used CRISM Emission Phase Function gimballed observations to investigate atmospheric dust/ice opacity and surface albedo in the south polar region for the first Mars year of MRO operations. This covers the MY28 "dust event" and cap recession.

Magnetospheric convection and the high-latitude F2 ionosphere

NASA Technical Reports Server (NTRS)

Knudsen, W. C.

1974-01-01

Behavior of the polar ionospheric F layer as it is convected through the cleft, over the polar cap, and through the nightside F layer trough zone is investigated. Passage through the cleft adds approximately 200,000 ions per cu cm in the vicinity of the F2 peak and redistributes the ionization above approximately 400-km altitude to conform with an increased electron temperature. The redistribution of ionization above 400-km altitude forms the 'averaged' plasma ring seen at 1000-km altitude. The F layer is also raised by approximately 20 km in altitude by the convection electric field. The time required for passage across the polar cap (25 deg) is about the same as that required for the F layer peak concentration to decay by e. The F layer response to passage through the nightside soft electron precipitation zone should be similar to but less than its response to passage through the cleft.

Advances in Inner Magnetosphere Passive and Active Wave Research

NASA Technical Reports Server (NTRS)

Green, James L.; Fung, Shing F.

2004-01-01

This review identifies a number of the principal research advancements that have occurred over the last five years in the study of electromagnetic (EM) waves in the Earth's inner magnetosphere. The observations used in this study are from the plasma wave instruments and radio sounders on Cluster, IMAGE, Geotail, Wind, Polar, Interball, and others. The data from passive plasma wave instruments have led to a number of advances such as: determining the origin and importance of whistler mode waves in the plasmasphere, discovery of the source of kilometric continuum radiation, mapping AKR source regions with "pinpoint" accuracy, and correlating the AKR source location with dipole tilt angle. Active magnetospheric wave experiments have shown that long range ducted and direct echoes can be used to obtain the density distribution of electrons in the polar cap and along plasmaspheric field lines, providing key information on plasmaspheric filling rates and polar cap outflows.

Workshop on the Polar Regions of Mars: Geology, Glaciology, and Climate History, part 1

NASA Technical Reports Server (NTRS)

Clifford, S. M. (Editor); Howard, A. D. (Editor); Paterson, W. S. B. (Editor)

1992-01-01

Papers and abstract of papers presented at the workshop are presented. Some representative titles are as follows: Glaciation in Elysium; Orbital, rotational, and climatic interactions; Water on Mars; Rheology of water-silicate mixtures at low temperatures; Evolution of the Martian atmosphere (the role of polar caps); Is CO2 ice permanent; Dust transport into Martian polar latitudes; Mars observer radio science (MORS) observations in polar regions; and Wind transport near the poles of Mars (timescales of changes in deposition and erosion).

Asymmetric ion trap

DOEpatents

Barlow, S.E.; Alexander, M.L.; Follansbee, J.C.

1997-12-02

An ion trap having two end cap electrodes disposed asymmetrically about a center of a ring electrode is disclosed. The inner surface of the end cap electrodes are conformed to an asymmetric pair of equipotential lines of the harmonic formed by the application of voltages to the electrodes. The asymmetry of the end cap electrodes allows ejection of charged species through the closer of the two electrodes which in turn allows for simultaneously detecting anions and cations expelled from the ion trap through the use of two detectors charged with opposite polarity. 4 figs.

Effect of surfactant and mineralizer on the dielectric properties of zirconia nanocrsytals

NASA Astrophysics Data System (ADS)

Maheswari, A. Uma; Mohan, Sreedevi R.; Sivakumar, M.

2018-01-01

The combined effect of surfactants (PVP/CTAB) and alkaline mineralizers (NaOH/NH4OH) on dielectric properties of zirconia nanocrystals is analyzed. It is found that, the stabilization of zirconia tetramers by surfactants and the rate of hydroxyl ions released by alkaline mineralizers have significant impact on the dielectric properties of nanocrystals. The PVP capped tetramers form highly conducting grains with insulating boundaries, whereas the grains of CTAB capped tetramers are highly insulating with conducting grain boundaries, as revealed by Nyquist plots. Consequently, the space charge polarization would be quite large in highly conducting grains resulting in higher dielectric constant values at lower frequencies. The higher dielectric constant of PVP capped nanocrystals is due to greater tetragonal coordination of 3d5/2 and 3d3/2 electrons of Zr4+ ions than that of CTAB capped nanocrystals. Further, the surface oxygen vacancies of PVP samples are higher, resulting in a high space charge polarization. The ESR signal corresponding to F+ centers appears stronger for PVP/NH4OH nanocrystals. Moreover, the larger ESR line width of PVP/NH4OH nanocrystals corresponding to more oxygen vacancies is in accordance with the inference attained from the XPS analysis.

Variability of Mars' North Polar Water Ice Cap: I. Analysis of Mariner 9 and Viking Orbiter Imaging Data

USGS Publications Warehouse

Bass, Deborah S.; Herkenhoff, Kenneth; Paige, David A.

2000-01-01

Previous studies interpreted differences in ice coverage between Mariner 9 and Viking Orbiter observations of Mars' north residual polar cap as evidence of interannual variability of ice deposition on the cap. However, these investigators did not consider the possibility that there could be significant changes in the ice coverage within the northern residual cap over the course of the summer season. Our more comprehensive analysis of Mariner 9 and Viking Orbiter imaging data shows that the appearance of the residual cap does not show large-scale variance on an interannual basis. Rather we find evidence that regions that were dark at the beginning of summer look bright by the end of summer and that this seasonal variation of the cap repeats from year to year. Our results suggest that this brightening was due to the deposition of newly formed water ice on the surface. We find that newly formed ice deposits in the summer season have the same red-to-violet band image ratios as permanently bright deposits within the residual cap. We believe the newly formed ice accumulates in a continuous layer. To constrain the minimum amount of deposited ice, we used observed albedo data in conjunction with calculations using Mie theory for single scattering and a delta-Eddington approximation of radiative transfer for multiple scattering. The brightening could have been produced by a minimum of (1) a ~35-μm-thick layer of 50-μm-sized ice particles with 10% dust or (2) a ~14-μm-thick layer of 10-μm-sized ice particles with 50% dust.

Polar Cap Pits

NASA Technical Reports Server (NTRS)

2005-01-01

17 August 2005 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows kidney bean-shaped pits, and other pits, formed by erosion in a landscape of frozen carbon dioxide. This images shows one of about a dozen different patterns that are common in various locations across the martian south polar residual cap, an area that has been receiving intense scrutiny by the MGS MOC this year, because it is visible on every orbit and in daylight for most of 2005.

Location near: 86.9oS, 6.9oW Image width: width: 3 km (1.9 mi) Illumination from: upper left Season: Southern Spring

Investigation on Surface Polarization of Al2O3-capped GaN/AlGaN/GaN Heterostructure by Angle-Resolved X-ray Photoelectron Spectroscopy.

PubMed

Duan, Tian Li; Pan, Ji Sheng; Wang, Ning; Cheng, Kai; Yu, Hong Yu

2017-08-17

The surface polarization of Ga-face gallium nitride (GaN) (2 nm)/AlGaN (22 nm)/GaN channel (150 nm)/buffer/Si with Al 2 O 3 capping layer is investigated by angle-resolved X-ray photoelectron spectroscopy (ARXPS). It is found that the energy band varies from upward bending to downward bending in the interface region, which is believed to be corresponding to the polarization variation. An interfacial layer is formed between top GaN and Al 2 O 3 due to the occurrence of Ga-N bond break and Ga-O bond forming during Al 2 O 3 deposition via the atomic layer deposition (ALD). This interfacial layer is believed to eliminate the GaN polarization, thus reducing the polarization-induced negative charges. Furthermore, this interfacial layer plays a key role for the introduction of the positive charges which lead the energy band downward. Finally, a N 2 annealing at 400 °C is observed to enhance the interfacial layer growth thus increasing the density of positive charges.

Multilayer Patch Antenna Surrounded by a Metallic Wall

NASA Technical Reports Server (NTRS)

Zawadzki, Mark; Huang, John

2003-01-01

A multilayer patch antenna, similar to a Yagi antenna, surrounded by a metallic wall has been devised to satisfy requirements to fit within a specified size and shape and to generate a beam with a half-power angular width of <=40 deg. This antenna provides a gain of about 14 dB; in contrast, the gain of a typical single-patch antenna lies between 5 and 6 dB. This antenna can be considered an alternative to a two-dimensional array of patch antenna elements, or to a horn or helical antenna. Unlike a two-dimensional array of patches, this antenna can function without need for a power-division network (unless circular polarization is needed). The profile of this antenna is lower than that of a horn or a helical antenna designed for the same frequency. The primary disadvantage of this antenna, relative to a horn or a helical antenna, is that its footprint is slightly larger.

Global characteristics of auroral Hall currents derived from the Swarm constellation: dependences on season and IMF orientation

NASA Astrophysics Data System (ADS)

Huang, Tao; Lühr, Hermann; Wang, Hui

2017-11-01

On the basis of field-aligned currents (FACs) and Hall currents derived from high-resolution magnetic field data of the Swarm constellation, the average characteristics of these two current systems in the auroral regions are comprehensively investigated by statistical methods. This is the first study considering both current types determined simultaneously by the same spacecraft in both hemispheres. The FAC distribution, derived from the novel Swarm dual-spacecraft approach, reveals the well-known features of Region 1 (R1) and Region 2 (R2) FACs. At high latitudes, Region 0 (R0) FACs appear on the dayside. Their flow direction, up or down, depends on the orientation of the interplanetary magnetic field (IMF) By component. Of particular interest is the distribution of auroral Hall currents. The prominent auroral electrojets are found to be closely controlled by the solar wind input, but we find no dependence of their intensity on the IMF By orientation. The eastward electrojet is about 1.5 times stronger in local summer than in winter. Conversely, the westward electrojet shows less dependence on season. As to higher latitudes, part of the electrojet current is closed over the polar cap. Here the seasonal variation of conductivity mainly controls the current density. During local summer of the Northern Hemisphere, there is a clear channeling of return currents over the polar cap. For positive (negative) IMF By a dominant eastward (westward) Hall current circuit is formed from the afternoon (morning) electrojet towards the dawn side (dusk side) polar cap return current. The direction of polar cap Hall currents in the noon sector depends directly on the orientation of the IMF By. This is true for both signs of the IMF Bz component. Comparable Hall current distributions can be observed in the Southern Hemisphere but for opposite IMF By signs. Around the midnight sector the westward substorm electrojet is dominating. As expected, it is highly dependent on magnetic activity, but it shows only little response to season and IMF By polarity. An important finding is that all the IMF By dependences of FACs and Hall currents practically disappear in the dark winter hemisphere.

The Subsurface Ice Probe (SIPR): A Low-Power Thermal Probe for the Martian Polar Layered Deposits

NASA Technical Reports Server (NTRS)

Cardell, G.; Hecht, M. H.; Carsey, F. D.; Engelhardt, H.; Fisher, D.; Terrell, C.; Thompson, J.

2004-01-01

The distinctive layering visible in images from Mars Global Surveyor of the Martian polar caps, and particularly in the north polar cap, indicates that the stratigraphy of these polar layered deposits may hold a record of Martian climate history covering millions of years. On Earth, ice sheets are cored to retrieve a pristine record of the physical and chemical properties of the ice at depth, and then studied in exacting detail in the laboratory. On the Martian north polar cap, coring is probably not a practical method for implementation in an autonomous lander. As an alternative, thermal probes that drill by melting into the ice are feasible for autonomous operation, and are capable of reasonable approximations to the scientific investigations performed on terrestrial cores, while removing meltwater to the surface for analysis. The Subsurface Ice Probe (SIPR) is such a probe under development at JPL. To explore the dominant climate cycles, it is postulated that tens of meters of depth should be profiled, as this corresponds to the vertical separation of the major layers visible in the MOC images [1]. Optical and spectroscopic analysis of the layers, presumably demarcated by embedded dust and possibly by changes in the ice properties, would contribute to the construction of a chronology. Meltwater analysis may be used to determine the soluble chemistry of the embedded dust, and to monitor gradients of atmospheric gases, particularly hydrogen and oxygen, and isotopic variations that reflect atmospheric conditions at the time the layer was deposited. Thermal measurements can be used to determine the geothermal gradient and the bulk mechanical properties of the ice.

Patterns Unique, Yet Familiar

NASA Image and Video Library

2017-08-21

This close-up image from NASA's Mars Reconnaissance Orbiter gives the impression of looking like bacterial cells and their internal structures which travel and split in the process of life. These features are fractal in nature: the same image is preserved through different scales, with the pattern repeating eternally. The reality is, we are looking at one of Mars' polar regions; the South Polar residual cap to be precise, and, as with many things in Martian planetary science, there is a precise reasoning behind the name. With the coming and going of the seasons, this is an area on Mars where ice remains even after the peak of summer arrives. The texture is very alien, bearing more of a resemblance to the universe of the very small, rather than the universe far, far away. But if this is a polar cap, then why does it not look like the polar caps on Earth? Indeed, there is no equivalent terrain observed here on Earth. The so-called "Swiss cheese terrain, referencing the numerous holes of the region, is a product of seasonal exchange between the surface and the Martian atmosphere. With a predominantly carbon dioxide content at 98 percent, the colder temperatures condense the gas out of the atmosphere to produce dry ice. The prevalence of water is more concentrated in the north, leaving the South polar region more carbon dioxide rich, and it's this difference in composition that generates the unusual texture of the Swiss cheese terrain. The Red Planet is one of the chief candidates in the search for life elsewhere in the Solar System; however, a quick glance at this image virtually gives the impression we have already found it. NB: The cutout image has been rotated so that north is approximately up. https://photojournal.jpl.nasa.gov/catalog/PIA21880

The Sublimation Rate of CO2 Under Simulated Mars Conditions and the Possible Climatic Implications

NASA Astrophysics Data System (ADS)

Bryson, Kathryn; Chevrier, V.; Roe, L.; White, K.; Blackburn, D.

2008-09-01

In order to understand the behavior of CO2 on Mars, we have studied the sublimation of dry ice under simulated martian conditions. Our experiments resulted in an average sublimation rate for CO2 ice of 1.20 ± 0.27 mm h-1. These results are very close to those observed of the martian polar caps retreat, and suggest a common process for the sublimation mechanism on Mars and in our chamber. Based on these results we created a model where irradiance from the sun is the primary source of heat on the martian polar surface. Our model predicts a 32 cm offset between the amount of CO2 ice sublimated and deposited in the southern polar region. The eccentricity of the martian orbit causes the southern hemisphere to sublimate more then it deposits back during one martian year. We have compared MOC and HiRISE images from approximately the same season (Ls 285.57º and 289.5º, respectively) from three martian years apart. These images indicate an average sublimation rate of 0.43 ± 0.04 m y-1, very close to the 0.32 m y-1 predicted by our model. Due to the length of Mars’ precession cycle, 93,000 martian years, it will take an extensive amount of time for the equinoxes to change. Therefore, we predict that the CO2 of the south polar cap will migrate entirely to the northern polar cap before such changes could occur. If the CO2 ice is only a thin layer above a much thicker water ice layer, this could expose large amounts of water ice, having a drastic climactic affect.

Conformational landscape of isolated capped amino acids: on the nature of non-covalent interactions*

NASA Astrophysics Data System (ADS)

González, Jorge; Martínez, Rodrigo; Fernández, José A.; Millan, Judith

2017-08-01

The intramolecular interactions for isolated capped amino acids were investigated computationally by characterizing the conformers for selected amino acids with charged (arginine), polar (asparagine and glutamine), non-polar (alanine, valine and isoleucine), and aromatic (phenylalanine, tryptophan and tyrosine) side chains. The computational method applied combined a molecular mechanics conformational search (with an MMFFs forced field) followed by structural and vibrational density-functional calculations (M06-2X with a triple- ζ Pople's basis set). The intramolecular forces in each amino acid were analyzed with the Non-Covalent Interactions (NCI) analysis. The results for the 15 most stable conformers studied showed that the structure of isolated capped amino acids resembles those found in proteins. In particular, the two most stable conformers of the nine amino acids investigated exhibit γ L and β L conformations with 7- and 5-membered rings, respectively, as a result of the balance between non-covalent interactions (hydrogen bonds and van der Waals).

Steady-state flow of solid CO2: preliminary results

USGS Publications Warehouse

Durham, William B.; Kirby, Stephen H.; Stern, Laura A.

1999-01-01

To help answer the question of how much solid CO2 exists in the Martian south polar cap, we performed a series of laboratory triaxial deformation experiments at constant displacement rate in compression on jacketed cylinders of pure, polycrystalline CO2. Test conditions were temperatures 150 −8 ≤ ε ≤4.3×10−4 s−1. Most of the measurements follow a constitutive law of the form ε = Aσnexp(−Q/RT), where σ is the applied differential stress, R is the gas constant, and the other constants have values as follows: A = 103 86 MPa−ns−1, n = 5.6, and Q = 33 kJ/mol. Solid CO2 is markedly weaker than water ice. Our results suggest that the south polar cap on Mars is unlikely to be predominately solid CO2, because the elevation and estimated age of the cap is difficult to reconcile with the very weak rheology of the material.

Palmer Quest: A Feasible Nuclear Fission "Vision Mission" to the Mars Polar Caps

NASA Technical Reports Server (NTRS)

Carsey, F. D.; Beegle, L. W.; Nakagawa, R.; Elliott, J. O.; Matthews, J. B.; Coleman, M. L.; Hecht, M. H.; Ivaniov, A. B.; Head, J. W.; Milkovich, S.

2005-01-01

We are engaged in a NASA Vision Mission study, called Palmer Quest after the American Antarctic explorer Nathaniel Palmer, to assess the presence of life and evaluate the habitability of the basal domain of the Mars polar caps. We address this goal through four objectives: 1. Determine the presence of amino acids, nutrients, and geochemical heterogeneity in the ice sheet. 2. Quantify and characterize the provenance of the amino acids in Mars ice. 3. Assess the stratification of outcropped units for indications of habitable zones. 4. Determine the accumulation of ice, mineralogic material, and amino acids in Mars ice caps over the present epoch. Because of the defined scientific goal for the vision mission, the Palmer Quest focus is astrobiological; however, the results of the study make us optimistic that aggressive multi-platform in-situ missions that address a wide range of objectives, such as climate change, can be supported by variations of the approach used on this mission. Mission Overview: The Palmer Quest baseline

The role of water ice clouds in the Martian hydrologic cycle

NASA Technical Reports Server (NTRS)

James, Philip B.

1990-01-01

A one-dimensional model for the seasonal cycle of water on Mars has been used to investigate the direction of the net annual transport of water on the planet and to study the possible role of water ice clouds, which are included as an independent phase in addition to ground ice and water vapor, in the cycle. The calculated seasonal and spatial patterns of occurrence of water ice clouds are qualitatively similar to the observed polar hoods, suggesting that these polar clouds are, in fact, an important component of water cycle. A residual dry ice in the south acts as a cold trap which, in the absence of sources other than the caps, will ultimately attract the water ice from the north cap; however, in the presence of a source of water in northern midlatitudes during spring, it is possible that the observed distribution of vapor and ice can be in a steady state even if a residual CO2 cap is a permanent feature of the system.

A Low-Profile Dual-Layer Patch Antenna with a Circular Polarizer Consisting of Dual Semicircular Resonators.

PubMed

Guo, Li; Tang, Ming-Chun; Li, Mei

2018-06-01

In this paper, a circular polarizer comprising dual semicircular split-rings (DSSRs) is presented. By placing it above an elliptical radiator that radiates linearly polarized (LP) waves, dual-layer patch antennas capable of radiating right-hand (RH) or left-hand (LH) circularly polarized (CP) waves are achieved in terms of the different offset direction of the bottom splits of the DSSRs. Because of both the capacitive coupling to the radiator and the degenerate modes existing in the excited DSSRs, the DSSRs collaboratively result in a circularly polarized radiation, successfully converting incident LP waves into CP ones. Simulated results show that the impedance, axial ratio (AR), and gain frequency response of both proposed CP antennas are identical, with a simulated 3-dB AR bandwidth of 72 MHz covering 2.402⁻2.474 GHz and a gain enhanced by 3.9 dB. The proposed antennas were fabricated and measured, revealing an operational bandwidth of 65 MHz (2.345⁻2.41 GHz) and a peak gain up to 9 dBi. Moreover, a low profile of 0.063λ₀ is maintained. The proposed CP antennas could be as a candidate for wireless target detection applications in terms of their identical frequency response property.

The analysis of initial Juno magnetometer data using a sparse magnetic field representation

NASA Astrophysics Data System (ADS)

Moore, Kimberly M.; Bloxham, Jeremy; Connerney, John E. P.; Jørgensen, John L.; Merayo, José M. G.

2017-05-01

The Juno spacecraft, now in polar orbit about Jupiter, passes much closer to Jupiter's surface than any previous spacecraft, presenting a unique opportunity to study the largest and most accessible planetary dynamo in the solar system. Here we present an analysis of magnetometer observations from Juno's first perijove pass (PJ1; to within 1.06 RJ of Jupiter's center). We calculate the residuals between the vector magnetic field observations and that calculated using the VIP4 spherical harmonic model and fit these residuals using an elastic net regression. The resulting model demonstrates how effective Juno's near-surface observations are in improving the spatial resolution of the magnetic field within the immediate vicinity of the orbit track. We identify two features resulting from our analyses: the presence of strong, oppositely signed pairs of flux patches near the equator and weak, possibly reversed-polarity patches of magnetic field over the polar regions. Additional orbits will be required to assess how robust these intriguing features are.

Interhemispheric differences in ionospheric convection: Cluster EDI observations revisited

NASA Astrophysics Data System (ADS)

Förster, M.; Haaland, S.

2015-07-01

The interaction between the interplanetary magnetic field and the geomagnetic field sets up a large-scale circulation in the magnetosphere. This circulation is also reflected in the magnetically connected ionosphere. In this paper, we present a study of ionospheric convection based on Cluster Electron Drift Instrument (EDI) satellite measurements covering both hemispheres and obtained over a full solar cycle. The results from this study show that average flow patterns and polar cap potentials for a given orientation of the interplanetary magnetic field can be very different in the two hemispheres. In particular during southward directed interplanetary magnetic field conditions, and thus enhanced energy input from the solar wind, the measurements show that the southern polar cap has a higher cross polar cap potential. There are persistent north-south asymmetries, which cannot easily be explained by the influence of external drivers. These persistent asymmetries are primarily a result of the significant differences in the strength and configuration of the geomagnetic field between the Northern and Southern Hemispheres. Since the ionosphere is magnetically connected to the magnetosphere, this difference will also be reflected in the magnetosphere in the form of different feedback from the two hemispheres. Consequently, local ionospheric conditions and the geomagnetic field configuration are important for north-south asymmetries in large regions of geospace.

Canadian High Arctic Ionospheric Network (CHAIN)

NASA Astrophysics Data System (ADS)

Jayachandran, P. T.; Langley, R. B.; MacDougall, J. W.; Mushini, S. C.; Pokhotelov, D.; Hamza, A. M.; Mann, I. R.; Milling, D. K.; Kale, Z. C.; Chadwick, R.; Kelly, T.; Danskin, D. W.; Carrano, C. S.

2009-02-01

Polar cap ionospheric measurements are important for the complete understanding of the various processes in the solar wind-magnetosphere-ionosphere system as well as for space weather applications. Currently, the polar cap region is lacking high temporal and spatial resolution ionospheric measurements because of the orbit limitations of space-based measurements and the sparse network providing ground-based measurements. Canada has a unique advantage in remedying this shortcoming because it has the most accessible landmass in the high Arctic regions, and the Canadian High Arctic Ionospheric Network (CHAIN) is designed to take advantage of Canadian geographic vantage points for a better understanding of the Sun-Earth system. CHAIN is a distributed array of ground-based radio instruments in the Canadian high Arctic. The instrument components of CHAIN are 10 high data rate Global Positioning System ionospheric scintillation and total electron content monitors and six Canadian Advanced Digital Ionosondes. Most of these instruments have been sited within the polar cap region except for two GPS reference stations at lower latitudes. This paper briefly overviews the scientific capabilities, instrument components, and deployment status of CHAIN. This paper also reports a GPS signal scintillation episode associated with a magnetospheric impulse event. More details of the CHAIN project and data can be found at http://chain.physics.unb.ca/chain.

Defense Meteorological Satellite Program Data in Dynamic Auroral Boundary Coordinates: New insights into Polar Cap and Auroral Dynamics

NASA Astrophysics Data System (ADS)

Knipp, D.

2016-12-01

Using reprocessed (Level-2) data from the Defense Meteorology Satellite Program magnetometer (SSM) and particle precipitation (SSJ) instruments we determine the boundaries of the central plasma sheet auroral oval, and then consider the relative locations and intensities of field aligned currents. Large-scale field-aligned currents (FAC) are determined using the Minimum Variance Analysis technique, and their influence is then removed from the magnetic perturbations allowing us to estimate intensity and scale-size of the smaller-scale currents. When sorted by dynamic auroral boundary coordinates we find that large- scale Region 1 (R1) FAC are often within the polar cap and Region 2 (R2) FAC show a strong dawn-dusk asymmetry (as in Ohtani et al., 2010). We find that mesoscale FAC are stronger in the summer and are most consistently present in the vicinity of dawnside (downward) R1 FAC. Further, mesoscale FAC are confined to auroral latitudes and above on the dawnside, but can be subaroural on the dusk side. Hotspots of mesoscale FAC occur in pre-midnight regions especially during summer. Finally, we show how this information can be combined with measurements from above and below the ionosphere-thermosphere to help explain significant perturbations in polar cap dynamics.

Possible contemporary evaporites formation at the Martian Northern Polar Cap

NASA Astrophysics Data System (ADS)

Losiak, Anna; Czechowski, Leszek

Evaporitic minerals are abundant on the surface of Mars (e.g., Wentworth et al. 2005, Velbel 2012, Clark and Van Hart 1981, Wang et al. 2006, Kuzmin et al. 2009), especially within the Circumpolar Dune Field and on the Northern Ice Cap itself (e.g., Langevin et al., 2005, Roach et al. 2007, Horgan et al. 2009, Masse et al. 2010, 2012). Most of their proposed formation mechanisms require significant amounts of liquid water and are thus not possible under current Martian conditions (Arvidson et al. 2006, Andrews-Hanna et al. 2007, Fishbaugh et al. 2007, Szynkiewicz et al. 2010). Some authors have considered the potential role of ice and ice- or snowmelt-related alteration in the weathering of Martian materials (e.g., Catling et al. 2006, Zolotov and Mironenko 2007, Niles and Michalski 2009, Masse et al. 2010). However, none of those studies discussed details of the process leading to the formation of the evaporites or the timing of the processes. The aim of this paper is to model numerically if the current radiant heating is sufficient to melt a thin layer of ice surrounding a single dust grain exposed within the south facing side of the Martian North Polar Cap trench. The results of our initial study suggest that for dust grains with basaltic properties and ice with low values of coefficient of heat conduction, and solar constant = 492 W/m2 liquid water may exist below a dust grain for up to 4 hours a sol. This suggest that contemporary evaporites formation on Martian Polar Cap is possible.

Stereo Topography of the South Polar of Mar: Volatile Inventory and Mars Polar Landing Landing Site

NASA Technical Reports Server (NTRS)

Schenk, Paul M.; Moore, Jeffrey M.

2000-01-01

Viking stereo images and topographic maps reveal that the south polar layered deposits of Mars are topographically complex and morphologically distinct from the north polar layered deposits. The dominant feature is a 500-km-wide topographic dome that rises 3 km above the surrounding plains. This dome underlies the residual ice cap but is at least 50% larger in area. Erosional scarps and terraces indicate that this dome was once more extensive and has undergone erosional retreat. Adjacent to the dome, layered deposits form a vast plateau 1-1.5 km high extending approximately 1000 km beyond and to one side of the residual south polar cap. This plateau is relatively flat at kilometer scales, although it is cut in places by troughs and depressions, which have locally steep scarps up to 2 km high and sloping up to roughly 10 deg. Contiguously flat kilometer-scale regions the size of the Mars Polar Lander (MPL) landing ellipse are present. These are in the form of plateaus 100-300 km wide and 1-2 km high. One of the largest of these plateaus has been proposed as a landing site for the Mars Polar Lander (MPL). The volume associated with the south polar layered deposits may be comparable to those of the layered deposits at the north pole. Although this doubles the current probable inventory of surface ice on Mars, it still falls far short of accounting for the inferred volume of water on Mars in the past.

The flow of plasma in the solar terrestrial environment

NASA Technical Reports Server (NTRS)

Schunk, R. W.; Birmingham, T. J.

1992-01-01

The scientific goals of the program are outlined, and some of the papers submitted for publication within the last six months are briefly highlighted. Some of the topics covered include ionosphere-magnetosphere coupling, polar cap arcs, polar wind, convection vortices, ionosphere-plasmasphere coupling, and the validity of macroscopic plasma flow models.

Findings of the wetland survey of the David Witherspoon, Inc., 1630 Site, South Knoxville, Knox County, Tennessee

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rosensteel, B.A.

1997-03-01

In accordance with Department of Energy (DOE) Regulations surveys for wetland presence or absence were conducted in September 1996 on the DWI-1630 site (Witherspoon Landfill) located in South Knoxville, Knox County, Tennessee. The DWI-1630 site includes a closed, capped landfill area, areas of past disturbance adjacent to the capped area, and patches of hardwood forest. Wetlands were identified on the landfill cap and in a small bottomland that was formerly used for a retention pond in the southwest corner of the DWI-1630 site. The wetlands identified on the cap are man-induced, atypical situation wetlands. These areas have hydrophytic vegetation andmore » wetland hydrology, but the soils do not have hydric characteristics. Wetland development appears to be due to a combination of the grading or subsidence of the clay landfill cap, the low permeability of the clay fill soil, and the absence of surface drainage outlets from the depressions. These atypical situation wetland areas may not be considered by the US Army Corps of Engineers or the State of Tennessee to be jurisdictional wetlands. The wetland in the former retention pond area has hydrophytic vegetation, wetland hydrology, and hydric soils and is a jurisdictional wetland.« less

Seasonal Nitrogen Cycles on Pluto

NASA Technical Reports Server (NTRS)

Hansen, Candice J.; Paige, David A.

1996-01-01

A thermal model, developed to predict seasonal nitrogen cycles on Triton, has been modified and applied to Pluto. The model was used to calculate the partitioning of nitrogen between surface frost deposits and the atmosphere, as a function of time for various sets of input parameters. Volatile transport was confirmed to have a significant effect on Pluto's climate as nitrogen moved around on a seasonal time scale between hemispheres, and sublimed into and condensed out of the atmosphere. Pluto's high obliquity was found to have a significant effect on the distribution of frost on its surface. Conditions that would lead to permanent polar caps on Triton were found to lead to permanent zonal frost bands on Pluto. In some instances, frost sublimed from the middle of a seasonal cap outward, resulting in a "polar bald spot". Frost which was darker than the substrate did not satisfy observables on Pluto, in contrast to our findings for Triton. Bright frost (brighter than the substrate) came closer to matching observables. Atmospheric pressure varied seasonally. The amplitudes, and to a lesser extent the phase, of the variation depended significantly on frost and substrate properties. Atmospheric pressure was found to be determined both by Pluto's distance from the sun and by the subsolar latitude. In most cases two peaks in atmospheric pressure were observed annually: a greater one associated with the sublimation of the north polar cap just as Pluto receded from perihelion, and a lesser one associated with the sublimation of the south polar cap as Pluto approached perihelion. Our model predicted frost-free dark substrate surface temperatures in the 50 to 60 K range, while frost temperatures typically ranged between 30 to 40 K. Temporal changes in frost coverage illustrated by our results, and changes in the viewing geometry of Pluto from the Earth, may be important for interpretation of ground-based measurements of Pluto's thermal emission.

Atmospheric Rotational Effects on Mars Based on the NASA Ames General Circulation Model: Angular Momentum Approach

NASA Technical Reports Server (NTRS)

Sanchez, Braulio V.; Haberle, Robert M.; Schaeffer, James

2004-01-01

The objective of the investigation is to determine the motion of the rotational axis of Mars as a result of mass variations in the atmosphere and condensation and sublimation of CO2 ice on the polar caps. A planet experiences this type of motion if it has an atmosphere, which is changing its mass distribution with respect to the solid body of the planet and/or it is asymmetrically changing the amount of ice at the polar caps. The physical principle involved is the conservation of angular momentum, one can get a feeling for it by sitting on a well oiled swivel chair holding a rotating wheel on a horizontal direction and then changing the rotation axis of the wheel to a vertical direction. The person holding the wheel and the chair would begin to rotate in opposite direction to the rotation of the wheel. The motions of Mars atmosphere and the ice caps variations are obtained from a mathematical model developed at the NASA Ames Research Center. The model produces outputs for a time span of one Martian year, which is equivalent to 687 Earth days. The results indicate that Mars axis of rotation moves in a spiral with respect to a reference point on the surface of the planet. It can move as far away as 35.3 cm from the initial location as a result of both mass variations in the atmosphere and asymmetric ice variations at the polar caps. Furthermore the pole performs close to two revolutions around the reference point during a Martian year. This motion is a combination of two motions, one produced by the atmospheric mass variations and another due to the variations in the ice caps. The motion due to the atmospheric variations is a spiral performing about two and a half revolutions around the reference point during which the pole can move as far as 40.9 cm. The motion due to variations in the ice caps is a spiral performing almost three revolutions during which the pole can move as far as 32.8 cm.

Assessment of glucose content in diabetic patients by examining the core of hair

NASA Astrophysics Data System (ADS)

Joshi, Narahari V.; Joshi, Virgina O. d.; Quintero, M.; Osuna, A.

1999-07-01

Glucose is known to be an optically active material and therefore in cross polarized light, a bright color will be visualized against a dark background. In non enzymatic glycation glucose is attached to (epsilon) -NH2 group of Lysine residues of proteins and therefore an irreversible alteration takes place. Glucose molecules along with proteins are deposited in the core of the hair in the growth process and when it is examined under cross polarized radiation bright colored patches, depending upon the thickness of glucose conglomerate, are expected. With this view, we have examined 25 diabetic patients and we have observed the presence of such patches. In controlled cases, these patches were absent provided that the hairs had not received any chemical or heat treatment. If properly exploited, this could be a very useful non-invasive diagnostic tool or guidance for diabetes related phenomena. Moreover, the proteins deposited in the hair core are not altered and are preserved for a long period and hence, it could reveal the history of the patient in relation with his glucose metabolism.

Circularly polarized triple band glass shaped monopole patch antenna with metallic reflector for bluetooth & wireless applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jangid, K. G.; Kulhar, V. S.; Choudhary, N.

This paper presents the design and performance of strip line fed glass shaped monopole patch antenna having with overall size 30mm × 30 mm × 1.59 mm. In the patch; an eight shaped slot and in the ground plane an eight shaped ring are introduced. A metallic ground plane is also introduced at appropriate location beneath the ground plane. The proposed antenna is simulated by applying CST Microwave Studio simulator. Antenna provides circularly polarized radiations, triple broad impedance bandwidth of 203MHz (2.306GHz to 2.510GHz), 42MHz (2.685GHz to 2.757GHz) & GHz (3.63 GHz to 6.05 GHz), high flat gain (close to 5dBi) and good radiationmore » properties in the desired frequency range. This antenna may be a very useful tool for 2.45GHz Bluetooth communication band as well as for 2.4GHz/5.2 GHz /5.8 GHz WLAN bands & 3.7GHz/5.5 GHz Wi-Max bands.« less

South polar residual cap of Mars: Features, stratigraphy, and changes

NASA Astrophysics Data System (ADS)

Thomas, P. C.; Malin, M. C.; James, P. B.; Cantor, B. A.; Williams, R. M. E.; Gierasch, P.

2005-04-01

The south residual polar cap of Mars, rich in CO 2 ice, is compositionally distinct from the north residual cap which is dominantly H 2O ice. The south cap is also morphologically distinct, displaying a bewildering variety of depressions formed in thin layered deposits, which have been observed to change by scarp retreat over an interval of one Mars year (Malin et al., 2001, Science 294, 2146-2148). The climatically sensitive locale of the residual caps suggests that their behavior may help in the interpretation of recent fluctuations or repeatability of the Mars climate. We have used Mars Global Surveyor Mars Orbiter Camera (MOC) images obtained in three southern summers to map the variety of features in the south residual cap and to evaluate changes over two Mars years (Mars y). The images show that there are two distinct layered units which were deposited at different times separated by a period of degradation. The older unit, ˜10 m thick, has layers approximately 2 m thick. The younger unit has variable numbers of layers, each ˜1 m thick. The older unit is eroding by scarp retreat averaging 3.6 m/Mars y, a rate greater than the retreat of 2.2 m/Mars y observed for the younger unit. The rates of scarp retreat and sizes of the different types of depressions indicate that the history of the residual cap has been short periods of deposition interspersed with longer erosional periods. Erosion of the older unit probably occupied ˜100-150 Mars y. One layer may have been deposited after the Mariner 9 observations in 1972. Residual cap layers appear to differ from normal annual winter deposits by having a higher albedo and perhaps by having higher porosities. These properties might be produced by differences in the depositional meteorology that affect the fraction of high porosity snow included in the winter deposition.

Regulation of Cdc42/Rac Signaling in the Establishment of Cell Polarity and Control of Cell Motility

DTIC Science & Technology

2004-08-01

Irazoqui Breast Cancer Predoctoral Traineeship Final Report Introduction Cdc42p, together with other polarity proteins, becomes polarized to a cap... Cancer Biology, Certificate in Cell and Molecular Biology. "* Awarded the Jane Coffin Childs Postdoctoral Fellowship for continuing research in the...Bemlp binds directly to both the Cdc42p-directed GEF Department of Pharmacology and Cancer Biology Duke University Medical Center, Durham, NC 27710

South Polar Region of Mars: Topography and Geology

NASA Technical Reports Server (NTRS)

Schenk, P. M.; Moore, J. M.

1999-01-01

The polar layered deposits of Mars represent potentially important volatile reservoirs and tracers for the planet's geologically recent climate history. Unlike the north polar cap, the uppermost surface of the bright residual south polar deposit is probably composed of carbon dioxide ice. It is unknown whether this ice extends through the entire thickness of the deposit. The Mars Polar Lander (MPL), launched in January 1999, is due to arrive in December 1999 to search for water and carbon dioxide on layered deposits near the south pole (SP) of Mars. Additional information is contained in the original extended abstract.

Three-dimensional radar imaging of structures and craters in the Martian polar caps.

PubMed

Putzig, Nathaniel E; Smith, Isaac B; Perry, Matthew R; Foss, Frederick J; Campbell, Bruce A; Phillips, Roger J; Seu, Roberto

2018-07-01

Over the last decade, observations acquired by the Shallow Radar (SHARAD) sounder on individual passes of the Mars Reconnaissance Orbiter have revealed the internal structure of the Martian polar caps and provided new insights into the formation of the icy layers within and their relationship to climate. However, a complete picture of the cap interiors has been hampered by interfering reflections from off-nadir surface features and signal losses associated with sloping structures and scattering. Foss et al. (2017) addressed these limitations by assembling three-dimensional data volumes of SHARAD observations from thousands of orbital passes over each polar region and applying geometric corrections simultaneously. The radar volumes provide unprecedented views of subsurface features, readily imaging structures previously inferred from time-intensive manual analysis of single-orbit data (e.g., trough-bounding surfaces, a buried chasma, and a basal unit in the north, massive carbon-dioxide ice deposits and discontinuous layered sequences in the south). Our new mapping of the carbon-dioxide deposits yields a volume of 16,500 km 3 , 11% larger than the prior estimate. In addition, the radar volumes newly reveal other structures, including what appear to be buried impact craters with no surface expression. Our first assessment of 21 apparent craters at the base of the north polar layered deposits suggests a Hesperian age for the substrate, consistent with that of the surrounding plains as determined from statistics of surface cratering rates. Planned mapping of similar features throughout both polar volumes may provide new constraints on the age of the icy layered deposits. The radar volumes also provide new topographic data between the highest latitudes observed by the Mars Orbiter Laser Altimeter and those observed by SHARAD. In general, mapping of features in these radar volumes is placing new constraints on the nature and evolution of the polar deposits and associated climate changes.

Three-dimensional radar imaging of structures and craters in the Martian polar caps

NASA Astrophysics Data System (ADS)

Putzig, Nathaniel E.; Smith, Isaac B.; Perry, Matthew R.; Foss, Frederick J.; Campbell, Bruce A.; Phillips, Roger J.; Seu, Roberto

2018-07-01

Over the last decade, observations acquired by the Shallow Radar (SHARAD) sounder on individual passes of the Mars Reconnaissance Orbiter have revealed the internal structure of the Martian polar caps and provided new insights into the formation of the icy layers within and their relationship to climate. However, a complete picture of the cap interiors has been hampered by interfering reflections from off-nadir surface features and signal losses associated with sloping structures and scattering. Foss et al. (The Leading Edge 36, 43-57, 2017, https://doi.org/10.1190/tle36010043.1) addressed these limitations by assembling three-dimensional data volumes of SHARAD observations from thousands of orbital passes over each polar region and applying geometric corrections simultaneously. The radar volumes provide unprecedented views of subsurface features, readily imaging structures previously inferred from time-intensive manual analysis of single-orbit data (e.g., trough-bounding surfaces, a buried chasma, and a basal unit in the north, massive carbon-dioxide ice deposits and discontinuous layered sequences in the south). Our new mapping of the carbon-dioxide deposits yields a volume of 16,500 km3, 11% larger than the prior estimate. In addition, the radar volumes newly reveal other structures, including what appear to be buried impact craters with no surface expression. Our first assessment of 21 apparent craters at the base of the north polar layered deposits suggests a Hesperian age for the substrate, consistent with that of the surrounding plains as determined from statistics of surface cratering rates. Planned mapping of similar features throughout both polar volumes may provide new constraints on the age of the icy layered deposits. The radar volumes also provide new topographic data between the highest latitudes observed by the Mars Orbiter Laser Altimeter and those observed by SHARAD. In general, mapping of features in these radar volumes is placing new constraints on the nature and evolution of the polar deposits and associated climate changes.

What Lies Below a Martian Ice Cap

NASA Technical Reports Server (NTRS)

2008-01-01

[figure removed for brevity, see original site] Click on image for larger annotated version

This image (top) taken by the Shallow Radar instrument on NASA's Mars Reconnaissance Orbiter reveals the layers of ice, sand and dust that make up the north polar ice cap on Mars. It is the most detailed look to date at the insides of this ice cap. The colored map below the radar picture shows the topography of the corresponding Martian terrain (red and white represent higher ground, and green and yellow lower).

The radar image reveals four never-before-seen thick layers of ice and dust separated by layers of nearly pure ice. According to scientists, these thick ice-free layers represent approximately one-million-year-long cycles of climate change on Mars caused by variations in the planet's tilted axis and its eccentric orbit around the sun. Adding up the entire stack of ice gives an estimated age for the north polar ice cap of about 4 million years a finding that agrees with previous theoretical estimates. The ice cap is about 2 kilometers (1.2 miles) thick.

The radar picture also shows that the boundary between the ice layers and the surface of Mars underneath is relatively flat (bottom white line on the right). This implies that the surface of Mars is not sagging, or bending, under the weight of the ice cap and this, in turn, suggests that the planet's lithosphere, a combination of the crust and the strong parts of the upper mantle, is thicker than previously thought.

A thicker lithosphere on Mars means that temperatures increase more gradually with depth toward the interior. Temperatures warm enough for water to be liquid are therefore deeper than previously thought. Likewise, if liquid water does exist in aquifers below the surface of Mars, and if there are any organisms living in that water, they would have to be located deeper in the planet.

The topography data are from Mars Orbiter Laser Altimeter, which was flown on NASA's Mars Global Surveyor mission.

NPLD stands for the north polar layered deposits.

BU stands for basal unit, an ice-sand deposit that lies beneath parts of the north polar layered deposits.

The Shallow Radar instrument was provided by the Italian Space Agency. Its operations are led by the University of Rome and its data are analyzed by a joint U.S.-Italian science team. JPL, a division of the California Institute of Technology, Pasadena, manages the Mars Reconnaissance Orbiter for the NASA Science Mission Directorate, Washington.

Transduction of the Root Gravitropic Stimulus: Can Apical Calcium Regulate Auxin Distribution?

NASA Technical Reports Server (NTRS)

Edwards, K. L.

1985-01-01

The hypothesis was tested that calcium, asymmetrically distributes in the root cap upon reorientation to gravity, affects auxin transport and thereby auxin distribution at the elongation zone. It is assumed that calcium exists in the root cap and is asymmetrically transported in root caps altered from a vertical to a horizontal position and that the meristem, the tissue immediately adjacent to the root cap and lying between the site of gravity perception and the site of gravity response, is essential for mediation of gravitropism. Tip calcium in root gravicurvature was implicated. The capstone evidence is that the root cap has the capacity to polarly translocate exogenous calcium downward when tissue is oriented horizontally, and that exogenous calcium, when supplied asymmetrically at the root tip, induces curvature and dictates the direction of curvature in both vertical and horizontal corn roots.

The Plunger Hypothesis: an overview of a new theory of stratosphere-troposphere dynamic coupling

NASA Astrophysics Data System (ADS)

Clark, S.; Baldwin, M. P.; Stephenson, D.

2015-12-01

I will demonstrate the advantages of a new method of quantifying polar stratosphere-troposphere coupling by considering large-scale movements of mass into and out of the polar stratosphere. This project aims to use these mass movements to explain pressure and temperature anomalies throughout the polar troposphere and lower stratosphere in the aftermath of extreme stratospheric events. We hypothesise that these mass movements are induced by deposition of momentum by breaking waves in the stratosphere, slowing the wintertime polar vortex, and so are associated with sudden stratospheric warmings (SSWs). Such a mass movement in the upper stratosphere acts to compress the polar atmosphere below it in the manner of a plunger. In this way the pressure anomaly in the upper polar stratosphere 'controls' the pressure and temperature anomalies below by adiabatic compression of the polar atmospheric column. Better understanding this method of control will allow us to use stratospheric data to improve medium-range forecasting ability in the troposphere. One of the key innovations featured in this project is considering pressure and temperature fields at fixed geopotential surfaces, allowing for the easy observation of mass movement into and out of a polar cap region (which we have defined as north of 65N) as a function of altitude. Reanalysis data considered in this manner demonstrates a relationship between tropospheric pressure anomalies and stratospheric anomalies in the polar cap, and so a way to predict tropospheric variability given stratospheric information. This work forms part of a three and a half year PhD project.

A user's manual for the Electromagnetic Surface Patch code: ESP version 3

NASA Technical Reports Server (NTRS)

Newman, E. H.; Dilsavor, R. L.

1987-01-01

This report serves as a user's manual for Version III of the Electromagnetic Surface Patch Code or ESP code. ESP is user-oriented, based on the method of moments (MM) for treating geometries consisting of an interconnection of thin wires and perfectly conducting polygonal plates. Wire/plate junctions must be about 0.1 lambda or more from any plate edge. Several plates may intersect along a common edge. Excitation may be by either a delta-gap voltage generator or by a plane wave. The thin wires may have finite conductivity and also may contain lumped loads. The code computes most of the usual quantities of interest such as current distribution, input impedance, radiation efficiency, mutual coupling, far zone gain patterns (both polarizations) and radar-cross-section (both/cross polarizations).

Reduction of the spatially mutual coupling between dual-polarized patch antennas using coupled metamaterial slabs.

PubMed

Pan, Bai Cao; Tang, Wen Xuan; Qi, Mei Qing; Ma, Hui Feng; Tao, Zui; Cui, Tie Jun

2016-07-22

Mutual coupling inside antenna array is usually caused by two routes: signal leakage via conducting currents on the metallic background or surface wave along substrates; radio leakage received from space between antenna elements. The former one can be depressed by changing the distribution of surface currents, as reported in literatures. But when it comes to the latter one, the radiation-leakage-caused coupling, traditional approaches using circuit manipulation may be inefficient. In this article, we propose and design a new type of decoupling module, which is composed of coupled metamaterial (MTM) slabs. Two classes of MTM particles, the interdigital structure (IS) and the split-ring resonators (SRRs), are adopted to provide the first and second modulations of signal. We validate its function to reduce the radiation leakage between two dual-polarized patch antennas. A prototype is fabricated in a volume with subwavelength scale (0.6λ × 0.3λ × 0.053λ) to provide 7dB improvement for both co-polarization and cross-polarization isolations from 1.95 to 2.2 GHz. The design has good potential for wireless communication and radar systems.

Reduction of the spatially mutual coupling between dual-polarized patch antennas using coupled metamaterial slabs

PubMed Central

Pan, Bai Cao; Tang, Wen Xuan; Qi, Mei Qing; Ma, Hui Feng; Tao, Zui; Cui, Tie Jun

2016-01-01

Mutual coupling inside antenna array is usually caused by two routes: signal leakage via conducting currents on the metallic background or surface wave along substrates; radio leakage received from space between antenna elements. The former one can be depressed by changing the distribution of surface currents, as reported in literatures. But when it comes to the latter one, the radiation-leakage-caused coupling, traditional approaches using circuit manipulation may be inefficient. In this article, we propose and design a new type of decoupling module, which is composed of coupled metamaterial (MTM) slabs. Two classes of MTM particles, the interdigital structure (IS) and the split-ring resonators (SRRs), are adopted to provide the first and second modulations of signal. We validate its function to reduce the radiation leakage between two dual-polarized patch antennas. A prototype is fabricated in a volume with subwavelength scale (0.6λ × 0.3λ × 0.053λ) to provide 7dB improvement for both co-polarization and cross-polarization isolations from 1.95 to 2.2 GHz. The design has good potential for wireless communication and radar systems. PMID:27444147

Multi-MICE: Nuclear Powered Mobile Probes to Explore Deep Interiors of the Ice Sheets on Mars and the Jovian Moons

DOE Office of Scientific and Technical Information (OSTI.GOV)

Maise, George; Powell, James; Paniagua, John

2007-01-30

The multi-kilometer thick Polar Caps on Mars contain unique and important data about the multi-million year history of its climate, geology, meteorology, volcanology, cosmic ray and solar activity, and meteor impacts. They also may hold evidence of past life on Mars, including microbes, microfossils and biological chemicals. The objective of this paper is to describe a probe that can provide access to the data locked in the Polar Caps. The MICE (Mars Ice Cap Explorer) system would explore the Polar Cap interiors using mobile probes powered by compact, lightweight nuclear reactors. The probes would travel 100's of meters per daymore » along melt channels in the ice sheets created by hot water jets from the 500 kW(th) nuclear reactors, ascending and descending, either vertically or at an angle to the vertical, reaching bedrock at kilometers beneath the surface. The powerful reactor will be necessary to provide sufficient hot water at high velocity to penetrate the extensive horizontal dust/sand layers that separate layers of ice in the Mars Ice Caps. MICE reactors can operate at 500 kW(th) for more than 4 years, and much longer in practice, since power level will be much lower when the probes are investigating locations in detail at low or zero speed. Multiple probes, e.g. six, would be deployed in an interactive network, continuously communicating by RF and acoustic signals with each other and with the surface lander spacecraft. In turn, the lander would continuously communicate in real time, subject to speed of light delays, with scientists on Earth to transmit data and receive instructions for the MICE probes. Samples collected by the probes could be brought to the lander, for return to the Earth at the end of the mission.« less

Recent Glaciers on Mars: Description and Solar System Perspective

NASA Astrophysics Data System (ADS)

Kargel, J. S.

2001-11-01

Active or recently active ice deposits occur on Mars at middle and high latitudes in fretted terrain, around massifs in highlands east of Hellas and in southern Argyre, on crater walls in the highlands, and in the south polar cap. Most mid-latitude icy flows are debris covered, apparently stagnant, and eroded by partial sublimation. Others are scarred by fresh crevasses and gullies, thus suggesting recent deformation and surface melting. Erosional features include a variety of small-scale relief elements due mainly to sublimation, but sublimation has not obliterated evidence of flow. Similar to terrestrial glaciers in many respects, there are also notable differences, especially in the nature of accumulation. Deformation of the south polar cap is indicated by folding, boudinage, strike-slip or normal faulting, forebulge tectonics near scarps, and thrust faulting. The north polar cap locally also exhibits flow indicators. The south cap's glacial features suggest interbedding of two or more types of ice of differing volatility and rheology, plus a locally deforming surficial dry-ice cap overlying the other materials. Major ice types may include two (or more) of the following, in order of highest to lowest mechanical strength: CO2 clathrate hydrate, water ice, water ice containing traces of liquid-soluble salts, water ice containing traces of solid-soluble acids, and CO2 ice; dust is another variable. Within our Solar System, the closest geomorphic analog to icy Martian flows are Earth's alpine glaciers, rock glaciers, and continental ice sheets, though key differences are apparent. If made dominantly of water ice, important and recent climatic shifts seem to be implicated. Ice-flow landforms also occur on some outer planet satellites; among them are Io, Europa, Enceladus, Ariel, and Triton. Volatile flows on these bodies may involve diverse materials, such as sulfur, water ice, hydrated salts, ammonia-water ices, and nitrogen ice. Most of these would not be suitable materials on Mars. This work was funded by grants from the NASA Mars Data Analysis Program.

High-Energy Emission From the Polar Cap and Slot Gap

NASA Technical Reports Server (NTRS)

Harding, Alice K.

2006-01-01

Thirty-five years after the discovery of rotation-powered pulsars, we still do not understand the fundamentals of their pulsed emission at any wavelength. I will review the latest developments in understanding the high-energy emission of rotation-powered pulsars, with particular emphasis on the polar cap and slot gap models. Special and general relativistic effects play important roles in pulsar emission, from inertial frame-dragging near the stellar surface to aberration, time-of-flight and retardation of the magnetic field near the light cylinder. Understanding how these effects determine what we observe at different wavelengths is critical to unraveling the emission physics. I will discuss how the next generation of gamma-ray detectors, AGILE and GLAST, will test prediction of these models.

Particle-based simulations of polarity establishment reveal stochastic promotion of Turing pattern formation

PubMed Central

Ramirez, Samuel A.; Elston, Timothy C.

2018-01-01

Polarity establishment, the spontaneous generation of asymmetric molecular distributions, is a crucial component of many cellular functions. Saccharomyces cerevisiae (yeast) undergoes directed growth during budding and mating, and is an ideal model organism for studying polarization. In yeast and many other cell types, the Rho GTPase Cdc42 is the key molecular player in polarity establishment. During yeast polarization, multiple patches of Cdc42 initially form, then resolve into a single front. Because polarization relies on strong positive feedback, it is likely that the amplification of molecular-level fluctuations underlies the generation of multiple nascent patches. In the absence of spatial cues, these fluctuations may be key to driving polarization. Here we used particle-based simulations to investigate the role of stochastic effects in a Turing-type model of yeast polarity establishment. In the model, reactions take place either between two molecules on the membrane, or between a cytosolic and a membrane-bound molecule. Thus, we developed a computational platform that explicitly simulates molecules at and near the cell membrane, and implicitly handles molecules away from the membrane. To evaluate stochastic effects, we compared particle simulations to deterministic reaction-diffusion equation simulations. Defining macroscopic rate constants that are consistent with the microscopic parameters for this system is challenging, because diffusion occurs in two dimensions and particles exchange between the membrane and cytoplasm. We address this problem by empirically estimating macroscopic rate constants from appropriately designed particle-based simulations. Ultimately, we find that stochastic fluctuations speed polarity establishment and permit polarization in parameter regions predicted to be Turing stable. These effects can operate at Cdc42 abundances expected of yeast cells, and promote polarization on timescales consistent with experimental results. To our knowledge, our work represents the first particle-based simulations of a model for yeast polarization that is based on a Turing mechanism. PMID:29529021

A Warmer Atmosphere on Mars Near the Noachian-Hesperian Boundary: Evidence from Basal Melting of the South Polar Ice Cap (Dorsa Argentea Formation)

NASA Astrophysics Data System (ADS)

Fastook, J. L.; Head, J. W.; Marchant, D. R.; Forget, F.; Madeleine, J.-B.

2011-03-01

Dorsa Argentea Formation (Noachian-Hesperian) eskers are evidence for basal melting. Ice-flow models show that the mean annual south polar temperature must be raised to -50° to -75°C, providing an independent estimate of elevated lower latitude surface temperature.

Magnetic Flux Cancellation as the Origin of Solar Quiet-region Pre-jet Minifilaments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Panesar, Navdeep K.; Sterling, Alphonse C.; Moore, Ronald L., E-mail: navdeep.k.panesar@nasa.gov

We investigate the origin of 10 solar quiet-region pre-jet minifilaments , using EUV images from the Solar Dynamics Observatory ( SDO )/Atmospheric Imaging Assembly (AIA) and magnetograms from the SDO Helioseismic and Magnetic Imager (HMI). We recently found that quiet-region coronal jets are driven by minifilament eruptions, where those eruptions result from flux cancellation at the magnetic neutral line under the minifilament. Here, we study the longer-term origin of the pre-jet minifilaments themselves. We find that they result from flux cancellation between minority-polarity and majority-polarity flux patches. In each of 10 pre-jet regions, we find that opposite-polarity patches of magneticmore » flux converge and cancel, with a flux reduction of 10%–40% from before to after the minifilament appears. For our 10 events, the minifilaments exist for periods ranging from 1.5 hr to 2 days before erupting to make a jet. Apparently, the flux cancellation builds a highly sheared field that runs above and traces the neutral line, and the cool transition region plasma minifilament forms in this field and is suspended in it. We infer that the convergence of the opposite-polarity patches results in reconnection in the low corona that builds a magnetic arcade enveloping the minifilament in its core, and that the continuing flux cancellation at the neutral line finally destabilizes the minifilament field so that it erupts and drives the production of a coronal jet. Thus, our observations strongly support that quiet-region magnetic flux cancellation results in both the formation of the pre-jet minifilament and its jet-driving eruption.« less

Improving the twilight model for polar cap absorption nowcasts

NASA Astrophysics Data System (ADS)

Rogers, N. C.; Kero, A.; Honary, F.; Verronen, P. T.; Warrington, E. M.; Danskin, D. W.

2016-11-01

During solar proton events (SPE), energetic protons ionize the polar mesosphere causing HF radio wave attenuation, more strongly on the dayside where the effective recombination coefficient, αeff, is low. Polar cap absorption models predict the 30 MHz cosmic noise absorption, A, measured by riometers, based on real-time measurements of the integrated proton flux-energy spectrum, J. However, empirical models in common use cannot account for regional and day-to-day variations in the daytime and nighttime profiles of αeff(z) or the related sensitivity parameter, m=A>/&sqrt;J. Large prediction errors occur during twilight when m changes rapidly, and due to errors locating the rigidity cutoff latitude. Modeling the twilight change in m as a linear or Gauss error-function transition over a range of solar-zenith angles (χl < χ < χu) provides a better fit to measurements than selecting day or night αeff profiles based on the Earth-shadow height. Optimal model parameters were determined for several polar cap riometers for large SPEs in 1998-2005. The optimal χl parameter was found to be most variable, with smaller values (as low as 60°) postsunrise compared with presunset and with positive correlation between riometers over a wide area. Day and night values of m exhibited higher correlation for closely spaced riometers. A nowcast simulation is presented in which rigidity boundary latitude and twilight model parameters are optimized by assimilating age-weighted measurements from 25 riometers. The technique reduces model bias, and root-mean-square errors are reduced by up to 30% compared with a model employing no riometer data assimilation.

Field-calibrated model of melt, refreezing, and runoff for polar ice caps: Application to Devon Ice Cap

NASA Astrophysics Data System (ADS)

Morris, Richard M.; Mair, Douglas W. F.; Nienow, Peter W.; Bell, Christina; Burgess, David O.; Wright, Andrew P.

2014-09-01

Understanding the controls on the amount of surface meltwater that refreezes, rather than becoming runoff, over polar ice masses is necessary for modeling their surface mass balance and ultimately for predicting their future contributions to global sea level change. We present a modified version of a physically based model that includes an energy balance routine and explicit calculation of near-surface meltwater refreezing capacity, to simulate the evolution of near-surface density and temperature profiles across Devon Ice Cap in Arctic Canada. Uniquely, our model is initiated and calibrated using high spatial resolution measurements of snow and firn densities across almost the entire elevation range of the ice cap for the summer of 2004 and subsequently validated with the same type of measurements obtained during the very different meteorological conditions of summer 2006. The model captures the spatial variability across the transect in bulk snowpack properties although it slightly underestimates the flow of meltwater into the firn of previous years. The percentage of meltwater that becomes runoff is similar in both years; however, the spatial pattern of this melt-runoff relationship is different in the 2 years. The model is found to be insensitive to variation in the depth of impermeable layers within the firn but is very sensitive to variation in air temperature, since the refreezing capacity of firn decreases with increasing temperature. We highlight that the sensitivity of the ice cap's surface mass balance to air temperature is itself dependent on air temperature.

Perchlorate Found by Phoenix Could Provide a Mobile Brine Sludge at the Bed of Mars Northern Ice Cap that Would Allow Flow with Very Low Basal Temperatures: Possible Mechanism for Water Table Re-Charge

NASA Astrophysics Data System (ADS)

Fisher, D. A.; Hecht, M.; Kounaves, S.; Catling, D.

2009-03-01

The north cap of Mars has basal temperature that precludes the flow of ice. Phoenix discovered polar soils contain perchlorate salts. These salts depress the melting point so it could form a sludge that provides a mobile bed that moves the ice outwards.

Multi-instrument data analysis for interpretation of the Martian North polar layered deposits

NASA Astrophysics Data System (ADS)

Mirino, Melissa; Sefton-Nash, Elliot; Witasse, Olivier; Frigeri, Alessandro

2017-04-01

The Martian polar caps have engendered substantial study due to their spiral morphology, layered structure and the seasonal variability in thickness of the uppermost H2O and CO2 ice layers. We demonstrate a multi-instrument study of exposed and buried north polar layers using data from ESA's Mars Express (MEx) and NASA's Mars Reconnaissance Orbiter (MRO) missions. We perform analysis of high resolution images from MRO's HiRISE, which provide textural and morphological information about surface features larger than 0.3m, with NIR hyperspectral data from MRO CRISM, which allows study of surface mineralogy at a maximum resolution of 18 m/pixel. Stereo-derived topography is provided by MEx's HRSC. Together with these surficial observations we interpret radargrams from MRO SHARAD to obtain information about layered structures at a horizontal resolution between 0.3 and 3 kilometers and a free-space vertical resolution of 15 meters (vertical resolution depends on the dielectric properties of the medium). This combination of datasets allows us to attempt to correlate polar layering, made visible by dielectric interfaces between beds, with surface mineralogies and structures outcropping at specific stratigraphic levels. We analyse two opposite areas of the north polar cap with the intention to characterise in multiple datasets each geologic unit identified in the north polar cap's stratigraphy (mapped by e.g. [1]). We selected deposits observed in Chasma Boreale and Olympia Cavi because these areas allow us to observe and map strata at opposing sides of the north polar cap. Using the CRISM Analysis Tool and spectral summary parameters [2] we map the spectral characteristics of the two areas that show H2O and CO2 ice layering exposed on polar scarps. Through spatial-registration in a GIS with HRSC topography and HiRISE imagery we assess the mineralogical and morphological characteristics of exposed layers. In order to constrain the cross section between the two selected localities we choose SHARAD radargrams that most closely align with the transect between the sites. We interpret sub-horizontal features to be due to dielectric interfaces involving the deposits analysed. Our interpretation of radargrams in the context of compositional and structural constraints, from areas where pertinent beds outcrop, illustrates how joint analysis of surface and sub-surface data can benefit geological interpretation of planetary surfaces and subsurfaces. This technique applied to Mars' north polar layered deposits may offer additional constraint on morphology of internal layering resulting from seasonal deposition/sublimation cycles over varying obliquity [3]. References: [1] Tanaka et al. (2008), Icarus, 196, p. 318-358, doi:10.1016/j.icarus.2008.01.021. [2] Viviano-Beck et al. (2014), J. Geophys. Res. Planets, 119, p. 1403-1431, doi:10.1002/2014JE004627..[3] Putzig et al. (2009), Icarus, 204, p. 443-457, doi:10.1016/j.icarus.2009.07.034.

Polarity of the ascidian egg cortex and relocalization of cER and mRNAs in the early embryo.

PubMed

Prodon, François; Dru, Philippe; Roegiers, Fabrice; Sardet, Christian

2005-06-01

The mature ascidian oocyte is a large cell containing cytoplasmic and cortical domains polarized along a primary animal-vegetal (a-v) axis. The oocyte cortex is characterized by a gradient distribution of a submembrane monolayer of cortical rough endoplasmic reticulum (cER) and associated maternal postplasmic/PEM mRNAs (cER-mRNA domain). Between fertilization and first cleavage, this cER-mRNA domain is first concentrated vegetally and then relocated towards the posterior pole via microfilament-driven cortical contractions and spermaster-microtubule-driven translocations. The cER-mRNA domain further concentrates in a macroscopic cortical structure called the centrosome attracting body (CAB), which mediates a series of asymmetric divisions starting at the eight-cell stage. This results in the segregation of determinant mRNAs and their products in posterior cells of the embryo precursors of the muscle and germ line. Using two species of ascidians (Ciona intestinalis and Phallusia mammillata), we have pursued and amplified the work initiated in Halocynthia roretzi. We have analysed the cortical reorganizations in whole cells and in cortical fragments isolated from oocytes and from synchronously developing zygotes and embryos. After fertilization, we observe that a cortical patch rich in microfilaments encircles the cER-mRNA domain, concentrated into a cortical cap at the vegetal/contraction pole (indicating the future dorsal pole). Isolated cortices also retain microtubule asters rich in cER (indicating the future posterior pole). Before mitosis, parts of the cER-mRNA domain are detected, together with short microtubules, in isolated posterior (but not anterior) cortices. At the eight-cell stage, the posteriorly located cER-mRNA domain undergoes a cell-cycle-dependant compaction into the CAB. The CAB with embedded centrosomal microtubules can be isolated with cortical fragments from eight-cell-stage embryos. These and previous observations indicate that cytoskeleton-driven repositioning and compaction of a polarized cortical domain made of rough ER is a conserved mechanism used for polarization and segregation of cortical maternal mRNAs in embryos of evolutionarily distant species of ascidians.

Receptor clustering drives polarized assembly of ankyrin.

PubMed

Jefford, G; Dubreuil, R R

2000-09-08

Expression of the L1 family cell adhesion molecule neuroglian in Drosophila S2 cells leads to cell aggregation and polarized ankyrin accumulation at sites of cell-cell contact. Thus neuroglian adhesion generates a spatial cue for polarized assembly of ankyrin and the spectrin cytoskeleton. Here we characterized a chimera of the extracellular and transmembrane domains of rat CD2 fused to the cytoplasmic domain of neuroglian. The chimera was used to test the hypothesis that clustering of neuroglian at sites of adhesion generates the signal that activates ankyrin binding. Abundant expression of the chimera at the plasma membrane was not a sufficient cue to drive ankyrin assembly, since ankyrin remained diffusely distributed throughout the cytoplasm of CD2-neuroglian-expressing cells. However, ankyrin became highly enriched at sites of antibody-induced capping of CD2-neuroglian. Spectrin codistributed with ankyrin at capped sites. A green fluorescent protein-tagged ankyrin was used to monitor ankyrin distribution in living cells. Enhanced green fluorescent protein-ankyrin behaved identically to antibody-stained endogenous ankyrin, proving that the polarized accumulation of ankyrin was not an artifact of fixing and staining cells. We propose a model in which clustering of neuroglian induces a conformational change in the cytoplasmic domain that drives polarized assembly of the spectrin cytoskeleton.

The Boeing Delta II rocket with Mars Polar Lander aboard lifts off at Pad 17B, CCAS

NASA Technical Reports Server (NTRS)

1999-01-01

Amid clouds of exhaust, a Boeing Delta II expendable launch vehicle with NASA's Mars Polar Lander clears Launch Complex 17B, Cape Canaveral Air Station, after launch at 3:21:10 p.m. EST. The lander is a solar-powered spacecraft designed to touch down on the Martian surface near the northern-most boundary of the south polar cap, which consists of carbon dioxide ice. The lander will study the polar water cycle, frosts, water vapor, condensates and dust in the Martian atmosphere. It is equipped with a robotic arm to dig beneath the layered terrain at the polar cap. In addition, Deep Space 2 microprobes, developed by NASA's New Millennium Program, are installed on the lander's cruise stage. After crashing into the planet's surface, they will conduct two days of soil and water experiments up to 1 meter (3 feet) below the Martian surface, testing new technologies for future planetary descent probes. The lander is the second spacecraft to be launched in a pair of Mars Surveyor '98 missions. The first is the Mars Climate Orbiter, which was launched aboard a Delta II rocket from Launch Complex 17A on Dec. 11, 1998.

The Boeing Delta II rocket with Mars Polar Lander aboard lifts off at Pad 17B, CCAS

NASA Technical Reports Server (NTRS)

1999-01-01

Silhouetted against the gray sky, a Boeing Delta II expendable launch vehicle with NASA's Mars Polar Lander lifts off from Launch Complex 17B, Cape Canaveral Air Station, at 3:21:10 p.m. EST. The lander is a solar-powered spacecraft designed to touch down on the Martian surface near the northern-most boundary of the south polar cap, which consists of carbon dioxide ice. The lander will study the polar water cycle, frosts, water vapor, condensates and dust in the Martian atmosphere. It is equipped with a robotic arm to dig beneath the layered terrain at the polar cap. In addition, Deep Space 2 microprobes, developed by NASA's New Millennium Program, are installed on the lander's cruise stage. After crashing into the planet's surface, they will conduct two days of soil and water experiments up to 1 meter (3 feet) below the Martian surface, testing new technologies for future planetary descent probes. The lander is the second spacecraft to be launched in a pair of Mars Surveyor '98 missions. The first is the Mars Climate Orbiter, which was launched aboard a Delta II rocket from Launch Complex 17A on Dec. 11, 1998.

The Boeing Delta II rocket with Mars Polar Lander aboard lifts off at Pad 17B, CCAS

NASA Technical Reports Server (NTRS)

1999-01-01

Amid clouds of exhaust and into a gray-clouded sky , a Boeing Delta II expendable launch vehicle lifts off with NASA's Mars Polar Lander at 3:21:10 p.m. EST from Launch Complex 17B, Cape Canaveral Air Station. The lander is a solar-powered spacecraft designed to touch down on the Martian surface near the northern- most boundary of the south polar cap, which consists of carbon dioxide ice. The lander will study the polar water cycle, frosts, water vapor, condensates and dust in the Martian atmosphere. It is equipped with a robotic arm to dig beneath the layered terrain at the polar cap. In addition, Deep Space 2 microprobes, developed by NASA's New Millennium Program, are installed on the lander's cruise stage. After crashing into the planet's surface, they will conduct two days of soil and water experiments up to 1 meter (3 feet) below the Martian surface, testing new technologies for future planetary descent probes. The lander is the second spacecraft to be launched in a pair of Mars Surveyor '98 missions. The first is the Mars Climate Orbiter, which was launched aboard a Delta II rocket from Launch Complex 17A on Dec. 11, 1998.

The Boeing Delta II rocket with Mars Polar Lander aboard lifts off at Pad 17B, CCAS

NASA Technical Reports Server (NTRS)

1999-01-01

A Boeing Delta II expendable launch vehicle lifts off with NASA's Mars Polar Lander into a cloud-covered sky at 3:21:10 p.m. EST from Launch Complex 17B, Cape Canaveral Air Station. The lander is a solar-powered spacecraft designed to touch down on the Martian surface near the northern-most boundary of the south polar cap, which consists of carbon dioxide ice. The lander will study the polar water cycle, frosts, water vapor, condensates and dust in the Martian atmosphere. It is equipped with a robotic arm to dig beneath the layered terrain at the polar cap. In addition, Deep Space 2 microprobes, developed by NASA's New Millennium Program, are installed on the lander's cruise stage. After crashing into the planet's surface, they will conduct two days of soil and water experiments up to 1 meter (3 feet) below the Martian surface, testing new technologies for future planetary descent probes. The lander is the second spacecraft to be launched in a pair of Mars Surveyor '98missions. The first is the Mars Climate Orbiter, which was launched aboard a Delta II rocket from Launch Complex 17A on Dec. 11, 1998.

O+ trough zones in the polar cap ionosphere-magnetosphere coupling region

NASA Astrophysics Data System (ADS)

Horwitz, James; Zeng, Wen; Jaafari, Fajer

Regions of low-density troughs in O+ have been observed at 1 RE altitude in the polar cap ionosphere-magnetosphere region by the Thermal Ion Dynamics Experiment(TIDE) on the POLAR spacecraft. In this presentation, the UT Arlington Dynamic Fluid-Kinetic (DyFK) code is employed to investigate the formation of such O+ density troughs. We utilize convection paths of flux tubes in the high-latitude region as prescribed by an empirical convection model with solar wind inputs to track the evolution of ionospheric plasma transport and in particular O+ densities along these tubes with time/space. The flux tubes are subjected to auroral processes of precipitation and wave-driven ion heating when they pass through the auroral oval, which tends to elevate the plasma densities in these tubes. When the F-regions of such tubes traverse locations where the F-region is in darkness, recombination there causes the higher-altitude regions to drain and the densities to decline throughout. Owing to the varying effects of these processes, significant and low trough-like densities at higher altitudes developed along these flux tubes. The modeled densities near 6000 km altitudes will be compared with multiple POLAR passes featuring POLAR/TIDE-measured O+ densities for inside and outside of such trough regions.

Design And Simulation Of Microstrip Antenna Of 2.4 GHz Using CST

NASA Astrophysics Data System (ADS)

Thakur, O. P.; Kushwaha, Alok K.

2011-12-01

This article describes the design, fabrication and testing of micro strip patch antennas operating at 2.4 GHz. Consideration is given on practical design technique, including substrate selection and antenna measurements. It is emphasised to the radiation properties of the antennas—the radiation pattern and polarization purity. A micro strip patch antenna consists of a very thin metallic patch placed a small fraction of a wavelength above a conducting ground-plane. The patch and ground-plane are separated by a dielectric. The patch conductor is normally copper and can assume any shape, but simple geometries generally are used, and this simplifies the analysis and performance prediction. The patches are usually photo etched on the dielectric substrate. The substrate is usually non-magnetic. The relative permittivity of the substrate is normally in the region between 1 and 4, which enhances the fringing fields that account for radiation, but higher values may be used in special circumstances. Due to its simple geometry, the half wave rectangular patch is the most commonly used micro strip antenna. It is characterized by its length L, width w and thickness h. The simplest method of feeding the patch is by a coplanar micro strip line, also photo etched on the substrate. Coaxial feeds are also widely used.

Volcano-ice interactions on Mars

NASA Technical Reports Server (NTRS)

Allen, C. C.

1979-01-01

Central volcanic eruptions beneath terrestrial glaciers have built steep-sided, flat-topped mountains composed of pillow lava, glassy tuff, capping flows, and cones of basalt. Subglacial fissure eruptions produced ridges of similar composition. In some places the products from a number of subglacial vents have combined to form widespread deposits. The morphologies of these subglacial volcanoes are distinctive enough to allow their recognition at the resolutions characteristic of Viking orbiter imagery. Analogs to terrestrial subglacial volcanoes have been identified on the northern plains and near the south polar cap of Mars. The polar feature provides probable evidence of volcanic eruptions beneath polar ice. A mixed unit of rock and ice is postulated to have overlain portions of the northern plains, with eruptions into this ground ice having produced mountains and ridges analogous to those in Iceland. Subsequent breakdown of this unit due to ice melting revealed the volcanic features. Estimated heights of these landforms indicate that the ice-rich unit once ranged from approximately 100 to 1200 m thick.

The magnetospheric electric field and convective processes as diagnostics of the IMF and solar wind

NASA Technical Reports Server (NTRS)

Kaye, S. M.

1979-01-01

Indirect measurements of the convection field as well as direct of the ionospheric electric field provide a means to at least monitor quanitatively solar wind processes. For instance, asymmetries in the ionospheric electric field and ionospheric Hall currents over the polar cap reflect the solar wind sector polarity. A stronger electric field, and thus convective flow, is found on the side of the polar cap where the y component of the IMF is parallel to the y component of the geomagnetic field. Additionally, the magnitude of the electric field and convective southward B sub Z and/or solar wind velocity, and thus may indicate the arrival at Earth of an interaction region in the solar wind. It is apparent that processes associated with the convention electric field may be used to predict large scale features in the solar wind; however, with present empirical knowledge it is not possible to make quantitative predictions of individual solar wind or IMF parameters.

The melting sea ice of Arctic polar cap in the summer solstice month and the role of ocean

NASA Astrophysics Data System (ADS)

Lee, S.; Yi, Y.

2014-12-01

The Arctic sea ice is becoming smaller and thinner than climatological standard normal and more fragmented in the early summer. We investigated the widely changing Arctic sea ice using the daily sea ice concentration data. Sea ice data is generated from brightness temperature data derived from the sensors: Defense Meteorological Satellite Program (DMSP)-F13 Special Sensor Microwave/Imagers (SSM/Is), the DMSP-F17 Special Sensor Microwave Imager/Sounder (SSMIS) and the Advanced Microwave Scanning Radiometer - Earth Observing System (AMSR-E) instrument on the NASA Earth Observing System (EOS) Aqua satellite. We tried to figure out appearance of arctic sea ice melting region of polar cap from the data of passive microwave sensors. It is hard to explain polar sea ice melting only by atmosphere effects like surface air temperature or wind. Thus, our hypothesis explaining this phenomenon is that the heat from deep undersea in Arctic Ocean ridges and the hydrothermal vents might be contributing to the melting of Arctic sea ice.

Mariner 9 television reconnaissance of Mars and its satellites: Preliminary results

USGS Publications Warehouse

Masursky, H.; Batson, R.M.; McCauley, J.F.; Soderblom, L.A.; Wildey, R.L.; Carr, M.H.; Milton, D.J.; Wilhelms, D.E.; Smith, B.A.; Kirby, T.B.; Robinson, J.C.; Leovy, C.B.; Briggs, G.A.; Duxbury, T.C.; Acton, C.H.; Murray, B.C.; Cutts, J.A.; Sharp, R.P.; Smith, S.; Leighton, R.B.; Sagan, C.; Veverka, J.; Noland, M.; Lederberg, J.; Levinthal, E.; Pollack, James B.; Moore, J.T.; Hartmann, W.K.; Shipley, E.N.; De Vaucouleurs, G.; Davies, M.E.

1972-01-01

At orbit insertion on 14 November 1971 the Martian surface was largely obscured by a dust haze with an extinction optical depth that ranged from near unity in the south polar region to probably greater than 2 over most of the planet. The only features clearly visible were the south polar cap, one dark spot in Nix Olympica, and three dark spots in the Tharsis region. During the third week the atmosphere began to clear and surface visibility improved, but contrasts remained a fraction of their normal value. Each of the dark spots that apparently protrude through most of the dust-filled atmosphere has a crater or crater complex in its center. The craters are rimless and have featureless floors that, in the crater complexes, are at different levels. The largest crater within the southernmost spot is approximately 100 kilometers wide. The craters apparently were formed by subsidence and resemble terrestrial calderas. The south polar cap has a regular margin, suggsting very flat topography. Two craters outside the cap have frost on their floors; an apparent crater rim within the cap is frost free, indicating preferential loss of frost from elevated ground. If this is so then the curvilinear streaks, which were frost covered in 1969 and are now clear of frost, may be low-relief ridges. Closeup pictures of Phobos and Deimos show that Phobos is about 25 ?? 5 by 21 ?? 1 kilometers and Deimos is about 13.5 ?? 2 by 12.0 ?? 0.5 kilometers. Both have irregular shapes and are highly cratered, with some craters showing raised rims. The satellites are dark objects with geometric albedos of 0.05.

Mariner 9 television reconnaissance of Mars and its satellites: preliminary results.

PubMed

Masursky, H; Batson, R M; McCauley, J F; Soderblom, L A; Wildey, R L; Carr, M H; Milton, D J; Wilhelms, D E; Smith, B A; Kirby, T B; Robinson, J C; Leovy, C B; Briggs, G A; Duxbury, T C; Acton, C H; Murray, B C; Cutts, J A; Sharp, R P; Smith, S; Leighton, R B; Sagan, C; Veverka, J; Noland, M; Lederberg, J; Levinthal, E; Pollack, J B; Moore, J T; Hartmann, W K; Shipley, E N; De Vaucouleurs, G; Davies, M E

1972-01-21

At orbit insertion on 14 November 1971 the Martian surface was largely obscured by a dust haze with an extinction optical depth that ranged from near unity in the south polar region to probably greater than 2 over most of the planet. The only features clearly visible were the south polar cap, one dark, spot in Nix Olympica, and three dark spots in the Tharsis region. During the third week the atmosphere began to clear and surface visibility improved, but contrasts remained a fraction of their normal value. Each of the dark spots that apparently protrude through most of the dust-filled atmosphere has a crater or crater complex in its center. The craters are rimless and have featureless floors that, in the crater complexes, are at different levels. The largest crater within the southernmost spot is approximately 100 kilometers wide. The craters apparently were formed by subsidence and resemble terrestrial calderas. The south polar cap has a regular margin, suggsting very flat topography. Two craters outside the cap have frost on their floors; an apparent crater rim within the cap is frost free, indicating preferentia loss of frost from elevated ground. If this is so then the curvilinear streaks, which were frost covered in 1969 and are now clear of frost, may be low-relief ridges. Closeup pictures of Phobos and Deimos show that Phobos is about 25 +/-5 by 21 +/-1 kilometers and Deimos is about 13.5 +/- 2 by 12.0 +/-0.5 kilometers. Both have irregular shapes and are highly cratered, with some craters showing raised rims. The satellites are dark objects with geometric albedos of 0.05.

Intermediate scale plasma density irregularities in the polar ionosphere inferred from radio occultation

NASA Astrophysics Data System (ADS)

Shume, E. B.; Komjathy, A.; Langley, R. B.; Verkhoglyadova, O. P.; Butala, M.; Mannucci, A. J.

2014-12-01

In this research, we report intermediate scale plasma density irregularities in the high-latitude ionosphere inferred from high-resolution radio occultation (RO) measurements in the CASSIOPE (CAScade Smallsat and IOnospheric Polar Explorer) - GPS (Global Positioning System) satellites radio link. The high inclination of the CASSIOPE satellite and high rate of signal receptionby the occultation antenna of the GPS Attitude, Positioning and Profiling (GAP) instrument on the Enhanced Polar Outflow Probe platform on CASSIOPE enable a high temporal and spatial resolution investigation of the dynamics of the polar ionosphere, magnetosphere-ionospherecoupling, solar wind effects, etc. with unprecedented details compared to that possible in the past. We have carried out high spatial resolution analysis in altitude and geomagnetic latitude of scintillation-producing plasma density irregularities in the polar ionosphere. Intermediate scale, scintillation-producing plasma density irregularities, which corresponds to 2 to 40 km spatial scales were inferred by applying multi-scale spectral analysis on the RO phase delay measurements. Using our multi-scale spectral analysis approach and Polar Operational Environmental Satellites (POES) and Defense Meteorological Satellite Program (DMSP) observations, we infer that the irregularity scales and phase scintillations have distinct features in the auroral oval and polar cap regions. In specific terms, we found that large length scales and and more intense phase scintillations are prevalent in the auroral oval compared to the polar cap region. Hence, the irregularity scales and phase scintillation characteristics are a function of the solar wind and the magnetospheric forcing. Multi-scale analysis may become a powerful diagnostic tool for characterizing how the ionosphere is dynamically driven by these factors.

An Electrochemical Impedimetric Aptasensing Platform for Sensitive and Selective Detection of Small Molecules Such as Chloramphenicol

PubMed Central

Pilehvar, Sanaz; Dierckx, Tarryn; Blust, Ronny; Breugelmans, Tom; De Wael, Karolien

2014-01-01

We report on the aptadetection of chloramphenicol (CAP) using electrochemical impedance spectroscopy. The detection principle is based on the changes of the interfacial properties of the electrode after the interaction of the ssDNA aptamers with the target molecules. The electrode surface is partially blocked due to the formation of the aptamer-CAP complex, resulting in an increase of the interfacial electron-transfer resistance of the redox probe detected by electrochemical impedance spectroscopy or cyclic voltammetry. We observed that the ratio of polarization resistance had a linear relationship with the concentrations of CAP in the range of 1.76–127 nM, and a detection limit of 1.76 nM was obtained. The covalent binding of CAP-aptamer on the electrode surface combined with the unique properties of aptamers and impedimetric transduction leads to the development of a stable and sensitive electrochemical aptasensor for CAP. PMID:25004156

Chasma Boreale in the North Polar Region

NASA Technical Reports Server (NTRS)

2006-01-01

This images shows a Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) full-resolution 'targeted image' of the edge of Mars' north polar cap. The region in the image, Chasma Boreale, is a valley several kilometers or miles deep that cuts about 400 kilometers (about 250 miles) into the edge of the cap.

This image was acquired at 0851 UTC (4:51 a.m. EDT) on Oct. 1, 2006, near 84.6 degrees north latitude, 3.6 degrees east longitude. It covers an area about 13 kilometers (8 miles) long and, at the narrowest point, about 9 kilometers (5.6 miles) wide. At the center of the image the spatial resolution is as good as 18 meters (60 feet) per pixel. The image was taken in 544 colors covering wavelengths of 0.36 to 3.92 micrometers. Two renderings of the data are shown here, both draped over topography without vertical exaggeration, and then viewed from a perspective diagonally above the site. The top view is an approximately true-color representation. The bottom view, constructed from infrared wavelengths, shows strength of the spectral signature of ice. Brighter areas are rich in ice, and dark areas have little ice.

The polar cap has long been recognized to contain layers composed of dust and ice, and hence has been named the polar layered deposit. This sits atop an underlying 'basal unit.' The upper part of the basal unit is dark at visible wavelengths and steeply sloped, whereas the lower part of the basal unit is brighter, redder, and layered like the polar layered deposits. The chasma floor is cratered, and in the foreground it is covered by dunes that are outliers of a north polar sand sea that surrounds the polar cap. The polar layered deposits and the basal unit form a steeply sloping scarp about 1.1 kilometers (0.7 miles) high.

CRISM's image of this region shows a number of previously unrecognized characteristics of the polar layered deposits and the basal unit. First, the ice-rich polar layered deposits exhibit coherent banding both at visible and infrared wavelengths. This banding shows a history of differences in the abundance of dust that accumulated in polar ice, differences in ice grain size, or both. Second, both parts of the basal unit are depleted in ice, except for triangle-shaped regions on the side of the scarp. Third, the spectral properties of the brighter, layered lower basal unit resemble those of the polar layered deposits. In contrast, the upper basal unit is distinct from both of them. Finally, spectral properties of the foreground dunes closely resemble those of the darkest layers within the upper basal unit, and may be debris from it.

CRISM is one of six science instruments on NASA's Mars Reconnaissance Orbiter. Led by The Johns Hopkins University Applied Physics Laboratory, the CRISM team includes expertise from universities, government agencies and small businesses in the United States and abroad.

CRISM's mission: Find the spectral fingerprints of aqueous and hydrothermal deposits and map the geology, composition and stratigraphy of surface features. The instrument will also watch the seasonal variations in Martian dust and ice aerosols, and water content in surface materials -- leading to new understanding of the climate.

NASA's Jet Propulsion Laboratory, a division of the California Institute of Technology, Pasadena, manages the Mars Reconnaissance Orbiter mission for the NASA Science Mission Directorate. Lockheed Martin Space Systems, Denver, is the prime contractor and built the spacecraft.

Solar cycle variations in polar cap area measured by the superDARN radars

NASA Astrophysics Data System (ADS)

Imber, S. M.; Milan, S. E.; Lester, M.

2013-10-01

present a long-term study, from January 1996 to August 2012, of the latitude of the Heppner-Maynard Boundary (HMB) measured at midnight using the northern hemisphere Super Dual Auroral Radar Network (SuperDARN). The HMB represents the equatorward extent of ionospheric convection and is used in this study as a measure of the global magnetospheric dynamics. We find that the yearly distribution of HMB latitudes is single peaked at 64° magnetic latitude for the majority of the 17 year interval. During 2003, the envelope of the distribution shifts to lower latitudes and a second peak in the distribution is observed at 61°. The solar wind-magnetosphere coupling function derived by Milan et al. (2012) suggests that the solar wind driving during this year was significantly higher than during the rest of the 17 year interval. In contrast, during the period 2008-2011, HMB distribution shifts to higher latitudes, and a second peak in the distribution is again observed, this time at 68° magnetic latitude. This time interval corresponds to a period of extremely low solar wind driving during the recent extreme solar minimum. This is the first long-term study of the polar cap area and the results demonstrate that there is a close relationship between the solar activity cycle and the area of the polar cap on a large-scale, statistical basis.

Solar Cycle Variations in Polar Cap Area Measured by the SuperDARN Radars

NASA Astrophysics Data System (ADS)

Imber, S. M.; Milan, S. E.; Lester, M.

2013-12-01

We present a long term study, from January 1996 - August 2012, of the latitude of the Heppner-Maynard Boundary (HMB) measured at midnight using the northern hemisphere SuperDARN radars. The HMB represents the equatorward extent of ionospheric convection, and is used in this study as a measure of the global magnetospheric dynamics and activity. We find that the yearly distribution of HMB latitudes is single-peaked at 64° magnetic latitude for the majority of the 17-year interval. During 2003 the envelope of the distribution shifts to lower latitudes and a second peak in the distribution is observed at 61°. The solar wind-magnetosphere coupling function derived by Milan et al. (2012) suggests that the solar wind driving during this year was significantly higher than during the rest of the 17-year interval. In contrast, during the period 2008-2011 HMB distribution shifts to higher latitudes, and a second peak in the distribution is again observed, this time at 68° magnetic latitude. This time interval corresponds to a period of extremely low solar wind driving during the recent extreme solar minimum. This is the first statistical study of the polar cap area over an entire solar cycle, and the results demonstrate that there is a close relationship between the phase of the solar cycle and the area of the polar cap on a large scale statistical basis.

Gravity Waves Near 300 km Over the Polar Caps

NASA Technical Reports Server (NTRS)

Johnson, F. S.; Hanson, W. B.; Hodges, R. R.; Coley, W. R.; Carignan, G. R.; Spencer, N. W.

1995-01-01

Distinctive wave forms in the distributions of vertical velocity and temperature of both neutral particles and ions are frequently observed from Dynamics Explorer 2 at altitudes above 250 km over the polar caps. These are interpreted as being due to internal gravity waves propagating in the neutral atmosphere. The disturbances characterized by vertical velocity perturbations of the order of 100 m/s and horizontal wave lengths along the satellite path of about 500 km. They often extend across the entire polar cap. The associated temperature perturbations indicate that the horizontal phase progression is from the nightside to the dayside. Vertical displacements are inferred to be of the order of 10 km and the periods to be of the order of 10(exp 3) s. The waves must propagate in the neutral atmosphere, but they usually are most clearly recognizable in the observations of ion vertical velocity and ion temperature. By combining the neutral pressure calculated from the observed neutral concentration and temperature with the vertical component of the neutral velocity, an upward energy flux of the order of 0.04 erg/sq cm-s at 250 km has been calculated, which is about equal to the maximum total solar ultraviolet heat input above that altitude. Upward energy fluxes calculated from observations on orbital passes at altitudes from 250 to 560 km indicate relatively little attenuation with altitude.

Polarization optics of the Brewster's dark patch visible on water surfaces versus solar height and sky conditions: theory, computer modeling, photography, and painting.

PubMed

Takács, Péter; Barta, András; Pye, David; Horváth, Gábor

2017-10-20

When the sun is near the horizon, a circular band with approximately vertically polarized skylight is formed at 90° from the sun, and this skylight is only weakly reflected from the region of the water surface around the Brewster's angle (53° from the nadir). Thus, at low solar heights under a clear sky, an extended dark patch is visible on the water surface when one looks toward the north or south quarter perpendicular to the solar vertical. In this work, we study the radiance distribution of this so-called Brewster's dark patch (BDP) in still water as functions of the solar height and sky conditions. We calculate the pattern of reflectivity R of a water surface for a clear sky and obtain from this idealized situation the shape of the BDP. From three full-sky polarimetric pictures taken about a clear, a partly cloudy, and an overcast sky, we determine the R pattern and compose from that synthetic color pictures showing how the radiance distribution of skylight reflected at the water surface and the BDPs would look under these sky conditions. We also present photographs taken without a linearly polarizing filter about the BDP. Finally, we show a 19th century painting on which a river is seen with a dark region of the water surface, which can be interpreted as an artistic illustration of the BDP.

The Water-Wheel IR (WIR): A Contact Survey Experiment for Water and Carbonates on Mars

NASA Technical Reports Server (NTRS)

Wang, Alian; Haskin, Larry A.; Freeman, John; Dong, Edward X.; Kuebler, Karla E.

2004-01-01

Minimum requirements for life include water and accessible carbon. Mars has both in its polar caps and atmosphere. Water (or water-equivalent hydrogen) is present at shallow depths (approx. 10-20 cm) at latitudes =60 and is heterogeneously distributed in other parts of Mars [1]. Mars may have once had surface water that could plausibly have produced carbonate deposits [2-5]. Mars shows signs of hydrothermal activity [6-8] that may have affected soil composition [9, 10]. The Thermal Emission Spectrometer on the Mars Global Surveyor found large and small patches of hematite that may have been water-borne or water-derived [11, 12]. Current orbiting spacecraft (MGS & Odyssey) have not found massive carbonate deposits, however [13]. Shales and limestones, which we associate with moist and benign environments on Earth, are apparently not abundant on Mars. Both carbonate and organic carbon occur as alteration products in Martian meteorites of igneous origin [14]. One study of MGS-TES data suggests 2-5 wt% carbonates (mainly MgCO3) in surface dust, but found no concentrated source [15]. Carbonates and H2O/OH bearing minerals will be sought by the mini-TES and Mossbauer experiments on the Mars Exploration Rovers, one of which landed successfully on Mars on January 3.

Empirical Orthogonal Function (EOF) Analysis of Storm-Time GPS Total Electron Content Variations

NASA Astrophysics Data System (ADS)

Thomas, E. G.; Coster, A. J.; Zhang, S.; McGranaghan, R. M.; Shepherd, S. G.; Baker, J. B.; Ruohoniemi, J. M.

2016-12-01

Large perturbations in ionospheric density are known to occur during geomagnetic storms triggered by dynamic structures in the solar wind. These ionospheric storm effects have long attracted interest due to their impact on the propagation characteristics of radio wave communications. Over the last two decades, maps of vertically-integrated total electron content (TEC) based on data collected by worldwide networks of Global Positioning System (GPS) receivers have dramatically improved our ability to monitor the spatiotemporal dynamics of prominent storm-time features such as polar cap patches and storm enhanced density (SED) plumes. In this study, we use an empirical orthogonal function (EOF) decomposition technique to identify the primary modes of spatial and temporal variability in the storm-time GPS TEC response at midlatitudes over North America during more than 100 moderate geomagnetic storms from 2001-2013. We next examine the resulting time-varying principal components and their correlation with various geophysical indices and parameters in order to derive an analytical representation. Finally, we use a truncated reconstruction of the EOF basis functions and parameterization of the principal components to produce an empirical representation of the geomagnetic storm-time response of GPS TEC for all magnetic local times local times and seasons at midlatitudes in the North American sector.

Polar Textures

NASA Image and Video Library

2016-10-04

This VIS image of the South Polar cap shows several different surface textures. It appears that the circular depressions (which look like swiss cheese) alter with time, appearing to lose the circular shape as the intervening walls of ice are removed. Orbit Number: 65187 Latitude: -87.0386 Longitude: 276.053 Instrument: VIS Captured: 2016-08-24 07:47 http://photojournal.jpl.nasa.gov/catalog/PIA21003

Role of the Cytoplasmic N-terminal Cap and Per-Arnt-Sim (PAS) Domain in Trafficking and Stabilization of Kv11.1 Channels*

PubMed Central

Ke, Ying; Hunter, Mark J.; Ng, Chai Ann; Perry, Matthew D.; Vandenberg, Jamie I.

2014-01-01

The N-terminal cytoplasmic region of the Kv11.1a potassium channel contains a Per-Arnt-Sim (PAS) domain that is essential for the unique slow deactivation gating kinetics of the channel. The PAS domain has also been implicated in the assembly and stabilization of the assembled tetrameric channel, with many clinical mutants in the PAS domain resulting in reduced stability of the domain and reduced trafficking. Here, we use quantitative Western blotting to show that the PAS domain is not required for normal channel trafficking nor for subunit-subunit interactions, and it is not necessary for stabilizing assembled channels. However, when the PAS domain is present, the N-Cap amphipathic helix must also be present for channels to traffic to the cell membrane. Serine scan mutagenesis of the N-Cap amphipathic helix identified Leu-15, Ile-18, and Ile-19 as residues critical for the stabilization of full-length proteins when the PAS domain is present. Furthermore, mutant cycle analysis experiments support recent crystallography studies, indicating that the hydrophobic face of the N-Cap amphipathic helix interacts with a surface-exposed hydrophobic patch on the core of the PAS domain to stabilize the structure of this critical gating domain. Our data demonstrate that the N-Cap amphipathic helix is critical for channel stability and trafficking. PMID:24695734

Spatial variability in the seasonal south polar CAP of Mars

NASA Astrophysics Data System (ADS)

Calvin, Wendy M.; Martin, Terry Z.

1994-10-01

The first comprehensive discussion of the south seasonal polar cap spectra obtained by the Mariner 7 infrared spectrometer in the short-wavelength region (2-4 microns) is presented. The infrared spectra is correlated with images acquired by the wide-angle camera. Significant spectral variation is noted in the cap interior and regions of varying water frost abundance, CO2 ice/frost cover, and CO2-ice path length can be distinguished. Many of these spectral variations correlate with heterogeneity noted in the camera images, but certain significant infrared spectral variations are not discernible in the visible. Simple reflectance models are used to classify the observed spectral variations into four regions. Region I is at the cap edge, where there is enhanced absorption beyond 3 microns inferred to be caused by an increased abundance of water frost. The increase in water abundance over that in the interior is on the level of a few parts per thousand or less. Region II is the typical cap interior characterized by spectral features of CO2 ice at grain sizes of several millimeters to centimeters. These spectra also indicate the presence of water frost at the parts per thousand level. A third, unusual region (III), is defined by three spectra in which weak CO2 absorption features are as much as twice as strong as in the average cap spectra and are assumed to be caused by an increased path length in the CO2. Such large paths are inconsistent with the high reflectance in the visible and at 2.2 microns and suggest layered structures or deposition conditions that are not accounted for in current reflectance models. The final region (IV) is an area of thinning frost coverage or transparent ice well in the interior of the seasonal cap. These spectra are a combination of CO2 and ground signatures.

Spatial variability in the seasonal south polar cap of Mars

NASA Technical Reports Server (NTRS)

Calvin, Wendy M.; Martin, Terry Z.

1994-01-01

The first comprehensive discussion of the south seasonal polar cap spectra obtained by the Mariner 7 infrared spectrometer in the short-wavelength region (2-4 microns) is presented. The infrared spectra is correlated with images acquired by the wide-angle camera. Significant spectral variation is noted in the cap interior and regions of varying water frost abundance, CO2 ice/frost cover, and CO2-ice path length can be distinguished. Many of these spectral variations correlate with heterogeneity noted in the camera images, but certain significant infrared spectral variations are not discernible in the visible. Simple reflectance models are used to classify the observed spectral variations into four regions. Region I is at the cap edge, where there is enhanced absorption beyond 3 microns inferred to be caused by an increased abundance of water frost. The increase in water abundance over that in the interior is on the level of a few parts per thousand or less. Region II is the typical cap interior characterized by spectral features of CO2 ice at grain sizes of several millimeters to centimeters. These spectra also indicate the presence of water frost at the parts per thousand level. A third, unusual region (III), is defined by three spectra in which weak CO2 absorption features are as much as twice as strong as in the average cap spectra and are assumed to be caused by an increased path length in the CO2. Such large paths are inconsistent with the high reflectance in the visible and at 2.2 microns and suggest layered structures or deposition conditions that are not accounted for in current reflectance models. The final region (IV) is an area of thinning frost coverage or transparent ice well in the interior of the seasonal cap. These spectra are a combination of CO2 and ground signatures.

Early climate on earth-reduced gas models and early climate on Mars-reduced gas and obliquity models

NASA Technical Reports Server (NTRS)

Toon, O. B.; Sagan, C.

1978-01-01

At high obliquity, Martian polar ground temperatures could exceed the melting point of ice for considerable periods of time (approximately 90 Earth days). Under special conditions ice itself might melt. Carbon dioxide adsorbed on the Martian regolith is not expected to buffer the seasonal pressure wave except in the unlikely event that the soil pore size is very large (50 micron). For a basaltic soil composition the maximum CO2 that could be desorbed over obliquity time scales due to thermal forces is a few millibars. At low obliquities the atmospheric pressures may drop, desorbing the soil. The only means to achieve higher CO2 pressures is to have much higher planet-wide temperatures due to some greenhouse effect, or to be at an epoch before the regolith or carbonates formed. The water ice budget between north and south polar caps was considered and summer sublimation rates imply that the ice could be exchanged between the poles during obliquity cycles. A critical factor in the polar cap water budget is the interaction of water and dust. The origin of the Martian polar laminae is probably due to variations in this interaction.

KSC-99pc05

NASA Image and Video Library

1999-01-03

KENNEDY SPACE CENTER, FLA. -- Amid clouds of exhaust, a Boeing Delta II expendable launch vehicle with NASA's Mars Polar Lander clears Launch Complex 17B, Cape Canaveral Air Station, after launch at 3:21:10 p.m. EST. The lander is a solar-powered spacecraft designed to touch down on the Martian surface near the northern-most boundary of the south polar cap, which consists of carbon dioxide ice. The lander will study the polar water cycle, frosts, water vapor, condensates and dust in the Martian atmosphere. It is equipped with a robotic arm to dig beneath the layered terrain at the polar cap. In addition, Deep Space 2 microprobes, developed by NASA's New Millennium Program, are installed on the lander's cruise stage. After crashing into the planet's surface, they will conduct two days of soil and water experiments up to 1 meter (3 feet) below the Martian surface, testing new technologies for future planetary descent probes. The lander is the second spacecraft to be launched in a pair of Mars Surveyor '98 missions. The first is the Mars Climate Orbiter, which was launched aboard a Delta II rocket from Launch Complex 17A on Dec. 11, 1998.

KSC-99pc04

NASA Image and Video Library

1999-01-03

KENNEDY SPACE CENTER, FLA. -- Amid clouds of exhaust and into a gray-clouded sky , a Boeing Delta II expendable launch vehicle lifts off with NASA's Mars Polar Lander at 3:21:10 p.m. EST from Launch Complex 17B, Cape Canaveral Air Station. The lander is a solar-powered spacecraft designed to touch down on the Martian surface near the northern-most boundary of the south polar cap, which consists of carbon dioxide ice. The lander will study the polar water cycle, frosts, water vapor, condensates and dust in the Martian atmosphere. It is equipped with a robotic arm to dig beneath the layered terrain at the polar cap. In addition, Deep Space 2 microprobes, developed by NASA's New Millennium Program, are installed on the lander's cruise stage. After crashing into the planet's surface, they will conduct two days of soil and water experiments up to 1 meter (3 feet) below the Martian surface, testing new technologies for future planetary descent probes. The lander is the second spacecraft to be launched in a pair of Mars Surveyor '98 missions. The first is the Mars Climate Orbiter, which was launched aboard a Delta II rocket from Launch Complex 17A on Dec. 11, 1998.

KSC-99pc06

NASA Image and Video Library

1999-01-03

KENNEDY SPACE CENTER, FLA. -- Silhouetted against the gray sky, a Boeing Delta II expendable launch vehicle with NASA's Mars Polar Lander lifts off from Launch Complex 17B, Cape Canaveral Air Station, at 3:21:10 p.m. EST. The lander is a solar-powered spacecraft designed to touch down on the Martian surface near the northern-most boundary of the south polar cap, which consists of carbon dioxide ice. The lander will study the polar water cycle, frosts, water vapor, condensates and dust in the Martian atmosphere. It is equipped with a robotic arm to dig beneath the layered terrain at the polar cap. In addition, Deep Space 2 microprobes, developed by NASA's New Millennium Program, are installed on the lander's cruise stage. After crashing into the planet's surface, they will conduct two days of soil and water experiments up to 1 meter (3 feet) below the Martian surface, testing new technologies for future planetary descent probes. The lander is the second spacecraft to be launched in a pair of Mars Surveyor '98 missions. The first is the Mars Climate Orbiter, which was launched aboard a Delta II rocket from Launch Complex 17A on Dec. 11, 1998.

KSC-99pc03

NASA Image and Video Library

1999-01-03

KENNEDY SPACE CENTER, FLA. -- A Boeing Delta II expendable launch vehicle lifts off with NASA's Mars Polar Lander into a cloud-covered sky at 3:21:10 p.m. EST from Launch Complex 17B, Cape Canaveral Air Station. The lander is a solar-powered spacecraft designed to touch down on the Martian surface near the northern-most boundary of the south polar cap, which consists of carbon dioxide ice. The lander will study the polar water cycle, frosts, water vapor, condensates and dust in the Martian atmosphere. It is equipped with a robotic arm to dig beneath the layered terrain at the polar cap. In addition, Deep Space 2 microprobes, developed by NASA's New Millennium Program, are installed on the lander's cruise stage. After crashing into the planet's surface, they will conduct two days of soil and water experiments up to 1 meter (3 feet) below the Martian surface, testing new technologies for future planetary descent probes. The lander is the second spacecraft to be launched in a pair of Mars Surveyor '98 missions. The first is the Mars Climate Orbiter, which was launched aboard a Delta II rocket from Launch Complex 17A on Dec. 11, 1998.

Early views of the martian surface from the Mars Orbiter Camera of Mars Global Surveyor.

PubMed

Malin, M C; Carr, M H; Danielson, G E; Davies, M E; Hartmann, W K; Ingersoll, A P; James, P B; Masursky, H; McEwen, A S; Soderblom, L A; Thomas, P; Veverka, J; Caplinger, M A; Ravine, M A; Soulanille, T A; Warren, J L

1998-03-13

High-resolution images of the martian surface at scales of a few meters show ubiquitous erosional and depositional eolian landforms. Dunes, sandsheets, and drifts are prevalent and exhibit a range of morphology, composition (inferred from albedo), and age (as seen in occurrences of different dune orientations at the same location). Steep walls of topographic depressions such as canyons, valleys, and impact craters show the martian crust to be stratified at scales of a few tens of meters. The south polar layered terrain and superposed permanent ice cap display diverse surface textures that may reflect the complex interplay of volatile and non-volatile components. Low resolution regional views of the planet provide synoptic observations of polar cap retreat, condensate clouds, and the lifecycle of local and regional dust storms.

Transport properties of nanocomposite and its simulation with L-R-C circuit

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gangopadhyay, Arnab, E-mail: agangulyphysics@gmail.com; Sarkar, Aditi, E-mail: agangulyphysics@gmail.com; Sarkar, A., E-mail: agangulyphysics@gmail.com

2014-04-24

The nano particles are represented in this communication by L-R-C equivalent circuit. The dc current voltage characteristics (CVC) of the proposed circuit have simulated using Circuit-Maker ® 2000. Experimental investigation on ZnO nano-composite with capping material gum acacia shows similar CVC. NPs are represented by C-R combinations to manifest the Coulomb blockade effect of a quantum dot. The capping material is represented by an inductor along with a resistance in series. Nine NPs with capping matrix are simulated. The dc current voltage characteristics (CVC) and gross feature of polarization nature obtained by experiment and simulation study are consistent.

A Plasma Trajectory Back-Tracing Tool Based on SuperDARN Convection Patterns

NASA Astrophysics Data System (ADS)

David, M.; Sojka, J. J.; Schunk, R. W.; Coster, A. J.; Sterne, K. T.

2017-12-01

Horizontal transport of plasma is one of the dominant factors in determining the distribution of plasma in the F-region ionosphere; this transport is driven by the magnetospheric convection electric field. When studying any electron density feature in the polar cap ionosphere, such as a density patch, TID, or tongue of ionization (TOI), one needs to know where that feature came from; was it generated by local production processes where it lies, or was it transported from another location? The path traveled by a plasma flux tube or plasma packet, which we call a trajectory, is determined by the time-varying convection electric field, and to whatever extent this electric field is known, one can back-trace the history of the plasma density feature in order to answer key questions about it, such as: Was this plasma exposed to sunlight in recent hours? Has this plasma packet passed through the auroral precipitation oval? Did it pass through the cusp? And since movement of a plasma flux tube toward the pole may cause upward ion drifts that result in density increases it is important to know whether the recent history of the density feature includes such convection toward (or away from) the pole.SuperDARN [Super Dual Auroral Radar Network] contains a data base of convection electric field patterns derived from ground station observations and the use of models to fill in gaps in the data. At Utah State University we have developed a software tool based on the SuperDARN convection patterns (which come at a time cadence of 2 minutes) to allow one to back-trace the history of polar cap plasma for an arbitrary length of time.The figure below shows a series of GPS TEC maps of the Northern Hemisphere in magnetic coordinates for 06 March 2016 in which a TOI feature forms at about 1700 UT. A series of locations, marked with X, are chosen such that they lie within the TOI at the time of the last panel (1730 UT); then, the plasma trajectory paths for these 15 locations are traced backward in time for 5 hours, and their locations are plotted on the TEC maps for universal times of 1230, 1330, 1430, 1530, and 1630.

Number and density discrimination rely on a common metric: Similar psychophysical effects of size, contrast, and divided attention.

PubMed

Tibber, Marc S; Greenwood, John A; Dakin, Steven C

2012-06-04

While observers are adept at judging the density of elements (e.g., in a random-dot image), it has recently been proposed that they also have an independent visual sense of number. To test the independence of number and density discrimination, we examined the effects of manipulating stimulus structure (patch size, element size, contrast, and contrast-polarity) and available attentional resources on both judgments. Five observers made a series of two-alternative, forced-choice discriminations based on the relative numerosity/density of two simultaneously presented patches containing 16-1,024 Gaussian blobs. Mismatches of patch size and element size (across reference and test) led to bias and reduced sensitivity in both tasks, whereas manipulations of contrast and contrast-polarity had varied effects on observers, implying differing strategies. Nonetheless, the effects reported were consistent across density and number judgments, the only exception being when luminance cues were made available. Finally, density and number judgment were similarly impaired by attentional load in a dual-task experiment. These results are consistent with a common underlying metric to density and number judgments, with the caveat that additional cues may be exploited when they are available.

Outer Dregs

NASA Image and Video Library

2006-05-15

This Mars MOC image shows the very edge of the south polar residual cap of Mars. The bright areas, which appear somewhat like pieces of sliced Swiss cheese, are composed mainly of frozen carbon dioxide

Hyperboreus Labyrinthus

NASA Image and Video Library

2012-08-22

The dissected appearing surface in this image captured by NASA Mars Odyssey spacecraft is called Hyperboreus Labyrinthus, located just south of the north polar cap. The linear depressions are most likely caused by tectonic stress.

Self-sustaining Mars colonies utilizing the North Polar Cap and the Martian atmosphere.

PubMed

Powell, J; Maise, G; Paniagua, J

2001-01-01

A revolutionary new concept for the early establishment of robust, self-sustaining Martian colonies is described. The colonies would be located on the North Polar Cap of Mars and utilize readily available water ice and the CO2 Martian atmosphere as raw materials to produce all of the propellants, fuel, air, water, plastics, food, and other supplies needed by the colony. The colonists would live in thermally insulated large, comfortable habitats under the ice surface, fully shielded from cosmic rays. The habitats and supplies would be produced by a compact, lightweight (~4 metric tons) nuclear powered robotic unit termed ALPH (Atomic Liberation of Propellant and Habitat), which would land 2 years before the colonists arrived. Using a compact, lightweight 5 MW (th) nuclear reactor/steam turbine (1 MW(e)) power source and small process units (e.g., H2O electrolyzer, H2 and O2 liquefiers, methanator, plastic polymerizer, food producer, etc.) ALPH would stockpile many hundreds of tons of supplies in melt cavities under the ice, plus insulated habitats, to be in place and ready for use when the colonists landed. With the stockpiled supplies, the colonists would construct and operate rovers and flyers to explore the surface of Mars. ALPH greatly reduces the amount of Earth supplied material needed and enables large permanent colonies on Mars. It also greatly reduces human and mission risks and vastly increases the capability not only for exploration of the surrounding Martian surface, but also the ice cap itself. The North Polar Cap is at the center of the vast ancient ocean that covered much of the Martian Northern Hemisphere. Small, nuclear heated robotic probes would travel deep (1 km or more) inside the ice cap, collecting data on its internal structure, the composition and properties of the ancient Martian atmosphere, and possible evidence of ancient life forms (microfossils, traces of DNA, etc.) that were deposited either by wind or as remnants of the ancient ocean. Details of the ALPH system, which is based on existing technology, are presented. ALPH units could be developed and demonstrated on Earth ice sheets within a few years. An Earth-Mars space transport architecture is described, in which Mars produced propellant and supplies for return journeys to Earth would be lifted with relatively low DeltaV to Mars orbit, and from there transported back to Earth orbit, enabling faster and lower cost trips from Earth to Mars. The exploration capability and quality of life in a mature Martian colony of 500 persons located on the North Polar Cap is outlined. c2001 International Astronautical Federation. Published by Elsevier Science Ltd.

The Polar Regions and Martian Climate: Studies with a Global Climate Model

NASA Technical Reports Server (NTRS)

Wilson, R. J.; Richardson, M. I.; Smith, M. D.

2003-01-01

Much of the interest in the polar regions centers on the fact that they likely contain the best record of Martian climate change on time scales from years to eons. This expectation is based upon the observed occurrence of weathering product deposits and volatile reservoirs that are coupled to the climate. Interpretation and understanding of these records requires understanding of the mechanisms that involve the exchange of dust, water, and carbon dioxide between the surface and atmosphere, and the atmospheric redistribution of these species. We will summarize our use of the GFDL Mars general circulation model (MGCM), to exploration aspects of the interaction between the global climate and the polar regions. For example, our studies have shown that while the northern polar cap is the dominant seasonal source for water, it can act as a net annual source or sink for water, depending upon the cap temperatures and the bulk humidity of the atmosphere. This behavior regulates the annual and global average humidity of the atmosphere, as the cap acts as a sink if the atmosphere is too wet and a source if it is too dry. We will then focus our presentation on the ability of the MGCM to simulate the observed diurnal variations of surface temperature. We are particularly interested in assessing the influence of dust aerosol and water ice clouds on simulated surface temperature and the comparison with observations. Surface thermal inertia and albedo are critical boundary inputs for MGCM simulations. Thermal inertia is also of intrinsic interest as it may be related to properties of the surface such as particle size and surface character.

Polarization-Engineered Ga-Face GaN-Based Heterostructures for Normally-Off Heterostructure Field-Effect Transistors

NASA Astrophysics Data System (ADS)

Kim, Hyeongnam; Nath, Digbijoy; Rajan, Siddharth; Lu, Wu

2013-01-01

Polarization-engineered Ga-face GaN-based heterostructures with a GaN cap layer and an AlGaN/ p-GaN back barrier have been designed for normally-off field-effect transistors (FETs). The simulation results show that an unintentionally doped GaN cap and p-GaN layer in the buffer primarily deplete electrons in the channel and the Al0.2Ga0.8N back barrier helps to pinch off the channel. Experimentally, we have demonstrated a normally-off GaN-based field-effect transistor on the designed GaN cap/Al0.3Ga0.7N/GaN channel/Al0.2Ga0.8N/ p-GaN/GaN heterostructure. A positive threshold voltage of 0.2 V and maximum transconductance of 2.6 mS/mm were achieved for 80- μm-long gate devices. The device fabrication process does not require a dry etching process for gate recessing, while highly selective etching of the GaN cap against a very thin Al0.3GaN0.7N top barrier has to be performed to create a two-dimensional electron gas for both the ohmic and access regions. A self-aligned, selective etch of the GaN cap in the access region is introduced, using the gate metal as an etch mask. The absence of gate recess etching is promising for uniform and repeatable threshold voltage control in normally-off AlGaN/GaN heterostructure FETs for power switching applications.

Characterization of Mars' seasonal caps using neutron spectroscopy

USGS Publications Warehouse

Prettyman, T.H.; Feldman, W.C.; Titus, T.N.

2009-01-01

Mars' seasonal caps are characterized during Mars years 26 and 27 (April 2002 to January 2006) using data acquired by the 2001 Mars Odyssey Neutron Spectrometer. Time-dependent maps of the column abundance of seasonal CO 2 surface ice poleward of 60?? latitude in both hemispheres are determined from spatially deconvolved, epithermal neutron counting data. Sources of systematic error are analyzed, including spatial blurring by the spectrometer's broad footprint and the seasonal variations in the abundance of noncondensable gas at high southern latitudes, which are found to be consistent with results reported by Sprague et al. (2004, 2007). Corrections for spatial blurring are found to be important during the recession, when the column abundance of seasonal CO2 ice has the largest latitude gradient. The measured distribution and inventory of seasonal CO2 ice is compared to simulations by a general circulation model (GCM) calibrated using Viking lander pressure data, cap edge functions determined by thermal emission spectroscopy, and other nuclear spectroscopy data sets. On the basis of the amount of CO2 cycled through the caps during years 26 and 27, the gross polar energy balance has not changed significantly since Viking. The distribution of seasonal CO2 ice is longitudinally asymmetric: in the north, deposition rates of CO2 ice are elevated in Acidalia, which is exposed to katabatic winds from Chasma Borealis; in the south, CO2 deposition is highest near the residual cap. During southern recession, CO 2 ice is present longer than calculated by the GCM, which has implications for the local polar energy balance. Copyright 2009 by the American Geophysical Union.

Mass balance of Mars' residual south polar cap from CTX images and other data

NASA Astrophysics Data System (ADS)

Thomas, P. C.; Calvin, W.; Cantor, B.; Haberle, R.; James, P. B.; Lee, S. W.

2016-04-01

Erosion of pits in the residual south polar cap (RSPC) of Mars concurrent with deposition and fluctuating cap boundaries raises questions about the mass balance and long term stability of the cap. Determining a mass balance by measurement of a net gain or loss of atmospheric CO2 by direct pressure measurements (Haberle, R.M. et al. [2014]. Secular climate change on Mars: An update using one Mars year of MSL pressure data. American Geophysical Union (Fall). Abstract 3947), although perhaps the most direct method, has so far given ambiguous results. Estimating volume changes from imaging data faces challenges, and has previously been attempted only in isolated areas of the cap. In this study we use 6 m/pixel Context Imager (CTX) data from Mars year 31 to map all the morphologic units of the RSPC, expand the measurement record of pit erosion rates, and use high resolution images to place limits on vertical changes in the surface of the residual cap. We find the mass balance in Mars years 9-31 to be -6 to +4 km3/♂y, or roughly -0.039% to +0.026% of the mean atmospheric CO2 mass/♂y. The indeterminate sign results chiefly from uncertainty in the amounts of deposition or erosion on the upper surfaces of deposits (as opposed to scarp retreat). Erosion and net deposition in this period appear to be controlled by summertime planetary scale dust events, the largest occurring in MY 9, another, smaller one in MY 28. The rates of erosion and the deposition observed since MY 9 appear to be consistent with the types of deposits and erosional behavior found in most of the residual cap. However, small areas (<10%) of the cap are distinguished by their greater thickness, polygonal troughs, and embayed contacts with thinner units. These deposits may require extended periods (>100 ♂y) of depositional and/or erosional conditions different from those occurring in the period since MY 9, although these environmental differences could be subtle.

Atmospheric precursors of and response to anomalous Arctic sea ice in CMIP5 models

NASA Astrophysics Data System (ADS)

Kelleher, Michael; Screen, James

2018-01-01

This study examines pre-industrial control simulations from CMIP5 climate models in an effort to better understand the complex relationships between Arctic sea ice and the stratosphere, and between Arctic sea ice and cold winter temperatures over Eurasia. We present normalized regressions of Arctic sea-ice area against several atmospheric variables at extended lead and lag times. Statistically significant regressions are found at leads and lags, suggesting both atmospheric precursors of, and responses to, low sea ice; but generally, the regressions are stronger when the atmosphere leads sea ice, including a weaker polar stratospheric vortex indicated by positive polar cap height anomalies. Significant positive midlatitude eddy heat flux anomalies are also found to precede low sea ice. We argue that low sea ice and raised polar cap height are both a response to this enhanced midlatitude eddy heat flux. The so-called "warm Arctic, cold continents" anomaly pattern is present one to two months before low sea ice, but is absent in the months following low sea ice, suggesting that the Eurasian cooling and low sea ice are driven by similar processes. Lastly, our results suggest a dependence on the geographic region of low sea ice, with low Barents-Kara Sea ice correlated with a weakened polar stratospheric vortex, whilst low Sea of Okhotsk ice is correlated with a strengthened polar vortex. Overall, the results support a notion that the sea ice, polar stratospheric vortex and Eurasian surface temperatures collectively respond to large-scale changes in tropospheric circulation.

CO2 Hourglass

NASA Image and Video Library

2006-04-24

This Mars MOC image shows a portion of the south polar residual cap of Mars. The bright, relatively homogeneous-appearing material extending from top north to bottom south is mainly composed of solid carbon dioxide

Clouds

NASA Image and Video Library

2010-09-14

Clouds are common near the north polar caps throughout the spring and summer. The clouds typically cause a haze over the extensive dune fields. This image from NASA Mars Odyssey shows the edge of the cloud front.

Mars Secular Obliquity Change Due to Water Ice Caps

NASA Technical Reports Server (NTRS)

Rubincam, David P.

1998-01-01

Mars may have substantially changed its average axial tilt over geologic time due to the waxing and waning of water ice caps. Depending upon Mars' climate and internal structure, the average obliquity could have increased or decreased through climate friction by tens of degrees. A decrease could account for the apparent youthfulness of the polar layered terrain. Alternatively, Mars' average obliquity may have changed until it became "stuck" at its present value of 24.4 deg.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rose, Brian E. J.; Cronin, Timothy W.; Bitz, Cecilia M., E-mail: brose@albany.edu

Planetary obliquity determines the meridional distribution of the annual mean insolation. For obliquity exceeding 55°, the weakest insolation occurs at the equator. Stable partial snow and ice cover on such a planet would be in the form of a belt about the equator rather than polar caps. An analytical model of planetary climate is used to investigate the stability of ice caps and ice belts over the widest possible range of parameters. The model is a non-dimensional diffusive Energy Balance Model, representing insolation, heat transport, and ice−albedo feedback on a spherical planet. A complete analytical solution for any obliquity ismore » given and validated against numerical solutions of a seasonal model in the “deep-water” regime of weak seasonal ice line migration. Multiple equilibria and unstable transitions between climate states (ice-free, Snowball, or ice cap/belt) are found over wide swaths of parameter space, including a “Large Ice-Belt Instability” and “Small Ice-Belt Instability” at high obliquity. The Snowball catastrophe is avoided at weak radiative forcing in two different scenarios: weak albedo feedback and inefficient heat transport (favoring stable partial ice cover), or efficient transport at high obliquity (favoring ice-free conditions). From speculative assumptions about distributions of planetary parameters, three-fourths to four-fifths of all planets with stable partial ice cover should be in the form of Earth-like polar caps.« less

Polar Textures

NASA Image and Video Library

2017-06-08

This VIS image of the south pole was taken at the end of summer. Frost will soon start to form as the season transitions into fall. Fall in the southern hemisphere means spring in the northern, so the north polar cap is just starting to thaw. Orbit Number: 67893 Latitude: -87.0251 Longitude: 275.679 Instrument: VIS Captured: 2017-04-04 06:19 https://photojournal.jpl.nasa.gov/catalog/PIA21679

Polar Wander on Triton and Pluto Due to Volatile Migration

NASA Technical Reports Server (NTRS)

Rubincam, David Parry

2002-01-01

Polar wander may occur on Triton and Pluto because of volatile migration. Triton, with its low obliquity, can theoretically sublimate volatiles (mostly nitrogen) at the rate of approximately 10(exp 14) kilograms per year from the equatorial regions and deposit them at the poles. Assuming Triton to be rigid on the sublimation timescale, after approximately 10(exp 5) years the polar caps would become large enough to cancel the rotational flattening, with a total mass equivalent to a global layer approximately 120-250 m in depth. At this point the pole wanders about the tidal bulge axis, which is the line joining Triton and Neptune. Rotation about the bulge axis might be expected to disturb the leading side/trailing side cratering statistics. Because no such disturbance is observed, it may be that Triton's mantle viscosity is too high but its surface volatile inventory is too low to permit wander. On the other hand, its mantle viscosity might be low, so that any uncompensated cap load might be expected to wander toward the tidal bulge axis. In this case, the axis of wander passes through the equator from the leading side to the trailing side; rotation about this wander axis would not disturb the cratering statistics. Low-viscosity polar wander may explain the bright southern hemisphere: this is the pole which is wandering toward the equator. In any case the permanent polar caps may be geologically very young. Polar wander may possibly take place on Pluto, due to its obliquity oscillations and perihelion-pole geometry. However, Pluto is probably not experiencing any wander at present. The Sun has been shining strongly on the poles over the last half of the obliquity cycle, so that volatiles should migrate to the equator, stabilizing the planet against wander. Spacecraft missions to Triton and Pluto which measure the dynamical flattening could give information about the accumulation of volatiles at the poles. Such information is best obtained by measuring gravity and topography from orbiters, as was done for Mars with the highly successful Mars Global Surveyor.

3-D Imaging of Mars’ Polar Ice Caps Using Orbital Radar Data

PubMed Central

Foss, Frederick J.; Putzig, Nathaniel E.; Campbell, Bruce A.; Phillips, Roger J.

2018-01-01

Since its arrival in early 2006, various instruments aboard NASA’s Mars Reconnaissance Orbiter (MRO) have been collecting a variety of scientific and engineering data from orbit around Mars. Among these is the SHAllow RADar (SHARAD) instrument, supplied by Agenzia Spaziale Italiana (ASI) and designed for subsurface sounding in the 15–25 MHz frequency band. As of this writing, MRO has completed over 46,000 nearly polar orbits of Mars, 30% of which have included active SHARAD data collection. By 2009, a sufficient density of SHARAD coverage had been obtained over the polar regions to support 3-D processing and analysis of the data. Using tools and techniques commonly employed in terrestrial seismic data processing, we have processed subsets of the resulting collection of SHARAD observations covering the north and south polar regions as SHARAD 3-D volumes, imaging the interiors of the north and south polar ice caps known, respectively, as Planum Boreum and Planum Australe. After overcoming a series of challenges revealed during the 3-D processing and analysis, a completed Planum Boreum 3-D volume is currently being used for scientific research. Lessons learned in the northern work fed forward into our 3-D processing and analysis of the Planum Australe 3-D volume, currently under way. We discuss our experiences with these projects and present results and scientific insights stemming from these efforts. PMID:29400351

Titan's plasma interaction: photoelectrons and negative ions

NASA Astrophysics Data System (ADS)

Coates, Coates; Welbrock, Anne; Desai, Ravi; Waite, Hunter

2016-06-01

We present a review of some of the most important results from the CAPS electron spectrometer.These include the role of photoelectrons and polar wind escape processes, and remarkable negative ion observations.

Impact of GaN cap on charges in Al₂O₃/(GaN/)AlGaN/GaN metal-oxide-semiconductor heterostructures analyzed by means of capacitance measurements and simulations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ťapajna, M., E-mail: milan.tapajna@savba.sk; Jurkovič, M.; Válik, L.

2014-09-14

Oxide/semiconductor interface trap density (D{sub it}) and net charge of Al₂O₃/(GaN)/AlGaN/GaN metal-oxide-semiconductor high-electron mobility transistor (MOS-HEMT) structures with and without GaN cap were comparatively analyzed using comprehensive capacitance measurements and simulations. D{sub it} distribution was determined in full band gap of the barrier using combination of three complementary capacitance techniques. A remarkably higher D{sub it} (∼5–8 × 10¹²eV⁻¹ cm⁻²) was found at trap energies ranging from E C-0.5 to 1 eV for structure with GaN cap compared to that (D{sub it} ∼ 2–3 × 10¹²eV⁻¹ cm⁻²) where the GaN cap was selectively etched away. D{sub it} distributions were then used for simulation of capacitance-voltage characteristics. A good agreement betweenmore » experimental and simulated capacitance-voltage characteristics affected by interface traps suggests (i) that very high D{sub it} (>10¹³eV⁻¹ cm⁻²) close to the barrier conduction band edge hampers accumulation of free electron in the barrier layer and (ii) the higher D{sub it} centered about E C-0.6 eV can solely account for the increased C-V hysteresis observed for MOS-HEMT structure with GaN cap. Analysis of the threshold voltage dependence on Al₂O₃ thickness for both MOS-HEMT structures suggests that (i) positive charge, which compensates the surface polarization, is not necessarily formed during the growth of III-N heterostructure, and (ii) its density is similar to the total surface polarization charge of the GaN/AlGaN barrier, rather than surface polarization of the top GaN layer only. Some constraints for the positive surface compensating charge are discussed.« less

Kinetics of antibody-induced modulation of respiratory syncytial virus antigens in a human epithelial cell line

PubMed Central

Sarmiento, Rosa E; Tirado, Rocio G; Valverde, Laura E; Gómez-Garcia, Beatriz

2007-01-01

Background The binding of viral-specific antibodies to cell-surface antigens usually results in down modulation of the antigen through redistribution of antigens into patches that subsequently may be internalized by endocytosis or may form caps that can be expelled to the extracellular space. Here, by use of confocal-laser-scanning microscopy we investigated the kinetics of the modulation of respiratory syncytial virus (RSV) antigen by RSV-specific IgG. RSV-infected human epithelial cells (HEp-2) were incubated with anti-RSV polyclonal IgG and, at various incubation times, the RSV-cell-surface-antigen-antibody complexes (RSV Ag-Abs) and intracellular viral proteins were detected by indirect immunoflourescence. Results Interaction of anti-RSV polyclonal IgG with RSV HEp-2 infected cells induced relocalization and aggregation of viral glycoproteins in the plasma membrane formed patches that subsequently produced caps or were internalized through clathrin-mediated endocytosis participation. Moreover, the concentration of cell surface RSV Ag-Abs and intracellular viral proteins showed a time dependent cyclic variation and that anti-RSV IgG protected HEp-2 cells from viral-induced death. Conclusion The results from this study indicate that interaction between RSV cell surface proteins and specific viral antibodies alter the expression of viral antigens expressed on the cells surface and intracellular viral proteins; furthermore, interfere with viral induced destruction of the cell. PMID:17608950

Coronal holes and high-speed wind streams

NASA Technical Reports Server (NTRS)

Zirker, J. B.

1977-01-01

Coronal holes, regions of unusually low density and low temperature in the solar corona, are identified as Bartel's M regions, i.e., sources of high-speed wind streams that produce recurrent geomagnetic variations. Throughout the Skylab period the polar caps of the sun were coronal holes, and at lower latitudes the most persistent and recurrent holes were equatorial extensions of the polar caps. The holes rotated 'rigidly' at the equatorial synodic rate. They formed in regions of unipolar photospheric magnetic field, and their internal magnetic fields diverged rapidly with increasing distance from the sun. The geometry of the magnetic field in the inner corona seems to control both the physical properties of the holes and the global distribution of high-speed wind streams in the heliosphere. Phenomenological models for the birth and decay of coronal holes have been proposed.

Water on Mars: Volatile history and resource availability

NASA Technical Reports Server (NTRS)

Jakosky, Bruce M.

1991-01-01

The existence of water on Mars is undisputed today. Measurements of atmospheric water vapor have shown that the abundance varies with location and season in a systematic way which depends on processes of exchange with the polar caps, regolith, and atmosphere. Channels, which give the appearance of having been carved by water or of having had water involved in their formation, appear in various locations on the surface; some were formed by catastrophic outflow of water from beneath the surface, while others form valley networks which give the appearance of having formed over long periods of time primarily early in the planet's history. The north polar residual cap consists of water ice, possibly containing an amount of water equivalent to a global layer several tens of meters thick. Finally, water is observed within the regolith, as adsorbed water or as water of hydration.

Chaotic obliquity and the nature of the Martian climate

NASA Technical Reports Server (NTRS)

Jakosky, Bruce M.; Henderson, Bradley G.; Mellon, Michael T.

1995-01-01

Recent calculations of the Martian obliquity suggests that it varies chaotically on timescales longer than about 10(exp 7) years and varies between about 0 and 60 deg. We examine the seasonal water behavior at obliquities between 40 and 60 deg. Up to several tens of centimeters of water may sublime from the polar caps each year, and possibly move to the equator, where it is more stable. The CO2 frost and CO2-H2O clathrate hydrate are stable in thepolar deposits below a few tens of meters depth, so that the polar cap could contain a significant CO2 reservoir. If CO2 is present, it could be left over from the early history of Mars; also, it could be released into the atmosphere during periods of high obliquity, causing occasional periods of more-clement climate.

Constraints on the Within Season and Between Year Variability of the North Residual Cap from MGS-TES

NASA Technical Reports Server (NTRS)

Calvin, W. M.; Titus, T. N.; Mahoney, S. A.

2003-01-01

There is a long history of telescopic and spacecraft observations of the polar regions of Mars. The finely laminated ice deposits and surrounding layered terrains are commonly thought to contain a record of past climate conditions and change. Understanding the basic nature of the deposits and their mineral and ice constituents is a continued focus of current and future orbited missions. Unresolved issues in Martian polar science include a) the unusual nature of the CO2 ice deposits ("Swiss Cheese", "slab ice" etc.) b) the relationship of the ice deposits to underlying layered units (which differs from the north to the south), c) understanding the seasonal variations and their connections to the finely laminated units observed in high-resolution images and d) the relationship of dark materials in the wind-swept lanes and reentrant valleys to the surrounding dark dune and surface materials. Our work focuses on understanding these issues in relationship to the north residual ice cap. Recent work using Mars Global Surveyor (MGS) data sets have described evolution of the seasonal CO2 frost deposits. In addition, the north polar residual ice cap exhibits albedo variations between Mars years and within the summer season. The Thermal Emission Spectrometer (TES) data set can augment these observations providing additional constraints such as temperature evolution and spectral properties associated with ice and rocky materials. Exploration of these properties is the subject of our current study.

The response of ionospheric convection in the polar cap to substorm activity

NASA Technical Reports Server (NTRS)

Lester, M.; Lockwood, M.; Yeoman, T. K.; Cowley, S. W. H.; Luehr, H.; Bunting, R.; Farrugia, C. J.

1995-01-01

We report multi-instrument observations during an isolated substorm on 17 October 1989. The European Incoherent Scatter (EISCAT) radar operated in the SP-UK-POLI mode measuring ionospheric convection at latitudes 71 deg Lambda - 78 deg Lambda. Sub-Auroral Magnetometer Network (SAMNET) and the EISCAT Magnetometer Cross provide information on the timing of substorm expansion phase onset and subsequent intensifications, as well as the location of the field aligned and ionospheric currents associated with the substorm current wedge. Interplanetary Monitoring Platform-8 (IMP-8) magnetic field data are also included. Evidence of a substorm growth phase is provided by the equatorward motion of a flow reversal boundary across the EISCAT radar field of view at 2130 MLT, following a southward turning of the interplanetary magnetic field (IMF). We infer that the polar cap expanded as a result of the addition of open magnetic flux in the tail lobes during this interval. The flow reversal boundary, which is a lower limit to the polar cap boundary, reached an invariant latitude equatorward of 71 deg Lambda by the time of the expansion phase onset. We conclude that the substorm onset region in the ionosphere, defined by the westward electrojet, mapped to a part of the tail radially earthward of the boundary between open and closed magnetic flux, the distant neutral line. Thus the substorm was not initiated at the distant neutral line, although there is evidence that it remained active during the expansion phase.

Occurrence of ion upflow associated with ion/electron heating in the polar cap and cusp regions

NASA Astrophysics Data System (ADS)

Ji, E. Y.; Jee, G.; Kwak, Y. S.

2017-12-01

We investigate the occurrence frequency of ion upflow in association with ion/electron heating in the polar cap and cusp regions, using the data obtained from the European Incoherent Scatter Svalbard radar (ESR) during the period of 2000 to 2010. We classify the upflow events by four cases: driven by ion heating (case 1), electron heating (case 2), both ion and electron heatings (case 3), and without any heating (case 4). The statistical analysis of the data shows that the upflow normaly starts at around 350 km altitude and the occurrence seems to peak at 11 MLT. Among the four cases, the occurrence frequency of the upflow is maximized for the case 3 and then followed by case 2, case 1 and case 3, which indicates that both ion and electron heatings are associated with ion upflow. At around 500 km altitude, however, the occurrence frequency is maximized when there is no heating (case 4). We also investigate the dependence of the occurrence frequency of the upflow on Kp and F10.7 indices. The maximum occurrence frequency seems to occur at moderate geomagnetic condition (2 ≤ Kp < 5). As for the solar activity, the occurrence frequency is higher for low solar activity than for high solar activity. The results of this study suggest that the ion upflow occurring in the polar cap/cusp region is mostly driven by both ion and electron heatings.

Orbitally-Induced, Quasi-Periodic Climate Change on Mars: Modelling Changes in the Global Cycling of Water and Carbon Dioxide

NASA Astrophysics Data System (ADS)

Mischna, M. A.; Richardson, M. I.; Wilson, R. J.

2002-12-01

Mars' orbital parameters (obliquity, eccentricity and argument of perihelion) are thought to have varied substantially on time scales >105 years. Such variations, especially in obliquity, may drastically affect the circulation of the atmosphere and volatile cycling. In this study, we focus on the response of the water and carbon dioxide cycles to changes in these orbital parameters, chiefly obliquity. The study employs the Geophysical Fluid Dynamics Laboratory Mars General Circulation Model, conducting simulations over a range of orbital states to examine changes in the cycling and deposition of these volatiles. This model contains full 3D accounting of atmospheric water and carbon dioxide as well as a basic dust cycle. The present martian obliquity is 25°, though it is believed to have recently varied between 15 and 45 degrees. Our simulations look at present martian conditions, only with obliquity varying between 5 and 60 degrees. Simulations are run out until water and carbon dioxide budgets have reached equilibrium--typically 30-40 years. As expected, volatile cycling on Mars increases with obliquity, as the polar caps are exposed to increased insolation, leading to greater seasonal ice caps and ultimately development of surface water ice in the now thermally favorible low latitudes. By 45°, water ice is stable in a broad band just north of the equator. Such an ice distribution has potential implications for the surface wind pattern through the ice-albedo effect on surface heating. Permanent polar CO2 caps are not stable under present conditions, but we find CO2 cap growth and corresponding atmospheric deflation to be evident at very low obliquities. We find that for most choices of orbital conditions, the northern hemisphere remains the stable pole for water ice, a result of the martian topographic dichotomy. We have begun to look at the impact of desorbed CO2 and H2O ice from the regolith on climatic conditions. Present estimates of the volatile abundance in the regolith vary greatly, but recent Mars Odyssey results hint at large abundances of water ice in the martian high-latitude regolith. The results of this study should better define models of polar volatile evolution, specifically those of layered terrain formation. The radiative feedback effects of increased atmospheric CO2 and H2O from the polar caps and regoliths has yet to be examined. Future plans include more accurate representations of dust injection and radiative transfer to tackle this problem.

An onboard data analysis method to track the seasonal polar caps on Mars

USGS Publications Warehouse

Wagstaff, K.L.; Castano, R.; Chien, S.; Ivanov, A.B.; Pounders, E.; Titus, T.N.; ,

2005-01-01

The Martian seasonal CO2 ice caps advance and retreat each year. They are currently studied using instruments such as the THermal EMission Imaging System (THEMIS), a visible and infra-red camera on the Mars Odyssey spacecraft [1]. However, each image must be downlinked to Earth prior to analysis. In contrast, we have developed the Bimodal Image Temperature (BIT) histogram analysis method for onboard detection of the cap edge, before transmission. In downlink-limited scenarios when the entire image cannot be transmitted, the location of the cap edge can still be identified and sent to Earth. In this paper, we evaluate our method on uncalibrated THEMIS data and find 1) agreement with manual cap edge identifications to within 28.2 km, and 2) high accuracy even with a smaller analysis window, yielding large reductions in memory requirements. This algorithm is currently being considered as a capability enhancement for the Odyssey second extended mission, beginning in fall 2006.

Buried CO2 Ice traces in South Polar Layered Deposits of Mars detected by radar sounder

NASA Astrophysics Data System (ADS)

Castaldo, L.; Mège, D.; Orosei, R.; Séjourné, A.

2014-12-01

SHARAD (SHAllow RADar) is the subsurface sounding radar provided by the Italian Space Agency (ASI) as a facility instrument to NASA's 2005 Mars Reconnaissance Orbiter (MRO). The Reduced Data Record of SHARAD data covering the area of the South Polar Layered Deposits (SPLD), has been used. The elaboration and interpretation of the data, aimed to estimate electromagnetic properties of surface layers, has been performed in terms of permittivity. The theory of electromagnetic scattering from fractal surfaces, and the estimation of geometric parameters from topographic data by Mars Orbiter Laser Altimeter (MOLA) which was one of five instruments on board the Mars Global Surveyor (MGS) spacecraft, has been used. A deep analysis of inversion has been made on all Mars and extended to the South Polar Caps in order to extract the area with a permittivity constant of CO2 ice. Several corrections have been applied to the data, moreover the calibration of the signal requires the determination of a constant that takes into account the power gain due to the radar system and the surface in order to compensate the power losses due to the orbitographic phenomena. The determination of regions with high probability of buried CO2 ice in the first layer of the Martian surface, is obtained extracting the real part of the permittivity constant of the CO2 ice (~2), estimated by other means. The permittivity of CO2ice is extracted from the Global Permittivity Map of Mars using the global standard deviation of itself as following: ɛCO2ice=ɛCO2ice+ Σ (1)where Σ=±std(ɛMapMars)/2Figure 1(a) shows the south polar areas where the values of the permittivity point to the possibility of a CO2 ice layer. Figure 1(b) is the corresponding geologic map. The comparison between the two maps indicates that the area with probable buried CO2 overlaps Hesperian and Amazonian polar units (Hp, Hesperian plains-forming deposits marked by narrow sinuous, anabranching ridges and irregular depressions, and Apu, Amazonian layered plateaus). From this analysis, the south polar cap could be covered by a thin frozen carbon dioxide coating. The perennial south polar cap is probably made of frozen carbon dioxide ca. 8 meters thick.

Synthesis of Environmentally Friendly Highly Dispersed Magnetite Nanoparticles Based on Rosin Cationic Surfactants as Thin Film Coatings of Steel

PubMed Central

Atta, Ayman M.; El-Mahdy, Gamal A.; Al-Lohedan, Hamad A.; Al-Hussain, Sami A.

2014-01-01

This work presents a new method to prepare monodisperse magnetite nanoparticles capping with new cationic surfactants based on rosin. Core/shell type magnetite nanoparticles were synthesized using bis-N-(3-levopimaric maleic acid adduct-2-hydroxy) propyl-triethyl ammonium chloride (LPMQA) as capping agent. Fourier transform infrared spectroscopy (FTIR) was employed to characterize the nanoparticles chemical structure. Transmittance electron microscopies (TEM) and X-ray powder diffraction (XRD) were used to examine the morphology of the modified magnetite nanoparticles. The magnetite dispersed aqueous acid solution was evaluated as an effective anticorrosion behavior of a hydrophobic surface on steel. The inhibition effect of magnetite nanoparticles on steel corrosion in 1 M HCl solution was investigated using potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS). Results obtained from both potentiodynamic polarisation and EIS measurements reveal that the magnetite nanoparticle is an effective inhibitor for the corrosion of steel in 1.0 M HCl solution. Polarization data show that magnetite nanoparticles behave as a mixed type inhibitor. The inhibition efficiencies obtained from potentiodynamic polarization and EIS methods are in good agreement. PMID:24758936