bluuebunny/crossref_metadata_2025 huggingface dataset:
Line of sight depth of the Large and Small Magellanic Clouds
Authors: Subramaniam Annapurni , Subramaniam Smitha
Published: March 2009

We used the red clump stars from the Optical Gravitational Lensing Experiment (OGLE II) survey and the Magellanic Cloud Photometric Survey (MCPS), to estimate the line-of-sight depth. The observed dispersion in the magnitude and colour distribution of red clump stars is used to estimate the line-of-sight depth, after correcting for the contribution due to other effects. This dispersion due to depth, has a range from minimum dispersion that can be estimated, to 0.46 mag (a depth of 500 pc to 10.44 kpc), in the LMC. In the case of the SMC, the dispersion ranges from minimum dispersion to 0.35 magnitude (a depth of 665 pc to 9.53 kpc). The thickness profile of the LMC bar indicates that it is flared. The average depth in the bar region is 4.0 ± 1.4 kpc. The halo of the LMC (using RR Lyrae stars) is found to have larger depth compared to the disk/bar, which supports the presence of an inner halo for the LMC. The large depth estimated for the LMC bar and the disk suggests that the LMC might have had minor mergers. In the case of the SMC, the bar depth (4.90 ± 1.23 kpc) and the disk depth (4.23 ± 1.48 kpc) are found to be within the standard deviations. We find evidence for an increase in depth near the optical center (up to 9 kpc). On the other hand, the estimated depth for the halo (RR Lyrae stars) and disk (RC stars) for the bar region of the SMC is found to be similar. Thus, increased depth and enhanced stellar as well as H i density near the optical center suggests that the SMC may have a bulge.
The state of molecular gas in the Small Magellanic Cloud
Authors: Leroy Adam K. , Bolatto Alberto D. , Rosolowsky Erik , Stanimirović Snežana , Mizuno Norikazu , Bot Caroline , Israel Frank , Walter Fabian , Blitz Leo
Published: March 2009

We compare the resolved properties of giant molecular clouds (GMCs) in the Small Magellanic Cloud (SMC) and other low mass galaxies to those in more massive spirals. When measured using CO line emission, differences among the various populations of GMCs are fairly small. We contrast this result with the view afforded by dust emission in the Small Magellanic Cloud. Comparing temperature-corrected dust opacity to the distribution of Hisuggests extended envelopes of CO-free H2, implying that CO traces only the highest density H2in the SMC. Including this CO-free H2, the gas depletion time, H2-to-Hiratio, and H2-to-stellar mass/light ratio in the SMC are all typical of those found in more massive irregular galaxies.
The Spitzer spectroscopic survey of the Small Magellanic Cloud: polycyclic aromatic hydrocarbon emission from SMC star-forming regions
Authors: Sandstrom Karin M. , Bolatto Alberto D. , Stanimirović Snežana , Smith J. D. T. , van Loon Jacco Th. , Leroy Adam K.
Published: March 2009

Because of its proximity, the Small Magellanic Cloud provides a unique opportunity to map the polycyclic aromatic hydrocarbon (PAH) emission from photo-dissociation regions (PDRs) in a low-metallicity (12 + log(O/H) ~ 8) galaxy at high spatial resolution in order to learn about their abundance and physical state. We present mid-IR spectral mapping observations of star-forming regions in the Small Magellanic Cloud obtained as part of the Spitzer Spectroscopic Survey of the SMC (S4MC) project. These observations allow us to map the distribution of PAH emission in these regions and the measure the variation of PAH band strengths with local physical conditions. In these proceedings we discuss preliminary results on the physical state of the PAHs, in particular their ionization fraction.
Properties of star forming regions in the Magellanic Clouds
Authors: Rubio Mónica
Published: March 2009

Understanding the process of star formation in low metallicity systems is one of the key studies in the early stages of galaxy evolution. The Magellanic Clouds, being the nearest examples of low metallicity systems, allow us to study in detail their star forming regions. As a consequence of their proximity we can resolve the molecular clouds and the regions of star formation individually. Therefore we can increase our knowledge of the interaction of young luminous stars with their environment. We will present results of multiwavelenghts studies of LMC and SMC massive star forming regions, which includes properties of the cold molecular gas, the embedded young population associated with molecular clouds, and the interaction of newly born stars with the surrounding interstellar medium, based on ASTE and APEX submillimeter observations complemented high sensitivity NIR groud based observations and Spitzer results.
Multiple stellar populations in massive LMC star clusters
Authors: Mackey A. D. , Nielsen P. Broby , Ferguson A. M. N. , Richardson J. C.
Published: March 2009

The recent discovery of multiple stellar populations in massive Galactic globular clusters poses a serious challenge for models of star cluster formation and evolution. A new angle on this problem is being provided by rich intermediate-age clusters in the Magellanic Clouds. In this contribution we describe the discovery of three such LMC clusters with peculiar main-sequence turn-off morphologies. The simplest interpretation of our observations is that each of these three clusters is comprised of two or more stellar populations spanning an age interval of ~300 Myr. Surprisingly, such features may not be unusual in this type of cluster.
Gemini/GMOS detection of stellar velocity variations in the ionising cluster of 30 Dor
Authors: Bosch Guillermo , Terlevich Elena , Terlevich Roberto
Published: March 2009

We have analysed spectra obtained with the Gemini Multi Object Spectrograph (GMOS) for more than 50 stars in the ionising cluster of 30 Doradus during a seven epochs observing campaign at Gemini South. We derive a binary candidate rate of about 50%, which is however consistent with an intrinsic 100% binary rate among massive stars. After decontaminating the sample from the stars that show binary orbital motions, we were able to calculate the “true” cluster velocity dispersion and found it to be about 8 km s−1. This value implies a virial mass of about 4.5 × 105 M⊙ which is consistent with previous photometric mass determinations therefore suggesting that NGC 2070 is a firm candidate for a future globular cluster.
The properties of early-type stars in the Magellanic Clouds
Authors: Evans Christopher J.
Published: March 2009

The past decade has witnessed impressive progress in our understanding of the physical properties of massive stars in the Magellanic Clouds, and how they compare to their cousins in the Galaxy. I summarise new results in this field, including evidence for reduced mass-loss rates and faster stellar rotational velocities in the Clouds, and their present-day compositions. I also discuss the stellar temperature scale, emphasizing its dependence on metallicity across the entire upper-part of the Hertzsprung-Russell diagram.
Supernova remnants in the Magellanic Clouds
Authors: Williams Rosa N. M.
Published: March 2009

At the 1998 IAU Symposium on the Magellanic Clouds, Dr. Robert Petre observed that we were reaching a time where it was possible “to study the MC SNRs at a level of detail comparable with many Galactic remnants”, while retaining the benefits of a global view in the MCs. Over the past decade, many researchers have taken advantage of these newly accessible populations. New MC-wide surveys at various wavelengths have enabled broader searches for SNR candidates, extending our census of MC SNRs to less prominent objects — older SNRs, SNRs in complex regions, et cetera. The use of light-echoes has provided a new avenue to probe young SNRs. Higher spatial and spectral resolutions in many wavelength regimes have enabled detailed studies of individual remnants, revealing progenitor types, pulsar-wind nebulae, expansion details, and environmental effects.

Perhaps the newest conceptual development is the increasing use of the MC SNRs to study physical problems of wider significance to many fields of astronomy. For example, researchers have examined the energy and hot gas inputs of MC SNRs to the ISM, including their collective effects within superbubbles, in order to evaluate their effects on stellar feedback cycles in a galaxy. Other scientists have investigated the fraction of SNR energies going to the acceleration of cosmic rays, which has significant implications for the role of SNRs in cosmic-ray production. Most recently, the onslaught of Spitzer data has led to new exploration of dust in MC SNRs, allowing us to probe dust creation, depletion, and destruction in the MC SNR populations. In summary, the study of SNRs in the MCs appears to have “come of age” over the past decade, becoming a mature field with rich potential for future scientific work.
The Magellanic Group and the Seven Dwarfs
Authors: D'Onghia Elena , Lake George
Published: March 2009

The Magellanic Clouds were the largest members of a group of dwarf galaxies that entered the Milky Way (MW) halo at late times. This group, dominated by the LMC, contained ~4% of the mass of the Milky Way prior to its accretion and tidal disruption, but ≈70% of the known dwarfs orbiting the MW. Our theory addresses many outstanding problems in galaxy formation associated with dwarf galaxies. First, it can explain the planar orbital configuration populated by some dSphs in the MW. Second, it provides a mechanism for lighting up a subset of dwarf galaxies to reproduce the cumulative circular velocity distribution of the satellites in the MW. Finally, our model predicts that most dwarfs will be found in association with other dwarfs. The recent discovery of Leo V (Belokurov et al. 2008), a dwarf spheroidal companion of Leo IV, and the nearby dwarf associations supports our hypothesis.
Changes in the concentration, biodegradability, and fluorescent properties of dissolved organic matter during stormflows in coastal temperate watersheds
Authors: Fellman Jason B. , Hood Eran , Edwards Richard T. , D'Amore David V.
Published: March 2009

Dissolved organic matter (DOM) transport during storms is studied because it is important in the annual watershed export budget for dissolved organic carbon (DOC). We sampled stream water from two watersheds (upland and wetland‐dominated) and three subcatchments (bog, forested wetland, and mineral forest) located within the wetland‐dominated watershed during a fall and summer storm to investigate changes in the magnitude and chemical quality of DOM during stormflows. Stormflow export of DOC ranged from 2.3 kg C ha−1 in the upland watershed to 13.9 kg C ha−1 in the bog subcatchment. Biodegradable DOC (BDOC) export for these same storms ranged from 0.6 kg C ha−1 in the upland watershed to 4.2 kg C ha−1 in the bog subcatchment. The percent BDOC decreased during both storms in the upland watershed, while percent BDOC increased in the three wetland streams. Parallel factor analysis (PARAFAC) modeling of fluorescence excitation‐emission matrices further showed that as stream water DOM concentrations increased during stormflows in the upland watershed, the contribution of protein‐like fluorescence decreased and humic‐like fluorescence increased. However, the contribution of protein‐like fluorescence increased and humic‐like fluorescence decreased slightly in the three wetland streams. These results indicate that shifts in the biodegradability and chemical quality of DOM are different for upland and wetland watersheds. Taken together, our findings suggest stormflows are responsible for substantial export of BDOC from coastal temperate watersheds. Moreover, we found that PARAFAC modeling of fluorescent DOM is an effective tool for elucidating shifts in the quality of stream water DOM during storms.
Neural Modulation by Rhythm Induced Temporal Expectations
Authors: Rohenkohl Gustavo , Dal Molin Anna , Nobre Anna
Published: March 2009

Time is an essential dimension of our experience, framing human behaviour at scales ranging from the millisecond organization of motor actions to circadian rhythms cycle, and beyond. Nevertheless, the mechanisms by which the brain keeps time and uses temporal information to organise behaviour remain unknown. Whereas the principles of the organisation of spatial cognition in the human brain are emerging, the same is not true for temporal cognition. The current study tested the influence of temporal expectations on attentional orienting to moving targets. In this task, a ball appeared at the left side of a screen and moved across the screen in steps following either a regular or irregular rhythm. After reaching an occluding band, the ball was temporarily occluded. When the ball reappeared, it contained either an upright (50%) or tilted (50%) cross. The task involved making a speeded perceptual discrimination about the target stimulus that reappears after the occlusion. The results indicated a strong behaviour benefit from temporal orienting. We recorded ERPs elicited by reappearance of the target stimulus, and investigated how temporal expectations influenced perceptual (e.g., visual P1 potential) and motor (lateralised readiness potential) stages of neural processing. The results showed that temporal expectations facilitated both early visual (P1) as well as motor (LRP) potentials. We are currently comparing induced frequency activity during the pre-occlusion and occlusion periods to look for modulation of rhythmic activity in lower frequency bands related to visual (alpha) and motor (mu) processing.
Val1483Ile in FASN Gene Is Linked to Central Obesity and Insulin Sensitivity in Adult White Men
Authors: Moreno‐Navarrete José M. , Botas Patricia , Valdés Sergio , Ortega Francisco J. , Delgado Elías , Vázquez‐Martín Alejandro , Bassols Judit , Pardo Gerard , Ricart Wifredo , Menéndez Javier A. , Fernández‐Real José M.
Published: March 2009

The Val1483Ile polymorphism in the human fatty acid synthase (FASN) gene is located within the interdomain region of the FASN close to the two dynamic active centers of the FASN enzyme and putatively affects FASN action. We aimed to evaluate the association of this polymorphism with obesity phenotypes, insulin sensitivity, and adipose tissue FASN activity in adult white subjects. The polymorphism was evaluated in association with metabolic variables in two independent studies: in a case–control study of 457 men (229 with normal glucose tolerance (NGT) and 228 with altered glucose tolerance (AGT)); and in 600 population‐based NGT subjects (274 men and 326 women). Adipose tissue FASN activity was analyzed using the method of Nepokroeff. The Ile variant was associated with a lower waist‐to‐hip ratio (WHR) and a lower increase in weight over a 7‐year period in NGT men. In a subset of 147 men, carriers of the Ile variant showed significantly increased insulin sensitivity. BMI (P < 0.001), WHR (P = 0.03), and Val1483Ile (P = 0.03), contributed independently to 37% of insulin sensitivity variance. In men from the population‐based study, the Ile variant was associated with a lower BMI, WHR, fasting glucose, and systolic blood pressure compared with carriers of the Val variant. In agreement with these results, the adipose tissue FASN activity was significantly lower in subjects with the Ile variant (P = 0.01). In summary, adult white men with the Ile 1483 variant of the FASN gene seem protected from developing central obesity through decreased adipose tissue FASN activity.
Differential Effects of Abdominal Adipose Tissue Distribution on Insulin Sensitivity in Black and White South African Women
Authors: Goedecke Julia H. , Levitt Naomi S. , Lambert Estelle V. , Utzschneider Kristina M. , Faulenbach Mirjam V. , Dave Joel A. , West Sacha , Victor Hendriena , Evans Juliet , Olsson Tommy , Walker Brian R. , Seckl Jonathan R. , Kahn Steven E.
Published: March 2009

Black South African women are more insulin resistant than BMI‐matched white women. The objective of the study was to characterize the determinants of insulin sensitivity in black and white South African women matched for BMI. A total of 57 normal‐weight (BMI 18–25 kg/m2) and obese (BMI > 30 kg/m2) black and white premenopausal South African women underwent the following measurements: body composition (dual‐energy X‐ray absorptiometry), body fat distribution (computerized tomography (CT)), insulin sensitivity (SI, frequently sampled intravenous glucose tolerance test), dietary intake (food frequency questionnaire), physical activity (Global Physical Activity Questionnaire), and socioeconomic status (SES, demographic questionnaire). Black women were less insulin sensitive (4.4 ± 0.8 vs. 9.5 ± 0.8 and 3.0 ± 0.8 vs. 6.0 ± 0.8 × 10−5/min/(pmol/l), for normal‐weight and obese women, respectively, P < 0.001), but had less visceral adipose tissue (VAT) (P = 0.051), more abdominal superficial subcutaneous adipose tissue (SAT) (P = 0.003), lower SES (P < 0.001), and higher dietary fat intake (P = 0.001) than white women matched for BMI. SI correlated with deep and superficial SAT in both black (R = −0.594, P = 0.002 and R = 0.495, P = 0.012) and white women (R = −0.554, P = 0.005 and R = −0.546, P = 0.004), but with VAT in white women only (R = −0.534, P = 0.005). In conclusion, body fat distribution is differentially associated with insulin sensitivity in black and white women. Therefore, the different abdominal fat depots may have varying metabolic consequences in women of different ethnic origins.
Application of Skeletal Buttress Analogy in Composite Facial Reconstruction
Authors: Bluebond-Langner Rachel , Rodriguez Eduardo D.
Published: March 2009

Reconstructive algorithms for composite craniofacial defects have focused on soft tissue flaps with or without bone grafts. However, volumetric loss over time limits long-term preservation of facial contour. Application of craniofacial skeletal buttress principles to high-energy trauma or oncologic defects with composite vascularized bone flaps restores the soft tissue as well as the buttresses and ultimately preserves facial contour. We conducted a retrospective review of 34 patients with craniofacial defects treated by a single surgeon with composite bone flaps at R Adams Cowley Shock Trauma Center and Johns Hopkins Hospital from 2001 to 2007. Data collected included age, sex, mechanism of injury, type of defect, type of reconstructive procedures, and outcome. Thirty-four patients with composite tissue loss, primarily males ( n = 24) with an average age of 37.4 years, underwent reconstruction with vascularized bone flaps (28 fibula flaps and 6 iliac crest flaps). There were 4 cranial defects, 8 periorbital defects, 18 maxillary defects, and 4 maxillary and periorbital defects. Flap survival rate was 94.1% with an average follow-up time of 20.5 months. Restoration of facial height, width, and projection is achieved through replacement of skeletal buttresses and is essential for facial harmony. Since 2001, our unit has undergone a paradigm shift with regard to treatment of composite oncologic and traumatic defects, advocating vascularized bone flaps to achieve predictable long-term outcomes.
Extended Transcaruncular Approach Using Detachment and Repositioning of the Inferior Oblique Muscle for the Traumatic Repair of the Medial Orbital Wall
Authors: Rodriguez Javier , Galan Ramon , Forteza Gabriel , Mateos Mario , Mommsen Jens , Bouso Olga Vazquez , Piera Veronica
Published: March 2009

The fracture of the medial orbital wall is relatively common in orbital trauma. Titanium mesh is possibly the actual standard material for orbital wall reconstruction. When the floor of the orbit and the medial wall are simultaneously affected, one larger mesh gives better results than two independent meshes that need to be fixated independently. However, large meshes need a wider surgical field. To gain sufficient exposure to the medial and inferior orbital walls simultaneously, we present an approach that combines the transconjunctival and transcaruncular incisions, detaching if needed the inferior oblique muscle and, placing our mesh, repositioning it beside the lacrimal duct. This technique should not entirely displace traditional approaches, but it widens the surgical exposure for middle- and upper-third facial trauma. This alternative has minimum morbidity and can save a great deal of surgery time.
Pressure effect on phase transitions and magnetocaloric effect in Gd5Ge4
Authors: Arnold Zdenek , Skorokhod Yuriy , Kamarad Jiri , Magen Cesar , Algarabel Pedro A.
Published: March 2009

We present the results of study of magnetocaloric effect in Gd5Ge4 under high hydrostatic pressure up to 9 kbar in magnetic field up to 5 T. At ambient pressure, temperature of the maximum value of the magnetic entropy change |ΔSM|max∼24 J∗ kg−1∗ K−1 [Δ(μ0H)=5 T] coincides with temperature of the field-induced first-order antiferromagnetic-ferromagnetic (AFM-FM) transition. The pressure-induced mixed-phase state with gradual dominance of the FM phase leads to a smoothing of a peak shape of the magnetic entropy change and to a pronounced reduction in the |ΔSM|max value at low pressure. Temperature of the maximum of the |ΔSM| increases remarkably with increasing pressure with a slope that corresponds to a pressure-induced increase in the Curie temperature TC(+4.8 K/kbar). The further growth of the pressure-induced FM phase and the increase in TC is accompanied by the increase in |ΔSM|max that is more pronounced at low magnetic fields where a combine effect of pressure and magnetic field is significant.
Mössbauer study of magnetic structure of cation-deficient iron sulfide Fe0.92S
Authors: Kim Woochul , Park Il Jin , Kim Chul Sung
Published: March 2009

We have investigated the magnetic hyperfine structure of iron sulfide Fe0.92S by Mössbauer spectroscopy and studied its magnetic properties. From the x-ray diffraction pattern, Fe0.92S is found to be a 3c-type superstructure of the NiAs hexagonal structure. Magnetization curve at room temperature for Fe0.92S showed a ferromagnetic behavior unlike that for antiferromagnetic FeS. A peak type anomaly is observed in zero-field-cooled magnetization curve under 100 Oe. Mössbauer spectra were taken at various temperatures ranging from 4.2 to 615 K. The spectra consist of three-component subspectra arising from three magnetically nonequivalent sites in the 3c superstructure. The magnetic hyperfine fields of the three A-, B-, and C-sites at 4.2 K are found to be 328, 277, and 246 kOe, respectively. These values are in the ratio of 18:15:14, which is close to the ratio of the magnitudes of magnetic hyperfine field in 18, 14, and 13 interplanar superexchange links (Fe–S–Fe) of A-, B-, and C-sites in Fe7S8. The absorption intensity for A-, B-, and C-sites changes substantially over the temperature range from 570 K, suggesting that a vacancy rearrangement is taking place. Isomer shifts indicate Fe2+ states for all three sites. The Néel temperature (TN) and the Debye temperature are found to be 615±1 and 238±5 K, respectively.
Structure and magnetic properties of hexagonal arrays of ferromagnetic nanowires
Authors: Hernández Eduardo Padrón , Azevedo A. , Rezende S. M.
Published: March 2009

Here we present a model that explains a number of the magnetic properties of arrays of cylindrical ferromagnetic nanowires. The model properly considers the magnetostatic contributions from the wire inhomogeneities, here taken as a chain of ellipsoidal grains, as well as the dipolar interactions summed in the overall array of hexagonal symmetry. Carrying out the complete sum of both the dipolar interactions between the ellipsoidal grains and between the nanowires, we obtain an analytical expression for the magnetostatic energy. The effective anisotropy field extracted from the magnetostatic energy predicts the change in the magnetization easy direction from parallel to perpendicular to the wire axis. The expressions contain information on microscopic parameters such as packing factor, length and diameter of the nanowires, and shape and size of the ellipsoids. The model has been used to interpret ferromagnetic resonance data of Ni nanowires fabricated by electrodeposition in porous anodic aluminum oxide membranes.
Enhanced field-effect mobility in pentacene based organic thin-film transistors on polyacrylates
Authors: Cheng Jung-An , Chuang Chiao-Shun , Chang Ming-Nung , Tsai Yun-Chu , Shieh Han-Ping D.
Published: March 2009

We reported on organic thin-film transistors (OTFTs) with high dielectric constant polymer, poly(2,2,2-trifluoroethyl methacrylate) (PTFMA), as the gate dielectric. In top-contact OTFTs, the field-effect mobility was enhanced by applying a dielectric buffer layer poly(α-methylstyrene) to the bare PTFMA. After improving interfacial affinity within the active layer/dielectrics, deposited pentacene grain size and device performance were enhanced dramatically. The corresponding mobility, threshold voltage, and on/off current ratio were 0.70 cm2 V−1 s−1, −10.5 V, and 5.4×105, respectively. The moderately improved interface also suppressed the hole-trapping effect, which led to less hysteresis and minimized threshold voltage shift.
Interfacial state and magnetic properties of Nd-Fe-B/Nd thin films
Authors: Matsuura Masashi , Sugimoto Satoshi , Goto Ryota , Tezuka Nobuki
Published: March 2009

Nd-Fe-B/Nd(-O) interfaces were prepared by thin film technique for the investigation of relationship between interfacial state and coercivity. A Nd-Fe-B layer was deposited by UHV magnetron sputtering and the film was oxidized under low vacuum conditions. On the oxidized Nd-Fe-B layer, a Nd layer was deposited and the film was annealed at 250–650 °C. The coercivity of Nd-Fe-B layer decreased after the oxidation. However, it recovered after the deposition of Nd layer and the annealing at 350 °C. High-resolution transmission electron microscopy (HRTEM) observations revealed that an fcc NdO phase forms after the oxidation and an amorphous phase exists along the interface between Nd2Fe14B and Nd2O3 phases after annealing at 350 °C. Therefore, the recovery of coercivity is related to the amorphous phase, which is considered to be formed by the transformation from NdO to Nd2O3 and α-Nd, and the release of strain at the interface.
A new method for high-frequency characterization of patterned ferromagnetic thin films
Authors: Zhang Hanqiao , Song Chunrong , Wang Pingshan
Published: March 2009

A new high-frequency method is presented for patterned ferromagnetic thin film characterization. Parasitic effects, which often overwhelm the signal from patterned ferromagnetic structures, are significantly reduced through an on-chip interference process. As a result, measurement sensitivity is greatly improved in comparison with conventional on-chip transmission line ferromagnetic resonance (FMR) methods. Algorithms are given to extract the complex permeability and FMR linewidth of ferromagnetic materials from scattering parameters obtained with the method. An on-chip 10 GHz structure was fabricated and experimentally demonstrated ∼20 dB parasitic effect cancellation efficiency. A patterned Permalloy (Py) array with 180 stripes is measured. Each stripe is 100 nm thick, 2 μm wide, and 20 μm long. The FMR frequency of the patterned Py thin films was tuned with an external static magnetic field. With a 676 G bias field, the obtained FMR frequency and linewidth are 9.68 and 1.4 GHz, respectively. These results are comparable with micromagnetic simulation results.
Multiscale modeling of lamellar mesophases
Authors: Kumaran V. , Krishna Babu Y. K. V. V. N. , Sivaramakrishna J.
Published: March 2009

The mesoscale simulation of a lamellar mesophase based on a free energy functional is examined with the objective of determining the relationship between the parameters in the model and molecular parameters. Attention is restricted to a symmetric lamellar phase with equal volumes of hydrophilic and hydrophobic components. Apart from the lamellar spacing, there are two parameters in the free energy functional. One of the parameters, r, determines the sharpness of the interface, and it is shown how this parameter can be obtained from the interface profile in a molecular simulation. The other parameter, A, provides an energy scale. Analytical expressions are derived to relate these parameters to r and A to the bending and compression moduli and the permeation constant in the macroscopic equation to the Onsager coefficient in the concentration diffusion equation. The linear hydrodynamic response predicted by the theory is verified by carrying out a mesoscale simulation using the lattice-Boltzmann technique and verifying that the analytical predictions are in agreement with simulation results. A macroscale model based on the layer thickness field and the layer normal field is proposed, and the relationship between the parameters in the macroscale model from the parameters in the mesoscale free energy functional is obtained.
Block-circulant matrices with circulant blocks, Weil sums, and mutually unbiased bases. II. The prime power case
Authors: Combescure Monique
Published: March 2009

In our previous paper [Combescure, M., “Circulant matrices, Gauss sums and the mutually unbiased bases. I. The prime number case,” Cubo A Mathematical Journal (unpublished)] we have shown that the theory of circulant matrices allows to recover the result that there exists p+1 mutually unbiased bases in dimension p, p being an arbitrary prime number. Two orthonormal bases B, B′ of Cd are said mutually unbiased if ∀b∊B, ∀b′∊B′ one has that |b⋅b′|=1/d (b⋅b′ Hermitian scalar product in Cd). In this paper we show that the theory of block-circulant matrices with circulant blocks allows to show very simply the known result that if d=pn (p a prime number and n any integer) there exists d+1 mutually unbiased bases in Cd. Our result relies heavily on an idea of Klimov et al. [“Geometrical approach to the discrete Wigner function,” J. Phys. A 39, 14471 (2006)]. As a subproduct we recover properties of quadratic Weil sums for p≥3, which generalizes the fact that in the prime case the quadratic Gauss sum properties follow from our results.
Fragmentation of adenine under energy control
Authors: Brédy Richard , Bernard Jérôme , Chen Li , Montagne Guillaume , Li Bin , Martin Serge
Published: March 2009

We present results on the fragmentation of adenine dication as a function of the excitation energy. The adenine molecule is charged and excited in a single collision with Cl+ ion at 3 keV and the excitation energy distribution is obtained for each fragmentation channel by measuring the kinetic energy loss of the projectile. This method named collision induced dissociation under energy control is based on the formation of a negative scattered projectile as a result of double electron capture from the target molecule. Comparison between the main dissociation channels of singly and doubly charged adenine shows that fragmentation patterns are very similar consisting mainly of the successive emission of neutral HCN or H2CN+. The energy distributions of the parent adenine dication and the kinetic energy release of the fragments measured for the most abundant fragmentation channels confirms the assumption of successive emission dynamics. A specific fragmentation pathway of the adenine requiring less energy than the usual successive emission of neutral HCN could be identified. It consists of the emission of a charged H2CN+ following on by the emission of a dimer of HCN (precisely HC2N2). This new channel, measured for a mean excitation energy of 8.4 eV for the adenine dication is very closed to the emission of HCN monomer measured at 7.9 eV. The implications of these results concern the formation of adenine in the sealed-tube reaction of HCN with liquid ammonia as well as the possible formation of the adenine molecule in the interstellar medium. This last point is briefly discussed in relation to astrobiology and exobiology interests.
First principles elaboration of low band gap ladder-type polymers
Authors: Pesant Simon , Dumont Guillaume , Langevin Sébastien , Côté Michel
Published: March 2009

Ladder-type polymers, obtained by small modifications of the atomic structure of ladder-type polythiophene, are studied using density-functional theory calculations. Within the local-density and GW approximations, it is found that upon a simple substitution of the sulfur atoms by nitrogen and boron atoms, the band structure of the resulting polymer exhibits band overlap between the occupied and the unoccupied states. However, the three-parameter Becke hybrid functional predicts these polymers to be small band gap semiconductors. Finally, results of time-dependent density-functional theory are reported on increasing length oligomers, indicating that the polymers would have very low excitation energies.
Fe nanoparticles embedded in MgO crystals
Authors: Shalimov A. , Potzger K. , Geiger D. , Lichte H. , Talut G. , Misiuk A. , Reuther H. , Stromberg F. , Zhou Shengqiang , Baehtz C. , Fassbender J.
Published: March 2009

Iron nanoparticles embedded in MgO crystals were synthesized by Fe+ ion implantation at an energy of 100 keV and varying fluences from 3×1016 to 3×1017 cm−2. Investigations of structural and magnetic properties of Fe nanoparticles have been performed using magnetometry, x-ray diffraction, transmission electron microscopy, and Mössbauer spectroscopy, as well as by theoretical Preisach modeling of bistable magnetic systems. It has been found that α- and γ-Fe nanoparticles are formed for all fluences. The content of the α-Fe phase increases at higher fluences and after annealing. The influence of postimplantation annealing at 800 °C in vacuum and under enhanced hydrostatic pressure on the formation of nanoparticles has been analyzed.
Piezoelectric properties of PbTiO3 thin films characterized with piezoresponse force and high resolution transmission electron microscopy
Authors: Morelli A. , Venkatesan Sriram , Kooi B. J. , Palasantzas G. , De Hosson J. Th. M.
Published: March 2009

In this paper we investigate the piezoelectric properties of PbTiO3 thin films grown by pulsed laser deposition with piezoresponse force microscopy and transmission electron microscopy. The as-grown films exhibit an upward polarization, inhomogeneous distribution of piezoelectric characteristics concerning local coercive fields, and piezoelectric coefficient. In fact, the data obtained reveal imprints during piezoresponse force microscopy measurements, nonlinearity in the piezoelectric deformation, and limited polarization reversal. Moreover, transmission electron microscopy shows the presence of defects near the film/substrate interface, which can be associated with the variations of piezoelectric properties.
Nanocrystal-mediated charge screening effects in nanowire field-effect transistors
Authors: Yoon C. J. , Yeom D. H. , Jeong D. Y. , Lee M. G. , Moon B. M. , Kim S. S. , Choi C. Y. , Koo S. M.
Published: March 2009

ZnO nanowire field-effect transistors having an omega-shaped floating gate (OSFG) have been successfully fabricated by directly coating CdTe nanocrystals (∼6±2.5 nm) at room temperature, and compared to simultaneously prepared control devices without nanocrystals. Herein, we demonstrate that channel punchthrough may occur when the depletion from the OSFG takes place due to the trapped charges in the nanocrystals. Electrical measurements on the OSFG nanowire devices showed static-induction transistorlike behavior in the drain output IDS-VDS characteristics and a hysteresis window as large as ∼3.1 V in the gate transfer IDS-VGS characteristics. This behavior is ascribed to the presence of the CdTe nanocrystals, and is indicative of the trapping and emission of electrons in the nanocrystals. The numerical simulations clearly show qualitatively the same characteristics as the experimental data and confirm the effect, showing that the change in the potential distribution across the channel, induced by both the wrapping-around gate and the drain, affects the transport characteristics of the device. The cross-sectional energy band and potential profile of the OSFG channel corresponding to the “programed (noncharged)” and “erased (charged)” operations for the device are also discussed on the basis of the numerical capacitance-voltage simulations.
Monolithic parallel tandem organic photovoltaic cell with transparent carbon nanotube interlayer
Authors: Tanaka S. , Mielczarek K. , Ovalle-Robles R. , Wang B. , Hsu D. , Zakhidov A. A.
Published: March 2009

We demonstrate an organic photovoltaic cell with a monolithic tandem structure in parallel connection. Transparent multiwalled carbon nanotube sheets are used as an interlayer anode electrode for this parallel tandem. The characteristics of front and back cells are measured independently. The short circuit current density of the parallel tandem cell is larger than the currents of each individual cell. The wavelength dependence of photocurrent for the parallel tandem cell shows the superposition spectrum of the two spectral sensitivities of the front and back cells. The monolithic three-electrode photovoltaic cell indeed operates as a parallel tandem with improved efficiency.
A new instrument for thermal electron attachment at high temperature: NF3 and CH3Cl attachment rate constants up to 1100 K
Authors: Miller Thomas M. , Friedman Jeffrey F. , Williamson John S. , Schaffer Linda C. , Viggiano A. A.
Published: March 2009

A new high temperature flowing afterglow Langmuir probe (HT-FALP) apparatus is described. A movable Langmuir probe and a four-needle reactant gas inlet were fitted to an existing high temperature flowing afterglow apparatus. The instrument is suitable for study of electron attachment from 300–1200 K, the upper limit set to avoid softening of the quartz flow tube. We present results for two reactions over extended ranges: NF3 (300–900 K) and CH3Cl (600–1100 K). Electron attachment rate constants for NF3 had been measured earlier using our conventional FALP apparatus. Those measurements were repeated with the FALP and then extended to 900 K with the HT-FALP. CH3Cl attaches electrons too weakly to study with the low temperature FALP but reaches a value of ∼10−9 cm3 s−1 at 1100 K. F− is produced in NF3 attachment at all temperatures and Cl− in CH3Cl attachment, as determined by a quadrupole mass spectrometer at the end of the flow tube. Future modifications to increase the plasma density should allow study of electron-ion recombination at high temperatures.
Weak exchange effect and large refrigerant capacity in a bulk metallic glass Gd0.32Tb0.26Co0.20Al0.22
Authors: Liu Yongsheng , Zhang Jincang , Wang Youquan , Zhu Yanyan , Yang Zhenglong , Chen Jing , Cao Shixun
Published: March 2009

The magnetic behavior and refrigeration capacity of Gd0.32Tb0.26Co0.20Al0.22, a bulk metallic glass (BMG) fabricated by a copper-mold suck-casting method, are investigated. The Curie temperature increases from 79 K at 200 Oe to 95 K at 50 000 Oe. A weak exchange field of 25 T in the BMG system, caused by the strong disorder, is derived by the mean-field approximation. The maximum magnetic entropy change (8.02 J kg−1 K−1) and the refrigerant capacity (642 J kg−1) for 5 T indicate the BMG has the better refrigerant efficiency compared to known magnetic refrigerants.
Nonvolatile memories using deep traps formed in Al2O3 by metal ion implantation
Authors: Kim Min Choul , Hong Seung Hui , Kim Hye Ryong , Kim Sung , Choi Suk-Ho , Elliman R. G. , Russo S. P.
Published: March 2009

We demonstrate the feasibility of an approach to nonvolatile memory (NVM) that exploits charge trapping at deep-energy levels formed in Al2O3 by metal doping. Our calculations show that V and Nb are expected to form such deep energy levels in the band gap of Al2O3. To demonstrate the effectiveness of this approach these metal ions were ion-implanted into test structures based on an Al2O3 trapping layer. Several structural analysis techniques and photocurrent spectroscopy show that the doped metal ions are located close to the Al2O3/SiO2 interface and exhibit characteristics consistent with some of the deep levels predicted in calculations. The resulting test devices are shown to exhibit promising NVM characteristics.
Efficient bilayer phosphorescent organic light-emitting diodes: Direct hole injection into triplet dopants
Authors: Liu Z. W. , Helander M. G. , Wang Z. B. , Lu Z. H.
Published: March 2009

In phosphorescent organic light-emitting diodes (OLEDs), a hole transporting layer is traditionally thought to be required to facilitate hole injection into the host molecule. It is found that fac-tris(2-phenylpyridine)iridium [Ir(ppy)3] doped into 4,4′-N,N′-dicarbazole-biphenyl can be used to directly inject and transport holes from an indium tin oxide anode, and thus simplify the device structure and selection of materials. The efficiencies of the simplified bilayer OLEDs exceed 41 lm/W and 57 cd/A at a brightness of 100 cd/m2. We attribute the excellent performance to direct hole injection from the anode to Ir(ppy)3 dopant.
Electrostatically tunable magnetoelectric inductors with large inductance tunability
Authors: Lou J. , Reed D. , Liu M. , Sun N. X.
Published: March 2009

A class of electrostatically tunable inductors with multiferroic composite cores consisting of Metglas/lead zirconate titanate/Metglas was demonstrated. These magnetoelectric inductors exhibit a large tunable inductance range ΔL/Lmin of up to 450%, together with improved quality factors. Such tunability of inductance and quality factor was due to a strong magnetoelectric coupling in the multiferroic composite core, which led to electric field induced permeability change. The concept of tuning inductance by electric field using multiferroic composite materials leads to a class of compact tunable inductors with minimum power consumption.
Local structure and conduction mechanism in amorphous In–Ga–Zn–O films
Authors: Cho Deok-Yong , Song Jaewon , Na Kwang Duk , Hwang Cheol Seong , Jeong Jong Han , Jeong Jae Kyeong , Mo Yeon-Gon
Published: March 2009

The local structures of amorphous In–Ga–Zn–O (InGaZnO4 and In2Ga2ZnO7) films were examined by x-ray absorption spectroscopy and fine structure analysis. The local metal-oxygen coordination in both films indicated bipyramidal GaO5, ZnO5, and trigonal InO6 clusters. Further analyses showed splitting of the Zn–O bond length suggesting distortion of the ZnO5 cluster, which evidenced the existence of localized holes in the Zn atoms. In combination with the abundance of In 5s electrons, this shows that the In–Zn hopping interactions contribute to electrical conduction.
Confinement effects on the kinetics and thermodynamics of protein dimerization
Authors: Wang Wei , Xu Wei-Xin , Levy Yaakov , Trizac E. , Wolynes P. G.
Published: March 2009

In the cell, protein complexes form by relying on specific interactions between their monomers. Excluded volume effects due to molecular crowding would lead to correlations between molecules even without specific interactions. What is the interplay of these effects in the crowded cellular environment? We study dimerization of a model homodimer when the mondimers are free and when they are tethered to each other. We consider a structured environment: Two monomers first diffuse into a cavity of size
L
and then fold and bind within the cavity. The folding and binding are simulated by using molecular dynamics based on a simplified topology based model. The confinement in the cell is described by an effective molecular concentration
C
∼
L
−3
. A two-state coupled folding and binding behavior is found. We show the maximal rate of dimerization occurred at an effective molecular concentration
C
op
≃ 1 mM, which is a relevant cellular concentration. In contrast, for tethered chains the rate keeps at a plateau when
C
<
C
op
but then decreases sharply when
C
>
C
op
. For both the free and tethered cases, the simulated variation of the rate of dimerization and thermodynamic stability with effective molecular concentration agrees well with experimental observations. In addition, a theoretical argument for the effects of confinement on dimerization is also made.
Mathematical test models for superparametrization in anisotropic turbulence
Authors: Majda Andrew J. , Grote Marcus J.
Published: March 2009

The complexity of anisotropic turbulent processes over a wide range of spatiotemporal scales in engineering turbulence and climate atmosphere ocean science requires novel computational strategies with the current and next generations of supercomputers. In these applications the smaller-scale fluctuations do not statistically equilibrate as assumed in traditional closure modeling and intermittently send significant energy to the large-scale fluctuations. Superparametrization is a novel class of seamless multi-scale algorithms that reduce computational labor by imposing an artificial scale gap between the energetic smaller-scale fluctuations and the large-scale fluctuations. The main result here is the systematic development of simple test models that are mathematically tractable yet capture key features of anisotropic turbulence in applications involving statistically intermittent fluctuations without local statistical equilibration, with moderate scale separation and significant impact on the large-scale dynamics. The properties of the simplest scalar test model are developed here and utilized to test the statistical performance of superparametrization algorithms with an imposed spectral gap in a system with an energetic −5/3 turbulent spectrum for the fluctuations.
Internationalist Mobilization during the Collapse of the Soviet Union: The Moldovan Elections of 1990
Authors: Mason John Alan
Published: March 2009

In September 1989, speaking to the Republican Strike Committee of the Moldovan Soviet Socialist Republic (MSSR), Erkin Nurzhanovich Auel'bekov, assistant chairman of the All-Union Soviet of Nationalities, asked a question of great importance to Soviet citizens in the increasingly fragile union: “Is there such a thing as a Sovietnarod(people), or is this just an empty fiction?” For Auel'bekov and the assembled strike committee, the answer was not in doubt. “Certainly for all of us here,” he continued, “there is such anarod.There is a passport, there are Soviet people (sovetskie liudi) and, moreover, there is justification for thinking that this is the most important achievement of the past seventy years of Soviet power.” Soviet patriots, they agreed, needed to protect thisnarodfrom the process of “nationalization” that threatened the Soviet Union and its constituent people both locally in Moldova and more broadly in the union in general. The protection of this achievement in Soviet nation building became the mission of an “internationalist' ” movement as it moved from a strike campaign to stop language laws in 1989 to an election campaign in 1990. The political strike of 1989 had achieved none of its immediate goals and as internationalist activists moved into the second phase of the conflict over the future of Moldova they invoked imperiled Soviet achievements as they first attempted to take the Moldovan government through the ballot box, and failing at that, to take the eastern region of Transnistria out of Moldova.
Focal Adhesion Kinase Modulates Cell Adhesion Strengthening via Integrin Activation
Authors: Michael Kristin E. , Dumbauld David W. , Burns Kellie L. , Hanks Steven K. , García Andrés J.
Published: March 2009

Focal adhesion kinase (FAK) is an essential nonreceptor tyrosine kinase regulating cell migration, adhesive signaling, and mechanosensing. Using FAK-null cells expressing FAK under an inducible promoter, we demonstrate that FAK regulates the time-dependent generation of adhesive forces. During the early stages of adhesion, FAK expression in FAK-null cells enhances integrin activation to promote integrin binding and, hence, the adhesion strengthening rate. Importantly, FAK expression regulated integrin activation, and talin was required for the FAK-dependent effects. A role for FAK in integrin activation was confirmed in human fibroblasts with knocked-down FAK expression. The FAK autophosphorylation Y397 site was required for the enhancements in adhesion strengthening and integrin-binding responses. This work demonstrates a novel role for FAK in integrin activation and the time-dependent generation of cell–ECM forces.