bluuebunny/crossref_metadata_2025 huggingface dataset:
Synoptic airborne thickness surveys reveal state of Arctic sea ice cover
Authors: Haas Christian , Hendricks Stefan , Eicken Hajo , Herber Andreas
Published: May 2010

While summer Arctic sea‐ice extent has decreased over the past three decades, it is subject to large interannual and regional variations. Methodological challenges in measuring ice thickness continue to hamper our understanding of the response of the ice‐thickness distribution to recent change, limiting the ability to forecast sea‐ice change over the next decade. We present results from a 2400 km long pan‐Arctic airborne electromagnetic (EM) ice thickness survey in April 2009, the first‐ever large‐scale EM thickness dataset obtained by fixed‐wing aircraft over key regions of old ice in the Arctic Ocean between Svalbard and Alaska. The data provide detailed insight into ice thickness distributions characteristic for the different regions. Comparison with previous EM surveys shows that modal thicknesses of old ice had changed little since 2007, and remained within the expected range of natural variability.
Wind‐controlled export of Antarctic Bottom Water from the Weddell Sea
Authors: Jullion L. , Jones S. C. , Naveira Garabato A. C. , Meredith M. P.
Published: May 2010

Recent studies suggest that the variability in Antarctic Bottom Water (AABW) properties in the Scotia Sea on time scales up to decadal may be linked to changes in the baroclinicity of the Weddell gyre, with vertical variations in the density structure at the gyre's northern edge acting to control the export of AABW over the South Scotia Ridge and toward the mid‐latitude South Atlantic. We test this hypothesis by analysing the AABW properties in fifteen occupations of the SR1b hydrographic section (1993–2009) in eastern Drake Passage alongside possible forcings as derived from atmospheric reanalysis data. We show that variability in the wind stress over the Weddell gyre leads changes in AABW properties in the SR1b section by approximately five months. The sign of the lagged correlation is consistent with the notion of the AABW export from the Weddell Sea being controlled by the gyre's baroclinic adjustment to wind forcing on time scales of several months. Variability in the regional winds is found to be closely linked to the Southern Annular Mode (SAM). These results suggest that there may be a causal relationship between the SAM's positive tendency observed in recent decades and the subsequent warming of AABW detected across much of the Atlantic Ocean.
Nighttime‐like quasi periodic echoes induced by a partial solar eclipse
Authors: Thampi Smitha V. , Yamamoto Mamoru , Liu Huixin , Saito Susumu , Otsuka Yuichi , Patra Amit Kumar
Published: May 2010

The first observations of solar eclipse induced mid‐latitude plasma irregularities using the middle and upper atmosphere radar (MU radar) at Shigaraki (34.85°N,136.1°E, 25.0°N geomagnetic) are presented. The observations were done during the partial solar eclipse on 22 July, 2009. The observations show that the sudden withdrawal of solar radiation could deplete the background E‐region densities, thereby unmasking the long‐lived metallic ions within the strong and patchy Sporadic E‐layers. As a result of this, Quasi‐Periodic (QP) echoes were generated, which were detected by the MU radar. These echoes resemble the normal post‐sunset QP echoes observed over mid‐latitudes as revealed by the multi‐channel interfereometry imaging. This example shows that over mid‐latitudes E‐region plasma irregularities can be generated during a partial solar eclipse, revealing a hitherto unobserved aspect of mid‐latitude ionospheric responses to eclipses.
Weekend effect: Anthropogenic or natural?
Authors: Kim Kwang‐Yul , Park Rokjin J. , Kim Kyung‐Ryul , Na Hanna
Published: May 2010

Human activities have been suggested to result in weekly changes of meteorological variables, called the “weekend effect.” Recent debates on its statistical significance, however, reveal that there still remain huge uncertainties as to the anthropogenic origin of the weekend effect. We show that atmospheric Rossby waves induce the “natural” weekend effect, which is much stronger than the “anthropogenic” weekend effect. The “natural” weekend effect does not completely disappear even with averaging over 61 years of data; as a result, true “anthropogenic” weekend effect is obscured by the natural component. We attempted to remove the “natural” component in the diurnal temperature range and the resulting pattern is an overall positive weekend effect over North America.
Temporal dynamics of Prochlorococcus ecotypes in the Atlantic and Pacific oceans
Authors: Malmstrom Rex R , Coe Allison , Kettler Gregory C , Martiny Adam C , Frias-Lopez Jorge , Zinser Erik R , Chisholm Sallie W
Published: May 2010

To better understand the temporal and spatial dynamics of Prochlorococcus populations, and how these populations co-vary with the physical environment, we followed monthly changes in the abundance of five ecotypes—two high-light adapted and three low-light adapted—over a 5-year period in coordination with the Bermuda Atlantic Time Series (BATS) and Hawaii Ocean Time-series (HOT) programs. Ecotype abundance displayed weak seasonal fluctuations at HOT and strong seasonal fluctuations at BATS. Furthermore, stable ‘layered’ depth distributions, where different Prochlorococcus ecotypes reached maximum abundance at different depths, were maintained consistently for 5 years at HOT. Layered distributions were also observed at BATS, although winter deep mixing events disrupted these patterns each year and produced large variations in ecotype abundance. Interestingly, the layered ecotype distributions were regularly reestablished each year after deep mixing subsided at BATS. In addition, Prochlorococcus ecotypes each responded differently to the strong seasonal changes in light, temperature and mixing at BATS, resulting in a reproducible annual succession of ecotype blooms. Patterns of ecotype abundance, in combination with physiological assays of cultured isolates, confirmed that the low-light adapted eNATL could be distinguished from other low-light adapted ecotypes based on its ability to withstand temporary exposure to high-intensity light, a characteristic stress of the surface mixed layer. Finally, total Prochlorococcus and Synechococcus dynamics were compared with similar time series data collected a decade earlier at each location. The two data sets were remarkably similar—testimony to the resilience of these complex dynamic systems on decadal time scales.
Meiofauna reduces bacterial mineralization of naphthalene in marine sediment
Authors: Näslund Johan , Nascimento Francisco J A , Gunnarsson Jonas S
Published: May 2010

The role of sediment-living meiofauna, benthic invertebrates smaller than 1000 μm such as nematodes and ostracods, on the mineralization of naphthalene, a common polycyclic aromatic hydrocarbon (PAH) in marine sediments, was studied in microcosms using radiorespirometry. A method to extract live meiofauna was developed and used in order to experimentally manipulate meiofauna abundance and group diversity. Higher abundances of meiofauna were found to significantly decrease naphthalene mineralization. Furthermore, a change in the bacterial community composition (studied using terminal restriction fragment length polymorphism) was also observed in presence of higher meiofauna abundance, as well as a lower number of cultivable naphthalene-degrading bacteria. The reduced mineralization of naphthalene and the altered bacterial community composition in the presence of increased meiofauna abundance is likely the result of top-down control by meiofauna. This study shows that higher abundances of meiofauna can significantly decrease the microbial mineralization of PAHs such as naphthalene and also significantly modify the bacterial community composition in natural marine sediments.
Vertebral Bone Marrow Fat Is Positively Associated With Visceral Fat and Inversely Associated With IGF‐1 in Obese Women
Authors: Bredella Miriam A. , Torriani Martin , Ghomi Reza Hosseini , Thomas Bijoy J. , Brick Danielle J. , Gerweck Anu V. , Rosen Clifford J. , Klibanski Anne , Miller Karen K.
Published: May 2010

Recent studies have demonstrated an important physiologic link between bone and fat. Bone and fat cells arise from the same mesenchymal precursor cell within bone marrow, capable of differentiation into adipocytes or osteoblasts. Increased BMI appears to protect against osteoporosis. However, recent studies have suggested detrimental effects of visceral fat on bone health. Increased visceral fat may also be associated with decreased growth hormone (GH) and insulin‐like growth factor 1 (IGF‐1) levels which are important for maintenance of bone homeostasis. The purpose of our study was to assess the relationship between vertebral bone marrow fat and trabecular bone mineral density (BMD), abdominal fat depots, GH and IGF‐1 in premenopausal women with obesity. We studied 47 premenopausal women of various BMI (range: 18–41 kg/m2, mean 30 ± 7 kg/m2) who underwent vertebral bone marrow fat measurement with proton magnetic resonance spectroscopy (1H‐MRS), body composition, and trabecular BMD measurement with computed tomography (CT), and GH and IGF‐1 levels. Women with high visceral fat had higher bone marrow fat than women with low visceral fat. There was a positive correlation between bone marrow fat and visceral fat, independent of BMD. There was an inverse association between vertebral bone marrow fat and trabecular BMD. Vertebral bone marrow fat was also inversely associated with IGF‐1, independent of visceral fat. Our study showed that vertebral bone marrow fat is positively associated with visceral fat and inversely associated with IGF‐1 and BMD. This suggests that the detrimental effect of visceral fat on bone health may be mediated in part by IGF‐1 as an important regulator of the fat and bone lineage.
Rosiglitazone Improves Glucose Metabolism in Obese Adolescents With Impaired Glucose Tolerance: A Pilot Study
Authors: Cali Anna M.G. , Pierpont Bridget M. , Taksali Sara E. , Allen Karin , Shaw Melissa M. , Savoye Mary , Caprio Sonia
Published: May 2010

Impaired glucose tolerance (IGT) is a prediabetic state fueling the rising prevalence of type 2 diabetes mellitus (T2DM) in adolescents with marked obesity. Given the importance of insulin resistance, the poor β‐cell compensation and the altered fat partitioning as underlying defects associated with this condition, it is crucial to determine the extent to which these underlying abnormalities can be reversed in obese adolescents. We tested, in a pilot study, whether rosiglitazone (ROSI) restores normal glucose tolerance (NGT) in obese adolescents with IGT by improving insulin sensitivity and β‐cell function. In a small randomized, double‐blind, placebo (PLA)‐controlled study, lasting 4 months, 21 obese adolescents with IGT received either ROSI (8 mg daily) (n = 12, 5M/7F, BMI z‐score 2.44 ± 0.11) or PLA (n = 9, 4M/5F, BMI z‐score 2.41 ± 0.09). Before and after treatment, all subjects underwent oral glucose tolerance test (OGTT), hyperinsulinemic‐euglycemic clamp, magnetic resonance imaging, and 1H NMR assessment. After ROSI treatment, 58% of the subjects converted to NGT compared to 44% in the PLA group (P = 0.528). Restoration of NGT was associated with a significant increase in insulin sensitivity (P < 0.04) and a doubling in the disposition index (DI) (P < 0.04), whereas in the PLA group, these changes were not significant. The short‐term use of ROSI appears to be safe in obese adolescents with IGT. ROSI restores NGT by increasing peripheral insulin sensitivity and β‐cell function, two principal pathophysiological abnormalities of IGT.
Cohesin: a regulator of genome integrity and gene expression
Authors: Feeney Katherine M. , Wasson Christopher W. , Parish Joanna L.
Published: May 2010

Following DNA replication, chromatid pairs are held together by a proteinacious complex called cohesin until separation during the metaphase-to-anaphase transition. Accurate segregation is achieved by regulation of both sister chromatid cohesion establishment and removal, mediated by post-translational modification of cohesin and interaction with numerous accessory proteins. Recent evidence has led to the conclusion that cohesin is also vitally important in the repair of DNA lesions and control of gene expression. It is now clear that chromosome segregation is not the only important function of cohesin in the maintenance of genome integrity.
Expression of oestrogen receptor β isoforms is regulated by transcriptional and post-transcriptional mechanisms
Authors: Smith Laura , Coleman Louise J. , Cummings Michele , Satheesha Sampoorna , Shaw Spencer O. , Speirs Valerie , Hughes Thomas A.
Published: May 2010

Although ERs (oestrogen receptors) mediate breast tumour behaviour, the precise role of ERβ remains unclear. This is mainly because analyses have been complicated by the presence in breast tissue of three ERβ protein variants (ERβ1, ERβ2 and ERβ5) that derive from differential 3′ splicing. We have recently identified the first known mechanisms responsible for the differential control of isoform expression, involving regulation of translation via 5′-UTRs (untranslated regions). In the present study, we have uncovered further complexity involving the influence of multiple promoters and cross-talk between 5′- and 3′-UTRs. We demonstrate that full-length ERβ mRNAs are transcribed from three separate promoters; two promoters are well-established within the literature, whereas the third represents a novel finding. Each promoter produces transcripts with distinct 5′-UTRs. The differential 3′ splicing that produces transcripts coding for the ERβ isoforms also defines isoform-specific 3′-UTRs. We identified exact 3′-UTR sequences for each isoform, and have shown that alternative polyadenylation sites are used in a cell-type specific manner to produce transcripts with 3′-UTRs of different lengths. Critically, we show that 5′- and 3′-UTRs combine to specify the efficiencies with which individual transcripts are translated, with 3′-UTR length having a key influence. In addition, we demonstrate how 17β-oestradiol, a key driver of breast cancer development, affects the regulation of ERβ expression at both transcriptional and translational levels.
La
(
Fe
,
Co
,
Si
)
13
bulk alloys and ribbons with high temperature magnetocaloric effect
Authors: Jasinski M. , Liu J. , Jacobs S. , Zimm C.
Published: May 2010

La ( Fe 1 − x − y Co x Si y ) 13 ingots with x=0.112, 0.154, and 0.170 and y=0.021, 0.042, 0.063, and 0.085 were processed by Ar arc melting and annealing at 1050 °C for different periods of time up to 12 days. For y=0.085, the Curie temperature of the specimens, optimally annealed to develop the cubic NaZn13-type phase, increases from 88 to 149, and 169 °C for x=0.112, 0.154, and 0.170, respectively. By adding La excess, it becomes more facile to eliminate the secondary bcc (Fe,Co) phase by annealing at 1050 °C, while the structure contains more La(Fe,Co)Si nonmagnetic precipitates. With the decrease in the Si content, it becomes harder to form the La(Fe,Co,Si)13 phase and the morphology of secondary phases are more complex with La(Fe,Co)Si precipitates in form of stripes within La3Co inclusions. Selected La(Fe0.745Co0.17Si0.085)13 ribbons prepared by melt spinning and annealed for a shorter time than ingots maintain residual bcc (Fe,Co) phase. The largest peak in magnetic entropy change occurred at 161 °C with 3.5 J/kg K for La(Fe0.767Co0.170Si0.063)13 specimens with the optimal 1:13 structure, under a field variation of 17 kOe. The peak of magnetic entropy change in annealed ribbons was smaller and broader than in the annealed ingot counterparts.
Ab initio study on copper ferrite
Authors: Feng Min , Yang Aria , Zuo Xu , Vittoria Carmine , Harris Vincent G.
Published: May 2010

The impact of cation distribution on electronic structure and magnetic properties is investigated by the first-principle calculation. The structure optimization is based on generalized gradient approximation (GGA) exchange-correlation and projector augmented wave method. The optimized structures of inverse and normal copper ferrite are tetragonal (c/a=1.06) and cubic, respectively. The optimized structure of partial inverse copper ferrites can be cubic, tetragonal, or triclinic depending on the distribution of copper ions. The calculation of electronic structure is based on full potential linear augmented plane wave method and GGA+U exchange-correlation. The calculated density of states shows that the distribution of Cu ions impacts the electronic structure significantly. The normal and inverse copper ferrite are half-metallic and semiconducting, respectively. The partial inverse copper ferrites are metallic or half-metallic.
Interfacial and bulk order in polycrystalline exchange bias systems
Authors: Kaeswurm B. , O’Grady K.
Published: May 2010

A study of the effect of the setting conditions on the two coercive fields HC1 and HC2 in an exchange bias system is presented. The study was performed on a polycrystalline thin film sample of composition Si/Cu(5 nm)/IrMn(10 nm)/CoFe(2 nm)/Ta(5 nm) with a median blocking temperature ⟨TB⟩=240 K. An experiment analogous to a thermoremanence experiment, where order is quenched in by field cooling, is compared to a setting field experiment at constant temperature. These processes can be used to probe the order of the interfacial spin clusters and the bulk of the antiferromagnet. HC1 and HC2 follow different setting temperature dependences, indicating that different mechanisms are dominant in the two branches of the loop.
Fabrication and magnetic properties of Fe nanostructures in anodic alumina membrane
Authors: Lim J.-H. , Chae W.-S. , Lee H.-O. , Malkinski L. , Min S.-G. , Wiley J. B. , Jun J.-H. , Lee S.-H. , Jung J.-S.
Published: May 2010

Several Fe nanostructures with different lengths, diameters, and separations of the constituting magnetic components have been synthesized using anodized alumina membranes (AAMs) to understand the influence of these parameters on their magnetic properties. Fe nanostructures with high crystallinity and (110) orientation were synthesized by electrodeposition at room temperature in regular AAMs and mild-hard AAM (Mi-Ha AAM). Fe nanostructures with different aspect ratios (1:1, 1:10, and 1:75) in the form of nanodots, nanorods, or nanowires were synthesized in regular AAMs with the 100 nm interpore distance. Mi-Ha AAMs with two different pore sizes (70 and 120 nm) and 250 nm interpore distances were used to investigate the effect of the interactions and of the diameter of the wires on their magnetic behavior. Nearly linear magnetization characteristics with small coercivity, observed for Fe nanowires, suggest the magnetization rotation to be the predominant magnetization process for the field applied transverse to the wires. The anisotropy of the arrays was governed by the shape anisotropy of the magnetic objects with different aspect ratios. Reduced interactions between the nanowires grown in Mi-Ha AAMs resulted in enhancement of the average anisotropy. It is believed that due to difference in spin configuration, the increased diameter of the nanowires led to reduction in the coercivity in the case of the field applied along the wires.
Synthesis and magnetic properties of platelet Fe–Co particles
Authors: Hiyama Hisanori , Kodama Daisuke , Matsumoto Takatoshi , Shinoda Kozo , Kasuya Ryo , Balachandran Jeyadevan
Published: May 2010

The synthesis scheme for hexagonal shaped Fe–Co platelets with magnetic properties comparable to the bulk is reported for the first time. The hexagonal Fe–Co platelets with the size of about 8 μm and an aspect ratio of about 5.4 were prepared by reducing the platelet shaped intermediate obtained in ethylene glycol-metal salts-sodium hydroxide system. The saturation magnetization and coercivity of the Fe–Co hexagonal platelets obtained by reducing the solid intermediate at 673 K in hydrogen atmosphere were above 220 emu/g and 25 Oe, respectively. Since the use of such particles in high frequency applications demand further reduction in size and increment in aspect ratio, a synthesis scheme for particle morphology control was devised. The proposed synthesis scheme using nucleating agents clearly demonstrated that the shape, size, and aspect ratio of the platelets can be controlled freely. Consequently, platelets with elongated shape and thickness of about few hundred nanometers were produced. Though further reduction in size and aspect ratio is demanded, the proposed synthesis scheme holds promise for the development of Fe–Co platelet particles suitable for high frequency applications.
Droplet electric separator microfluidic device for cell sorting
Authors: Guo Feng , Ji Xing-Hu , Liu Kan , He Rong-Xiang , Zhao Li-Bo , Guo Zhi-Xiao , Liu Wei , Guo Shi-Shang , Zhao Xing-Zhong
Published: May 2010

A simple and effective droplet electric separator microfluidic device was developed for cell sorting. The aqueous droplet without precharging operation was influenced to move a distance in the channel along the electric field direction by applying dc voltage on the electrodes beside the channel, which made the target droplet flowing to the collector. Single droplet can be isolated in a sorting rate of ∼100 Hz with microelectrodes under a required pulse. Single or multiple mammalian cell (HePG2) encapsulated in the surfactant free alginate droplet could be sorted out respectively. This method may be used for single cell operation or analysis.
Abrupt dimensionality crossover in thin-film ferromagnets: Quantum size effect
Authors: Bramfeld T. S. , Won H. , Willis Roy F.
Published: May 2010

We report experimental results which show that the order parameter β, which determines the long-range (spin) ordering in magnetic thin films [M∝(1−T/TC)β], changes abruptly due to a crossover in dimensionality at different thicknesses in Ni(100), Ni(110), and Ni(111) films. We argue that the different critical thicknesses arise from finite-size quantization energies of the (spin) excitations, which are dependent on the magnitudes of associated wave vectors spanning the different crystallographic directions of the fcc Fermi surface. Experimental data on Ni alloys support this view.
High magnetic permeability of ε-GaxFe2−xO3 magnets in the millimeter wave region
Authors: Namai Asuka , Kurahashi Shinji , Hachiya Hiroshi , Tomita Kohtaro , Sakurai Shunsuke , Matsumoto Kazuyuki , Goto Takashi , Ohkoshi Shin-ichi
Published: May 2010

In this study, the magnetic permeability of a series of metal substituted ε-Fe2O3 was first measured. The electromagnetic wave absorption properties were measured in the region of 50–75 GHz (V band), and the materials exhibited absorption peaks at 64 GHz (ε-Ga0.51Fe1.49O3), 59 GHz (ε-Ga0.56Fe1.44O3), and 55 GHz (ε-Ga0.61Fe1.39O3). From the reflectance and transmittance measurements, the magnetic permeability (μ′-jμ″) and dielectric constant (ε′-jε″) of ε-GaxFe2−xO3 were evaluated. The μ″ values of ε-GaxFe2−xO3 are the highest values among reported magnetic millimeter wave absorbers in the V-band region.
Noncontact evaluation of surface-modified materials by a model-assisted hysteresis measurement technique
Authors: Lo C. C. H.
Published: May 2010

This paper reports on a model-assisted magnetic hysteresis measurement method for noncontact characterization of surface-modified materials whose magnetic properties vary with depth. The technique involves measuring hysteresis loops from a test sample using a surface sensor probe in close proximity to the sample without any direct contact with it. The sensor outputs were simulated based on an extended magnetic hysteresis model to describe the magnetic hysteresis of the sample and its influence on the magnetic reluctance of the magnetic circuit. The technique was applied to characterize a series of surface hardened Fe–C samples with hardening depths ranging from 1.09 to 5.68 mm. The hysteresis behavior of the samples was modeled using a parametrized function to describe the depth profile of domain wall pinning strength. The midpoints of the inverted pinning strength profiles were found to agree with those of the measured hardness profiles, demonstrating the potential of the model-assisted technique for quantitative evaluation of surface-modified magnetic materials.
Magnetic and structural characterization of thiol capped ferromagnetic Ag nanoparticles
Authors: Goikolea E. , Garitaonandia J. S. , Insausti M. , Gil de Muro I. , Suzuki M. , Uruga T. , Tanida H. , Suzuki K. , Ortega D. , Plazaola F. , Rojo T.
Published: May 2010

Dodecanethiol capped Ag nanoparticles (NPs) have been independently synthesized by the well-known Brust method under the same physical-chemical conditions. The obtained NP present similar sizes (∼2 nm) but different magnetic behaviors. The extended x-ray absorption fine structure analyses at the K-edge of Ag did not reveal any noticeable structural nor topological differences among the samples. In clear contrast with the structure provided for thiol capped ferromagnetic Au NPs, the analysis also brings out the existence of Ag–S bonds in a diffuse region surrounding a reduced Ag core where the magnetism of the Ag NPs would be located.
Size and composition control of core-shell structured iron/iron-oxide nanoparticles
Authors: Khurshid H. , Tzitzios V. , Li Wanfeng , Hadjipanayis C. G. , Hadjipanayis G. C.
Published: May 2010

Metallic iron nanoparticles with a crystalline iron oxide shell were synthesized by the thermal decomposition of iron pentacarbonyl [Fe(CO)5] in octadecene in the presence of oleic acid and oleylamine. The effect of different synthetic parameters was investigated in details including the refluxing time and temperature, the injection temperature of iron precursor and the surfactant concentrations. The particles size can be tuned by controlling the injection temperature of iron precursor. Particle composition was adjusted by controlling the refluxing time. Both XRD diffraction and magnetic measurements indicated that these particles are very stable against oxidation which was further evidenced by microstructure analysis.
Macroscopic Maxwell’s equations and negative index materials
Authors: Gralak B. , Tip A.
Published: May 2010

We study the linear phenomenological Maxwell’s equations in the presence of a polarizable and magnetizable medium (magnetodielectric). For a dispersive, nonabsorptive, medium with equal electric and magnetic permeabilities ε(ω) and μ(ω), the latter can assume the value of −1 (+1 is their vacuum value) for a discrete set of frequencies ±ω̂n, i.e., for these frequencies the medium behaves as a negative index material (NIM). We show that such systems have a well-defined time evolution. In particular, the fields remain square integrable (and the electromagnetic energy finite) if this is the case at some initial time. Next we turn to Green’s function G(x,y,z) (a tensor), associated with the electric Helmholtz operator for a set of parallel layers filled with a material. We express it in terms of the well-known scalar s and p ones. For a half space filled with the material and with a single dispersive Lorentz form for ε(ω)=μ(ω), we obtain an explicit form for G. We find the usual behavior for NIMs for ω=±ω̂, there is no refection outside the evanescent regime and the transmission (refraction) shows the usual NIM behavior. We find that G has poles in ±ω̂, which lead to a modulation of the radiative decay probability of an excited atom. The formalism is free from ambiguities in the sign of the refractive index.
On the existence of quantum representations for two dichotomic measurements
Authors: Fritz Tobias
Published: May 2010

Under which conditions do outcome probabilities of measurements possess a quantum-mechanical model? This kind of problem is solved here for the case of two dichotomic von Neumann measurements which can be applied repeatedly to a quantum system with trivial dynamics. The solution uses methods from the theory of operator algebras and the theory of moment problems. The ensuing conditions reveal surprisingly simple relations between certain quantum-mechanical probabilities. It also shown that generally, none of these relations holds in general probabilistic models. This result might facilitate further experimental discrimination between quantum mechanics and other general probabilistic theories.
Unique decompositions, faces, and automorphisms of separable states
Authors: Alfsen Erik , Shultz Fred
Published: May 2010

Let Sk be the set of separable states on B(Cm⊗Cn) admitting a representation as a convex combination of k pure product states, or fewer. If m>1, n>1, and k⩽max(m,n), we show that Sk admits a subset Vk such that Vk is dense and open in Sk, and such that each state in Vk has a unique decomposition as a convex combination of pure product states, and we describe all possible convex decompositions for a set of separable states that properly contains Vk. In both cases we describe the associated faces of the space of separable states, which in the first case are simplexes, and in the second case are direct convex sums of faces that are isomorphic to state spaces of full matrix algebras. As an application of these results, we characterize all affine automorphisms of the convex set of separable states and all automorphisms of the state space of B(Cm⊗Cn) that preserve entanglement and separability.
Dust ion acoustic solitons in a plasma with kappa-distributed electrons
Authors: Baluku T. K. , Hellberg M. A. , Kourakis I. , Saini N. S.
Published: May 2010

Dust ion acoustic solitons in an unmagnetized dusty plasma comprising cold dust particles, adiabatic fluid ions, and electrons satisfying a κ distribution are investigated using both small amplitude and arbitrary amplitude techniques. Their existence domain is discussed in the parameter space of Mach number M and electron density fraction f over a wide range of values of κ. For all κ>3/2, including the Maxwellian distribution, negative dust supports solitons of both polarities over a range in f. In that region of parameter space solitary structures of finite amplitude can be obtained even at the lowest Mach number, the acoustic speed, for all κ. These cannot be found from small amplitude theories. This surprising behavior is investigated, and it is shown that fc, the value of f at which the KdV coefficient A vanishes, plays a critical role. In the presence of positive dust, only positive potential solitons are found.
The electrostatics of solvent and membrane interfaces and the role of electronic polarizability
Authors: Vorobyov Igor , Allen Toby W.
Published: May 2010

The electrostatics of solvent and lipid bilayer interfaces are investigated with the aim of understanding the interaction of ions and charged peptides with biological membranes. We overcome the lacking dielectric response of hydrocarbon by carrying out atomistic molecular dynamics simulations using a polarizable model. For air-solvent or solvent-solvent interfaces, the effect of polarizability itself is small, yet changes in the fixed atomic charge distribution are responsible for substantial changes in the potential. However, when electrostatics is probed by finite solutes, a cancellation of dominant quadrupolar terms from the macroscopic and microscopic (solute-solvent) interfaces eliminates this dependence and leads to small net contributions to partitioning thermodynamics. In contrast, the membrane dipole potential exhibits considerable dependence on lipid electronic polarizability, due to its dominant dipolar contribution. We report the dipole potential for a polarizable lipid hydrocarbon membrane model of 480–610 mV, in better accord with experimental measurements.
Direct spectral phase measurement with Spectral Interferometry Resolved in Time Extra Dimensional
Authors: Bigourd D. , Luce J. , Mazataud E. , Hugonnot E. , Rouyer C.
Published: May 2010

The complete spectral characterization of ultrashort pulses is demonstrated with a new diagnostic called Spectral Interferometry Resolved in Time Extra Dimensional. This method, based on spectral shearing interferometry, is self-referenced and self-calibrated. It yields directly to an interferogram pattern displaying an intuitive representation of the derivative of the spectral phase. No iterative algorithm is needed for phase measurement making this method suitable for real time and easy characterization. This technique is highlighted by the spectral phase characterization of pulses out of a folded nondispersive line and the pulse shape is compared with a trace recorded with an intensity autocorrelator.
Count of eigenvalues in the generalized eigenvalue problem
Authors: Chugunova Marina , Pelinovsky Dmitry
Published: May 2010

We study isolated and embedded eigenvalues in the generalized eigenvalue problem defined by two self-adjoint operators with a positive essential spectrum and a finite number of isolated eigenvalues. The generalized eigenvalue problem determines the spectral stability of nonlinear waves in infinite-dimensional Hamiltonian systems. The theory is based on Pontryagin’s invariant subspace theorem and extends beyond the scope of earlier papers of Pontryagin, Krein, Grillakis, and others. Our main results are (i) the number of unstable and potentially unstable eigenvalues equals the number of negative eigenvalues of the self-adjoint operators, (ii) the total number of isolated eigenvalues of the generalized eigenvalue problem is bounded from above by the total number of isolated eigenvalues of the self-adjoint operators, and (iii) the quadratic forms defined by the two self-adjoint operators are strictly positive on the subspace related to the continuous spectrum of the generalized eigenvalue problem. Applications to the localized solutions of the nonlinear Schrödinger equations are developed from the general theory.
Theoretical studies of acrolein hydrogenation on Au20 nanoparticle
Authors: Li Zhe , Chen Zhao-Xu , He Xiang , Kang Guo-Jun
Published: May 2010

Gold nanoparticles play a key role in catalytic processes. We investigated the kinetics of stepwise hydrogenation of acrolein on Au20 cluster model and compared with that on Au(110) surface. The rate-limiting step barrier of CC reduction is about 0.5 eV higher than that of CO hydrogenation on Au(110) surface. On Au20 nanoparticle, however, the energy barrier of the rate-determining step for CC hydrogenation turns out to be slightly lower than the value for the CO reduction. The selectivity difference on the two substrate models are attributed to different adsorption modes of acrolein: via the CC on Au20, compared to through both CC and CO on Au(110). The preference switch implies that the predicted selectivity of competitive hydrogenation depends on substrate model sensitively, and particles with more low-coordinated Au atoms than flat surfaces are favorable for CC hydrogenation, which is in agreement with experimental result.
Flow, turbulence, and pollutant dispersion in urban atmospheres
Authors: Fernando H. J. S. , Zajic D. , Di Sabatino S. , Dimitrova R. , Hedquist B. , Dallman A.
Published: May 2010

The past half century has seen an unprecedented growth of the world’s urban population. While urban areas proffer the highest quality of life, they also inflict environmental degradation that pervades a multitude of space-time scales. In the atmospheric context, stressors of human (anthropogenic) origin are mainly imparted on the lower urban atmosphere and communicated to regional, global, and smaller scales via transport and turbulence processes. Conversely, changes in all scales are transmitted to urban regions through the atmosphere. The fluid dynamics of the urban atmospheric boundary layer and its prediction is the theme of this overview paper, where it is advocated that decision and policymaking in urban atmospheric management must be based on integrated models that incorporate cumulative effects of anthropogenic forcing, atmospheric dynamics, and social implications (e.g., health outcomes). An integrated modeling system juxtaposes a suite of submodels, each covering a particular range of scales while communicating with models of neighboring scales. Unresolved scales of these models need to be parametrized based on flow physics, for which developments in fluid dynamics play an indispensible role. Illustrations of how controlled laboratory, outdoor (field), and numerical experiments can be used to understand and parametrize urban atmospheric processes are presented, and the utility of predictive models is exemplified. Field experiments in real urban areas are central to urban atmospheric research, as validation of predictive models requires data that encapsulate four-dimensional complexities of nature.
Perpendicular propagating electromagnetic envelope solitons in electron-positron-ion plasma
Authors: Jehan Nusrat , Salahuddin M. , Mirza Arshad M.
Published: May 2010

The nonlinear amplitude modulation of electromagnetic waves propagating perpendicular to the direction of ambient magnetic field in a uniform collisionless magnetized electron-positron-ion plasma is studied. The Krylov–Bogoliubov–Mitropolsky perturbation method is employed to derive nonlinear Schrödinger equation, which describes the amplitude dynamics of perturbed magnetic field. The modulation instability criterion reveals that the low frequency mode is always stable, whereas the high frequency mode becomes modulationally unstable for certain ranges of wave number and positron-to-electron density ratio. Furthermore, the positron-to-electron density ratio as well as the strength of ambient magnetic field is found to have significant effect on the solitary wave solutions of the nonlinear Schrödinger equation, namely, dark and bright envelope solitons.
Absorption/expulsion of oligomers and linear macromolecules in a polymer brush
Authors: Milchev A. , Egorov S. A. , Binder K.
Published: May 2010

The absorption of free linear chains in a polymer brush was studied with respect to chain size L and compatibility ψ with the brush by means of Monte Carlo (MC) simulations and density functional theory (DFT)/self-consistent field theory (SCFT) at both moderate, σg=0.25, and high, σg=1.00, grafting densities using a bead-spring model. Different concentrations of the free chains 0.0625≤ϕo≤0.375 are examined. Contrary to the case of ψ=0 when all species are almost completely ejected by the polymer brush irrespective of their length L, for ψ<0 we find that the degree of absorption (absorbed amount) Γ(L) undergoes a sharp crossover from weak to strong (≈100%) absorption, discriminating between oligomers, 1≤L≤8, and longer chains. For a moderately dense brush, σg=0.25, the longer species, L>8, populate predominantly the deep inner part of the brush, whereas in a dense brush σg=1.00 they penetrate into the “fluffy” tail of the dense brush only. Gyration radius Rg and end-to-end distance Re of absorbed chains thereby scale with length L as free polymers in the bulk. Using both MC and DFT/SCFT methods for brushes of different chain length 32≤N≤256, we demonstrate the existence of unique critical value of compatibility ψ=ψc<0. For ψc(ϕo) the energy of free chains attains the same value, irrespective of length L whereas the entropy of free chain displays a pronounced minimum. At ψc all density profiles of absorbing chains with different L intersect at the same distance from the grafting plane. The penetration/expulsion kinetics of free chains into the polymer brush after an instantaneous change in their compatibility ψ displays a rather rich behavior. We find three distinct regimes of penetration kinetics of free chains regarding the length L: I (1≤L≤8), II (8≤L≤N), and III (L>N), in which the time of absorption τ grows with L at a different rate. During the initial stages of penetration into the brush one observes a power-law increase of Γ∝tα with power α∝−ln ϕo, whereby penetration of the free chains into the brush gets slower as their concentration rises.
Hyperfine coupling constants of the nitrogen and phosphorus atoms: A challenge for exact-exchange density-functional and post-Hartree–Fock methods
Authors: Kaupp Martin , Arbuznikov Alexei V. , Heßelmann Andreas , Görling Andreas
Published: May 2010

The isotropic hyperfine coupling constants of the free N(S4) and P(S4) atoms have been evaluated with high-level post-Hartree–Fock and density-functional methods. The phosphorus hyperfine coupling presents a significant challenge to both types of methods. With large basis sets, MP2 and coupled-cluster singles and doubles calculations give much too small values for the phosphorus atom. Triple excitations are needed in coupled-cluster calculations to achieve reasonable agreement with experiment. None of the standard density functionals reproduce even the correct sign of this hyperfine coupling. Similarly, the computed hyperfine couplings depend crucially on the self-consistent treatment in exact-exchange density-functional theory within the optimized effective potential (OEP) method. Well-balanced auxiliary and orbital basis sets are needed for basis-expansion exact-exchange-only OEP approaches to come close to Hartree–Fock or numerical OEP data. Results from the localized Hartree–Fock and Krieger–Li–Iafrate approximations deviate notably from exact OEP data in spite of very similar total energies. Of the functionals tested, only full exact-exchange methods augmented by a correlation functional gave at least the correct sign of the P(S4) hyperfine coupling but with too low absolute values. The subtle interplay between the spin-polarization contributions of the different core shells has been analyzed, and the influence of even very small changes in the exchange-correlation potential could be identified.
Attenuation of the wake of a sphere in an intense incident turbulence with large length scales
Authors: Amoura Zouhir , Roig Véronique , Risso Frédéric , Billet Anne-Marie
Published: May 2010

We report an investigation of the wake of a sphere immersed in a uniform turbulent flow for sphere Reynolds numbers ranging from 100 to 1000. An original experimental setup has been designed to generate a uniform flow convecting an isotropic turbulence. At variance with previous works, the integral length scale of the turbulence is of the same order as the sphere diameter and the turbulence intensity is large. In consequence, the most intense turbulent eddies are capable of influencing the flow in the close vicinity of the sphere. Except in the attached region downstream of the sphere where the perturbation of the mean velocity is larger than the standard deviation of the incident turbulence, the flow is controlled by the incident turbulence. The distortion of the turbulence while the flow goes round the sphere leads to an increase in the longitudinal fluctuation and a decrease in the transversal one. The attenuation of the transversal fluctuations is still significant at 30 radii downstream of the sphere whereas the longitudinal fluctuations relax more rapidly toward the incident value. The more striking result however concerns the evolution of the mean velocity defect with the distance x from the sphere. It decays as x−2 and scales with the standard deviation of the incident turbulence instead of scaling with the mean incident velocity.
Simulations of a non-Markovian description of nucleation
Authors: Kuipers J. , Barkema G. T.
Published: May 2010

In most nucleation theories, the state of a nucleating system is described by a distribution of droplet masses and this distribution evolves as a memoryless stochastic process. This is incorrect for a large class of nucleating systems. In a recent paper [J. Kuipers and G. T. Barkema, Phys. Rev. E 79, 062101 (2009)], we presented a non-Markovian model for droplet growth that includes memory effects and this model was treated analytically in the absence of a free energy landscape. In this paper, the model is considered with a free energy barrier present. Nucleation rates are measured in the prototypical example of nucleation in the Ising model. Results of direct simulations and the non-Markovian theory agree within a factor of 2 for spin-flip dynamics, and within 20% for local spin-exchange dynamics, even though the measured nucleation rates vary over 27 orders of magnitude.
Evolution of locally excited avalanches in semiconductors
Authors: Yuan Z. L. , Dynes J. F. , Sharpe A. W. , Shields A. J.
Published: May 2010

We show that semiconductor avalanche photodiodes can exhibit diminutive amplification noise during the early evolution of avalanches. The noise is so low that the number of locally excited charges that seed each avalanche can be resolved. These findings constitute an important step towards realization of a solid-state noiseless amplifier for quantum information processing. Moreover, we believe that the experimental setup used, i.e., time-resolving locally excited avalanches, will become a useful tool for optimizing the number resolution.
Semicrystalline woodpile photonic crystals without complicated alignment via soft lithography
Authors: Lee Jae-Hwang , Kuang Ping , Leung Wai , Kim Yong-Sung , Park Joong-Mok , Kang Henry , Constant Kristen , Ho Kai-Ming
Published: May 2010

We report the fabrication and characterization of woodpile photonic crystals with up to 12 layers through titania nanoparticle infiltration of a polymer template made by soft lithography. Because the complicated alignment in the conventional layer-by-layer fabrication associated with diamondlike symmetry is replaced by a simple 90° alignment, the fabricated photonic crystal has semicrystalline phase. However, the crystal performs similarly to a perfectly aligned crystal for the light propagation integrated from the surface normal to 30° at the main photonic band gap.
SAMRAI: A novel variably polarized angle-resolved photoemission beamline in the VUV region at UVSOR-II
Authors: Kimura Shin-Ichi , Ito Takahiro , Sakai Masahiro , Nakamura Eiken , Kondo Naonori , Horigome Toshio , Hayashi Kenji , Hosaka Masahito , Katoh Masahiro , Goto Tomohiro , Ejima Takeo , Soda Kazuo
Published: May 2010

A novel variably polarized angle-resolved photoemission spectroscopy beamline in the vacuum-ultraviolet (VUV) region has been installed at the UVSOR-II 750 MeV synchrotron light source. The beamline is equipped with a 3 m long APPLE-II type undulator with horizontally/vertically linear and right/left circular polarizations, a 10 m Wadsworth type monochromator covering a photon energy range of 6–43 eV, and a 200 mm radius hemispherical photoelectron analyzer with an electron lens of a ±18° acceptance angle. Due to the low emittance of the UVSOR-II storage ring, the light source is regarded as an entrance slit, and the undulator light is directly led to a grating by two plane mirrors in the monochromator while maintaining a balance between high-energy resolution and high photon flux. The energy resolving power (hν/Δhν) and photon flux of the monochromator are typically 1×104 and 1012 photons/s, respectively, with a 100 μm exit slit. The beamline is used for angle-resolved photoemission spectroscopy with an energy resolution of a few meV covering the UV-to-VUV energy range.