bluuebunny/crossref_metadata_2025 huggingface dataset:
RACIALIZED CRIME CONTROL AND SOCIETAL EXCLUSION
Authors: Ward Geoff K.
Published: June 2012

In 1930, W. E. B. Du Bois warned of an approaching backlash of racialized crime control and the two-pronged threat this posed to Black civil society. These were not altogether new threats—American criminal law and crime control practices had always been mechanisms of racialized societal exclusion—but Du Bois anticipated unprecedented levels of Black criminalization and incarceration in the second half of the twentieth century, and some of the collateral damage that would ensue. Du Bois's (1930) warning focused on juvenile crime and justice, “a problem which one can easily see among the better colored people of New York and Philadelphia, of Indianapolis and Chicago, of Pittsburgh and Baltimore, and all of our major cities” (p. 352). Du Bois (1916) had long been concerned with issues of child development and youth justice, since the fate of the “immortal child” inevitably defined the prospects and conditions of the race (Diggs 1976).
Maternal experiences of racial discrimination and child weight status in the first 3 years of life
Authors: Dixon B. , Rifas-Shiman S. L. , James-Todd T. , Ertel K. , Krieger N. , Kleinman K. P. , Rich-Edwards J. W. , Gillman M. W. , Taveras E. M.
Published: June 2012

Among US racial/ethnic minority women, we examined associations between maternal experiences of racial discrimination and child growth in the first 3 years of life. We analyzed data from Project Viva, a pre-birth cohort study. We restricted analyses to 539 mother–infant pairs; 294 were Black, 127 Hispanic, 110 Asian and 8 from additional racial/ethnic groups. During pregnancy, mothers completed the Experiences of Discrimination survey that measured lifetime experiences of racial discrimination in diverse domains. We categorized responses as 0, 1–2 or ⩾3 domains. Main outcomes were birth weight for gestational age z-score; weight for age (WFA) z-score at 6 months of age; and at 3 years of age, body mass index (BMI) z-score. In multivariable analyses, we adjusted for maternal race/ethnicity, nativity, education, age, pre-pregnancy BMI, household income and child sex and age. Among this cohort of mostly (58.2%) US-born and economically non-impoverished mothers, 33% reported 0 domains of discrimination, 33% reported discrimination in 1–2 domains and 35% reported discrimination in ⩾3 domains. Compared with children whose mothers reported no discrimination, those whose mothers reported ⩾3 domains had lower birth weight for gestational age z-score (β −0.25; 95% CI: −0.45, −0.04), lower 6 month WFA z-score (β −0.34; 95% CI: −0.65, −0.03) and lower 3-year BMI z-score (β −0.33; 95% CI: −0.66, 0.00). In conclusion, we found that among this cohort of US racial/ethnic minority women, mothers’ report of experiencing lifetime discrimination in ⩾ 3 domains was associated with lower fetal growth, weight at 6 months and 3-year BMI among their offspring.
Transient nature of Arctic spring systems driven by subglacial meltwater
Authors: Scheidegger J. M. , Bense V. F. , Grasby S. E.
Published: June 2012

In the High Arctic, supra‐ and proglacial springs occur at Borup Fiord Pass, Ellesmere Island. Spring waters are sulfur bearing and isotope analysis suggests springs are fed by deeply circulating glacial meltwater. However, the mechanism maintaining spring flow is unclear in these areas of thick permafrost which would hamper the discharge of deep groundwater to the surface. It has been hypothesized that fracture zones along faults focus groundwater which discharges initially underneath wet‐based parts of the ice. With thinning ice, the spring head is exposed to surface temperatures, tens of degrees lower than temperatures of pressure melting, and permafrost starts to develop. Numerical modeling of coupled heat and fluid flow suggest that focused groundwater discharge should eventually be cut off by permafrost encroaching into the feeding channel of the spring. Nevertheless, our model simulations show that these springs can remain flowing for millennia depending on the initial flow rate and ambient surface temperature. These systems might provide a terrestrial analog for the possible occurrence of Martian springs recharged by polar ice caps.
Mass loss of Larsen B tributary glaciers (Antarctic Peninsula) unabated since 2002
Authors: Berthier Etienne , Scambos Ted A. , Shuman Christopher A.
Published: June 2012

Ice mass loss continues at a high rate among the large glacier tributaries of the Larsen B Ice Shelf following its disintegration in 2002. We evaluate recent mass loss by mapping elevation changes between 2006 and 2010/11 using differencing of digital elevation models (DEMs). The measurement accuracy of these elevation changes is confirmed by a ‘null test’, subtracting DEMs acquired within a few weeks. The overall 2006–2010/11 mass loss rate (9.0 ± 2.1 Gt a−1) is similar to the 2001/02–2006 rate (8.8 ± 1.6 Gt a−1), derived using DEM differencing and laser altimetry. This unchanged overall loss masks a varying pattern of thinning and ice loss for individual glacier basins. On Crane Glacier, the thinning pulse, initially greatest near the calving front, is now broadening and migrating upstream. The largest losses are now observed for the Hektoria/Green glacier basin, having increased by 33% since 2006. Our method has enabled us to resolve large residual uncertainties in the Larsen B sector and confirm its state of ongoing rapid mass loss.
Flux estimates of ions from the lunar exosphere
Authors: Sarantos M. , Hartle R. E. , Killen R. M. , Saito Y. , Slavin J. A. , Glocer A.
Published: June 2012

We compare estimates for the ion fluxes of twelve expected constituents of the lunar exosphere with estimates for the ion fluxes ejected from the lunar surface by solar wind ions and electrons. Our estimates demonstrate that measurements of lunar ions will help constrain the abundances of many undetected species in the lunar exosphere, particularly Al and Si, because the expected ion flux levels from the exosphere exceed those from the surface. To correctly infer the relative abundances of exospheric ions and neutrals from Kaguya Ion Mass Analyzer (IMA) measurements, we must take into account the velocity distributions of local ions. The predicted spectrum underestimates the measured levels of O+ relative to other lunar ion species, a result that may suggest contributions by molecular ions to the measured O+ rates.
A thermo‐hydro‐mechanical coupled model in local thermal non‐equilibrium for fractured HDR reservoir with double porosity
Authors: Gelet R. , Loret B. , Khalili N.
Published: June 2012

The constitutive thermo‐hydro‐mechanical equations of fractured media are embodied in the theory of mixtures applied to three‐phase poroelastic media. The solid skeleton contains two distinct cavities filled with the same fluid. Each of the three phases is endowed with its own temperature. The constitutive relations governing the thermomechanical behavior, generalized diffusion and transfer are structured by, and satisfy, the dissipation inequality. The cavities exchange both mass and energy. Mass exchanges are driven by the jump in scaled chemical potential, and energy exchanges by the jump in coldness. The finite element approximation uses the displacement vector, the two fluid pressures and the three temperatures as primary variables. It is used to analyze a generic hot dry rock geothermal reservoir. Three parameters of the model are calibrated from the thermal outputs of Fenton Hill and Rosemanowes HDR reservoirs. The calibrated model is next applied to simulate circulation tests at the Fenton Hill HDR reservoir. The finer thermo‐hydro‐mechanical response provided by the dual porosity model with respect to a single porosity model is highlighted in a parameter analysis. Emphasis is put on the influence of the fracture spacing, on the effective stress response and on the permeation of the fluid into the porous blocks. The dual porosity model yields a thermally induced effective stress that is less tensile compared with the single porosity response. This effect becomes significant for large fracture spacings. In agreement with field data, fluid loss is observed to be high initially and to decrease with time.
Stress‐induced permeability evolution in a quasi‐brittle geomaterial
Authors: Massart T. J. , Selvadurai A. P. S.
Published: June 2012

This paper presents the application of a computational homogenization technique to examine the stress‐induced permeability evolution in a quasi‐brittle material susceptible to damage. The concepts involved in the constitutive modeling and the computational procedures are summarized. The developments are applied to investigate the response of the model in simulating experimental investigations of permeability evolution in a granitic rock. The influence of both the isotropic and the deviatoric stress states on the evolution of the spatially averaged permeability is derived from the computational simulations and is compared with experimental observations. It is shown that with the provision of supplemental material parameters the computational approach is able to satisfactorily match the experimental results.
Sea surface temperatures in cooler climate stages bear more similarity with atmospheric CO2 forcing
Authors: Das Sharma S. , Ramesh D. S. , Bapanayya C. , Raju P. A.
Published: June 2012

The interglacial Marine Isotope Stage (MIS) 11 received special attention due to its remarkable resemblance with present‐day climate. Based on synchronicity of marine, ice sheet and terrestrial proxy responses, warm episodes with intervening cool phase(s) at MIS 11 are qualitatively established. Here we quantitatively evaluate 15 climate proxies during 368–552 kyr intervals adopting a novel long‐range cross‐correlation approach and information theory based similarity measures. We also estimate the information flow rate and dominant flow direction between these climate variables using transfer entropy and the related directionality index. Our results unequivocally establish that atmospheric CO2 (pCO2) is the driving signal while all other proxies used in this study are the responses. The climate forcing greenhouse gas, the atmospheric CO2 (pCO2) and the response signals like sea surface temperature (SST) and carbon isotope composition of total organic carbon (δ13CTOC) proxies are strongly correlated (∼1 or −1) without significant observable time lag (less than 1 kyr). Various substages of MIS 11 are recognizable in the SST data alone based on normalized similarity measures. Additionally, eight more proxies from lacustrine sediments are identified as primary. During the cooler substages these proxies bear more similarity with ambient atmospheric pCO2. Thus, the information theory–based similarity measures suggest that atmospheric CO2 fluctuations are best captured by at least 9 climate proxies during cooler interglacial events. Based on the results related to interglacial MIS 11 and 13 obtained in this study, an important implication relevant to anthropogenic CO2input to the present‐day atmosphere can be distilled. It is that sensitive and better‐coupled response proxies such as SST and MAT, which already show an increasing trend, are likely to behave in a more dissimilar manner in future. That is, they tend to behave more independently in the near future (∼0.75 kyr).
Morphometry of Great Basin pluvial shore landforms: Implications for paleolake basins on Mars
Authors: Irwin Rossman P. , Zimbelman James R.
Published: June 2012

Many basins with relict contributing valley networks and outlet valleys in the Martian highlands indicate past flowing and ponded water on the surface. These likely paleolakes motivate an investigation of pluvial shore landforms in the Great Basin region of the western United States, as confident identification of strandlines on Mars would facilitate analyses of its past hydrology and climate. The purpose of this study is to characterize the scale of Late Pleistocene erosional and depositional shore landforms in an endorheic setting, determine the preservation potential of similar forms from multiple epochs in early Martian history, and identify the data products that would be necessary to detect them. We use Differential Global Positioning System field surveys to measure the dimensions and elevations of shore landforms; compare shore platform widths to theoretical maxima; and note the minimum scale of landforms that have survived since the Late Noachian and Early Hesperian Epochs on Mars. We find that due to impact gardening and aeolian erosion, Martian highland paleolakes like those in the pluvial Great Basin would likely not have well‐preserved shore landforms, unless they were unusually large and formed in the Late Hesperian or later. Individual strandlines are often not equally well expressed around an entire basin, so correlating shore landforms in plan view imaging and using their consistency in elevation as a hypothesis test for paleolakes can be challenging. Detection of younger shore landforms like those examined here would require meter‐resolution imaging and topography such as stereo digital elevation models.
On the application of simple rift basin models to the south polar region of Enceladus
Authors: Walker C. C. , Bassis J. N. , Liemohn M. W.
Published: June 2012

The south polar terrain (SPT) of Saturn's moon Enceladus is a mysteriously active region that exhibits intriguing tectonic signatures and widespread fracturing. The central region of the nearly‐circular SPT is depressed into the surface by a few hundred meters and bounded by a ring of cliffs roughly 1 km high. In this study, we investigate whether this depression and surrounding mountainous uplift is consistent with the morphology of terrestrial rift basins and the possibility that the SPT could have formed during a tectonic event analogous to those of such rift basins on Earth. Using three mechanical models of basin formation, we compare our predicted topography of the SPT with observed topography of the region. The first of three models we consider assumes crustal stretching by factor β, and predicts a basin depth of roughly 600 m, closely matching previously published estimates of the depth at the SPT. Models of extension and compression, assuming an elastic response in the ice crust, predict best‐fit mountain uplift of roughly 1820 m and 1130 m, respectively. Our preferred model suggests that the icy shell in the SPT has been stretched, but the extension is (partially) balanced by compression along the edges of the basin leading to the uplift of the mountains along the boundary, thereby implying that the SPT may have a tectonic origin analogous to that of a terrestrial basin.
Exploring the role of organic matter accumulation on delta evolution
Authors: Lorenzo‐Trueba Jorge , Voller Vaughan R. , Paola Chris , Twilley Robert R. , Bevington Azure E.
Published: June 2012

We explore the role of plant matter accumulation in the sediment column in determining the response of fluvial‐deltas to base‐level rise and simple subsidence profiles. Making the assumption that delta building processes operate to preserve the geometry of the delta plain, we model organic sedimentation in terms of the plant matter accumulation and accommodation (space made for sediment deposition) rates. A spatial integration of the organic sedimentation, added to the known river sediment input, leads to a model of delta evolution that estimates the fraction of organic sediments preserved in the delta. The model predicts that the maximum organic fraction occurs when the organic matter accumulation rate matches the accommodation rate, a result consistent with field observations. The model also recovers the upper limit for coal accumulation previously reported in the coal literature. Further, when the model is extended to account for differences in plant matter accumulation between fresh and saline environments (i.e., methanogenesis versus sulfate reduction) we show that an abrupt shift in the location of the fresh‐salt boundary can amplify the speed of shoreline retreat.
Sphingolipid Content of Human Adipose Tissue: Relationship to Adiponectin and Insulin Resistance
Authors: Blachnio‐Zabielska Agnieszka U. , Koutsari Christina , Tchkonia Tamara , Jensen Michael D.
Published: June 2012

Ceramides (Cer) are implicated in obesity‐associated skeletal muscle and perhaps adipocyte insulin resistance. We examined whether the sphingolipid content of human subcutaneous adipose tissue and plasma varies by obesity and sex as well as the relationship between ceramide content and metabolic indices. Abdominal subcutaneous adipose biopsies were performed on 12 lean adults (males = 6), 12 obese adults (males = 6) for measurement of sphingolipid content and activity of the main ceramide metabolism enzymes. Blood was sampled for glucose, insulin (to calculate homeostasis model assessment‐estimated insulin resistance (HOMAIR)) adiponectin, and interleukin‐6 (IL‐6) concentrations. Compared to lean controls, total ceramide content (pg/adipocyte) was increased by 31% (P < 0.05) and 34% (P < 0.05) in obese females and males, respectively. In adipocytes from obese adults sphingosine, sphinganine, sphingosine‐1‐phosphate, C14‐Cer, C16‐Cer, and C24‐Cer were all increased. C18:1‐Cer was increased in obese males and C24:1‐Cer in obese females. For women only, there was a negative correlation between C16‐Cer ceramide and plasma adiponectin (r = −0.77, P = 0.003) and a positive correlation between total ceramide content and HOMAIR (r = 0.74, P = 0.006). For men only there were significant (at least P < 0.05), positive correlations between adipocyte Cer‐containing saturated fatty acid and plasma IL‐6 concentration. We conclude that the sexual dimorphism in adipose tissue behavior in humans extends to adipose tissue sphingolipid content its association with adiponectin, IL‐6 and insulin resistance.
Impact of Information About Obesity Genomics on the Stigmatization of Overweight Individuals: An Experimental Study
Authors: Lippa Natalie C. , Sanderson Saskia C.
Published: June 2012

Advances in genomic technologies are rapidly leading to new understandings of the roles that genetic variations play in obesity. Increasing public dissemination of information regarding the role of genetics in obesity could have beneficial, harmful, or neutral effects on the stigmatization of obese individuals. This study used an online survey and experimental design to examine the impact of genetic versus non‐genetic information on obesity stigma among self‐perceived non‐overweight individuals. Participants (n = 396) were randomly assigned to read either genetic, non‐genetic (environment), or gene—environment interaction obesity causal information. A total of 48% of participants were female; mean age was 42.7 years (range = 18–86 years); 75% were white; 45.2% had an annual household income of less than $40,000; mean BMI was 23.4 kg/m2. Obesity stigma was measured using the Fat Phobia Scale — short form (FPS‐S). After reading the experimental information, participants in the genetic and gene—environment conditions were more likely to believe that genetics increase obesity risk than participants in the non‐genetic condition (both P < 0.05), but did not differ on obesity stigma. Obesity stigma was higher among whites and Asians than Hispanics and African Americans (P = 0.029), and associated with low self‐esteem (P = 0.036). Obesity stigma was also negatively associated with holding 'germ or virus' (P = 0.033) and 'overwork' (P = 0.016) causal beliefs about obesity, and positively associated with 'diet or eating habits' (P = 0.001) and 'lack of exercise' (P = 0.004) causal beliefs. Dissemination of brief information about the role of genetics in obesity may have neither a beneficial nor a harmful impact on obesity stigmatization compared with non‐genetic information among self‐perceived non‐overweight individuals.
Malaria parasite type 4 equilibrative nucleoside transporters (ENT4) are purine transporters with distinct substrate specificity
Authors: Frame I. J. , Merino Emilio F. , Schramm Vern L. , Cassera María B. , Akabas Myles H.
Published: June 2012

Malaria, caused by Plasmodia parasites, affects hundreds of millions of people. As purine auxotrophs, Plasmodia use transporters to import host purines for subsequent metabolism by the purine salvage pathway. Thus purine transporters are attractive drug targets. All sequenced Plasmodia genomes encode four ENTs (equilibrative nucleoside transporters). During the pathogenic intraerythrocytic stages, ENT1 is a major route of purine nucleoside/nucleobase transport. Another plasma membrane purine transporter exists because Plasmodium falciparum ENT1-knockout parasites survive at supraphysiological purine concentrations. The other three ENTs have not been characterized functionally. Codon-optimized Pf- (P. falciparum) and Pv- (Plasmodium vivax) ENT4 were expressed in Xenopus laevis oocytes and substrate transport was determined with radiolabelled substrates. ENT4 transported adenine and 2′-deoxyadenosine at the highest rate, with millimolar-range apparent affinity. ENT4-expressing oocytes did not accumulate hypoxanthine, a key purine salvage pathway substrate, or AMP. Micromolar concentrations of the plant hormone cytokinin compounds inhibited both PfENT4 and PvENT4. In contrast with PfENT1, ENT4 interacted with the immucillin compounds in the millimolar range and was inhibited by 10 μM dipyridamole. Thus ENT4 is a purine transporter with unique substrate and inhibitor specificity. Its role in parasite physiology remains uncertain, but is likely to be significant because of the strong conservation of ENT4 homologues in Plasmodia genomes.
Mitochondrial free [Ca2+] dynamics measured with a novel low-Ca2+ affinity aequorin probe
Authors: de la Fuente Sergio , Fonteriz Rosalba I. , de la Cruz Pedro J. , Montero Mayte , Alvarez Javier
Published: June 2012

Mitochondria have a very large capacity to accumulate Ca2+ during cell stimulation driven by the mitochondrial membrane potential. Under these conditions, [Ca2+]M (mitochondrial [Ca2+]) may well reach millimolar levels in a few seconds. Measuring the dynamics of [Ca2+]M during prolonged stimulation has been previously precluded by the high Ca2+ affinity of the probes available. We have now developed a mitochondrially targeted double-mutated form of the photoprotein aequorin which is able to measure [Ca2+] in the millimolar range for long periods of time without problems derived from aequorin consumption. We show in the present study that addition of Ca2+ to permeabilized HeLa cells triggers an increase in [Ca2+]M up to an steady state of approximately 2–3 mM in the absence of phosphate and 0.5–1 mM in the presence of phosphate, suggesting buffering or precipitation of calcium phosphate when the free [Ca2+] reaches 0.5–1 mM. Mitochondrial pH acidification partially re-dissolved these complexes. These millimolar [Ca2+]M levels were stable for long periods of time provided the mitochondrial membrane potential was not collapsed. Silencing of the mitochondrial Ca2+ uniporter largely reduced the rate of [Ca2+]M increase, but the final steady-state [Ca2+]M reached was similar. In intact cells, the new probe allows monitoring of agonist-induced increases of [Ca2+]M without problems derived from aequorin consumption.
Toll-like receptor 9 activation: a novel mechanism linking placenta-derived mitochondrial DNA and vascular dysfunction in pre-eclampsia
Authors: Goulopoulou Styliani , Matsumoto Takayuki , Bomfim Gisele F. , Webb R. Clinton
Published: June 2012

Emerging evidence suggests that in addition to being the ‘power houses’ of our cells, mitochondria facilitate effector responses of the immune system. Cell death and injury result in the release of mtDNA (mitochondrial DNA) that acts via TLR9 (Toll-like receptor 9), a pattern recognition receptor of the immune system which detects bacterial and viral DNA but not vertebrate DNA. The ability of mtDNA to activate TLR9 in a similar fashion to bacterial DNA stems from evolutionarily conserved similarities between bacteria and mitochondria. mtDNA may be the trigger of systemic inflammation in pathologies associated with abnormal cell death. PE (pre-eclampsia) is a hypertensive disorder of pregnancy with devastating maternal and fetal consequences. The aetiology of PE is unknown and removal of the placenta is the only effective cure. Placentas from women with PE show exaggerated necrosis of trophoblast cells, and circulating levels of mtDNA are higher in pregnancies with PE. Accordingly, we propose the hypothesis that exaggerated necrosis of trophoblast cells results in the release of mtDNA, which stimulates TLR9 to mount an immune response and to produce systemic maternal inflammation and vascular dysfunction that lead to hypertension and IUGR (intra-uterine growth restriction). The proposed hypothesis implicates mtDNA in the development of PE via activation of the immune system and may have important preventative and therapeutic implications, because circulating mtDNA may be potential markers of early detection of PE, and anti-TLR9 treatments may be promising in the management of the disease.
The dissociation/recombination reaction CH4 (+M) ⇔ CH3 + H (+M): A case study for unimolecular rate theory
Authors: Troe J. , Ushakov V. G.
Published: June 2012

The dissociation/recombination reaction CH4 (+M) ⇔ CH3 + H (+M) is modeled by statistical unimolecular rate theory completely based on dynamical information using ab initio potentials. The results are compared with experimental data. Minor discrepancies are removed by fine-tuning theoretical energy transfer data. The treatment accounts for transitional mode dynamics, adequate centrifugal barriers, anharmonicity of vibrational densities of states, weak collision and other effects, thus being “complete” from a theoretical point of view. Equilibrium constants between 300 and 5000 K are expressed as Kc = krec/kdis = exp(52 044 K/T) [10−24.65 (T/300 K)−1.76 + 10−26.38 (T/300 K)0.67] cm3 molecule−1, high pressure recombination rate constants between 130 and 3000 K as krec,∞ = 3.34 × 10−10 (T/300 K)0.186 exp(−T/25 200 K) cm3 molecule−1 s−1. Low pressure recombination rate constants for M = Ar are represented by krec,0 = [Ar] 10−26.19 exp[−(T/21.22 K)0.5] cm6 molecule−2 s−1, for M = N2 by krec,0 = [N2] 10−26.04 exp[−(T/21.91 K)0.5] cm6 molecule−2 s−1 between 100 and 5000 K. Weak collision falloff curves are approximated by asymmetric broadening factors [J. Troe and V. G. Ushakov, J. Chem. Phys. 135, 054304 (2011)10.1063/1.3615542] with center broadening factors of Fc ≈ 0.262 + [(T − 2950 K)/6100 K]2 for M = Ar. Expressions for other bath gases can also be obtained.
Direct and quantitative evidence for buckling instability as a mechanism for roughening of polymer during plasma etching
Authors: Lin T.-C. , Bruce R. L. , Oehrlein G. S. , Phaneuf R. J. , Kan H.-C.
Published: June 2012

We investigate elastic buckling as a driving force for roughening of polystyrene, a model resist, during plasma etching. Force curve measurements of the effective modulus of etched polystyrene films, along with modeling which accounts for adhesive forces and surface corrugation, show that an extremely stiff modified layer results from Ar-ion etching, with the modulus increasing with incident energy. The results are in good quantitative agreement with analysis based on the observed dominant corrugation wavelength, and buckling theory providing the corrugation is taken into account.
Production of a beam of highly vibrationally excited CO using perturbations
Authors: Bartels Nils , Schäfer Tim , Hühnert Jens , Field Robert W. , Wodtke Alec M.
Published: June 2012

An intense molecular beam of CO (X1Σ+) in high vibrational states (v = 17, 18) was produced by a new approach that we call PUMP – PUMP – PERTURB and DUMP. The basic idea is to access high vibrational states of CO e3Σ− via a two-photon doubly resonant transition that is perturbed by the A1Π state. DUMP -ing from this mixed (predominantly triplet) state allows access to high vibrational levels of CO (X1Σ+). The success of the approach, which avoids the use of vacuum UV radiation in any of the excitation steps, is proven by laser induced fluorescence and resonance enhanced multi-photon ionization spectroscopy.
Ultrafast absorption of intense x rays by nitrogen molecules
Authors: Buth Christian , Liu Ji-Cai , Chen Mau Hsiung , Cryan James P. , Fang Li , Glownia James M. , Hoener Matthias , Coffee Ryan N. , Berrah Nora
Published: June 2012

We devise a theoretical description for the response of nitrogen molecules (N2) to ultrashort and intense x rays from the free electron laser Linac Coherent Light Source (LCLS). We set out from a rate-equation description for the x-ray absorption by a nitrogen atom. The equations are formulated using all one-x-ray-photon absorption cross sections and the Auger and radiative decay widths of multiply-ionized nitrogen atoms. Cross sections are obtained with a one-electron theory and decay widths are determined from ab initio computations using the Dirac-Hartree-Slater (DHS) method. We also calculate all binding and transition energies of nitrogen atoms in all charge states with the DHS method as the difference of two self-consistent field (SCF) calculations (ΔSCF method). To describe the interaction with N2, a detailed investigation of intense x-ray-induced ionization and molecular fragmentation are carried out. As a figure of merit, we calculate ion yields and the average charge state measured in recent experiments at the LCLS. We use a series of phenomenological models of increasing sophistication to unravel the mechanisms of the interaction of x rays with N2: a single atom, a symmetric-sharing model, and a fragmentation-matrix model are developed. The role of the formation and decay of single and double core holes, the metastable states of \documentclass[12pt]{minimal}\begin{document}${\rm N}_2^{2+}$\end{document}N22+, and molecular fragmentation are explained.
A novel alignment mechanism employing orthogonal connected multi-layered flexible hinges for both leveling and centering
Authors: Zhao Jian , Wang Hongxi , Gao Renjing , Hu Ping , Yang Yintang
Published: June 2012

To eliminate the effects of motion coupling for measuring cylindrical work pieces, a novel alignment mechanism integrating functions of both leveling and centering is designed and fabricated by introducing multi-layered orthogonal connected flexible hinges as the key supporting and joining elements. Different from traditional leveling mechanisms with many separate parts fabricated together, all of the flexible hinges were integrated in one three-dimensioned machining part without assembling process, and thus synchronously simplifying the structure and reducing assembly errors. Based on the screw theory, the mathematic model of the proposed alignment mechanism is established for any resolution requirements depending on screw characteristics. A millimeter-sized device is fabricated with the alignment precision of 1.0 μm for centering within the range of ±1 mm and 1 in. for leveling within ±1°. The experiment results are in very close agreement to those obtained by simulation, which validate the feasibility of introducing multi-layered orthogonal flexible hinges in the centering and leveling mechanisms.
Lagrange-Pizzetti theorem for the quasihomogeneous N-body problem
Authors: Paraschiv Victor
Published: June 2012

We consider the N-body problem given by quasihomogeneous force functions of the form C1/r a + C2/r b (C1, C2, a, b positive constants and a ⩽ b) and address the fundamentals of homographic solutions. Generalizing techniques of the classical N-body problem, we prove that if the homographic solution is not flat, then it is homothetic; if the homographic solution is flat, then it is planar. Using them, we prove an analogue of the Lagrange-Pizzetti theorem for quasihomogeneous potentials.
Cyclic mutually unbiased bases, Fibonacci polynomials and Wiedemann's conjecture
Authors: Seyfarth Ulrich , Ranade Kedar S.
Published: June 2012

We relate the construction of a complete set of cyclic mutually unbiased bases, i.e., mutually unbiased bases generated by a single unitary operator, in power-of-two dimensions to the problem of finding a symmetric matrix over \documentclass[12pt]{minimal}\begin{document}$\mathbb {F}_2$\end{document}F2 with an irreducible characteristic polynomial that has a given Fibonacci index. For dimensions of the form \documentclass[12pt]{minimal}\begin{document}$2^{2^k}$\end{document}22k, we present a solution that shows an analogy to an open conjecture of Wiedemann in finite field theory. Finally, we discuss the equivalence of mutually unbiased bases.
Measuring protein concentration with entangled photons
Authors: Crespi Andrea , Lobino Mirko , Matthews Jonathan C. F. , Politi Alberto , Neal Chris R. , Ramponi Roberta , Osellame Roberto , O’Brien Jeremy L.
Published: June 2012

Optical interferometry is amongst the most sensitive techniques for precision measurement. By increasing the light intensity, a more precise measurement can usually be made. However, if the sample is light sensitive entangled states can achieve the same precision with less exposure. This concept has been demonstrated in measurements of known optical components. Here, we use two-photon entangled states to measure the concentration of a blood protein in an aqueous buffer solution. We use an opto-fluidic device that couples a waveguide interferometer with a microfluidic channel. These results point the way to practical applications of quantum metrology to light-sensitive samples.
Terahertz multichannel microfluidic sensor based on parallel-plate waveguide resonant cavities
Authors: Astley Victoria , Reichel Kimberly S. , Jones Jonathan , Mendis Rajind , Mittleman Daniel M.
Published: June 2012

We demonstrate a terahertz multichannel microfluidic sensor based on a parallel-plate waveguide geometry with two independent integrated resonant cavities. The resonant frequency of each cavity exhibits an approximately linear dependence on the index of refraction of the material inside the cavity and each cavity is demonstrated to respond independently with no measurable crosstalk. The sensitivities of the two cavities in terms of the change in resonant wavelength per refractive index unit (RIU) are measured to be 1.21 × 106 nm/RIU and 6.77 × 105 nm/RIU.
Design and performance of a combined secondary ion mass spectrometry-scanning probe microscopy instrument for high sensitivity and high-resolution elemental three-dimensional analysis
Authors: Wirtz Tom , Fleming Yves , Gerard Mathieu , Gysin Urs , Glatzel Thilo , Meyer Ernst , Wegmann Urs , Maier Urs , Odriozola Aitziber Herrero , Uehli Daniel
Published: June 2012

State-of-the-art secondary ion mass spectrometry (SIMS) instruments allow producing 3D chemical mappings with excellent sensitivity and spatial resolution. Several important artifacts however arise from the fact that SIMS 3D mapping does not take into account the surface topography of the sample. In order to correct these artifacts, we have integrated a specially developed scanning probe microscopy (SPM) system into a commercial Cameca NanoSIMS 50 instrument. This new SPM module, which was designed as a DN200CF flange-mounted bolt-on accessory, includes a new high-precision sample stage, a scanner with a range of 100 μm in x and y direction, and a dedicated SPM head which can be operated in the atomic force microscopy (AFM) and Kelvin probe force microscopy modes. Topographical information gained from AFM measurements taken before, during, and after SIMS analysis as well as the SIMS data are automatically compiled into an accurate 3D reconstruction using the software program “SARINA,” which was developed for this first combined SIMS-SPM instrument. The achievable lateral resolutions are 6 nm in the SPM mode and 45 nm in the SIMS mode. Elemental 3D images obtained with our integrated SIMS-SPM instrument on Al/Cu and polystyrene/poly(methyl methacrylate) samples demonstrate the advantages of the combined SIMS-SPM approach.
The sensitivity of graphene “snap-through” to substrate geometry
Authors: Wagner Till J. W. , Vella Dominic
Published: June 2012

We study theoretically the deposition of few layer graphene sheets onto a grooved substrate incorporating adhesion between substrate and sheet. We develop a model to understand the equilibrium of the sheet allowing for partial conformation of sheet to substrate. This model gives physical insight into recent observations of “snap-through” from flat to conforming states and emphasizes the crucial role of substrate shape in determining the nature of this transition. Our analytical results are consistent with numerical simulations using a van der Waals-like interaction. Finally, we propose a substrate shape that should exhibit a continuous, rather than “snap-through”, transition.
Quantum corrected Liouville model: Mathematical analysis
Authors: Morandi O.
Published: June 2012

A quantum corrected dynamical model for charged particles is derived. The corrections to the Newton motion are obtained within the Liouville formalism and are expressed by an effective nonlinear force. This effective force describes the non-local character of the quantum particles. The well posedness of the quantum-corrected problem is studied from the mathematical point of view. Existence and uniqueness of the solution are proved for a mollified version of the effective force. Numerical tests are performed and the range of validity of the model is investigated.
Nonlinear shear wave in a non Newtonian visco-elastic medium
Authors: Banerjee D. , Janaki M. S. , Chakrabarti N. , Chaudhuri M.
Published: June 2012

An analysis of nonlinear transverse shear wave has been carried out on non-Newtonian viscoelastic liquid using generalized hydrodynamic model. The nonlinear viscoelastic behavior is introduced through velocity shear dependence of viscosity coefficient by well known Carreau-Bird model. The dynamical feature of this shear wave leads to the celebrated Fermi-Pasta-Ulam problem. Numerical solution has been obtained which shows that initial periodic solutions reoccur after passing through several patterns of periodic waves. A possible explanation for this periodic solution is given by constructing modified Korteweg de Vries equation. This model has application from laboratory to astrophysical plasmas as well as in biological systems.
Extraction of second order piezoelectric parameters in bulk acoustic wave resonators
Authors: van Hemert Tom , Reimann Klaus , Hueting Raymond J. E.
Published: June 2012

In this paper we demonstrate a method to extract the electric field dependence of first order piezoelectric parameters. We fit the Mason model to measured frequency dependent electrical impedance data of aluminum-nitride bulk acoustic wave resonators for various DC biasing. The impedance was fitted accurately at the mechanical resonances and in the quasi-static regime well below the resonance frequency. This revealed the dependence of the piezoelectric stiffness, charge constant, and permittivity on the electric field. From this the four second order piezoelectric parameters were calculated.
Regions of azimuthal instability in gyrotrons
Authors: Dumbrajs O. , Nusinovich G. S. , Antonsen T. M.
Published: June 2012

This paper is devoted to the analysis of the instability of operating modes in high-power gyrotrons with cylindrically symmetric resonators. This instability manifests itself in destruction of the azimuthally uniform wave envelope rotating in a gyrotron resonator having a transverse size greatly exceeding the wavelength. The appearance of azimuthally nonuniform solutions can be interpreted as simultaneous excitation of modes with different azimuthal indices. This problem is studied self-consistently, i.e., taking into account the temporal evolution of both the azimuthal and axial structures of the wave envelope. The region of gyrotron operation free from this instability is identified. The efficiency achievable in this region can be only 1%–2% lower than the maximum efficiency. It is also possible to address the difference between the theory of mode interaction developed under assumption that all modes have fixed axial structure and the self-consistent theory presented here. As known, for fixed axial mode profiles, single-mode high-efficiency oscillations remain stable no matter how dense is the spectrum of competing modes, while the self-consistent theory predicts stable high-efficiency operation only when the azimuthal index does not exceed a certain critical value. It is shown that the azimuthal instability found in the self-consistent theory is caused by excitation of modes having axial structures different from that of the desired central mode.
Viscosity and surface-free energy effects in thermal shrinking of solid-state nanopores
Authors: Billo Joseph A. , Jones Jared , Asghar Waseem , Carter Ronald L. , Iqbal Samir M.
Published: June 2012

Solid-state nanopores are fabricated by either drilling these in thin membranes or by shrinking large pores with electron/ion beam. Simple heating of thin membranes with many large pores has been shown recently to controllably shrink these to nanoscale in parallel. Thermal heating of solid membrane in furnace changes the physical material properties. A model for the experimental nanopore shrinking data is developed. The parametric variations of viscosity, movement of adatoms and diffusion coefficients at temperature points around 1000 °C are characterized. The model provides a framework to understand and predict thermal shrinking of nanopores.
Extension of the measurement capabilities of the quadrupole resonator
Authors: Junginger T. , Weingarten W. , Welsch C.
Published: June 2012

The quadrupole resonator, designed to measure the surface resistance of superconducting samples at 400 MHz has been refurbished. The accuracy of its RF-dc compensation measurement technique is tested by an independent method. It is shown that the device enables also measurements at 800 and 1200 MHz and is capable to probe the critical RF magnetic field. The electric and magnetic field configuration of the quadrupole resonator are dependent on the excited mode. It is shown how this can be used to distinguish between electric and magnetic losses.
Angular distribution of photoelectrons in small molecules: A molecular quantum defect calculation
Authors: Vega M. V. , Lavín C. , Velasco A. M.
Published: June 2012

The molecular quantum defect orbital (MQDO) method, previously used in the determination of molecular photoionization cross sections, is applied here to calculate the angular distribution of photoelectrons arising from the molecular photoionization. Calculations are performed for the ionization from outer valence orbitals of HF, H2O, NH3, N2O, and H2CO molecules. The results are compared with previous measurements and with theoretical curves found in the literature. Profiles of the angular distribution parameter as a function of photoelectron energy covering a range from the photoionization threshold to 120 eV are presented for the above molecules. The energy dependence of the angular distributions predicted by the MQDO calculations agrees fairly well with predictions from more sophisticated theories and with observed results.
Relativistic potential energy surfaces of initial oxidations of Si(100) by atomic oxygen: The importance of surface dimer triplet state
Authors: Kim Tae-Rae , Shin Seokmin , Choi Cheol Ho
Published: June 2012

The non-relativistic and relativistic potential energy surfaces (PESs) of the symmetric and asymmetric reaction paths of Si(100)-2×1 oxidations by atomic oxygen were theoretically explored. Although only the singlet PES turned out to exist as a major channel leading to “on-dimer” product, both the singlet and triplet PESs leading to “on-top” products are attractive. The singlet PESs leading to the two surface products were found to be the singlet combinations (open-shell singlet) of the low-lying triplet state of surface silicon dimer and the ground 3P state of atomic oxygen. The triplet state of the “on-top” product can also be formed by the ground singlet state of the surface silicon dimer and the same 3P oxygen. The attractive singlet PESs leading to the “on-dimer” and “on-top” products made neither the intersystem crossings from triplet to singlet PES nor high energy 1D of atomic oxygen necessary. Rather, the low-lying triplet state of surface silicon dimer plays an important role in the initial oxidations of silicon surface.
Structure and diffusion of nanoparticle monolayers floating at liquid/vapor interfaces: A molecular dynamics study
Authors: Cheng Shengfeng , Grest Gary S.
Published: June 2012

Large-scale molecular dynamics simulations are used to simulate a layer of nanoparticles floating on the surface of a liquid. Both a low viscosity liquid, represented by Lennard-Jones monomers, and a high viscosity liquid, represented by linear homopolymers, are studied. The organization and diffusion of the nanoparticles are analyzed as the nanoparticle density and the contact angle between the nanoparticles and liquid are varied. When the interaction between the nanoparticles and liquid is reduced the contact angle increases and the nanoparticles ride higher on the liquid surface, which enables them to diffuse faster. In this case the short-range order is also reduced as seen in the pair correlation function. For the polymeric liquids, the out-of-layer fluctuation is suppressed and the short-range order is slightly enhanced. However, the diffusion becomes much slower and the mean square displacement even shows sub-linear time dependence at large times. The relation between diffusion coefficient and viscosity is found to deviate from that in bulk diffusion. Results are compared to simulations of the identical nanoparticles in 2-dimensions.
Partially unzipped carbon nanotubes as magnetic field sensors
Authors: Costamagna S. , Schulz A. , Covaci L. , Peeters F.
Published: June 2012

The conductance through graphene nanoribbons (GNR) connected to a partially unzipped carbon nanotube (CNT) is studied in the presence of an external magnetic field applied parallel to the long axis of the tube by means of non-equilibrium Green’s function technique. We consider CNTs that are partially unzipped to form armchair-GNR/zigzag-CNT/armchair-GNR or zigzag-GNR/armchair-CNT/zigzag-GNR junctions. We find that the inclusion of a longitudinal magnetic field affects the electronic states only in the CNT region, leading to the suppression of the conductance at low energies. We demonstrate that both types of junctions can be used as magnetic field sensors.
Facile large-area photolithography of periodic sub-micron structures using a self-formed polymer mask
Authors: Chen Kevin , Azhar Ebraheem , Ma Teng , Jiang Hanqing , Yu Hongbin
Published: June 2012

This letter reports the methodology of a low-cost fabrication technique for producing periodic sub-micron structures over a large area, using a polymer mask. A thin film of gold/palladium or silica is deposited on a stretched polydimethylsiloxane (PDMS) substrate. Release of the tension forms a buckling sinusoidal pattern on the surface. The PDMS substrates are then used as masks in soft contact optical lithography, bypassing the need for an expensive lithographic process toward creating regular patterns on a traditional masks. Pattern transfers are conducted using an ultraviolet lamp and the fabrication of more complex periodic structures through multiple exposures is reported.
Analysis of thermal conductance of ballistic point contacts
Authors: Jeong Changwook , Lundstrom Mark
Published: June 2012

Substantial reduction of thermal conductance (Kph) was recently reported for air gap heterostructures (AGHs) in which two bulk layers were connected by low-density nanopillars. We analyze Kph using a full phonon dispersion and including important phonon scattering. We find a transition from ballistic at low temperatures to quasi-ballistic transport near room temperature and explain the slow roll-off in Kph that occurs near room temperature. We show that the density of nanopillars deduced from the analysis depends strongly on the phonon dispersion assumed. Our model provides a good agreement with experiment that will be necessary to design AGHs for thermoelectric applications.