bluuebunny/crossref_metadata_2025 huggingface dataset:
How much should I eat? A comparison of suggested portion sizes in the UK
Authors: Lewis Hannah B , Ahern Amy L , Jebb Susan A
Published: April 2012

Objective

To identify and compare suggested food portion sizes in UK schemes.

Design

The study collated and compared suggested portion sizes from selected UK schemes intended both for general advice and weight-loss advice.

Setting

Portion size schemes were included if they were relevant to the UK, provided actual portion size information, were intended for adults and were obtainable from the public domain in November 2010. Included schemes were from the food industry, non-governmental organisations and health-care professionals. Suggested portion sizes of foods occurring in at least one scheme for general advice and at least one scheme for weight loss were included. Own brand on-pack portion size labelling from a large UK-wide supermarket was added to represent portion size advice from UK food retailers.

Subjects

Not applicable.

Results

The suggested portion sizes in the weight-loss advice schemes were often concordant, as were the general advice schemes, except one general advice scheme from a non-governmental organisation which was more closely aligned with the portion sizes for weight loss. Overall there were substantial discrepancies between suggested portion sizes for muesli and crunchy breakfast cereals, rice, pasta and potatoes, meat, fish and pulses, whereas portion sizes for cooked vegetables, dried fruit, some breakfast cereals and cheese were broadly consistent.

Conclusions

There is a lack of consistency in the portion sizes communicated to the public. An independent and authoritative scheme of suggested portion sizes for all foods, with distinct recommendations for general advice and for weight-loss advice, could be of benefit.
Counterstreaming auroral structures during substorm expansion
Authors: Kornilova Tatyana A. , Kornilov Ilya A.
Published: April 2012

Using of high‐quality keograms constructed by filtered and averaged images from the Lovozero all‐sky imager (ASI) station and THEMIS all‐sky imager array allowed us to investigate in detail optical signatures of poleward forms propagating equatorward and getting involved in the auroral pattern in the course of substorm expansion. We found that weak, nearly east‐west oriented auroral arcs often penetrate into poleward expanding regions of active auroras from preceding breakup activations in the south. In total, 40 such events have been analyzed. The major point that we aimed to clarify is whether these weak forms fade, disperse, or keep moving equatorward in such occasions. We were able to trace their fate and demonstrate that they keep their equatorward motion against the background of bright, poleward expanding auroras, forming a counterstreaming auroral pattern at substorm expansion.
Paleoclimatic implications of magnetic susceptibility in Late Pliocene–Quaternary sediments from deep drilling core SG‐1 in the western Qaidam Basin (NE Tibetan Plateau)
Authors: Zhang Weilin , Appel Erwin , Fang Xiaomin , Yan Maodu , Song Chunhui , Cao Liwan
Published: April 2012

Lake sediments are important archives of paleoclimate change and erosion history. A 938.5 m long core (SG‐1) of lacustrine sediments, dated at 2.77 Ma to 0.1 Ma, was obtained from the western Qaidam Basin in the northeastern Tibetan Plateau, consisting of dark grayish mudstone and grayish siltstone, intercalated with salts and fine sandstones in the upper part. Magnetic susceptibility data, combined with detailed rock magnetic properties, were analyzed for revealing the significance of ferro(i)magnetic concentration for past changes of climate and erosion. Mass‐specific susceptibility (χ) shows a striking cyclic and long‐term variation. Samples with high χ values are dominated by magnetite and maghemite with pseudo‐single‐domain properties. In contrast, samples with low χ values contain maghemite from single‐domain to multidomain and, additionally, a significant fraction of hematite. The driving mechanism of χ variation can be explained by three alternative models: (1) different source regions with alternations of wind and cryoclastic erosion in a wider hinterland (dry‐cold climate) and surface runoff erosion from a narrower area (more humid climate) and (2 and 3) low‐temperature oxidation, occurring either in the lake sediments (dry climate) or in the catchment area during weathering (more humid climate). Trends of χ match with changes in sedimention rates and are roughly synchronous with the deep‐sea δ18O record on a glacial‐interglacial timescale. Therefore, the concentration of magnetic minerals in the western Qaidam Basin sediments is likely controlled by both tectonic influence and paleoenvironmental changes but can be best interpreted by alternations and trends of dry‐cold and more humid periods due to Asian drying and global cooling.
Sensitivity of contrail cirrus radiative forcing to air traffic scheduling
Authors: Newinger Christina , Burkhardt Ulrike
Published: April 2012

Air traffic effects high cloudiness and therefore the Earth's radiation budget by producing contrail cirrus. Contrail cirrus comprise of line‐shaped contrails and irregularly shaped ice clouds that originate from them. The warming effect of contrail cirrus is disproportionally large at night, since at daytime the cooling due to the short wave cloud albedo effect acts toward compensating the long wave warming effect. Therefore it has been suggested to restrict air traffic to daytime in order to reduce its climate impact. The potential for reducing the contrail cirrus radiative forcing by shifting air traffic to daytime depends on the diurnal cycle of contrail cirrus coverage which is in turn determined by the diurnal cycle of air traffic and the contrail cirrus lifetimes. Simulations with a global atmospheric general circulation model indicate that the annual mean contrail cirrus coverage may be almost constant over the day even in areas where air traffic is close to zero at night. A conceptual model describing the temporal evolution of contrail cirrus coverage reveals that this is due to the large variability in contrail cirrus lifetimes in combination with the spreading of contrail cirrus. This large variability of lifetimes is consistent with observational evidence but more observations are needed to constrain the contrail lifetime distribution. An idealized mitigation experiment, shifting nighttime flights to daytime, indicates that contrail cirrus radiative forcing is not significantly changed.
A hypothesis‐driven approach to optimize field campaigns
Authors: Nowak Wolfgang , Rubin Yoram , de Barros Felipe P. J.
Published: April 2012

Most field campaigns aim at helping in specified scientific or practical tasks, such as modeling, prediction, optimization, or management. Often these tasks involve binary decisions or seek answers to yes/no questions under uncertainty, e.g., Is a model adequate? Will contamination exceed a critical level? In this context, the information needs of hydro(geo)logical modeling should be satisfied with efficient and rational field campaigns, e.g., because budgets are limited. We propose a new framework to optimize field campaigns that defines the quest for defensible decisions as the ultimate goal. The key steps are to formulate yes/no questions under uncertainty as Bayesian hypothesis tests, and then use the expected failure probability of hypothesis testing as objective function. Our formalism is unique in that it optimizes field campaigns for maximum confidence in decisions on model choice, binary engineering or management decisions, or questions concerning compliance with environmental performance metrics. It is goal oriented, recognizing that different models, questions, or metrics deserve different treatment. We use a formal Bayesian scheme called PreDIA, which is free of linearization, and can handle arbitrary data types, scientific tasks, and sources of uncertainty (e.g., conceptual, physical, (geo)statistical, measurement errors). This reduces the bias due to possibly subjective assumptions prior to data collection and improves the chances of successful field campaigns even under conditions of model uncertainty. We illustrate our approach on two instructive examples from stochastic hydrogeology with increasing complexity.
Assessment of hydrological model predictive ability given multiple conceptual geological models
Authors: Seifert Dorte , Sonnenborg Torben O. , Refsgaard Jens Christian , Højberg Anker L. , Troldborg Lars
Published: April 2012

In this study six hydrological models that only differ with respect to their conceptual geological models are established for a 465 km2 area. The performances of the six models are evaluated in differential split‐sample tests against a unique data set with well documented groundwater head and discharge data for different periods with different groundwater abstractions. The calibration results of the six models are comparable, with no model being superior to the others. Though, the six models make very different predictions of changes in groundwater head and discharges as a response to changes in groundwater abstraction. This confirms the utmost importance of the conceptual geological model for making predictions of variables and conditions beyond the calibration situation. In most cases the observed changes in hydraulic head and discharge are within the range of the changes predicted by the six models implying that a multiple modeling approach can be useful in obtaining more robust assessments of likely prediction errors. We conclude that the use of multiple models appear to be a good alternative to traditional differential split‐sample schemes. A model averaging analysis shows that model weights estimated from model performance in the calibration or validation situation in many cases are not optimal for making other predictions. Hence, the critical assumption that is always made in model averaging, namely that the model weights derived from the calibration situation are also optimal for model predictions, cannot be assumed to be generally valid.
A new method for calibrating a simple, watershed‐scale model of evapotranspiration: Maximizing the correlation between observed streamflow and model‐inferred storage
Authors: Tuttle Samuel E. , Salvucci Guido D.
Published: April 2012

A simple model was developed to estimate area‐averaged evapotranspiration (ET) at the watershed scale, using widely available records of streamflow, precipitation, and basic meteorological data. The pivotal assumption of the model is that area‐averaged basin‐wide water storage (V) can be used to determine basin‐wide ET efficiency. With this assumption, ET was modeled as a function of watershed storage, Priestley‐Taylor potential evapotranspiration, and one free parameter (α) controlling the relation between basin‐wide ET efficiency and storage. Watershed storage was found by integrating the water balance equation forward in time with observed precipitation and streamflow. By exploiting a hypothesized positive correlation between storage and streamflow, a method was developed to estimate the parameter α without calibration to measured ET, thus allowing the model to be applied in any watershed with measured precipitation, streamflow, and meteorological variables. The model was tested at sites within the AmeriFlux network in a variety of climates and ecosystems, using downstream U.S. Geological Survey streamflow to define the watershed boundary and measured AmeriFlux evapotranspiration to judge model performance. At most sites, the dynamics of modeled ET closely matched those of measured ET: daily root‐mean‐square errors averaged 0.067 cm d−1. In general, water storage and ET efficiency, especially during dry downs, were captured by the model, and the free parameter determined from the storage‐streamflow correlation criteria was close to the optimal fit found through direct calibration. The performance of both the model and the indirect calibration strategy was best in arid to semiarid sites.
Towards the robust selection of Thellier‐type paleointensity data: The influence of experimental noise
Authors: Paterson Greig A. , Biggin Andrew J. , Yamamoto Yuhji , Pan Yongxin
Published: April 2012

The process of data selection in paleointensity studies is an essential step to ensure data fidelity. There is, however, no consensus as to the best approach to consistently select data with most studies using arbitrarily defined thresholds for selection. We present a new numerical model that simulates the variability of paleointensity data from hypothetical ideal samples acquiring a thermoremanent magnetization (TRM) by incorporating experimental noise, which has been constrained using over 75,000 data measurements. Using Monte Carlo analyses, we investigate the behavior of simulated data and characterize the distributions of parameters typically used to select paleointensity data. We use the 95th percentiles of the distributions to define thresholds for the maximum likely parameter values that can result from experimental noise. These represent values below which we cannot distinguish non‐ideal behavior from noise. We find that a number of parameters are highly sensitive to noise and laboratory field strength (e.g., partial TRM, pTRM, checkCDRAT and pTRM tail check δt*); this sensitivity may diminish their ability to identify non‐ideal behavior. The fractional (f) dependence of some parameters and the proportion of inaccurate results provide justification for f≥ 0.35 when selecting data from both Thellier‐Thellier and Coe protocol experiments. The manifestation of noise in the original Thellier method, however, is different to that of methods that use zero‐field heating steps. This suggests that the data selection procedure for the Thellier method should be different, but it also suggests that, contrary to previous analyses, the accuracy and scatter of results from this method are more sensitive to noise than methods that use zero‐field heating steps. The general approach taken here is shown to be a powerful means of understanding the behavior of selection parameters and has the potential to be extended to models incorporating non‐ideal behavior resulting from alteration and multidomain grains.
Downward continued multichannel seismic refraction analysis of Atlantis Massif oceanic core complex, 30°N, Mid‐Atlantic Ridge
Authors: Henig A. S. , Blackman D. K. , Harding A. J. , Canales J.‐P. , Kent G. M.
Published: April 2012

Detailed seismic refraction results show striking lateral and vertical variability of velocity structure within the Atlantis Massif oceanic core complex (OCC), contrasting notably with its conjugate ridge flank. Multichannel seismic (MCS) data are downward continued using the Synthetic On Bottom Experiment (SOBE) method, providing unprecedented detail in tomographic models of the P‐wave velocity structure to subseafloor depths of up to 1.5 km. Velocities can vary up to 3 km/s over several hundred meters and unusually high velocities (∼5 km/s) are found immediately beneath the seafloor in key regions. Correlation within situand dredged rock samples, video and records from submersible dives, and a 1.415 km drill core, allow us to infer dominant lithologies. A high velocity body(ies) found to shoal near to the seafloor in multiple locations is interpreted as gabbro and is displaced along isochrons within the OCC, indicating a propagating magmatic source as the origin for this pluton(s). The western two‐thirds of the Southern Ridge is capped in serpentinite that may extend nearly to the base of our ray coverage. The distribution of inferred serpentinite indicates that the gabbroic pluton(s) was emplaced into a dominantly peridotitic host rock. Presumably the mantle host rock was later altered via seawater penetration along the detachment zone, which controlled development of the OCC. The asymmetric distribution of seismic velocities and morphology of Atlantis Massif are consistent with a detachment fault with a component of dip to the southeast. The lowest velocities observed atop the eastern Central Dome and conjugate crust are most likely volcanics. Here, an updated model of the magmatic and extensional faulting processes at Atlantis Massif is deduced from the seismic results, contributing more generally to understanding the processes controlling the formation of heterogeneous lithosphere at slow‐rate spreading centers.
Depth‐dependent mode of tremor migration beneath Kii Peninsula, Nankai subduction zone
Authors: Obara Kazushige , Matsuzawa Takanori , Tanaka Sachiko , Maeda Takuto
Published: April 2012

We investigated the migration mode of deep non‐volcanic tremor activity beneath Kii Peninsula, southwest Japan. Major tremor episodes are characterized by long‐term migration with a velocity of about 10 km/day, propagating along the strike of the subducting plate. Similar tremor migration in Cascadia is accompanied by reverse propagation at speeds on the order of 100 km/day and much faster slip‐parallel migration at speeds on the order of 1000 km/day. We systematically searched for migrating tremor with clear linearity in space and time. As a result, we found tremor migrations at speeds ranging from 1 to 60 km/hr depending on the along‐dip position in the tremor zone. The observed decrease in migration speed with increasing measurement time scale suggests that migration is controlled by a diffusion process. The along‐strike migration at lower speeds, including both forward and backward directions relative to the long‐term migration episode, is concentrated at the updip side of the tremor zone, whereas the faster slip‐parallel migration is distributed over the entire zone. The long‐term migration seems to consist of and be excited by the propagation of along‐strike creep at the updip part. The concentration of along‐strike migrating tremor sequences at the updip side may reflect the existence of abundant fluid that accumulates at the corner of the mantle wedge. The faster slip‐parallel migrations represent projections of along‐strike fluctuations in slip pulse propagation controlled by striations along the plate interface.
Imposing strong constraints on tropical terrestrial CO2 fluxes using passenger aircraft based measurements
Authors: Niwa Yosuke , Machida Toshinobu , Sawa Yousuke , Matsueda Hidekazu , Schuck Tanja J. , Brenninkmeijer Carl A. M. , Imasu Ryoichi , Satoh Masaki
Published: April 2012

Because very few measurements of atmospheric carbon dioxide (CO2) are available in the tropics, estimates of surface CO2 fluxes in tropical regions are beset with considerable uncertainties. To improve estimates of tropical terrestrial fluxes, atmospheric CO2 inversion was performed using passenger aircraft based measurements of the Comprehensive Observation Network for Trace gases by Airliner (CONTRAIL) project in addition to the surface measurement data set of GLOBALVIEW–CO2. Regional monthly fluxes at the earth's surface were estimated using the Bayesian synthesis approach focusing on the period 2006–2008 using the Nonhydrostatic Icosahedral Atmospheric Model‐based Transport Model (NICAM‐TM). By adding the aircraft to the surface data, the posterior flux errors were greatly reduced; specifically, error reductions of up to 64% were found for tropical Asia regions. This strong impact is closely related to efficient vertical transport in the tropics. The optimized surface fluxes using the CONTRAIL data were evaluated by comparing the simulated atmospheric CO2 distributions with independent aircraft measurements of the Civil Aircraft for the Regular Investigation of the atmosphere Based on an Instrument Container (CARIBIC) project. The inversion with the CONTRAIL data yields the global carbon sequestration rates of 2.22 ± 0.28 Pg C yr−1 for the terrestrial biosphere and 2.24 ± 0.27 Pg C yr−1 for the oceans (the both are adjusted by riverine input of CO2). For the first time the CONTRAIL CO2 measurements were used in an inversion system to identify the areas of greatest impact in terms of reducing flux uncertainties.
Functional metagenomics reveals novel salt tolerance loci from the human gut microbiome
Authors: Culligan Eamonn P , Sleator Roy D , Marchesi Julian R , Hill Colin
Published: April 2012

Metagenomics is a powerful tool that allows for the culture-independent analysis of complex microbial communities. One of the most complex and dense microbial ecosystems known is that of the human distal colon, with cell densities reaching up to 1012 per gram of faeces. With the majority of species as yet uncultured, there are an enormous number of novel genes awaiting discovery. In the current study, we conducted a functional screen of a metagenomic library of the human gut microbiota for potential salt-tolerant clones. Using transposon mutagenesis, three genes were identified from a single clone exhibiting high levels of identity to a species from the genus Collinsella (closest relative being Collinsella aerofaciens) (COLAER_01955, COLAER_01957 and COLAER_01981), a high G+C, Gram-positive member of the Actinobacteria commonly found in the human gut. The encoded proteins exhibit a strong similarity to GalE, MurB and MazG. Furthermore, pyrosequencing and bioinformatic analysis of two additional fosmid clones revealed the presence of an additional galE and mazG gene, with the highest level of genetic identity to Akkermansia muciniphila and Eggerthella sp. YY7918, respectively. Cloning and heterologous expression of the genes in the osmosensitive strain, Escherichia coli MKH13, resulted in increased salt tolerance of the transformed cells. It is hoped that the identification of atypical salt tolerance genes will help to further elucidate novel salt tolerance mechanisms, and will assist our increased understanding how resident bacteria cope with the osmolarity of the gastrointestinal tract.
Josephson effect and nonequilibrium superconductivity in superconducting tunnel structures
Authors: Rudenko E. M.
Published: April 2012

Nonequilibrium superconductivity induced by tunnel current injection of quasiparticles is studied. It is found that an instability in the form of a negative voltage jump in the oscillator current-voltage characteristic (CVC), which leads to an inhomogeneous state, as well as the spatial structure of the inhomogeneous state are very sensitive to low magnetic fields. The shape of the CVC of low-resistance tunnel junctions for bias voltages V ≈ 2Δ/e depends strongly on the junction dimensions and barrier transparency. These results are interpreted in terms of Josephson vortices (fluxons) in a tunnel oscillator. Studies of the nonequilibrium phenomena, with the Josephson properties of low-resistance tunnel structures taken into account, reveal a number of new effects, such as nonequilibrium suppression of the energy gap at bias voltages V < 2Δ/e, the possible existence of an entire series of instabilities of the nonequilibrium superconducting state during tunnel injection, and inhomogeneity in the tunnel injector effect.
Inhomogeneous dephasing masks coherence lifetimes in ensemble measurements
Authors: Pelzer Kenley M. , Griffin Graham B. , Gray Stephen K. , Engel Gregory S.
Published: April 2012

An open question at the forefront of modern physical sciences is what role, if any, quantum effects may play in biological sensing and energy transport mechanisms. One area of such research concerns the possibility of coherent energy transport in photosynthetic systems. Spectroscopic evidence of long-lived quantum coherence in photosynthetic light-harvesting pigment protein complexes (PPCs), along with theoretical modeling of PPCs, has indicated that coherent energy transport might boost efficiency of energy transport in photosynthesis. Accurate assessment of coherence lifetimes is crucial for modeling the extent to which quantum effects participate in this energy transfer, because such quantum effects can only contribute to mechanisms proceeding on timescales over which the coherences persist. While spectroscopy is a useful way to measure coherence lifetimes, inhomogeneity in the transition energies across the measured ensemble may lead to underestimation of coherence lifetimes from spectroscopic experiments. Theoretical models of antenna complexes generally model a single system, and direct comparison of single system models to ensemble averaged experimental data may lead to systematic underestimation of coherence lifetimes, distorting much of the current discussion. In this study, we use simulations of the Fenna-Matthews-Olson complex to model single complexes as well as averaged ensembles to demonstrate and roughly quantify the effect of averaging over an inhomogeneous ensemble on measured coherence lifetimes. We choose to model the Fenna-Matthews-Olson complex because that system has been a focus for much of the recent discussion of quantum effects in biology, and use an early version of the well known environment-assisted quantum transport model to facilitate straightforward comparison between the current model and past work. Although ensemble inhomogeneity is known to lead to shorter lifetimes of observed oscillations (simply inhomogeneous spectral broadening in the time domain), this important fact has been left out of recent discussions of spectroscopic measurements of energy transport in photosynthesis. In general, these discussions have compared single-system theoretical models to whole-ensemble laboratory measurements without addressing the effect of inhomogeneous dephasing. Our work addresses this distinction between single system and ensemble averaged observations, and shows that the ensemble averaging inherent in many experiments leads to an underestimation of coherence lifetimes in individual systems.
Effect of dynamical friction on interchange motion of plasma filaments
Authors: Kube R. , Garcia O. E.
Published: April 2012

Theory and numerical simulations are presented for interchange motion of plasma filaments in the presence of dynamical friction and allowing large relative filament amplitudes. When friction is negligible, the filament velocity is proportional to the square root of gravity and its cross-field size. For strong friction, the filament velocity is independent of the cross-field size, proportional to gravity, and inversely proportional to the friction coefficient. In this frictional regime, the filament moves a large distance with nearly constant velocity and shape. The transition between these velocity scaling regimes and the amplitude dependence are revealed. The results presented here complement previous theories for irregularities in the equatorial ionosphere and are in excellent agreement with recent experiments on simply magnetized toroidal plasmas. The relevance to blob-like structures in the scrape-off layer of magnetically confined plasmas is also discussed.
Consistent anomalies in translation-invariant noncommutative gauge theories
Authors: Varshovi Amir Abbass
Published: April 2012

Translation-invariant noncommutative gauge theories are discussed in the setting of matrix modeled gauge theories. Using the matrix model formulation the explicit form of consistent anomalies and consistent Schwinger terms for translation-invariant noncommutative gauge theories are derived.
Projected Hartree–Fock theory
Authors: Jiménez-Hoyos Carlos A. , Henderson Thomas M. , Tsuchimochi Takashi , Scuseria Gustavo E.
Published: April 2012

Projected Hartree–Fock (PHF) theory has a long history in quantum chemistry. PHF is here understood as the variational determination of an N-electron broken symmetry Slater determinant that minimizes the energy of a projected state with the correct quantum numbers. The method was actively pursued for several decades but seems to have been abandoned. We here derive and implement a “variation after projection” PHF theory using techniques different from those previously employed in quantum chemistry. Our PHF methodology has modest mean-field computational cost, yields relatively simple expressions, can be applied to both collinear and non-collinear spin cases, and can be used in conjunction with deliberate symmetry breaking and restoration of other molecular symmetries like complex conjugation and point group. We present several benchmark applications to dissociation curves and singlet-triplet energy splittings, showing that the resulting PHF wavefunctions are of high quality multireference character. We also provide numerical evidence that in the thermodynamic limit, the energy in PHF is not lower than that of broken-symmetry HF, a simple consequence of the lack of size consistency and extensivity of PHF.
Effective-mass Dirac equation for Woods-Saxon potential: Scattering, bound states, and resonances
Authors: Aydoğdu Oktay , Arda Altuğ , Sever Ramazan
Published: April 2012

Approximate scattering and bound state solutions of the one-dimensional effective-mass Dirac equation with the Woods-Saxon potential are obtained in terms of the hypergeometric-type functions. Transmission and reflection coefficients are calculated by using behavior of the wave functions at infinity. The same analysis is done for the constant mass case. It is also pointed out that our results are in agreement with those obtained in literature. Meanwhile, an analytic expression is obtained for the transmission resonance and it is observed that the expressions for bound states and resonances are equal for the energy values E = ±m.
Selective emitters design and optimization for thermophotovoltaic applications
Authors: Nefzaoui E. , Drevillon J. , Joulain K.
Published: April 2012

Among several solutions to exploit solar energy, thermophotovoltaics have been popularized and have known great breakthroughs during the past two decades. Yet, existing systems still have low efficiencies since the wavelength range of optimal photovoltaic (PV) conversion is very small compared to the emitter spectral range. Selective emitters are a very promising solution to this problem. We developed numerical tools to design and optimize such emitters. Some of the resulting structures composed of two or four layers of metals and semiconductors are presented in this paper. We also show that the usual PV devices efficiency limits (30% for crystalline silicon under solar radiation, according to Shockley-Queisser model) can be easily overcome thanks to these structures.
Helium irradiation effects in polycrystalline Si, silica, and single crystal Si
Authors: Abrams K. J. , Hinks J. A. , Pawley C. J. , Greaves G. , van den Berg J. A. , Eyidi D. , Ward M. B. , Donnelly S. E.
Published: April 2012

Transmission electron microscopy (TEM) has been used to investigate the effects of room temperature 6 keV helium ion irradiation of a thin (≈55 nm thick) tri-layer consisting of polycrystalline Si, silica, and single-crystal Si. The ion irradiation was carried out in situ within the TEM under conditions where approximately 24% of the incident ions came to rest in the specimen. This paper reports on the comparative development of irradiation-induced defects (primarily helium bubbles) in the polycrystalline Si and single-crystal Si under ion irradiation and provides direct measurement of a radiation-induced increase in the width of the polycrystalline layer and shrinkage of the silica layer. Analysis using TEM and electron energy-loss spectroscopy has led to the hypothesis that these result from helium-bubble-induced swelling of the silicon and radiation-induced viscoelastic flow processes in the silica under the influence of stresses applied by the swollen Si layers. The silicon and silica layers are sputtered as a result of the helium ion irradiation; however, this is estimated to be a relatively minor effect with swelling and stress-related viscoelastic flow being the dominant mechanisms of dimensional change.
On the deformation of gas bubbles in liquids
Authors: Legendre Dominique , Zenit Roberto , Velez-Cordero J. Rodrigo
Published: April 2012

We consider the deformation of gas bubbles rising in different liquids over a wide range of Morton numbers, from O(10−11) to O(1), and bubble diameters. We have collected data from the literature and performed new experiments for relatively large Morton numbers. A simple expression is proposed to describe the evolution of the bubble deformation, which is consistent with the analytical solution of Moore [“The rise of a gas bubble in a viscous liquid,” J. Fluid Mech. 6, 113 (1959)]. It appears that deformation can be predicted correctly by considering the Morton and Weber numbers. The variation of the bubble interfacial area is also analyzed; this quantity is very important for the case of bubbly flow modeling but has not been measured directly to date.
Multi-layer thermoelectric-temperature-mapping microbial incubator designed for geo-biochemistry applications
Authors: Wu Jin-Gen , Liu Man-Chi , Tsai Ming-Fei , Yu Wei-Shun , Chen Jian-Zhang , Cheng I-Chun , Lin Pei-Chun
Published: April 2012

We demonstrate a novel, vertical temperature-mapping incubator utilizing eight layers of thermoelectric (TE) modules mounted around a test tube. The temperature at each layer of the TE module is individually controlled to simulate the vertical temperature profile of geo-temperature variations with depth. Owing to the constraint of non-intrusion to the filled geo-samples, the temperature on the tube wall is adopted for measurement feedback. The design considerations for the incubator include spatial arrangement of the energy transfer mechanism, heating capacity of the TE modules, minimum required sample amount for follow-up instrumental or chemical analysis, and the constraint of non-intrusion to the geo-samples during incubation. The performance of the incubator is experimentally evaluated with two tube conditions and under four preset temperature profiles. Test tubes are either empty or filled with quartz sand, which has comparable thermal properties to the materials in the geo-environment. The applied temperature profiles include uniform, constant temperature gradient, monotonic-increasing parabolic, and parabolic. The temperature on the tube wall can be controlled between 20 °C and 90 °C with an averaged root mean squared error of 1 °C.
Wide-band acousto-optic deflectors for large field of view two-photon microscope
Authors: Jiang Runhua , Zhou Zhenqiao , Lv Xiaohua , Zeng Shaoqun
Published: April 2012

Acousto-optic deflector (AOD) is an attractive scanner for two-photon microscopy because it can provide fast and versatile laser scanning and does not involve any mechanical movements. However, due to the small scan range of available AOD, the field of view (FOV) of the AOD-based microscope is typically smaller than that of the conventional galvanometer-based microscope. Here, we developed a novel wide-band AOD to enlarge the scan angle. Considering the maximum acceptable acoustic attenuation in the acousto-optic crystal, relatively lower operating frequencies and moderate aperture were adopted. The custom AOD was able to provide 60 MHz 3-dB bandwidth and 80% peak diffraction efficiency at 840 nm wavelength. Based on a pair of such AOD, a large FOV two-photon microscope was built with a FOV up to 418.5 μm (40× objective). The spatiotemporal dispersion was compensated simultaneously with a single custom-made prism. By means of dynamic power modulation, the variation of laser intensity within the FOV was reduced below 5%. The lateral and axial resolution of the system were 0.58–2.12 μm and 2.17–3.07 μm, respectively. Pollen grain images acquired by this system were presented to demonstrate the imaging capability at different positions across the entire FOV.
Experimental parametric subharmonic instability in stratified fluids
Authors: Joubaud Sylvain , Munroe James , Odier Philippe , Dauxois Thierry
Published: April 2012

Internal gravity waves contribute to fluid mixing and energy transport, not only in oceans but also in the atmosphere and in astrophysical bodies. An efficient way to transfer energy from large scale to smaller scale is the parametric subharmonic instability. We provide here the first experimental measurement of the growth rate of this instability. We make careful and quantitative comparisons with theoretical predictions for propagating vertical modes in laboratory experiments.
Alternative interpretations of power-law distributions found in nature
Authors: Penland Cécile , Sardeshmukh Prashant D.
Published: April 2012

We investigate two inherently different classes of probability density functions (pdfs) that share the common property of power law tails: the α-stable Lévy process and the linear Markov diffusion process with additive and multiplicative Gaussian noise. Dynamical processes described by these distributions cannot be uniquely identified as belonging to one or the other class either by diverging variance due to power-law tails in the pdf or by the possible existence of skew. However, there are distinguishing features that may be found in sufficiently well sampled time series. We examine these features and discuss how they may guide the development of proper approximations to equations of motion underlying dynamical systems. An additional result of this research was the identification of a variable describing the relative importance of the multiplicative and independent additive noise forcing in our linear Markov process. The distribution of this variable is generally skewed, depending on the level of correlation between the additive and multiplicative noise.
Deflection of a cantilever rectangular plate induced by surface stress with applications to surface stress measurement
Authors: Zeng Xianwei , Deng Jiaquan , Luo Xi
Published: April 2012

Surface stress plays important roles in the fabrication and applications of thin-film substrate systems. Bending test of cantilever microbeams has been commonly applied to characterize the surface stress. Stoney’s equation, ideally valid for completely unconstrained plates, is typically used to convert the measured deflection to a surface stress. To assess the validity of Stoney’s equation for the more complicated case of a plate with a clamped end, an analytical solution has been obtained in this study for the deflection of a cantilever rectangular plate due to surface stresses at its upper and lower surfaces. The analytical solution is given by the summation of single Fourier cosine series in the length and the width directions of the plate and a lower order polynomial. Numerical results for the deflection, slope, and curvature for the midpoint of the free end are presented for cantilever plates with aspect ratios ranging from 0.1 to 10 and for different Poisson’s ratios. In most practical measurements of surface stress, the aspect ratio is greater than one and the maximum percentage errors of Stoney’s equation for the deflection, slope, and curvature for the midpoint of the free end are 16%, 16%, and 10%, respectively. The present analytical solution based on Fourier cosine series with the first two leading terms can provide a significant improvement over Stoney’s equation. The maximum percentage errors for the deflection, slope, and curvature for the midpoint of the free end are reduced to 3%, 2%, and 3%, respectively.
Evaluation of cancellation coil for precision magnetic measurements with strong prepolarization field inside shielded environment
Authors: Hwang Seong-min , Kim Kiwoong , Seok Kang Chan , Lee Seong-Joo , Lee Yong-Ho
Published: April 2012

Many precision magnetic measurements can benefit significantly from or even require strong prepolarization fields (Bp) and magnetically shielded environments. We describe here in detail a cancellation coil (CC) which can neutralize the Bp on the electrically conductive shield walls that may otherwise induce currents on the walls to produce a lingering transient residual field (Btr) inside the shielded environment and disrupt the measurement operations. The CC was designed using the inverse problem method to effectively neutralize magnetic fields generated on the shield walls by the Bp coil. The implemented CC was evaluated by measuring Btr using a fluxgate magnetometer at different magnetometer positions and cancellation coil currents (ICC). Multi-mode component analysis on the Btr measurements revealed two dominant components, where the component with shorter time constant comes from the current induced around the shield side walls and the other with longer time constant from the current induced on the ceiling and floor of the magnetically shielded room. The analysis also revealed the optimal ICC for each of the top, side, and bottom sections of the CC, which enables significantly easier fine-tuning of individual sections of the CC to enhance CC performance.
Thermal conductivity of ZnO thin film produced by reactive sputtering
Authors: Xu Yibin , Goto Masahiro , Kato Ryozo , Tanaka Yoshihisa , Kagawa Yutaka
Published: April 2012

ZnO thin films have been produced by reactive sputtering with different oxygen contents in the sputtering gas. As a result of transmission electronic microscopy observation, each film consist of two layers: an interfacial layer close to the substrate, with a thickness of about 200 nm, composed of very fine crystal grains and an upper layer above the interfacial layer, composed of column-shaped grains aligned along the out-plane direction. The grain diameter ranges from 35 to 100 nm depending on the oxygen partial pressure. The in-plane and out-plane thermal conductivity have been measured at room temperature. The out-plane thermal conductivity of the interfacial layer is 2.3 W m−1 K−1, independent on the oxygen partial pressure. The out-plane thermal conductivity of the upper layer is 5.4, 7.1, and 4.0 W m−1 K−1, and the in-plane thermal conductivity 4.86, 6.01, and 2.66 W m−1 K−1, for the O2 30%, 60%, and 90% ZnO film, respectively. Both out-plane and in-plane thermal conductivity decrease with the decrease of grain diameter. The thermal conductance of grain boundary has been estimated with the phonon diffusion mismatch model, and the intrinsic thermal conductivity within ZnO grains has been calculated with a cylinder-structured composite model. The result shows that the thermal conductivity of the ZnO thin films is dominated by the intrinsic thermal conductivity, which is a function of grain size.
Biosensors for immune cell analysis—A perspective
Authors: Revzin Alexander , Maverakis Emanual , Chang H.-C.
Published: April 2012

Massively parallel analysis of single immune cells or small immune cell colonies for disease detection, drug screening, and antibody production represents a “killer app” for the rapidly maturing microfabrication and microfluidic technologies. In our view, microfabricated solid-phase and flow cytometry platforms of the future will be complete with biosensors and electrical/mechanical/optical actuators and will enable multi-parametric analysis of cell function, real-time detection of secreted signals, and facile retrieval of cells deemed interesting.
Large-area nanostructured substrates for surface enhanced Raman spectroscopy
Authors: Shevchenko Andriy , Ovchinnikov Victor , Shevchenko Anna
Published: April 2012

We demonstrate substantial enhancement of Raman transitions of organic molecules by nanostructured gold-coated substrates at the excitation wavelength of 785 nm and experimentally study the factors that influence the enhancement. The substrates are fabricated by using a robust and cost-effective nanopatterning technique that allows us to create high-density gold- or silver-coated nanopillars simultaneously on the whole surface of a standard silicon wafer.
Communication: Density functional theory overcomes the failure of predicting intermolecular interaction energies
Authors: Podeszwa Rafał , Szalewicz Krzysztof
Published: April 2012

Density-functional theory (DFT) revolutionized the ability of computational quantum mechanics to describe properties of matter and is by far the most often used method. However, all the standard variants of DFT fail to predict intermolecular interaction energies. In recent years, a number of ways to go around this problem has been proposed. We show that some of these approaches can reproduce interaction energies with median errors of only about 5% in the complete range of intermolecular configurations. Such errors are comparable to typical uncertainties of wave-function-based methods in practical applications. Thus, these DFT methods are expected to find broad applications in modelling of condensed phases and of biomolecules.
Ca2+ waves across gaps in non-excitable cells induced by femtosecond laser exposure
Authors: He Hao , Wang Shaoyang , Li Xun , Li Shiyang , Hu Minglie , Cao Youjia , Wang Ching-Yue
Published: April 2012

Calcium is a second messenger in all cells for various cellular processes. It was found in astrocytes and neurons that femtosecond laser stimulation could induce Ca2+ wave propagation. In this work, a femtosecond laser with a power above a certain threshold was focused on single HeLa/HEK293T cells for Ca2+ mobilization. Several types of Ca2+ oscillation patterns were found in neighboring cells. The Ca2+ wave propagated very fast across 40-μm gaps in the Ca2+-free medium mediated by the adenosine-triphosphate released from cells. This approach could provide a clean methodology to investigate the Ca2+ dynamics in non-excitable cells.
Investigation of perpendicular magnetic anisotropy of CoFeB by x-ray magnetic circular dichroism
Authors: Tsai W. C. , Liao S. C. , Hou H. C. , Yen C. T. , Wang Y. H. , Tsai H. M. , Chang F. H. , Lin H. J. , Lai Chih-Huang
Published: April 2012

We have studied the variation of perpendicular magnetic anisotropy (PMA) of CoFeB layers with the oxidation degree of the MgO buffer layers. After annealing at 330 °C, the out-of-plane anisotropy field (Hk) of 1.5-nm CoFeB could be optimized to 3.1 kOe. To investigate the orbital hybridization of the Fe-3d and O-2p, the orbital moments per hole (morb/Nh) of Fe in annealed CoFeB layers were extracted by using x-ray magnetic circular dichroism. The dependence of morb/Nh on the oxidation time of MgO coincided with that of Hk, which revealed that PMA of annealed CoFeB originated from the interfacial orbital hybridization.
Strong mid-infrared radiation from self-guided fast electron bunch propagating along a grated target surface in laser-solid interaction
Authors: Zhuo H. B. , Jin Z. , Yu M. Y. , Sheng Z. M. , Xu H. , Ma Y. Y. , Yin Y. , Shao F. Q. , Zhou W. M. , Kodama R.
Published: April 2012

Generation of 1012 W/cm2 Smith-Purcell radiation in the infrared (5-20μm) regime from the interaction of high-density laser-produced MeV electrons is proposed. The electron bunch is produced by impinging an intense ultrashort laser pulse on a metallic target with a grated upper surface. Particle-in-cell simulation shows that the electron bunch can efficiently couple to the periodic structure through the quasistatic self-generated electric and magnetic fields there. An analytical model for predicting the dependence of the radiation intensity on the laser and grating parameters is also proposed. With appropriate laser and grating parameters, the proposed scheme provides a tunable source for intense radiation in the infrared regime.