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Filamentary structures can form within the beam of protons accelerated during the interaction of an intense laser pulse with an ultrathin foil target. Such behaviour is shown to be dependent upon the formation time of quasi-static magnetic field structures throughout the target volume and the extent of the rear surface proton expansion over the same period. This is observed via both numerical and experimental investigations. By controlling the intensity profile of the laser drive, via the use of two temporally separated pulses, both the initial rear surface proton expansion and magnetic field formation time can be varied, resulting in modification to the degree of filamentary structure present within the laser-driven proton beam.
Whether genetic factors influence the associations of fatty acids with the risk of sudden cardiac arrest (SCA) is largely unknown. To investigate possible gene–fatty acid interactions on SCA risk, we used a case-only approach and measured fatty acids in erythrocyte samples from 1869 SCA cases in a population-based repository with genetic data. We selected 191 SNP in ENCODE-identified regulatory regions of fifty-five candidate genes in fatty acid metabolic pathways. Using linear regression and additive genetic models, we investigated the association of the selected SNP with erythrocyte levels of fatty acids, including DHA, EPA and trans-fatty acids among the SCA cases. The assumption of no association in non-cases was supported by analysis of publicly available datasets containing over 8000 samples. None of the SNP–fatty acid associations tested among the cases reached statistical significance after correction for multiple comparisons. One SNP, rs4654990 near PLA2G2A, with an allele frequency of 0·33, was nominally associated with lower levels of DHA and EPA and higher levels of trans-fatty acids. The strongest association was with DHA levels (exponentiated coefficient for one unit (1 % of total fatty acids), 0·90, 95 % CI 0·85, 0·97; P = 0·003), indicating that for subjects with a coded allele, the OR of SCA associated with one unit higher DHA is about 90 % what it is for subjects with one fewer coded allele. These findings suggest that the associations of circulating n-3 and trans-fatty acids with SCA risk may be more pronounced in carriers of the rs4654990 G allele.
Stange Ice Shelf is the most south-westerly ice shelf on the Antarctic Peninsula, a region where positive trends in atmospheric and oceanic temperatures have been recently documented. In this paper, we use a range of remotely sensed datasets to evaluate the structural and dynamic responses of Stange Ice Shelf to these environmental changes. Ice shelf extent and surface structures were examined at regular intervals from optical and radar satellite imagery between 1973 and 2011. Surface speeds were estimated in 1989, 2004 and 2010 by tracking surface features in successive satellite images. Surface elevation change was estimated using radar altimetry data acquired between 1992 and 2008 by the European Remote Sensing Satellite (ERS) -1, -2 and Envisat. The mean number of surface melt days was estimated using the intensity of backscatter from Envisat’s Advanced Synthetic Aperture Radar instrument between 2006 and 2012. These results show significant shear fracturing in the southern portion of the ice shelf linked to enhanced flow speed as a consequence of measured thinning. However, we conclude that, despite the observed changes, Stange Ice Shelf is currently stable.
Since mid-2007 we have carried out a dedicated long-term monitoring programme at 15 GHz using the Owens Valley Radio Observatory 40 meter telescope (OVRO 40m). One of the main goals of this programme is to study the relation between the radio and gamma-ray emission in blazars and to use it as a tool to locate the site of high energy emission. Using this large sample of objects we are able to characterize the radio variability, and study the significance of correlations between the radio and gamma-ray bands. We find that the radio variability of many sources can be described using a simple power law power spectral density, and that when taking into account the red-noise characteristics of the light curves, cases with significant correlation are rare. We note that while significant correlations are found in few individual objects, radio variations are most often delayed with respect to the gamma-ray variations. This suggests that the gamma-ray emission originates upstream of the radio emission. Because strong flares in most known gamma-ray-loud blazars are infrequent, longer light curves are required to settle the issue of the strength of radio-gamma cross-correlations and establish confidently possible delays between the two. For this reason continuous multiwavelength monitoring over a longer time period is essential for statistical tests of jet emission models.
We report about first results of the RoboPol project. RoboPol is a large-sample, high-cadence, polarimetric monitoring program of blazars in optical wavelengths, using a camera specifically constructed for this project, mounted at the University of Crete's Skinakas Observatory 1.3 m telescope. The analysis of RoboPol data is conducted in conjunction with Fermi LAT gamma-ray data, and multifrequency radio data from the OVRO (Caltech), F-GAMMA (MPIfR), and Torun (NCU) monitoring programs. Using carefully selected samples of gamma-ray bright and weak blazars we investigate a connection between their optical polarization behaviour and variability properties in gamma. We examine a relationship of gamma flares with polarization angle rotations relying on robust statistical criteria. We analyse also the optical polarization variability itself in order to establish some restrictions on physical models of blazars jets.
Flow and transport through aquatic vegetation is characterized by a wide range of length scales: water depth (), plant height (), stem diameter (), the inverse of the plant frontal area per unit volume () and the scale(s) over which varies. Turbulence is generated both at the scale(s) of the mean vertical shear, set in part by , and at the scale(s) of the stem wakes, set by . While turbulence from each of these sources is dissipated through the energy cascade, some shear-scale turbulence bypasses the lower wavenumbers as shear-scale eddies do work against the form drag of the plant stems, converting shear-scale turbulence into wake-scale turbulence. We have developed a – model that accounts for all of these energy pathways. The model is calibrated against laboratory data from beds of rigid cylinders under emergent and submerged conditions and validated against an independent data set from submerged rigid cylinders and a laboratory data set from a canopy of live vegetation. The new model outperforms existing – models, none of which include the scale, both in the emergent rigid cylinder case, where existing – models break down entirely, and in the submerged rigid cylinder and live plant cases, where existing – models fail to predict the strong dependence of turbulent kinetic energy on . The new model is limited to canopies dense enough that dispersive fluxes are negligible.
Weed management in furrow-irrigated corn is challenging because of weed emergence associated with each irrigation event. Residual herbicides that provide extended in-season control of a broad spectrum of weeds would be beneficial to producers in this system. Field experiments were conducted in 2005 and 2006 in Yellowstone County, Montana, to evaluate KIH-485 for the control of velvetleaf, kochia, and wild buckwheat in furrow-irrigated corn. KIH-485 was applied at three rates (166, 209, and 250 g ai/ha) and two timings (PRE and POST) and compared to standard rates of S-metolachlor, acetochlor, and pendimethalin. All PRE treatments were applied alone, whereas POST treatments were combined with 1,261 g ae/ha of glyphosate. All rates of KIH-485 applied PRE controlled velvetleaf and kochia 88% or greater at 4 mo after planting (MAP). Wild buckwheat was controlled 89% or greater with the high rate of KIH-485 applied PRE, which was superior to control achieved with any other PRE herbicide treatment. Velvetleaf, kochia, and wild buckwheat were controlled 91% or greater when any herbicide treatment was combined with glyphosate. Corn treated with KIH-485 applied at 209 g ai/ha PRE produced yield that was similar to that produced by the weed-free control in both years.
Glaucoma is a major cause of blindness and is characterized by death
of retinal ganglion cells. In a rat model of glaucoma in which intraocular
pressure is raised by cautery of episcleral veins, the somata and
dendritic arbors of surviving retinal ganglion cells expand. To assess
physiological consequences of this change, we have measured visual
receptive-field size in a primary retinal target, the superior colliculus.
Using multiunit recording, receptive-field sizes were measured for
glaucomatous eyes and compared to both those measured for contralateral
control eyes and to homolateral eyes of unoperated animals. Episcleral
vein occlusion increased intraocular pressure. This was accompanied by a
significant increase in receptive-field size across the superior
colliculus. The expansion of receptive fields was proportional to both
degree and duration of the increase of intraocular pressure. We suggest
that this increase in the size of receptive fields of glaucomatous eyes
may be related to the increase in the size of dendritic arbors of the
surviving ganglion cells in retina.
Products formed from reactions of methyl iodide, 1-chloropropane, 1-iodopropane and 1-bromopropane with Na0 treated and untreated NaX and NaY zeolites were studied using solid state 13C NMR and IR spectroscopy. At room temperature, methyl iodide dissociates to form framework methoxy in untreated NaX with no reaction observed in untreated NaY. Upon Na0 treatment, both NaX and NaY reacts with methyl iodide to form framework methoxy, methane and ethane. Longer carbon chain 1-iodo, bromo and chloropropane were also studied. 1-iodopropane undergoes dehalogenation to form framework propoxy while 1-chloropropane and 1-bromopropane undergoes dehalogenation/ dehydrohalogenation to form framework propoxy and propene.
Copper / silver alloy thin films form with a fine, polycrystalline, metastable crystal structure. The expected effects of annealing include grain growth, transformation into the two stable phases, coarsening of the phases, texture formation, and the formation and growth of pinholes or voids. Copper/silver alloy films were deposited on single crystal sodium chloride substrates, via pulsed laser deposition ablation of an alloy target, of the eutectic composition. Free-standing films of 20-30 nm thickness were studied as-deposited and after annealing on copper TEM grids at 100°C for various times. Although several of the expected degradation processes involve short-range diffusion – essentially single atomic jumps – these were not observed, while other, longer-range diffusion effects were clearly identifiable. In particular, void shrinkage was observed in the films at short times, and void growth occurred at longer times.
Poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) ferroelectric thin films are a potentially promising material for sensors or non-volatile memories. Imprint, the time-dependent resistance to polarization reversal, is a key material property that limits applications and is poorly understood. Based on experimental time and temperature dependences, we propose and investigate the link between imprint and charge trap states. A novel fast-ramp thermally stimulated current (TSC) measurement was developed to quantify and characterize the traps in an appropriate time-frame.
Thin films of P(VDF-TrFE) on oxidized Si substrates were characterized following controlled initialization, fatigue, polarization, and imprint. Trap states were thermally filled/emptied by temperature cycling between 20–100 °C, using heating and cooling rates between 1 and 5 °C/s. Dynamics of this fast-ramp TSC indicate the presence of not only trap states, but also reversible and non-reversible charge accumulation. The presence of electrically active traps were verified by measurements over 1–10 s imprint times. Trapped charge directly correlated with the log of the imprint time, with a rate of ∼0.12 /μC/cm2/decade.
We have investigated the switching properties of ferroelectric lead strontium titanate (Pbx Sr1-x)TiO3 (PST) capacitors using epitaxial and polycrystalline La0.5Sr0.5CoO3 (LSCO) electrodes to evaluate its potential for non-volatile memory applications (FRAM'S). The electrical performance of the PST based capacitors grown on epitaxial and polycrystalline LSCO substrates were evaluated through Polarization-Voltage (P-V) and Fatigue measurements. The  preferentially oriented PST ferroelectric capacitor did not show a decrease in polarization up to 108 switching cycles at an applied voltage of 4 volts and a frequency of 100 kHz. Polycrystalline PST films, on the other hand were severely fatigued. It is proposed that the good performance of the PST capacitors can be attributed to the high degree of orientation of the PST films in the  direction induced by the epitaxial LSCO film. However, after 1010 switching cycles in the fatigue tests, the decay of the non-volatile polarization of these films was about 18% of its initial value. We use a simple model to describe two major microscopic scenarios for the suppression of polarization at the electrodes interfaces. This model is supported by Auger Electron Spectroscopy to determine the bulk and interfacial characteristics. The depth distribution of the elements of the PST film is nearly uniform throughout the volume of the film; however the relative concentrations of Pb and O were abnormally distributed on the surface. It is concluded that, in spite of the good performance due to the favorable conditions for the growth of the PST films provided by the textured LSCO, higher quality interfaces and better control of composition is necessary to improve on fatigue.
Because of aggressive downscaling to increase transistor performance, the physical thickness of the SiO2 gate dielectric is rapidly approaching the limit where it will only consist of a few atomic layers. As a consequence, this will result in very high leakage currents due to direct tunneling. To allow further scaling, materials with a k-value higher than SiO2 (“high-k materials”) are explored, such that the thickness of the dielectric can be increased without degrading performance.
Based on our experimental results, we discuss the potential of MOCVD-deposited HfO2 to scale to (sub)-1-nm EOTs (Equivalent Oxide Thickness). A primary concern is the interfacial layer that is formed between the Si and the HfO2, during the MOCVD deposition process, for both H-passivated and SiO2-like starting surfaces. This interfacial layer will, because of its lower k-value, significantly contribute to the EOT and reduce the benefit of the high-k material. In addition, we have experienced serious issues integrating HfO2 with a polySi gate electrode at the top interface depending on the process conditions of polySi deposition and activation anneal used. Furthermore, we have determined, based on a thickness series, the k-value for HfO2 deposited at various temperatures and found that the k-value of the HfO2 depends upon the gate electrode deposited on top (polySi or TiN).
Based on our observations, the combination of MOCVD HfO2 with a polySi gate electrode will not be able to scale below the 1-nm EOT marker. The use of a metal gate however, does show promise to scale down to very low EOT values.
In the quest for ever smaller transistor dimensions, the well-known and reliable SiO2 gate dielectric material needs to be replaced by alternatives whith higher dielectric constants in order to reduce the gate leakage. Candidate materials are metal oxides such as HfO2. Themost promising deposition techniques, next to Physical Vapor Deposition, appear to be ALCVD and MOCVD. In this paper, we compare the most important characteristics of layers from both proces techniques and assess their relevance to gate stack applications: density, crystallisation, impurities, growth mechanism, interfacial layers, dielectric constant, mobility. Although we find some minor differences, layers from both techniques mostly show striking similarities in many aspects, both positive and negative.
The continual drive for faster interconnects requires the development of new interlayer dielectricmaterials with k values less than 2.1. Porous SiLKTM semiconductor dielectric resin wasdeveloped to achieve these low dielectric constants by introducing nanometer-sized pores intothe dense SiLK resin matrix. A quantitative description of the nano-porous morphology in low-kinterlayer dielectrics can be difficult to achieve for many reasons, including: complexities in theporous structure (size range, geometry, pore/pore interaction), inadequate mathematicaldescriptors, limitations of existing metrology technology, and availability of “tailor-made” experimental samples with a wide range of pore morphologies. On-wafer quantification of poremorphology is even more difficult as data must be obtained from extremely limited samplevolumes (thin films of ∼100-500 nm) residing on thick silicon (Si) wafer substrates.
This paper will focus on the design, development and successful application of on-wafer smallangle x-ray scattering (SAXS) technology to characterize the morphology of porous SiLK resin.It will be demonstrated, by example, that this technology is able to deliver rapid quantificationover the entire pore size range for these systems. Recently developed data acquisition, reductionand analysis tools will be described. Direct evaluation of the strengths and challenges of severalmodels used to generate average pore size and pore size distribution will be reviewed. Finally,additional capabilities offered by this technology (wafer mapping and detection of “killer” pores)will also be discussed.
At the 65 nm node, silicide faces formidable challenges. Co is the current process of record for most integrated circuit manufacturers and thus becomes baseline silicide for 65 nm. However, Ni is the likely replacement. Both silicides are challenged to meet the requirements at the 65 nm node. This manuscript reviews the current CoSi2 challenges (dopant interactions, Ge interactions, linewidth extendibility, impurity effects, agglomeration issues, etc). Ni consumes less Si but has its own challenges, including issues with contact leakage and thermal budget, excessive diffusion and oxidation, interactions with dopant and impurities. Both silicides have formation and stability issues in the presence of Ge. Additions of Ge increase the temperature at which a low resistance CoSi2 is formed due to film segregation into CoSi2 and Ge-rich Si-Ge grains. With Ni, additions of Ge decrease the temperature at which NiSi converts to a NiSi2, lead to agglomeration at a lower temperature and lead to germanosilicide formation.