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To understand how foraging decisions impact individual fitness of herbivores, nutritional ecologists must consider the complex in vivo dynamics of nutrient–nutrient interactions and nutrient–toxin interactions associated with foraging. Mathematical modeling has long been used to make foraging predictions (e.g. optimal foraging theory) but has largely been restricted to a single currency (e.g. energy) or using simple indices of nutrition (e.g. fecal nitrogen) without full consideration of physiologically based interactions among numerous co-ingested phytochemicals. Here, we describe a physiologically based model (PBM) that provides a mechanistic link between foraging decisions and demographic consequences. Including physiological mechanisms of absorption, digestion and metabolism of phytochemicals in PBMs allows us to estimate concentrations of ingested and interacting phytochemicals in the body. Estimated phytochemical concentrations more accurately link intake of phytochemicals to changes in individual fitness than measures of intake alone. Further, we illustrate how estimated physiological parameters can be integrated with the geometric framework of nutrition and into integral projection models and agent-based models to predict fitness and population responses of vertebrate herbivores to ingested phytochemicals. The PBMs will improve our ability to understand the foraging decisions of vertebrate herbivores and consequences of those decisions and may help identify key physiological mechanisms that underlie diet-based ecological adaptations.
We performed a new series of measurements on samples that were part of early measurements on radiocarbon (14C) dating made in 1948–1949. Our results show generally good agreement to the data published in 1949–1951, despite vast changes in technology, with only two exceptions where there was a discrepancy in the original studies. Our new measurements give calibrated ages that overlap with the known ages. We dated several samples at four different laboratories, and so we were also able to make a small intercomparison at the same time. In addition, new measurements on samples from other Egyptian materials used by Libby and co-workers were made at UC Irvine. Samples of tree rings used in the original studies (from Broken Flute Cave and Centennial Stump) were obtained from the University of Arizona Laboratory of Tree-Ring Research archive and remeasured. New data were compared to the original studies and other records.
Salmonella is a leading cause of bacterial foodborne illness. We report the collaborative investigative efforts of US and Canadian public health officials during the 2013–2014 international outbreak of multiple Salmonella serotype infections linked to sprouted chia seed powder. The investigation included open-ended interviews of ill persons, traceback, product testing, facility inspections, and trace forward. Ninety-four persons infected with outbreak strains from 16 states and four provinces were identified; 21% were hospitalized and none died. Fifty-four (96%) of 56 persons who consumed chia seed powder, reported 13 different brands that traced back to a single Canadian firm, distributed by four US and eight Canadian companies. Laboratory testing yielded outbreak strains from leftover and intact product. Contaminated product was recalled. Although chia seed powder is a novel outbreak vehicle, sprouted seeds are recognized as an important cause of foodborne illness; firms should follow available guidance to reduce the risk of bacterial contamination during sprouting.
A coronal mass ejection (CME) event was observed on December 23, 1996 with the Ultraviolet Coronagraph Spectrometer in both ultraviolet and visible light channels at 0.5 R⊙ over the solar limb. The CME was followed during its evolution in the bright lines of Lyα (1216Å), Lyβ (1026Å), Lyγ (972Å), C III (977Å) and the OVI doublet (1032, 1037Å) and in several weaker lines. The Lyα peak intensity shows an excursion of two orders of magnitude during the CME evolution, and blue shifts up to 0.8Å (~200 km/sec). The data provide the emission measure in the Log T range 4.0–5.5 with a 0.3 sampling. Line intensities and profiles have been measured, providing important diagnostics for a detailed study of the CME’s physical and dynamical parameters.
In situ observations of comet Halley provided the first photographs of a cometary nucleus and yielded information about its environment, including the emitted gas and dust. The relation between these measurements and properties of and processes on the nucleus is established by theoretical modelling, while laboratory experiments may provide some of the physical parameters needed. In addition, laboratory tests can stimulate new ideas for processes that may be relevant to cometary physics. Processes to be studied in detail by large-scale laboratory experiments may include: (1) heat transport phenomena during sublimation of porous ice-dust mixtures, (2) material modification and chemical fractionation caused by the sublimation processes, (3) buildup and destruction of dust mantles, (4) detailed studies of gas release from mixtures of volatile ices, and (S) the investigation of ice and dust particle release mechanisms. The KOSI-team (Kometensimulation) carried out sublimation experiments with ice-mineral mixtures in a large Space Simulator. During initial experiments, cylindrical samples of 30-cm diameter and 15-cm thickness were irradiated with up to 2700–W/m2 light energy. The samples consisted of water-ice or water- and CO2-ice mineral mixtures. The experiments showed the importance of advection for heat transport into the interior. It was found that the sublimation of CO2 advances into the sample at a higher speed than that of water vapor release. Therefore, emission of volatile gases responded to insolation changes with a time lag of several hours. The ratio of the emitted gas species, as well as the dust-to-gas mass ratio, differs significantly from the values within the sample. A partly permeable refractory mantle of minerals and carbonaceous material developed with time. Dust and ice particle emission has been observed to occur from irradiated dirty ices as well as from dust mantles.
This case of a 65-year-old male with dermatillomania, diffuse anxiety symptoms, and avoidant personality disorder (PD) illustrates the interference of attention-deficit hyperactivity disorder (ADHD) in the diagnostic process and during schema-focused therapy. In conclusion, ADHD in older adults and interference with PD is a subject of clinical importance and worth further investigation.
Investigations describing the utilization pattern and comparing the outcome from emergency and mass casualty situations are limited by the lack of a reliable and valid patient classification system. In this study we briefly describe the use of APACHE (Acute Physiology and Chronic Health Evaluation), a physiologically based classification system for measuring severity of illness in groups of critically ill patients, as a tool in comparing outcomes of 1437 ICU admissions from eight European and five American hospitals. Because of the successful results from this pilot effort, we believe that APACHE could be used to compare the performance of hospitals in an emergency or mass casualty situation.
We present here a method for fabrication of air-gaps between Cu-interconnects to achieve low intralevel dielectric constant, using a sacrificial polymer as a ‘place holder’. IC compatible metallization and CMP processes were used in a single damascene process. The air-gap occupies the entire intralevel volume between the copper lines with fully densified SiO2 as the planer interlevel dielectric. The width of the air-gaps was 286 nm and the width of the copper lines was 650 nm. The effective intralevel dielectric constant was calculated to be 2.19. The thickness of the interlevel SiO2 and copper lines were 1100 nm and 700 nm, respectively. Further reduction in the value of intralevel dielectric constant is possible by optimization of the geometry of the metal/air-gap structure, and by use of a low k interlevel dielectric material.
In this method of forming air-gaps, the layer of sacrificial polymer was spin-coated onto the substrate and formed into the desired pattern using an oxide or metal mask and reactive-ion-etching. The intralevel Cu trench is then inlaid using a damascene process. After the CMP of copper, interlevel SiO2 is deposited by plasma-CVD. Finally, the polymer place-holder is thermally decomposed with the decomposition products permeating through the interlevel dielectric material. The major advantages of this method over other reported methods of formation of air-gaps are excellent control over the geometry of the air-gaps; no protrusion of air-gaps into the interlevel dielectric; no deposition of SiO2 over the side-walls, and no degradation of the interlevel dielectric during the formation of air-gap.
In this work, we investigated the electrocatalytic oxygen reduction reaction (ORR) activity of vertically aligned, single-layer, carbon-free, and single crystal Pt nanorod arrays utilizing cyclic voltammetry (CV) and rotating-disk electrode (RDE) techniques. A glancing angle deposition (GLAD) technique was used to fabricate 200 nm long Pt nanorods, which corresponds to Pt loading of 0.16 mg/cm2, on glassy carbon (GC) electrode at a glancing angle of 85° as measured from the substrate normal. An electrode comprised of conventional carbon-supported Pt nanoparticles (Pt/C) was also prepared for comparison with the electrocatalytic ORR activity and stability of Pt nanorods. CV results showed that the Pt nanorod electrocatalyst exhibits a more positive oxide reduction peak potential compared to Pt/C, indicating that GLAD Pt nanorods are less oxophilic. In addition, a series of CV cycles in acidic electrolyte revealed that Pt nanorods are significantly more stable against electrochemically-active surface area loss than Pt/C. Moreover, room temperature RDE results demonstrated that GLAD Pt nanorods exhibit higher area-specific ORR activity than Pt/C. The enhanced electrocatalytic ORR activity of Pt nanorods is attributed to their larger crystallite size, single-crystal property, and the dominance of (110) crystal planes on the large surface area nanorods sidewalls, which has been found to be the most active plane for ORR. However, the Pt nanorods showed lower mass specific activity than the Pt/C electrocatalyst due to the large diameter of the Pt nanorods.
The profiles of features etched photoelectrochemically in n-InP are studied to determine the factors which govern their distortions and to determine the factor limiting spatial resolution for etch depths in the 100–200−μm range. The optimal conditions for etching straight grooves using laser light are determined. The application to front-to-back mask registration will be discussed.
Previous work has demonstrated the potential of polytetrafluoroethylene (PTFE) thin films for ULSI applications. The films are deposited from PTFE nanoemulsions. They have an ultra-low dielectric constant of 1.7 to 2.0, a leakage current of less than 1.0 nA/cm2 @ 0.2 MV/cm and a dielectric strength of from 0.5 to 2.4 MV/cm. They are thermally stable (isothermal weight loss < 1.0 %/hr at 450 °C), uniform (thickness standard deviation < 2%), and have excellent gap-fill properties (viscosity of 1.55 cP and surface tension of 18 mN/m). The films are inert with respect to all known semiconductor process chemicals, yet they are easily etched in an oxygen plasma.
This paper discusses the processing technology that has been developed to process PTFE films with these properties. Specifically, it addresses two recent discoveries: 1) Good adhesion of spin-coated PTFE to SiO2 surfaces; and 2) high dielectric strength of PTFE thin films spin-coat deposited onto rigid substrates. The adhesion-promoting and thermal treatments necessary to produce these properties are detailed. Stud pull test results and test results from metal-insulator-metal (MIM) capacitor structures are given.
Improvements in the properties of Parylene may enable their use in high performance integrated circuits. Parylenes are a class of polymers formed by chemical vapor deposition which nearly meet the high standards of the low-k triumvirate, namely, 1) adhesion, particularly to SiO2, 2) thermal stability above 400 Celsius, and 3) permittivity less than 2.7. Parylene-N has been incorporated into both aluminum-1 and copper-2 based metallization schemes, however, improvements in the adhesion and thermal stability are still needed to simplify and increase the robustness of the integration schemes. Additionally, a reduction in the permittivity would be beneficial from both device performance and extendibility points-of-view. We have synthesized various Parylene-N-based copolymers with improved adhesion, thermal stability, and permittivity. We discovered that a copolymer of tetravinyl-tetramethyl-cyclotetrasiloxane and Parylene-N has a permittivity of close to 2.1 and both the adhesion to SiQ2 and thermal stability are measurably improved compared to the homopolymer.
Metalized polypropylene film used in high energy density capacitors has been mechanically characterized to determine its elastic constants. The out of plane coefficient of thermal expansion (CTE) of the orthotropic film is 10 times as large as the smaller in plane CTE. The out of plane modulus is twice as large compared to one of the in plane moduli. The effect of interfacial pressure on the dielectric breakdown is also studied for the same film. It is observed that the dielectric strength of the film decreases at first and then increases above 4 MPa of compressive stress.
Polyamic amides or polyamic esters are alternative polyimides precursors exhibiting a better storage-stability than classical polyamic acids. Two original synthetic routes to these polymers were investigated through either diisoimides and diimidazolides in order to enhance stability and to obtain pure para catenation.
Electron Spectroscopic Imaging (ESI) in an energy filtering TEM is a new analytical technique which allows one to obtain two-dimensional elemental distribution images. In the present paper the detection limits of the new technique will be discussed. Si3N4 ceramics with different thicknesses of the amorphous oxide grain boundary layers have been chosen as a model system. Quantitative results have been obtained on three different energy filtering instruments and will be compared with the results of theoretical calculations. The application of ESI for the mapping of near edge fine structure will be discussed.
This paper presents a study of the effects of electron beam (e-beam) exposure on the chemical and physical properties of FLARE™ 1.0X, a non-fluorinated member of the FLARE™ family of poly(arylene ether) dielectric coatings. Spin-coated films of this poly(arylene ether) were cured by large-area e-beam exposure, as well as by conventional thermal processing. Neither swelling nor dissolution was observed for the e-beam cured films after immersion in N-methylpyrrolidone (NMP) at 90 °C for 1 hour. The glass transition temperature (Tg) for films cured with a low e-beam dose is slightly higher than, or nearly the same as, the (Tg) for thermally-cured films (∼ 270 °C). However, the Tg for films cured with a high e-beam dose exceeds 400 °C. Dielectric constants of e-beam cured films and thermally cured films are nearly the same. FTIR spectra of FLARE™ films obtained before and after e-beam exposure suggest that e-beam curing does not induce any significant change in the chemical structure. Increased solvent resistance, higher Tg, and low dielectric constant are properties that make this e-beam cured poly(arylene ether) film an excellent candidate for interlevel dielectric integration processes.
One potential low dielectric constant material for ULSI multilevel interconnect applications is parylene AF-4, an organic polymer more formally known as Poly (α, α, α’, α’ - tetrafluoro-p-xylylene). In this study parylene AF-4 films were vapor-deposited on silicon wafers by pyrolytic decomposition of the cyclic dimer, cyclodi(α, α, α’, α’ - tetrafluoro-p-xylylene) using four different deposition conditions. Two different wafer temperatures and two different vaporizer temperatures were used, while the chamber pressure was kept constant. High vaporizer temperature and low wafer temperature give the highest deposition rates. It was found that the surface roughness of films of similar thickness showed a dependence on the deposition conditions. The films deposited at a low vaporizer temperature exhibit a smooth surface (RMS ∼ 4 nm) while those deposited at high vaporizer temperature have a rougher surface (RMS ∼ 16 nm). However, other properties of the films remained very similar. The FTIR spectra and refractive indices, both TE and TM, were measured for the films deposited using the four different deposition processes and showed no dependence on deposition conditions. These results indicate that the change in surface roughness is not due to a large difference in the chemical bonding among the films deposited using the four processes. Also, both weight loss and thickness loss of the films were measured after thermal cycling the films to 450°C and no significant differences were observed. This result indicates that the observed increase in surface roughness with increased vaporizer temperature cannot be related to a change in dimer incorporation in the films. Further experiments are planned to investigate the role of the initiation stage of the polymerization on film surface morphology.
A novel polymer has been developed for use as a thin film dielectric in the interconnect structure of high density integrated circuits. The coating is applied to the substrate as an oligomeric solution, SiLK*, using conventional spin coating equipment and produces highly uniform films after curing at 400 °C to 450 °C. The oligomeric solution, with a viscosity of ca. 30 cPs, is readily handled on standard thin film coating equipment. Polymerization does not require a catalyst. There is no water evolved during the polymerization. The resulting polymer network is an aromatic hydrocarbon with an isotropie structure and contains no fluorine.
The properties of the cured films are designed to permit integration with current ILD processes. In particular, the rate of weight-loss during isothermal exposures at 450 °C is ca. 0.7 wt.%/hour. The dielectric constant of cured SiLK has been measured at 2.65. The refractive index in both the in-plane and out-of-plane directions is 1.63. The flow characteristics of SiLK lead to broad topographic planarization and permit the filling of gaps at least as narrow as 0.1 μm. The glass transition temperature for the fully cured film is greater than 490 °C. The coefficient of thermal expansivity is 66 ppm/°C below the glass transition temperature. The stress in fully cured films on Si wafers is ca. 60 MPa at room temperature. The fracture toughness measured on thin films is 0.62 MPa m ½. Thin coatings absorb less than 0.25 wt.% water when exposed to 80% relative humidity at room temperature.
XPS studies of Cu(I)hfac(COD)adsorbed on clean and alumina-modified Teflon-AF surfaces show that on the clean polymer surface, Cu(0) formation occurs between 300 K and 600 K in UHV. The corresponding reduction is hindered by the presence of an alumina adlayer. In addition, the Cu Auger kinetic energies indicate the formation of nanoparticles on the alumina surface at both 300 K and 600 K. Annealing from 300 K to 600 K results in a ∼4 eV shift of the Cu(2p) transitions to higher binding energies. These facts indicate that the Cu precursor reacts with the alumina surface and results in limited mobility and hindered Cu(I) to Cu(0) reduction on the modified polymer surface.