Some comments on post extrusion swelling phenomena: Die entrance or die passage

The mechanistic origins of the post extrusion swelling phenomenon have been the subject of considerable debate. Conflicting theories have postulated that it is caused either by (1) deformations at the die entrance which are recovered upon die exit as a consequence of viscoelastic memory or (2) elastic enorgy, which is stored during capillary flow by the action of normal stress, and subsequently released upon die exit or by both (1) and (2). We have described these situations by mathematical models and show that the resulting equations are similar despite different origins. The difficulties in interpreting the results mechanistically are discussed. Empirically, the results can be described as being exponential in capillary residence irrespective of cause.     

The Design of Gradings with Small Interconnection Numbers for Random Hunt Selectors

An earlier paper [2] presented algorithms for designing gradings for random hunt selectors, The gradings were designed to have a particular kind of combinatorial symmetry called "uniform overlap." The uniform overlap condition is a necessary but not a sufficient condition for grading design. The lack of sufficiency is particularly apparent for gradings With small interconnection numbers. The structural characteristics of such gradings are examined and desirable characteristics of practical gradings are identified. A parameterTis defined as a grading characteristic and procedures are presented for designing gradings having minimal values ofT. Since there is, in general, no unique solution to the problem of designing a uniform overlap grading, the recommendation is made for given reasons that the solution selected should have the smallest value ofT.     

Alteration to lake trophic status as a means to control arsenic mobility in a mine-impacted lake

The relationship between lake trophic status, sedimentary redox conditions and As mobility was examined in mine-impacted Balmer Lake, Canada. Under the current redox regime, the reductive dissolution of As-bearing Fe(III) oxyhydroxides occurs in close proximity to the sediment–water interface, resulting in the remobilization of dissolved As in the shallow porewaters to values as high as 8.5 mg L⁻¹. The shallow depth of the oxic zone limits the extent to which As can be re-sorbed in the interfacial horizons, and as a result, a proportion of the remobilized As escapes into the water column where it poses a water quality concern. Examination of the relationship between summer average chlorophyll a and total P at spring overturn in the lake water column demonstrates that Balmer Lake is currently eutrophic as a result of mining-derived inputs of P (domestic waters) and N (blasting residues and cyanide breakdown products). The results suggest that actively pushing the system towards oligotrophy by reducing non-natural P loadings to the system will decrease rates of in situ production and associated sediment oxygen demand, which will in turn result in increased thickness of the aerobic zone and enhanced As scavenging. Such conclusions are supported by porewater data which indicate that the flux of As to the water column is significantly reduced when the Fe(III) redox cline is situated at deeper sediment depths. In the absence of detailed P-loading data, it is recommended that P inputs be reduced to 10% of the estimated pre-mining P loading of 200 kg yr⁻¹. This implies reducing the collective P-loadings from the two mine sites adjacent to the lake from the approximate current value (150 kg yr⁻¹) to 20 kg yr⁻¹. It is proposed that establishment of oligotrophy in the lake should significantly mitigate the current level of dissolved As in lake waters.     

An UTRA/FDD Direct-Downconversion Mixer in 0.25 μm CMOS

In this paper the design of a 2 GHz direct-downconversion mixer for a UTRA/FDD receiver is presented. The mixer is implemented using a standard low-cost 0.25 m, single-poly, six-metal CMOS process. An on-chip passive balun is used to generate a balanced RF input signal. In-house optimized device models are used for both active and passive components to achieve a voltage conversion gain of 12.8 dB, an iIP₂ of 25 dBm, an iIP₃ of –3.1 dBm, and a noise figure of 8 dB. The circuit provides I and Q signal path outputs while drawing 6 mA from a 2.5 V supply.     

Examples of density, orientation, and shape-optimal 2D-design for stiffness and/or strength with orthotropic materials

The balance between stiffness and strength design is considered in the present paper. For materials with different levels of orthotropy (including isotropy), we optimize the density distribution as well as the orientational distribution for a short cantilever problem, and discuss the tendencies in design and response (energy distributions and stress directions). For a hole in a biaxial stress field, the shape design of the boundary hole is also incorporated.The resulting tapered density distributions may be difficult to manufacture, for example, in micro-mechanics production. For such problems a penalization approach to obtain black and white designs, i.e. uniform material or holes, is often applied in optimal design. A specific example is studied to show the effect of the penalization, but is restricted here to an isotropic material.When the total amount of material is not specified, a conflict between optimal design for stiffness and optimal design for strength appears. The computational results of such a case study are shown.     

Assessment of prosthetic aortic valve performance by magnetic resonance velocity imaging

Objectives Magnetic resonance (MRI) velocity mapping was used to evaluate non-invasively the flow profiles of the ascending aorta in normal volunteers and in patients with an aortic (mechanical) valve prosthesis. Background In patients with artificial aortic valves the flow profile in the ascending aorta is severely altered. These changes have been associated with an increased risk of thrombus formation and mechanical hemolysis. Methods Velocity profiles were determined 30 mm distal to the aortic valve in six healthy volunteers and seven patients with aortic valve replacement (replacement within the last 2 years) using ECG triggered phase contrast MRI. Peak flow, mean flow and mean reverse flow were measured in intervals of 25 ms during the entire heart cycle. Systolic reverse flow, end-systolic closing and diastolic leakage volume were calculated for all subjects. Results Peak flow velocity during mid-systole was significantly higher in patients with valvular prosthesis than in normals (mean±SD, 1.9±0.4 m/s vs. 1.2±0.03 m/s,P<0.001) with a double peak and a zone of reversed flow close to the inner (left lateral) wall of the ascending aorta of the patients. Closing volume was significantly larger in patients than in controls (−3.3±1.2 ml/beat vs. −0.9±0.5 ml/beat;P<0.001). There was reverse flow during systole in valvular patients amounting to 15.7±6.7% of total cardiac output compared to 2.3±1.2% in controls (P<0.001). Diastolic mean flow was negative in patients after valve replacement but not in controls (−11.0±15.2 ml/beat vs. 6.8±3.2 ml/beat;P<0.01). Conclusions The following three major quantitative observations have been made in the present study: (1) Mechanical valve prostheses have an increased peak flow velocity with a systolic reverse flow at the inner (left lateral) wall of the ascending aorta. (2) A double peak flow velocity pattern can be observed in patients with bileaflet (mechanical) prosthesis. (3) The blood volume required for leaflet closure and the diastolic leakage blood volume are significantly higher for the examined bileaflet valve than for native heart valves.     

Isotropic scattering by penetrable cylinders

Isotropic scattering is considered for infinite cylinders thin in the sense that ka < 1, although ?k'a? and cross-sectional shape can be arbitrary within limits (k and k' are, respectively, free-space and interior propagation constants, and a is a characteristic dimension of the cylinder). For circular cylinders, scattering width is found to saturate at its perfectly conducting value, and absorption width is found to peak, when skin depth becomes comparable with cylinder diameter. For a variety of cylinders with and without edges, both scattering and absorption widths are then found to be effectively identical to those of the circular cylinder with equal cross-sectional area. A new analytical formula is obtained for high but not infinite conductivity, and the connection with scattering cross sections of corresponding finite cylinders is discussed.     

Development of a measure of drinking and driving expectancies for youth.

The present study constructs and provides initial validation for a measure of positive expectancies for drinking and driving for use with adolescents and young adults (PEDD-Y). In Study 1, items were generated through open-ended responses from high school- and college-age youth. Data collected from a 2nd sample of college students (n = 404) identified a 29 item, 4 factor questionnaire. Two of the PEDD-Y factors (Convenience, Avoiding Consequences) explained additional variance in drinking and driving behavior above and beyond other cognitions about drinking and driving. Study 2 extended these results to a high school sample (n = 185). Study 3 demonstrated test-retest reliability of the PEDD-Y in college-age youth (n = 165). These results provide initial evidence for the utility of the PEDD-Y in assessing drinking and driving risk in adolescents and college students. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Gasochromic switching of reactively sputtered molybdenumoxide films: A correlation between film properties and deposition pressure

Molybdenumoxide (MoO_x) thin films can change their optical properties upon exposure to hydrogen. Since the film properties strongly depend on process parameters we have studied how the films are affected by the total pressure during deposition. Stoichiometric and sub-stoichiometric MoO_x films were prepared by reactive direct current magnetron sputtering in an atmosphere of argon and oxygen. Substoichiometric films were coated with platinum as a catalyst and were colored in diluted hydrogen atmosphere and bleached in air. Optical spectroscopy, X-ray reectometry, spectroscopic ellipsometry and simulations of the measured spectra were used to characterize the films ex situ. In situ switching characteristics as revealed by optical spectroscopy and changes in stress were measured as well. We find that the total pressure during sputter deposition has a strong influence on the optical constants, the film density, and the sputter rate. The mechanical stresses and switching Preprint submitted to Elsevier Science 10 March 2006 cycles during the film coloration and bleaching also strongly depend on the total pressure. The influence of the sputter pressure on film properties is explained by the kinetics during the sputter process.