7,194 research outputs found
Preliminary Results of Aerodynamic Heating Studies on the X-15 Airplane
Aerodynamic heating analysis of X-15 aircraft in fligh
How Well Can You Tailor the Charge of Lipid Vesicles?
Knowledge and control of surface charge or potential is important for tailoring colloidal interactions. In this work, we compare widely used zeta potential (ζ) measurements of charged lipid vesicle surface potential to direct measurements using the surface force apparatus (SFA). Our measurements show good agreement between the two techniques. On varying the fraction of anionic lipids dimyristoylphosphatidylserine (DMPS) or dimyristoylphosphatidylglycerol (DMPG) mixed with zwitterionic dimyristoylphosphatidylcholine (DMPC) from 0 to 100 mol % we observed a near-linear increase in membrane surface charge or potential up to 20-30 mol % charged lipids beyond which charge saturation occurred in physiological (high) salt conditions. Similarly, in low salt concentrations, a linear increase in charge/potential was found but only up to ∼5-10 mol % charged lipids beyond which the surface charge or potential leveled off. While a lower degree of ionization is expected due to the lower dielectric constant (ε ∼ 4) of the lipid acyl chain environment, increasing intramembrane electrostatic repulsion between neighboring charged lipid head groups at higher charge loading contributes to charge suppression. Measured potentials in physiological salt solutions were consistent with predictions using the Gouy-Chapman-Stern-Grahame (GCSG) model of the electrical double layer with Langmuir binding of counterions, but in low salt conditions, the model significantly overestimated the surface charge/potential. The much lower ionization in low salt (maximum ∼1-2% of total lipids ionized) instead was consistent with counterion condensation at the bilayer surface which limited the charge that could be obtained. The strong interplay between membrane composition, lipid headgroup ionization, electrolyte concentration, and solution pH complicates exact prediction and tuning of membrane surface charge for applications. However, the theoretical frameworks used here can provide guidelines to understand this interplay and establish a range of achievable potentials for a system and predict the response to triggers like pH and salt concentration changes
Probing Localization in Absorbing Systems via Loschmidt Echos
We measure Anderson localization in quasi-one-dimensional waveguides in the
presence of absorption by analyzing the echo dynamics due to small
perturbations. We specifically show that the inverse participation number of
localized modes dictates the decay of the Loschmidt echo, differing from the
Gaussian decay expected for diffusive or chaotic systems. Our theory, based on
a random matrix modeling, agrees perfectly with scattering echo measurements on
a quasi one-dimensional microwave cavity filled with randomly distributed
scatterers.Comment: cross-reference with nonlin.CD-Chaotic Dynamic
Disordered graphene and boron nitride in a microwave tight-binding analog
Experiments on hexagonal graphene-like structures using microwave measuring
techniques are presented. The lowest transverse-electric resonance of coupled
dielectric disks sandwiched between two metallic plates establishes a
tight-binding configuration. The nearest-neighbor coupling approximation is
investigated in systems with few disks. Taking advantage of the high
flexibility of the disks positions, consequences of the disorder introduced in
the graphene lattice on the Dirac points are investigated. Using two different
types of disks, a boron-nitride-like structure (a hexagonal lattice with a
two-atom basis) is implemented, showing the appearance of a band gap.Comment: 12 pages, 14 figure
Microwave fidelity studies by varying antenna coupling
The fidelity decay in a microwave billiard is considered, where the coupling
to an attached antenna is varied. The resulting quantity, coupling fidelity, is
experimentally studied for three different terminators of the varied antenna: a
hard wall reflection, an open wall reflection, and a 50 Ohm load, corresponding
to a totally open channel. The model description in terms of an effective
Hamiltonian with a complex coupling constant is given. Quantitative agreement
is found with the theory obtained from a modified VWZ approach [Verbaarschot et
al, Phys. Rep. 129, 367 (1985)].Comment: 9 pages 5 figur
Numerical simulation of inductive heating processes
For product optimization regarding weight reduction, material properties have
to be adapted efficiently. To achieve this, new compositions of materials can be created
or the manufacturing process can be changed in a way that heterogeneous distributions
of material properties are enabled. An example for such an improved process chain is
the production of thermo-mechanically graded structures like shafts. The manufacturing
method mainly consists of three stages. The first one is characterized by a local temperature
increase of the workpiece due to inductive heating. In the second phase the workpiece
is deformed and simultaneously cooled throughout the contact with the forming die. In
the last step, however, a high pressured air stream is applied, leading to a partial cooling
of the workpiece.
The inductive heating step is controlled by an alternating current inducing a high frequency
magnetic field, which causes a temperature increase due to the resulting eddy
currents. To analyse this process, the coupling between the electric and the magnetic
field is described by the fully coupled Maxwell equations. Moreover the heat conduction
equation is considered to describe thermal effects. To solve this multifield the
equations are in the first step decoupled using an additional time differentiation. In the
second step an axisymmetric case is considered, motivated by the fact that the inductive
heating process of a cylindrical shaft is analysed. Afterwards the resulting equations are
spatially discretized by the Galerkin finite element method. The temporal discretization
is carried out via the Newmark method so that afterwards the electrical source
distribution can be achieved. As a consequence the temperature evolution is determined
in a postprocessing step
Preweaning and Postweaning Performance of Crossbred Calves--0, 1 or 2 Ralgro Implants
The preweaning performance of 221 steer and heifer calves given differing numbers of Ralgro implants was evaluated. The steer and heifer calves given one implant had an additional 23 and 33 lb weaning weight compared to those receiving no implant. No additional response was shown by steer calves receiving a second implant 100 days after the first was given. Average daily gains during the 105-day growing period were not significantly faster than those receiving two implants during the 103-day finishing phase. This work supports other studies indicating that implanting calves at weaning time is an economical management practice. The work further indicates to feeders that calfhood implants have little or no effect on subsequent performance in the feedlot
Effect of Length of Feeding Period on Performance of British and Exotic Crossbred Yearling Heifers
Seventy-two heifers were fed for 47, 61 and 75 days to determine the optimum feeding period for exotic cross and black baldy heifers. Average daily gains and feed conversions of the heifers were similar among treatments. Carcass weight, quality grade and yield grade increased with time on feed. Fat thickness, quality grade and yield grade increased faster for the black baldy heifers. Cost per pound of gain was similar for all treatments. The optimum weight at which to slaughter the black baldy yearling heifers appeared to be between 1000 and 1050 lb., both from a quality and economic view point. The optimum weight for slaughtering the exotic cross heifers was apparently not reached, as the last slaughter group was still gaining rapidly and efficiently with little increase in condition. The limited research conducted in this study indicates that a producer with mixed lots of cattle needs to be aware of the weight at which different types of cattle reach optimum condition. The feeder has greater flexibility in marketing the larger framed exotic cross type cattle as compared to the relatively smaller framed English breeds
Feeding Value of Pro-Sil Treated High-Moisture Ground Ear Corn with Two Groups of Crossbred Heifers
Pro-Sil, an ammonia-molasses-mineral suspension, has been shown to be a highly effective commercial additive for corn silage in studies at SDSU and other midwest universities. When added to corn silage at the time of ensiling, this product stimulates beneficial fermentation and increases the crude protein content of the silage, thereby reducing or eliminating the need for protein supplementation at the time of feeding. While Pro-Sil has been thoroughly tested with whole plant corn silage, no research has been conducted with ensiled high-moisture ear corn (HMEC). Since the crude protein content of HMEC is low compared to the needs of feedlot cattle, research is needed to evaluate economical methods of boosting the level of this critical nutrient. Thus, the major objective of this initial study was to compare the feedlot performance of cattle fed Pro-Sil treated HMEC or regular HMEC mixed with either a control or a urea-based protein supplement at the time of feeding. Both types of HMEC were ensiled in a plastic Silopress bag to examine the effectiveness of this storage method with HMEC. The relative performance of exotic and British crossbred yearling heifers was also studied in this trial
Two-Dimensional Magnetic Resonance Tomographic Microscopy using Ferromagnetic Probes
We introduce the concept of computerized tomographic microscopy in magnetic
resonance imaging using the magnetic fields and field gradients from a
ferromagnetic probe. We investigate a configuration where a two-dimensional
sample is under the influence of a large static polarizing field, a small
perpendicular radio-frequency field, and a magnetic field from a ferromagnetic
sphere. We demonstrate that, despite the non-uniform and non-linear nature of
the fields from a microscopic magnetic sphere, the concepts of computerized
tomography can be applied to obtain proper image reconstruction from the
original spectral data by sequentially varying the relative sample-sphere
angular orientation. The analysis shows that the recent proposal for atomic
resolution magnetic resonance imaging of discrete periodic crystal lattice
planes using ferromagnetic probes can also be extended to two-dimensional
imaging of non-crystalline samples with resolution ranging from micrometer to
Angstrom scales.Comment: 9 pages, 11 figure
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