84,509 research outputs found
Noise-assisted Mound Coarsening in Epitaxial Growth
We propose deposition noise to be an important factor in unstable epitaxial
growth of thin films. Our analysis yields a geometrical relation H=(RWL)^2
between the typical mound height W, mound size L, and the film thickness H.
Simulations of realistic systems show that the parameter R is a characteristic
of the growth conditions, and generally lies in the range 0.2-0.7. The
constancy of R in late-stage coarsening yields a scaling relation between the
coarsening exponent 1/z and the mound height exponent \beta which, in the case
of saturated mound slope, gives \beta = 1/z = 1/4.Comment: 4 pages, RevTex Macros, 3 eps figure
The prospect of detecting single-photon force effects in cavity optomechanics
Cavity optomechanical systems are approaching a strong-coupling regime where
the coherent dynamics of nanomechanical resonators can be manipulated and
controlled by optical fields at the single photon level. Here we propose an
interferometric scheme able to detect optomechanical coherent interaction at
the single-photon level which is experimentally feasible with state-of-the-art
devices.Comment: 8 pages, 2 figure
A co-operating solver approach to building simulation
This paper describes the co-operating solver approach to building simulation as encapsulated within the ESP-r system. Possible adaptations are then considered to accommodate new functional requirements
Some t-tests for N-of-1 trials with serial correlation
N-of-1 trials allow inference between two treatments given to a single
individual. Most often, clinical investigators analyze an individual's N-of-1
trial data with usual t-tests or simple nonparametric methods. These simple
methods do not account for serial correlation in repeated observations coming
from the individual. Existing methods accounting for serial correlation require
simulation, multiple N-of-1 trials, or both. Here, we develop t-tests that
account for serial correlation in a single individual. The development includes
effect size and precision calculations, both of which are useful for study
planning. We then evaluate and compare their Type I and II errors and interval
estimators to those of usual t-tests analogues via Monte Carlo simulation. The
serial t-tests clearly outperform the usual t-tests commonly used in reporting
N-of-1 results. Examples from N-of-1 clinical trials in fibromyalgia patients
and from a behavioral health setting exhibit how accounting for serial
correlation can change inferences. These t-tests are easily implemented and
more appropriate than simple methods commonly used; however, caution is needed
when analyzing only a few observations. Keywords: Autocorrelation; Cross-over
studies; Repeated measures analysis; Single-case experimental design;
Time-seriesComment: 23 pages, 6 figures, 6 table
An observation of cosmic ray positrons from 10-20 GeV
A balloon flight of the University of Chicago electron telescope was performed. Making use of the east-west asymmetry in the geomagnetic cut off rigidity, the cosmic ray positrons and negatrons were separated over the range 10 GeV to 20 GeV. The positron to electron ratio, e+/(e++e-), was measured to be 17% + or - 5%, significantly higher than the ratio measured in the 1 GeV to 10 GeV range by other experiments. This increase appears to suggest that either a primary component of positrons become significant above 10 GeV, or that the spectrum of primary negatrons decreases above 10 GeV more sharply than that of secondary positrons
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
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