26,031 research outputs found
2H and 13C NMR studies on the temperature-dependent water and protein dynamics in hydrated elastin, myoglobin and collagen
2H NMR spin-lattice relaxation and line-shape analyses are performed to study
the temperature-dependent dynamics of water in the hydration shells of
myoglobin, elastin, and collagen
Atomic screening of nuclear transitions
In the analysis of time-reversal and Mössbauer absorption experiments, it is important to consider atomic processes which interfere with the direct nuclear transition. Interaction of the photon with the atomic electrons causes the radiation to acquire a phase shift, specified by the interference parameter ξ(L_π). We present theoretical expressions for ξ and compare our calculated values with experiment. Satisfactory agreement is obtained. In particular, an apparent violation of time-reversal invariance in the 129-keV transition of ^(191)Ir is fully explained by these effects
Scanning probe microscopy imaging of metallic nanocontacts
We show scanning probe microscopy measurements of metallic nanocontacts
between controlled electromigration cycles. The nanowires used for the thinning
process are fabricated by shadow evaporation. The highest resolution obtained
using scanning force microscopy is about 3 nm. During the first few
electromigration cycles the overall slit structure of the nanocontact is
formed. The slit first passes along grain boundaries and then at a later stage
vertically splits grains in the course of consuming them. We find that first
the whole wire is heated and later during the thinning process as the slit
forms the current runs over several smaller contacts which needs less power.Comment: 4 pages, 4 figure
Kinetostatic Analysis and Solution Classification of a Planar Tensegrity Mechanism
Tensegrity mechanisms have several interesting properties that make them
suitable for a number of applications. Their analysis is generally challenging
because the static equilibrium conditions often result in complex equations. A
class of planar one-degree-of-freedom (dof) tensegrity mechanisms with three
linear springs is analyzed in detail in this paper. The kinetostatic equations
are derived and solved under several loading and geometric conditions. It is
shown that these mechanisms exhibit up to six equilibrium configurations, of
which one or two are stable. Discriminant varieties and cylindrical algebraic
decomposition combined with Groebner base elimination are used to classify
solutions as function of the input parameters.Comment: 7th IFToMM International Workshop on Computational Kinematics, May
2017, Poitiers, France. 201
Use of tunable nanopore blockade rates to investigate colloidal dispersions
Tunable nanopores in elastomeric membranes have been used to study the
dependence of ionic current blockade rate on the concentration and
electrophoretic mobility of particles in aqueous suspensions. A range of
nanoparticle sizes, materials and surface functionalities has been tested.
Using pressure-driven flow through a pore, the blockade rate for 100 nm
carboxylated polystyrene particles was found to be linearly proportional to
both transmembrane pressure (controlled between 0 and 1.8 kPa) and particle
concentration (between 7 x 10^8 and 4.5 x 10^10 mL^-1). This result can be
accurately modelled using Nernst-Planck transport theory. Using only an applied
potential across a pore, the blockade rates for carboxylic acid and amine
coated 500 nm and 200 nm silica particles were found to correspond to changes
in their mobility as a function of the solution pH. Scanning electron
microscopy and confocal microscopy have been used to visualise changes in the
tunable nanopore geometry in three dimensions as a function of applied
mechanical strain. The pores observed were conical in shape, and changes in
pore size were consistent with ionic current measurements. A zone of inelastic
deformation adjacent to the pore has been identified as critical in the tuning
process
A mobile antineutrino detector with plastic scintillators
We propose a new type segmented antineutrino detector made of plastic
scintillators for the nuclear safeguard application. A small prototype was
built and tested to measure background events. A satisfactory unmanned field
operation of the detector system was demonstrated. Besides, a detailed Monte
Carlo simulation code was developed to estimate the antineutrino detection
efficiency of the detector.Comment: 23 pages, 11 figures; accepted for publication in Nuclear Instruments
and Methods in Physics Research
Locating the source of projectile fluid droplets
The ill-posed projectile problem of finding the source height from spattered
droplets of viscous fluid is a longstanding obstacle to accident reconstruction
and crime scene analysis. It is widely known how to infer the impact angle of
droplets on a surface from the elongation of their impact profiles. However,
the lack of velocity information makes finding the height of the origin from
the impact position and angle of individual drops not possible. From aggregate
statistics of the spatter and basic equations of projectile motion, we
introduce a reciprocal correlation plot that is effective when the polar launch
angle is concentrated in a narrow range. The vertical coordinate depends on the
orientation of the spattered surface, and equals the tangent of the impact
angle for a level surface. When the horizontal plot coordinate is twice the
reciprocal of the impact distance, we can infer the source height as the slope
of the data points in the reciprocal correlation plot. If the distribution of
launch angles is not narrow, failure of the method is evident in the lack of
linear correlation. We perform a number of experimental trials, as well as
numerical calculations and show that the height estimate is insensitive to
aerodynamic drag. Besides its possible relevance for crime investigation,
reciprocal-plot analysis of spatter may find application to volcanism and other
topics and is most immediately applicable for undergraduate science and
engineering students in the context of crime-scene analysis.Comment: To appear in the American Journal of Physics (ms 23338). Improved
readability and organization in this versio
Production of radioactive isotopes through cosmic muon spallation in KamLAND
Radioactive isotopes produced through cosmic muon spallation are a background for rare-event detection in ν detectors, double-β-decay experiments, and dark-matter searches. Understanding the nature of cosmogenic backgrounds is particularly important for future experiments aiming to determine the pep and CNO solar neutrino fluxes, for which the background is dominated by the spallation production of ^(11)C. Data from the Kamioka liquid-scintillator antineutrino detector (KamLAND) provides valuable information for better understanding these backgrounds, especially in liquid scintillators, and for checking estimates from current simulations based upon MUSIC, FLUKA, and GEANT4. Using the time correlation between detected muons and neutron captures, the neutron production yield in the KamLAND liquid scintillator is measured to be Y_n=(2.8±0.3)×10^(-4) μ^(-1) g^(-1) cm^2. For other isotopes, the production yield is determined from the observed time correlation related to known isotope lifetimes. We find some yields are inconsistent with extrapolations based on an accelerator muon beam experiment
Electron Glass Dynamics
Examples of glasses are abundant, yet it remains one of the phases of matter
whose understanding is very elusive. In recent years, remarkable experiments
have been performed on the dynamical aspects of glasses. Electron glasses offer
a particularly good example of the 'trademarks' of glassy behavior, such as
aging and slow relaxations. In this work we review the experimental literature
on electron glasses, as well as the local mean-field theoretical framework put
forward in recent years to understand some of these results. We also present
novel theoretical results explaining the periodic aging experiment.Comment: Invited review to appear in Annual Review of Condensed Matter Physic
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