5,856 research outputs found
Nano-scale analysis of titanium dioxide fingerprint-development powders
Titanium dioxide based powders are regularly used in the development of latent fingerprints on dark surfaces. For analysis of prints on adhesive tapes, the titanium dioxide is suspended in a surfactant and used in the form of a small particle reagent (SPR). Analysis of commercially available products shows varying levels of effectiveness of print development, with some powders adhering to the background as well as the print. Scanning electron microscopy (SEM) images of prints developed with different powders show a range of levels of aggregation of particles.
Analytical transmission electron microscopy (TEM) of the fingerprint powder shows TiO2 particles with a surrounding coating, tens of nanometres thick, consisting of Al and Si rich material. X ray photoelectron spectroscopy (XPS) is used to determine the composition and chemical state of the surface of the powders; with a penetration depth of approximately 10nm, this technique demonstrates differing Ti: Al: Si ratios and oxidation states between the surfaces of different powders. Levels of titanium detected with this technique demonstrate variation in the integrity of the surface coating. The thickness, integrity and composition of the Al/Si-based coating is related to the level of aggregation of TiO2 particles and efficacy of print development
Demystifying our Grandparent's De Bruijn Sequences with Concatenation Trees
Some of the most interesting de Bruijn sequences can be constructed in
seemingly unrelated ways. In particular, the "Granddaddy" and "Grandmama" can
be understood by joining necklace cycles into a tree using simple parent rules,
or by concatenating smaller strings (e.g., Lyndon words) in lexicographic
orders. These constructions are elegant, but their equivalences seem to come
out of thin air, and the community has had limited success in finding others of
the same ilk. We aim to demystify the connection between cycle-joining trees
and concatenation schemes by introducing "concatenation trees". These
structures combine binary trees and ordered trees, and traversals yield
concatenation schemes for their sequences.
In this work, we focus on the four simplest cycle-joining trees using the
pure cycling register (PCR): "Granddaddy" (PCR1), "Grandmama" (PCR2), "Granny"
(PCR3), and "Grandpa" (PCR4). In particular, we formally prove a previously
observed correspondence for PCR3 and we unravel the mystery behind PCR4. More
broadly, this work lays the foundation for translating cycle-joining trees to
known concatenation constructions for a variety of underlying feedback
functions including the complementing cycling register (CCR), pure summing
register (PSR), complementing summing register (CSR), and pure run-length
register (PRR)
Incoherent dynamics in neutron-matter interaction
Coherent and incoherent neutron-matter interaction is studied inside a
recently introduced approach to subdynamics of a macrosystem. The equation
describing the interaction is of the Lindblad type and using the Fermi
pseudopotential we show that the commutator term is an optical potential
leading to well-known relations in neutron optics. The other terms, usually
ignored in optical descriptions and linked to the dynamic structure function of
the medium, give an incoherent contribution to the dynamics, which keeps
diffuse scattering and attenuation of the coherent beam into account, thus
warranting fulfilment of the optical theorem. The relevance of this analysis to
experiments in neutron interferometry is briefly discussed.Comment: 15 pages, revtex, no figures, to appear in Phys. Rev.
Direct evidence for the magnetic ordering of Nd ions in NdFeAsO by high resolution inelastic neutron scattering
We investigated the low energy excitations in the parent compound NdFeAsO of
the Fe-pnictide superconductor in the eV range by a back scattering
neutron spectrometer. The energy scans on a powder NdFeAsO sample revealed
inelastic peaks at E = 1.600 eV at T = 0.055 K on both energy
gain and energy loss sides. The inelastic peaks move gradually towards lower
energy with increasing temperature and finally merge with the elastic peak at
about 6 K. We interpret the inelastic peaks to be due to the transition between
hyperfine-split nuclear level of the Nd and Nd isotopes with
spin . The hyperfine field is produced by the ordering of the
electronic magnetic moment of Nd at low temperature and thus the present
investigation gives direct evidence of the ordering of the Nd magnetic
sublattice of NdFeAsO at low temperature
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Effects of Process Variables and Size Scale on Solidification Microstructure in Laser-Based Solid Freeform Fabrication of Ti-6Al-4V
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ACE Data from the ACE Science Center
The purpose of the ACE Science Center (ASC) is to perform level 1 processing of data from the nine science instruments aboard the Advanced Composition Explorer (ACE) spacecraft and to facilitate access to all ACE data by both the instrument investigators and the space physics community. We describe the ACE data products available from the ASC and the methods by which users may access the data
Observer with a constant proper acceleration
Relying on the equivalence principle, a first approach of the general theory
of relativity is presented using the spacetime metric of an observer with a
constant proper acceleration. Within this non inertial frame, the equation of
motion of a freely moving object is studied and the equation of motion of a
second accelerated observer with the same proper acceleration is examined. A
comparison of the metric of the accelerated observer with the metric due to a
gravitational field is also performed.Comment: 5 figure
Nuclear Incompressibility in Asymmetric Systems at Finite Temperature and Entropy
The nuclear incompressibility is investigated in asymmetric systems
in a mean field model. The calculations are done at zero and finite
temperatures and include surface, Coulomb and symmetry energy terms for several
equations of state. Also considered is the behavior of the incompressibility at
constant entropy which is shown to have a very different behavior
than the isothermal . Namely, decreases with increasing
entropy while the isothermal increases with increasing . A duality
is found between the adiabatic and the T=0 isothermal .
Analytic and also simple approximate expressions for are given.Comment: 11 page
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