1,361 research outputs found
Polyurethane Elastomers as Maxillofacial Prosthetic Materials
A series of polyurethane elastomers based on an aliphatic diisocyanate and a polyether macroglycol was polymerized with various crosslink densities and OH/NCO ratios. Stoichiometries yielding between 8,600 and 12,900 gm/ mole/crosslink and an OH/NCO ratio of 1.1 resulted in polymers with the low modulus, yet high strength and elongation necessary for maxillofacial applications.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/68299/2/10.1177_00220345780570040501.pd
All-Optical Broadband Excitation of the Motional State of Trapped Ions
We have developed a novel all-optical broadband scheme for exciting,
amplifying and measuring the secular motion of ions in a radio frequency trap.
Oscillation induced by optical excitation has been coherently amplified to
precisely control and measure the ion's secular motion. Requiring only laser
line-of-sight, we have shown that the ion's oscillation amplitude can be
precisely controlled. Our excitation scheme can generate coherent motion which
is robust against variations in the secular frequency. Therefore, our scheme is
ideal to excite the desired level of oscillatory motion under conditions where
the secular frequency is evolving in time. Measuring the oscillation amplitude
through Doppler velocimetry, we have characterized the experimental parameters
and compared them with a molecular dynamics simulation which provides a
complete description of the system.Comment: 8 pages, 10 figure
Bimodal Expansion of the Lymphatic Vessels Is Regulated by the Sequential Expression of IL-7 and Lymphotoxin α1ÎČ2 in Newly Formed Tertiary Lymphoid Structures.
Lymphangiogenesis associated with tertiary lymphoid structure (TLS) has been reported in numerous studies. However, the kinetics and dynamic changes occurring to the lymphatic vascular network during TLS development have not been studied. Using a viral-induced, resolving model of TLS formation in the salivary glands of adult mice we demonstrate that the expansion of the lymphatic vascular network is tightly regulated. Lymphatic vessel expansion occurs in two distinct phases. The first wave of expansion is dependent on IL-7. The second phase, responsible for leukocyte exit from the glands, is regulated by lymphotoxin (LT)ÎČR signaling. These findings, while highlighting the tight regulation of the lymphatic response to inflammation, suggest that targeting the LTα1ÎČ2/LTÎČR pathway in TLS-associated pathologies might impair a natural proresolving mechanism for lymphocyte exit from the tissues and account for the failure of therapeutic strategies that target these molecules in diseases such as rheumatoid arthritis
On observability of Renyi's entropy
Despite recent claims we argue that Renyi's entropy is an observable
quantity. It is shown that, contrary to popular belief, the reported domain of
instability for Renyi entropies has zero measure (Bhattacharyya measure). In
addition, we show the instabilities can be easily emended by introducing a
coarse graining into an actual measurement. We also clear up doubts regarding
the observability of Renyi's entropy in (multi--)fractal systems and in systems
with absolutely continuous PDF's.Comment: 18 pages, 1 EPS figure, REVTeX, minor changes, accepted to Phys. Rev.
Traveling wave solutions for a predator-prey system with Sigmoidal response function
We study the existence of traveling wave solutions for a diffusive
predator-prey system. The system considered in this paper is governed by a
Sigmoidal response function which is more general than those studied
previously. Our method is an improvement to the original method introduced in
the work of Dunbar \cite{Dunbar1,Dunbar2}. A bounded Wazewski set is used in
this work while unbounded Wazewski sets were used in \cite{Dunbar1,Dunbar2}.
The existence of traveling wave solutions connecting two equilibria is
established by using the original Wazewski's theorem which is much simpler than
the extended version in Dunbar's work
Metacognition and lifelong e-learning: a contextual and cyclical process
Metacognition is arguably an important conceptualisation within the area of lifelong e- learning, with many theorists and practitioners claiming that it enhances the learning process. However, the lifelong, cyclical and flexible aspects of 'before', 'during' and 'after' metacognitions within lifelong e-learning (inclusive of whether an 'input' necessarily leads to a completed 'output') seem marginal within current areas of practical and theoretical debate. This article analyses Reeves's (1997) model of web-based learning in the context of the ADAPT project; a study of lifelong learners based in small and medium sized enterprises. The article focuses upon an analysis of this model's view of metacognition, and in the light of the project findings and literature review, aims to put forward an extended and expanded version of the model with reference to lifelong e-learnin
Dynamical stability of infinite homogeneous self-gravitating systems: application of the Nyquist method
We complete classical investigations concerning the dynamical stability of an
infinite homogeneous gaseous medium described by the Euler-Poisson system or an
infinite homogeneous stellar system described by the Vlasov-Poisson system
(Jeans problem). To determine the stability of an infinite homogeneous stellar
system with respect to a perturbation of wavenumber k, we apply the Nyquist
method. We first consider the case of single-humped distributions and show
that, for infinite homogeneous systems, the onset of instability is the same in
a stellar system and in the corresponding barotropic gas, contrary to the case
of inhomogeneous systems. We show that this result is true for any symmetric
single-humped velocity distribution, not only for the Maxwellian. If we
specialize on isothermal and polytropic distributions, analytical expressions
for the growth rate, damping rate and pulsation period of the perturbation can
be given. Then, we consider the Vlasov stability of symmetric and asymmetric
double-humped distributions (two-stream stellar systems) and determine the
stability diagrams depending on the degree of asymmetry. We compare these
results with the Euler stability of two self-gravitating gaseous streams.
Finally, we determine the corresponding stability diagrams in the case of
plasmas and compare the results with self-gravitating systems
Correlations Between Charge Ordering and Local Magnetic Fields in Overdoped YBaCuO
Zero-field muon spin relaxation (ZF-SR) measurements were undertaken on
under- and overdoped samples of superconducting YBaCuO to
determine the origin of the weak static magnetism recently reported in this
system. The temperature dependence of the muon spin relaxation rate in
overdoped crystals displays an unusual behavior in the superconducting state. A
comparison to the results of NQR and lattice structure experiments on highly
doped samples provides compelling evidence for strong coupling of charge, spin
and structural inhomogeneities.Comment: 4 pages, 4 figures, new data, new figures and modified tex
A terminal assessment of stages theory : introducing a dynamic states approach to entrepreneurship
Stages of Growth models were the most frequent theoretical approach to understanding entrepreneurial business growth from 1962 to 2006; they built on the growth imperative and developmental models of that time. An analysis of the universe of such models (N=104) published in the management literature shows no consensus on basic constructs of the approach, nor is there any empirical confirmations of stages theory. However, by changing two propositions of the stages models, a new dynamic states approach is derived. The dynamic states approach has far greater explanatory power than its precursor, and is compatible with leading edge research in entrepreneurship
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