6,385 research outputs found
Walter Campbell:A distinguished life
An efficient and simple synthesis approach to form stable (68) Ga-labeled nanogels is reported and their fundamental properties investigated. Nanogels are obtained by self-assembly of amphiphilic statistical prepolymers derivatised with chelating groups for radiometals. The resulting nanogels exhibit a well-defined spherical shape with a diameter of 290 +/- 50 nm. The radionuclide (68) Ga is chelated in high radiochemical yields in an aqueous medium at room temperature. The phagocytosis assay demonstrates a highly increased internalization of nanogels by activated macrophages. Access to these (68) Ga-nanogels will allow the investigation of general behavior and clearance pathways of nanogels in vivo by nuclear molecular imaging
The Eastwood-Singer gauge in Einstein spaces
Electrodynamics in curved spacetime can be studied in the Eastwood--Singer
gauge, which has the advantage of respecting the invariance under conformal
rescalings of the Maxwell equations. Such a construction is here studied in
Einstein spaces, for which the Ricci tensor is proportional to the metric. The
classical field equations for the potential are then equivalent to first
solving a scalar wave equation with cosmological constant, and then solving a
vector wave equation where the inhomogeneous term is obtained from the gradient
of the solution of the scalar wave equation. The Eastwood--Singer condition
leads to a field equation on the potential which is preserved under gauge
transformations provided that the scalar function therein obeys a fourth-order
equation where the highest-order term is the wave operator composed with
itself. The second-order scalar equation is here solved in de Sitter spacetime,
and also the fourth-order equation in a particular case, and these solutions
are found to admit an exponential decay at large time provided that
square-integrability for positive time is required. Last, the vector wave
equation in the Eastwood-Singer gauge is solved explicitly when the potential
is taken to depend only on the time variable.Comment: 13 pages. Section 6, with new original calculations, has been added,
and the presentation has been improve
Ammonia Inhibition in Thermophilic Anaerobic Digestion of Dairy Cattle Manure
This study investigated the effect of five different concentrations of total ammonia nitrogen (TAN)and free ammonia (FA) on the methane yield and digester performance under thermophilic conditions(50°C). Five identical continuously fed digesters were used. The experiment was run for four timeshydraulic retention time (HRT). Data were statitically analysed using the data Analysis Tool Packavailable with the Microsoft Excel program. Different ammonia levels were obtained by pulsing urea toobtain the target level of TAN and FA, and to subsequently maintaining the concentration of ammonialevels by daily urea additions. The result showed a strong negative correlation between both TAN andFA concentrations and methane yield. The methane yield was reduced by 24, 30, 52 and 66% indigesters that had TAN levels of 2.9, 3.6, 4.4 and 5.1 g/L, respectively, corresponding to 0.7, 1.1,1.5 and1.8 g/L FA. Total volatile fatty acid and especially isovaleric and isobutyric acid concentrations wereelevated during ammonia inhibition. Concentration of TAN in the biogas digester exceeding 3 g/Lindicating that very often the full biogas potential is not achieved due to ammonia inhibition and thatlonger HRT should be used to compensate or a lower process temperature should be chosen
Comment on "Giant absorption cross section of ultracold neutrons in Gadolinium"
Rauch et al (PRL 83, 4955, 1999) have compared their measurements of the Gd
cross section for Ultra-cold neutrons with an exptrapolation of the cross
section for thermal neutrons and interpreted the discrepancy in terms of
coherence properties of the neutron. We show the extrapolation used is based on
a misunderstanding and that coherence properties play no role in absorption.Comment: 2 pages, 1 postscript figure, comment on Rauch et al, PRL 83,4955
(1999
A Composite HST Spectrum of Quasars
We construct a composite quasar spectrum from 284 HST FOS spectra of 101
quasars with redshifts z > 0.33. The spectrum covers the wavelengths between
350 and 3000 A in the rest frame. There is a significant steepening of the
continuum slope around 1050 A. The continuum between 1050 and 2200 A can be
modeled as a power law with alpha = -0.99. For the full sample the power-law
index in the extreme ultraviolet (EUV) between 350 and 1050 A is alpha = -1.96.
The continuum flux in the wavelengths near the Lyman limit shows a depression
of about 10 percent. The break in the power-law index and the slight depression
of the continuum near the Lyman limit are features expected in Comptonized
accretion-disk spectra.Comment: 10 figures To appear in the February 1, 1997, issue of the Ap.
The Properties of Field Elliptical Galaxies at Intermediate Redshift. I: Empirical Scaling Laws
We present measurements of the Fundamental Plane (FP) parameters (the
effective radius, the mean effective surface brightness, and the central
velocity dispersion) of six field elliptical galaxies at intermediate redshift.
The imaging is taken from the Medium Deep Survey of the Hubble Space Telescope,
while the kinematical data are obtained from long-slit spectroscopy using the
3.6-m ESO telescope. The Fundamental Plane appears well defined in the field
even at redshift 0.3. The data show a shift in the FP zero point with
respect to the local relation, possibly indicating modest evolution, consistent
with the result found for intermediate redshift cluster samples. The FP slopes
derived for our field data, plus other cluster ellipticals at intermediate
redshift taken from the literature, differ from the local ones, but are still
consistent with the interpretation of the FP as a result of homology, of the
virial theorem and of the existence of a relation between luminosity and mass,
. We also derive the surface brightness vs. effective
radius relation for nine galaxies with redshift up to , and data
from the literature; the evolution that can be inferred is consistent with what
is found using the FP.Comment: 17 pages, including 9 figures, MNRAS, accepte
Correlations between EMG jaw muscle activity and facial morphology in complete denture wearers
In a sample of fifteen partially edentulous subjects assigned for immediate complete denture treatment, a correlation analysis was performed between pre-extraction facial morphology determined from lateral cephalograms, and EMG activity of the anterior temporal and masseter muscles in maximal clench and tapping of teeth. Marked correlations observed between vertical and sagittal jaw relations and mean voltages of the jaw-closing muscles indicated strong biting activity in subjects with a square facial type. No significant associations were observed between biting strength and the age of the subjects. Correlations between facial morphological changes and changes in EMG biting activity after denture insertion and during 1 year of denture wear indicated that the anterior temporal muscles were extremely sensitive to sagittal changes in anterior occlusion. The masseter muscles were less sensitive, but responded in some instances to changes in vertical jaw relationship.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73816/1/j.1365-2842.1983.tb00105.x.pd
On Teaching Discrete Mathematics to Freshman Computer Science Students
Discrete Mathematics is an inevitable part of any undergraduate computer science degree programme. However, today's computer science student typically finds this to be at best a necessary evil with which they struggle to engage. Twenty years ago, we started to address this issue seriously in our university, and we have instituted a number of innovations throughout the years which have had a positive effect on engagement and, thus, attainment. In this paper, we describe and motivate the innovations which we introduced, and provide a detailed analysis of how and why engagement and attainment levels varied over two decades as a direct result of these innovation
Towards a Notion of Distributed Time for Petri Nets
We set the ground for research on a timed extension of Petri nets where time parameters are associated with tokens and arcs carry constraints that qualify the age of tokens required for enabling. The novelty is that, rather than a single global clock, we use a set of unrelated clocks --- possibly one per place --- allowing a local timing as well as distributed time synchronisation. We give a formal definition of the model and investigate properties of local versus global timing, including decidability issues and notions of processes of the respective models
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