5,713 research outputs found
The governance of innovation diffusion â a socio-technical analysis of energy policy
This paper describes a dynamic price mechanism to coordinate electric power generation from micro Combined Heat and Power (micro-CHP) systems in a network of households. It is assumed that the households are prosumers, i.e. both producers and consumers of electricity. The control is done on household level in a completely distributed manner. Avoiding a centralized controller both eases computation complexity and preserves communication structure in the network. Local information is used to decide to turn on or off the micro-CHP, but through price signals between the prosumers the network as a whole operates in a cooperative way
Ammonia assimilation in Bacillus polymyxa. 15N NMR and enzymatic studies
Pathways of ammonia assimilation into glutamic acid and alanine in Bacillus polymyxa were investigated by 15N NMR spectroscopy in combination with measurements of the specific activities of glutamate dehydrogenase, glutamine synthetase, glutamate synthetase, alanine dehydrogenase, and glutamic-alanine transaminase. Ammonia was found to be assimilated into glutamic acid predominantly by NADPH-dependent glutamate dehydrogenase with a Km of 2.9 mM for NH4+ not only in ammonia-grown cells but also in nitrate-grown and nitrogen-fixing cells in which the intracellular NH4+ concentrations were 11.2, 1.04, and 1.5 mM, respectively. In ammonia-grown cells, the specific activity of alanine dehydrogenase was higher than that of glutamic-alanine transaminase, but the glutamate dehydrogenase/glutamic-alanine transaminase pathway was found to be the major pathway of 15NH4+ assimilation into [15N]alanine. The in vitro specific activities of glutamate dehydrogenase and glutamine synthetase, which represent the rates of synthesis of glutamic acid and glutamine, respectively, in the presence of enzyme-saturating concentrations of substrates and coenzymes are compared with the in vivo rates of biosynthesis of [15N]glutamic acid and [alpha,gamma-15N]glutamine observed by NMR, and implications of the results for factors limiting the rates of their biosynthesis in ammonia- and nitrate-grown cells are discussed
Glutamate biosynthesis in Bacillus azotofixans. 15N NMR and enzymatic studies
Pathways of ammonia assimilation into glutamic acid in Bacillus azotofixans, a recently characterized nitrogen-fixing species of Bacillus, were investigated through observation by NMR spectroscopy of in vivo incorporation of 15N into glutamine and glutamic acid in the absence and presence of inhibitors of ammonia-assimilating enzymes, in combination with measurements of the specific activities of glutamate dehydrogenase, glutamine synthetase, glutamate synthase, and alanine dehydrogenase. In ammonia-grown cells, both the glutamine synthetase/glutamate synthase and the glutamate dehydrogenase pathways contribute to the assimilation of ammonia into glutamic acid. In nitrate-grown and nitrogen-fixing cells, the glutamine synthetase/glutamate synthase pathway was found to be predominant. NADPH-dependent glutamate dehydrogenase activity was detectable at low levels only in ammonia-grown and glutamate-grown cells. Thus, B. azotofixans differs from Bacillus polymyxa and Bacillus macerans, but resembles other N2-fixing prokaryotes studied previously, as to the pathway of ammonia assimilation during ammonia limitation. Implications of the results for an emerging pattern of ammonia assimilation by alternative pathways among nitrogen-fixing prokaryotes are discussed, as well as the utility of 15N NMR for measuring in vivo glutamate synthase activity in the cell
Effect of the nitrogen source on glutamine and alanine biosynthesis in Neurospora crassa. An in vivo 15N nuclear magnetic resonance study
The influences of different nitrogen sources on the relative rates of biosynthesis of glutamine and alanine have been studied by 15N nuclear magnetic resonance spectroscopy of intact Neurospora crassa mycelia suspensions. The rate of glutamine synthesis was fastest after growth in media deficient in free ammonium ion, whereas it was slowest following growth in media containing both glutamic acid and glutamine. The reverse trend was observed for the biosynthesis of alanine. A competition between the two biosynthetic pathways for the same substrate, glutamic acid, was found to limit the rate of alanine synthesis when glutamine synthesis was rapid. The observed in vivo rates of these reactions are compared to the reported specific activities of the enzymes catalyzing the reactions, and implications of these results for nitrogen regulation of these pathways under various physiological conditions are discussed
Leadership considerations for executive vice chairs, new chairs, and chairs in the 21st century.
The need to fulfill academic goals in the context of significant economic challenges, new regulatory requirements, and ever-changing expectations for leadership requires continuous adaptation. This paper serves as an educational resource for emerging leaders from the literature, national leaders, and other âbest practicesâ in the following domains: 1. Mentorship; 2. Faculty Development; 3. Promotion; 4. Demonstrating value in each of the academic missions; 5. Marketing and communications; and 6. Barrier
Off-shell pion electromagnetic form factor from a gauge-invariant Nambu-Jona-Lasinio model
The off--shell electromagnetic vertex function of pions and kaons is studied
in a bosonized Nambu--Jona-Lasinio model with a gauge--invariant proper--time
cutoff. The slope of the pion form factor with respect to the pion 4--momentum
is found to be equal to the on--shell pion charge radius in the chiral limit.
The off--shell slope of the form factor is zero, that of the
about 15\% smaller than that of the pion. We compare our results with those of
a recent calculation in chiral perturbation theory.Comment: (9 p., standard LaTeX, 1 PostScript figure appended) UNITUE-THEP-7/9
Periodic orbits of linear endomorphisms on the 2-torus and its lattices
Counting periodic orbits of endomorphisms on the 2-torus is considered, with
special focus on the relation between global and local aspects and between the
dynamical zeta function on the torus and its analogue on finite lattices. The
situation on the lattices, up to local conjugacy, is completely determined by
the determinant, the trace and a third invariant of the matrix defining the
toral endomorphism.Comment: 22 page
On the detection of Lorentzian profiles in a power spectrum: A Bayesian approach using ignorance priors
Aims. Deriving accurate frequencies, amplitudes, and mode lifetimes from
stochastically driven pulsation is challenging, more so, if one demands that
realistic error estimates be given for all model fitting parameters. As has
been shown by other authors, the traditional method of fitting Lorentzian
profiles to the power spectrum of time-resolved photometric or spectroscopic
data via the Maximum Likelihood Estimation (MLE) procedure delivers good
approximations for these quantities. We, however, show that a conservative
Bayesian approach allows one to treat the detection of modes with minimal
assumptions (i.e., about the existence and identity of the modes).
Methods. We derive a conservative Bayesian treatment for the probability of
Lorentzian profiles being present in a power spectrum and describe an efficient
implementation that evaluates the probability density distribution of
parameters by using a Markov-Chain Monte Carlo (MCMC) technique.
Results. Potentially superior to "best-fit" procedure like MLE, which only
provides formal uncertainties, our method samples and approximates the actual
probability distributions for all parameters involved. Moreover, it avoids
shortcomings that make the MLE treatment susceptible to the built-in
assumptions of a model that is fitted to the data. This is especially relevant
when analyzing solar-type pulsation in stars other than the Sun where the
observations are of lower quality and can be over-interpreted. As an example,
we apply our technique to CoRoT observations of the solar-type pulsator HD
49933.Comment: 12 pages, 11 figures, accepted for publication in Astronomy and
Astrophysic
Nucleon form factors and a nonpointlike diquark
Nucleon form factors are calculated on q^2 in [0,3] GeV^2 using an Ansatz for
the nucleon's Fadde'ev amplitude motivated by quark-diquark solutions of the
relativistic Fadde'ev equation. Only the scalar diquark is retained, and it and
the quark are confined. A good description of the data requires a nonpointlike
diquark correlation with an electromagnetic radius of 0.8 r_pi. The composite,
nonpointlike nature of the diquark is crucial. It provides for diquark-breakup
terms that are of greater importance than the diquark photon absorption
contribution.Comment: 5 pages, REVTEX, epsfig, 3 figure
Field-induced dynamics in the quantum Brownian oscillator: An exact treatment
We consider a quantum linear oscillator coupled to a bath in equilibrium at
an arbitrary temperature and then exposed to an external field arbitrary in
form and strength. We then derive the reduced density operator in closed form
of the coupled oscillator in a non-equilibrium state at an arbitrary time.Comment: Accepted for publication in Physics Letters
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