571 research outputs found
Rubidium spacecraft atomic timing system Final report
Rubidium 87 atomic time and frequency reference system for manned space fligh
Electrochemical titration of the S = 32 and S = 12 states of the iron protein of nitrogenase
AbstractThe iron protein of nitrogenase delivers electrons and ATP to the iron-molybdenum protein, which in turn reduces dinitrogen to ammonia. The iron protein contains a single four-iron, four-sulfur prosthetic group, detectable by ESR spectroscopy m its reduced form. Until recently, spin quantitations suggested that only a portion of the reduced iron protein was being detected by ESR, but recent work in several laboratories has shown that there is a spin = 32 signal near g = 5 in addition to the well characterized spin = 12 signal near g = 1.94. In this paper we characterize the redox properties of both states in the presence and absence of ATP and ADP, and find that the new spin state has identical redox properties to those previously determined for the spin = 12 state
Synthesis of N-Substituted Diamino-Propanols and their Physiological Effects
The p-toluiclinc-epichlorohydrin 1:1 addition compound has been reacted with pipericline, pyrrolicline, and morpholine to give disubstitutecl 2-propanols. 1-(p-Toluiclino)-3-pyrrolidino-2-propanol was fed to male rats and organ and body weights measured. The data do not permit us to evaluate adequately the physiological effects of the compound, but differences were observed in the size of the heart, kidneys, and thymus of the test animals
Super congruences and Euler numbers
Let be a prime. We prove that
, where E_0,E_1,E_2,... are Euler numbers. Our new approach is of
combinatorial nature. We also formulate many conjectures concerning super
congruences and relate most of them to Euler numbers or Bernoulli numbers.
Motivated by our investigation of super congruences, we also raise a conjecture
on 7 new series for , and the constant
(with (-) the Jacobi symbol), two of which are
and
\sum_{k>0}(15k-4)(-27)^{k-1}/(k^3\binom{2k}{k}^2\binom{3k}k)=K.$
On the structure and function of nitrogenase from W5
Molybdoferredoxin from W5 was fractionated into MoFd with two atoms of molybdenum per 220,000 daltons and a specific activity of 2.6 [mu]moles C2H2 reduced/min/mg protein and into a catalytically inactive species with an identical protein moiety but an incomplete active centre. Native MoFd is a tetramer composed of two 50,000 and two 60,000 dalton subunits. At low protein concentrations the tetramer is in equilibrium with a dimer. Under low ionic strength and at low pH further dissociation into monomers occurs. MoFd and azoferredoxin have distinct electron paramagnetic resonance spectra. The EPR spectrum of AzoFd and that of the combination of the two nitrogenase components undergoes characteristic changes upon addition of MgATP2-.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/34037/1/0000314.pd
From Demonstrations to Task-Space Specifications:Using Causal Analysis to Extract Rule Parameterization from Demonstrations
Learning models of user behaviour is an important problem that is broadly
applicable across many application domains requiring human-robot interaction.
In this work, we show that it is possible to learn generative models for
distinct user behavioural types, extracted from human demonstrations, by
enforcing clustering of preferred task solutions within the latent space. We
use these models to differentiate between user types and to find cases with
overlapping solutions. Moreover, we can alter an initially guessed solution to
satisfy the preferences that constitute a particular user type by
backpropagating through the learned differentiable models. An advantage of
structuring generative models in this way is that we can extract causal
relationships between symbols that might form part of the user's specification
of the task, as manifested in the demonstrations. We further parameterize these
specifications through constraint optimization in order to find a safety
envelope under which motion planning can be performed. We show that the
proposed method is capable of correctly distinguishing between three user
types, who differ in degrees of cautiousness in their motion, while performing
the task of moving objects with a kinesthetically driven robot in a tabletop
environment. Our method successfully identifies the correct type, within the
specified time, in 99% [97.8 - 99.8] of the cases, which outperforms an IRL
baseline. We also show that our proposed method correctly changes a default
trajectory to one satisfying a particular user specification even with unseen
objects. The resulting trajectory is shown to be directly implementable on a
PR2 humanoid robot completing the same task.Comment: arXiv admin note: substantial text overlap with arXiv:1903.0126
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Kinetic and Spectroscopic Analysis of the Inactivating Effects of Nitric Oxide on the Individual Components of Azotobacter vinelandii Nitrogenase
The effects of nitric oxide (NO) on the individual components of Azotobacter vinelandii
nitrogenase have been examined by kinetic and spectroscopic methods. Incubation of the Fe protein (Av2)
for 1 h with stoichiometries of 4- and 8-fold molar excesses of NO to Av2 dimer resulted in a complete
loss of activity of Av2 in C2H2-reduction assays. The kinetics of inactivation indicated that the minimum
stoichiometry of NO to Av2 required to fully inactivate Av2 lies between 1 and 2. The rate of inactivation
of Av2 activity by NO was stimulated up to 2-fold by the presence of MgATP and MgADP but was
unaffected by the presence of sodium dithionite. Unexpectedly, complete inactivation of Av2 by low ratios
of NO to Av2 also resulted in a complete loss of its ability to bind MgATP and MgADP. UV-visible
spectroscopy indicated that the effect of NO on Av2 involves oxidation of the [4Fe-4S] center. EPR
spectroscopy revealed that the loss of activity during inactivation of Av2 by NO correlated with the loss
of the S = 1/2 and S = 3/2 signals. Appearance of the classical and intense iron-nitrosyl signal (g = 2.03)
was only observed when Av2 was incubated with large molar excesses of NO and the appearance of this
signal did not correlate with the loss of Av2 activity. The effects of NO on the MoFe protein (Avl) were
more complex than for Av2. A time-dependent inactivation of Avl activity (C2H2 reduction) was observed
which required considerably higher concentrations of NO than those required to inactivate Av2 (up to 10
P a ) . In addition, the effects of NO on Avl were significantly affected by the presence of sodium dithionite.
In fact, kinetic evidence suggests that an Avl-catalyzed, NO-dependent consumption of dithionite occurs
before Avl is inactivated by NO. A correlation between UV-visible and EPR spectral features and the
extent of NO inactivation has been established. The inactivation of either nitrogenase component by NO
did not lead to aggregation or dissolution into their constitutive subunits. However, NO inactivation did
cause changes in both proteins since neither NO-treated protein inhibited C2H2-reducing activity in assays
containing equimolar concentrations of untreated protein. The effects of NO on both nitrogenase components
are interpreted in terms of the known reactivity of NO with Fe-S centers
International Commercial Arbitration: Fifty Years After the New York Convention
a one-day conference held at the Dean Rusk Center on January 30, 2009. The event, co-sponsored by the Georgia Journal of International and Comparative Law, featured Gary Born as keynote speaker and other leaders in the field of international commercial arbitration including Robert Davidson, Executive Director of JAMS Arbitration Practice; William K. Slate, II, President, American Arbitration Association; and Anne Marie Whitesell, Former Secretary General of the ICC International Court of Arbitration
Innovatively Supporting Teachers’ Implementation of School-Based Sex Education: Developing A Web-Based Coaching Intervention From Problem to Solution
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