39,470 research outputs found
Chromatographic separation and identification of some peptides in partial hydroylsates of gelatin
Recently we have been engaged in a study of the chemical structure of collagen and gelatin with the object of determining the sequence of the amino acid residues in the polypeptide chains of these proteins. In the course of this study we have made considerable progress in the chromatographic analysis of complex mixtures of peptides and we have isolated and identified several simple peptides which occur in partial hydrolysates of gelatin. The initial separation of the mixture into zones of one or more peptides has been made on a column of ion exchange resin; further separation of the peptides in each zone has been achieved by chromatographing in the form of dinitrophenyl (DNP) peptides on columns of silicic acid-Celite. It is to be hoped that the particular combination of chromatographic methods which has been successfully used in the present study will be helpful in the resolution of the complex mixtures which result from the partial hydrolysis of other proteins
Aerodynamic performance of 0.5 meter-diameter, 337 meter-per-second tip speed, 1.5 pressure-ratio, single-stage fan designed for low noise aircraft engines
Overall and blade-element aerodynamic performance of a 0.271-scale model of QF-1 are presented, examined, and then compared and evaluated with that from similar low noise fan stage designs. The tests cover a wide range of speeds and weight flows along with variations in stator setting angle and stator axial spacing from the rotor. At design speed with stator at design setting angle and a fixed distance between stage measuring stations, there were no significant effects of increasing the axial spacing between rotor stator from 1.0 to 3.5 rotor chords on stage overall pressure ratio, efficiency or stall margin
T Tauri variability in the context of the beat-frequency model
We examine the implications of a beat frequency modulated model of T Tauri
accretion. In particular we show that measurements of the variability of
accretion generated lines can be used in conjunction with existing photometry
to obtain a measurement of the underlying photospheric and disc flux. This
provides an independent way of checking spectral energy distribution modelling.
In addition, we show how spectroscopy of T Tauri stars can reveal the
inclination angle between the magnetic axis and the plane of the disc.Comment: uuencoded compressed postscript. The preprint is also available at
http://www.ast.cam.ac.uk/preprint/PrePrint.htm
7.2% efficient polycrystalline silicon photoelectrode
After etching, n-type cast polycrystalline silicon photoanodes immersed in a solution of methanol and a substituted ferrocene reagent exhibit photoelectrode efficiencies of 7.2%±0.7% under simulated AM2 illumination. Scanning laser spot data indicate that the grain boundaries are active; however, the semiconductor/liquid contact does not display the severe shunting effects which are observed at a polycrystalline Si/Pt Schottky barrier. Evidence for an interfacial oxide on the operating polycrystalline Si photoanode is presented. Some losses in short circuit current can be ascribed to bulk semiconductor properties; however, despite these losses, photoanodes fabricated from polycrystalline substrates exhibit efficiencies comparable to those of single crystal material. Two major conclusions of our studies are that improved photoelectrode behavior in the polycrystalline silicon/methanol system will primarily result from changes in bulk electrode properties and from grain boundary passivation, and that Fermi level pinning by surface states does not prevent the design of efficient silicon-based liquid junctions
A 14% efficient nonaqueous semiconductor/liquid junction solar cell
We describe the most efficient semiconductor/liquid junction solar cell reported to date. Under Wâhalogen (ELH) illumination, the device is a 14% efficient twoâelectrode solar cell fabricated from an nâtype silicon photoanode in contact with a nonaqueous electrolyte solution. The cellâČs central feature is an ultrathin electrolyte layer which simultaneously reduces losses which result from electrode polarization, electrolyte light absorption, and electrolyte resistance. The thin electrolyte layer also eliminates the need for forced convection of the redox couple and allows for precise control over the amount of water (and other electrolyte impurities) exposed to the semiconductor. After one month of continuous operation under ELH light at 100 mW/cm^2, which corresponds to the passage of over 70â000 C/cm^2, thinâlayer cells retained over 90% of their efficiency. In addition, when made with Wacker Silso cast polycrystalline Si, cells yield an efficiency of 9.8% under simulated AMl illumination. The thinâlayer cells employ no external compensation yet surpass their corresponding experimental (threeâelectrode) predecessors in efficiency
Monodisperse self-assembly in a model with protein-like interactions
We study the self-assembly behaviour of patchy particles with `protein-like'
interactions that can be considered as a minimal model for the assembly of
viral capsids and other shell-like protein complexes. We thoroughly explore the
thermodynamics and dynamics of self assembly as a function of the parameters of
the model and find robust assembly of all target structures considered. Optimal
assembly occurs in the region of parameter space where a free energy barrier
regulates the rate of nucleation, thus preventing the premature exhaustion of
the supply of monomers that can lead to the formation of incomplete shells. The
interactions also need to be specific enough to prevent the assembly of
malformed shells, but whilst maintaining kinetic accessibility. Free-energy
landscapes computed for our model have a funnel-like topography guiding the
system to form the target structure, and show that the torsional component of
the interparticle interactions prevents the formation of disordered aggregates
that would otherwise act as kinetic traps.Comment: 11 pages; 10 figure
Frobenius theorem and invariants for Hamiltonian systems
We apply Frobenius integrability theorem in the search of invariants for
one-dimensional Hamiltonian systems with a time-dependent potential. We obtain
several classes of potential functions for which Frobenius theorem assures the
existence of a two-dimensional foliation to which the motion is constrained. In
particular, we derive a new infinite class of potentials for which the motion
is assurately restricted to a two-dimensional foliation. In some cases,
Frobenius theorem allows the explicit construction of an associated invariant.
It is proven the inverse result that, if an invariant is known, then it always
can be furnished by Frobenius theorem
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