516 research outputs found
Coherent and Incoherent Dynamic Structure Function of the Free Fermi Gas
A detailed calculation of the coherent and incoherent dynamic structure
functions of the free Fermi gas, starting from their expressions in terms of
the one- and semi-diagonal two-body density matrices, is derived and discussed.
Their behavior and evolution with the momentum transfer is analyzed, and
particular attention is devoted to the contributions that both functions
present at negative energies. Finally, an analysis of the energy weighted sum
rules satisfied by both responses is also performed. Despite of the simplicity
of the model, some of the conclusions can be extended to realistic systems.Comment: LaTeX, 3 figure
Intrinsic Mean Square Displacements in Proteins
The thermal mean square displacement (MSD) of hydrogen in proteins and its
associated hydration water is measured by neutron scattering experiments and
used an indicator of protein function. The observed MSD as currently determined
depends on the energy resolution width of the neutron scattering instrument
employed. We propose a method for obtaining the intrinsic MSD of H in the
proteins, one that is independent of the instrument resolution width. The
intrinsic MSD is defined as the infinite time value of that appears in
the Debye-Waller factor. The method consists of fitting a model to the
resolution broadened elastic incoherent structure factor or to the resolution
dependent MSD. The model contains the intrinsic MSD, the instrument resolution
width and a rate constant characterizing the motions of H in the protein. The
method is illustrated by obtaining the intrinsic MSD of heparan sulphate
(HS-0.4), Ribonuclease A and Staphysloccal Nuclase (SNase) from data in the
literature
Excitations of amorphous solid helium
We present neutron scattering measurements of the dynamic structure factor,
, of amorphous solid helium confined in 47 pore diameter
MCM-41 at pressure 48.6 bar. At low temperature, = 0.05 K, we observe
of the confined quantum amorphous solid plus the bulk
polycrystalline solid between the MCM-41 powder grains. No liquid-like
phonon-roton modes, other sharply defined modes at low energy ( 1.0
meV) or modes unique to a quantum amorphous solid that might suggest superflow
are observed. Rather the of confined amorphous and bulk
polycrystalline solid appear to be very similar. At higher temperature ( 1
K), the amorphous solid in the MCM-41 pores melts to a liquid which has a broad
peaked near 0 characteristic of normal liquid
He under pressure. Expressions for the of amorphous and
polycrystalline solid helium are presented and compared. In previous
measurements of liquid He confined in MCM-41 at lower pressure the
intensity in the liquid roton mode decreases with increasing pressure until the
roton vanishes at the solidification pressure (38 bars), consistent with no
roton in the solid observed here
Some phases of narrative art
Submitted in partial fulfillment of the requirements for the degree of Master of ArtsText from page 76: "The progress of narrative art, especially in its relation to naturalism, has been traced. Though it cannot be maintained that narrative art is characteristic cf naturalistic periods, it has been shown that naturalism is favorable to the development of such a style. The scarcity of narration in the present period of naturalistic tendenocies is due, probably, to two reasons: the presence of interests other than the human element, which must dominate narrative art, and the symbolical and allegorical treatment of the human element when it is retained by the modern artist."Includes bibliographical references (pages 78-82
Condensate fraction in liquid 4He at zero temperature
We present results of the one-body density matrix (OBDM) and the condensate
fraction n_0 of liquid 4He calculated at zero temperature by means of the Path
Integral Ground State Monte Carlo method. This technique allows to generate a
highly accurate approximation for the ground state wave function Psi_0 in a
totally model-independent way, that depends only on the Hamiltonian of the
system and on the symmetry properties of Psi_0. With this unbiased estimation
of the OBDM, we obtain precise results for the condensate fraction n_0 and the
kinetic energy K of the system. The dependence of n_0 with the pressure shows
an excellent agreement of our results with recent experimental measurements.
Above the melting pressure, overpressurized liquid 4He shows a small condensate
fraction that has dropped to 0.8% at the highest pressure of p = 87 bar.Comment: 12 pages. 4 figures. Accepted for publication on "Journal of Low
Temperature Physics
From Research to Practice Change–Achieving Adoption through Regionally Packaged Technology and Farm Systems
The rate and extent of adoption of grazing systems technology is limited by the relevance of recommendations and the complexity of integrating new practices into farming systems. This paper describes how, through development of regional information packages, a national project is enhancing adoption of the outputs from research investment. Every farm has unique goals, soils, landscape, enterprise setup and existing practices. When making investment decisions, farmers consider the cost and potential impact of each option compared to other competing options, the fit into their existing management philosophy and other changes necessary to realise the potential benefit. Overlaying this, farmers consider whether the innovation applies to their region, and commonly cite lack of regional applicability as a reason not to adopt. We argue that development of regional packages is a powerful means of targeting the needs unique to each region. Such packages can include recommendations from whole-farm system experiments, modelling and case studies which tell the full story around profit, risk, natural resource management and lifestyle impacts of change options, and adviser training for supporting farmer adoption decision processes. By focusing on communicating how research outputs are relevant to local farming systems, utilising local input, regional packages have the capacity to change the way R,D & E is conducted and delivered, accelerating delivery of industry and environmental benefits
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