31,782 research outputs found
One way to Characterize the compact structures of lattice protein model
On the study of protein folding, our understanding about the protein
structures is limited. In this paper we find one way to characterize the
compact structures of lattice protein model. A quantity called Partnum is given
to each compact structure. The Partnum is compared with the concept
Designability of protein structures emerged recently. It is shown that the
highly designable structures have, on average, an atypical number of local
degree of freedom. The statistical property of Partnum and its dependence on
sequence length is also studied.Comment: 10 pages, 5 figure
Mirroring within the Fokker-Planck formulation of cosmic ray pitch angle scattering in homogeneous magnetic turbulence
The Fokker-Planck coefficient for pitch angle scattering, appropriate for cosmic rays in homogeneous, stationary, magnetic turbulence, is computed from first principles. No assumptions are made concerning any special statistical symmetries the random field may have. This result can be used to compute the parallel diffusion coefficient for high energy cosmic rays moving in strong turbulence, or low energy cosmic rays moving in weak turbulence. Becuase of the generality of the magnetic turbulence which is allowed in this calculation, special interplanetary magnetic field features such as discontinuities, or particular wave modes, can be included rigorously. The reduction of this results to previously available expressions for the pitch angle scattering coefficient in random field models with special symmetries is discussed. The general existance of a Dirac delta function in the pitch angle scattering coefficient is demonstrated. It is proved that this delta function is the Fokker-Planck prediction for pitch angle scattering due to mirroring in the magnetic field
Group-theoretical approach to a non-central extension of the Kepler-Coulomb problem
Bound and scattering states of a non-central extension of the
three-dimensional Kepler-Coulomb Hamiltonian are worked out analytically within
the framework of the potential groups of the problem, SO(7) for bound states
and SO(6,1) for scattering states. In the latter case, the S matrix is
calculated by the method of intertwining operators.Comment: 12 pages, to appear in J. Phys. A : Math. Theo
The Fokker-Planck coefficient for pitch-angle scattering of cosmic rays
For the case of homogeneous, isotropic magnetic field fluctuations, it is shown that most theories which are based on the quasi-linear and adiabatic approximation yield the same integral for the Fokker-Planck coefficient for the pitch angle scattering of cosmic rays. For example, despite apparent differences, the theories due to Jokipii and to Klimas and Sandri yield the same integral. It is also shown, however, that this integral in most cases has been evaluated incorrectly in the past. For large pitch angles these errors become significant, and for pitch angles of 90 deg the actual Fokker-Planck coefficient contains a delta function. The implications for these corrections relating cosmic ray diffusion coefficients to observed properties of the interplanetary magnetic field are discussed
Influence of environmental factors during seed development and after full-ripeness on pre-harvest sprouting in wheat
Results on environmental and genotypic factors influencing preharvest sprouting of wheat are summarized. Other possible areas where additional research is needed is suggested
Acoustic and aerodynamic performance of a 6-foot-diameter fan for turbofan engines. 2 - Performance of QF-1 fan in nacelle without acoustic suppression
Low noise turbofan engine without aerodynamic blade loadin
Finite Order BFFT Method
We have proposed a method in the context of BFFT approach that leads to
truncation of the infinite series regarded to constraints in the extended phase
space, as well as other physical quantities (such as Hamiltonian). This has
been done for cases where the matrix of Poisson brackets among the constraints
is symplectic or constant. The method is applied to Proca model, single self
dual chiral bosons and chiral Schwinger models as examples.Comment: 14 pages, no figure to appear in Int. J. of Mod. Phys.
Nutation versus angular dependent NQR spectroscopy and the impact of underdoping on charge inhomogeneities in YBaCuO
We describe two different nuclear quadrupole resonance (NQR) based
techniques, designed to measure the local asymmetry of the internal electric
field gradient, and the tilt angle of the main NQR principal axis z from the
crystallographic axis c. These techniques use the dependence of the NQR signal
on the duration of the radio frequency (rf) pulse and on the direction of the
rf field H1 with respect to the crystal axis. The techniques are applied to
oriented powder of YBaCuO fully enriched with 63Cu.
Measurements were performed at different frequencies, corresponding to
different in-plane copper sites with respect to the dopant. Combining the
results from both techniques, we conclude that oxygen deficiency in the chain
layer lead to a rotation of the NQR main principal axis at the nearby Cu on the
CuO2 planes by 20+-degrees. This occurs with no change to the asymmetry. The
axis rotation associated with oxygen deficiency means that there must be
electric field inhomogeneities in the CuO2 planes only in the vicinity of the
missing oxygen.Comment: 9 pages, 10 figure
Dynamics of Human Walking
The problem of biped locomotion at steady speeds is discussed through a
Lagrangian formulation developed for velocity-dependent, body driving forces.
Human walking on a level surface is analyzed in terms of the data on the
resultant ground-reaction force and the external work. It is shown that the
trajectory of the center of mass is due to a superposition of its rectilinear
motion with a given speed and a backward rotation along a shortened
hypocycloid. A stiff-to-compliant crossover between walking gaits is described
and the maximum speed for human walking, given by an instability of the
trajectory, is predicted.
Key words: locomotion, integrative biology, muscles, bipedalism, human
walking, biomechanics.Comment: 9 pages, 4 figure
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