Modeling methods for high-fidelity rotorcraft flight mechanics simulation

The cooperative effort being carried out under the agreements of the United States-Israel Memorandum of Understanding is discussed. Two different models of the AH-64 Apache Helicopter, which may differ in their approach to modeling the main rotor, are presented. The first model, the Blade Element Model for the Apache (BEMAP), was developed at Ames Research Center, and is the only model of the Apache to employ a direct blade element approach to calculating the coupled flap-lag motion of the blades and the rotor force and moment. The second model was developed at the Technion-Israel Institute of Technology and uses an harmonic approach to analyze the rotor. The approach allows two different levels of approximation, ranging from the 'first harmonic' (similar to a tip-path-plane model) to 'complete high harmonics' (comparable to a blade element approach). The development of the two models is outlined and the two are compared using available flight test data

Attenuation of Seismic Energy in the Upper Mantle

The amplitude attenuation and phase dispersion for Love and Rayleigh waves in the period range 50 to 300 sec is determined from two earthquakes by digital techniques. A distribution of Q, or anelasticity, is determined for the upper mantle which satisfies the amplitude decay data for Love and Rayleigh waves and which is consistent with available body wave data. An argument is made for a longitudinal wave Q of about 2.4 to 2.6 times the Q for shear waves. This implies that very small losses are involved in pure compression compared to the losses in shear. This is an argument against the importance of certain mechanisms, such as thermoelastic losses, in the mantle. The Q for shear waves in the upper 400 km of the mantle seems to vary from about 50 to about 150. The Q for mantle Rayleigh waves is greater than the Q for mantle Love waves, both theoretically and experimentally. However, it is predicted that Q_R becomes less than Q_L at some period shorter than 50 sec, the crossover period being diagnostic of the thickness of the 'Q crust' or lithosphere

Adult and periadolescent rats differ in expression of nicotinic cholinergic receptor subtypes and in the response of these subtypes to chronic nicotine exposure

ABSTRACTAdolescence is a time of significant brain development, and exposure to nicotine during this period is associated with higher subsequent rates of dependence. Chronic nicotine exposure alters expression of nicotinic acetylcholine receptors (nAChRs), changing the pattern of nicotine responsiveness. We used quantitative autoradiography to measure three major subtypes of nAChRs after chronic nicotine exposure by osmotic minipump in adult and periadolescent rats. Comparison of control animals at the two different ages revealed that periadolescents express consistently greater numbers of α4β2⁎ nAChRs compared to the same brain regions of adults. Similar but less pronounced increases in α7 nAChRs were found in control periadolescent rats compared to adults. Binding of [125I]α-conotoxin MII (largely to α6⁎ nAChRs) did not systematically differ between adults and periadolescents. The response to chronic nicotine exposure also differed by age. Up-regulation of α4β2⁎ nAChRs was prominent and widespread in adult animals; in periadolescents, α4β2⁎ up-regulation also occurred, but in fewer regions and to a lesser extent. A similar pattern of response was seen with α7 receptors: adults were more responsive than periadolescents to nicotine-induced up-regulation. In adult animals, chronic nicotine exposure did not cause up-regulation of α6⁎ nAChRs; binding was down-regulated in three regions. Unlike the other subtypes, the response of α6⁎ nAChRs to chronic nicotine was greater in periadolescents, with more regions showing greater down-regulation compared to adults. These differences in receptor expression and regulation between age groups are likely to be important given the unique vulnerability of adolescents to nicotine-induced behavioral changes and susceptibility to drug abuse

Attenuation of dispersed waves

A measure of the absorption of elastic waves is the specific absorption coefficient 1/Q. In dispersive mediums, whether the dispersion is due to geometry, inhomogeneity, or both, measurements are often made outside the body and the measurements must be interpreted as to the distribution of values of 1/Q within the body. Two definitive experiments of this type are those performed using standing waves set up in a confined sample of the body and with waves that propagate through or on the surface of the body. Typical examples of these experiments involve the measurement of the damping coefficient of the free modes of vibration of the earth and the measurement of the attenuation factor of propagating surface waves on the earth. These two types of experiments can themselves be interpreted in terms of dimensionless attenuation factors. We call the dimensionless attenuation factors in the standing wave and propagating wave experiments 1/Q_T and 1/Q_x, defined as the logarithmic decrements π/QT and π/Q_x in each experiment. Then in a damped standing wave the amplitude will diminish with time t at a fixed point as exp (−πt/TQ_T), where T is the period. In a propagating monochromatic wave the amplitude will diminish with distance x as exp (−πx/cTQ_x), where c is the phase velocity

Interaction potential in compact three-dimensional QED with mixed action

We use a variational wave function to calculate the energy of the interaction between external charges in the compact Abelian gauge theory in 2+1 dimensions with mixed action. Our variational wave functions preserve the compact gauge invariance of the theory both in the vacuum and in the charged sectors. We find that a good estimate of the interaction energy is obtained only when we allow more variational parameters in the charged sector than in the vacuum sector. These extra parameters are the profile of an induced electric field. We find that the theory has a two-phase structure: When the charge-2 coupling is large and negative there is no mass gap in the theory and no confinement, while otherwise a mass gap is generated dynamically and the theory confines charges. The pure Wilson theory is in the confining phase.Comment: 22 pages, Latex -- final version, minor changes from first versio

Composite defect extends cosmology - 3He analogy

Spin-mass vortices have been observed to form in rotating superfluid 3He-B following the absorption of a thermal neutron and a rapid transition from the normal to superfluid state. The spin-mass vortex is a composite defect which consists of a planar soliton (wall) which terminates on a linear core (string). This observation fits well within the framework of a cosmological scenario for defect formation, known as the Kibble-Zurek mechanism. It suggests that in the early Universe analogous cosmological defects might have formed.Comment: RevTeX file, 5 pages, 2 figures, submitted to Phys. Rev. Lett., modified according to referee repor

CORE Technology and Exact Hamiltonian Real-Space Renormalization Group Transformations

The COntractor REnormalization group (CORE) method, a new approach to solving Hamiltonian lattice systems, is presented. The method defines a systematic and nonperturbative means of implementing Kadanoff-Wilson real-space renormalization group transformations using cluster expansion and contraction techniques. We illustrate the approach and demonstrate its effectiveness using scalar field theory, the Heisenberg antiferromagnetic chain, and the anisotropic Ising chain. Future applications to the Hubbard and t-J models and lattice gauge theory are discussed.Comment: 65 pages, 9 Postscript figures, uses epsf.st

Hippocampal Synaptic Plasticity in Mice Overexpressing an Embryonic Subunit of the NMDA Receptor

The effects of changing NMDA receptor subunit composition on synaptic plasticity in the hippocampus were analyzed by creating transgenic mice overexpressing NR2D, a predominantly embryonic NMDA receptor subunit. NMDA-evoked currents in the transgenic mice had smaller amplitudes and slower kinetics. The transgenics also displayed age-dependent deficits in synaptic plasticity in area CA1 of the hippocampus. Long-term depression was selectively impaired in juvenile mice when NR2D overexpression was moderate. In mature mice, overexpression of NR2D was associated with a reduction of both NR2B and Ca^(2+)-independent activity of Ca^(2+)- and calmodulin-dependent protein kinase II. These biochemical changes were correlated with a marked impairment of NMDA-dependent long-term potentiation, but spatial behavior was normal in these mice. These results show that the developmental regulation of NMDA receptor subunit composition alters the frequency at which modification of synaptic responses occur after afferent stimulation