913 research outputs found
Transition probabilities in OH A 2 sigma + - X 2 pi i: Bands with v prime = 0 and 1, v double prime = 0 to 4
Experimental results for relative vibrational band transition probabilities for v prime = 0 and 1, and v double prime = 0 to 4 in the A-X electronic system of OH are presented. The measurements, part of a larger set involving v prime = 0 to 4 and v double prime = 0 to 6, were made using spectrally dispersed laser-induced fluorescence (LIF) in the burnt gases of a flame. These Einstein coefficients will be useful in dynamics experiments for quantitative LIF determinations of OH radical concentrations in high v double prime
The pulpit and reform
Thesis (M.A.)--Boston Universit
Space physics educational outreach
The goal of this Space Physics Educational Outreach project was to develop a laboratory experiment and classroom lecture on Earth's aurora for use in lower division college physics courses, with the particular aim of implementing the experiment and lecture at Saint Mary's College of California. The strategy is to teach physics in the context of an interesting natural phenomenon by investigating the physical principles that are important in Earth's aurora, including motion of charged particles in electric and magnetic fields, particle collisions and chemical reactions, and atomic and molecular spectroscopy. As a by-product, the undergraduate students would develop an appreciation for naturally occurring space physics phenomena
Non-divergence of gravitational self-interactions for Goto-Nambu strings
The classical linearised gravitational self interaction of a Goto-Nambu
string is examined in four spacetime dimensions. Using a conveniently gauge
independent tensorial treatment, the divergent part of the self-force is shown
to be exactly zero. This is due to cancelation by a contribution that was
neglected in the previous treatments. This result has implications for many
applications.Comment: 7 Pages. Final version to be published in Phys. Lett. B
X-type and Y-type junction stability in domain wall networks
We develop an analytic formalism that allows one to quantify the stability
properties of X-type and Y-type junctions in domain wall networks in two
dimensions. A similar approach might be applicable to more general defect
systems involving junctions that appear in a range of physical situations, for
example, in the context of F- and D-type strings in string theory. We apply
this formalism to a particular field theory, Carter's pentavac model, where the
strength of the symmetry breaking is governed by the parameter .
We find that for low values of the symmetry breaking parameter X-type junctions
will be stable, whereas for higher values an X-type junction will separate into
two Y-type junctions. The critical angle separating the two regimes is given by
\alpha_c = 293^{\circ}\sqrt{|\epsilon|} and this is confirmed using simple
numerical experiments. We go on to simulate the pentavac model from random
initial conditions and we find that the dominant junction is of \ytype for
|\epsilon| \geq 0.02 and is of \xtype for |\epsilon| \leq 0.02\epsilon\qsubrm{N}{dw}\propto
t^{-1}\epsilont^{-1}$ lore.Comment: 24 pages, 13 figures; typos fixe
Bound States Can Stabilize Electroweak Strings
We show that the electroweak string can be stabilized by the presence of
bound states of a complex scalar field. We argue that fermions coupled to the
scalar field of the string can also make the string stable and discuss the
physical case where the string is coupled to quarks and leptons. This
stabilization mechanism is expected to work for other embedded defects and also
for unstable solutions such as the sphaleron.Comment: 11 pages (1 figure available on request), Tufts preprint# TU-92-1
Temperature Dependence of the Collisional Removal of O2(A(sup 3)Sigma(sup +)(sub u), upsilon=9 ) with O2 and N2
The temperature dependence of the collisional removal of O2 molecules in the upsilon = 9 level of the A(sup 3)Sigma(sup +)(sub u) electronic state has been studied for the colliders O2 and N2, over the temperature range 150 to 300 K. In a cooled flow cell, the output of a pulsed dye laser excites the O2 to the upsilon = 9 level of the A(sup 3)Sigma(sup +)(sub u) state, and the output of a time-delayed second laser monitors the temporal evolution of this level via a resonance-enhanced ionization. We find the u thermally averaged removal cross section for O2 collisions is constant (approx. 10 A(sup 2)) between room temperature and 200 K, then increases rapidly with decreasing temperature, doubling by 150 K. In contrast, the N2 cross section at 225 K is approx. 8% smaller and gradually increases to a value at 150 K that is approx. 60% larger than the room temperature value. The difference between the temperature dependence of the O2 and N2 collision cross section implies that the removal by oxygen becomes more important at the lower temperatures found in the mesosphere, but removal by N2 still dominates
Predissociation in N2(C'4, 1 Sigma u +) and other N2 states and its importance in the atmospheres of Titan and Triton
The objectives of this program are to further the understanding of the upper atmospheres of Titan, Triton, and the Earth in terms of the observed emissions of the 13-14 eV states of N2. These states are generated at quite high rates, yet very little emission is observed from them. The reasons are complex, involving resonance trapping and predissociation, and it is desired to quantify the effects of predissociation, particularly on the c(sub 4)' 1 Sigma(sub u),(sup +) state of N2. Earlier experiments had indicated that predissociation of the c(sub 4)' state was of little importance, yet over the last two years a growing body of evidence has shown that for levels above v = 2, predissociation is in fact a major process. It is the v = 0 level for which production by electron bombardment and photoexcitation is highest, and so it has been most important to evaluate the effects of predissociation on this particular level. The goal has been to target c(sub 4)' (v = 0) for a thorough analysis, in which both the extent of predissociation as a function of rotational level and the atomic product branching ratio, where the only possible products are N(4S) + N(4S) and N(2D) + N(4S), are determined. For the first year of funding, the intention was to demonstrate two-photon excitation of the intermediate N2(a(sup 1) Pi(sub g)) state, so that the gap to the 13 eV energy region could be bridged, and then use a second laser to reach the c(sub 4)' state itself
LIM kinase and Diaphanous cooperate to regulate serum response factor and actin dynamics
The small GTPase RhoA controls activity of serum response factor (SRF) by inducing changes in actin dynamics. We show that in PC12 cells, activation of SRF after serum stimulation is RhoA dependent, requiring both actin polymerization and the Rho kinase (ROCK)–LIM kinase (LIMK)–cofilin signaling pathway, previously shown to control F-actin turnover. Activation of SRF by overexpression of wild-type LIMK or ROCK-insensitive LIMK mutants also requires functional RhoA, indicating that a second RhoA-dependent signal is involved. This is provided by the RhoA effector mDia: dominant interfering mDia1 derivatives inhibit both serum- and LIMK-induced SRF activation and reduce the ability of LIMK to induce F-actin accumulation. These results demonstrate a role for LIMK in SRF activation, and functional cooperation between RhoA-controlled LIMK and mDia effector pathways
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