633 research outputs found
Springs of Florida
bulletin
which documented the major and important springs in the state (Ferguson et al., 1947).
This publication was revised in 1977, with many previously undocumented springs and
many new water-quality analyses being added (Rosenau et al., 1977). The Florida
Geological Survey's report on first magnitude springs (Scott et al., 2002) was the initial step
in once again updating and revising the Springs of Florida bulletin. The new bulletin
includes the spring descriptions and water-quality analyses from Scott et al. (2002). Nearly
300 springs were described in 1977. As of 2004, more than 700 springs have been recognized
in the state and more are reported each year. To date, 33 first magnitude springs (with a
flow greater than 100 cubic feet per second or approximately 64.6 million gallons of water
per day) have been recognized in Florida, more than any other state or country (Rosenau et
al., 1977). Our springs are a unique and invaluable natural resource. A comprehensive
understanding of the spring systems will provide the basis for their protection and wise use.
(Document pdf contains 677 pages
Theory of Shubnikov--De Haas Oscillations Around the Filling Factor of the Landau Level: Effect of Gauge Field Fluctuations
We present a theory of magnetooscillations around the Landau level
filling factor based on a model with a fluctuating Chern--Simons field. The
quasiclassical treatment of the problem is appropriate and leads to an
unconventional behavior of the
amplitude of oscillations. This result is in good qualitative agreement with
available experimental data.Comment: Revtex, 4 pages, 1 figure attached as PostScript fil
Instantons and the spectral function of electrons in the half-filled Landau level
We calculate the instanton-anti-instanton action in
the gauge theory of the half-filled Landau level. It is found that for a class of interactions between electrons. This means that the instanton-anti-instanton
pairs are confining so that a well defined `charged' composite fermion can
exist. It is also shown that can be used to calculate
the spectral function of electrons from the microscopic theory within a
semiclassical approximation. The resulting spectral function varies as at low
energies.Comment: 13 pages, Plain Tex, MIT-CMT-APR-9
Beyond the random phase approximation in the Singwi-Sj\"olander theory of the half-filled Landau level
We study the Chern-Simons system and consider a self-consistent
field theory of the Singwi-Sj\"olander type which goes beyond the random phase
approximation (RPA). By considering the Heisenberg equation of motion for the
longitudinal momentum operator, we are able to show that the zero-frequency
density-density response function vanishes linearly in long wavelength limit
independent of any approximation. From this analysis, we derive a consistency
condition for a decoupling of the equal time density-density and
density-momentum correlation functions. By using the Heisenberg equation of
motion of the Wigner distribution function with a decoupling of the correlation
functions which respects this consistency condition, we calculate the response
functions of the system. In our scheme, we get a density-density
response function which vanishes linearly in the Coulomb case for
zero-frequency in the long wavelength limit. Furthermore, we derive the
compressibility, and the Landau energy as well as the Coulomb energy. These
energies are in better agreement to numerical and exact results, respectively,
than the energies calculated in the RPA.Comment: 9 Revtex pages, 4 eps figures, typos correcte
Specific heat and validity of quasiparticle approximation in the half-filled Landau level
We calculate the specific heat of composite fermion system in the half-filled
Landau level. Two different methods are used to examine validity of the
quasiparticle approximation when the two-body interaction is given by (). The singular part of the specific heat
is calculated from the free energy of the gauge field, which is compared with
the specific heat calculated from the quasiparticle approximation via the
singular self-energy correction due to the gauge field fluctuations. It turns
out that two results are in general different and they coincide only for the
case of the Coulomb interaction (). This result supports the fact
that the quasiparticle approximation is valid only for the case of the Coulomb
interaction. It is emphasized that this result is obtained by looking at a
gauge-invariant quantity -- the specific heat.Comment: 8 pages, Revte
SIN-dependent phosphoinhibition of formin multimerization controls fission yeast cytokinesis
Many eukaryotes accomplish cell division by building and constricting a medial actomyosin-based cytokinetic ring (CR). In Schizosaccharomyces pombe, a Hippo-related signaling pathway termed the septation initiation network (SIN) controls CR formation, maintenance, and constriction. However, how the SIN regulates integral CR components was unknown. Here, we identify the essential cytokinetic formin Cdc12 as a key CR substrate of SIN kinase Sid2. Eliminating Sid2-mediated Cdc12 phosphorylation leads to persistent Cdc12 clustering, which prevents CR assembly in the absence of anillin-like Mid1 and causes CRs to collapse when cytokinesis is delayed. Molecularly, Sid2 phosphorylation of Cdc12 abrogates multimerization of a previously unrecognized Cdc12 domain that confers F-actin bundling activity. Taken together, our findings identify a SIN-triggered oligomeric switch that modulates cytokinetic formin function, revealing a novel mechanism of actin cytoskeleton regulation during cell division. © 2013 Bohnert et al
Edge magnetoplasmons in periodically modulated structures
We present a microscopic treatment of edge magnetoplasmons (EMP's) within the
random-phase approximation for strong magnetic fields, low temperatures, and
filling factor , when a weak short-period superlattice potential is
imposed along the Hall bar. The modulation potential modifies both the spatial
structure and the dispersion relation of the fundamental EMP and leads to the
appearance of a novel gapless mode of the fundamental EMP. For sufficiently
weak modulation strengths the phase velocity of this novel mode is almost the
same as the group velocity of the edge states but it should be quite smaller
for stronger modulation. We discuss in detail the spatial structure of the
charge density of the renormalized and the novel fundamental EMP's.Comment: 8 pages, 4 figure
The Haldane-Rezayi Quantum Hall State and Magnetic Flux
We consider the general abelian background configurations for the
Haldane-Rezayi quantum Hall state. We determine the stable configurations to be
the ones with the spontaneous flux of with .
This gives the physical mechanism by which the edge theory of the state becomes
identical to the one for the 331 state. It also provides a new experimental
consequence which can be tested in the enigmatic plateau in a single
layer system.Comment: RevTex, 5 pages, 2 figures. v2:minor corrections. v4: published
version. Discussion on the thermodynamic limit adde
Surface acoustic wave attenuation by a two-dimensional electron gas in a strong magnetic field
The propagation of a surface acoustic wave (SAW) on GaAs/AlGaAs
heterostructures is studied in the case where the two-dimensional electron gas
(2DEG) is subject to a strong magnetic field and a smooth random potential with
correlation length Lambda and amplitude Delta. The electron wave functions are
described in a quasiclassical picture using results of percolation theory for
two-dimensional systems. In accordance with the experimental situation, Lambda
is assumed to be much smaller than the sound wavelength 2*pi/q. This restricts
the absorption of surface phonons at a filling factor \bar{\nu} approx 1/2 to
electrons occupying extended trajectories of fractal structure. Both
piezoelectric and deformation potential interactions of surface acoustic
phonons with electrons are considered and the corresponding interaction
vertices are derived. These vertices are found to differ from those valid for
three-dimensional bulk phonon systems with respect to the phonon wave vector
dependence. We derive the appropriate dielectric function varepsilon(omega,q)
to describe the effect of screening on the electron-phonon coupling. In the low
temperature, high frequency regime T << Delta (omega_q*Lambda
/v_D)^{alpha/2/nu}, where omega_q is the SAW frequency and v_D is the electron
drift velocity, both the attenuation coefficient Gamma and varepsilon(omega,q)
are independent of temperature. The classical percolation indices give
alpha/2/nu=3/7. The width of the region where a strong absorption of the SAW
occurs is found to be given by the scaling law |Delta \bar{\nu}| approx
(omega_q*Lambda/v_D)^{alpha/2/nu}. The dependence of the electron-phonon
coupling and the screening due to the 2DEG on the filling factor leads to a
double-peak structure for Gamma(\bar{\nu}).Comment: 17 pages, 3 Postscript figures, minor changes mad
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