2,782 research outputs found
The three-dimensional instability of strained vortices in a viscous fluid
The recent theory describing 3-D exact solutions of the Navier–Stokes equations is applied to the problem of stability of 2-D viscous flow with elliptical streamlines. An intrinsically inviscid instability mechanism persists in all such flows provided the length scale of the disturbance is sufficiently large. Evidence is presented that this mechanism may be responsible for 3-D instabilities in high Reynolds number flows whose vortex structures can be locally described by elliptical streamlines
Flow cytometric characterization of freshwater crayfish hemocytes for the examination of physiological status in wild and captive animals
Enumeration of invertebrate hemocytes is a potentially powerful tool for the determination of physiological effects of extrinsic stressors, such as hypoxia, disease, and toxicant exposure. A detailed flow cytometric method of broad application was developed for the objective characterization and enumeration of the hemocytes of New Zealand freshwater crayfish Paranephrops planifrons for the purpose of physiological health assessment. Hemocyte populations were isolated by flow cytometric sorting based on differential light scatter properties followed by morphological characterization via light microscopy and software image analysis. Cells were identified as hyaline, semigranular, and granular hemocytes based on established invertebrate hemocyte classification. A characteristic decrease in nuclear size, an increase in granularity between the hyaline and granular cells, and the eccentric location of nuclei in granular cells were also observed. The granulocyte subpopulations were observed to possess varying degrees of granularity. The developed methodology was used to perform total and differential hemocyte counts from three lake populations and between wild and captive crayfish specimens. Differences in total and differential hemocyte counts were not observed among the wild populations. However, specimens held in captivity for 14 d exhibited a significant 63% reduction in total hemocyte count, whereas the relative hemocyte proportions remained the same. These results demonstrate the utility of this method for the investigation of subacute stressor effects in selected decapod crustaceans
Ecology of common bully (Gobiomorphus cotidianus) in the Tarawera and Rangitaiki rivers: isolation by inland distance or anthropogenic discharge?
Previous research has identified distinct genetic, life-history and reproductive differences between populations of common bully (Gobiomorphus cotidianus) upstream and downstream of a pulp and paper mill outfall on the Tarawera River in the Bay of Plenty, New Zealand. This study investigated the distribution of common bully in the Tarawera River by examining fish collected from upstream (37 km inland) and downstream (20 km inland) locations and comparing them to fish from similar inland locations (40 km and 17 km inland, respectively) in the nearby Rangitaiki River. Reproductive divergence was observed between upstream and downstream sites of both rivers by differing annual trends in gonadosomatic index. Stable carbon and nitrogen isotopes confirmed residency at each sampling site and otolith microchemistry demonstrated different life-history strategies between upstream and downstream populations. Diadromous recruits dominated in both downstream river populations, with a general disappearance of diadromy upstream. A mixture of diadromous and non-diadromous fish were found in the upstream Rangitaiki River, whereas diadromous recruits were absent in the upstream Tarawera River. A reduction in oculoscapular canal structures also coincided with loss of diadromy in fish from both rivers. A behavioural study to determine whether pulp and paper mill effluent may deter fish migration within the Tarawera River demonstrated a strong avoidance of effluent, but only at concentrations (>25%) greater than those that naturally occur in the river (<15%). The results of this study suggest that combinations of influences coupled with inland distance are likely to be responsible for the isolation of common bully subpopulations within the Tarawera River
Unified microscopic approach to the interplay of pinned-Wigner-solid and liquid behavior of lowest-Landau-level states in the neighborhood of nu=1/3
Motivated by recent experiments, and using the rotating-and-vibrating
electron-molecule (RVEM) theory [Yannouleas and Landman, Phys. Rev. B 66,
115315 (2002); Phys. Rev. A 81, 023609 (2010)], in conjunction with exact
diagonalization, we develop a unified microscopic approach for the interplay
between liquid fractional-quantum-Hall-effect (FQHE) states and Wigner-solid
states in the lowest Landau level (LLL) in the neighborhood of nu=1/3. Liquid
characteristics of the FQHE states are associated with the symmetry-conserving
rotations and vibrations of the electron molecule. Although the electron
densities of the symmetry-conserving LLL states do not exhibit crystalline
patterns, the intrinsic crystalline correlations are reflected in the
conditional probability distributions and the emergence of cusp yrast states in
the LLL spectra. It is shown that away from the exact fractional fillings, weak
pinning perturbations (due to weak disorder) may overcome the energy gaps
between adjacent global states and generate pinned broken symmetry ground
states as a superposition of symmetry-conserving LLL states with different
total angular momenta. The electron densities of such mixed states (without
good angular momentum quantum numbers) exhibit oscillating patterns that
correspond to molecular crystallites. These pinned Wigner crystallites
represent finite-size precursors of the bulk Wigner-solid state. It is further
shown that the emergence of these molecular crystallites is a consequence of
the presence of RVEM components in the symmetry-conserving LLL states. In
addition, it is shown that the RVEM approach accounts for the Wigner-solid
state in the neighborhood of nu=1, which was also found in the experiments. We
utilize results for sizes in a wide range from N=6 to N=29 electrons, and we
address the extrapolation to the thermodynamic limit.Comment: 19 pages, 17 figures, 4 tables. For related papers, see
http://www.prism.gatech.edu/~ph274cy
Coronal and chromospheric physics
Achievements and completed results are discussed for investigations covering solar activity during the solar maximum mission and the solar maximum year; other studies of solar activity and variability; infrared and submillimeter photometry; solar-related atomic physics; coronal and transition region studies; prominence research; chromospheric research in quiet and active regions; solar dynamics; eclipse studies; and polarimetry and magnetic field measurements. Contributions were also made in defining the photometric filterograph instrument for the solar optical telescope, designing the combined filter spectrograph, and in expressing the scientific aims and implementation of the solar corona diagnostic mission
Tempestas ex machina: A review of machine learning methods for wavefront control
As we look to the next generation of adaptive optics systems, now is the time
to develop and explore the technologies that will allow us to image rocky
Earth-like planets; wavefront control algorithms are not only a crucial
component of these systems, but can benefit our adaptive optics systems without
requiring increased detector speed and sensitivity or more effective and
efficient deformable mirrors. To date, most observatories run the workhorse of
their wavefront control as a classic integral controller, which estimates a
correction from wavefront sensor residuals, and attempts to apply that
correction as fast as possible in closed-loop. An integrator of this nature
fails to address temporal lag errors that evolve over scales faster than the
correction time, as well as vibrations or dynamic errors within the system that
are not encapsulated in the wavefront sensor residuals; these errors impact
high contrast imaging systems with complex coronagraphs. With the rise in
popularity of machine learning, many are investigating applying modern machine
learning methods to wavefront control. Furthermore, many linear implementations
of machine learning methods (under varying aliases) have been in development
for wavefront control for the last 30-odd years. With this work we define
machine learning in its simplest terms, explore the most common machine
learning methods applied in the context of this problem, and present a review
of the literature concerning novel machine learning approaches to wavefront
control.Comment: SPIE Proceeding: 2023 / 12680-1
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