6,354 research outputs found
Effect of the number of vortices on the torque scaling in Taylor-Couette flow
Torque measurements in Taylor-Couette flow, with large radius ratio and large
aspect ratio, over a range of velocities up to a Reynolds number of 24 000 are
presented. Following a specific procedure, nine states with distinct number of
vortices along the axis were found and the aspect ratio of the vortices were
measured. The relationship between the speed and the torque for a given number
of vortices is reported. In the turbulent Taylor vortex flow regime, at
relatively high Reynolds number, a change in behaviour is observed
corresponding to intersections of the torque-speed curves for different states.
Before each intersection, the torque for a state with larger number of vortices
is higher. After each intersection, the torque for a state with larger number
of vortices is lower. The exponent, from the scaling laws of the torque, always
depends on the aspect ratio of the vortices. When the Reynolds number is
rescaled using the mean aspect ratio of the vortices, only a partial collapse
of the exponent data is found.Comment: 11 pages, 6 figure
The young stellar population of NGC 4214 as observed with HST. I. Data and methods
We present the data and methods that we have used to perform a detailed
UV-optical study of the nearby dwarf starburst galaxy NGC 4214 using
multifilter HST/WFPC2+STIS photometry. We explain the process followed to
obtain high-quality photometry and astrometry of the stellar and cluster
populations of this galaxy. We describe the procedure used to transform
magnitudes and colors into physical parameters using spectral energy
distributions. The data show the existence of both young and old stellar
populations that can be resolved at the distance of NGC 4214 (2.94 Mpc) and we
perform a general description of those populations.Comment: 33 pages, 9 figures, and 8 table
A Symmetry Adapted Approach to Molecular Spectroscopy: The Anharmonic Oscillator Symmetry Model
We apply the Anharmonic Oscillator Symmetry Model to the description of
vibrational excitations in and molecules. A
systematic procedure can be used to establish the relation between the
algebraic and configuration space formulations, by means of which new
interactions are found in the algebraic model, leading to reliable
spectroscopic predictions. We illustrate the method for the case of -triatomic molecules and the Be-cluster.Comment: 12 pages, invited talk at XIX Oaxtepec Symposium on Nuclear Physics,
January 199
Bose-Einstein condensation of the magnetized ideal Bose gas
We study the charged non-relativistic Bose gas interacting with a constant
magnetic field but which is otherwise free. The notion of Bose-Einstein
condensation for the three dimensional case is clarified, and we show that
although there is no condensation in the sense of a phase transition, there is
still a maximum in the specific heat which can be used to define a critical
temperature. Although the absence of a phase transition persists for all values
of the magnetic field, we show how as the magnetic field is reduced the curves
for the specific heat approach the free field curve. For large values of the
magnetic field we show that the gas undergoes a "dimensional reduction" and
behaves effectively as a one-dimensional gas except at very high temperatures.
These general features persist for other spatial dimensions D and we show
results for D=5. Finally we examine the magnetization and the
Meissner-Ochsenfeld effect.Comment: 4 pages RevTex 2 column format with 4 eps figures, uses epsf.
Replaced version has missing acknowledgements and a discussion of two
references is corrected thanks to discussions with J. Daicic and N. Franke
Dynamic stability of crack fronts: Out-of-plane corrugations
The dynamics and stability of brittle cracks are not yet fully understood.
Here we use the Willis-Movchan 3D linear perturbation formalism [J. Mech. Phys.
Solids {\bf 45}, 591 (1997)] to study the out-of-plane stability of planar
crack fronts in the framework of linear elastic fracture mechanics. We discuss
a minimal scenario in which linearly unstable crack front corrugations might
emerge above a critical front propagation speed. We calculate this speed as a
function of Poisson's ratio and show that corrugations propagate along the
crack front at nearly the Rayleigh wave-speed. Finally, we hypothesize about a
possible relation between such corrugations and the long-standing problem of
crack branching.Comment: 5 pages, 2 figures + supplementary informatio
SU(2) Kinetic Mixing Terms and Spontaneous Symmetry Breaking
The non-abelian generalization of the Holdom model --{\it i.e.} a theory with
two gauge fields coupled to the kinetic mixing term -- is considered. Contrarily to the abelian case, the group
structure is explicitly broken to . For SU(2) this fact implies
that the residual gauge symmetry as well as the Lorentz symmetry is
spontaneusly broken. We show that this mechanism provides of masses for the
involved particles. Also, the model presents instanton solutions with a
redefined coupling constant.Comment: 9pp. typos and clarifications are adde
Influence of MWCNT/surfactant dispersions on the mechanical properties of Portland cement pastes
This work studies the reinforcing effect of Multi Walled Carbon Nanotubes (MWCNT) on cement pastes. A 0.35% solid concentration of MWCNT in powder was dispersed in deionized water with sodium dodecyl sulfate (cationic surfactant), cetylpyridinium chloride (anionic surfactant) and triton X-100 (amphoteric surfactant) using an ultrasonic tip processor. Three concentrations of each surfactant (1mM, 10mM and 100mM) were tested, and all samples were sonicated until an adequate dispersion degree was obtained. Cement pastes with additions of carbon nanotubes of 0.15% by mass of cement were produced in two steps; first the dispersions of MWCNT were combined with the mixing water using an ultrasonic tip processor to guarantee homogeneity, and then cement was added and mixed until a homogeneous paste was obtained. Direct tensile strength, apparent density and open porosity of the pastes were measured after 7 days of curing. It was found that the MWCNT/surfactants dispersions decrease the mechanical properties of the cement based matrix due to an increased porosity caused by the presence of surfactants. © Published under licence by IOP Publishing Ltd
Phase transitions in the Interacting Boson Fermion Model: the gamma-unstable case
The phase transition around the critical point in the evolution from
spherical to deformed gamma-unstable shapes is investigated in odd nuclei
within the Interacting Boson Fermion Model. We consider the particular case of
an odd j=3/2 particle coupled to an even-even boson core that undergoes a
transition from spherical U(5) to gamma-unstable O(6) situation. The particular
choice of the j=3/2 orbital preserves in the odd case the condition of
gamma-instability of the system. As a consequence, energy spectrum and
electromagnetic transitions, in correspondence of the critical point, display
behaviours qualitatively similar to those of the even core. The results are
also in qualitative agreement with the recently proposed E(5/4) model, although
few differences are present, due to the different nature of the two schemes.Comment: In press in PRC as rapid communication. 7 pages, 4 figure
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