1,156 research outputs found

### Dynamics of a two-dimensional vapor bubble confined between superheated or subcooled parallel plates

The dynamics of a long, two-dimensional vapor bubble confined in the gap between two superheated or subcooled parallel plates is analyzed theoretically. The unsteady expansion and/or contraction of the bubble is driven by mass transfer between the liquid and the vapor. The analysis uses the approach developed by Wilson et al. J. Fluid Mech. 391, 1 1999 for a situation with 'large' gaps and 'small' superheating or subcooling to consider a situation with small gaps and large superheating or subcooling in which the mass transfer from or to the semicircular nose of the bubble is comparable to that from or to the thin liquid films on the plates. In order to permit a semi- analytical treatment the analysis is restricted to low Prandtl number liquids. When both plates are superheated the bubble always expands. In this case there are two possible constant-velocity continuous-film solutions for the expansion of the bubble, namely, an unstable fast mode and a stable slow mode. The evolution of the bubble is calculated numerically for a range of values of the parameters. In particular, these calculations show that eventually the bubble expands either with the constant velocity of the slow mode or exponentially. When both plates are subcooled the bubble always collapses to zero length in a finite time. When one plate is subcooled and the other plate is superheated the situation is rather more complicated. If the magnitude of the subcooling is less than that of the superheating then if the magnitude of the subcooling is greater than a critical value then a variety of complicated behaviors including the possibility of an unexpected 'waiting time' behavior in which the bubble remains almost stationary for a finite period oftime can occur before the bubble eventually collapses to a finite length in an infinite time, whereas if it is less than this critical value then the bubble always expands and eventually does so exponentially. If the magnitude of the subcooling is greater than that of the superheating then the bubble always collapses to zero length in a finite time

### Primary vaginal Ewingâ€™s sarcoma/primitive neuroectodermal tumour: diagnostic and treatment challenges

Extra osseous Ewingâ€™s sarcoma/primitive neuroectodermal tumour (PNET) of the genital tract of women is scarcely\ud
described in the literature and involvement of the vagina is even rarer with a very few cases reported so far. We present\ud
50-year-old-woman who presented with a vaginal mass that was diagnosed to be a malignant round cell tumour which\ud
later was confirmed to be primary vaginal Ewingâ€™s sarcoma/ PNET on light microscopy and immunohistochemical\ud
staining. She was then treated with induction chemotherapy followed by local radiotherapy and further maintenance\ud
chemotherapy. This rare case of primary vaginal Ewingâ€™s sarcoma/PNET emphasizes the need for combining\ud
morphological features with immunohistochemistry with a panel of antibodies in establishing the diagnosis of Ewingâ€™s\ud
sarcoma/PNET at an uncommon site. Further, the case also highlights the use of induction chemotherapy followed by\ud
radiation therapy and subsequent maintenance chemotherapy as a treatment modality

### Vanishing magnetic mass in QED$_{3}$ with a Chern-Simons term

We show that, at one loop, the magnetic mass vanishes at finite temperature
in QED in any dimension. In QED$_{3}$, even the zero temperature part can be
regularized to zero. We calculate the two loop contributions to the magnetic
mass in QED$_{3}$ with a Chern-Simons term and show that it vanishes. We give a
simple proof which shows that the magnetic mass vanishes to all orders at
finite temperature in this theory. This proof also holds for QED in any
dimension.Comment: revtex, 7 pages, 5 figure

### Temperature dependence of the effective spin-mixing conductance probed with lateral non-local spin valves

We report the temperature dependence of the effective spin-mixing conductance between a normal metal (aluminium, Al) and a magnetic insulator (Y3Fe5O12, YIG). Non-local spin valve devices, using Al as the spin transport channel, were fabricated on top of YIG and SiO2 substrates. By comparing the spin relaxation lengths in the Al channel on the two different substrates, we calculate the effective spin-mixing conductance (Gs) to be 3.3 Ã— 1012 â„¦âˆ’1mâˆ’2 at 293 K for the Al/YIG interface. A decrease of up to 84% in Gs is observed when the temperature (T) is decreased from 293 K to 4.2 K, with Gs scaling with (T /Tc)3/2. The real part of the spin-mixing conductance (Gr â‰ˆ 5.7 Ã— 1013 â„¦âˆ’1mâˆ’2), calculated from the experimentally obtained Gs, is found to be approximately independent of the temperature. We evidence a hitherto unrecognized underestimation of Gr extracted from the modulation of the spin signal by rotating the magnetization direction of YIG with respect to the spin accumulation direction in the Al channel, which is found to be 50 times smaller than the calculated value

### Cold Plasma Dispersion Relations in the Vicinity of a Schwarzschild Black Hole Horizon

We apply the ADM 3+1 formalism to derive the general relativistic
magnetohydrodynamic equations for cold plasma in spatially flat Schwarzschild
metric. Respective perturbed equations are linearized for non-magnetized and
magnetized plasmas both in non-rotating and rotating backgrounds. These are
then Fourier analyzed and the corresponding dispersion relations are obtained.
These relations are discussed for the existence of waves with positive angular
frequency in the region near the horizon. Our results support the fact that no
information can be extracted from the Schwarzschild black hole. It is concluded
that negative phase velocity propagates in the rotating background whether the
black hole is rotating or non-rotating.Comment: 27 pages, 11 figures accepted for publication in Gen. Relat. & Gravi

### Stable Magnetic Universes Revisited

A regular class of static, cylindrically symmetric pure magnetic field
metrics is rederived in a different metric ansatz in all dimensions. Radial,
time dependent perturbations show that for dimensions d>3 such spacetimes are
stable at both near r\approx0 and large radius r\rightarrow\infty. In a
different gauge these stability analysis and similar results were known
beforehand. For d=3, however, simultaneous stability requirement at both, near
and far radial distances can not be reconciled for time - dependent
perturbations. Restricted, numerical geodesics for neutral particles reveal a
confinement around the center in the polar plane. Charged, time-like geodesics
for d=4 on the other hand are shown numerically to run toward infinity.Comment: 11 pages, 3figure

### Confined growth of a vapour bubble in a capillary tube at initially uniform superheat : experiments and modelling

Bubble growth was triggered in a capillary tube closed at one end and vented to the atmosphere at the other and initially filled with uniformly superheated water. Measurements of the rate of axial growth and the varying pressure at the closed end were used to test under these simplified conditions assumptions employed in one-dimensional models for bubble growth applicable to the more complex conditions of confined-bubble flow boiling in micro-channels. Issues included the thickness of the liquid films round confined bubbles and changes in saturation temperature due to the changes in pressure generated by bubble motion. Modelling features requiring further attention were identified, such as the possibility of "roll-up" of the liquid film due to a large dynamic contact angle

### Canonical BRST Quantisation of Worldsheet Gravities

We reformulate the BRST quantisation of chiral Virasoro and $W_3$ worldsheet
gravities. Our approach follows directly the classic BRST formulation of
Yang-Mills theory in employing a derivative gauge condition instead of the
conventional conformal gauge condition, supplemented by an introduction of
momenta in order to put the ghost action back into first-order form. The
consequence of these simple changes is a considerable simplification of the
BRST formulation, the evaluation of anomalies and the expression of Wess-Zumino
consistency conditions. In particular, the transformation rules of all fields
now constitute a canonical transformation generated by the BRST operator $Q$,
and we obtain in this reformulation a new result that the anomaly in the BRST
Ward identity is obtained by application of the anomalous operator $Q^2$,
calculated using operator products, to the gauge fermion.Comment: 27 pages. (Some factors of \hbar corrected

### Black Hole Entropy from a Highly Excited Elementary String

Suggested correspondence between a black hole and a highly excited elementary
string is explored. Black hole entropy is calculated by computing the density
of states for an open excited string. We identify the square root of oscillator
number of the excited string with Rindler energy of black hole to obtain an
entropy formula which, not only agrees at the leading order with the
Bekenstein-Hawking entropy, but also reproduces the logarithmic correction
obtained for black hole entropy in the quantum geometry framework. This
provides an additional supporting evidence for correspondence between black
holes and strings.Comment: revtex, 4 page

### Dynamic correlations of the Coulomb Luttinger liquid

The dynamic density response function, form-factor, and spectral function of
a Luttinger liquid with Coulomb electron-electron interaction are studied with
the emphasis on the short-range electron correlations. The Coulomb interaction
changes dramatically the density response function as compared to the case of
the short-ranged interaction. The form of the density response function is
smoothing with time, and the oscillatory structure appears. However, the
spectral functions remain qualitatively the same. The dynamic form-factor
contains the $\delta$-peak in the long-wave region, corresponding to one-boson
excitations. Besides, the multi-boson-excitations band exists in the
wave-number region near to $2k_F$. The dynamic form-factor diverges at the
edges of this band, while the dielectric function goes to zero there, which
indicates the appearance of a soft mode. We develop a method to analyze the
asymptotics of the spectral functions near to the edges of the
multi-boson-excitations band.Comment: 11 pages, 3 figures, submitted to PR

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