42,662 research outputs found
Gravitational Wave Production At The End Of Inflation
We consider gravitational wave production due to parametric resonance at the
end of inflation, or ``preheating''. This leads to large inhomogeneities which
source a stochastic background of gravitational waves at scales inside the
comoving Hubble horizon at the end of inflation. We confirm that the present
amplitude of these gravitational waves need not depend on the inflationary
energy scale. We analyze an explicit model where the inflationary energy scale
is ~10^9 GeV, yielding a signal close to the sensitivity of Advanced LIGO and
BBO. This signal highlights the possibility of a new observational ``window''
into inflationary physics, and provides significant motivation for searches for
stochastic backgrounds of gravitational waves in the Hz to GHz range, with an
amplitude on the order of \Omega_{gw}(k)h^2 ~ 10^-11. Finally, the strategy
used in our numerical computations is applicable to the gravitational waves
generated by many inhomogeneous processes in the early universe.Comment: 4 pages, Revtex, 2 figures. v2 References added, discussion clarified
and improved. v3 further clarification, typo regarding source corrected.
Basic results unchange
A New Mechanism for Bubble Nucleation: Classical Transitions
Given a scalar field with metastable minima, bubbles nucleate quantum
mechanically. When bubbles collide, energy stored in the bubble walls is
converted into kinetic energy of the field. This kinetic energy can facilitate
the classical nucleation of new bubbles in minima that lie below those of the
"parent" bubbles. This process is efficient and classical, and changes the
dynamics and statistics of bubble formation in models with multiple vacua,
relative to that derived from quantum tunneling.Comment: 4 pages, 4 figures, animations related to figures can be found at
http://www.perimeterinstitute.ca/personal/jgiblin/BubbleMovies.htm
How to Run Through Walls: Dynamics of Bubble and Soliton Collisions
It has recently been shown in high resolution numerical simulations that
relativistic collisions of bubbles in the context of a multi-vacua potential
may lead to the creation of bubbles in a new vacuum. In this paper, we show
that scalar fields with only potential interactions behave like free fields
during high-speed collisions; the kick received by them in a collision can be
deduced simply by a linear superposition of the bubble wall profiles. This
process is equivalent to the scattering of solitons in 1+1 dimensions. We
deduce an expression for the field excursion (shortly after a collision), which
is related simply to the field difference between the parent and bubble vacua,
i.e. contrary to expectations, the excursion cannot be made arbitrarily large
by raising the collision energy. There is however a minimum energy threshold
for this excursion to be realized. We verify these predictions using a number
of 3+1 and 1+1 numerical simulations. A rich phenomenology follows from these
collision induced excursions - they provide a new mechanism for scanning the
landscape, they might end/begin inflation, and they might constitute our very
own big bang, leaving behind a potentially observable anisotropy.Comment: 15pgs, 14 figures, v2, thanks for the feedback
Association of Diethylstilbestrol Exposure and Uterine Leiomyoma in African American Women
poster abstractUterine leiomyoma, commonly called fibroids, are highly prevalent benign tumors which are leading contributors to hysterectomies. Associated symptoms include reproductive problems, pelvic pain and heavy menstrual bleeding. Fibroids have an elevated occurrence in African American women, along with increased symptom severity and earlier onset among younger age groups. It has been established that hormones influence fibroid development, and recent studies suggest that fibroid development is influenced by fetal and childhood exposures to hormones which later impact how a woman’s body responds to hormonal challenges as an adult. Early life exposure to diethylstilbestrol (DES), which is a teratogenic synthetic estrogen, has been found to cause fibroids in laboratory rodent models. The purpose of this research is to investigate how the mechanisms of DES exposure contribute to disparities in fibroid development in African American women. Coupled with the established role of inheritance in fibroid development, this project hypothesizes that there will be a strong correlation between fetal exposure to DES and the prevalence and severity of fibroids in African American women. The impact of this research will have direct relevance as it can offer insight into preventative medical care by reducing the inheritability of the disease, offer alternative treatment methods and reduce existing health disparities
Molecular Gas in the Powerful Radio Galaxies 3C~31 and 3C~264: Major or Minor Mergers?
We report the detection of CO~() and CO~()
emission from the central regions (--) of the two
powerful radio galaxies 3C~31 and 3C~264. Their individual CO emission exhibits
a double-horned line profile that is characteristic of an inclined rotating
disk with a central depression at the rising part of its rotation curve. The
inferred disk or ring distributions of the molecular gas is consistent with the
observed presence of dust disks or rings detected optically in the cores of
both galaxies. For a CO to H conversion factor similar to that of our
Galaxy, the corresponding total mass in molecular hydrogen gas is in 3C~31 and in 3C~264. Despite their relatively large molecular-gas masses
and other peculiarities, both 3C~31 and 3C~264, as well as many other powerful
radio galaxies in the (revised) 3C catalog, are known to lie within the
fundamental plane of normal elliptical galaxies. We reason that if their gas
originates from the mergers of two gas-rich disk galaxies, as has been invoked
to explain the molecular gas in other radio galaxies, then both 3C~31 and
3C~264 must have merged a long time (a few billion years or more) ago but their
remnant elliptical galaxies only recently (last tens of millions of years or
less) become active in radio. Instead, we argue that the cannibalism of
gas-rich galaxies provides a simpler explanation for the origin of molecular
gas in the elliptical hosts of radio galaxies. Given the transient nature of
their observed disturbances, these galaxies probably become active in radio
soon after the accretion event when sufficient molecular gas agglomerates in
their nuclei.Comment: 16 pages, 1 JPEG figure attached, accepted for publication in ApJ
High On/Off Ratio Graphene Nanoconstriction Field Effect Transistor
We report a method to pattern monolayer graphene nanoconstriction field
effect transistors (NCFETs) with critical dimensions below 10 nm. NCFET
fabrication is enabled by the use of feedback controlled electromigration (FCE)
to form a constriction in a gold etch mask that is first patterned using
conventional lithographic techniques. The use of FCE allows the etch mask to be
patterned on size scales below the limit of conventional nanolithography. We
observe the opening of a confinement-induced energy gap as the NCFET width is
reduced, as evidenced by a sharp increase in the NCFET on/off ratio. The on/off
ratios we obtain with this procedure can be larger than 1000 at room
temperature for the narrowest devices; this is the first report of such large
room temperature on/off ratios for patterned graphene FETs.Comment: 18 pages, 6 figures, to appear in Smal
Discovery of Radio Emission from the Tight M8 Binary: LP 349-25
We present radio observations of 8 ultracool dwarfs with a narrow spectral
type range (M8-M9.5) using the Very Large Array at 8.5 GHz. Only the tight M8
binary LP 349-25 was detected. LP 349-25 is the tenth ultracool dwarf system
detected in radio and its trigonometric parallax pi = 67.6 mas, recently
measured by Gatewood et al., makes it the furthest ultracool system detected by
the Very Large Array to date, and the most radio-luminous outside of obvious
flaring activity or variability. With a separation of only 1.8 AU, masses of
the components of LP 349-25 can be measured precisely without any theoretical
assumptions (Forveille et al.), allowing us to clarify their fully-convective
status and hence the kind of magnetic dynamo in these components which may play
an important role to explain our detection of radio emission from these
objects. This also makes LP 349-25 an excellent target for further studies with
better constraints on the correlations between X-ray, radio emission and
stellar parameters such as mass, age, temperature, and luminosity in ultracool
dwarfs.Comment: accepted by ApJ, referee's comments included, typo in equation 1
correcte
Primary care summary of the British Thoracic Society Guidelines for the management of community acquired pneumonia in adults:2009 update. Endorsed by the Royal College of General Practitioners and the Primary Care Respiratory Society UK
- …