8,176 research outputs found
Axion perturbation spectra in string cosmologies
We discuss the semi-classical perturbation spectra produced in the massless
fields of the low energy string action in a pre big bang type scenario. Axion
fields may possess an almost scale-invariant spectrum on large scales dependent
upon the evolution of the dilaton and moduli fields to which they are coupled.
As an example we calculate the spectra for three axion fields present in a
truncated type IIB model and show that they are related with at least one of
the fields having a scale-invariant or red perturbation spectrum. In the
simplest pre big bang scenario this may be inconsistent with the observed
isotropy of the microwave background. More generally, relations between the
perturbation spectra in low energy string cosmologies reflect the symmetries of
the theory.Comment: 9 pages, latex with epsf, 1 figure. Revised estimate of amplitude of
density perturbations and extended discussion of possible conflict with
isotropy of cosmic microwave background. To appear in Physics Letters
Cumulative Exams (with a twist)
When first hearing about cumulative exams, students generally have a negative reaction – their impression is that cumulative exams are more difficult because knowledge has to be retained for longer periods of time.https://digitalscholarship.unlv.edu/btp_expo/1030/thumbnail.jp
Software for Digital Acquisition System and Application to Environmental Monitoring
Criteria for selection of a minicomputer for use as a core resident acquisition system were developed for the ODU Mobile Air Pollution Laboratory. A comprehensive data acquisition program named MONARCH was instituted in a DEC-8/E-8K 12-bit computer. Up to 32 analog voltage inputs are scanned sequentially, converted to BCD, and then to actual numbers. As many as 16 external devices (valves or any other two-state device) are controlled independently. MONARCH is written as a foreground-background program, controlled by an external clock which interrupts once per minute. Transducer voltages are averaged over user specified time intervals and, upon completion of any desired time sequence, outputted are: day, hour, minute, second; state of external valves; average value of each analogue voltage (E Format); as well as standard deviations of these values. Output is compatible with any serially addressed media
How is a Closed String Loop like a Black Hole?
We demonstrate that under plausible assumptions the entropy and temperature
associated with the small oscillations on a circular loop of radius and a
black hole of mass are identical.Comment: 6 pages, uses harvma
Salt stabilizer for preventing chlorine depletion and increasing shelf-life of potable water - A concept
Proposed concept, based on law of mass action uses addition of salt to increase chlorine ions produced in sodium hydrochlorite solutions, thereby increasing solution shelf-life. This technique is not costly. Usefulness will be determined by acceptability of salt in product undergoing long shelf-life
Fluid injection device for high-pressure systems
Screw activated device, consisting of a compressor, shielded replaceable ampules, a multiple-element rubber gland, and a specially constructed fluid line fitting, injects measured amounts of fluids into a pressurized system. It is sturdy and easily manipulated
Constraining the quintessence equation of state with SnIa data and CMB peaks
Quintessence has been introduced as an alternative to the cosmological
constant scenario to account for the current acceleration of the universe. This
new dark energy component allows values of the equation of state parameter
, and in principle measurements of cosmological distances to
Type Ia supernovae can be used to distinguish between these two types of
models. Assuming a flat universe, we use the supernovae data and measurements
of the position of the acoustic peaks in the Cosmic Microwave Background (CMB)
spectra to constrain a rather general class of Quintessence potentials,
including inverse power law models and recently proposed Supergravity inspired
potentials. In particular we use a likelihood analysis, marginalizing over the
dark energy density , the physical baryon density
and the scalar spectral index , to constrain the slopes of our Quintessence
potential. Considering only the first Doppler peak the best fit in our range of
models gives . However, including the SnIa data and the three
peaks, we find an upper limit on the present value of the equation of state
parameter, at , a result that appears to
rule out a class of recently proposed potentials.Comment: Accepted for pubblication in PRD, 7 pages, 6 figures. New revised
analysi
Gravitational instantons, extra dimensions and form fields
A broad class of higher dimensional instanton solutions are found for a
theory which contains gravity, a scalar field and antisymmetric tensor fields
of arbitrary rank. The metric used, a warp product of an arbitrary number of
any compact Einstein manifolds, includes many of great interest in particle
physics and cosmology. For example 4D FRW universes with additional dimensions
compactified on a Calabi-Yau three fold, a torus, a compact hyperbolic manifold
or a sphere are all included. It is shown that the solution of this form which
dominates the Hartle Hawking path integral is always a higher dimensional
generalisation of a Hawking Turok instanton when the potential of the scalar
field is such that these instantons can exist. On continuation to Lorentzian
signature such instantons give rise to a spacetime in which all of the spatial
dimensions are of equal size and where the spatial topology is that of a
sphere. The extra dimensions are thus not hidden. In the case where the
potential for the scalar field is generated solely by a dilatonic coupling to
the form fields we find no integrable instantons at all. In particular we find
no integrable solutions of the type under consideration for the supergravity
theories which are the low energy effective field theories of superstrings.Comment: 11 pages, 4 figure
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