6,307 research outputs found
Ability of LIGO and LISA to probe the equation of state of the early Universe
The expansion history of the Universe between the end of inflation and the
onset of radiation-domination (RD) is currently unknown. If the equation of
state during this period is stiffer than that of radiation, , the
gravitational wave (GW) background from inflation acquires a blue-tilt
at
frequencies corresponding to modes re-entering the horizon
during the stiff-domination (SD), where is the frequency today of
the horizon scale at the SD-to-RD transition. We characterized in detail the
transfer function of the GW energy density spectrum, considering both 'instant'
and smooth modelings of the SD-to-RD transition. The shape of the spectrum is
controlled by , , and (the Hubble scale of
inflation). We determined the parameter space compatible with a detection of
this signal by LIGO and LISA, including possible changes in the number of
relativistic degrees of freedom, and the presence of a tensor tilt. Consistency
with upper bounds on stochastic GW backgrounds, however, rules out a
significant fraction of the observable parameter space. We find that this
renders the signal unobservable by Advanced LIGO, in all cases. The GW
background remains detectable by LISA, though only in a small island of
parameter space, corresponding to scenarios with an equation of state in the
range and a high inflationary scale , but low reheating temperature (equivalently, ). Implications for early
Universe scenarios resting upon an SD epoch are briefly discussed.Comment: Matching published version in JCAP, 32 pages, 8 figure
Inconsistency of an inflationary sector coupled only to Einstein gravity
From a model-building perspective, the inflationary sector might very well
have no direct couplings to other species, apart from inevitable gravitational
interactions. Within the context of General Relativity, a thermal universe can
still emerge after inflation if: some radiation sector is excited towards
the end of inflation, and the post-inflationary equation of state becomes
sufficiently stiff , with a
threshold depending on the inflationary scale and the initial
radiation-to-inflaton energy ratio . Furthermore, a stiff period in
the expansion history enhances significantly the inflationary gravitational
wave (GW) background, making this signal (potentially) observable by aLIGO,
LISA and other experiments. The very same enhancement leads however to an
inconsistency of the scenario: the energy of the GWs becomes too large compared
to the rest of the radiation sector, violating standard BBN and CMB bounds on
GW backgrounds. Except for very special scenarios where the initial radiation
sector comprises hundreds of fields with couplings tuned to specific values,
our result applies independently of , and . This suggests
that in order to reheat the universe, the inflationary sector should be coupled
directly to other particle species. Alternatively the inflationary sector could
be implemented in modified gravity theories.Comment: Comments added to match published version in JCAP, 22 pages (+
appendix + references), 4 figure
Braze alloys for high temperature service
Two groups of refractory metal compositions have been developed that are very useful as high temperature brazing alloys for sealing between ceramic and metal parts. Each group consists of various compositions of three selected refractory metals which, when combined, have characteristics required of good braze alloys
Detection of HIV-1 infection in dried blood spots from a 12-year-old ABO bedside test card
Background and Objectives: We tested dried blood from an ABO bedside test card which had been stored at room temperature for 12 years, to prove that a patient with HIV-1 infection had been infected by blood transfusion. Materials and Methods: Immunoblots for HIV-1 antibodies and threefold PCRs with half-nested primers for the HIV-1 integrase gene were done with eluates from the dried blood spots. Results: HIV-1 antibodies and HIV-1 DNA could be detected in the sample from one unit of blood, but not from the two other units or from the recipient before transfusion. Conclusion: Further studies should be done on the validity of stored dried blood as an alternative to the storage of frozen donor serum for several years for `look-back' studies
Clearing The Air: Deconstructing The Myths And Misconceptions About Buying Broadcast Stations
Desain Pembuatan dan Uji Coba Kumparan Helmholtz Berbentuk Lingkaran
Design and study of Helmholtz coils have been carried out. The coils diameter was designed of about 13 cm and number of turns of 50, 100, 150, 200 and 250. Magnetic field that produced by those coils was measured using pasco magnetic probe PS-2162 as a function of an applied current, distances and number of turns. As comparison, then the magnetic field produced by these coils had been compared to the standard one. Maximum value of magnetic field was obtained at the center of the coil. For an applied current of 2 A, then the magnetic field at the center of the coils either standard one or the designed one was 7.156 x 10-5T and 5.907 x 10-5T respectively. The value of magnetic field increases as number of turns and current are increased, for the coils with number of turns of 50 and 250 that carrying current of 1.0 A produced a magnetic field of 5.241 x 10-5T and 6.208 x 10-5T respectively. This is due to the direct relationship between current (I) and number of turns (N) against magnetic field as expected. The value of magnetic field decreases as moving away from the center of coil either in horizontal or vertical direction
Shear dispersion along circular pipes is affected by bends, but the torsion of the pipe is negligible
The flow of a viscous fluid along a curving pipe of fixed radius is driven by
a pressure gradient. For a generally curving pipe it is the fluid flux which is
constant along the pipe and so I correct fluid flow solutions of Dean (1928)
and Topakoglu (1967) which assume constant pressure gradient. When the pipe is
straight, the fluid adopts the parabolic velocity profile of Poiseuille flow;
the spread of any contaminant along the pipe is then described by the shear
dispersion model of Taylor (1954) and its refinements by Mercer, Watt et al
(1994,1996). However, two conflicting effects occur in a generally curving
pipe: viscosity skews the velocity profile which enhances the shear dispersion;
whereas in faster flow centrifugal effects establish secondary flows that
reduce the shear dispersion. The two opposing effects cancel at a Reynolds
number of about 15. Interestingly, the torsion of the pipe seems to have very
little effect upon the flow or the dispersion, the curvature is by far the
dominant influence. Lastly, curvature and torsion in the fluid flow
significantly enhance the upstream tails of concentration profiles in
qualitative agreement with observations of dispersion in river flow
- …