482 research outputs found
Detecting very-high-frequency relic gravitational waves by electromagnetic wave polarizations in a waveguide
The polarization vector (PV) of an electromagnetic wave (EW) will experience
a rotation in a region of spacetime perturbed by gravitational waves (GWs).
Based on this idea, Cruise's group has built an annular waveguide to detect
GWs. We give detailed calculations of the rotations of the polarization vector
of an EW caused by incident GWs from various directions and in various
polarization states, and then analyze the accumulative effects on the
polarization vector when the EW passes n cycles along the annular waveguide. We
reexamine the feasibility and limitation of this method to detect GWs of high
frequency around 100 MHz, in particular, the relic gravitational waves (RGWs).
By comparing the spectrum of RGWs in the accelerating universe with the
detector sensitivity of the current waveguide, it is found that the amplitude
of the RGWs is too low to be detected by the waveguide detectors currently
running. Possible ways of improvements on detection are discussed also.Comment: 18pages, 10 figures, accepted by ChJA
Construction and testing of the optical bench for LISA pathfinder
eLISA is a space mission designed to measure gravitational radiation over a frequency range of 0.1–100 mHz (European Space Agency LISA Assessment Study Report 2011). It uses laser interferometry to measure changes of order in the separation of inertial test masses housed in spacecraft separated by 1 million km. LISA Pathfinder (LPF) is a technology demonstrator mission that will test the key eLISA technologies of inertial test masses monitored by laser interferometry in a drag-free spacecraft. The optical bench that provides the interferometry for LPF must meet a number of stringent requirements: the optical path must be stable at the few level; it must direct the optical beams onto the inertial masses with an accuracy of better than ±25 μm, and it must be robust enough not only to survive launch vibrations but to achieve full performance after launch. In this paper we describe the construction and testing of the flight optical bench for LISA Pathfinder that meets all the design requirements
Solution of Three-Constraint Entropy-Based Velocity Distribution
A two-dimensional velocity profile based upon the principle of maximum entropy (POME) for wide open channel flows is presented. The derivation is based on the conservation of mass and momentum. The resulting profile involves three parameters that are determined from observations of mean velocity and the velocity at the water surface. The velocity profile is verified using field data in a river with a live bed. A comparison with three existing methods shows that the profile presented is the most accurate of the three, especially near the bed
Revisit relic gravitational waves based on the latest CMB observations
According to the CMB observations, Mielczarek (\cite{Mielczarek}) evaluated
the reheating temperature, which could help to determine the history of the
Universe. In this paper, we recalculate the reheating temperature using the new
data from WMAP 7 observations. Based on that, we list the approximate solutions
of relic gravitational waves (RGWs) for various frequency bands. With the
combination of the quantum normalization of RGWs when they are produced and the
CMB observations, we obtain the relation between the tensor-to-scalar ratio
and the inflation index for a given scalar spectral index . As a
comparison, the diagram in the slow-roll inflation model is also
given. Thus, the observational limits of from CMB lead to the constraints
on the value of . Then, we illustrate the energy density spectrum of
RGWs with the quantum normalization for different values of and the
corresponding . For comparison, the energy density spectra of RGWs with
parameters based on slow-roll inflation are also discussed. We find that the
values of affect the spectra of RGWs sensitively in the very high
frequencies. Based on the current and planed gravitational wave detectors, we
discuss the detectabilities of RGWs.Comment: 16 pages, 6 figures, accepted for publication in Class. Quantum Gra
Thermal history of the plasma and high-frequency gravitons
Possible deviations from a radiation-dominated evolution, occurring prior the
synthesis of light nuclei, impacted on the spectral energy density of
high-frequency gravitons. For a systematic scrutiny of this situation, the
CDM paradigm must be complemented by (at least two) physical
parameters describing, respectively, a threshold frequency and a slope. The
supplementary frequency scale sets the lower border of a high-frequency domain
where the spectral energy grows with a slope which depends, predominantly, upon
the total sound speed of the plasma right after inflation. While the infra-red
region of the graviton energy spectrum is nearly scale-invariant, the expected
signals for typical frequencies larger than 0.01 nHz are hereby analyzed in a
model-independent framework by requiring that the total sound speed of the
post-inflationary plasma be smaller than the speed of light. Current (e.g.
low-frequency) upper limits on the tensor power spectra (determined from the
combined analysis of the three large-scale data sets) are shown to be
compatible with a detectable signal in the frequency range of wide-band
interferometers. In the present context, the scrutiny of the early evolution of
the sound speed of the plasma can then be mapped onto a reliable strategy of
parameter extraction including not only the well established cosmological
observables but also the forthcoming data from wide band interferometers.Comment: 47 pages, 31 included figures, to appear in Classical and Quantum
Gravit
Spacelab Science Results Study
Beginning with OSTA-1 in November 1981 and ending with Neurolab in March 1998, a total of 36 Shuttle missions carried various Spacelab components such as the Spacelab module, pallet, instrument pointing system, or mission peculiar experiment support structure. The experiments carried out during these flights included astrophysics, solar physics, plasma physics, atmospheric science, Earth observations, and a wide range of microgravity experiments in life sciences, biotechnology, materials science, and fluid physics which includes combustion and critical point phenomena. In all, some 764 experiments were conducted by investigators from the U.S., Europe, and Japan. The purpose of this Spacelab Science Results Study is to document the contributions made in each of the major research areas by giving a brief synopsis of the more significant experiments and an extensive list of the publications that were produced. We have also endeavored to show how these results impacted the existing body of knowledge, where they have spawned new fields, and if appropriate, where the knowledge they produced has been applied
Optimal Location of Two Laser-interferometric Detectors for Gravitational Wave Backgrounds at 100 MHz
Recently, observational searches for gravitational wave background (GWB) have
been developed and given constraints on the energy density of GWB in a broad
range of frequencies. These constraints have already resulted in the rejection
of some theoretical models of relatively large GWB spectra. However, at 100
MHz, there is no strict upper limit from direct observation, though an indirect
limit exists due to He4 abundance due to big-bang nucleosynthesis. In our
previous paper, we investigated the detector designs that can effectively
respond to GW at high frequencies, where the wavelength of GW is comparable to
the size of a detector, and found that the configuration, a so-called
synchronous-recycling interferometer is best at these sensitivity. In this
paper, we investigated the optimal location of two synchronous-recycling
interferometers and derived their cross-correlation sensitivity to GWB. We
found that the sensitivity is nearly optimized and hardly changed if two
coaligned detectors are located within a range 0.2 m, and that the sensitivity
achievable in an experiment is far below compared with the constraint
previously obtained in experiments.Comment: 17 pages, 6 figure
Development of soil moisture profiles through coupled microwave–thermal infrared observations in the southeastern United States
The principle of maximum entropy (POME) can be used to develop
vertical soil moisture (SM) profiles. The minimal inputs required by the POME
model make it an excellent choice for remote sensing applications. Two of the
major input requirements of the POME model are the surface boundary condition
and profile-mean moisture content. Microwave-based SM estimates from the Advanced
Microwave Scanning Radiometer (AMSR-E) can supply the surface boundary
condition whereas thermal infrared-based moisture estimated from the
Atmospheric Land EXchange Inverse (ALEXI) surface energy balance model can
provide the mean moisture condition. A disaggregation approach was followed
to downscale coarse-resolution ( ∼ 25 km) microwave SM estimates to match
the finer resolution ( ∼ 5 km) thermal data. The study was conducted over
multiple years (2006–2010) in the southeastern US. Disaggregated soil
moisture estimates along with the developed profiles were compared with the
Noah land surface model (LSM), as well as in situ measurements from 10
Natural Resource Conservation Services (NRCS) Soil Climate Analysis Network
(SCAN) sites spatially distributed within the study region. The overall
disaggregation results at the SCAN sites indicated that in most cases
disaggregation improved the temporal correlations with unbiased root mean
square differences (ubRMSD) in the range of 0.01–0.09 m3 m−3. The
profile results at SCAN sites showed a mean bias of 0.03 and 0.05
(m3 m−3); ubRMSD of 0.05 and 0.06 (m3 m−3); and correlation
coefficient of 0.44 and 0.48 against SCAN observations and Noah LSM,
respectively. Correlations were generally highest in agricultural areas where
values in the 0.6–0.7 range were achieved.</p
The relation between school leadership from a distributed perspective and teachers' organizational commitment: examining the source of the leadership function
Purpose: In this study the relationship between school leadership and teachers’ organizational commitment is examined by taking into account a distributed leadership perspective. The relation between teachers’ organizational commitment and contextual variables of teachers’ perceptions of the quality and the source of the supportive and supervisory leadership function, participative decision making, and cooperation within the leadership team are examined. Research Design: A survey was set up involving 1,522 teachers from 46 large secondary schools in Flanders (Belgium). Because the data in the present study have an inherent hierarchical structure, that is, teachers are nested into schools, hierarchical linear modeling techniques are applied. Findings: The analyses reveal that 9% of the variance in teachers’ organizational commitment is attributable to differences between schools. Teachers’ organizational commitment is mainly related to quality of the supportive leadership, cooperation within the leadership team, and participative decision making. Who performed the supportive leadership function plays only a marginally significant positive role. The quality of the supervisory leadership function and the role of the leadership team members in this function were not significantly related to teachers’ organizational commitment. Conclusions: The implications of the findings are that to promote teachers’ organizational commitment teachers should feel supported by their leadership team and that this leadership team should be characterized by group cohesion, role clarity, and goal orientedness. Recommendations for further research are provided
Gravitational wave detection using electromagnetic modes in a resonance cavity
We present a proposal for a gravitational wave detector, based on the
excitation of an electromagnetic mode in a resonance cavity. The mode is
excited due to the interaction between a large amplitude electromagnetic mode
and a quasi-monochromatic gravitational wave. The minimum metric perturbation
needed for detection is estimated to the order 7.10^(-23) using current data on
superconducting niobium cavities. Using this value together with different
standard models predicting the occurrence of merging neutron star or black hole
binaries, the corresponding detection rate is estimated to 1-20 events per
year, with a `table top' cavity of a few meters length.Comment: 8 pages, 1 figure, references adde
- …