Near-field radiative heat transfer allows heat to propagate across a small vacuum gap in quantities that are several orders of magnitude greater then the heat transfer by far-field, blackbody radiation. Although heat transfer via near-field effects has been discussed for many years, experimental verification of this theory has been very limited. We have measured the heat transfer between two macroscopic sapphire plates, finding an increase in agreement with expectations from theory. These experiments, conducted near 300 K, have measured the heat transfer as a function of separation over mm to µm and as a function of temperature differences between 2.5 and 30 K. The experiments demonstrate that evanescence can be put to work to transfer heat from an object without actually touching it.PACS numbers: 44.40.+a,78.20.Ci Humans knew of radiative heat transfer at least as early as the discovery of fire, and physicists have investigated this process for centuries, culminating in the blackbody theory of Planck and the birth of the quantum theory. Planck's equation for black-body radiation contains only the temperature and some fundamental constants. When actual materials are involved, their emissivities enter the discussion, but little else. For example, the heat transfer per unit area between two semi-infinite planes is set by their temperatures and integrated emissivities but does not depend on their separation or other geometrical quantities. When the two planes approach each other closely the situation changes. In this near-field regime, each material interacts with exponentially decaying evanescent electromagnetic fields generated in and existing outside the other material; these fields can drive currents and generate heat. [1][2][3] This near-field radiative heat transfer can be several orders of magnitude greater than far-field blackbody radiation.Much like the Casimir and van der Waals force, nearfield heat transfer deals with fluctuations that only exist over small distances. The first in-depth theory for nearfield heat transfer between planar surfaces was derived by Polder and Van Hove,[2] building on the work of Rytov [1]. There have been several other theoretical approaches, and in general the theory seems complete, except perhaps at distances comparable to atomic dimensions. [4] Although heat transfer via near-field effects has been discussed for many years, experimental verification of the theory for heat transfer between two planar surfaces has been limited. Hargreaves[5] has presented room temperature observations for two Cr surfaces at distances as small as 1 µm. Domoto et al. [6] reported results at cryogenic temperatures but for relatively large (50 µm) separations, where near-field effects were barely observable. Neither study compared experiment to theory. A comparison at a fixed spacing has been put forward, but the plates were separated by polyethylene spacers, so the distance could not be varied. [7] There have also been several recent results using a sphere-plane geometry. [4,[7][8][9] There ...

We report on an all-sky search with the LIGO detectors for periodic gravitational waves in the frequency range 50 -1000 Hz and with the frequency's time derivative in the range ÿ1 10 ÿ8 Hz s ÿ1 to zero. Data from the fourth LIGO science run (S4) have been used in this search. Three different semicoherent methods of transforming and summing strain power from short Fourier transforms (SFTs) of the calibrated data have been used. The first, known as StackSlide, averages normalized power from each SFT. A ''weighted Hough'' scheme is also developed and used, which also allows for a multiinterferometer search. The third method, known as PowerFlux, is a variant of the StackSlide method in which the power is weighted before summing. In both the weighted Hough and PowerFlux methods, the weights are chosen according to the noise and detector antenna-pattern to maximize the signal-to-noise ratio. The respective advantages and disadvantages of these methods are discussed. Observing no evidence of periodic gravitational radiation, we report upper limits; we interpret these as limits on this radiation from isolated rotating neutron stars. The best population-based upper limit with 95% confidence on the gravitational-wave strain amplitude, found for simulated sources distributed isotropically across the sky and with isotropically distributed spin axes, is 4:28 10 ÿ24 (near 140 Hz). Strict upper limits are also obtained for small patches on the sky for best-case and worst-case inclinations of the spin axes.

We carry out two searches for periodic gravitational waves using the most sensitive few hours of data from the second LIGO science run. Both searches exploit fully coherent matched filtering and cover wide areas of parameter space, an innovation over previous analyses which requires considerable algorithm development and computational power. The first search is targeted at isolated, previously unknown neutron stars, covers the entire sky in the frequency band 160 -728.8 Hz, and assumes a frequency derivative of less than 4 10 ÿ10 Hz=s. The second search targets the accreting neutron star in the lowmass x-ray binary Scorpius X-1 and covers the frequency bands 464-484 Hz and 604-624 Hz as well as the two relevant binary orbit parameters. Because of the high computational cost of these searches we limit the analyses to the most sensitive 10 hours and 6 hours of data, respectively. Given the limited sensitivity and duration of the analyzed data set, we do not attempt deep follow-up studies. Rather we concentrate on demonstrating the data analysis method on a real data set and present our results as upper limits over large volumes of the parameter space. In order to achieve this, we look for coincidences in parameter space between the Livingston and Hanford 4-km interferometers. For isolated neutron stars our 95% confidence level upper limits on the gravitational wave strain amplitude range from 6:6 10 ÿ23 to 1 10 ÿ21 across the frequency band; for Scorpius X-1 they range from 1:7 10 ÿ22 to 1:3 10 ÿ21 across the two 20-Hz frequency bands. The upper limits presented in this paper are the first broadband wide parameter space upper limits on periodic gravitational waves from coherent search techniques. The methods developed here lay the foundations for upcoming hierarchical searches of more sensitive data which may detect astrophysical signals.

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For 17 days in August and September 2002, the LIGO and GEO interferometer gravitational wave detectors were operated in coincidence to produce their first data for scientific analysis. Although the detectors were still far from their design sensitivity levels, the data can be used to place better upper limits on the flux of gravitational waves incident on the earth than previous direct measurements. This paper describes the instruments and the data in some detail, as a companion to analysis papers based on the first data. r