497 research outputs found
Effect of Optical Coating and Surface Treatments on Mechanical Loss in Fused Silica
We report on the mechanical loss in fused silica samples with various surface
treatments and compare them with samples having an optical coating. Mild
surface treatments such as washing in detergent or acetone were not found to
affect the mechanical loss of flame-drawn fused silica fibers stored in air.
However, mechanical contact (with steel calipers) significantly increased the
loss. The application of a high-reflective optical coating of the type used for
the LIGO test masses was found to greatly increase the mechanical loss of
commercially polished fused silica microscope slides. We discuss the
implications for the noise budget of interferometers.Comment: 7 pages, 2 figures. Accepted for publication in the Proceedings of
the Third Eduardo Amaldi Conference on Gravitational Waves, July 12-16, 1999.
Updated version contains a correction of Eq. 3 and an estimate for the loss
angle of a LIGO coating. (Neither of these revisions are included in the
version published in the conference proceedings.
Theory of a magnetic microscope with nanometer resolution
We propose a theory for a type of apertureless scanning near field microscopy
that is intended to allow the measurement of magnetism on a nanometer length
scale. A scanning probe, for example a scanning tunneling microscope (STM) tip,
is used to scan a magnetic substrate while a laser is focused on it. The
electric field between the tip and substrate is enhanced in such a way that the
circular polarization due to the Kerr effect, which is normally of order 0.1%
is increased by up to two orders of magnitude for the case of a Ag or W tip and
an Fe sample. Apart from this there is a large background of circular
polarization which is non-magnetic in origin. This circular polarization is
produced by light scattered from the STM tip and substrate. A detailed retarded
calculation for this light-in-light-out experiment is presented.Comment: 17 pages, 8 figure
Improved microarray gene expression profiling of virus-infected cells after removal of viral RNA
<p>Abstract</p> <p>Background</p> <p>Sensitivity and accuracy are key points when using microarrays to detect alterations in gene expression under different conditions. Critical to the acquisition of reliable results is the preparation of the RNA. In the field of virology, when analyzing the host cell's reaction to infection, the often high representation of viral RNA (vRNA) within total RNA preparations from infected cells is likely to interfere with microarray analysis. Yet, this effect has not been investigated despite the many reports that describe gene expression profiling of virus-infected cells using microarrays.</p> <p>Results</p> <p>In this study we used coronaviruses as a model to show that vRNA indeed interferes with microarray analysis, decreasing both sensitivity and accuracy. We also demonstrate that the removal of vRNA from total RNA samples, by means of virus-specific oligonucleotide capturing, significantly reduced the number of false-positive hits and increased the sensitivity of the method as tested on different array platforms.</p> <p>Conclusion</p> <p>We therefore recommend the specific removal of vRNA, or of any other abundant 'contaminating' RNAs, from total RNA samples to improve the quality and reliability of microarray analyses.</p
Pendulum Mode Thermal Noise in Advanced Interferometers: A comparison of Fused Silica Fibers and Ribbons in the Presence of Surface Loss
The use of fused-silica ribbons as suspensions in gravitational wave
interferometers can result in significant improvements in pendulum mode thermal
noise. Surface loss sets a lower bound to the level of noise achievable, at
what level depends on the dissipation depth and other physical parameters. For
LIGO II, the high breaking strength of pristine fused silica filaments, the
correct choice of ribbon aspect ratio (to minimize thermoelastic damping), and
low dissipation depth combined with the other achievable parameters can reduce
the pendulum mode thermal noise in a ribbon suspension well below the radiation
pressure noise. Despite producing higher levels of pendulum mode thermal noise,
cylindrical fiber suspensions provide an acceptable alternative for LIGO II,
should unforeseen problems with ribbon suspensions arise.Comment: Submitted to Physics Letters A (Dec. 14, 1999). Resubmitted to
Physics Letters A (Apr. 3, 2000) after internal (LSC) review process. PACS -
04.80.Nn, 95.55.Ym, 05.40.C
On Metal-Insulator Transitions due to Self-Doping
We investigate the influence of an unoccupied band on the transport
properties of a strongly correlated electron system. For that purpose,
additional orbitals are coupled to a Hubbard model via hybridization. The
filling is one electron per site. Depending on the position of the additional
band, both, a metal--to--insulator and an insulator--to--metal transition occur
with increasing hybridization. The latter transition from a Mott insulator into
a metal via ``self--doping'' was recently proposed to explain the low carrier
concentration in . We suggest a restrictive parameter regime for
this transition making use of exact results in various limits. The predicted
absence of the self--doping transition for nested Fermi surfaces is confirmed
by means of an unrestricted Hartree--Fock approximation and an exact
diagonalization study in one dimension. In the general case metal--insulator
phase diagrams are obtained within the slave--boson mean--field and the
alloy--analog approximation.Comment: 9 pages, Revtex, 6 postscript figure
- …