9,848 research outputs found
Determining the Statistical Significance of Observed Frequencies of Short DNA Motifs in a Genome
Until recently over 90 percent of the DNA in the human genome was considered junk DNA, with no known function. However, this non-coding DNA is now known to harbor elements that perform important functions in gene regulation. In particular, there is currently much interest in the search for short DNA motifs collectively known as cis-regulatory elements. Most studies attempt to identify these elements by means of cross-species comparisons. We have approached the problem of finding cis-regulatory elements by searching for conserved DNA motifs within genomes. This requires searching for DNA motifs that are repeated in the genomes either more or less frequently than expected by random chance. However, the usual chi-squared test cannot be used to test for the statistical significance of any observed frequency since overlapping regions of the genome are checked for DNA motif matches. We present here a statistical measure that has been developed to quantify the expectation and variance of the frequency of a given DNA motif in a given target sequence that may contain overlapping regions
Determining the Statistical Significance of Observed Frequencies of Short DNA Motifs in a Genome
Until recently over 90 percent of the DNA in the human genome was considered junk DNA, with no known function. However, this non-coding DNA is now known to harbor elements that perform important functions in gene regulation. In particular, there is currently much interest in the search for short DNA motifs collectively known as cis-regulatory elements. Most studies attempt to identify these elements by means of cross-species comparisons. We have approached the problem of finding cis-regulatory elements by searching for conserved DNA motifs within genomes. This requires searching for DNA motifs that are repeated in the genomes either more or less frequently than expected by random chance. However, the usual chi-squared test cannot be used to test for the statistical significance of any observed frequency since overlapping regions of the genome are checked for DNA motif matches. We present here a statistical measure that has been developed to quantify the expectation and variance of the frequency of a given DNA motif in a given target sequence that may contain overlapping regions
Evidence for a New Dissipationless Regime in 2D Electronic Transport
In an ultra-clean 2D electron system (2DES) subjected to crossed
millimeterwave (30--150 GHz) and weak (B < 2 kG) magnetic fields, a series of
apparently dissipationless states emerges as the system is detuned from
cyclotron resonances. Such states are characterized by an exponentially
vanishing low-temperature longitudinal resistance and a classical Hall
resistance. The activation energies associated with such states exceeds the
Landau level spacing by an order of magnitude. Our findings are likely
indicative of a collective ground state previously unknown for 2DES.Comment: 4 pages, 2 figure
Microwave photoresistance of a high-mobility two-dimensional electron gas in a triangular antidot lattice
The microwave (MW) photoresistance has been measured on a high-mobility
two-dimensional electron gas patterned with a shallow triangular antidot
lattice, where both the MW-induced resistance oscillations (MIRO) and
magnetoplasmon (MP) resonance are observed superposing on sharp commensurate
geometrical resonance (GR). Analysis shows that the MIRO, MP, and GR are
decoupled from each other in these experiments.Comment: 5 pages, 4 figures, paper accepted by PR
Initial data for Einstein's equations with superposed gravitational waves
A method is presented to construct initial data for Einstein's equations as a
superposition of a gravitational wave perturbation on an arbitrary stationary
background spacetime. The method combines the conformal thin sandwich formalism
with linear gravitational waves, and allows detailed control over
characteristics of the superposed gravitational wave like shape, location and
propagation direction. It is furthermore fully covariant with respect to
spatial coordinate changes and allows for very large amplitude of the
gravitational wave.Comment: Version accepted by PRD; added convergence plots, expanded
discussion. 9 pages, 9 figure
An All-Cryogenic THz Transmission Spectrometer
This paper describes a THz transmission spectrometer for the spectral range
of 2-65 cm^-1 (100 GHz to 2 THz) with a spectral resolution of at least 1.8
cm^-1 (50 GHz) where the source, sample, and detector are all fully contained
in a cryogenic environment. Cyclotron emission from a two-dimensional electron
gas heated with an electrical current serves as a magnetic field tunable
source. The spectrometer is demonstrated at 4.2 K by measuring the resonant
cyclotron absorption of a second two dimensional electron gas. Unique aspects
of the spectrometer are that 1) an ultra-broadband detector is used and 2) the
emitter is run quasi-continuously with a chopping frequency of only 1 Hz. Since
optical coupling to room temperature components is not necessary, this
technique is compatible with ultra-low temperature (sub 100 mK) operation.Comment: 7 pages, 5 figures. Author affiliation and funding acknowledgements
clarifie
Current Path Properties of the Transport Anisotropy at Filling Factor 9/2
To establish the presence and orientation of the proposed striped phase in
ultra-high mobility 2D electron systems at filling factor 9/2, current path
transport properties are determined by varying the separation and allignment of
current and voltage contacts. Contacts alligned orthogonal to the proposed
intrinsic striped phase produce voltages consistent with current spreading
along the stripes; current driven along the proposed stripe direction results
in voltages consistent with channeling along the stripes. Direct comparison is
made to current spreading/channeling properties of artificially induced 1D
charge modulated systems, which indicates the 9/2 direction.Comment: 10 pages, 4 figure
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