9,054 research outputs found
Sugar additives for MALDI matrices improve signal allowing the smallest nucleotide change (A:T) in a DNA sequence to be resolved
Sample preparation for matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS) of DNA is critical for obtaining high quality mass spectra. Sample impurity, solvent content, substrate surface and environmental conditions (temperature and humidity) all affect the rate of matrix–analyte co-crystallization. As a result, laser fluence threshold for desorption/ionization varies from spot to spot. When using 3-hydroxypicolinic acid (3-HPA) as the matrix, laser fluence higher than the threshold value reduces mass resolution in time-of-flight (TOF) MS as the excess energy transferred to DNA causes metastable decay. This can be overcome by either searching for ‘hot’ spots or adjusting the laser fluence. However, both solutions may require a significant amount of operator manipulation and are not ideal for automatic measurements. We have added various sugars for crystallization with the matrix to minimize the transfer of excess laser energy to DNA molecules. Fructose and fucose were found to be the most effective matrix additives. Using these additives, mass resolution for DNA molecules does not show noticeable deterioration as laser energy increases. Improved sample preparation is important for the detection of single nucleotide polymorphisms (SNPs) using primer extension with a single nucleotide. During automatic data acquisition it is difficult to routinely detect heterozygous A/T mutations, which requires resolving a mass difference of 9 Da, unless a sugar is added during crystallization
Combination of common mtDNA variants results in mitochondrial dysfunction and a connective tissue dysregulation
Mitochondrial dysfunction can be associated with a range of clinical manifestations. Here, we report a family with a complex phenotype including combinations of connective tissue, neurological, and metabolic symptoms that were passed on to all surviving children. Analysis of the maternally inherited mtDNA revealed a novel genotype encompassing the haplogroup J - defining mitochondrial DNA (mtDNA
SnapShot: Histone Modifications
Histone proteins are decorated by a variety of protein posttranslational modifications called histone marks that modulate chromatin structure and function, contributing to the cellular gene expression program. This SnapShot summarizes the reported human, mouse, and rat histone marks, including recently identified lysine acylation marks
Chandra and Hubble Study of a New Transient X-ray Source in M31
We present X-ray and optical observations of a new transient X-ray source in
M31 first detected 23-May-2004 at R.A.=00:43:09.940 +/- 0.65'',
Dec.=41:23:32.49 +/- 0.66''. The X-ray lightcurve shows two peaks separated by
several months, reminiscent of many Galactic X-ray novae. The location and
X-ray spectrum of the source suggest it is a low mass X-ray binary (LMXB).
Follow-up HST ACS observations of the location both during and after the
outburst provide a high-confidence detection of variability for one star within
the X-ray position error ellipse. This star has B ~ 1 mag, and there is
only a ~1% chance of finding such a variable in the error ellipse. We consider
this star a good candidate for the optical counterpart of the X-ray source. The
luminosity of this candidate provides a prediction for the orbital period of
the system of 2.3 days.Comment: 17 pages, 3 figures, 4 tables, accepted for publication in Ap
Variable Star Candidates in an ACS Field of M31
A search for variable stars is performed using two epochs of Hubble Space
Telescope (HST) Advanced Camera for Surveys (ACS) imaging data for a 9.28
square arcminute portion of M31. This data set reveals 254 sources that vary by
at least 4-sigma between epochs. The positions and 2-epoch B-band (equivalent)
photometry of these sources are presented. The photometry suggests that this
catalog includes most of the RR Lyrae population of this portion of M31.Comment: 22 pages, 3 tables, 5 figures, accepted for publication in A
Optical Constraints on an X-ray Transient Source in M31
We have detected a transient X-ray source in the M31 bulge through a
continuing monitoring campaign with the Chandra ACIS-I camera. The source was
detected at R.A.=00:42:33.428 +/- 0.11'', Dec.=+41:17:03.37 +/- 0.11'' in only
a single observation taken 2004 May 23. Fortuitous optical HST/ACS imaging of
the transient location prior to the X-ray outburst, along with follow-up
HST/ACS imaging during and after the outburst, reveals no transient optical
source brighter than B (equivalent) = 25.5. The location of the source and its
X-ray properties suggest it is a low mass X-ray binary (LMXB). Assuming the
transient is similar to many Galactic X-ray novae, the X-ray luminosity of (3.9
+/- 0.5) X 10 erg s and the upper-limit on the optical luminosity
provide a prediction of <1.6 days for the orbital period of the binary system.Comment: 15 pages, 3 figures, accepted for publication in Ap
Computational Fluid Dynamics (CFD) Analyses in Support of Space Shuttle Main Engine (SSME) Heat Exchanger (HX) Vane Cracking Investigation
Integration issues involved with installing the alternate turbopump (ATP) High Pressure Oxygen Turbopump (HPOTP) into the SSME have raised questions regarding the flow in the HPOTP turnaround duct (TAD). Steady-state Navier-Stokes CFD analyses have been performed by NASA and Pratt & Whitney (P&W) to address these questions. The analyses have consisted of two-dimensional axisymmetric calculations done at Marshall Space Flight Center and three-dimensional calculations performed at P&W. These analyses have identified flowfield differences between the baseline ATP and the Rocketdyne configurations. The results show that the baseline ATP configuration represents a more severe environment to the inner HX guide vane. This vane has limited life when tested in conjunction with the ATP but infinite life when tested with the current SSME HPOTP. The CFD results have helped interpret test results and have been used to assess proposed redesigns. This paper includes details of the axisymmetric model, its results, and its contribution towards resolving the problem
A Soft X-ray Transient in the M31 Bulge
We have examined a probable soft X-ray transient source in the M31 bulge at
R.A.=0:42:41.814 +/- 0.08", Dec. = 41:16:35.86 +/- 0.07". On the three
occasions we observed the source, its spectrum was soft (kT_{in} ~1 keV). The
brightest detection of the source was 2004 July 17 with a 0.3-7 keV luminosity
of ~5 X 10^{37} erg/s. The only previous detection of the source was in 1979 by
the Einstein observatory. The multiple detections over 25 years suggest the
duty cycle of the source is in the range 0.02-0.06. Coordinated HST/ACS imaging
before, during, and after the outburst revealed no variable optical source
within the position errors of the X-ray source. The optical data place a firm
upper limit on the brightness of the counterpart of the X-ray outburst of
B>24.7, suggesting the binary has a period <5.2 days. The X-ray spectrum and
lack of bright stars at the source location indicate the source was a soft
transient event occurring in a low-mass X-ray binary, making this source a good
black hole candidate in M31.Comment: 18 pages, 4 tables, 3 figures, accepted for publication in Ap
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