7079909
Convergent Evolution of a New Arsenic Binding Site in the ArsR/SmtB Family of Metalloregulators*
Acidithiobacillus ferrooxidans has an arsenic resistance operon that is controlled by an As(III)-responsive transcriptional repressor, AfArsR, a member of the ArsR/SmtB family of metalloregulators. AfArsR lacks the As(III) binding site of the ArsRs from plasmid R773 and Escherichia coli, which have a Cys32-Val-Cys34-Asp-Leu-Cys37 sequence in the DNA binding site. In contrast, it has three cysteine residues, Cys95, Cys96, and Cys102, that are not present in the R773 and E. coli ArsRs. The results of direct As(III) binding measurements and x-ray absorption spectroscopy show that these three cysteine residues form a 3-coordinate As(III) binding site. DNA binding studies indicate that binding of As(III) to these cysteine residues produces derepression. Homology modeling indicates that As(III) binding sites in AfArsR are located at the ends of antiparallel C-terminal helices in each monomer that form a dimerization domain. These results suggest that the As(III)-S3 binding sites in AfArsR and R773 ArsR arose independently at spatially distinct locations in their three-dimensional structures.
119207145
Mid-Infrared Frequency Comb Fourier Transform Spectrometer
Optical frequency-comb-based-high-resolution spectrometers offer enormous potential for spectroscopic applications. Although various implementations have been demonstrated, the lack of suitable mid-infrared comb sources has impeded explorations of molecular fingerprinting. Here we present for the first time a frequency-comb Fourier transform spectrometer operating in the 2100-to-3700-cm-1 spectral region that allows fast and simultaneous acquisitions of broadband absorption spectra with up to 0.0056 cm-1 resolution. We demonstrate part-per-billion detection limits in 30 seconds of integration time for various important molecules including methane, ethane, isoprene, and nitrous oxide. Our system enables precise concentration measurements even in gas mixtures that exhibit continuous absorption bands, and it allows detection of molecules at levels below the noise floor via simultaneous analysis of multiple spectral features. This system represents a near real-time, high-resolution, high-bandwidth mid-infrared spectrometer which is ready to replace traditional Fourier transform spectrometers for many applications in trace gas detection, atmospheric science, and medical diagnostics.
2486417
Precision test of mass-ratio variations with lattice-confined ultracold molecules.
We propose a precision measurement of time variations of the proton-electron mass ratio using ultracold molecules in an optical lattice. Vibrational energy intervals are sensitive to changes of the mass ratio. In contrast to measurements that use hyperfine-interval-based atomic clocks, the scheme discussed here is model independent and does not require separation of time variations of different physical constants. The possibility of applying the zero-differential-Stark-shift optical lattice technique is explored to measure vibrational transitions at high accuracy.
20964607
Human breath analysis via cavity-enhanced optical frequency comb spectroscopy
To date, researchers have identified over 1000 different compounds contained in human breath. These molecules have both endogenous and exogenous origins and provide information about physiological processes occurring in the body as well as environment-related ingestion or absorption of contaminants1,2. While the presence and concentration of many of these molecules are poorly understood, many 'biomarker' molecules have been correlated to specific diseases and metabolic processes. Such correlations can result in non-invasive methods of health screening for a wide variety of medical conditions. In this article we present human breath analysis using an optical-frequency-comb-based trace detection system with excellent performance in all criteria: detection sensitivity, ability to identify and distinguish a large number of biomarkers, and measurement time. We demonstrate a minimum detectable absorption of 8 x 10-10 cm-1, a spectral resolution of 800 MHz, and 200 nm of spectral coverage from 1.5 to 1.7 micron where strong and unique molecular fingerprints exist for many biomarkers. We present a series of breath measurements including stable isotope ratios of CO2, breath concentrations of CO, and the presence of trace concentrations of NH3 in high concentrations of H2O.
31462099
Precision stabilization of femtosecond lasers to high-finesse optical cavities
We report on direct stabilization of a femtosecond laser by a high-finesse passive optical cavity. Detailed comparison of two distinct stabilization schemes leads to new understanding of the optimum conditions for cavity stabilization and limitations on the ability to transfer the frequency stability of the cavity to the microwave domain. The stability of the frequency comb is explored in both the optical and the radio frequency domain. With an independent, stable cw laser, we verify that the linewidth and stability of the optical comb components, respectively, reach below 300 Hz and 53 10 ˛14 at 1 s averaging time, both limited by the
2120691
Optical interferometers with reduced sensitivity to thermal noise
Thermal phase noise in optical interferometry can be compensated by exploiting coherence for underlying stochastic displacements and strains. The phase upon reflection from a fluctuating mirror's surface can thereby have reduced sensitivity to thermal noise.
33025887
Lifetime Test for Optical Transmitters in the ATLAS Liquid Argon Calorimeter Readout System 1
Accelerated lifetime test has been carried out for 147 days on the custom-made optical transmitters used in the ATLAS Liquid Argon Calorimeter front-end electronics readout system. The lifetime of these optical transmitters is estimated to be greater than 200 years and exceeds the design goal for the LHC. The random failure rate has been estimated at 9.6×10 -7 per hour at 90% confidence level.
18930090
Installation and Commissioning of the ATLAS LAr Readout Electronics
The Liquid Argon Calorimeter (LAr) is a subsystem in the ATLAS experiment which is being assembled at the Large Hadron Collider (LHC) at CERN. The readout electronics system for the LAr is discussed here. The front‐end of the readout will work in radiation environment. This special requirement has led to the development of a large number of rad‐hard ASICs. The back‐end of the readout employs DSPs to process data to reduce transmission bandwidth. The installation and commissioning of this readout is also discussed here.
111270365
The miniature optical transmitter and transceiver for the High-Luminosity LHC (HL-LHC) experiments
We present the design and test results of the Miniature optical Transmitter (MTx) and Transceiver (MTRx) for the high luminosity LHC (HL-LHC) experiments. MTx and MTRx are Transmitter Optical Subassembly (TOSA) and Receiver Optical Subassembly (ROSA) based. There are two major developments: the Vertical Cavity Surface Emitting Laser (VCSEL) driver ASIC LOCld and the mechanical latch that provides the connection to fibers. In this paper, we concentrate on the justification of this work, the design of the latch and the test results of these two modules with a Commercial Off-The-Shelf (COTS) VCSEL driver.
121333267
Single-event upset studies of a high-speed digital optical data link
The results from a series of neutron and photon irradiation tests of a high-speed digital optical data link based on a commercial serialiser and a vertical cavity surface emitting laser are described. The link was developed as a candidate for the front-end readout of the ATLAS electromagnetic calorimeter. The components at the emitting end of the link were unaffected by neutron and photon irradiation levels exceeding those expected during 10 years of LHC running. However, the link suffered from Single-Event Upsets (SEUs) when irradiated with energetic neutrons. A very general method based on the Burst Generation Rate (BGR) model has been developed and is used to extrapolate the error rate observed during tests to that expected at the LHC. A model-independent extrapolation was used to check the BGR approach and the results were consistent once systematic errors were taken into account.
17176468
Status report on the LOC ASIC
Based on a commercially available 0.25 μm Silicon on Sapphire CMOS technology, we are developing the LOC ASIC for high speed serial data transmission in the front-end electronics systems of the ATLAS upgrade for the SLHC 1 . Evaluation of this technology for applications in the SLHC, based on a dedicated test chip, has been performed with irradiation tests in gamma (Co-60) and in 230 MeV proton beams. Test results indicate that this may be a candidate technology of ASIC developments for the SLHC. More thorough evaluation tests will be carried out under another R&D program supported through the Advanced Detector Research (ADR) from the Department of Energy. Characterization tests on the first prototype serializer, LOC1, have been carried out in lab. Based on the lessons learned from this chip, we propose a new architecture design of the second prototype, LOC2, aiming for a serial data rate in the range of 5 Gbps. Simulation on key components of LOC2 are being carried out and the results we have so far are presented in this note. LOC2 is scheduled to be submitted for fabrication in the first half of 2009.