Frequency multiplexed superconducting quantum interference device readout of large bolometer arrays for cosmic microwave background measurements

A technological milestone for experiments employing transition edge sensor bolometers operating at sub-Kelvin temperature is the deployment of detector arrays with 100s-1000s of bolometers. One key technology for such arrays is readout multiplexing: the ability to read out many sensors simultaneously on the same set of wires. This paper describes a frequency-domain multiplexed readout system which has been developed for and deployed on the APEX-SZ and South Pole Telescope millimeter wavelength receivers. In this system, the detector array is divided into modules of seven detectors, and each bolometer within the module is biased with a unique ～MHz sinusoidal carrier such that the individual bolometer signals are well separated in frequency space. The currents from all bolometers in a module are summed together and pre-amplified with superconducting quantum interference devices operating at 4 K. Room temperature electronics demodulate the carriers to recover the bolometer signals, which are digitized separately and stored to disk. This readout system contributes little noise relative to the detectors themselves, is remarkably insensitive to unwanted microphonic excitations, and provides a technology pathway to multiplexing larger numbers of sensors.     

Chemical kinetic study of a novel lignocellulosic biofuel: Di-n-butyl ether oxidation in a laminar flow reactor and flames

The combustion characteristics of promising alternative fuels have been studied extensively in the recent years. Nevertheless, the pyrolysis and oxidation kinetics for many oxygenated fuels are not well characterized compared to those of hydrocarbons. In the present investigation, the first chemical kinetic study of a long-chain linear symmetric ether, di-n-butyl ether (DBE), is presented and a detailed reaction model is developed. DBE has been identified recently as a candidate biofuel produced from lignocellulosic biomass. The model includes both high temperature and low temperature reaction pathways with reaction rates generated using appropriate rate rules. In addition, experimental studies on fundamental combustion characteristics, such as ignition delay times and laminar flame speeds have been performed. A laminar flow reactor was used to determine the ignition delay times of lean and stoichiometric DBE/air mixtures. The laminar flame speeds of DBE/air mixtures were measured in the stagnation flame configuration for a wide rage of equivalence ratios at atmospheric pressure and an unburned reactant temperature of 373 K. All experimental data were modeled using the present kinetic model. The agreement between measured and computed results is satisfactory, and the model was used to elucidate the oxidation pathways of DBE. The dissociation of keto-hydroperoxides, leading to radical chain branching was found to dominate the ignition of DBE in the low temperature regime. The results of the present numerical and experimental study of the oxidation of di-n-butyl ether provide a good basis for further investigation of long chain linear and branched ethers.     

MAD analysis of FHIT, a putative human tumor suppressor from the HIT protein family

BACKGROUND: The fragile histidine triad (FHIT) protein is a member of the large and ubiquitous histidine triad (HIT) family of proteins. It is expressed from a gene located at a fragile site on human chromosome 3, which is commonly disrupted in association with certain cancers. On the basis of the genetic evidence, it has been postulated that the FHIT protein may function as a tumor suppressor, implying a role for the FHIT protein in carcinogenesis. The FHIT protein has dinucleoside polyphosphate hydrolase activity in vitro, thus suggesting that its role in vivo may involve the hydrolysis of a phosphoanhydride bond. The structural analysis of FHIT will identify critical residues involved in substrate binding and catalysis, and will provide insights into the in vivo function of HIT proteins. RESULTS: The three-dimensional crystal structures of free and nucleoside complexed FHIT have been determined from multiwavelength anomalous diffraction (MAD) data, and they represent some of the first successful structures to be measured with undulator radiation at the Advanced Photon Source. The structures of FHIT reveal that this protein exists as an intimate homodimer, which is based on a core structure observed previously in another human HIT homolog, protein kinase C interacting protein (PKCI), but has distinctive elaborations at both the N and C termini. Conserved residues within the HIT family, which are involved in the interactions of the proteins with nucleoside and phosphate groups, appear to be relevant for the catalytic activity of this protein. CONCLUSIONS: The structure of FHIT, a divergent HIT protein family member, in complex with a nucleotide analog suggests a metal-independent catalytic mechanism for the HIT family of proteins. A structural comparison of FHIT with PKCI and galactose-1-phosphate uridylyltransferase (GaIT) reveals additional implications for the structural and functional evolution of the ubiquitous HIT family of proteins.     

Broadband operation of InGaAsP-InGaAs GRIN-SC-MQW BH amplifiers with 115 mW output power

Broadband operation of GRIN-SC-MQW BH amplifiers is reported with 115 mW output power at 1.54 mu m and 3 dB gain compression. Gain is flat to 0.7 dB over the range 1.42-1.55 mu m. Polarisation sensitivity reduces from 4.5 dB at 1.55 mu m to 1.4 dB at 1.415 mu m.<>     

Ventilatory dynamics during transient arousal from NREM sleep: implications for respiratory control stability

The polysomnographic and ventilatory patterns of nine normal adults were measured during non-rapid-eye-movement (NREM) stage 2 sleep before and after repeated administrations of a tone (40-72 dB) lasting 5 s. The ventilatory response to arousal (VRA) was determined in data sections showing electrocortical arousal following the start of the tone. Mean inspiratory flow and tidal volume increased significantly above control levels in the first seven breaths after the start of arousal, with peak increases (64.2% > control) occurring on the second breath. Breath-to-breath occlusion pressure 100 ms after the start of inspiration showed significant increases only on the second and third postarousal breaths, whereas upper airway resistance declined immediately and remained below control for > or = 7 consecutive breaths. These results suggest that the first breath and latter portion of the VRA are determined more by upper airway dynamics than by changes in the neural drive to breathe. Computer model simulations comparing different VRA time courses show that sustained periodic apnea is more likely to occur when the fall in the postarousal increase in ventilation is more abrupt.     

Effect of glutamine on methotrexate efficacy and toxicity

OBJECTIVE: To examine the effect of oral glutamine (GLN) on the efficacy and toxicity of methotrexate (MTX). SUMMARY BACKGROUND DATA: The use of high-dose chemotherapy regimens is limited by the severity of their toxicities. Oral GLN has been shown to decrease the gut toxicity seen with MTX treatment while enhancing its tumoricidal effect. METHODS AND RESULTS: Studies were done in laboratory rats and in breast cancer outpatients. Fischer 344 rats were randomized to 48 hours of prefeeding with GLN (1 g/kg/day) or an isonitrogenous amount of glycine. Rats were killed 24 hours after receiving a 20-mg/kg intraperitoneal dose of MTX. In the GLN group, there was a threefold increase in total MTX in the tumor as compared with the control group, and this increase was in both the diglutamated and pentaglutamated MTX. Inversely, there was a significant decrease in the total polyglutamated MTX in the gut in the GLN group. Given the results of this preclinical study, the authors performed a phase I trial. Nine patients diagnosed with inflammatory breast cancer received GLN (0.5 g/kg/day) during MTX neoadjuvant therapy, escalating from doses of 40 mg/m2 to 100 mg/m2 weekly for 3 weeks, followed by a doxorubicin-based regimen. No toxicity of oral GLN was detected. No patient showed any sign of chemotherapy-related toxicity. One patient had a grade I mucositis. Except for one, all patients responded to the chemotherapy regimen. Median survival was 35 months. CONCLUSIONS: These studies suggest that GLN supplementation is safe in its administration to the tumor-bearing host receiving MTX. By preferentially increasing tumor retention of MTX over that of normal host tissue, GLN may serve to increase the therapeutic window of this chemotherapeutic age.     

New approach to the manufacture of low-threshold 1.5 ?m distributed feedback lasers

Low-threshold-current (85 mA), oxide isolated InGaAsP/InP distributed feedback (DFB) lasers operating at a wavelength of ? = 1.5 ?m have been produced for the first time using electron-beam-written DFB corrugations overgrown by MOCVD. The control and flexibility afforded by these techniques considerably ease the complexity of DFB laser manufacture.     

Monolithic 1.5 ?m hybrid DFB/DBR lasers with 5 nm tuning range

A new tunable single-longitudinal-mode laser structure is reported. This monolithic hybrid DFB/DBR laser can be electrically tuned over a 5 nm wavelength range. The tuning mechanism employs the depression in the refractive index with injected carrier density, and the tuning range is linked to the period of an internal diffraction grating.