Excess Heat Capacity in Mo/Au Transition Edge Sensor Bolometric Detectors.

Excess heat capacity in a bolometric detector has the consequence of increasing or leading to multiple device time constants. The Mo/Au bilayer transition edge sensor (TES) bolometric detectors initially fabricated for the high resolution mid-infrared spectrometer (HIRMES) exhibited two response thermalization scales, one of which is a few times longer than estimates based upon the properties of the bulk materials employed in the design. The relative contribution of this settling time to the overall time response of the detectors is roughly proportional to the pixel area, which ranges between ~0.3 and 2.6 mm2. Use of laser ablation to remove sections of the silicon membranes comprising the pixels results in a detector response with a smaller contribution from the secondary time constant. Additional information about the nature of this excess heat capacity is gleaned from glancing incidence x-ray diffraction, which reveals the presence of molybdenum silicides near the silicon surface which is a consequence of the bi-layer deposition. Quantitative analysis of the concentration of excess molybdenum, estimated with secondary ion mass spectroscopy, is commensurate to the additional heat capacity needed to explain the anomalous time response of the detectors.

Sub-Kelvin cooling for two kilopixel bolometer arrays in the PIPER receiver.

The Primordial Inflation Polarization Explorer (PIPER) is a balloon-borne telescope mission to search for inflationary gravitational waves from the early universe. PIPER employs two 32 × 40 arrays of superconducting transition-edge sensors, which operate at 100 mK. An open bucket Dewar of liquid helium maintains the receiver and telescope optics at 1.7 K. We describe the thermal design of the receiver and sub-Kelvin cooling with a continuous adiabatic demagnetization refrigerator (CADR). The CADR operates between 70 and 130 mK and provides ≈10 µW cooling power at 100 mK, nearly five times the loading of the two detector assemblies. We describe electronics and software to robustly control the CADR, overall CADR performance in flightlike integrated receiver testing, and practical considerations for implementation in the balloon float environment.

Tracing the first stars with fluctuations of the cosmic infrared background.

The deepest space- and ground-based observations find metal-enriched galaxies at cosmic times when the Universe was less than 1 Gyr old. These stellar populations had to be preceded by the metal-free first stars, known as 'population III'. Recent cosmic microwave background polarization measurements indicate that stars started forming early--when the Universe was < or =200 Myr old. It is now thought that population III stars were significantly more massive than the present metal-rich stellar populations. Although such sources will not be individually detectable by existing or planned telescopes, they would have produced significant cosmic infrared background radiation in the near-infrared, whose fluctuations reflect the conditions in the primordial density field. Here we report a measurement of diffuse flux fluctuations after removing foreground stars and galaxies. The anisotropies exceed the instrument noise and the more local foregrounds; they can be attributed to emission from population III stars, at an era dominated by these objects.

Phase II study of paclitaxel in patients with previously treated osteosarcoma and its variants.

BACKGROUND: Patients with osteosarcoma and its variants who did not respond to standard chemotherapy including doxorubicin, ifosfamide, cisplatin, and high dose methotrexate were treated with paclitaxel so that its therapeutic activity in these patients could be determined. METHODS: We conducted a Phase II study of paclitaxel in patients with conventional osteosarcoma (10), malignant fibrous histiocytoma of the bone (3) and dedifferentiated chondrosarcoma (2) whose disease had progressed after prior standard chemotherapy including doxorubicin, cisplatin, ifosfamide, and high dose methotrexate. Paclitaxel was administered at a starting dose of 175 mg/m2 as a 24-hour infusion with standard premedication every 21 days or upon hematologic recovery (absolute granulocyte count [AGC] > 1500/microliters, platelets > 100,000/microliters). Neupogen was not used routinely. The study was conducted based on a two-stage design. A total of 17 patients were entered into the protocol. Two were ineligible since they had Ewing's sarcoma. Responses were assessed radiographically and pathologically when feasible, using standard criteria. RESULTS: Fifteen eligible patients were treated in the first stage of the study. Median age of the patients was 31 years (range, 19-61 yrs). There were 8 females and 7 males with a Zubrod performance status of 0 or 1. One patient achieved a mixed response and 14 developed progressive disease. Median AGC nadir was 0.3, on Day 13, lasting 5 days. Median platelet nadir was 134, on Day 8. There were no Grade III or IV nonhematologic toxicities and no deaths related to treatment. CONCLUSIONS: Paclitaxel, at this dose and schedule, is well tolerated but inactive in this patient population.

Characterization of a submillimeter high-angular-resolution camera with a monolithic silicon bolometer array for the Caltech Submillimeter Observatory.

We constructed a 24-pixel bolometer camera operating in the 350- and 450-µm atmospheric windows for the Caltech Submillimeter Observatory (CSO). This instrument uses a monolithic silicon bolometer array that is cooled to approximately 300 mK by a single-shot (3)He refrigerator. First-stage amplification is provided by field-effect transistors at approximately 130 K. The sky is imaged onto the bolometer array by means of several mirrors outside the Dewar and a cold off-axis elliptical mirror inside the cryostat. The beam is defined by cold aperture and field stops, which eliminates the need for any condensing horns. We describe the instrument, present measurements of the physical properties of the bolometer array, describe the performance of the electronics and the data-acquisition system, and demonstrate the sensitivity of the instrument operating at the observatory. Approximate detector noise at 350 µm is 5 × 10(-15) W/√Hz, referenced to the entrance of the Dewar, and the CSO system noise-equivalent flux density is approximately 4 Jy/√Hz. These values are within a factor of 2.5 of the background limit.

Scientific results from the Cosmic Background Explorer (COBE).

The National Aeronautics and Space Administration (NASA) has flown the COBE satellite to observe the Big Bang and the subsequent formation of galaxies and large-scale structure. Data from the Far-Infrared Absolute Spectrophotometer (FIRAS) show that the spectrum of the cosmic microwave background is that of a black body of temperature T = 2.73 +/- 0.06 K, with no deviation from a black-body spectrum greater than 0.25% of the peak brightness. The data from the Differential Microwave Radiometers (DMR) show statistically significant cosmic microwave background anisotropy, consistent with a scale-invariant primordial density fluctuation spectrum. Measurements from the Diffuse Infrared Background Experiment (DIRBE) provide new conservative upper limits to the cosmic infrared background. Extensive modeling of solar system and galactic infrared foregrounds is required for further improvement in the cosmic infrared background limits.

Postdispersion system for astronomical observations with Fourier transform spectrometers in the thermal infrared.

A postdispersion system for astronomical observations with Fourier transform spectrometers in the thermal infrared has been developed. Postdispersion improves the sensitivity of radiation noise limited observations by reducing the spectral range incident on the detector. The instrument is described and various uses are discussed.