A low-drift, low-noise, multichannel dc voltage source for segmented-electrode Paul traps.

We present the design, construction, and characterization of a multichannel, low-drift, low-noise dc voltage source specially designed for biasing the electrodes of segmented linear Paul traps. The system produces 20 output voltage pairs having a common-mode range of 0 to +120 V with 3.7 mV/LSB (least significant bit) resolution and differential ranges of ±5 V with 150 µV/LSB or ±16 V with 610 µV/LSB resolution. All common-mode and differential voltages are independently controllable, and all pairs share the same ground reference. The measured drift of the voltages after warm-up is lower than 1 LSB peak-to-peak on the time scale of 2 h. The noise of an output voltage measured with respect to ground is <10 µVRMS within 10 Hz-100 kHz, with spectral density lower than 3 nV Hz-1/2 above 50 kHz. The performance of the system is limited by the external commercial multichannel DAC unit NI 9264, and in principle, it is possible to achieve higher stability and lower noise with the same voltage ranges. The system has a compact, modular, and scalable architecture, having all parts except for the DAC chassis housed within a single 19″ 3HE rack.

Note: An avalanche transistor-based nanosecond pulse generator with 25 MHz repetition rate.

We have developed an avalanche transistor-based pulse generator for driving the photocathode of an image intensifier, which comprises a mainly capacitive load on the order of 100 pF. The circuit produces flat-top pulses with a rise time of 2 ns, a FWHM of 10 ns, and an amplitude of tens of V at a high repetition rate in the range of tens of MHz. The generator is built of identical avalanche transistor sections connected in parallel and triggered in a sequence, synchronized to a reference rf signal. The described circuit and mode of operation overcome the power dissipation limit of avalanche transistor generators and enable a significant increase of pulse repetition rates. Our approach is naturally suited for synchronized imaging applications at low light levels.

Note: cryogenic low-noise dc-coupled wideband differential amplifier based on SiGe heterojunction bipolar transistors.

Silicon-germanium heterojunction bipolar transistors can be used to construct low-noise cryogenic amplifiers. We present a dc-coupled differential amplifier capable of operating down to 10 K. In this temperature regime it has bandwidth of 15 MHz and noise temperature as low as 1.3 K. When operated at liquid nitrogen temperature of 77 K, the measured noise temperature is lower than 3 K. The amplifier is based on the commercially available transistors NESG3031 and operational amplifier OPA836 and is capable of standalone operation without any additional stages at room temperature.

Postoperative sternal stability assessed by vibration: a preliminary study.

PURPOSE: Mechanical stability of the postoperative sternum was assessed using novel analysis based on vibration response. DESCRIPTION: The response to controlled vibration in the 50 Hz to 1,500 Hz range was studied in 22 elective cardiac surgical patients with an accelerometer, recorded, and processed on a personal computer. Each patient had four measurement sessions. The mechanical transfer function of the sternum was estimated, and several descriptive factors were extracted from it to determine how they reflect changes occurring in the bone during the recovery from sternotomy. EVALUATION: Complete datasets were obtained from 14 patients. The most informative variable for the sternal healing was the P(600-1500) index, which reflects transmittance in the wide frequency band between 600 Hz and 1500 Hz. The index dropped after surgery, indicating a decrease in transmission. The postoperative measurements revealed a reverse trend in the same variable, which can be attributed to healing. CONCLUSIONS: Significant changes caused by the sternotomy and subsequent healing processes were observed using vibration measurement.