High resolution kinematics of galactic globular clusters. II. On the significance of velocity dispersion measurements

Small number statistics may heavily affect the structure of the broadening function in integrated spectra of galactic globular cluster centers. As a consequence, it is a priori unknown how closely line broadening measure- ments gauge the intrinsic velocity dispersions at the cores of these stel- lar systems. We have tackled this general problem by means of Monte Carlo simulations. An examination of the mode and the frequency distribution of the measured values of the simulations indicates that the low value measured for the velocity dispersion of M30 (Zaggia etal 1992) is likely a reliable estimate of the velocity dispersion at the center of this cluster. The same methodology applied to the case of M15 suggests that the steep inward rise of the velocity dispersion found by Peterson, Seitzer and Cudworth (1989) is real, although less pronounced. Large-aperture observa- tions are less sensitive to statistical fluctuations, but are unable to detect strong variations in the dispersion wich occur within the aperture itself.Comment: 6 pages, 8 figures upon request, Latex A&A style version 3.0, DAPD-20

Determination of the Wind Speed and Direction by Means of Fluidic-Domain Signal Processing

This paper presents an analytical model for a recently introduced class of 2-D directional anemometers based on fluidic structures capable of averaging the differential pressure developed by the wind across distinct diameters of the transverse cross-section of a single cylinder. In previous works, it was found that performing the average over a proper set of diameters produces a differential pressure that depends on the wind direction according to a cosine law, allowing simple direction estimation. This fact, which was not investigated in previous articles, is explained in this paper taking into account symmetry and angular spectral properties of the pressure distribution. Besides analyzing previously proposed devices, this paper introduces several new configurations, which are classified according to the type of average and number of diameters involved. Comparison of the estimated performances with the experimental results obtained in earlier works clearly shows that prototypes proposed so far were far from achieving the best theoretical accuracy, suggesting that significant improvements can be obtained by re-design of the fluidic structures

On the Cepheid variables of nearby galaxies III. NGC 3109

We extended to the R and I bands the light curve coverage for 8 Cepheids already studied in B and V by Capaccioli et al [AJ, 103, 1151 (1992)]. Sixteen additional Cepheid candidates have been identified and preliminary periods are proposed. The new Cepheids allow the period-luminosity relation to be extended one magnitude fainter. Apparent B, V, R, and I distance moduli have been calculated. Combining the data at different wavelengths, and assuming a true distance modulus of 18.50 mag for the LMC, we obtain for NGC 3109 a true distance modulus $(m-M)_0=25.67\pm0.16$, corresponding to $1.36\pm0.10$ Mpc. Adopting $E(B-V)=0.08$ for the LMC, the interstellar reddening for the Cepheids in NGC 3109 is consistent with 0. A discussion on the possible implications of this result is presented. A comparison of the period-color, period-amplitude, and period-luminosity relations suggests similar properties for the Cepheids in the LMC, NGC 3109, Sextans A, Sextans B, and IC 1613, though the uncertainties in the main parameter determination are still unsatisfactorily high for a firm conclusion on the universality of the period-luminosity relation.Comment: 35 pages, aaspp4.sty, accepted for pubblication on Astron.

Precise measurement of gas volumes by means of low-offset MEMS flow sensors with µL/min resolution

Experiments devoted to evaluate the performance of a MEMS thermal flow sensor in measuring gas volumes are described. The sensor is a single-chip platform, including several sensing structures and a low-offset, low-noise readout interface. A recently proposed offset compensation approach is implemented obtaining low temperature drift and excellent long time stability. The sensor is fabricated by applying a simple micromachining procedure to a chip produced using the BCD6s process of STMicroelectronics. Application of a gas conveyor allowed inclusion of the sensing structure into a channel of sub-millimeter cross-section. The results of measurements performed by making controlled air volumes pass through the sensor channel in both directions at rates from 0.1 to 5 mL/min are described

Integrated smart gas flow sensor with 2.6 mW total power consumption and 80 dB dynamic range

A thermal flow sensor including sensing structures and a read-out interface in a single chip is proposed. The sensing structure is a microcalorimeter based on a double heater configuration while the low noise electronic interface performs signal reading and offset compensation. The device has been fabricated with a commercial CMOS process followed by a post-processing procedure. Post-processing has been customized in order to increase the thermal insulation of the sensing structures from the silicon substrate and improve the heat exchange between the sensor and the gas flow. Device characterization confirms the effectiveness of the proposed fabrication method in increasing the sensitivity at constant power consumption without affecting the dynamic range

A Compact CMOS Compatible micro-Pirani Vacuum Sensor with Wide Operating Range and Low Power Consumption

A micro-Pirani vacuum sensor with an operating pressure range of more than 5 decades is described. The device is fabricated by applying a low-resolution and potentially low-cost front-side bulk micromachining step to a chip produced with a commercial CMOS technology. Maximization of the thermally coupled surfaces has been obtained by stacking all layers available by default in the CMOS process. This design choice and the integration of a low-noise, low-power readout interface allowed achievement of state-of-art performances with a fabrication approach affordable even to SMEs and small University laboratories

A Compact, Dual Channel Flow-based Differential Pressure Sensor with mPa Resolution and Sub-10 mW Power Consumption

In this work, we propose a single-chip sensor for the detection of two extremely low, independent differential pressures. The operating principle consists in measuring the airflow induced by the pressure through a channel of sub-millimeter cross-section [1]. The airflow is measured by differential thermal flow sensors, implementing a recently proposed drift-free offset compensation approach. Use of a low-noise, low-power readout interface, integrated on the same chip as the sensing structures, allowed the achievement of resolutions of 1.29 mPa, which are one order of magnitude lower than state-of-art devices. This performance has been obtained with power consumptions suitable for battery-powered applications

Thermal Noise-Boosting Effects in Hot-Wire-Based Micro Sensors

This article proposes an original approach aimed at modelling the noise density in sensors based on a single hot wire or pairs of thermally coupled wires. The model consists in an original combination of a previous electrothermal model of the wire with well-established assumptions on the thermal noise in conductors that carry moderate current densities. A simple method for estimating the model parameters with simple impedance spectroscopy is suggested. The predicted power spectral densities of the wire thermal noise differ from the result of previously presented analytical models, stimulating further experimental studies. The effects of the electrothermal feedback of both hot wires and hot-wire pairs on flicker noise is also intrinsically covered by the proposed approach

Low voltage acoustic particle velocity sensor with integrated low noise chopper pre-amplifier

Novel acoustic particle velocity (APV) sensors suitable for low voltage, battery-powered systems are proposed. The sensing structure consists of four silicide polysilicon wires placed over suspended dielectric membranes and arranged in a Wheatstone full-bridge configuration. The device has been fabricated combining a commercial CMOS process with a simple and low cost post-processing technique. An ultra low noise chopper pre-amplifier has been integrated on the same chip. Preliminary noise and acoustic characterization is presented

Automatic compensation of pressure effects on smart flow sensors in the analog and digital domain

Two different approaches for the automatic compensation of pressure effects on thermal flow sensors are investigated. One approach operates in the analog domain and it is based on a closed-loop circuit that uses a pressure dependent signal to keep the sensor output constant. The digital approach operates in an open loop fashion and is capable of producing also a pressure reading. The effectiveness of the proposed methods has been verified by means of a smart flow sensor integrating on the same chip the sensing structures and a configurable electronic interface performing signal reading and non idealities compensation. The chip has been designed with a commercial CMOS process and fabricated by means of a post-processing technique. The experimental results performed in nitrogen confirm that both methods are capable of reducing the sensitivity of the flow sensor output signal to pressure variation