Disk M Dwarf Luminosity Function From HST Star Counts

We study a sample of 257 Galactic disk M dwarfs (8<M_V<18.5) found in images obtained using HST. These include 192 stars in 22 fields imaged with the repaired WFC2 with mean limiting mag I=23.7 and 65 stars in 162 fields imaged with the pre-repair Planetary Camera with mean limiting mag V=21.3. We find that the disk luminosity function (LF) drops sharply for M_V>12 (M<0.25 \ms), decreasing by a factor \gsim 3 by M_V~14 (M~0.14\ms). This decrease in the LF is in good agreement with the ground-based photometric study of nearby stars by Stobie et al. (1989), and in mild conflict with the most recent LF measurements based on local parallax stars by Reid et al. (1995). The local LF of the faint Galactic disk stars can be transformed into a local mass function using an empirical mass-M_V relation. The mass function can be represented analytically over the mass range 0.1\ms<M<1.6\ms by \log(\phi)=-1.35-1.34\log(M/\ms)-1.85 [\log(M/\ms)]^2 where \phi is the number density per logarithmic unit of mass. The total column density of M stars is only \Sigma_M=11.8\pm 1.8\ms\pc^{-2}, implying a total `observed' disk column density of \Sigma_\obs~=39\ms\pc^{-2}, lower than previously believed, and also lower than all estimates with which we are familiar of the dynamically inferred mass of the disk. The measured scale length for the M-star disk is 3.0\pm 0.4 kpc. The optical depth to microlensing toward the LMC by the observed stars in the Milky Way disk is \tau~1x10^{-8}, compared to the observed optical depth found in ongoing experiments \tau_\obs~ 10^{-7}. The M-stars show evidence for a population with characteristics intermediate between thin disk and spheroid populations. Approximating what may be a continuum of populations by two separate component, we find characteristic exponential scale heights of ~210 pc and ~740 pc.Comment: 30 pages, uuencoded postscript, includes 3 figures, 2 table

Thermoelectric Energy Harvesting

Thermoelectricity can be used to generate electrical power from temperature gradients or differences in naturally occurring geothermal heat and rocks, or from waste heat in man-made equipment and industrial processes. Thermoelectric energy harvesting systems are finding commercial applications to replace or recharge batteries in low power electronic systems. This chapter provides the fundamental thermoelectric theory related to power generation, including the theoretical analysis and numerical calculations required to calculate the thermoelectric efficiency and electrical power generated when a single thermoelectric couple, and a 127 couple thermoelectric module, are subject to different temperature gradients. A thermoelectric energy harvesting system, incorporating a low power boost converter and DC to DC converter, coupled with electrical energy storage in supercapacitors, is presented and enables a thermoelectric energy harvesting system to provide sufficient electrical power to operate low power electronic components and systems. The short-term challenge for thermoelectric energy harvesting is to become a cost effective and practical solution to replace batteries, and to be scaled to provide sufficient power to operate electrical rotating machines such as low power motors and pumps. The long-term challenge is to improve the efficiency, power output, and cost of thermoelectric modules and energy harvesting systems, and to develop from low power to low-to-medium power applications

Novel battery model of an all-electric personal rapid transit vehicle to determine state-of-health through subspace parameter estimation and a Kalman Estimator

Abstract--The paper describes a real-time adaptive battery model for use in an all-electric Personal Rapid Transit vehicle. Whilst traditionally, circuit-based models for lead-acid batteries centre on the well-known Randles’ model, here the Randles’ model is mapped to an equivalent circuit, demonstrating improved modelling capabilities and more accurate estimates of circuit parameters when used in Subspace parameter estimation techniques. Combined with Kalman Estimator algorithms, these techniques are demonstrated to correctly identify and converge on voltages associated with the battery State-of-Charge, overcoming problems such as SoC drift (incurred by coulomb-counting methods due to over-charging or ambient temperature fluctuations). Online monitoring of the degradation of these estimated parameters allows battery ageing (State-of-Health) to be assessed and, in safety-critical systems, cell failure may be predicted in time to avoid inconvenience to passenger networks. Due to the adaptive nature of the proposed methodology, this system can be implemented over a wide range of operating environments, applications and battery topologies

Rapid steady-state analysis of CLL resonant power converters

Cyclic averaging techniques are applied to the CLL resonant power converter to provide steady-state converter characteristics for rapid stress analysis. This is shown to facilitate the determination of mode duties and initial conditions through knowledge of the operational modes of the rectifier at various operating frequencies. Comparisons are made with FMA-based cyclic analyses, and Spice simulations, that show, respectively, improved accuracy and vastly improved execution speeds

Carbon-Free Power

There is a new world order in electrical energy production. Solar and wind power are established as the low-cost leaders. However, these energy sources are highly variable and electrical power is needed 24/7. Alternative sources must fill the gaps, but only a few are both economical and carbon-free or -neutral. This book presents one alternative: small modular nuclear reactors (SMRs). The authors describe the technology, including its safety and economic aspects, and assess its fit with other carbon-free energy sources, storage solutions, and industrial opportunities. They also explain the challenges with SMRs, including public acceptance. The purpose of the book is to help readers consider these relatively new reactors as part of an appropriate energy mix for the future and, ultimately, to make their own judgments on the merits of the arguments for SMRs.Publishe

Analysis of CLL voltage-output resonant converters using describing functions

A new ac equivalent circuit for the CLL voltage output resonant converter is presented, that offers improved accuracy compared with traditional FMA-based techniques. By employing describing function techniques, the nonlinear interaction of the parallel inductor, rectifier and load is replaced by a complex impedance, thereby facilitating the use of ac equivalent circuit analysis methodologies. Moreover, both continuous and discontinuous rectifier-current operating conditions are addressed. A generic normalized analysis of the converter is also presented. To further aid the designer, error maps are used to demonstrate the boundaries for providing accurate behavioral predictions. A comparison of theoretical results with those from simulation studies and experimental measurements from a prototype converter, are also included as a means of clarifying the benefits of the proposed techniques

Thermoelectric water meter energy harvesting

Domestic electronic water meters are installed by water meter utility companies to accurately measure household water usage for billing purposes, progressing from simple electromechanical systems to state-of-the art volumetric electronic smart meters with RF radio transmission, remote reading, and automatic billing capability. The motivation for this work is to replace, or increase the lifetime of, the on-board lithium-ion battery installed in electronic water meters with a thermoelectric energy harvesting solution to create a business advantage. Practical field experiments at several different water meter installations in the UK, USA, and Australia have demonstrated a temperature difference can exist between the top-side and bottom-side of a water meter, and between several different areas of the meter and the surrounding air. This temperature difference can be harnessed to generate electrical power using thermoelectricity. A prototype thermoelectric water meter energy harvesting system has been designed, and experiments demonstrate the system will operate when a temperature difference is present across the thermoelectric module, giving an output voltage of 3.7V to power the water meter electronics directly or to provide a charge current for the existing lithium-ion battery to increase its lifetime. The work concludes it is feasible, although still challenging, to develop a solution for a novel thermoelectric powered water meter. Further work is required to address the commercial challenges that exist, develop and optimise the prototype solution into a production ready prototype, and conduct further tests using a standard UK domestic water profile at a UK water meter test site

Thermoelectric cooling and heating of human body temperature

The cooling and/or heating of human body temperature is of critical importance and interest in a myriad of applications, however, the use of thermoelectric cooling has made little impact in this area. Current solutions focus on the use of wearable materials that assist the natural temperature regulation of the human body, or the use of liquid cooling techniques reliant on refrigerant fluid or large quantities of dry ice, often used in astronaut spacesuits, worn by surgeons during long surgical procedures, firefighters, military personnel, and motor racing drivers. The motivation for this work is to investigate the feasibility of using thermoelectricity to achieve the cooling process, replacing the existing use of refrigerant fluid and associated compressor and refrigeration components or the use of large quantities of dry ice to create chilled or cooled water. A thermoelectric cooling/heating prototype system has been designed and tested, and successfully demonstrates the temperature of circulating water within small tubes incorporated into a person?s vest undergarment can be used to regulate body temperature. The system briefly comprises: a small reservoir tank of water; a thermoelectric module, heatsink and electronic fan; a small electronic water pump; a proportional, integral, and derivative (PID) controller; interconnecting tubing to carry the circulating water; and a vest undergarment that is worn by the user to help regulate their body temperature. Results presented demonstrate the thermoelectric module successfully cools or heats the water circulating around the vest undergarment, which when worn by a user can be used to lower or increase their external body temperature and improve their temperature comfort levels. The thermoelectric cooling/heating system has several advantages over existing solutions including; a significant decrease in size and weight; system cost; accurate temperature control; ability to provide cooling or heating under user control; no moving parts within the thermoelectric module contributing to high reliability and reduced maintenance requirements; quiet in operation; the elimination of dry ice in the cooling process; and no use of refrigerate fluid or other harmful chemicals. Further work will optimize the design, scale the system to achieve specific cooling/heating targets, and demonstrate the effectiveness of the system in improving a user?s temperature comfort levels

M Dwarfs from Hubble Space Telescope Star Counts. IV

We study a sample of about 1400 disk M dwarfs that are found in 148 fields observed with the Wide Field Camera 2 (WFC2) on the Hubble Space Telescope and 162 fields observed with pre-repair Planetary Camera 1 (PC1), of which 95 of the WFC2 fields are newly analyzed. The method of maximum likelihood is applied to derive the luminosity function and the Galactic disk parameters. At first, we use a local color-magnitude relation and a locally determined mass-luminosity relation in our analysis. The results are consistent with those of previous work but with considerably reduced statistical errors. These small statistical errors motivate us to investigate the systematic uncertainties. Considering the metallicity gradient above the Galactic plane, we introduce a modified color-magnitude relation that is a function of Galactic height. The resultant M dwarf luminosity function has a shape similar to that derived using the local color-magnitude relation but with a higher peak value. The peak occurs at $M_V \sim 12$ and the luminosity function drops sharply toward $M_V \sim 14$. We then apply a height-dependent mass-luminosity function interpolated from theoretical models with different metallicities to calculate the mass function. Unlike the mass function obtained using local relations, which has a power-law index $\alpha = 0.47$, the one derived from the height-dependent relations tends to be flat ($\alpha = -0.10$). The resultant local surface density of disk M dwarfs (12.2 +/- 1.6 M_sun pc^{-2}) is somewhat smaller than the one obtained using local relations (14.3 +/- 1.3 M_sun pc^{-2}). Our measurement favors a short disk scale length, H = 2.75 +/- 0.16 (statistical) +/- 0.25 (systematic) kpc.Comment: 20 pages, 10 ps figures, accepted for publication in Ap