METALLIC MICRO HEAT EXCHANGERS: PROPERTIES, APPLICATIONS AND LONG TERM STABILITY

Micro heat exchangers, which until recently have been implemented only at laboratory scale, are now being available for industrial applications. They are well known for their superior heat transfer properties due to the large surface-to-volume ratio. But there are little data available on the long term stability of these devices. In this paper application several application examples for micro heat exchangers made of stainless steel are presented. The devices consist of stainless steel foils providing numerous micro channels generated by mechanical micromachining or wet chemical etching. A number of the foils are arranged in a specific way and bonded together. Device property descriptions as well as some possible application examples show the potential of metallic microstructure devices. Results on two crossflow microstructure heat exchangers running in long term tests are presented. Both devices have been tested for more than 8000 hours each, using deionised water as test fluid. Experimental data on the heat transfer properties and the pressure drop are given and compared. It was found that the heat transfer capabilities were significantly decreased within the first few hundred hours of testing and then run into a saturation state. Performance degradation may be due to a fouling layer deposited on the heat exchange surface. Some other experimental applications in which fouling was expected to cause problems are described briefly

Abundance and conservation status of two newly described lemur species in northwestern Madagascar (Microcebus danfossi, Lepilemur grewcockorum)

The distribution and abundance of Danfoss’ mouse lemurs (Microcebus danfossi) and Grewcock’s sportive lemurs (Lepilemur grewcockorum), two regional endemics from northwestern Madagascar, were studied from May to December 2008 in the Sofia region between the rivers Sofia and Maevarano. The goal was to investigate the size and quality of forest fragments and to determine the presence and abundance of the recently described M. danfossi and L. grewcockorum. They are confined to this region and their conservation status has not yet been determined. A total of eleven sites were visited and systematic census observations were carried out in each of them. M. danfossi was present in ten of eleven sites and its abundance ranged from 4.5 to 8.5 individuals per kilometer. L. grewcockorum was present in only three of eleven sites and its abundance ranged from 0.8 to one individual per kilometre. Based on the results of this study M. danfossi should be listed as Vulnerable and L. grewcockorum as Endangered. Based on the abundance data, the size and the general condition of the fragments, the forests of Anjajavy, Ambarijeby and Bekofafa are most favorable for future protection, because they still contain the most intact nocturnal lemur communities. KEYWORDS: Mouse lemur, distribution, fragmentation, primates, sportive lemur

A Gas Monitoring Chamber for the ATLAS Muon Monitored Drift Tube(MDT) System

The ATLAS Muon Spectrometer incorporates MDT precision chambers used for precise track reconstruction. Since the MDT resolution depends crucially on the electron drift velocity in the operating gas, a monitoring chamber is designed and constructed to precisely monitor the gas properties in real time. This chamber continuously samples the operating gas and measures the electron drift velocity in the operating gas over a wide range of electric field strength with very high resolution and short response time. In order to validate the feasibility and optimize the design, extensive simulations based on Garfield and 3D/2D finite element method(FEM) are done, which include mechanics, electrostatics, thermodynamics and computational fluid dynamics(CFD). This monitoring chamber enables the measurement of the drift velocity spectra over a varying electric field with a wide range, then very small changes and contaminations of the gas mixture can be detected. Results obtained at CERN and in the lab will be presented as well

Low frequency radio and X-ray properties of core-collapse supernovae

Radio and X-ray studies of young supernovae probe the interaction between the supernova shock waves and the surrounding medium and give clues to the nature and past of the progenitor star. Here we discuss the early emission from type Ic SN 2002ap and argue that repeated Compton boosting of optical photons by hot electrons presents the most natural explanation of the prompt X-ray emission. We describe the radio spectrum of another type Ic SN 2003dh (GRB030329) obtained with combined GMRT and VLA data. We report on the low frequency radio monitoring of SN 1995N and our objectives of distinguishing between competing models of X-ray emission from this SN and the nature of its progenitor by X-ray spectroscopy. Radio studies on SN 2001gd, SN 2001ig and SN 2002hh are mentioned.Comment: 5 pages, 4 figures. Uses svmult.cls. To appear in proceedings of IAU Colloquium 192 "Supernovae (10 years of SN 1993J)", April 2003, Valencia, Spain, eds. J. M. Marcaide and K. W. Weile

The X-ray Spectrum and Light Curve of Supernova 1995N

We report on multi-epoch X-ray observations of the Type IIn (narrow emission line) supernova SN 1995N with the ROSAT and ASCA satellites. The January 1998 ASCA X-ray spectrum is well fitted by a thermal bremsstrahlung (kT~10 keV, N_H~6e20 cm^-2) or power-law (alpha~1.7, N_H~1e21 cm^-2) model. The X-ray light curve shows evidence for significant flux evolution between August 1996 and January 1998: the count rate from the source decreased by 30% between our August 1996 and August 1997 ROSAT observations, and the X-ray luminosity most likely increased by a factor of ~2 between our August 1997 ROSAT and January 1998 ASCA observations, although evolution of the spectral shape over this interval is not ruled out. The high X-ray luminosity, L_X~1e41 erg/sec, places SN 1995N in a small group of Type IIn supernovae with strong circumstellar interaction, and the evolving X-ray luminosity suggests that the circumstellar medium is distributed inhomogeneously.Comment: MNRAS accepted. 6 pages, 2 figures; uses mn.sty and psfi

Detection of pulsations and a spectral feature in the X-ray emission of the isolated neutron star 1RXS J214303.7+065419/RBS 1774

We report on the results of a deep XMM-Newton observation of RBS 1774, the most recent dim isolated neutron star candidate found in the ROSAT archive data. Spectral and timing analysis of the high-quality PN and MOS data confirm the association of this source with an isolated neutron star. The spectrum is thermal and blackbody-like, and there is evidence at a significance level > 4sigma that the source is an X-ray pulsar, with spin period of 9.437 s. Spectral fitting reveils the presence of an absorption feature at ~0.7 keV, but at this level data do not have enough resolution to allow us to discriminate between an absorption line or an edge. We compare the newly measured properties of RBS 1774 with those of other known dim isolated neutron stars, and discuss possible interpretations for the absorption feature.Comment: 21 pages, 5 figures, ApJ accepte