A Pre-Protostellar Core in L1551. II. State of Dynamical and Chemical Evolution

Both analytic and numerical radiative transfer models applied to high spectral resolution CS and N2H+ data give insight into the evolutionary state of L1551 MC. This recently discovered pre-protostellar core in L1551 appears to be in the early stages of dynamical evolution. Line-of-sight infall velocities of >0.1km/s are needed in the outer regions of L1551 MC to adequately fit the data. This translates to an accretion rate of ~ 1e-6 Msun/yr, uncertain to within a factor of 5 owing to unknown geometry. The observed dynamics are not due to spherically symmetric gravitational collapse and are not consistent with the standard model of low-mass star formation. The widespread, fairly uniform CS line asymmetries are more consistent with planar infall. There is modest evidence for chemical depletion in the radial profiles of CS and C18O suggesting that L1551 MC is also chemically young. The models are not very sensitive to chemical evolution. L1551 MC lies within a quiescent region of L1551 and is evidence for continued star formation in this evolved cloud.Comment: 27 pages, 7 figures, ApJ accepte

A Pre-Protostellar Core in L1551

Large field surveys of NH3, C2S, 13CO and C18O in the L1551 dark cloud have revealed a prolate, pre-protostellar molecular core (L1551-MC) in a relatively quiescent region to the northwest of the well-known IRS 5 source. The kinetic temperature is measured to be 9K, the total mass is ~2Msun, and the average particle density is 10^4-10^5 cm^(-3). L1551-MC is 2.25' x 1.11' in projection oriented at a position angle of 133deg. The turbulent motions are on the order of the sound speed in the medium and contain 4% of the gravitational energy, E_{grav}, of the core. The angular momentum vector is projected along the major axis of L1551-MC corresponding to a rotational energy of 2.5E-3(sin i)^(-2)|E_{grav}|. The thermal energy constitutes about a third of |E_{grav}| and the virial mass is approximately equal to the total mass. L1551-MC is gravitationally bound and in the absence of strong, ~160 microgauss, magnetic fields will likely contract on a ~0.3 Myr time scale. The line profiles of many molecular species suggest that the cold quiescent interior is surrounded by a dynamic, perhaps infalling envelope which is embedded within the ambient molecular gas of L1551.Comment: 27 pages, 7 figures, ApJ accepte

FIRE Cirrus on October 28, 1986: LANDSAT; ER-2; King Air; theory

A simultaneous examination was conducted of cirrus clouds in the FIRE Cirrus IFO-I on 10/28/86 using a multitude of remote sensing and in-situ measurements. The focus is cirrus cloud radiative properties and their relationship to cloud microphysics. A key element is the comparison of radiative transfer model calculations and varying measured cirrus radiative properties (emissivity, reflectance vs. wavelength, reflectance vs. viewing angle). As the number of simultaneously measured cloud radiative properties and physical properties increases, more sharply focused tests of theoretical models are possible

Regulation of fluid reabsorption in rat or mouse proximal renal tubules by asymmetric dimethylarginine and dimethylarginine dimethylaminohydrolase 1

Nitric oxide prevents hypertension yet enhances proximal tubule Na+ reabsorption. Nitric oxide synthase is inhibited by asymmetric dimethylarginine (ADMA) that is metabolized by dimethylarginine dimethylaminohydrolase (DDAH) whose type 1 isoform is expressed abundantly in the proximal tubule (PT). We hypothesize that ADMA metabolized by DDAH-1 inhibits fluid reabsorbtion (Jv) by the proximal tubule. S2 segments of the PT were microperfused between blocks in vivo to assess Jv in anesthetized rats. Compared with vehicle, microperfusion of ADMA or Nω-nitro-l-arginine methyl ester (l-NAME) in the proximal tubule reduced Jv dose dependently. At 10−4 mol/l both reduced Jv by ~40% (vehicle: 3.2 ± 0.7 vs. ADMA: 2.1 ± 0.5, P < 0.01 vs. l-NAME: 1.9 ± 0.4 nl·min−1·mm−1, P < 0.01; n = 10). Selective inhibition of DDAH-1 in rats with intravenous L-257 (60 mg/kg) given 2 h before and L-257 (10−5 mol/l) perfused in the proximal tubule for 5 min reduced Jv by 32 ± 4% (vehicle: 3.2 ± 0.5 vs. L-257: 2.2 ± 0.5 nl·min−1·mm−1; P < 0.01) and increased plasma ADMA by ≈50% (vehicle: 0.46 ± 0.03 vs. L-257: 0.67 ± 0.03 µmol/l, P < 0.0001) without changing plasma symmetric dimethylarginine. Compared with nontargeted control small-interference RNA, knock down of DDAH-1 in mice by 60% with targeted small-interference RNAs (siRNA) reduced Jv by 29 ± 5% (nontargeted siRNA: 2.8 ± 0.20 vs. DDAH-1 knockdown: 1.9 ± 0.31 nl·min−1·mm−1, P < 0.05). In conclusion, fluid reabsorption in the proximal tubule is reduced by tubular ADMA or by blocking its metabolism by DDAH-1. L-257 is a novel regulator of proximal tubule fluid reabsorption

Interconnecting Distributed Legacy Systems: Virtual Environment Domain Example

As the power and utility of virtual reality environments increases, so do the potential benefits found from combinding several such environments. But doing so presents the developer with a host of difficult distributed systems issues. This paper explores what some of these issues are within the VE domain, relates our successes to date in overcoming these problems by means of various automated tools, and suggests ways to apply our results other target domains. (Also cross-referenced as UMIACS-TR-96-88

Software Engineering of Virtual Environments: Integration and Interconnection

Virtual Environments(VEs) are proving to be valuable resources in many fields, and they are even more useful when they involve multiple users in distributed environments. Many useful VEs were designed to be stand-alone applications, without consideration for integrating them into a distributed VE. Our approach to connecting VEs is to define an abstract model for the interconnection, use integration tools to do as much of the work automatically as possible, and use a run-time environment to support the interconnection. With our experiences to date, we are learning that certain classes of techniques are common to all solutions using this approach. We have summarized these in a set of requirements and are building a system that features these techniques as first class objects. In the future you will be able to solve these interconnection problems cheaply, plus engineers of future VEs will have some guidance on how they should organize their implementations so that interconnection with other VEs will be easier. In this paper we coin the phrase "software engineering of virtual environments" (SEVE) to describe the above activities. (Also cross-referenced as UMIACS-TR-96-89

The 27-28 October 1986 FIRE IFO cirrus case study: Comparison of satellite and aircraft derived particle size

Theoretical calculations predict that cloud reflectance in near infrared windows such as those at 1.6 and 2.2 microns should give lower reflectances than at visible wavelengths. The reason for this difference is that ice and liquid water show significant absorption at those wavelengths, in contrast to the nearly conservative scattering at wavelengths shorter than 1 micron. In addition, because the amount of absorption scales with the path length of radiation through the particle, increasing cloud particle size should lead to decreasing reflectances at 1.6 and 2.2 microns. Measurements at these wavelengths to date, however, have often given unpredicted results. Twomey and Cocks found unexpectedly high absorption (factors of 3 to 5) in optically thick liquid water clouds. Curran and Wu found expectedly low absorption in optically thick high clouds, and postulated the existence of supercooled small water droplets in place of the expected large ice particles. The implications of the FIRE data for optically thin cirrus are examined