10,260 research outputs found
Contact structures on open 3-manifolds
In this paper, we study contact structures on any open 3-manifold V which is
the interior of a compact 3-manifold. To do this, we introduce proper contact
isotopy invariants called the slope at infinity and the division number at
infinity. We first prove several classification theorems for T^2 x [0, \infty),
T^2 x R, and S^1 x R^2 using these concepts. This investigation yields
infinitely many tight contact structures on T^2 x [0,\infty), T^2 x R, and S^1
x R^2 which admit no precompact embedding into another tight contact structure
on the same space. Finally, we show that if V is irreducible and has an end of
nonzero genus, then there are uncountably many tight contact structures on V
that are not contactomorphic, yet are isotopic. Similarly, there are
uncountably many overtwisted contact structures on V that are not
contactomorphic, yet are isotopic.Comment: 18 pages, 3 figures, additions to intro, clearer statement of thm 1.1
(same proof), Modifications made to section 6 giving shorter proof of thm 1.2
and 1.
Municipal Conservation Outreach and Technical Assistance, Taylor, J
The New Hampshire Estuaries project awarded a grant of 18,660,000 of new money available for conservation projects in those towns. Past the term of the grant, additional towns will be voting on increasing the amount of money from the Land Use Change Tax going to their conservation funds in 2004. Eight more towns in the estuaries area are considering open space bond proposals for the 2004 town meeting season, for a possible total of $19,600,000 in new funds for permanent land conservation. The coming challenge for the New Hampshire land conservation community will be to encourage the towns with these new sources of money to invest it wisely. Properties need to be selected according to guidelines that reflect a mix of natural resource values and local interests. Projects need to be conducted in a professional manner to insure long-term viability and excellent stewardship
Tracing baryons in the warm-hot intergalactic medium with broad Ly alpha absorption
We discuss physical properties and baryonic content of broad Ly alpha
absorbers (BLAs) at low redshift. These absorption systems, recently discovered
in high-resolution, high-signal to noise quasar absorption line spectra,
possibly trace the warm-hot intergalactic medium (WHIM) in the temperature
range between 10^5 and 10^6 K. To extend previous BLA measurements we have
analyzed STIS data of the two quasars H 1821+643 and PG 0953+415 and have
identified 13 BLA candidates along a total (unblocked) redshift path of
dz=0.440. Combining our measurements with previous results for the lines of
sight toward PG 1259+593 and PG 1116+215, the resulting new BLA sample consists
of 20 reliably detected systems as well as 29 additional tentative cases,
implying a BLA number density of dN/dz=22-53. We estimate that the contribution
of BLAs to the baryon density at z=0 is Omega_b(BLA)>0.0027 h_70^-1 for
absorbers with log (N/b)>11.3. This number indicates that WHIM broad Ly alpha
absorbers contain a substantial fraction of the baryons in the local Universe.
(Abridged abstract)Comment: 17 pages, 7 figures; Accepted for publication in A&
STEREOCHEMISTRY OF HEXENYL RADICAL CYCLIZATIONS WITH TERT-BUTYL AND RELATED LARGE GROUPS: SUBSTITUENT AND TEMPERATURE EFFECTS
The long held notion that hexenyl radicals bearing large substituents on the radical carbon cyclize to give 1,2-trans-substituted cyclopentanes is experimentally disproved by study of the radical cyclization of an assortment of simple and complex substrates coupled with careful product analysis and rigorous assignment of configurations. X-ray studies and syntheses of authentic samples establish that the published assignments for cis- and trans-1-tert-butyl-2-methylcyclopentane must be reversed. The original assignment based on catalytic hydrogenation of 1-tert-butyl-2-methylenecyclopentane was compromised by migration of the double bond prior to hydrogenation. The cyclization of 1-tert-butylhexenyl radical is moderately cis selective, and the selectivity is increased by geminal substitution on carbon 3. This selectivity trend is general and extends to relatively complex substrates. It has allowed Ihara to reduce the complexity of an important class of round trip radical cyclizations to make linear triquinanes to the point where two tricyclic products, cis-syn-cis and cis-anti-cis, account for about 80% of the products. However, the further increase in selectivity that was proposed by lowering the temperature is shown to be an artifact of the analysis methods and is not correct. This work solidifies "1,2-cis selectivity" in cyclizations of 1-subsituted hexenyl radicals as one of the most general stereochemical trends in radical cyclizations.ii
Determination of the Hubble Constant Using a Two-Parameter Luminosity Correction for Type Ia Supernovae
In this paper, we make a comprehensive determination of the Hubble constant
by using two parameters - the B-V color and the rate of decline - to simultaneously standardize the luminosities of all nearby
Cepheid-calibrated type Ia supernovae (SNe Ia) and those of a larger, more
distant sample of 29 SNe Ia. Each group is treated in as similar a manner as
possible in order to avoid systematic effects. A simultaneous
minimization yields a standardized absolute luminosity of the
Cepheid-calibrated supernovae as well as the Hubble constant obtained from the
more distant sample. We find and a standardized
absolute magnitude of -19.46. The sensitivity of to a metallicity
dependence of the Cepheid-determined distances is investigated. The total
uncertainty , dominated by uncertainties in the primary Cepheid
distance indicator, is estimated to be 5 km/s Mpc^{-1}.Comment: To appear in Ap
Application of automobile emission control technology to light piston aircraft engines
The possibility was evaluated for achieving the EPA Standards for HC and CO emissions through the use of air-fuel ratio enleanment at selected power modes combined with improved air-fuel mixture preparation, and in some cases improved cooling. Air injection was also an effective approach for the reduction of HC and CO, particularly when combined with exhaust heat conservation techniques such as exhaust port liners
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