1,902 research outputs found
The Quantasyn, an improved quantum detector
Quantasyn provides absolute measurement of radiation flux in the range 1000 A to 4500 A and into the vacuum ultraviolet. This radiation detector cimbines the high quantum efficiency and inherent linearity of the silicon solar cell with the constant quantum response of the fluorescent organic compound liumogen
Krieger's Finite Generator Theorem for Ergodic Actions of Countable Groups.
For an ergodic probability-measure-preserving action of a countable group G, we define the Rokhlin entropy to be the infimum of the Shannon entropies of countable generating partitions. It is known that for free ergodic actions of amenable groups this notion coincides with classical Kolmogorov--Sinai entropy. It is thus natural to view Rokhlin entropy as a close analogue to classical entropy. Under this analogy we prove that Krieger's finite generator theorem holds for all countably infinite groups. Specifically, if the Rokhlin entropy is bounded above by log(k) then there exists a generating partition consisting of k sets. Using this result, we study the properties of Rokhlin entropy as an isomorphism invariant and investigate the still unsolved isomorphism problem for Bernoulli shifts. Under the assumption that every countable group admits a free ergodic action of positive Rokhlin entropy, we prove that Bernoulli shifts having base spaces of unequal Shannon entropy are non-isomorphic and that Gottschalk's surjunctivity conjecture and Kaplansky's direct finiteness conjecture are true.PhDMathematicsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/111377/1/bseward_1.pd
Opposing shear senses in a subdetachment mylonite zone: Implications for core complex mechanics
[1] Global studies of metamorphic core complexes and lowâangle detachment faults have highlighted a fundamental problem: Since detachments excise crustal section, the relationship between the mylonitic rocks in their footwalls and the brittle deformation in their hanging walls is commonly unclear. Mylonites could either reflect ductile deformation related to exhumation along the detachment fault, or they could be a more general feature of the extending middle crust that has been âcaptured â by the detachment. In the first case we would expect the kinematics of the mylonite zone to mirror the sense of movement on the detachment; in the second case both the direction and sense of shear in the mylonites could be different. The northern Snake Range dĂ©collement (NSRD) is a classic Basin and Range detachment fault with a wellâdocumented topâeast of displacement. We present structural, paleo-magnetic, geochronological, and geothermometric evidence to suggest that the mylonite zone below the NSRD locally experienced phases of both east â and westâdirected shear, inconsistent with movement along a single detachment fault. We therefore propose that the footwall mylonites represent a predetachment dis-continuity in the middle crust that separated localized deformation above from distributed crustal flow below (localizedâdistributed transition (LDT)). The mylonites were subsequently captured by a moderately dipping brittle detachment that soled down to the middle crust and exhumed them around a rolling hinge into a subhorizontal orientation at the surface, produc-ing the presentâday NSRD. In this interpretation the brittle hanging wall represents a series of rotated upper crustal normal faults, whereas the mylonitic footwall represents one or more exhumed middl
ROSAT Observations of the Vela Pulsar
The ROSAT HRI was used to monitor X-ray emission from the Vela Pulsar. Six
observations span 2-1/2 years and 3 glitches. The summed data yield a
determination of the pulse shape, and X-ray emission from the pulsar is found
to be 12 % pulsed with one broad and two narrow peaks. One observation occurred
15 days after a large glitch. No change in pulse structure was observed and any
change in X-ray luminosity, if present, was less than 3 %. Implications for
neutron star structure are discussed.Comment: To be publisned in the Astrophysical Journa
ASCA observations of two SNRs and NEI analysis
Based on the data from the \asca observation of SNRs Kes79 and W49B, we
present here the analysis of their X-ray spectra and morphologies. The Kes79
spectrum can be well fitted by a single NEI component, and the narrow-band
images of that source show an inhomogeneous distribution of heavy elements. The
heavy elements are richest in the positions S, SE and SW of Kes79, where there
may exist interaction between shocks and molecular clouds implied by radio
observations. For W49B we present here the non-equilibrium ionization (NEI)
analysis based on its emission line diagnostics, and the spectral fit using two
NEI components. The reverse shock in W49B may be still hot and we don't find
evidence for a hotter blast wave in \asca spectra.Comment: Contributed talk in 32nd COSPAR E1.1, 1998, Nagoya. To appear in Adv.
Space Res., 1999, 6 pages, LaTe
X-ray Timing of PSR J1852+0040 in Kesteven 79: Evidence of Neutron Stars Weakly Magnetized at Birth
The 105-ms X-ray pulsar J1852+0040 is the central compact object (CCO) in SNR
Kes 79. We report a sensitive upper limit on its radio flux density of 12 uJy
at 2 GHz using the NRAO GBT. Timing using XMM and Chandra over a 2.4 yr span
reveals no significant change in its spin period. The 2 sigma upper limit on
the period derivative leads, in the dipole spin-down formalism, to an energy
loss rate E-dot < 7e33 ergs/s, surface magnetic field strength B_p < 1.5e11 G,
and characteristic age tau_c = P/2P-dot > 8 Myr. This tau_c exceeds the age of
the SNR by 3 orders of magnitude, implying that the pulsar was born spinning at
its current period. However, the X-ray luminosity of PSR J1852+0040, L(bol) ~
3e33(d/7.1 kpc)^2 ergs/s is a large fraction of E-dot, which challenges the
rotation-powered assumption. Instead, its high blackbody temperature,
0.46+/-0.04 keV, small blackbody radius ~ 0.8 km, and large pulsed fraction, ~
80%, may be evidence of accretion onto a polar cap, possibly from a fallback
disk made of supernova debris. If B_p < 1e10 G, an accretion disk can penetrate
the light cylinder and interact with the magnetosphere while resulting torques
on the neutron star remain within the observed limits. A weak B-field is also
inferred in another CCO, the 424-ms pulsar 1E 1207.4-5209, from its steady spin
and soft X-ray absorption lines. We propose this origin of radio-quiet CCOs:
the B-field, derived from a turbulent dynamo, is weaker if the NS is formed
spinning slowly, which enables it to accrete SN debris. Accretion excludes
neutron stars born with both B_p 0.1 s from radio pulsar
surveys, where B_p
40 Myr) or recycled pulsars. Finally, such a CCO, if born in SN 1987A, could
explain the non-detection of a pulsar there.Comment: 8 pages, 3 figures, to appear in The Astrophysical Journa
Incorporating Tobacco Cessation with Health Promotion Activities in a Psychosocial Rehabilitation Clubhouse
Many people with Severe Mental Illness (SMI) use smoking to manage symptoms, stress, or increase social contact, and consume nearly half of all tobacco sold in the US. Compared with the general population, individuals with SMI are at greater risk of co-morbid health problems and premature death. Often individuals with SMI are unaware that services like Quitlines, Nicotine Anonymous (NIC-A) meetings, and/or NRT exist. To compound matters, many states (e.g. Massachusetts) have cut tobacco cessation funding, and few programs provide integrated approaches to tobacco cessation in mental health settings that include peer supports. The lack of services and large disparities in smoking rates and health outcomes in people with SMI have resulted in a national crisis. There is a need to implement and evaluate cost-effective interventions that attempt to decrease morbidity and mortality associated with tobacco use among people with SMI. Our efforts engage this population in integrating a manualized tobacco control intervention, âLearning About Healthy Livingâ (LAHL) and training in use of Breath Carbon Monoxide (CO Meters) to track the progress of tobacco use among members and staff in the Clubhouse Model. Our project joins experts in tobacco dependence treatment for adults with SMI from UMass with leaders in the Clubhouse Model from Genesis Club in Worcester, MA
An ASCA Study of the W51 Complex
We present the analysis of ASCA archival data from the Galactic source W51.
The ASCA spectra show that the soft (kT<= 2.5 keV) X-rays are of thermal origin
and are compatible with W51C being a single, isothermal (kT~0.3 keV) supernova
remnant at the far-side of the Sagittarius arm. The ASCA images reveal hard
(kT>=2.5 keV) X-ray sources which were not seen in previous X-ray observations.
Some of these sources are coincident with massive star-forming regions and the
spectra are used to derive X-ray parameters. By comparing the X-ray absorbing
column density with atomic hydrogen column density, we infer the location of
star-forming regions relative to molecular clouds. There are unidentified hard
X-ray sources superposed on the supernova remnant and we discuss the
possibility of their association.Comment: 13 pages, 11 figures, to be published in Astronomical Journa
- âŠ