The Origin of the Initial Mass Function

We review recent advances in our understanding of the origin of the initial mass function (IMF). We emphasize the use of numerical simulations to investigate how each physical process involved in star formation affects the resulting IMF. We stress that it is insufficient to just reproduce the IMF, but that any successful model needs to account for the many observed properties of star forming regions including clustering, mass segregation and binarity. Fragmentation involving the interplay of gravity, turbulence, and thermal effects is probably responsible for setting the characteristic stellar mass. Low-mass stars and brown dwarfs can form through the fragmentation of dense filaments and disks, possibly followed by early ejection from these dense environments which truncates their growth in mass. Higher-mass stars and the Salpeter-like slope of the IMF are most likely formed through continued accretion in a clustered environment. The effects of feedback and magnetic fields on the origin of the IMF are still largely unclear. Lastly, we discuss a number of outstanding problems that need to be addressed in order to develop a complete theory for the origin of the IMF.Comment: PPV conference paper, 16 pages, 11 figur

Formation of toxaphene-like contaminants during simulated paper pulp bleaching

Toxaphene is a persistent pesticide which is highly toxic to a broad range of organisms including freshwater fish. The sources of Toxaphene are still not clearly understood. Atmospheric transport from the cotton growing districts of the southeastern United States is presently considered the most plausible hypothesis. This mechanism, however, does not adequately explain all of the data on Toxaphene concentrations in different geographical regions of the U.S. In particular, concentrations in the immediate vicinity of the Great Lakes have been increasing, whereas decreases have been observed at Midwestern sites not near these lakes. It is conceivable that environmental chlorination reactions, not involving the manufacture or application of Toxaphene at all, may be generating materials closely related to or indistinguishable from Toxaphene. The objective of our research was to simulate pulp bleaching conditions in the laboratory and determine if Toxaphene-like materials could be produced. The aqueous chlorination of the monoterpenes, camphene, limonene, apinene and 8-pinene produced complex polychlorinated product mixtures. The extent of chlorination was primarily dependent on pH and light conditions. At pH 2 and exposed to sunlight product mixtures were obtained that had striking similarities to Toxaphene. At higher pH or in the dark, less extensive but still substantial chlorination took place; these lower chlorinated compounds could be mistaken for biologically degraded Toxaphene in environmental samples. We conclude that Toxaphene-like mixtures may conceivably be formed under environmental conditions, but the actual extent of formation of such mixtures and the degree to which they may contribute to apparent Toxaphene in natural samples remain to be assessed.U.S. Department of the InteriorU.S. Geological SurveyOpe

Observing IMBH-IMBH Binary Coalescences via Gravitational Radiation

Recent numerical simulations have suggested the possibility of forming double intermediate mass black holes (IMBHs) via the collisional runaway scenario in young dense star clusters. The two IMBHs formed would exchange into a common binary shortly after their birth, and quickly inspiral and merge. Since space-borne gravitational wave (GW) observatories such as LISA will be able to see the late phases of their inspiral out to several Gpc, and LIGO will be able to see the merger and ringdown out to similar distances, they represent potentially significant GW sources. In this Letter we estimate the rate at which LISA and LIGO will see their inspiral and merger in young star clusters, and discuss the information that can be extracted from the observations. We find that LISA will likely see tens of IMBH--IMBH inspirals per year, while advanced LIGO could see ~10 merger and ringdown events per year, with both rates strongly dependent on the distribution of cluster masses and densities.Comment: Accepted for publication in ApJL. Minor changes to reflect accepted version. 4 pages in emulateapj, 3 figure

Geology of the Millers River Delta

Guidebook for field trips in southwestern New Hampshire, southeastern Vermont, and north-central Massachusetts: New England Intercollegiate Geological Conference, 80th annual meeting, October 14, 15 and 16, 1988, Keene, New Hampshire: Trip B-

Forest and Soil Studies in Southern Iowa

This paper deals with the present forest lands in southern Iowa counties, giving their relations to topography, soils and settlement; setting forth their local distribution, variations and condition; the depletion due to intensive culling and grazing and the responses of the trees in form and growth to slope, aspect and soil characters. Laboratory analyses have been made of different soil types which support the native trees and efforts will be made to correlate soil depth and quality with form and rate of growth of the trees. The report includes data on age classes and stand densities in that region

Using Partial Queue-Length Information to Improve the Queue Inference Engine's Performance

The Queue Inference Engine (QIE) uses queue departure time data over a single congestion period to infer queue statistics. With partial queue-length information, the queue statistics become more accurate and the computational burden is reduced. We first consider the case in which we are given that the queue length never exceeded a given length L. We then consider the more general case in which we are given the times of all L-to-(L + 1) and (L + 1)-to-L queue-length transitions. We present algorithms, parallel to the QIE algorithms,for deriving the queue statistics under the new conditioning information. We also present computational results, comparing both accuracy and computation time, under the QIE and the new algorithms, for several sample runs

Prognosis and Therapy When Acute Promyelocytic Leukemia and Other “Good Risk” Acute Myeloid Leukemias Occur as a Therapy-Related Myeloid Neoplasm

Treatment for a pre-existing condition using chemotherapy, radiation therapy, immunosuppressive therapy, or a combination of these modalities may lead to the devastating complication of therapy-related myelodysplastic syndrome or acute myeloid leukemia (t-MDS/t-AML), collectively known as therapy-related myeloid neoplasm (t-MN). This disorder arises as a direct consequence of mutational events induced by the primary treatment. The outcomes for these patients have been historically poor compared to people who develop AML de novo. Currently comprising 10–20% of all cases of AML, t-MN is relatively resistant to conventional leukemia therapies, and is associated with s ort survival times. Median life expectancy from diagnosis is about 8–10 months in most series. Although the spectrum of cytogenetic abnormalities in t-AML is similar to AML de novo, the frequency of unfavorable cytogenetics, such as a complex karyotype or deletion or loss of chromosomes 5 and/or 7, is considerably higher in t-MN. Two distinct groups of patients with t-MN have been described. The more common subtype, seen in about 75% of patients, typically occurs 5–7 years after first exposure to alkylating agents or radiation, is often preceded by a myelodysplastic syndrome (MDS), and is frequently accompanied by clonal cytogenetic abnormalities such as the loss of all or part of chromosomes 5 or 7. Mutations of the P53 tumor suppressor gene are also common. The risk is related to total cumulative exposure over time to alkylating agents. In contrast, among individuals who develop t-AML after treatment with topoisomerase II inhibitors, the latency period to the development of t-AML is often only 1–3 years, antecedent MDS is rare, and gene rearrangements involving MLL at 11q23 or RUNX1/AML1 at 21q22 are common. It is now well recognized that APL and other subtypes of AML with balanced translocations sometimes occur as therapy-related myeloid neoplasms (t-MN) in patients who have previously received cytotoxic therapy or ionizing radiation therapy (RT). The most of this review will focus on these “good risk” leukemias, i.e. those with APL or inv(16)/t(16;16) or t(8;21)

High-angle-of-attack pneumatic lag and upwash corrections for a hemispherical flow direction sensor

As part of the NASA F-14 high angle of attack flight test program, a nose mounted hemispherical flow direction sensor was calibrated against a fuselage mounted movable vane flow angle sensor. Significant discrepancies were found to exist in the angle of attack measurements. A two fold approach taken to resolve these discrepancies during subsonic flight is described. First, the sensing integrity of the isolated hemispherical sensor is established by wind tunnel data extending to an angle of attack of 60 deg. Second, two probable causes for the discrepancies, pneumatic lag and upwash, are examined. Methods of identifying and compensating for lag and upwash are presented. The wind tunnel data verify that the isolated hemispherical sensor is sufficiently accurate for static conditions with angles of attack up to 60 deg and angles of sideslip up to 30 deg. Analysis of flight data for two high angle of attack maneuvers establishes that pneumatic lag and upwash are highly correlated with the discrepancies between the hemispherical and vane type sensor measurements