1,600 research outputs found
The Testing of Coniferous Tree Seeds at the School of Forestry, Yale University, 1906-1926
Quality in forest tree seed centers in (a) origin; (b) genuineness; (c) purity; and (d) viability. The purchaser should insist on knowing the origin of the seed and the locality where it was collected.
Without seed testing establishments for investigating forest tree seeds by standardized methods under an established technique, nurserymen and foresters will continue to sow seed beds and undertake direct seeding without an adequate knowledge of the origin, genuineness, purity, and viability of the seeds used
GaAs/GaAlAs distributed Bragg reflector laser with a focused ion beam, low dose dopant implanted grating
We report, for the first time, the performance of a GaAs/GaAlAs distributed Bragg reflector (DBR) laser using a focused ion beam implanted grating (FIB‐DBR). Stripes of Si+ + with a period of 2300 Å and a dose ∼1014 cm−2 are directly implanted into the passive large optical cavity layer to provide the distributed feedback. Surface‐emitting light from the second‐order grating is observed. Threshold current of 110 mA and single DBR mode operation from 20 to 40 °C are obtained. The wavelength tuning rate with temperature is 0.8 Å/°C. The coupling coefficient is estimated to be 15 cm−1. The results show that FIB technology is practical for distributed feedback and DBR lasers and optoelectronic integrated circuits
Large spatial variations in the flux balance along the front of a Greenland tidewater glacier
The frontal flux balance of a medium-sized tidewater glacier in western
Greenland in the summer is assessed by quantifying the individual components
(ice flux, retreat, calving, and submarine melting) through a combination of
data and models. Ice flux and retreat are obtained from satellite data.
Submarine melting is derived using a high-resolution ocean model informed by
near-ice observations, and calving is estimated using a record of calving
events along the ice front. All terms exhibit large spatial variability along
the ∼ 5 km wide ice front. It is found that submarine melting accounts
for much of the frontal ablation in small regions where two subglacial
discharge plumes emerge at the ice front. Away from the subglacial plumes,
the estimated melting accounts for a small fraction of frontal ablation.
Glacier-wide, these estimates suggest that mass loss is largely controlled by
calving. This result, however, is at odds with the limited presence of
icebergs at this calving front – suggesting that melt rates in regions
outside of the subglacial plumes may be underestimated. Finally, we argue
that localized melt incisions into the glacier front can be significant
drivers of calving. Our results suggest a complex interplay of melting and
calving marked by high spatial variability along the glacier front.</p
X-ray observations of Be/X-ray binaries in the SMC
(shortened) Fifteen Be/X-ray binaries and candidates in the SMC were observed
serendipitously with the EPIC instruments of XMM-Newton during two observations
of SNR 0047-73.5 and SNR 0103-72.6 in October 2000. A total of twelve of those
sources are detected. For eleven of them an accurate position and in part
detection of X-ray pulsations support the proposed identification as Be/X-ray
binaries. The detection of pulsations (172.2 s, 320.1 s and 751 s) from three
hard X-ray sources with periods known from ASCA observations confirm their
proposed identifications with ROSAT sources and their optical Be star
counterparts. In addition, pulsations with a period of 263.6 s were found from
XMMUJ004723.7-731226=RXJ0047.3-7312. For SAXJ0103.2-7209 a pulse period of
341.20.5 s was determined, continuing the large spin-up seen with ASCA,
BeppoSAX and Chandra between 1996 and 1999 with a period derivative of 1.6 s
yr covering now 4.5 years. The 0.3-10.0 keV EPIC spectra of all eleven
Be/X-ray binaries and candidates are consistent with power-law energy
distributions with derived photon indices strongly peaked at 1.00 with a
standard deviation of 0.16. No pulsations are detected from RXJ0049.2-7311 and
RXJ0049.5-7310 (both near the 9 s pulsar AXJ0049-732) and RXJ0105.1-7211 (near
AXJ0105-722, which may pulsate with 3.3 s), leaving the identification of the
ASCA sources with ROSAT and corresponding XMM-Newton objects still unclear. We
present an updated list of high mass X-ray binaries (HMXBs) and candidates in
the SMC incorporating improved X-ray positions obtained from Chandra and
XMM-Newton observations. Including the results from this work and recent
publications the SMC HMXB catalogue comprises 65 objects with at least 37
showing X-ray pulsations.Comment: 10 pages, 7 figures, accepted for publication in A&
Designing electronic collaborative learning environments
Electronic collaborative learning environments for learning and working are in vogue. Designers design them according to their own constructivist interpretations of what collaborative learning is and what it should achieve. Educators employ them with different educational approaches and in diverse situations to achieve different ends. Students use them, sometimes very enthusiastically, but often in a perfunctory way. Finally, researchers study them and—as is usually the case when apples and oranges are compared—find no conclusive evidence as to whether or not they work, where they do or do not work, when they do or do not work and, most importantly, why, they do or do not work. This contribution presents an affordance framework for such collaborative learning environments; an interaction design procedure for designing, developing, and implementing them; and an educational affordance approach to the use of tasks in those environments. It also presents the results of three projects dealing with these three issues
1965: Abilene Christian College Bible Lectures - Full Text
LIFT UP YOUR EYES”
Being the Abilene Christian College Annual Bible Lectures 1965
Price: $3.95
Published by
ABILENE CHRISTIAN COLLEGE STUDENTS EXCHANGE
ACC Station Abilene. Texa
A Dodecalogue of Basic Didactics from Applications of Abstract Differential Geometry to Quantum Gravity
We summarize the twelve most important in our view novel concepts that have
arisen, based on results that have been obtained, from various applications of
Abstract Differential Geometry (ADG) to Quantum Gravity (QG). The present
document may be used as a concise, yet informal, discursive and peripatetic
conceptual guide-cum-terminological glossary to the voluminous technical
research literature on the subject. In a bonus section at the end, we dwell on
the significance of introducing new conceptual terminology in future QG
research by means of `poetic language'Comment: 16 pages, preliminary versio
The Public Health Impact of Coccidioidomycosis in Arizona and California
The numbers of reported cases of coccidioidomycosis in Arizona and California have risen dramatically over the past decade, with a 97.8% and 91.1% increase in incidence rates from 2001 to 2006 in the two states, respectively. Of those cases with reported race/ethnicity information, Black/African Americans in Arizona and Hispanics and African/Americans in California experienced a disproportionately higher frequency of disease compared to other racial/ethnic groups. Lack of early diagnosis continues to be a problem, particularly in suspect community-acquired pneumonia, underscoring the need for more rapid and sensitive tests. Similarly, the inability of currently available therapeutics to reduce the duration and morbidity of this disease underscores the need for improved therapeutics and a preventive vaccine
Interferometric imaging with the 32 element Murchison Wide-field Array
The Murchison Wide-field Array (MWA) is a low frequency radio telescope,
currently under construction, intended to search for the spectral signature of
the epoch of re-ionisation (EOR) and to probe the structure of the solar
corona. Sited in Western Australia, the full MWA will comprise 8192 dipoles
grouped into 512 tiles, and be capable of imaging the sky south of 40 degree
declination, from 80 MHz to 300 MHz with an instantaneous field of view that is
tens of degrees wide and a resolution of a few arcminutes. A 32-station
prototype of the MWA has been recently commissioned and a set of observations
taken that exercise the whole acquisition and processing pipeline. We present
Stokes I, Q, and U images from two ~4 hour integrations of a field 20 degrees
wide centered on Pictoris A. These images demonstrate the capacity and
stability of a real-time calibration and imaging technique employing the
weighted addition of warped snapshots to counter extreme wide field imaging
distortions.Comment: Accepted for publication in PASP. This is the draft before journal
typesetting corrections and proofs so does contain formatting and journal
style errors, also has with lower quality figures for space requirement
Streptococcal necrotising fasciitis from diverse strains of Streptococcus pyogenes in tropical northern Australia: case series and comparison with the literature
BACKGROUND: Since the mid-1980's there has been a worldwide resurgence of severe disease from group A streptococcus (GAS), with clonal clusters implicated in Europe and the United States. However GAS associated sepsis and rheumatic fever have always remained at high levels in many less developed countries. In this context we aimed to study GAS necrotising fasciitis (NF) in a region where there are high background rates of GAS carriage and disease. METHODS: We describe the epidemiology, clinical and laboratory features of 14 consecutive cases of GAS NF treated over a seven year period from tropical northern Australia. RESULTS: Incidence rates of GAS NF in the Aboriginal population were up to five times those previously published from other countries. Clinical features were similar to those described elsewhere, with 7/14 (50%) bacteremic and 9/14 (64%) having associated streptococcal toxic shock syndrome. 11/14 (79%) had underlying chronic illnesses, including all four fatalities (29% mortality overall). Important laboratory differences from other series were that leukocytosis was absent in 9/14 (64%) but all had substantial lymphopenia. Sequence typing of the 14 NF-associated GAS isolates showed no clonality, with only one emm type 1 and two emm type 3 strains. CONCLUSIONS: While NF clusters can occur from a single emergent GAS clone, this was not evident in our tropical region, where high rates of NF parallel high overall rates of GAS infection from a wide diversity of strains. The specific virulence factors of GAS strains which do cause NF and the basis of the inadequate host response in those patients who develop NF on infection with these GAS require further elucidation
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