6,743 research outputs found
Use of acrylic sheet molds for elastomeric products
Molds constructed of acrylic sheet are more easily machined than metal, are transparent to ensure complete filling during injection, and have smooth surfaces free of contamination. Technique eliminates flashing on molded parts and mold release agents
Evaluation of equilibrium moisture content in ligno-cellulosic residues of olive culture
The use of ligno-cellulosic residuals from agriculture as means for renewable energy production is well known; nonetheless significant problems still exist on development of bioenergy value chains. Moisture content and hygroscopicity are among these problems. Higher moisture content of the biomass means lower calorific value and higher perishability, hence storage difficulties. For this reason it is important to evaluate how the moisture content of the material varies while it is stored and how the calorific value of the feedstock is affected by it. The purpose of this study is to determine the variation of moisture content and its influence on lower calorific value (LCV) of four types of solid residual biomass: oven dried chipped olive tree trimmings, milled olive pomace; oven dried olive tree trimmings and fresh olive tree trimmings. Moisture content of the samples is calculated by means of thermogravimetric analysis (TGA) according to standard CEN/TS 14774-2:2004, while the LCVs are calculated by means of a calorimeter, following standard UNI EN 14918:2010. All the biomass samples were left to reach equilibrium moisture content (EMC) in a temperature and humidity controlled environment. Two different phases were analyzed with respect to moisture uptake rates: 1) fast moisture uptake rate phase (first four hours of exposure) and 2) slow moisture uptake rate, (the days following the first four hours of exposure). Samples experiencing fast moisture uptake rate, during the first four hours of exposure, were kept in a monitored ambient at T=22 \ub1 1oC and RH=59 \ub1 2%, while samples exposed to slow moisture uptake rate were kept in a climatic chamber at three different set of temperature and humidity controlled environment simulating the climatic conditions in different periods of the year in Enna province: 10oC - 80% RH (winter), 15oC - 70% RH (spring/autumn) and 20oC - 55% RH, (summer). The results obtained show that the olive pruning chips (0.425 mm to 1.00 mm and 1.00 mm to 2.00 mm particle size ranges) stored in a heap in a controlled climatic chamber require approximately 20 days to reach EMC. Depending on the particle size range EMCs reach the values of 6.2 and 7.5% by weight in the "summer" condition, 14.3% and 16.9% in "spring/autumn" condition, 24.1% and 28.2% in "winter" condition. Moisture is absorbed gradually over time and results show that in the first four hours, the dry sample exposed to ambient condition (T=22 \ub1 1 oC and RH=59 \ub1 2%) reaches a moisture content between 0.75 and 0.96% of its weight; the LCV at equilibrium is evaluated between 18, 576 J\u2022odg-1 and 18, 793 J\u2022odg-1, the higher value related to the bigger particle size range examined. Pomace heap under the same experimental set up and time period, reaches an equilibrium moisture content of 8.5% and 9.7% (summer conditions), 19.2% and 22.0% (spring/autumn condition) and between 30.9% and 34.1% (winter condition). Olive pomace accumulates moisture relatively faster than olive trimmings as dry sample recovers about 1.61% to 1.97% of moisture in the first four hours of exposure. The LCV at equilibrium is determined between 20, 145 J\u2022odg-1 and 20, 436 J\u2022odg-1. Pruning dried samples reach an EMC equal to 6.1% in approximately 25 days, with a LCV equal to18, 921 J\u2022odg-1 \ub1 1.9%. Heaps of fresh prunings reach an EMC of 8.2% in approximately 20 days; LCV of the feedstock is 19, 356 J\u2022odg-1\ub1 1.6%.\ua92006-2014 Asian Research Publishing Network (ARPN). All rights reserved
HST/NICMOS observations of the GLIMPSE9 stellar cluster
We present HST/NICMOS photometry, and low-resolution K-band spectra of the
GLIMPSE9 stellar cluster. The newly obtained color-magnitude diagram shows a
cluster sequence with H-Ks =1 mag, indicating an interstellar extinction
Aks=1.6\pm0.2 mag. The spectra of the three brightest stars show deep CO
band-heads, which indicate red supergiants with spectral type M1-M2. Two 09-B2
supergiants are also identified, which yield a spectrophotometric distance of
4.2\pm0.4 kpc. Presuming that the population is coeval, we derive an age
between 15 and 27 Myr, and a total cluster mass of 1600\pm400 Msun, integrated
down to 1 Msun. In the vicinity of GLIMPSE9 are several HII regions and SNRs,
all of which (including GLIMPSE 9) are probably associated with a giant
molecular cloud (GMC) in the inner galaxy. GLIMPSE9 probably represents one
episode of massive star formation in this GMC. We have identified several other
candidate stellar clusters of the same complex.Comment: 13 pages, 14 figures. accepted for publication in ApJ. A version with
high-resolution figures can be found at the following location
ftp://ftp.rssd.esa.int/pub/mmessine/ms.pdf New version with updated
reference
Massive stars in the Cl 1813-178 Cluster. An episode of massive star formation in the W33 complex
Young massive (M >10^4 Msun) stellar clusters are a good laboratory to study
the evolution of massive stars. Only a dozen of such clusters are known in the
Galaxy. Here we report about a new young massive stellar cluster in the Milky
Way. Near-infrared medium-resolution spectroscopy with UIST on the UKIRT
telescope and NIRSPEC on the Keck telescope, and X-ray observations with the
Chandra and XMM satellites, of the Cl 1813-178 cluster confirm a large number
of massive stars. We detected 1 red supergiant, 2 Wolf-Rayet stars, 1 candidate
luminous blue variable, 2 OIf, and 19 OB stars. Among the latter, twelve are
likely supergiants, four giants, and the faintest three dwarf stars. We
detected post-main sequence stars with masses between 25 and 100 Msun. A
population with age of 4-4.5 Myr and a mass of ~10000 Msun can reproduce such a
mixture of massive evolved stars. This massive stellar cluster is the first
detection of a cluster in the W33 complex. Six supernova remnants and several
other candidate clusters are found in the direction of the same complex.Comment: 11 Figures. Accepted for publication in Ap
Models of the Sociology Minor at Institutions of Higher Education in the United States
Although the structure and content of the sociology major has been addressed by a variety of scholars and several American Sociological Association (ASA) task forces over the past three decades, the structure, content, and even the purpose of the sociology minor has been ignored. In this article, we address this gap in the literature through two investigations. The first utilizes an examination of the websites and academic handbooks of 248 bachelor’s degree-granting institutions to discern the structure and contents of the sociology minor. We identify four models for the sociology minor found in U.S. higher education. The second study utilizes data gathered through the ASA 2019–2020 Department Survey. Included in the survey were a variety of questions regarding department chairs’ perceptions of the sociology minor. We conclude by suggesting that we should not only be concerned with what the sociology minor currently is but also consider what the minor could be
Detections of massive stars in the cluster MCM2005b77, in the star-forming regions GRS G331.3400.36 (S62) and GRS G337.9200.48 (S36)
Large infrared and millimeter wavelength surveys of the Galactic plane have
unveiled more than 600 new bubble HII regions and more than 3000 candidate star
clusters. We present a study of the candidate clusters MCM2005b72, DBS2003-157,
DBS2003-172, and MCM2005b77, based on near-infrared spectroscopy taken with
SofI on the NTT and infrared photometry from the 2MASS, VVV, and GLIMPSE
surveys. We find that (1) MCM2005b72 and DBS2003-157 are subregions of the same
star-forming region, HII GRS G331.34-00.36 (bubble S62). MCM2005b72 coincides
with the central part of this HII region, while DBS2003-157 is a bright
mid-infrared knot of the S62 shell. We detected two O-type stars at extinction
\Aks=1.0-1.3 mag. Their spectrophotometric properties are consistent with the
near-kinematic distance to GRS G331.34-00.36 of 3.9pm0.3 kpc. (2) DBS2003-172
coincides with a bright mid-infrared knot in the S36 shell (GRS G337.92-00.48),
where we detected a pair of candidate He I stars embedded in a small cometary
nebula. (3) The stellar cluster MCM2005b77 is rich in B-type stars, has an
average Aks of 0.91 mag, and is adjacent to the HII region IRAS 16137-5025. The
average spectrophotometric distance of kpc matches the
near-kinematic distance to IRAS 16137-5025 of 5.2pm0.1 kpc.Comment: 22 pages, 11 Figures, ApJ accepte
On the suitability of thermogravimetric balances for the study of biomass pyrolysis
In fixed-bed pyrolysis reactors, the stacking of sample particles often leads to higher yields of solid pyrolysis products (chars) than are obtained from other types of reactors. This phenomenon is particularly emphasised in thermogravimetric (TG) balances, which unlike many fixed-bed reactors, do not sweep gas through the stationary bed of pyrolysing sample. Gas is swept through the sample bed to reduce the residence time of tar vapours in close proximity to chars, which affects the extent to which these vapours will condense onto the surface of chars and repolymerise, thus increasing char yield. Depth of the sample bed affects this residence time, and thus affects char yield. In this work, the sensitivity of typical analyses of biomass thermogravimetry to variations in bed depth have been assessed. Results of these analyses, including product distributions, proximate compositions, and kinetic predictions, carried out on microcrystalline cellulose and birch wood hydrochar samples produced at temperatures ranging from 160 to 280 °C, have been shown to be sensitive to variations in bed depth, and it has been demonstrated that this sensitivity is amplified at higher heating rates and temperatures. Thus, when a single sample mass is used for any of these typical TG analyses, as is common in published literature, the results are not fundamental properties of the material tested but rather a product of the exact experimental design employed. Future work is needed to identify reactor and experimental design guidelines to minimise this sensitivity in fixed-bed reactors
Measurements of vacuum magnetic birefringence using permanent dipole magnets: the PVLAS experiment
The PVLAS collaboration is presently assembling a new apparatus (at the INFN
section of Ferrara, Italy) to detect vacuum magnetic birefringence (VMB). VMB
is related to the structure of the QED vacuum and is predicted by the
Euler-Heisenberg-Weisskopf effective Lagrangian. It can be detected by
measuring the ellipticity acquired by a linearly polarised light beam
propagating through a strong magnetic field. Using the very same optical
technique it is also possible to search for hypothetical low-mass particles
interacting with two photons, such as axion-like (ALP) or millicharged
particles (MCP). Here we report results of a scaled-down test setup and
describe the new PVLAS apparatus. This latter one is in construction and is
based on a high-sensitivity ellipsometer with a high-finesse Fabry-Perot cavity
() and two 0.8 m long 2.5 T rotating permanent dipole magnets.
Measurements with the test setup have improved by a factor 2 the previous upper
bound on the parameter , which determines the strength of the nonlinear
terms in the QED Lagrangian: T
95% c.l. Furthermore, new laboratory limits have been put on the inverse
coupling constant of ALPs to two photons and confirmation of previous limits on
the fractional charge of millicharged particles is given
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