220 research outputs found
Post processing of additively manufactured metal parts by using pulse electrochemical machining
In response of the growing demand for higher product requirements concerning quality, durability and efficiency by simultaneously decreasing product life cycles, the product development has to consider suitable production technologies at an early stage of the development process. This implicates also the choice of new manufacturing or technology approaches. Additively manufactured parts can be produced with a high geometrical complexity. To produce such geometrically complex parts from metal, the so called selective laser melting (SLM) technology is often the method of choice. In order to produce SLM-parts, support structures have to be used. They have several functions, such as connecting the component to a building platform, supporting overhanging and tilted areas but they also dissipate the heat of fusion. However, those support structures have to be removed for the use of the component, which often involves numerous time- consuming and difficult to automatize operation steps. A promising alternative can be pulse electrochemical machining (PECM) as there is no contact between tool and workpiece. This allows the adaption of the tool to complex geometries and the improvement of the workpiece surface quality in one machining step. Therefore, a fundamental study of the electrochemical dissolution behavior and machinability aspects of the support structures is performed
Latency hiding in parallel systems: a quantitative approach
In many parallel applications, network latency causes a dramatic
loss in processor utilization. This paper examines software
pipelining as a technique for network latency hiding. It
quantifies the potential improvements with
detailed,instruction-level simulations.
The benchmarks used are the Livermore Loop kernels and BLAS Level
1.
These were parallelized and run on the instruction-level RISC
simulator DLX, extended with both a blocking and a pipelined
network. Our results show that prefetch in a pipelined network
improves performance by a factor of 2 to 9, provided the network
has sufficient bandwidth to accept at least 10 requests per
processor
Efficient parallel computation on workstation clusters
We present novel hard- and software that efficiently implements
communication primitives for parallel execution on Workstation
clusters. We provide low communication latencies, minimal protocol,
zero operating system overhead, and high throughput. With this
technology, it is possible to build effective parallel systems
using off-the-shelf workstations. Our goal is to develop a standard
interfaceboard and the necessary software for interfacing any
number of computers, from a workstation to a cabinet full of
workstation-boards
SOFIA/FORCAST and Spitzer/IRAC Imaging of the Ultra Compact H II Region W3(OH) and Associated Protostars in W3
We present infrared observations of the ultra-compact H II region W3(OH) made
by the FORCAST instrument aboard SOFIA and by Spitzer/IRAC. We contribute new
wavelength data to the spectral energy distribution, which constrains the
optical depth, grain size distribution, and temperature gradient of the dusty
shell surrounding the H II region. We model the dust component as a spherical
shell containing an inner cavity with radius ~ 600 AU, irradiated by a central
star of type O9 and temperature ~ 31,000 K. The total luminosity of this system
is 71,000 L_solar. An observed excess of 2.2 - 4.5 microns emission in the SED
can be explained by our viewing a cavity opening or clumpiness in the shell
structure whereby radiation from the warm interior of the shell can escape. We
claim to detect the nearby water maser source W3 (H2O) at 31.4 and 37.1 microns
using beam deconvolution of the FORCAST images. We constrain the flux densities
of this object at 19.7 - 37.1 microns. Additionally, we present in situ
observations of four young stellar and protostellar objects in the SOFIA field,
presumably associated with the W3 molecular cloud. Results from the model SED
fitting tool of Robitaille et al. (2006, 2007} suggest that two objects (2MASS
J02270352+6152357 and 2MASS J02270824+6152281) are intermediate-luminosity (~
236 - 432 L_solar) protostars; one object (2MASS J02270887+6152344) is either a
high-mass protostar with luminosity 3000 L_solar or a less massive young star
with a substantial circumstellar disk but depleted envelope; and one object
(2MASS J02270743+6152281) is an intermediate-luminosity (~ 768 L_solar)
protostar nearing the end of its envelope accretion phase or a young star
surrounded by a circumstellar disk with no appreciable circumstellar envelope.Comment: 12 pages, 8 figures, 2 tables, accepted by Ap
Spitzer, Near-Infrared, and Submillimeter Imaging of the Relatively Sparse Young Cluster, Lynds 988e
We present {\it Spitzer} images of the relatively sparse, low luminosity
young cluster L988e, as well as complementary near-infrared (NIR) and
submillimeter images of the region. The cluster is asymmetric, with the western
region of the cluster embedded within the molecular cloud, and the slightly
less dense eastern region to the east of, and on the edge of, the molecular
cloud. With these data, as well as with extant H data of stars
primarily found in the eastern region of the cluster, and a molecular CO
gas emission map of the entire region, we investigate the distribution of
forming young stars with respect to the cloud material, concentrating
particularly on the differences and similarities between the exposed and
embedded regions of the cluster. We also compare star formation in this region
to that in denser, more luminous and more massive clusters already investigated
in our comprehensive multi-wavelength study of young clusters within 1 kpc of
the Sun.Comment: 21 pages, 6 tables, 13 figures. Full resolution figures at:
http://astro.pas.rochester.edu/~tom/Preprints/L988e.pd
First Science Observations with SOFIA/FORCAST: Properties of Intermediate-Luminosity Protostars and Circumstellar Disks in OMC-2
We examine eight young stellar objects in the OMC-2 star forming region based
on observations from the SOFIA/FORCAST early science phase, the Spitzer Space
Telescope, the Herschel Space Observatory, 2MASS, APEX, and other results in
the literature. We show the spectral energy distributions of these objects from
near-infrared to millimeter wavelengths, and compare the SEDs with those of
sheet collapse models of protostars and circumstellar disks. Four of the
objects can be modelled as protostars with infalling envelopes, two as young
stars surrounded by disks, and the remaining two objects have double-peaked
SEDs. We model the double-peaked sources as binaries containing a young star
with a disk and a protostar. The six most luminous sources are found in a dense
group within a 0.15 x 0.25 pc region; these sources have luminosities ranging
from 300 L_sun to 20 L_sun. The most embedded source (OMC-2 FIR 4) can be fit
by a class 0 protostar model having a luminosity of ~50 L_sun and mass infall
rate of ~10^-4 solar masses per year.Comment: Accepted by ApJ Letter
HCMV-infection in a human arterial organ culture model: effects on cell proliferation and neointimal hyperplasia
<p>Abstract</p> <p>Background</p> <p>The impact of infections with the human cytomegalovirus (HCMV) for the development of atherosclerosis and restenosis is still unclear. Both a clear correlation and no correlation at all have been reported in clinical, mostly serological studies. In our study we employed a human non-injury ex vivo organ culture model to investigate the effect of an in vitro permissive HCMV-infection on cell proliferation and neointimal hyperplasia for a period of 56 days.</p> <p>Results</p> <p>During routine-nephrectomies parts of renal arteries from 71 patients were obtained and prepared as human organ cultures. Cell free HCMV infection was performed with the fibroblast adapted HCMV strain AD169, the endotheliotropic strain TB40E, and a clinical isolate (AN 365). After 3, 7, 14, 21, 28, 35, and 56 days in culture staining of HCMV-antigens was carried out and reactive cell proliferation and neointimal thickening were analysed. Successful HCMV-infection was accomplished with all three virus strains studied. During the first 21 days in organ culture no cell proliferation or neointimal hyperplasia was detected. At day 35 and day 56 moderate cell proliferation and neointimal hyperplasia was found both in HCMV-infected segments and mock infected controls. Neointimal hyperplasia in productively HCMV-infected segments was lower than in non infected at day 35 and day 56, but relatively higher after infection with the endotheliotropic TB40E in comparison with the two other strains.</p> <p>Conclusion</p> <p>The data do not support the hypothesis that HCMV-infection triggers restenosis via a stimulatory effect on cell proliferation and neointimal hyperplasia in comparison to non infected controls. Interestingly however, even after lytic infection, a virus strain specific difference was observed.</p
CCAT-prime: a novel telescope for submillimeter astronomy
The CCAT-prime telescope is a 6-meter aperture, crossed-Dragone telescope,
designed for millimeter and sub-millimeter wavelength observations. It will be
located at an altitude of 5600 meters, just below the summit of Cerro
Chajnantor in the high Atacama region of Chile. The telescope's unobscured
optics deliver a field of view of almost 8 degrees over a large, flat focal
plane, enabling it to accommodate current and future instrumentation fielding
>100k diffraction-limited beams for wavelengths less than a millimeter. The
mount is a novel design with the aluminum-tiled mirrors nested inside the
telescope structure. The elevation housing has an integrated shutter that can
enclose the mirrors, protecting them from inclement weather. The telescope is
designed to co-host multiple instruments over its nominal 15 year lifetime. It
will be operated remotely, requiring minimum maintenance and on-site activities
due to the harsh working conditions on the mountain. The design utilizes
nickel-iron alloy (Invar) and carbon-fiber-reinforced polymer (CFRP) materials
in the mirror support structure, achieving a relatively temperature-insensitive
mount. We discuss requirements, specifications, critical design elements, and
the expected performance of the CCAT-prime telescope. The telescope is being
built by CCAT Observatory, Inc., a corporation formed by an international
partnership of universities. More information about CCAT and the CCAT-prime
telescope can be found at www.ccatobservatory.org.Comment: Event: SPIE Astronomical Telescope + Instrumentation, 2018, Austin,
Texas, USA; Proceedings Volume 10700, Ground-based and Airborne Telescopes
VII; 107005X (2018
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