392 research outputs found
Analysis of 3D Printer Schedule
With recent innovations in technology, 3D printing has become a rapidly expanding manufacturing method that is being used for a wide range of applications. Their ability to build parts layer by layer instead of cutting away initial material allows this method to have almost no wasted material, creating the potential for a much more efficient, cost effective process. In order to continue the growth of this manufacturing strategy, the performance of 3D printers need to be enhanced to ensure equal or higher quality of produced parts in comparison to other manufacturing methods that are more commonly used. One important part of the performance that is key to making high quality parts is the stability of the 3D printer’s frame. No matter how accurate the printer head is, if the structure moves while the printing process is taking place, the accuracy of the produced will be limited.
A detailed analysis was done to study the base corner bracket of the 3D printer structure that is used in the IME labs so that the part can be redesigned to reduce the frames motion. The original design for this part was 3D printed and was made out of ABS plastic. Even though the part seemed extremely strong, by using simulation software, it was found that while the printer is operating, this part can deform as much as 1.34*10^-4 mm at specific locations. By making this part out of 1/8 steel sheet metal, the same loads would cause this part to deform 1.54*10^-5 mm. This mean that the new design would allow for the deflection of this part to be reduced by almost 90%. This may not seem significant, however, 3D printers are able to print layers that are as thin as .001 . To give some perspective, a human hair is approximately .003 thick, so as one could imagine, when dealing with dimensions this small, any amount of improvement is advantageous.
In addition to analyzing the stability, a manufacturing process was established, and a scaling and economic analysis was conducted. The manufacturing process is simple and allows for minimal expertise needed in order to create a function part. Also it was found that with sheet metal only available up to ¼ thick, this design could most likely be used in 3D printers that are twice the size as the one in the IME labs. Lastly, the sheet metal design proved to be economically justifiable in many ways if produced in large quantities, however, the automation involved with 3D printing would most likely provide benefits that would require a much more detailed manufacturing process to be established to come to any realistic conclusions
Asynchronous timing and Doppler recovery in DSP based DPSK modems for fixed and mobile satellite applications
While conventional analog modems employ some kind of clock wave regenerator circuit for synchronous timing recovery, in sampled modem receivers the timing is recovered asynchronously to the incoming data stream, with no adjustment being made to the input sampling rate. All timing corrections are accomplished by digital operations on the sampled data stream, and timing recovery is asynchronous with the uncontrolled, input A/D system. A good timing error measurement algorithm is a zero crossing tracker proposed by Gardner. Digital, speech rate (2400 - 4800 bps) M-PSK modem receivers employing Gardner's zero crossing tracker were implemented and tested and found to achieve BER performance very close to theoretical values on the AWGN channel. Nyguist pulse shaped modem systems with excess bandwidth factors ranging from 100 to 60 percent were considered. We can show that for any symmetric M-PSK signal set Gardner's NDA algorithm is free of pattern jitter for any carrier phase offset for rectangular pulses and for Nyquist pulses having 100 percent excess bandwidth. Also, the Nyquist pulse shaped system is studied on the mobile satellite channel, where Doppler shifts and multipath fading degrade the pi/4-DQPSK signal. Two simple modifications to Gardner's zero crossing tracker enable it to remain useful in the presence of multipath fading
The 8Li Calibration Source for the Sudbury Neutrino Obervatory
A calibration source employing 8Li (t_1/2 = 0.838s) has been developed for
use with the Sudbury Neutrino Observatory (SNO). This source creates a spectrum
of beta particles with an energy range similar to that of the SNO 8B solar
neutrino signal. The source is used to test the SNO detector's energy response,
position reconstruction and data reduction algorithms. The 8Li isotope is
created using a deuterium-tritium neutron generator in conjunction with a 11B
target, and is carried to a decay chamber using a gas/aerosol transport system.
The decay chamber detects prompt alpha particles by gas scintillation in
coincidence with the beta particles which exit through a thin stainless steel
wall. A description is given of the production, transport, and tagging
techniques along with a discussion of the performance and application of the
source.Comment: 11 pages plus 9 figures, Sumbitted to Nuclear Instruments and Methods
Resourcing a Mosaic Force: Lesions from an Acquisition Wargame
Excerpt from the Proceedings of the Nineteenth Annual Acquisition Research SymposiumDARPA has an ambitious vision for Mosaic Warfare, conceived by its Strategic Technology Office (STO) leadership as both a warfighting concept and a means to greatly accelerate capability development and fielding. Although the success of Mosaic depends on DARPA advancing multiple technologies, the Mosaic vision is inherently more challenging to “transition” than is a program or technology. Anticipating this challenge, DARPA sponsored RAND to examine the opportunities and challenges associated with developing and fielding a Mosaic force under existing or alternative governance models and management processes, as would be required for the vision to move from DARPA to widespread acceptance by DoD. To this end, RAND designed and executed a policy game that immersed participants in the task of fielding a Mosaic and required them to operate within the authorities, responsibilities, and constraints of the existing and an alternative governance model. This article presents select findings on the capacity of the existing acquisition resourcing system (i.e., the Planning, Programming, Budgeting, and Execution [or PPBE] process) to exploit STO’s vision of Mosaic Warfare.Approved for public release; distribution is unlimited
Resourcing a Mosaic Force: Lessons from an Acquisition Wargame
Symposium PresentationApproved for public release; distribution is unlimited
Deuteron photo-disintegration with polarised photons in the energy range 30 - 50 MeV
The reaction d(\vec\gamma,np) has been studied using the tagged and polarised
LADON gamma ray beam at an energy 30 - 50 MeV to investigate the existence of
narrow dibaryonic resonances recently suggested from the experimental
measurements in a different laboratory. The beam was obtained by Compton
back-scattering of laser light on the electrons of the storage ring ADONE.
Photo-neutron yields were measured at five neutron angle \vartheta_n = 22,
55.5, 90, 125 and 157 degrees in the center of mass system.Our results do not
support the existence of such resonances.Comment: 16 pages, Latex, 22 figures, 1 table. Nucl. Phys. A to appea
A Candidate Young Massive Planet in Orbit around the Classical T Tauri Star CI Tau
The ~2 Myr old classical T Tauri star CI Tau shows periodic variability in
its radial velocity (RV) variations measured at infrared (IR) and optical
wavelengths. We find that these observations are consistent with a massive
planet in a ~9-day period orbit. These results are based on 71 IR RV
measurements of this system obtained over 5 years, and on 26 optical RV
measurements obtained over 9 years. CI Tau was also observed photometrically in
the optical on 34 nights over ~one month in 2012. The optical RV data alone are
inadequate to identify an orbital period, likely the result of star spot and
activity induced noise for this relatively small dataset. The infrared RV
measurements reveal significant periodicity at ~9 days. In addition, the full
set of optical and IR RV measurements taken together phase coherently and with
equal amplitudes to the ~9 day period. Periodic radial velocity signals can in
principle be produced by cool spots, hot spots, and reflection of the stellar
spectrum off the inner disk, in addition to resulting from a planetary
companion. We have considered each of these and find the planet hypothesis most
consistent with the data. The radial velocity amplitude yields an Msin(i) of
~8.1 M_Jup; in conjunction with a 1.3 mm continuum emission measurement of the
circumstellar disk inclination from the literature, we find a planet mass of
~11.3 M_Jup, assuming alignment of the planetary orbit with the disk.Comment: 61 pages, 13 figures, accepted for publication in The Astrophysical
Journa
A Planarity Test via Construction Sequences
Optimal linear-time algorithms for testing the planarity of a graph are
well-known for over 35 years. However, these algorithms are quite involved and
recent publications still try to give simpler linear-time tests. We give a
simple reduction from planarity testing to the problem of computing a certain
construction of a 3-connected graph. The approach is different from previous
planarity tests; as key concept, we maintain a planar embedding that is
3-connected at each point in time. The algorithm runs in linear time and
computes a planar embedding if the input graph is planar and a
Kuratowski-subdivision otherwise
Follow-Up Observations of PTFO 8-8695: A 3 MYr Old T-Tauri Star Hosting a Jupiter-mass Planetary Candidate
We present Spitzer 4.5\micron\ light curve observations, Keck NIRSPEC radial
velocity observations, and LCOGT optical light curve observations of
PTFO~8-8695, which may host a Jupiter-sized planet in a very short orbital
period (0.45 days). Previous work by \citet{vaneyken12} and \citet{barnes13}
predicts that the stellar rotation axis and the planetary orbital plane should
precess with a period of days. As a consequence, the observed
transits should change shape and depth, disappear, and reappear with the
precession. Our observations indicate the long-term presence of the transit
events ( years), and that the transits indeed do change depth, disappear
and reappear. The Spitzer observations and the NIRSPEC radial velocity
observations (with contemporaneous LCOGT optical light curve data) are
consistent with the predicted transit times and depths for the $M_\star = 0.34\
M_\odot$ precession model and demonstrate the disappearance of the transits. An
LCOGT optical light curve shows that the transits do reappear approximately 1
year later. The observed transits occur at the times predicted by a
straight-forward propagation of the transit ephemeris. The precession model
correctly predicts the depth and time of the Spitzer transit and the lack of a
transit at the time of the NIRSPEC radial velocity observations. However, the
precession model predicts the return of the transits approximately 1 month
later than observed by LCOGT. Overall, the data are suggestive that the
planetary interpretation of the observed transit events may indeed be correct,
but the precession model and data are currently insufficient to confirm firmly
the planetary status of PTFO~8-8695b.Comment: Accepted for publication in The Astrophysical Journa
Optical-Model Description of Time-Reversal Violation
A time-reversal-violating spin-correlation coefficient in the total cross
section for polarized neutrons incident on a tensor rank-2 polarized target is
calculated by assuming a time-reversal-noninvariant, parity-conserving
``five-fold" interaction in the neutron-nucleus optical potential. Results are
presented for the system for neutron incident energies
covering the range 1--20 MeV. From existing experimental bounds, a strength of
keV is deduced for the real and imaginary parts of the five-fold
term, which implies an upper bound of order on the relative -odd
strength when compared to the central real optical potential.Comment: 11 pages (Revtex
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